Advanced Ceramics and Applications 9783110627992, 9783110625134

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Rainer Gadow, Vojislav V. Mitic (Eds.) Advanced Ceramics and Applications

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Advanced Ceramics and Applications Edited by Rainer Gadow and Vojislav V. Mitic

Editors Prof. Dr. Rainer Gadow University of Stuttgart Institute for Manufacturing Technologies of Ceramic Components and Composites Allmandring 7b 70569 Stuttgart Germany [email protected] Prof. Dr. Vojislav V. Mitic University of Niš Department of Microelectronics Knez Mihajlova 35 11000 Belgrad Serbia [email protected]

ISBN 978-3-11-062513-4 e-ISBN (PDF) 978-3-11-062799-2 e-ISBN (EPUB) 978-3-11-062516-5 Library of Congress Control Number: 2021932222 Bibliographic information published by the Deutsche Nationalbibliothek The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available on the Internet at http://dnb.dnb.de. © 2021 Walter de Gruyter GmbH, Berlin/Boston Cover image: Gettyimages / undefined undefined Typesetting: Integra Software Services Pvt. Ltd. Printing and binding: CPI books GmbH, Leck www.degruyter.com

Foreword: Proceedings – Paper selection “Advanced Ceramics and Applications” It is a pleasure to notice that the Conference on “Advanced Ceramics and Applications” organized under the auspices of the Serbian Ceramics Society and the Serbian Academy of Sciences is developing successfully. Advanced ceramics as well functional as structural are most important in view of the future industrial innovation and will play an important role in the whole spectrum of applications as energy and transport technologies, information and communication, health care, etc. This conference is of great importance for the promotion of research, technology and industrial development in the Balkan countries as well as at universities, research centers and industry and to establish contacts and collaboration with foreign countries especially in Western Europe, Asia and the United States. After a decade-long operation, the conference is becoming known and recognized, and experienced scientists, professors and industrialists are becoming lecturers from all over the globe and shown interest to come to Belgrade, share experience and seek for joint research activities. It looks that researchers from Asian countries like China, South Korea and Japan have special interest to establish links with the Balkan Ceramics and composites science regions. The Conference receives the full support and promotion of the International Ceramic Federation (ICF) and European Academy of Sciences and Arts (EASA) which includes all Western and Eastern European ceramics societies, and this is a good sign to strengthen the contacts within Europe. A statement should also be made that the prestigious American Ceramics Society, with the Chapter in Serbia, also subscribes support. The conference itself treats a broad spectrum of topics within the ceramics area covering fundamental aspects, applied research, and industrial and applications in hospitals. New developments are reported in ceramics for energy, nuclear, transport sectors, but also innovations in health care with highlights in the field of orthopedics, as well as nice contributions for informatics and communication branches. A very positive point is that the conference is attended by a young generation of students and researchers, and this fact is very promising for the future. Finally, the efforts of Professor V. Mitic in collaboration with the Serbian Ceramics Society and the Serbian Academy for Sciences are greatly appreciated and should be given the courage to continue their efforts for the benefits of Serbia and the whole Balkan region. As one of the founders of this conference in Serbia, I am quite proud to tell that the conference has not only reached the level of recognition in all Balkan countries but also penetrated Western European research and industry circles and even made the conference worldwide known. https://doi.org/10.1515/9783110627992-202

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Foreword: Proceedings – Paper selection “Advanced Ceramics and Applications”

The proceeding are of high level and worthwhile to read and may inspire many young researchers and motivate industrialists from Western Europe to integrate the Balkan ceramic researchers in their European Research Programmes in future with special attention to the new European Commission Research Programme 2021–2027 just started. Marcel van de Voorde, Prof. Dr. Dr. h.c Professor: University of Technology DELFT(NL) Former CERN-Geneva, European Commission Research, Max Planck Institute Stuttgart Director: World Academy for Sciences & Arts and World Academy Consortium – California Council Member of the French Senate and National Assembly, Paris Vojislav V. Mitic and Rainer Gadow

Contents Foreword: Proceedings – Paper selection “Advanced Ceramics and Applications” V List of contributors

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Shabana P. S. Shaikh, Vojislav V. Mitic 1 A review on current status and future scope of hydrogen fuel cell technology in India and across globe 1 Qinglei Liu, Danmiao Kang, Jiajun Gu, Wang Zhang, Di Zhang 2 Porous graphitic carbons derived from seaweed for supercapacitors and the effect of the nanotexture on the rate performance 11 Frank Kern 3 Rare earth oxide-stabilized zirconia ceramics and composites with enhanced mechanical and functional properties 29 Rainer Gadow, Andreas Killinger, Venancio Martinez 4 Glass and glass ceramic layer composites with functional coatings Zaffar M. Khan, Saad Nauman, M. Ali Nasir 5 Structural health monitoring of glass fiber composite materials by piezoelectric nanosensors under cyclic loading 61 Dragan Djurdjević, Vojkan Mitić, Miroslav Stevanović, Ljubiša Kocić 6 Fractal tools in combating terrorism and money laundering 71 Rainer Gadow, Steffen Esslinger, Matthias Blum 7 Inkjet three-dimensional printing of bioceramics and bioglass

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Jih Ru Hwu, Shwu-Chen Tsay, Shih Ching Hung, Ming-Hua Hsu, Ji-Yuan Ma, Vojislav V. Mitic, Goran Lazovic, Shang-Shing P. Chou 8 Identification of radicals responsible for DNA cleavage by photolysis of bis-oxime esters 101

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Wang Zhang, Qinlei Liu, Jiajun Gu, Di Zhang, Branislav Jelenković, Dejan V. Pantelić 9 Fabrication of hierarchical replicas with near-perfect microstructure using modified biotemplate method 109 Žarko Mitić, Sanja Stojanović, Stevo Najman, Mike Barbeck, Miroslav Trajanović 10 Analysis of the in vivo course of foreign body response to a phycogenic bone substitute using FTIR spectroscopy 117 Dragana Jugović 11 Synthesis and structural characterization of some cathode materials for lithium-ion batteries 123 Aleksandar Radunovic, Zoran Popovic, Aleksandar Matic, Maja Vulovic 12 Application of ceramic components in knee arthroplasties 155 Pelemiš S., Mirjanić D. Lj., Mirjanić V., Mirjanić Dj., Vuković S. 13 Nanomaterials application in dentistry 165 Aleksandar Radunovic, Zoran Popovic, Ognjen Radunovic, Maja Vulovic 14 Complications of utilizing ceramic components in orthopedic surgery Zorica Ž. Lazarević, Martina Gilić, Aleksandra Milutinović, Nebojša Romčević, Hana Ibrahim Elswie, Vesna Radojević, Dalibor L. Sekulić 15 Growth and characterization of calcium fluoride single crystals 179 Marija Stojmenović, Vladimir Dodevski 16 Ceramic electrolytes for solid oxide fuel cells (SOFCs) as alternative energy sources 205 Silvana B. Dimitrijević, Stevan P. Dimitrijević 17 E-scrap processing: theory and practice

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Mirjanić D. Lj., Pelemiš S. 18 Intelligent nanomaterials for medicine diagnostic and therapy application 263

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S. Petrović, N. Starčević, M. Ćosić, N. Nešković 19 On the doughnut effect and the rainbow proton–silicon interaction potential 271 Ana Radosavljević-Mihajlović, Vojislav Mitic 20 The methods of safe storage of spent nuclear fuel and waste

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Zoran B. Vosika, Vojislav V. Mitić, Goran Lazović, Vesna Paunović, Ljubiša Kocić 21 Fractal corrected Schottky potential and Heywang model 293

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List of contributors Shabana P. S. Shaikh Department of Physics, SP Pune University, Ganeshkhind Road, Pune 411007 Maharashtra, India [email protected] Vojislav V. Mitic University of Niš, Faculty of Electronic Engineering Institute of Technical Sciences-SASA Belgrade, Serbia [email protected] Qinglei Liu State Key Laboratory of Metal Matrix Composites Shanghai Jiao Tong University 800 Dongchuan Road, Shanghai China, 200240 [email protected] Danmiao Kang State Key Laboratory of Metal Matrix Composites Shanghai Jiao Tong University 800 Dongchuan Road, Shanghai China, 200240 Jiajun Gu State Key Laboratory of Metal Matrix Composites Shanghai Jiao Tong University 800 Dongchuan Road, Shanghai China, 200240 Wang Zhang State Key Laboratory of Metal Matrix Composites Shanghai Jiao Tong University 800 Dongchuan Road, Shanghai China, 200240

https://doi.org/10.1515/9783110627992-204

Di Zhang State Key Laboratory of Metal Matrix Composites Shanghai Jiao Tong University 800 Dongchuan Road, Shanghai China, 200240 Frank Kern IFKB University of Stuttgart Stuttgart, Germany [email protected] Rainer Gadow Universität Stuttgart Institut für Fertigungstechnologie keramischer Bauteile (IFKB) Stuttgart, Germany [email protected] Andreas Killinger Universität Stuttgart Institut für Fertigungstechnologie keramischer Bauteile (IFKB) Stuttgart, Germany Venancio Martinez Universität Stuttgart Institut für Fertigungstechnologie keramischer Bauteile (IFKB) Stuttgart, Germany Zaffar M. Khan Aeronautics and Astronautics Department Institute of Space Technology, Islamabad, Pakistan Saad Nauman Materials Science and Engineering Department Institute of Space Technology Islamabad, Pakistan

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List of contributors

M. Ali Nasir Mechanical Engineering Department University of Engineering & Technology Taxila, Pakistan Miroslav Stevanović Academy of National Security Belgrade, Serbia Ljubiša Kocić Faculty of Electronic Engineering, University of Niš, Serbia Dragan Djurdjević Academy of National Security Belgrade, Serbia Steffen Esslinger Graduate School of Excellence advanced Manufacturing Engineering GSaME University of Stuttgart Stuttgart, Germany Matthias Blum Institute for Manufacturing Technologies of Ceramic Components and Composites University of Stuttgart Stuttgart, Germany Jih Ru Hwu Department of Chemistry, National Tsing Hua University & Frontier Research Center on Fundamental and Applied Sciences of Matters, Hsinchu 30013, Taiwan [email protected] Shwu-Chen Tsay Department of Chemistry, National Tsing Hua University & Frontier Research Center on Fundamental and Applied Sciences of Matters, Hsinchu 30013, Taiwan Shih Ching Hung Department of Chemistry, National Tsing Hua University & Frontier Research Center on Fundamental and Applied Sciences of Matters, Hsinchu 30013, Taiwan

Ming-Hua Hsu Department of Chemistry, National Tsing Hua University & Frontier Research Center on Fundamental and Applied Sciences of Matters, Hsinchu 30013, Taiwan Ji-Yuan Ma Department of Chemistry, Fu Jen Catholic University New Taipei 24205, Taiwan [email protected] Goran Lazovic University of Belgrade Faculty of Mechanical Engineering Belgrade, Serbia Shang-Shing P. Chou Department of Chemistry, Fu Jen Catholic University New Taipei 24205, Taiwan Wang Zhanga State Key Lab of Metal Matrix Composites Shanghai Jiao Tong University 200240, Shanghai, P. R. China [email protected] Qinlei Liua State Key Lab of Metal Matrix Composites Shanghai Jiao Tong University 200240, Shanghai, P. R. China Jiajun Gua State Key Lab of Metal Matrix Composites Shanghai Jiao Tong University 200240, Shanghai, P. R. China Di Zhanga State Key Lab of Metal Matrix Composites Shanghai Jiao Tong University 200240, Shanghai, P. R. China Branislav Jelenkovićb Institute of Physics Belgrade University of Belgrade Pregrevica 118 11080 Zemun, Belgrade, Serbia

List of contributors

Dejan V. Pantelić Institute of Physics Belgrade University of Belgrade Pregrevica 118 11080 Zemun, Belgrade, Serbia Žarko Mitić University of Niš, Faculty of Medicine Department of Chemistry Bul. Zorana Đinđića 81 RS-18000 Niš, Serbia [email protected] Sanja Stojanović University of Niš, Faculty of Medicine, Department for Cell and Tissue Engineering Department of Biology and Human Genetics Bul. Zorana Đinđića 81, RS-18000 Niš, Serbia [email protected] Stevo Najman University of Niš, Faculty of Medicine, Department for Cell and Tissue Engineering Department of Biology and Human Genetics Bul. Zorana Đinđića 81, RS-18000 Niš, Serbia [email protected] Mike Barbeck University Hospital Hamburg-Eppendorf, Department of Oral and Maxillofacial Surgery Section for Regenerative Orofacial Medicine Martinistrasse 52, D-20246 Hamburg Germany [email protected] Miroslav Trajanović University of Niš, Faculty of Mechanical Engineering, Laboratory for Intelligent Production Systems Aleksandra Medvedeva 14 RS-18000 Niš, Serbia [email protected] Dragana Jugović Institute of Technical Sciences of SASA Belgrade, Serbia [email protected]

Aleksandar Radunovic Clinic for orthopedic surgery and traumatology Military medical academy Belgrade, Serbia [email protected] Popovic Zoran Vozd clinic Belgrade, Serbia Aleksandar Matic Clinic for orthopedic surgery Clinical center Kragujevac Kragujevac, Serbia Vulovic Maja Department of anatomy Faculty of medical sciences University of Kragujevac Kragujevac, Serbia S. Pelemiš Faculty of Technology University of East Sarajevo Bosnia and Herzegovina D. Lj. Mirjanić Academy of Sciences and Arts of Republic of Srpska Bosnia and Herzegovina V. Mirjanić Faculty of Medicine Department of Dentistry University of Banja Luka Bosnia and Herzegovina Dj. Mirjanić Faculty of Medicine Department of Dentistry University of Banja Luka Bosnia and Herzegovina Vuković S. Faculty of Technology University of East Sarajevo Bosnia and Herzegovina

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List of contributors

Aleksandar Radunovic Clinic for orthopedic surgery and traumatology Military medical academy Belgrade, Serbia [email protected] Popovic Zoran Vozd clinic Belgrade, Serbia Ognjen Radunovic Faculty of medicine University of Belgrade Belgrade, Serbia Vulovic Maja Department of anatomy Faculty of medical sciences University of Kragujevac Kragujevac, Serbia Zorica Ž. Lazarević Institute of Physics University of Belgrade Belgrade, Serbia [email protected] Martina Gilić Institute of Physics University of Belgrade Belgrade, Serbia Aleksandra Milutinović Institute of Physics University of Belgrade Belgrade, Serbia Nebojša Romčević Institute of Physics University of Belgrade Belgrade, Serbia Hana Ibrahim Elswie Faculty of Technology and Metallurgy University of Belgrade Belgrade, Serbia [email protected]

Vesna Radojević Faculty of Technology and Metallurgy University of Belgrade Belgrade, Serbia Dalibor L. Sekulić Faculty of Technical Sciences University of Novi Sad Novi Sad, Serbia [email protected] Marija Stojmenović Department of materials science, “VINČA” Institute of Nuclear Sciences – National Institute of the Republic of Serbia, University of Belgrade, Belgrade, Serbia Vladimir Dodevski Department of materials science, “VINČA” Institute of Nuclear Sciences – National Institute of the Republic of Serbia, University of Belgrade, Belgrade, Serbia Silvana B. Dimitrijević Mining and Metallurgy Institute Bor Bor, Serbia [email protected] Stevan P. Dimitrijević Innovation center of the TMF Faculty, Belgrade, Serbia, University of Belgrade Belgrade, [email protected] S. Petrović Laboratory of Physics Vinča Institute of nuclear sciences University of Belgrade Belgrade, P. O. Box 522 Belgrade, Serbia N. Starčević Laboratory of Physics Vinča Institute of nuclear sciences University of Belgrade Belgrade, P. O. Box 522 Belgrade, Serbia

List of contributors

M. Ćosić Laboratory of Physics Vinča Institute of nuclear sciences University of Belgrade Belgrade, P. O. Box 522 Belgrade, Serbia N. Nešković Laboratory of Physics Vinča Institute of nuclear sciences University of Belgrade Belgrade, P. O. Box 522 Belgrade, Serbia Ana Radosavljević-Mihajlović Institute for Technology of Nuclear and Other Mineral Raw Materials P.O. Box 390 Franche d’Epere Street 86 11000 Belgrade, Serbia Zoran B. Vosika University of Niš Faculty of Electronic Engineering Aleksandra Medvedeva 14 Niš, Serbia

Goran Lazović University of Belgrade Faculty of Mechanical Engineering Belgrade, Serbia Vesna Paunović University of Niš Faculty of Electronic Engineering Aleksandra Medvedeva 14 Niš, Serbia Ljubiša Kocić University of Niš Faculty of Electronic Engineering Aleksandra Medvedeva 14 Niš, Serbia

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1 A review on current status and future scope of hydrogen fuel cell technology in India and across globe Abstract: Fuel cell is a electrochemical device that generates electricity from chemical energy through a chemical process between oxidizing and reducing agents. Due to the rapid vanishing of fossil fuel, there is a need to focus on the alternative energy sources to fulfil the need of electrical energy in the near future. Fuel cell is one of the best alternatives to provide the required energy in day to day and automotive and industrialapplications. Among all types of fuel cell, solid oxide fuel cell is the most potential fuel cell for generating high-efficiency power of energy above 100 KW due to reforming process without any pollution. Thus, this chapter will be helpful for young researchers and scientists to know the status of fuel cell in near future. Keywords: fuel cell, solid oxide fuel cell, R and D directions

1.1 Introduction 1.1.1 What is fuel cell? Fuel cell (FC) is an electrochemical device that generates electricity from chemical energy through a chemical process between oxidizing and reducing agents. FCs can generate high efficiency. In an FC, since the chemical energy of the fuel is directly converted to electricity, an FC can operate at much higher efficiencies than internal combustion engines, extracting more electricity from the same amount of fuel. FC can produce 80% of energy above 100 kW due to the reforming process [1]. FC supplies a reliable and efficient source of energy with zero pollution as they have no moving parts and the only emission of water and hydrogen due to the chemical reaction. The efficiency of power generation by FC depends on the rate of fuel load, Acknowledgments: The author S. P. S. Shaikh is very thankful to the UGC, New Delhi, India, for providing financial support through DS Kothari Postdoctoral Fellowship award no. PH-0030 and also thankful to the Department of Physics, SP Pune University, Pune. Also, special thanks goes to Prof. Voji for reviewing this chapter. Shabana P. S. Shaikh, Department of Physics, SP Pune University, Ganeshkhind Road, Pune-411007, Maharashtra, India, [email protected] Vojislav V. Mitic, University of Niš, Faculty of Electronic Engineering, Institute of Technical Sciences-SASA, Belgrade, Serbia, [email protected] https://doi.org/10.1515/9783110627992-001

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as electricity is generated in FC due to chemical reaction at the electrode/electrolyte interface. FC is a very environmental friendly source of energy for the near future due to its pollution free, noise free and highly efficient capabilities. However, FCs are providing electricity to spacecrafts since 1960, which could also be used as power source in exhaust-free automobiles [2]. FC was used for the first time as power generation system in 1970, in Apollo space mission. In the recent era, apart from space application, FCs are used in stationary and mobile applications as well. From the literature survey, it is discovered that FC is the most efficient power generation system without pollution in the near upcoming future as there is no other more potential replacement for fossil fuel. Nowadays, many researchers across the world are trying to develop hydrogen FC for vehicular application due to the flexible availability of hydrogen through various sources of hydrocarbon by splitting method [3]. Recently, more efforts being put on the development of new nanomaterials in order to have sustainable, secure and competitive energy, through production and storage of hydrogen for FC applications, such as car, mobile phones, laptops and desktop computers, electrical home appliances, and for use in industries and other remote communications such as short transportation and power generation as shown in Figure 1.1, to support at national as well as at international levels with much focus to emerge India by 2020 as a energy-rich country in Asia.

Automotive Applications

Figure 1.1: Application of hydrogen fuel cell technology [4].

Hydrogen fuel cell technology (HFCT) may be one of the safe and clean potential sources of energy generation with high efficiency for multiple applications. In this chapter

1 A review on current status and future scope of hydrogen fuel cell technology

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it is believed that HFCT is an essential component in low carbon economy and which plays a significant role in new energy and transport system across the globe. The world is facing power generation problem due to the day by day deteriorating of the sources of fossil fuel. High demand of energy may be expected by 2050 due to rise in population globally. Thus, investigating new alternative sources of energy is the matter of concern in today’s era. The fuel crisis is one of the most concerned aspects in today’s life. The research on increased efficiency of existing power generating devices has almost reached to the saturation. The power generation phenomenon in these devices has almost become predictable. All these aspects have attracted a great deal of attention in the present proposal for finding alternative power generating sources of electricity, and it seems that the electrochemical power source, in general, and FC, in particular, can also live up to the requirement in India as well as in other countries like Japan, the United States, China, Australia, Malaysia and Singapore. Thus, it is observed that hydrogen FCs such as PEMFC and SOFC are the most potential that provide more efficient, cleaner sources of energy. It is found that hydrogen is more relevant to all energy sectors, transportation, buildings and various industries, in implementation process. From the report of literature survey of 2014, it is found that PEM FC will be useful for stationary as well as portable applications for at least 5 years [2, 7, 8]. Especially in the industries of chemicals and fertilizers and in remote areas, the reliability, flexibility and longevity are more important factors to be considered than the cost of investment. From the latest report, it is known that India is also focusing on the energy sources other than fossil fuel, which can increase the power generating efficiency to about 40% by 2022 with capacity from 57 GW to 175 GW [9]. Thus, these reviews help to investigate the degradation mechanisms and their mitigation during continuous operation apart from materials research based on the following objectives:

1.2 Objectives based on the current review – – – – – – –

To develop new compatible nonmaterial for FC component To reduce the manufacturing cost by developing new synthesis technique To design nanosize FC To decrease the operating temperature To increase the energetic efficiency To improve the cell feasibility To make FC available in market for day-to-day life requirements

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– To increase the generation of electrical energy efficiency in the range of milliwatt and megawattW – To develop sustainable hydrogen production and to prepare for the transition to clean energy carriers – To foster commercial use of both FCs and hydrogen

1.3 Hydrogen production and energy storage There are various ways of producing hydrogen. Natural gas reforming, coal gasification and water electrolysis are proven technologies for hydrogen production today and are applied at an industrial scale all over the world. The current production methods can also be used for renewable energy sources, such as electrolysis for wind and solar-generated electricity, gasification of biomass or fossil fuel-based production in combination with carbon capture and storage (CCS). Decarburizing hydrogen production is a clear objective of the hydrogen production sector. By 2020, the goal is 50% of hydrogen for energy applications to come from CO2 emission-free production methods. Furthermore, hydrogen is also used as a by-product in industrial installations. In the future, also direct production of hydrogen, for example, by photocatalytic splitting of water or by employing bioprocesses (e.g., bacteria and algae, fermentation) might become feasible routes for low-temperature/low-energy hydrogen production. Another major challenge is the integration of the fast growing share of renewables in the energy supply system. To facilitate this change from demand-oriented production to supply-oriented production from wind and solar energy, storage options will be required to balance the system. Hydrogen can be safely stored in gaseous, liquid form or in solid state, in industrial as well as domestic environments [2]. The storage capacity of hydrogen is virtually unlimited, offering stored energy up to the terawatt hour level which can remain available for extended periods of time, as opposed to storage in batteries, for example. Therefore, development of hydrogen technologies offers a huge opportunity at national as well as at international levels.

1.4 The role of FCs and hydrogen in transport and logistics The latest report takes a close look at this emerging technology, both at the national and international levels, in terms of scientific, engineering and technological advancements. It also covers the different fuels used for FCs, the various technological routes, the global status of different types of FCs and various application areas.

1 A review on current status and future scope of hydrogen fuel cell technology

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Fuel cell electric vehicles (FCEVs) provide a clean alternative and clear advantages for passenger and light duty mobility. There are no major performance compromises to be made by the user in terms of size, driving range or speed, refuelling time or other driving comforts in comparison to traditional cars [4]. The FCEVs have no tail-pipe emissions, are silent and hydrogen can be produced from all (renewable) feed stocks. FCEVs offer the opportunity for zero-emission transport and provide a clean alternative for all travel circumstances, urban, intercity and longer-distance. FCEVs are also suited for larger passenger cars (e.g., family cars) which represent more than 70% of CO2 emissions [8]. In addition to passenger cars, identified as the market that can reduce overall cost as a result of its scale, buses and the logistics sectorare also promising markets [9] for hydrogen FC.

1.5 Working operation of fuel cell An FC consists of basic components: anode, cathode and electrolyte. An electrolyte is sandwiched between anode and cathode. Fuel is fed continuously to anode (negative electrode) and an oxidant to cathode (positive electrode). The electrochemical reaction takes place at the anode/electrolyte and cathode/electrolyte interface to produce electric current, which performs work on the load [10]. In particular, FC produces energy for as long as fuel is supplied to the electrode externally, through the following reaction: At anode: 2H2 ⇨ 4H+ + e− At cathode: O2 + 4e− + 4H ⇨ 2H2O Overall reaction: H2 + 1/2 O2 ⇨ H2O

1.6 Status of fuel cell technology in India As per the literature survey, there is need to strengthen the research and development work on FC technology in India to emerge as one of the energy-rich countries in Asia hopefully by 2050. In India, Fuel Cell Program is largely supported by the government. The major organizations working in the field include: National Chemical Laboratory (NCL), Pune, Indian Institute of Technology, Madras, Vellore Institute of Technology, Central Glass and Ceramic Institute and Bhaba Atomic Research Centre in collaboration with Bharat Heavy Electronics Limited, India for stationary applications up to milliwatt to 10 MW as per the report in 2014 by fuel cell [1].

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1.6.1 Status of fuel cell technology at global level At least eight of the world’s largest automobile manufacturers have plans to bring fuel cell vehicles (FCVs) to market sometime between 2020 and 2050. Governments in the Members of the European Union (EU), United States, Japan and Korea have developed plans to deploy hydrogen refuelling infrastructure to support the early market introduction of hydrogen FCVs. This study assesses the current status of FC technology and the plans for deploying of refuelling infrastructure. At present, all significant FC development activities appear to be concentrated in the United States, Germany, Japan and Korea with some modest developments in China and India. Europe is playing a major role in manufacturing and showcasing FC powered passenger cars, with several major development and demonstration initiatives [1]. Japan and the United States are today’s leading players in HFCT development, followed by Europe [4]. Emerging countries, such as China and Korea are catching up rapidly. Targeted governmental support and intervention has led to significant advances over the past couple of years. Without adequate action, Europe’s global leadership position is at stake. Japan is the global leader in FC deployment. From the literature survey, it is observed that the residential FCs have been commercially available since 2009 and more than 5,000 stations have been offered subsidy through a subsidization scheme which was estimated at $75 million in 2010. In early 2011, Japan launched the hydrogen town demonstration project including testing of feasibility of a hydrogen infrastructure. The government and energy companies are also funding hydrogen refueling stations needed for the widespread use of cars. Clear political commitment has been made for rolling out a hydrogen infrastructure in 2017. By 2020–2030, demand from power suppliers, automobile companies, residential builders and electronics companies is expected to create FC and hydrogen markets worth $3.9 billion at global level [2]. The United States is currently leading the material handling vehicles sector. As a result of government incentives [3], FC electric forklifts represent an estimated 2% penetration of annual sales of electric forklifts in the United States. In 2009, the United States announced $42 million in Recovery Act funding to accelerate FC commercialization and deployment. With approximately $54 million in cost-share funding from industry participants, the new funding supports the deployment of a significant number of FC systems primarily intended for emergency backup power and material handling (plus infrastructure). The US Department of Energy (DoE) has devoted $170 million for Hydrogen Fuel Cell R&D, demonstration and commercialization activities in 2010 and 2011, and foresees to commit more than $100 million for 2012. In addition to the DoE federal program, many states have financial incentives to support the installation of hydrogen and FC stations [4]. Canada also is a significant player with a strong hydrogen and FC industry focused on near-to-market application deployments. Also, China urgently needs energy and natural resources to support its growth. The drivers for China’s FC and hydrogen R&D are concerned about energy supply, distribution and

1 A review on current status and future scope of hydrogen fuel cell technology

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security, air pollution and the desire for manufacturing leadership. China considers FCs and hydrogen as central to its long-term science and technology development strategy. Till date, China has invested approximately $2.8 billion in FC and infrastructure R&D. These activities are focused on portable, stationary and mobile applications and on the production of hydrogen from solar, biomass, natural gas and coal resources. South Korea announced a program to subsidize 80% of the costs of residential FCs for heat and power. The subsidy will fall to 50% from 2015 to 2016 and to 30% for the period from 2017 to 2020. South Korea has also announced an ambitious goal to supply 20% of the worldwide shipments of FCs by 2025 and create 560,000 jobs in South Korea [5, 6]. A strategic plan for the city of Seoul includes 47% of renewable energy generation from FCs by 2030. In general, India and China, with their large population and growing economies – and Africa, with large telecoms market and poor power-system are identified as growth-markets for the next decades. In particular, India and China present huge market potential, including the opportunity for new technologies to leapfrog conventional ones, as there are no established markets yet and state of the art solutions can be deployed from the start. Japan is mainly driven by environment, energy security and industrial competitiveness. The United States is driven particularly by energy security and reliability, air quality, industrial development and wealth generation. Impressive technological progress has been made by European companies, especially in the transport sector, also due to good support from projects developed jointly under the European R&D framework program. However, as per the report on financial and technology outlook 2014, current funding levels and financial mechanisms will be required to significantly increase if Europe’s ambitions are to be met in 2020. Thus at global level, the developers such as Fuel Cell Energy, UTC Fuel Cells, Ford, Hyundai and Siemens are trying to focus and putting more efforts to make it commercialize for stationary use (Figure 1.2). In Asia, only Korea is focusing to develop FCs for stationary use while Japan and China are interested in transport and stationary units. The United States, Canada, Switzerland, Japan and Australia are dominating this sector in vehicular application including FC-driven electric powertrains [7–9].

1.6.2 Limitations in commercialization of fuel cell technology The introduction of new clean technologies to replace mature existing applications is a slow and costly process that will not be facilitated by the market on its own (Figure 1.3). The initial investment cost and risks are too great factors for private initiatives alone. This means that society needs to share the initial risk with the private sector in order to bridge the gap to the market.

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Figure 1.2: Hydrogen fuel station.

Figure 1.3: Fuel versus efficiency.

1 A review on current status and future scope of hydrogen fuel cell technology

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1.6.3 Applications of hydrogen fuel cell FCs have a wide range of applications including stationary power generation (MW), portable power generation (KW) and transportation (KW), and in early Market Applications such as wheelchairs, vehicles for luggage transport or for moving airplanes on the ground of airports, boats for the lakes and rivers and tractors.

1.6.4 Suggestions and future directions In India, it is most difficult to make the availability of fuel currently. Government, industry and NGO groups are specially doing more sound efforts by planning such projects through R&D work. To make FC technology commercial, most specifically in the near future in India, there is a need to work collectively in collaboration with R&D institutes, stakeholders and industries by developing new compatible nanomaterials to form a stack of FC components. The handsome amount needs to invest in the upliftment and development of HFCT with improved infrastructure of hydrogen production and storage tank for refuelling the cars. The FC electric vehicle can be commercialized if sound investment could be made in the next 10 years in the stationary and transportation applications, which will play a major role to reduce pollution in the environment.

References [1] [2]

Water electrolysis & renewable energy systems, Fuel Cell Today, 2014. Fuel cell and hydrogen technologies in Europe financial and technology outlook on the European sector ambition 2014–2020. [3] Gupta R, Mishra AK, Majhi MR, Suresh MB. Synthesis and analysis of highly efficient GDC20 as electrolyte for IT-Sofcs application. Int J Eng Innovative Technol 3, September 2013, 3. [4] Today FC. 2013. Fuel Cell Electric Vehicles: The Road Ahead, Royston, UK, www.fuelcelltoday.com. [5] Hua T, Ahluwalia R, Peng JK, Kromer M, Lasher S, McKenney K, Law J, Sinha J. Technical Assessment of Compressed Hydrogen Storage Tank Systems for Automotive Applications. ANL-10/24, Argonne, Illinois: Argonne National Laboratory, September, 2010. [6] James BD, Spisak AB. 2012. Mass production cost estimation of direct H2 PEM fuel cell systems for transportation applications: 2012 update, Strategic Analysis, Arlington, Virginia, October 18. [7] James BD, Moton JM, Colella WG, 2013. Fuel Cell Transportation Cost Analysis. [8] U.S. Department of Energy 2013. Annual Merit Review and Peer Evaluation Meeting for the Hydrogen and Fuel Cell Technologies Program, Arlington, Virginia, May 14. [9] Status and Prospects of the Global Automotive Fuel Cell Industry and Plans for Deployment of Fuel Cell Vehicles and Hydrogen Refuelling Infrastructure, Greene D, OaK Ridge, National Energy laboratory, July 2013. [10] Shaikh SP, et al. Renewable Sustainable Energy Rev 51, 1.

Qinglei Liu, Danmiao Kang, Jiajun Gu, Wang Zhang, Di Zhang

2 Porous graphitic carbons derived from seaweed for supercapacitors and the effect of the nanotexture on the rate performance Abstract: Porous graphitic carbons with high surface areas have been developed by a facile combination of activation and catalytic graphitization of seaweed-derived charcoals. The obtained porous graphitic carbons exhibit high specific surface areas (up to 1,745 m2 g−1), tunable mesopore size distributions and good electrical conductivity. When used as the electrodes of supercapacitors, the carbons offer high specific capacitance and especially excellent high rate performance. The superior performance is demonstrated to be closely related to the coupled effect of pore structures and graphitic nanostructures, which can be readily tuned by manipulating the catalytic graphitization process. Keywords: energy storage, carbon materials, supercapacitors, rate performance, porous carbon

2.1 Introduction Supercapacitors (SCs) are considered as advanced electrical energy storage devices because of their merits of large power density, long cycle life and high coulombic efficiency [1, 2]. Thus, they have promising applications in hybrid electric vehicle, uninterrupted power supply and backup power. Different kinds of materials have been widely studied for use as electrode materials of SCs, such as carbon, metal oxides and so on [3–7]. However, activated carbon, the currently used electrode material for SCs, still suffers from low capacitance and poor rate performance resulted from its tortuous pore channels and bad electrical conductivity [8].

Acknowledgments: This work was supported by the National Natural Science Foundation of China (Nos. 51001070, 51171110), Shanghai Science and Technology Committee (14JC1403300, 14520710100), Research Fund for the Doctoral Program of Higher Education of China (20120073130001) and SMC-Chen Xing Young Scholar Award of SJTU. J.G greatly thanks the support from Program for New Century Excellent Talents in University, Ministry of Education, China. Authors also thank SJTU Instrument Analysis Centre for the measurements. Qinglei Liu, Danmiao Kang, Jiajun Gu, Wang Zhang, Di Zhang, State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, China, [email protected] https://doi.org/10.1515/9783110627992-002

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To seek novel carbonaceous electrode materials with high capacitance and good rate performance, a great variety of nanoporous carbon materials have been recently developed with high specific surface areas (SSAs) and tunable pore structures [1, 2, 8–16]. Carbon nanotubes have excellent conductivity and mesoporous channels, but the specific capacitance is usually less than 100 F g−1 as a result of low SSAs [9, 17]. Templated carbons, including microporous templated carbons [8, 9], ordered mesoporous carbons [10, 11] and hierarchical porous carbons, have been produced for SCs by precisely replicating the original pore structures of various templates [14, 18]. However, the preparation of these template-based carbons was relatively complicated with low cost-efficiency for mass production. Graphene could provide high SSA (2,630 m2 g−1 in theory) and excellent conductivity for high-performance SCs, but its application was still limited by several practical issues associated with the nano-scale particle size as well as high cost [16, 17]. Biomass-derived carbons have received intense attention recently for their potential usage in SCs [19–23]. For example, carbons obtained by directly pyrolysis of the seaweed have excellent performance when used as electrode materials of SCs, which was due to the tuned porous structure and surficial functional groups [19]. However, the rate performance was still limited since the surficial functional groups were inactivated at high rate and the limited graphitic degree of the carbons also led to a low electron transport ability of the carbons. Porous graphitic carbons (PGCs) are a class of solid carbon materials possessing both developed pore structures and graphitic structures. The structural features make them greatly promising for SCs. To obtain porous graphitic electrodes, catalytic graphitization has been widely utilized to in situ formed graphitic nanostructures within carbon frameworks derived from polymeric carbon precursors (poly (benzoxazine-co-resol) [24] furfuryl alcohol [25], etc.) with the aid of transition metallic catalysts (Fe, Co, Ni). In general, the SSAs of the obtained materials are low (normally 0.45, demonstrating

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the existence of a large number of mesopores. In a typical chemical activation process, KOH attacks the defects on carbon surface to create micropores, which were further widened as the reaction continues [32–34]. The AC sample had a much more absorbed volume of N2 than the DC at low pressure (p/p0 < 0.1), indicating the presence of numerous micropores in AC introduced by the activation [32–34] The SSA of AC was calculated to be 1,858 m2 g−1, much higher than that of the DC (1,045 m2 g−1). The isotherm of AC exhibited as a plateau at middle pressure (p/p0 = 0.2–0.8) indicates that there was almost no mesopores on the carbon matrix. The DC had a broad PSD ranging from 2 to 10 nm, while the AC had a narrow PSD between 1 and 3 nm (Figure 2.4b).

Figure 2.4: Nitrogen sorption isotherms (a) and pore size distributions (b) of the seaweed-derived porous carbons.

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The GDC and GAC samples had lower absorbed volumes of N2 compared to their nongraphitic counterparts. In addition, the hysteresis loop of the GDC centered at higher pressures than that of DC, indicates the decay of micropores and widening of mesopores during catalytic graphitization. The result was confirmed by the PSD as well. As shown in the inset of Figure 2.4b, the location of the strongest peak was moved from 3 nm for the DC to 10 nm for the GDC after the catalytic graphitization. The result matched well with the HRTEM measurement in Figure 2.4b and c, which showed open mesopores of ca. 10 nm in size generated during the catalytic graphitization. A similar change in pore structures was observed for the AC and GAC samples (Figure 2.4b). The GDC and GAC had SSAs of 559 and 1,745 m2 g−1, respectively. As discussed above, chemical activation and catalytic graphitization provided effective approaches to adjust pore structures of the obtained porous carbons in terms of creating micropores and mesopores, respectively [35]. Thus, by carefully manipulating the processing, carbon materials with optimized pore structures and carbon textures for SCs can be obtained.

2.3.3 Capacitive performance Figure 2.5 shows the capacitive performance of the seaweed-derived porous carbons. In the CV (Figure 2.5a) and GCD measurements (Figure 2.5b), we chose a low scan rate (10 mV s−1) and charge/discharge rate (0.1 A g−1), respectively, to study the charge-storing ability of samples, at which electrolyte ions had enough time to reach accessible surface area through pore channels [36]. In Figure 2.5a, all the CV curves exhibited rectangular shapes, implying an electric double-layer (EDL) dominant capacitive mechanism for all samples. In comparison, the GDC and GAC samples had more rectangular CV curves than their nongraphitic counterparts. This indicated that the graphitic porous carbons had quicker responses at high rates. The CV curves of the DC and AC showed abrupt increase in current at high voltage (>0.6 V) due to the decomposition of electrolyte in the narrow pores [36, 37]. In Figure 2.5b, the GCD curves of the DC, GDC and GAC were generally symmetric, demonstrating an ideal EDL effect during the charge/discharge process. The asymmetric shape of the AC curve arose from the occurrence of fast redox reaction between heteroatoms and electrolyte ions during the charging/discharging. However, the redox peaks were not found in the CV curve, which was ascribed to the wide range of voltage under which various redox reactions took place [36]. Figure 5c illustrates the Nyquist plots of the four samples. All the tests were taken under the same conditions, so the four curves had an equal series resistance (Rs), which was mainly associated with the resistance of electrolyte and electrode materials, and the contact resistance between them. At low frequency, all the samples exhibited as ideal EDL capacitors with vertical lines [38]. Charge transport resistance (RCT) values were calculated to be 1.4, 2.7, 0.9 and 1.0 Ω for the DC, AC,

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Figure 2.5: (a) Cyclic voltammetry curves of seaweed-derived porous carbons at a scan rate of 10 mv s−1. (b) Galvanic charge-discharge curves at a current density of 0.1 A g−1. (c) Nyquist plots over a frequency range from 105 to 10–2 Hz. (d) Bode phase plots. (e) Specific capacitance at current densities ranging from 0.1 to 10 A g−1.

GDC and GAC, respectively. The high RCT of AC was related to its existence of heteroatoms, low graphitic degree, and high ion transport resistance caused by its narrow pore channels. In comparison, the other three samples had much lower RCT values. Considering that the GDC and GAC also had high contents of heteroatoms, we concluded that PSDs and conductivity had more crucial effects on the RCT values. The result was also supported by the Bode phase plots (Figure 5d). At the frequency that the capacitance was 50% of its maximum value, the GDC and GAC

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displayed better frequency response than the DC and AC because of their broader PSDs and graphitic nanotextures. Moreover, the GDC exhibited better frequency response than the GAC because of the higher graphitization degree as well as more reasonable PSD in mesoporous range (Figure 2.4b). To give a direct comparison of the capacitive performance of the four samples, the specific capacitance as a function of current density was illustrated in Figure 2.5e. With the highest SSA, the AC had the highest initial specific capacitance of 254 F g−1 at 0.1 A g−1. The initial specific capacitance of GAC, DC, GDC was 239, 170 and 160 F g−1, respectively. As the current density increased, the fading in capacitance of the AC was the severest, giving rise to a capacitance of 150 F g−1 at 5 A g−1 and 140 A g−1 at 10 A g−1. The corresponding capacitance retention (C5A/g/C0.1A/g) was 59%. The low value was mainly ascribed to its tortuous pore channels and low conductivity. The DC had a higher capacitance retention value of 69%, which was associated with its broader PSD. After the catalytic graphitization, the obtained GDC and GAC had increased capacitance retention of 77 and 75%, respectively, demonstrating the positive effect on rate performance of the additional mesopores as well as graphitic nanostructures both generated during the catalytic graphitization. With a high SSA, together with an appropriate PSD and partially graphitic nanotextures, the GAC exhibited specific capacitance of 239 F g−1 at 0.1 A g−1, and even 170 F g−1 at 10 A g−1. The values are much better than those of previously reported polymer-based PGCs via catalytic graphitization, which are usually less than 100 F g−1 at 10 A g−1 [24–26], demonstrating the superiority of seaweed with natural pore structures than conventional polymers as carbon precursors for PGCs. Compared with other biomass-derived carbons, the GACs as obtained here show better rate performance [8, 19, 22]. Since there are fewer functional groups on the obtained carbons, the loss of faradic capacitance has less effect on GACs, while the capacitance fading of the other biomass-derived carbons is obvious at high current density. Previous study also added CNTs as nanotexturing agents to improve the rate performance [20] and our results here are comparable with the best performance with an additive of CNTS of 10%.

2.3.4 The influence of microstructures on the capacitive performance Since PGCs contain pore structures and graphitic nanostructures, both of which have effects on capacitive performance, it is necessary to clarify the influence of these microstructures. Based on the above results, we made a tailoring on the microstructures of the GAC by manipulating the impregnated Ni2+ concentration of the AC before catalytic graphitization. Since all samples were derived from the same precursor and processing, it is more convincing to be as a group of control samples to study the effects of pore structures and graphitization degree on capacitive performance. The results showed

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that as the impregnated Ni2+ concentration increased, the SSA of the obtained GAC decreased gradually to 1,124 m2 g−1 (Figure 2.6a) as a result of decrease in micropores and simultaneously increase in mesopores. In addition, the PSD of the GAC over the mesopore range became much broader as shown in the inset of Figure 2.6b. The Ig/Id value calculated from Raman spectra increased from 0.27 of the AC to 0.47 of the GAC-0.8. Moreover, the standard deviation of the Ig/Id tended to decrease

Figure 2.6: Specific surface areas (a) and pore size distributions (b) of AC and its derived GACs. The inset in (b) shows the PSDs over 6–100 nm. (c) Ig/Id values. (d) Rate performance over 0.1–5 A g−1 current density range. (e) Specific capacitance at different current densities versus specific surface area. (f) The capacitance retention, ratio of mesopore volume to micropore volume (Vme/Vmi) and Ig/Id value versus the impregnated Ni2+ concentration.

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with more generated graphitic nanostructure (Figure 6c). As a result of decrease in SSAs, the GACs showed lower specific capacitances at 0.1 A g−1 than the AC precursor (Figure 6d). The AC had a specific capacitance of 254 F g−1, while the GACs had capacitance values between 239 and 160 F g−1. At a current density of 3 A g−1, the GAC-0.2 exhibited a specific capacitance of 185 F g−1, higher than that of the AC (168 F g−1). Although the GAC-0.8 exhibited the best capacitance retention, its capacitance was lower than that of the AC over the whole measured range, implying that an appropriate degree of catalytic graphitization was necessary to obtain optimized microstructures for desired capacitive performance. It is known that at low charge current densities, the electrolyte ions have enough time to fulfil the effective pores, generating a linear relationship between the specific capacitance and the SSA of the sample [39]. Figure 2.6e displayed the evolution of the specific capacitance at different current densities as a function of the SSA of seaweedderived carbons. A linear relationship was observed at a current density of 0.1 A g−1, matching well with the results of other porous carbons previously reported [39]. As the current density increased to 0.3 A g−1, the capacitance value of AC began to deviate from the fitted line, and the deviation degree was severe at high current densities (e.g., 3 and 5 A g−1), implying that some interior surface in AC became inaccessible. This demonstrated that the GACs had higher proportion of effective surface area (SSAeff) than the AC precursor after the catalytic graphitization process, during which additional mesopores generated as ion transportation channels to interior surface (Figure 2.6b). The change in the capacitance retention, ratio of mesopore volume to micropore volume (Vme/Vmi), and Ig/Id value were plotted as a function of the Ni2+ concentration as shown in Figure 2.6f. A positive correlation was found between the capacitance retention and Vme/Vmi, indicating the contribution of mesopores to the SSAeff values [40]. Another factor that affects the rate performance of carbon materials is conductivity. It has been well-established that electrode with acetylene black as conductive agent has limited effect on the capacitance retention when the mass fraction of the additive exceeds 5 wt% [41]. In our experiments, the weight ratio of conductive additive in electrodes was 10 wt%. Hence, the increased conductivity caused by the catalytic graphitization should have limited influence on the capacitance retention. The increased Ig/Id value was attributed to have a secondary effect on rate performance.

2.4 Conclusions We have developed highly porous graphitic materials from seaweed for SCs by the combination of activation and catalytic graphitization. The chemical activation increases the number of micropores and SSAs, while the catalytic graphitization generates mesoporous channels of around 10 nm and increases graphitization degree. The obtained

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materials have high SSAs up to 1,745 m2 g−1, exhibiting high specific capacitance of 193 F g−1 at 1 A g−1 and excellent rate performance (91% retention at 5 A g−1). Thus, catalytic graphitization of seaweed carbon is a promising way to produce high performance electrode materials with tunable microstructures for SCs.

Abbreviations SCs SSAs PGCs DC AC GAC GDC FT-IR TGA TEM SEM XRD PSD DFT GCD CV EDL

supercapacitors specific surface areas porous graphitic carbons derived charcoal activated carbon graphitic activated carbon graphitic directly carbonized carbon fourier transform infrared spectra thermogravimetric analysis transmission electron microscopy scanning electron microscope X-ray diffraction pore size distribution density function theory galvanic charge-discharge cyclic voltammetry electric double-layer

References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]

Conway BE. Electrochemical Supercapacitors. New York: Kluwer Academic Publishers/Plenum Press, 1999. Gogotsi Y, Simon P. Science 2011, 334, 917. Brousse T, Toupin M, Belanger D. J Electrochem Soc 2004, 151, A614. Devaraj S, Munichandraiah N. J Electrochem Soc 2007, 154, A80. Lin TW, Hsiao MC, Chou SW, Shen HH, Lin JY. J Electrochem Soc 2015, 162, A1493. Ragupathy P, Vasan H, Munichandraiah N. J Electrochem Soc 2008, 155, A34. Wang YG, Yu L, Xia YY. J Electrochem Soc 2006, 153, A743. Chmiola J, Yushin G, Gogotsi Y, Portet C, Simon P, Taberna P-L. Science 2006, 313, 1760. Chmiola J, Largeot C, Taberna PL, Simon P, Gogotsi Y. Science 2010, 328, 480. Liang C, Li Z, Dai S. Angew Chem Int Edit 2008, 47, 3696. Wang DW, Li F, Chen ZG, Lu GQ, Cheng H-M. Chem Mater 2008, 20, 7195. Lee KT, Lytle JC, Ergang NS, Oh SM, Stein A. Adv Funct Mate 2005, 15, 547. Wang DW, Li F, Liu M, Lu GQ, Cheng HM. Angew Chem Int Edit 2008, 47, 373. Li Z, Wu D, Liang Y, Xu F, Fu R. Nanoscale 2013, 5, 10824. Centeno TA, Sevilla M, Fuertes AB, Stoeckli F. Carbon 2005, 43, 3012.

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[16] Zhu Y, Murali S, Stoller MD, Ganesh K, Cai W, Ferreira PJ, Pirkle A, Wallace RM, Cychosz KA, Thommes M. Science 2011, 332, 1537. [17] Liu C, Yu Z, Neff D, Zhamu A, Jang BZ. Nano Lett 2010, 10, 4863. [18] Barranco V, Celorrio V, Lázaro M, Rojo J. J Electrochem Soc 2012, 159, A464. [19] Raymundo Piñero E, Cadek M, Béguin F. Adv Funct Mate 2009, 19, 1032. [20] Raymundo Piñero E, Cadek M, Wachtler M, Béguin F. ChemSusChem 2011, 4, 943. [21] Raymundo Piñero E, Leroux F, Béguin F. Adv Mater 2006, 18, 1877. [22] Bichat M, Raymundo Piñero E, Béguin F. Carbon 2010, 48, 4351. [23] Zhu H, Wang X, Yang F, Yang X. Adv Mater 2011, 23, 2745. [24] Sevilla Solís M, Fuertes Arias AB. Carbon 2013, 56, 155. [25] Wang Z, Zhang X, Liu X, Lv M, Yang K, Meng J. Carbon 2011, 49, 161. [26] Fuertes AB, Centeno TA. J Mate Chem 2005, 15, 1079. [27] Liu Y, Liu Q, Gu J, Kang D, Zhou F, Zhang W, Wu Y, Zhang D. Carbon 2013, 64, 132. [28] Xia Y, Xiao Z, Dou X, Huang H, Lu X, Yan R, Gan Y, Zhu W, Tu J, Zhang W. ACS nano 2013, 7, 7083. [29] Ōya A, Marsh H. J Mate Sci 1982, 17, 309. [30] Sevilla M, Sanchís C, Valdés-Solís T, Morallón E, Fuertes A. Carbon 2008, 46, 931. [31] Li Z, Zhang L, Amirkhiz BS, Tan X, Xu Z, Wang H, Olsen BC, Holt C, Mitlin D. Adv Energy Mater 2012, 2, 431. [32] Lozano-Castello D, Lillo-Rodenas M, Cazorla-Amoros D, Linares-Solano A. Carbon 2001, 39, 741. [33] Lillo-Ródenas M, Cazorla-Amorós D, Linares-Solano A. Carbon 2003, 41, 267. [34] Lillo-Ródenas M, Juan-Juan J, Cazorla-Amorós D, Linares-Solano A. Carbon 2004, 42, 1371. [35] Bleda-Martínez MJ, Maciá-Agulló JA, Lozano-Castelló D, Morallón E, Cazorla-Amorós D, Linares-Solano A. Carbon 2005, 43, 2677. [36] Gu W, Sevilla M, Magasinski A, Fuertes AB, Yushin G. Energy Environ Sci 2013, 6, 2465. [37] Lu M, Beguin F, Frackowiak E. Supercapacitors: Materials Systems and Applications. John Wiley & Sons, 2013. [38] Taberna P, Simon P, Fauvarque J-F. J Electrochem Soc 2003, 150, A292. [39] Vix-Guterl C, Frackowiak E, Jurewicz K, Friebe M, Parmentier J, Béguin F. Carbon 2005, 43, 1293. [40] Zhang L, Yang X, Zhang F, Long G, Zhang T, Leng K, Zhang Y, Huang Y, Ma Y, Zhang M. J Am Chem Soc 2013, 135, 5921. [41] Zhang H, Zhang W, Cheng J, Cao G, Yang Y. Solid State Ionics 2008, 179, 1946.

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Appendix: Porous graphitic carbons derived from seaweed for supercapacitors and the effect of the nanotexture on the rate performance

Figure A.1: (a) The morphology of Lessionia Trabeculata. The seaweed has three main parts, meristoderm, cortex and medullar. (b) Magnification photograph of cortex, the main part of the seaweed.

Figure A.2: FT-IR spectrum (a) and TGA-DTG curve (b) of Lessionia Trabeculata.

2 Porous graphitic carbons derived from seaweed for supercapacitors

Figure A.3: SEM images of the DC sample prepared by the direct carbonization of seaweed at 900 °C. (a–c) Cross section and (d–f) longitudinal section.

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Figure A.4: SEM images of the derived carbon.

Table A.1: The proportion of the functional groups on AC and GAC (%).

AC GAC

C-OH

COC

C=O

C(O)O

. .

. .

. .

. .

N-

N-

N-Q

. .

. .

. .

Table A.2: The pore structures of the AC and PGCs.

AC GAC-. GAC-. GAC-. GAC-.

SBET(m g−)

Vt(cm g−)

Vme(cm g−)

Vmi(cm g−)

    

. . . . .

. . . . .

. . . . .

Frank Kern

3 Rare earth oxide-stabilized zirconia ceramics and composites with enhanced mechanical and functional properties Abstract: Zirconia-based materials have become commodities used in biomedical and engineering applications. New types of tetragonal zirconia polycrystals with tailored stabilizer formulation can provide combinations of mechanical and functional properties which would have been considered impossible using state-ofthe-art materials. In this chapter, two types of yttria–neodymia-stabilized zirconia composites are presented: an alumina-toughened zirconia providing high strength and fracture resistance and a zirconia–tungsten carbide composite providing excellent mechanical properties in addition to electrical conductivity and electric discharge machinability. Keywords: ceramics, zirconia, mechanical properties, microstructure, electric discharge machining

3.1 Introduction The high strength and toughness of partially stabilized zirconia structural ceramics is caused by “transformation toughening” [1, 2]. Tetragonal zirconia retained metastable by addition of stabilizer oxides transforms to monoclinic phase associated with volume expansion and shear. In the wake of a proceeding crack, a process zone under compressive stress reduces the stress intensity at the crack tip. For tetragonal zirconia polycrystals, the type of material with the finest grain size and highest strength, typically yttria (Y-TZP) or ceria (Ce-TZP) are used as stabilizers. This leads to materials which offer either high strength and moderate fracture resistance (Y-TZP) or extremely high toughness but only moderate strength (Ce-TZP) [2]. Moreover Ce-TZP is resistant against low temperature degradation while Y-TZP is not [3, 4]. For many applications, a combination of high strength and high toughness is desirable which is difficult to achieve with these two basic materials. It has

Acknowledgments: The author would like to acknowledge the contribution of Mrs. Bianca Schwanda for ED-machining tests on TZP-WC materials during her student research project. Frank Kern, IFKB, University of Stuttgart, Stuttgart, Germany, [email protected] https://doi.org/10.1515/9783110627992-003

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been shown, however, by various authors, that co-stabilization of zirconia can lead to enhanced mechanical properties [5–9]. Materials presented were either Yttriaceria costabilized or rare earth costabilized (Y-Nd-TZP; Yb-Nd-TZP, Gd-Nd-TZP). Some results are already available for composite materials with alumina [7, 10, 11] or electrically conductive dispersions like titanium nitride, titanium carbonitride or tungsten carbide [12–15]. In this study, examples for both types are given to demonstrate the potential of this approach.

3.2 Materials and methods The basic principle of the stabilizer coating procedure has been presented by Yuan [16]. Unstabilized monoclinic zirconia starting powders are coated with rare earth oxides dissolved in nitric acid. After drying and calcination, the rare earth nitrates are converted to oxides and fixed on the surface of the starting powders, the procedure has been shown in detail elsewhere [17]. For the study, two different starting powders were used: one with 15 m2/g for the TZP-alumina composites and one with 60 m2g for the TZP-WC composites. Different Y-Nd-TZP compositions were tested. Alumina-toughened zirconia (ATZ) always contained 20 vol-% alumina (SBET = 8 m2/g). TZP-WC samples contained 25 (SBET = 2.5 m2/g). Samples were consolidated by hot pressing at 1350 °C/1 h/60 MPa (ATZ) or spark plasma sintering 1250 °C/5 min/60 MPa (TZP-WC). Measurement of mechanical properties included Vickers hardness HV10 (Bareiss, Germany), 4-pt bending strength (Zwick, Germany, 20 mm outer/10 mm inner span), fracture resistance by indentation strength in bending (ISB) method (same setup as bending strength), direct crack length measurement (DCM), Cook&Lawn test and stable indentation crack growth in bending SIGB [18–21]. The microstructure and the structure of ED-machined surfaces was studied by SEM (Zeiss, Germany), phase composition of zirconia was evaluated by XRD according to Toraya [22]. Feasibility electric discharge machining was studied by die-sinking tests with machine settings for different energy input (AEG, Germany). Machining speed was calculated by weighing samples before and after electric discharge machining of rectangular cavities (5 × 5 mm2) for a fixed time of 30 min. Surface roughness of samples was evaluated by tactile method (Mahr, Germany).

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3.3 Results 3.3.1 Alumina-toughened zirconia 3.3.1.1 Microstructure The microstructure of three different ATZ materials is shown in Figure 3.1. As can be clearly seen, the materials are extremely fine grained and are composed of three

Figure 3.1: Microstructure of different TZP-20% alumina materials, numbers refer to stabilizer contents in mol% rare earth oxide RE2O3.

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structural units: a fine grain matrix of an average grain size 1,000 MPa can be retained and fracture resistance values can be boosted to a level well beyond 10 MPa√m. While alumina in the ATZ materials is added to improve the hardness and abrasion resistance, the addition of a percolating tungsten carbide dispersion can be applied to introduce a functional property. Electrical conductivity enables electric discharge machining, a non-conventional machining method, to manufacture complex shaped components irrespective of hardness and abrasion resistance of the workpiece. In the field of ED-machinable ceramics produced for manufacturing of customized components in mechanical engineering, even higher strength of up to 1,500 MPa can be achieved coupled with fracture toughness values slightly below 10 MPa√m. Here, improving the toughness goes along with an improvement of strength and reliability, a strength reduction due to R-curve effects as in the case of ATZ, was not observed. Due to the limited thermal conductivity of TZP based

38

Frank Kern

composites, ED-machining has to be carried out with great care. Too high energy input during machining leads to surface damage or even to the protrusion of cracks from the surface of the materials into the bulk. Hot pressing and spark plasma sintering can be applied to manufacture fully dense and very fine grain TZP-matrix nanocomposite ceramics at very moderate sintering temperatures and short dwell.

References [1] [2] [3] [4] [5]

[6] [7] [8] [9] [10] [11] [12] [13]

[14] [15] [16] [17]

Kelly PM, Rose LRF. The martensitic transformation of ceramics – its role in transformation toughening. Progr Mat Sci 2002, 67, 463–557. Hannink RHJ, Kelly PM, Muddle BB. Transformation Toughening in Zirconia-Containing Ceramics. J Am Ceram Soc 2000, 83(3), 461–87. Chevalier J, Gremillard L, Deville S. Low temperature degradation of zirconia and implications for biomedical implants. Annu Rev Mater Res 2007, 37, 1–32. Chevalier J, Drouin JM, Cales B. Low-Temperature Aging of Y-TZP Ceramics. J Am Ceram Soc 1999, 82(8), 2150–54. Vleugels J, Xu T, Huang S, Kan Y, Wang P, Li PL, Van Der Biest O. Characterization of (Nd,Y)TZP ceramics prepared by a colloidal suspension coating technique. J Eur Ceram Soc 2007, 27, 1339–43. Xu T, Vleugels J, Van der Biest O, Wang P. Mechanical properties of Nd2O3/Y2O3-coated zirconia ceramics. Mat Sci Eng A 2004, 374, 239–43. Kern F. Gadolinia-Neodymia-Co-Stabilized zirconia materials with high toughness and strength. J Ceram Sci Techn 2012, 3(3), 119–30. Kern F. Ytterbia–neodymia–costabilized TZP—Breaking the limits of strength–toughness correlations for zirconia? J Eur Ceram Soc 2013, 33, 965–73. Kern F. High toughness and strength in yttria neodymia costabilized zirconia ceramics. Scr Mater 2012, 67, 301–04. Gadow R, Kern F, Gadow R, Kern F. Novel zirconia-alumina nanocomposites combining high strength and toughness. Adv Eng Mat 2010, 12(12), 1220–23. Kern F. Mechanical properties and microstructure of 1Y2Nd-TZP/20 vol.% alumina nanocomposites. Materialy Ceramiczne/Ceramic Mater 2012, 64(2), 168–71. Jiang D, Van der Biest O, Vleugels J. ZrO2–WC nanocomposites with superior properties. J Eur Ceram Soc 2007, 27, 1247–51. Bonny K, De Baets P, Vleugels J, Salehi A, Van der Biest O, Lauwers B, Liu W. Influence of electrical discharge machining on tribological behavior of ZrO2–TiN composites. Wear 2008, 265, 1884–92. Vanmeensel K, Laptev A, Van der Biest O, Vleugels J. Field assisted sintering of electroconductive ZrO2-based composites. J Eur Ceram Soc 2007, 27, 979–85. Salehi S, Yüksel B, Vanmeensel K, Van der Biest O, Vleugels J. Y2O3–Nd2O3 double stabilized ZrO2–TiCN nanocomposites. Mat Chem Phys 2009, 113, 596–601. Yuan ZX, Vleugels J, Van der Biest O. Preparation of Y2O3-coated ZrO2 powder by suspension drying. J Mat Sci Lett 2000, 19, 359–61. Kern F, Gadow R. Tough to brittle transition with increasing grain size in 3Yb-TZP ceramics manufactured from stabilizer coated nanopowder. J Ceram Soc Jap 2016, 124(10), 1083–89.

3 Rare earth oxide-stabilized zirconia ceramics and composites

39

[18] Anstis GR, Chantikul P, Lawn BR, Marshall DB. A critical evaluation of indentation techniques for measuring fracture toughness: I, direct crack measurements. J Am Ceram Soc 1981, 64(9), 533–38. [19] Chantikul P, Anstis GR, Lawn BR, Marshall DB. A critical evaluation of indentation techniques for measuring fracture toughness: II, strength method. J Am Ceram Soc 1981, 64(9), 539–43. [20] Dransmann GW, Steinbrech RW, Pajares A, Guiberteau F, Dominguez-Rodriguez A, Heuer A. Indentation studies on Y,O,-stabilized ZrO: II, toughness determination from stable growth of indentation-induced cracks. J Am Ceram Soc 1994, 77(5), 1194–201. [21] Cook RF, Lawn BR. A modified indentation toughness technique. J Am Ceram Soc 1983, 66(11), C-200-C-201. [22] Toraya H, Yoshimura M, Somiya S. Calibration curve for quantitative analysis of the monoclinic-tetragonal ZrO2 system by X-ray diffraction. J Am Ceram Soc 1984, 67(6), C119–21. [23] Cook RF, Braun LM, Cannon WR. Trapped cracks at indentations, Part I Experiments on yttriatetragonal zirconia polycrystals. J Mat Sci 1994, 29(8), 2133–42. [24] Cook RF, Braun LM. Trapped cracks at indentations, Part II Fracture mechanics model. J Mat Sci 1994, 29(8), 2192–204. [25] Swain MV, Rose LRF. Strength limitations of transformation-toughened zirconia alloys. J Am Ceram Soc 1986, 69(7), 511–18.

Rainer Gadow, Andreas Killinger, Venancio Martinez

4 Glass and glass ceramic layer composites with functional coatings Materials and process engineering, product development and applications Abstract: Functional coating deposition by thermal spraying is a sophisticated and versatile solution to improve superficial properties of machine components and system parts in various technical applications. They feature high flexibility, easy integration and high productivity with reduced production cost. The manufacturing by thermal spray technology of functional coatings with insulating and electrically conductive properties on glass or glass ceramic substrates is of outstanding interest for new application fields in environmental engineering, technical physics and advanced consumer industries, such as ozonizer tubes, solar absorbers, new energy efficient cooking plates or advanced sensors in packaging technology in this study. Due to the specific thermophysical properties of the substrate materials glass and glass ceramic, that is, low or even negative CTE, low heat conductivity and inability of plastic deformation, modified or new production processes in comparison to the established coating operations on metal substrates are required. It is of highest importance to prevent coating failure or the layer composite component collapse, due to the evolution and distribution of critical residual stresses in the composite induced during and after the deposition process, as well as by operational load stresses. In the described product development approach, the three coatings systems, metal oxide layer-composites, ceramic-metal mixed layers and ceramic mono-layers as conductive or insulating coatings on glass ceramics were thermally sprayed by APS with a predefined geometry. The influence of different process parameters on electrophysical and mechanical properties and residual stress distribution through the coating and substrate is analyzed. Finally, a concept to manage the mismatch of thermophysical properties by optimized heat and mass transfer as well as by application of sophisticated robot trajectories during coating operation is introduced and elaborated. Keywords: functional coatings, glass and glass ceramic, atmospheric plasma spraying (APS), oxide-metal layer composite, thermophysical properties, residual stresses, electrical conductivity, sensors in packaging technology Acknowledgment: The authors would like to thank Dr.-Ing. Miriam Floristán for her contribution to this work. Rainer Gadow, Andreas Killinger, Venancio Martinez, Universität Stuttgart, Institut für Fertigungstechnologie keramischer Bauteile (IFKB), Stuttgart, Germany, [email protected] https://doi.org/10.1515/9783110627992-004

42

Rainer Gadow, Andreas Killinger, Venancio Martinez

4.1 Introduction Thermal spraying is a well established technology to create and improve superficial properties of machine components and parts in various technical systems, with high flexibility, easy integration, high productivity and reduced production cost. A sophisticated and versatile solution for the deposition of a wide range of materials on metal substrates is thos process, but nowadays, the coating market requires coating operations and layer composite developments on new substrate materials. An important case to be considered is glass and glass ceramic substrate materials, which are characterized by specific thermophysical properties, that is, low or even negative CTE, low heat conductivity and inability of plastic deformation. However, modified or new production processes in comparison to the established coating operations on metal substrates have to be developed to overcome these special issues. The manufacturing by thermal spray technology of functional coatings with insulating and electrically conductive properties on glass or glass ceramic substrates are presented in new application fields for environmental engineering, technical physics and advanced consumer industries, such as ozonizer tubes, solar absorbers, new energy efficient cooking plates or special sensors in packaging technology. Due to the previously mentioned special characteristics of these substrate materials, it is of highest importance to prevent coating failure or the collapse of layer composite component, due to the evolution of critical residual stresses in the composite induced during and after the deposition process, as well as by operational load stresses [1]. In the described product development approach, three coatings systems, metal oxide layer-composites, ceramic-metal mixed layers and ceramic mono-layers as conductive coatings on glass ceramics were thermally sprayed by APS with a predefined geometry. A well-established ceramic material for coatings solutions with excellent mechanical stability is the titanium oxide. This titania oxide material shows a decrease of the electrical resistivity with the oxygen loss produced during thermal spraying, with good properties as semiconductor and sufficient electrical conductivity for this case of study. In this work, the development of electrically conductive coatings on glass ceramics substrates is presented. Atmospheric Plasma Spraying (APS) is used to deposit TiO2 and mixed TiO2/NiCrAlY coatings and compare the results with NiCrAlY top coating and Al2O3 bond coating systems, which are more established. The influence of different process parameters on coating electrical and mechanical properties and residual stress distribution through the coating and substrate is analyzed. Finally, a concept to manage the mismatch of thermophysical properties by optimzed heat and mass transfer as well as by sophisticated robot trajectories during coating operation are introduced and elaborated.

4 Glass and glass ceramic layer composites with functional coatings

43

4.2 Substrate material and spray powders

Thermal expansion coefficient [10-61/K]

The coating experiments were carried out on samples of commercial glass ceramic Robax® (Schott Glas AG), a transparent glass ceramic with a slight amber color designed on the basis of the system LAS (LiO2-Al2O3-SiO2) glass ceramic. The substrate glass ceramics are polycrystalline solids formed by controlled micro crystallization of glass. The production process of these materials can be divided in two steps. First, batches of defined composition are melted and the resulting parent glass is then formed in the desired shape. Second, the obtained glassy object is submitted to a specific heat treatment in order to transform it into glass ceramic material. During this process, the base glass material is first heated above the transformation temperature to form a nucleation phase. Next, higher temperatures are applied and crystallization of the material takes place. Glass ceramics contain crystalline phases and a residual glass phase up to 50% [2, 3]. Due to the effect of some crystalline phases with negative thermal expansion coefficients, such as β-quartz solid solution, β-eucryptite or β-spodumen, coupled with the presence of residual glass phases, characterized by positive thermal expansion coefficient, the resulting thermal expansion coefficient has a exceptional value close to zero or very low [3]. To determine the thermal expansion coefficient of the materials, as shown in Figure 4.1, a DIL 402C mechanical dilatometer (Netzsch-Gerätebau GmbH, Germany) was used. The measurements were performed form room temperature up to 1,000 °C with 5 K/min heating rate in atmospheric conditions. For the coating on glass ceramic, three coating systems were selected. The first coating system consists of a bilayer coating with a Al2O3 bond coating and a NiCrAlY top coating. The second system consists of a TiO2 nonstoichiometric coating. The third system consists of mixed TiO2–NiCrAlY coating. All powders were characterized to determine the particle size and morphology

16 NiCrAlY

14 12 10

TiO2

8 6

Al2O3

4 Glass ceramic

2 0 0

200

400

600

800

1000

Temperature [°C] Figure 4.1: Thermal expansion of coating and substrate materials determined by dilatometry [4].

44

Rainer Gadow, Andreas Killinger, Venancio Martinez

with a laser diffraction particle size analyzer model Mastersize S (Malvern Ltd, UK) and a scanning electron microscope (SEM) model LEO 483 VP (Carl Zeiss SMT AG, Germany), respectively. The alumina powder was supplied by CERAM GmbH (Germany), with a purity of 99.7%, acid washed, fused and crushed, and a particle size of −22 + 5 µm. Al2O3 coatings are used as insulating layer. For the deposition of the electrical conductive layer, water atomized NiCrAlY powder (GTV GmbH, Germany) with particle size −38 + 15 µm was used. Two different titania powder were used. The first titania powder from CERAM (CERAM GmbH, Germany) used was a fused and crushed powder with particle size −38 + 15 µm. The second titania powder from AMPERIT (H.C. Stark GmbH, Germany) used was a fused and crushed powder with particle size −38 + 15 µm. The substrate used is Robax® glass ceramic. Coated samples of 3 × 4 × 6 mm3 were used for the measured thermal expansion coefficient measurements, which results are represented in Figure 4.1. For the analysis optimized titania coating, only the CERAM powder is used due to the larger particle size distribution. SEM micrographs of the powders are shown in Figure 4.2.

a)

b)

10 μm

10 μm

d)

c)

10 μm

10 μm

Figure 4.2: SEM micrographs of (a) Al2O3 powder −22 + 5 µm, (b) NiCrAlY powder and (c) CERAM TiO2 powder −38 + 15 µm and (d) AMPERIT TiO2 powder −20 + 5 µm [5].

4 Glass and glass ceramic layer composites with functional coatings

45

4.3 Conductive coatings on glass ceramic substrates To produce the coating, a F6 atmospheric plasma spraying torch (GTV, Germany) was used. A Type RX 130 B industrial robot (Stäubli Tec-Systems GmbH, Germany) was used to move the torch with a meander movement to cover the surface samples. The dimensions of the glass ceramic substrates are 120 × 50 × 5 mm3. One of the most important process parameters are the substrate pretreatment processes, which are determining the adhesion of the coating. The conditions of the substrate surface during the coating process, such as roughness and temperature, define the splat morphology as well as the bonding mechanisms. Many studies have been carried out to analyze the surface substrate conditions and their influence on the coating build-up process. Heating the substrates previously to spraying gives tendency to disk-form splats and reduce the formation of microsplats to splash is reduced [6].The substrate roughness improves the mechanical interlocking between the splats and the substrate, but nevertheless can produce higher splashing of the splats [7]. Grit blasting is critical as pretreatment for glass substrates, due to the impact of the high velocity particles and the brittle nature of the material, being able to damage the surface of glass ceramics and decrease its strength. Previous studies have been carried out to analyze the bonding mechanisms between the coating and the glass or glass ceramic substrate, determining the chemical nature induced by thermal pretreatment as the main bonding mechanism [8]. All the samples in this work were pretreated by grit blasting and thermal treatment for the deposition of multilayer coatings on glass ceramic and the adhesion and stability of the coatings were analyzed. Cleaning and degreasing of the samples was carried out with acetone. The grit blasting process was performed with corundum particles, which are pneumatically accelerated against the sample surfaces, obtaining roughened slides. The coating efficiency increases in a range of 26% for roughened samples in comparison with the coating of smooth not grit blasted samples. Some of the roughened samples showed cracks at the substrate surface, as shown in Figure 4.3. The effect of grit blasting on the stress distribution in the layer and substrate is analyzed. The incremental microhole milling and drilling method is a well-known technique for the determination of residual stresses in themal spray coatings [9]. This technique had been implemented in this work to determine the residual stress depth profiles in the sprayed coatings, using 0.9 mm diameter diamont tools to drill and Vishay CEA-06-062UM120 strain gauge rosettes (0°, 45°, 120° directions) to determine the superficial strains. The experimentes were performed with a drilling hole diameter of 1.8 mm, drilling depth of 500 μm and incremental drilling steps of 10 μm. For thermal treatments of the samples, a structure composed of heating elements covered by a glass ceramic substrate holder sheet was used. Due to the mismatch in the thermophysical properties between glass ceramic and metals, the

46

Rainer Gadow, Andreas Killinger, Venancio Martinez

a)

b)

Al2O3

Glass ceramic

100 μm

50 μm

Figure 4.3: SEM image of (a) a grit blasted (0.6 MPa) glass ceramic substrate and (b) Al2O3 coated sample micrograph presenting cracks at the substrate surface caused by the grit blasting process.

deposition of the electrically conductive metal layer directly over the substrate leads to the formation of strong thermal stresses [10]. Experiments were carried out to determine the optimized sample heating temperature, which, in previous studies were in the range between 300 and 400 °C for glass or glass ceramic substrates [7, 8]. In the present work, these temperatures are too high and give rise to micro and macro cracks at the substrate surface in the coated areas, and lead to delamination of the coating system. Optimized heating temperature of 150 °C was determined with a preheated time of 10 minutes, until the substrate temperature was stabilized at 150 °C during the deposition process of the Al2O3 coating. For this reason, an intermediate ceramic oxide layer was deposited over the substrate before applying the electrically conductive coating. Al2O3 coatings of approximately 50 µm and metallic coatings of around 30 µm thickness were deposited. Al2O3 coatings on smooth and roughened heated samples presented high stability. It was after the deposition of the NiCrAlY layer that the adhesion mechanisms for smooth coated samples resulted in failure. A remarkable improvement in the adhesion of the coatings was recognized for the roughened samples. Adhesion measurements on Al2O3–NiCrAlY coatings with smooth and roughened surfaces were performed acording to the pull-off test. Stubs were fixed by an adhesive to the coating and an increasing load was applied using a standard universal testing machine (Zwick GmbH & Co, Germany). This test provides the maximal applied load to the stubcoating surface, until the stub was pulled off. Different surface roughnesses were analyzed. Samples were grit blasted with different air pressure, obtaining the average roughness values for the adhesion of Al2O3–NiCrAlY system represented in Figure 4.4. Adhesion pull-off test results are calculated as the average of six measurements and are shown in Figure 4.4. The adhesion measurement results should be interpreted carefully for some of the coating

4 Glass and glass ceramic layer composites with functional coatings

Substrate roughness [μm]

7.5

Surface roughness

30

Bond strength

25

6

20

4.5

15

3

10

1.5

5

Bond strength [MPa]

35

10.5 9

47

0

0 0

0.2 0.4 Grit blasting presure air [MPA]

0.6

Figure 4.4: Adhesion test results depending on the substrate roughness for Al2O3–NiCrAlY system.

systems, because the break down between the sample and the glued stub used to perform the adhesion test took place inside the glass ceramic and not precisely at the interface between the coating and the substrate. Therefore, only the results for the adhesion of Al2O3–NiCrAlY system were studied, because for the TiO2 and mixed TiO2–NiCrAlY coating could not be determined quantitatively. Residual stresses in the coating system are generated during the spraying process due to the mismatch between in thermophysical properties, as well as nonhomogeneous elastic and elastic-plastic deformation in macroscopic and microscopic scale owing to thermal and mechanical loads [9]. During the deposition process, the splats are deposited, splashed, cooled down and solidified, with a heat transfer to the substrate and environment. This leads to contraction of the individual splats, which is constrained by the small expansion of the substrate, resulting in tensile stresses in the coating. When the substrate and coating temperatures are compensated, the composite cools down to room temperature. During this process, the mismatch between the coefficient of thermal expansion (CTE) of coating and substrate leads to the formation of thermal stresses. In this case, these stresses are mainly of tensile nature, as the coating normally has a CTE higher than the glass ceramic substrate. If the residual stresses reach a critical value, the coating composite can lead to coating failure in form of cracks and delamination in the coating interface or plastic material deformation [11]. Results of residual stress measurements for thermally treated Al2O3 coated smooth and roughened samples are presented in Figure 4.5. Both samples had been coated with the same parameters and heating temperature. The coating applied over the smooth sample presents a maximum value of around 60 Mpa for tensile residual stresses. The sample which was grit blasted prior to the coating operation, although presenting stresses at the coating surface with similar value to the other sample, has a stress distribution in the coating around 20 MPa lower. It can be explained by the effect of the grit blasting process which induces compressive stresses at the substrate surface and therefore reduces the tensile residual stress value in comparison

48

Rainer Gadow, Andreas Killinger, Venancio Martinez

100 Al2O3 coating on smooth sample

Residual Stress [MPa]

80

Al2O3 coating on grit blasted sample NCrAlY-Al2O3 coating

60 40 20

0 -20 0

50

100

200 150 Drilling depth [μm]

250

300

Figure 4.5: Residual stress measurements in Al2O3 coating on not grit-blasted smooth glass ceramic substrate, Al2O3 and NiCrAlY–Al2O3 coatings on grit-blasted glass ceramic substrate [13].

with the not roughened samples. The deposition of NiCrAlY layer appeared to be a decisive factor in the development of residual stresses in the composite, forming cracks in the previously stable alumina coatings or delamination of the coatings, as shown in Figure 4.6. Experimental tests carried out in which NiCrAlY coatings over 50 µm thickness led to extreme residual stress distributions and delamination of the coating. a)

b)

Al2O3-NiCrAlY coating NiCrAlY

Al2O3

crack

Glass ceramic

40 μm

200 μm

Figure 4.6: (a) Microcrack originated after the deposition of the NiCrAlY coating, and (b) delamination of the coating system due to the residual stresses [13].

High amount of vertical cracks are observed in TiO2 coatings, as shown in Figure 4.7a, which are not desired for properties such as electrical conductivity. Cracks have a behavior like pores, regions with entrapped air, which act as electrical barriers along the coating. Coatings sprayed under high thermal load presents high density of cracks,

4 Glass and glass ceramic layer composites with functional coatings

a)

49

b) delamination

crack TiO2

Mixed TiO2–NiCrAlY 50 μm

1 cm

Figure 4.7: (a) Microcrack originated on TiO2 coating and (b) delamination on mixed TiO2–NiCrAlY coating on glass ceramic substrate system due to the residual stresses.

which are induced by tensile stresses formed during the cooling of the sample with high tamperature gradients, reducing the composite lifetime under dynamic load because they favour vertical crack formation and propagation [12]. For mixed TiO2/ NiCrAlY coatings, delamination of the coating is present, as shown in Figure 4.7b. Delamination is present in general TiO2/NiCrAlY 90/10 vol% coatings under all coating conditions, except for the short spray distance of 120 mm.

4.4 Coating optimization 4.4.1 Al2O3–NiCrAlY bilayer coating system In the present work, 5 mm width conductive coatings following a complex path with high dimensional accuracy were required. A first set of tests were performed with a wide area of Al2O3 and a thinner NiCrAlY top coating path with predefined pattern geometry, as shown in Figure 4.8a. A second set of tests with both Al2O3 and NiCrAlY coatings were applied over the same area following the predefined geometry, is shown in Figure 4.8b. It was found that the stability of the coating is strongly affected by the geometrical relation of thin coated paths of the Al2O3 and NiCrAlY coatings. Due to the stress concentration on the edges of the coating system, samples, where both coatings were deposited accurately following the same path geometry, present delamination of the whole Al2O3–NiCrAlY system at the interface with the substrate surface in some locations of the coating. Therefore, it is preferable to avoid this effect of stress accumulation at the edge of the layer composite system. To obtain coatings with the desired shape, masks are used during the spraying process and they must be resistant to the high thermal load of the flame and the

50

Rainer Gadow, Andreas Killinger, Venancio Martinez

a) NiCrAlY Al2O3

Glass ceramic substrate

5 cm

b) NiCrAlY Al2O3

Glass ceramic substrate

Figure 4.8: Cross section and area comparation between (a) coating system with wider bond coating and thinner top coating and (b) complex path coating system with same width for both bond and top coating [5].

elevated temperatures used to heat up the substrate. Moreover, the masking systems should allow the continuous deposition of the desired path for both Al2O3 and NiCrAlY coatings. Conventional metallic or PTFE (Teflon) massive masks are not suitable for this application due to the high thermal load during the process which leads to high deformation of the masks. The masking systems tested and analyzed are: PTFE sheet (Ammerflon GmbH, Germany), glass fiber spinnaker (SAHLBERG GmbH & Co, Germany), silicon coated glass fiber (Green Belting Industries limited, Canada) and silicon coated glass fiber/aluminium foil (Green Belting Industries limited, Canada). Best results are obtained with the silicon coated glass fiber mask, which fulfill the requirements in terms of dimensional stability, resistance to the thermal load and the possibility to use one single mask for the grit blasting and the whole coating process of the ceramic and metallurgical layers while maintaining an accurate geometry. For the Al2O3 and NiCrAlY coatings, samples were coated with varying meander offsets. For the alumina layer, offsets of 1 mm, 3 mm and 5 mm were studied, obtaining that the coating roughness and porosity decrease with the decrese of the meander offset, as shown in Figure 4.9. With lower offset, the distance between two consecutive passes of the robot over the substrate is decreased and the coating is built up in a more compact way over the substrate surface.

4.4.2 TiO2 coating system Many transition metal oxides present variations of their physical properties with the existence of phases with large variations from the apparent stoichiometric composition, which are the so-called homologous series. The composition of oxide phases

4 Glass and glass ceramic layer composites with functional coatings

Porosity [%]

8

10

Porosity Roughness

8

6

6

4

4

2

2

0

Roughness [μm]

10

51

0 1

3 Meander offset [mm]

5

Figure 4.9: Porosity and roughness values for samples coated with Al2O3 using different meander offsets [13].

for thermally sprayed TiO2 coatings is described by TinO2n −1, where n can present values between 4 and 10. The so-called denoted Magnéli phases are nonstoichiometry TiO2 with general oxygen deficiency in the crystal lattice, as well as oxygen vacancies or interstitial metal atoms [10, 14, 15]. The heating of TiO2 under pressure atmosphere with low oxygen or reducing hydrogen involves the formation of a ntype semiconductor. Rutile TiO2 is transformed in nonstoichiometric TiO2−x, TinO2n−1 Magnéli phase series, Ti3O5 and Ti2O3 by reduction, modifying thereby the electrical conductivity [16, 17]. Different coating parameters for TiO2 are studied, as shown in Table 4.1. The coating coloration, nonhomogeneity and differences in the colour distribution can Table 4.1: Coating parameters for TiO2 coatings [5]. Coating powder

TiO (– +  µm)

Coating distance

 mm

Electric arc current

 A

Plasma forming gas flow rate

 slpm Ar/ slpm H

Powder feed rate

 g/min

Carrier gas flow rate

 slpm Ar

Coating passes

 cycles

52

Rainer Gadow, Andreas Killinger, Venancio Martinez

Table 4.1 (continued) Modified spraying parameters Sample ref.

Torch velocity (mm/s)

Meander offset (mm)

Cooling

A





No

B





No

C D

 

 

No No

E





Yes

F





Yes

G





Yes

H





Yes

be used as a indicator of the titania oxide stoichimetry [5, 18]. Low torch velocity, meander offset or no compressed air cooling entails higher thermal load during the coating process, showing a dominance of the dark grey phases corresponding with rich in Ti and poor in oxygen areas, and therefore high substoichiometry (Magnéli: TiO1.750–1.900; Ti3O5: TiO1.667). Coatings under lower thermal loading due to simultaneous air cooling showed brighter coloration, regions closer to stoichiometry. The bigger phase contrast differences can be found between samples sprayed under opposite parameters concerning compressed air cooling, torch velocity and meander offset, as shown in samples A and H, whose cross-sectional micrographs are shown in Figure 4.10 and analysis of bright and dark spots are presented in Table 4.2. This analysis confirms that higher H2 contents in the plasma gases enhance the generation of substoichiometric phases [19]. Atmospheric plasma-sprayed coatings can present oxides due to the entrainment of oxygen in the plasma jet from the environment. This phenomenon is amplified with the use of compressed air cooling and higher oxidation is induced.

a)

b)

100 μm

5

c)

100 μm

4

2

1

7

3

6

50 μm

Figure 4.10: Cross section micrographs of (a) sample A, (b) sample H and (c) WDS analysis points of sample A [5].

4 Glass and glass ceramic layer composites with functional coatings

53

Table 4.2: WDS analysis in bright and dark spots of coating micrographs to obtain the atomic concentration [5]. Gray color Bright

Dark

Sample ref.

Ti conc. (%)

O conc. (%)

O/Ti ratio

A

.

.

.

B

.

.

.

C

.

.

.

D

.

.

.

E

.

.

.

F

.

.

.

G

.

.

.

Other coating characteristic to take into account for the coating optimization is the presence of vertical cracking, which has a similar effect as pores, acting as electrical barriers due to the entrapped air. Image analysis is performed to determine the vertical crack density in coatings per unit of length. The crack width per unit length of the coating was also determined as the section width of entrapped area in vertical cracks. It shows again that coating conditions with high thermal loads in the sample induce higher residual stresses that increase the density and width of the cracks, as shown in Figure 4.10c. These coatings present a well-defined network of vertical cracking with crack width values up to 12 μm/mm and high electrical resistivity. Tensile stresses are induced during the cooling down of the sample with high temperature gradients, favoring the formation and propagation of vertical crack and reducing the lifetime of the component under dynamic loads [8]. Coatings produced with compressed air didn’t present macrocracks, which presents crack density values down to 0.5–1.5 μm/mm and resistivity values as low as 100 mΩ cm. The best results of electrical conductivity are obtained in sample H. Therefore, these coating parameters are selected as standard parameter for further coating optimization. Further investigations of the most influencing parameters were carried out, such as H2 contents in the plasma gas and spray distance. In this case, a reduction of the spray distance must carry out a reduction of oxidation of the in-flight particles and therefore the coating. Furthermore, induced residual stresses are managed by the used of compressed air cooling and cracks are no more relevant, being therefore the coating electrical conductivity no more affected by this phenomenon and porosity determines the coating conductivity, as shown in Figure 4.11. An approximately 130 mm spray distance presents a critical point for the coating porosity and an optimal spray distance of 90 mm is given. H2 content in plasma gases was studied and samples to determine its effect keeping a constant vale of 56 slpm for the plasma gas flow, defined as the mixture

Rainer Gadow, Andreas Killinger, Venancio Martinez

400

4 Electrical Resisticity

300

3

Porosity

200

2

100

1

0

Porosity [%]

Electrical Resisticity [mΩ·cm]

54

0 90

210

120 150 180 Spray distance [mm]

Figure 4.11: Spray distance influence on TiO2 electrical resistivity and porosity values [5].

200

2 Elec. Res. Porosity

150

1.5

100

1

50

0.5

0

Porosity [%]

Electrical Resisticity [mΩ·cm]

of Ar and H2 gases. Experiments with different percentages of H2 between 10.7% and 23.2% in the plasma gas were carried out, obtaining a reduction of the electrical resistivity down to 50 mΩ cm. A similar trend for porosity and the electrical resistivity of the coating is observed, which decreases as the percentage of H2 decreases in the plasma gas, as shown in Figure 4.12.

0 10

15 20 H2 content in the plasma gas [%]

25

Figure 4.12: H2 content in the plasma gas influence on TiO2 electrical resistivity and porosity values [5].

As final results, it is concluded that higher contents of H2 produce higher loss of oxygen in TiO2, as shown in previous works [20]. A clear relationship between the contents of H2 in plasma gas and the crack density has not been observed.

4.4.3 TiO2/NiCrAlY coating system In order to improve the electrical conductivity of TiO2 coatings and also to reduce the production time in comparison to the Al2O3–NiCrAlY bilayer system, a NiCrAlY and TiO2 mixed feedstock powder is used. Diferent mixtures of TiO2/NiCrAlY with 10 vol%, 30 vol% and 50 vol% of NiCrAlY contents were sprayed on the glass

4 Glass and glass ceramic layer composites with functional coatings

55

ceramic substrates. Four spray distances between 120 and 265 mm for each powder composition were studied. From the performed experiments, adhesion problems and highly delaminated were present during the cooling down of coatings with 50 vol% NiCrAlY. Partial delamination is present in coating with 30 vol% NiCrAlY. According to the spray distance, best results of coating mechanical stability were observed in coating with 10 vol% NiCrAlY coated at a distance of 120 mm, but the TiO2 content in the mixture decreases with the increase of the distance and therefore the coating efficiency decreases. The lower coating TiO2 contents were observed as a color change, as well as a increase of the residual stresses, giving rise to layer delamination [5]. Three diferent colors can be observed in coating cross sections, corresponding to three phases. White color phases are observed strongly mixed with black color phases, which are attributed to oxidized NiCrAlY [21, 22]. A mixed dark grey color is observed as third phase, which corresponds to TiO2, as shown in Figure 4.13. The analysis of coating micrographs by image analysis provides the percentage in volume for each material, including the porosity volume percentage in the results for NiCrAlY oxide content due to impossibility to differentiate both of them. From the analysis of coatings with 10 and 30 vol% NiCrAlY, it is determined that NiCrAlY % content increases with the spray distance, with a tipping point around 140 mm, which is explained by the relationship between the deposition efficieny and the spray distance observed in the TiO2 coating system. The higher adhesion at 120 mm can be explained in this way, providing the mechanical stability for no delamination, with a lower level of residual stresses and higher adhesion values.

NiCrAlY content [%]

60 60 40 20 0 90

150

150 Spray distance [mm]

NiCrAlY 30 vol%: NiCrAlY 10 vol%:

Coating Coating

250

300

Feeding powder Feeding powder

Figure 4.13: Spray distance influence on NiCrAlY contents of TiO2/NiCrAlY coatings [5].

The electrical resistivity of both powder mixtures reduces with the increment of the spray distance, which is explained by the increase in the coating of the NiCrAlY contents. The coating resisitivity values for 30 vol% NiCrAlY are lower in comparison

56

Rainer Gadow, Andreas Killinger, Venancio Martinez

Electrical Resisticity [mΩ·cm]

with the coating with contents of only 10 vol% NiCrAlY, as expected and observed in Figure 4.14. 30 NiCrAlY 30 vol%

25

NiCrAlY 10 vol% 20 15 10 5 0 120

170 220 Spray distance [mm]

265

Figure 4.14: Spray distance influence on electrical resistivity of TiO2/NiCrAlY coatings [5].

4.4.4 Comparison between the different coating systems The different coating systems were deposited with a coating thickness around 100 µm to be comparable with the residual stress results. Coating with nonstoichiometric TiO2 shows the lowest tensile stresses, with values under 45 MPa. TiO2 powders mixed with 10 vol% NiCrAlY powder present an increase of the residual stresses up to values greater than 130 Mpa. In the case of the bilayer system consisting Al2O3 bond coating and NiCrAlY top coating, the maximal value of residual stresses is under 70 MPa. The analysis of the residual stresses at the interface between coating and substrate reflects that the values for all coating systems are around between 0 and 25 MPa, which is of great importance and critical for the coating stability because they can produce the coating failure by delamination due to adhesion failure. An overview of the most relevant characteristics of the three coating systems are presented in Table 4.3. Cross-sectional micrograph of the three coating systems are shown in Figure 4.15. A coating thickness of 100 µm is also selected to compare the electrical conductivity of the different coating systems as electrical conductor, showing that the most suitable coating system for the application is the coating system with Al2O3 bond coating and NiCrAlY conductive top coating. One-layer systems are interesting for the case in which the electrical conductivity requirements are fulfilled with the advantage of lower production time and lower cost. Of special interest is the TiO2 coating system, which presents low residual stress levels and therefore good adhesion, providing good mechanical stability.

57

4 Glass and glass ceramic layer composites with functional coatings

Table 4.3: Comparison between the three coating systems [5]. Coating system AlO–NiCrAlY

TiO/NiCrAlY / vol%

TiO

Min. electrical resistivity

 ± mΩ·cm

 ±  mΩ·cm

 ±  mΩ·cm

Max. tensile stress

 MPa

 MPa

 MPa

Coating adhesion

++

+

+++

Porosity

AlO: . ± .% NiCrAlY: n. d. %

. ± .%

. ± .%

Microhardness HV .

AlO: ±  NiCrAlY:  ± 

 ± 

 ± 

a)

b)

NiCrAlY

TiO2

c) TiO2 / NiCrAlY 90/10% vol

Al2O3 Glass ceramic

Glass ceramic

Glass ceramic 100 μm

100 μm

100 μm

Figure 4.15: Cross-sectional micrographs of the three studied coating sytsmes: (a) bilayer Al2O3–NiCrAlY, (b) TiO2 and (c) mixed phases TiO2/NiCrAlY coatings [5].

4.5 Conclusions This chapter presents an overview of the IFKB research activities in the development of functional electrically conductive APS sprayed coatings on glass ceramic substrates, with the extra requirement of high geometrical accuracy following the deposition path. The considerable differences between the substrates of glass ceramics and the traditional metals in mechanical engineering applications regarding their thermo-physical behavior, especially for the CTE with the low or even negative values, requires novel and adapted processes in order to control the development of thermal stresses in the system and not to damage the sensitive substrate. Three coating systems have been described. In comparison with the conventional bilayer coating system, formed by a first Al2O3 bond coating and second NiCrAlY top coating, new developments of a one-layer system are studied, due to advantages of the reduction of the production time and manufacturing cost. TiO2 and TiO2/NiCrAlY mixed phases with electrically conductive properties were produced by atmospheric plasma spraying.

58

Rainer Gadow, Andreas Killinger, Venancio Martinez

Plasma sprayed TiO2 coatings present an electrical conductivity, which is not only an intrinsic material characteristic but is further controlled by process induced micro structural patterns based on the formation of residual stress-induced cracks. Tensile stresses are generated by the high thermal gradients due to the thermal loads coming from thermal spraying, which produce cracks in the coating and in extreme cases, the failure of the system by coating delamination. The implementation of simultaneous compressed air cooling and the optimization of the process kinematics reduce the applied thermal load and therefore a control of the crack formation by residual stresses in the coating system. High H2 contents in the plasma gas mixture induce chemical reactions of TiO2, reducing the amount of oxygen and forming suboxide phases. Large spray distances enhance the particle oxidation and decrease the formation of substoichiometric phases. Simultaneous cooling has a similar effect. On the other hand, coating systems of TiO2/NiCrAlY mixed phases present a modification in the metal content with the spray distance. Spray distances over 130 mm reduce in turn the deposition efficiency of TiO2 and increase the NiCrAlY contents, which are leading to an increment of the electrical conductivity values, and also to increase the residual stresses in tensile values and reduce the coating adhesion. In conclusion, the nonstoichiometric TiO2 coating system presents the most mechanical stable coating, with the lowest tensile stress values and the higher coating adhesion, as well as an easier processing with not lower resistivity values than 50 mΩ·cm. For applications that require high conductive values, the bilayer Al2O3– NiCrAlY coating system is the most suitable.

References [1]

[2] [3] [4] [5] [6] [7]

Killinger A. Funktionskeramische Schichten durch thermokinetische Beschichtungsverfahren, Habilitationsschrift, Fakultät für Maschinenbau. Aachen: Universität Stuttgart, Shaker Verlag GmbH, ISBN 978-3-8322-9394-9, 2010. Bach H, Krause D. Analysis of the Composition and Structure of Glass and Glass Ceramics. Germany: Springer-Verlag Berlin Heidelberg, 1999. Bach H. Low Thermal Expansion Glass Ceramics. Germany: Springer-Verlag Berlin Heidelberg, 1995. Floristán M, Killinger A, Gadow R. Overview on developed functional plasma sprayed coatings on glass and glass ceramic substrates. Key Eng Mater 2013, 533, 115–31. Floristán M, Fontarnau R, Killinger A, Gadow R. Development of electrically conductive plasma sprayed coatings on glass ceramic substrates. Surf Coat Technol 2010, 205(4), 1021–28. McDonald A, Lamontagne M, Moreau C, Chandra S. Impact of Plasma-Sprayed Metal Particles on Hot and Cold Glass Surfaces. Thin Solid Films 2006, 514(1–2), 212–22. McDonald A, Chandra S, Moreau C, Spreading of Plasma-Sprayed Molybdenum on Grit-Blasted Glass, Thermal Spray 2008: Crossing Borders, DVS-Verlag, June 2–4, 2008 (Maastricht, The Netherlands), ASM International, 2008.

4 Glass and glass ceramic layer composites with functional coatings

[8] [9]

[10] [11]

[12]

[13]

[14] [15]

[16]

[17]

[18]

[19]

[20] [21] [22]

59

Gadow R, Killinger A, Li C. Ceramic on Glass and Glass-Ceramic Layer Composites for Industrial Applications. Ceram Eng Sci Proc 2002, 23(4), 125–38. Escribano M, Gadow R, Buchmann M. Residual stress analysis in thermally sprayed layer composites, using microhole milling and drilling method. J Therm Spray Technol 2005, 14(1), 100–08. Friedrich CJ, Atmospheric plasma sprayed dielectrical oxide coatings for ozone generators, Ph.D. Thesis, Universität Stuttgart, Shaker Verlag GmbH, Aachen, 2002. Wenzelburger M, Escribano M, Gadow R. Modeling of thermally sprayed coatings on light metal substrates: Layer growth and residual stress formation. Surf Coat Technol 2004, 180, 429–35. Floristán M, Montesinos JA, García-Marín JA, Killinger A, Gadow R. Robot trajectory planning for high quality thermal spray coating processes on complex shaped components, Thermal Spray 2012: Proceedings from the International Thermal Spray Conference and Exposition, May 21–24, Houston, Texas, USA, pp. 448–53, 2012. Floristán M, Gadow R, Killinger A, Electrically conductive plasma sprayed oxide-metal coatings on glass ceramic substrates, Thermal Spray 2009: Proceedings from the International Thermal Spray Conference and Exposition, May 4–7, Las Vegas, Nevada, USA, pp. 612–17, 2009. Li C, Herstellung und Optimierung plasmagespritzter Schichten auf Glaskeramik für elektrische Anwendungen. Ph.D. Thesis, Universität Stuttgart, Shaker Verlag GmbH, Aachen, 2003. Escribano M, Gadow R, Killinger A, Wenzelburger M. Metallic and dielectric coatings on glass ceramic – characterization and modelling of residual stresses. In: Kriven WM, Lin H-T, (eds.), Ceramic Engineering and Science Proceedings. Westerville: The American Ceramic Society, 2003, 193–200. Bao Y, Zhang T, Gawne DT. Computational Model for the Prediction of the Temperature in the Coating during Thermal Spraying, Thermal Spray 2004: Advances in Technology and Application. DVS-Verlag, May 10–12, Osaka, Japan, ASM International, 2004. Davids ES, Duncan SR, Grant PS, Modelling and validation of substrate heat transfer coefficient distribution in vacuum plasma spraying, Thermal Spray 2006: Building 100 Years of Success, B. R. Marple, M. M. Hyland, Y. C. Lau, C. J. Li, R. S. Lima and J. Voyer, Ed., May 15–18, Seattle, USA, ASM International, 2006. Branland N, Meillot E, Fauchais P, Vardelle A, Gitzhofer F, Boulos M. Relationships between microstructure and electrical properties of RF and DC plasma-sprayed titania coatings. J Therm Spray Technol 2006, 15(1), 53–62. Toma FL, Sokolov D, Bertrand G, Klein D, Coddet C, Meunier C. Comparison of the photocatalytic behavior of TiO2 coatings elaborated by different thermal spraying processes. J Therm Spray Technol 2006, 15(4), 576–81. Ohmori A, Park K-C, Inuzuka M, Arata Y, Inoue K, Iwamoto N. Electrical conductivity of plasma-sprayed titanium oxide (rutile) coatings. Thin Solid Films 1991, 201(1), 1–8. Killinger A, Gadow R. Thermally sprayed coating composites for film heating devices. Adv Sci Technol 2006, 45, 1230–39. Wu YN, Zhang G, Feng ZC, Zhang BC, Liang Y, Liu FJ. Oxidation behavior of laser remelted plasma sprayed NiCrAlY and NiCrAlY–Al2O3 coatings. Surf Coat Technol 2001, G. Eason, B. Noble, and I.N. Sneddon, On certain integrals of Lipschitz-Hankel type involving products of Bessel functions, Phil. Trans. Roy. Soc. London, vol. A247, pp. 529–51, 1955, 138(1), 56–60.

Zaffar M. Khan, Saad Nauman, M. Ali Nasir

5 Structural health monitoring of glass fiber composite materials by piezoelectric nanosensors under cyclic loading Abstract: In this chapter, we have investigated cyclic response of smart sensing layer deposited on glass fiber composite material substrate. The smart layer was composed of a thermoplastic matrix (high-density polystyrene) and a dispersed nanofiller (carbon nanoparticles). This is in continuation of our earlier work where we successfully demonstrated structural health monitoring capability of such smart layers. Cyclic tests were performed to demonstrate the repeatability of the sensor as well as various characteristics such as linearity, saturation and general response characteristics. The substrate chosen was glass fiber laminated composite comprising eight layers of woven fabric reinforcements fabricated using vacuum-assisted resin transfer molding technique. The smart sensing layer was deposited on the composite specimens in the center using doctor blade and a slot die. The dynamic response of the smart layer reveals that the sensors are able to follow loading and unloading cycles without any delay. The response of the sensor is frequency dependent with saturation/noise observed at high-frequency cyclic testing. The smart layer also demonstrates repeatability when cyclic loads are applied. Keywords: cyclic loading, sensor, composites, smart layer, structural health monitoring

5.1 Introduction In recent times, industry has witnessed wide application of high-strength composite materials especially in the areas of aerospace, automotives, civil engineering and sports/leisure. Their success in these fields has been due to their exceptional mechanical properties and a mix of supplementary traits such as corrosion resistance, shaping ability and parts consolidation. For reliable use of composite materials, their design schemes should be well understood and maintenance procedures should be developed. Maintenance requires inspection, which is generally scheduled

Zaffar M. Khan, Aeronautics and Astronautics Department, Institute of Space Technology, Islamabad, Pakistan Saad Nauman, Materials Science and Engineering Department, Institute of Space Technology, Islamabad, Pakistan M. Ali Nasir, Mechanical Engineering Department, University of Engineering and Technology, Taxila, Pakistan https://doi.org/10.1515/9783110627992-005

62

Zaffar M. Khan, Saad Nauman, M. Ali Nasir

in case of traditional metal parts where damage has limited types and causes. On the other hand, due to the anisotropic nature of fiber reinforced composite materials, damage can occur and propagate in a number of ways. As a consequence, scheduled inspection might be too late to avoid the loss of life and property. Continuous monitoring of composite parts during their service life is one possible solution to this problem. In service, structural health assessment of FRPs enhances operational reliability by providing means for safe operating conditions. It might be said therefore that the development of cost-effective online structural health monitoring schemes is the need of the hour. The use of different sensing mechanisms has been thoroughly researched and reviewed in literature. Acoustic emission, X-ray tomography, fiber Bragg gratings and digital image correlation have been reported as structural health and integrity monitoring methods [1–6]. The use of smart materials as sensing members of the structure has also been investigated as an alternative structural health monitoring method. Exploiting electrical properties of materials has proven to be a useful tool of making a material sensitive to load or strain. For instance, electrical response in relation to an applied strain or deformation can be monitored in real time for extracting useful information about a structure’s health [7]. Carbon-based smart materials owing to their strength and piezoresistive properties can be used to make strain gauges with gauge factors exceeding those of traditional metal foil types. These strain sensors are widely reported to provide useful information about the mechanism of failure of composites in cyclic loading above and below the strength level of material [8–11]. Conductive nanofillers of carbon such as carbon nanoparticles (CNPs), carbon nanotubes (CNTs) and graphene nanoplatelets can be used in conjunction with a suitable matrix to enhance conductivity up to appreciable levels [12, 13]. For carefully maintained concentration levels, these composites can be made piezoresistive owing to the tunneling effect at percolation threshold of the nanofiller [14–19]. Incorporation of such fillers in a suitable thermoplastic or an elastomer can result in composites that can serve as sensors when attached to the target substrate just like a metal foil strain gauge. The main advantages of such smart gauges for strain sensing are their low cost, ability to engineer properties/geometry and their exceptionally high sensitivities/gauge factors [20, 21]. Smart composites have been a subject of intensive academic research. Many different approaches have been investigated in this regard. Among these, fiber Bragg grating sensors [4, 22–25] and use of nanofillers for in situ monitoring of composites [15–18] appear to be the forerunners as far as composite structures are concerned. Different aspects of these smart composites have been investigated recently. Zheng et al. [25] reported the behavior of polymer matrix composites (PMCs) with highdensity polyethylene as the matrix and carbon black as the filler material at percolation threshold under low number of tensile cycles. The effect of maximum applied strain on residual resistance of GFRP/CB composites has also been studied [11] and

5 Structural health monitoring of glass fiber composite materials

63

it was found that residual resistance of composite structures can be used to determine previously applied maximum strain. The behavior of CB/polypropylene (PP) and CNT/PP composites under cyclic tensile loading was discussed by Zhao et al. [26]. They proposed possible reasons for different behaviors of CB/PP and CNT/PP composites. According to their findings, in CNT/PP, due to gradual loading and unloading, a better conductive network was developed owing to hysteresis effect which is the direct result of viscoelastic nature of composite materials. This chapter investigates the behavior of polystyrene (PS)/CB smart coatings under cyclic loading for online in situ structural health monitoring. This smart coating has already been investigated under monotonic loading in one of our earlier research works [15].

5.2 Experimental 5.2.1 Preparation of smart sensing layer High-density PS was selected as the matrix material whereas CNPs supplied by Degussa were used as nanoparticles. These particles have spherical geometry and their average diameter is reported to be 50 nm. It has been found through repeated and systematic investigations that when weight concentration of these particles is maintained at 35%, the resulting PMC becomes piezoresistive [18, 27] since the said concentration pertains to the percolation threshold of these nanoparticles in the PS. The dispersion was prepared by adding PS and CNPs in benzene solvent. The mixture was stirred overnight to allow nanoparticles to disperse thoroughly in the matrix.

5.2.2 Fabrication of composite specimens The composite substrate chosen for the purpose of smart layer deposition was laminated structures comprising eight plies of plain woven glass fabric supplied by Interglas Technologies GmbH (Interglass 92110). The epoxy resin used was Araldite LY5052 with hardener Aradur 5052 supplied by Huntsman®. The process used was vacuum-assisted resin transfer molding. In this way, sheets of composite laminates were prepared.

5.2.3 Specimen geometry The sheets of composite laminates were cut into rectangular specimens using Metacut M-350. Thereafter, smart sensing layer was deposited in the middle of

64

Zaffar M. Khan, Saad Nauman, M. Ali Nasir

these specimens (described in the next section). The exact dimensions of composite specimens along with the length of deposited smart layers have been reported in Table 5.1. Table 5.1: Specimens’ geometric parameters. Specimen no.

Specimen width (mm)

Specimen length (cm)

Thickness (mm)

Smart layer length (mm)



.

.

.





.

.

.

.



.

.

.

.



.

.

.

.



.

.

.

.



.

.

.

.

5.2.4 Deposition of smart layer The smart layer was deposited in the middle of the specimen surface using doctor blade technique while employing a slot die of the dimensions roughly equal to that of the intended smart layer. The deposited smart layer is shown in Figure 5.1. The exact dimensions of these layers, after deposition on different specimens are reported in Table 5.1.

5.2.5 Data acquisition and filtering Commercially available data acquisition module, KUSB 3100, was used for the purpose of data acquisition. For data amplification, an instrumentation amplifier INA101 was employed. The unknown resistance of the smart sensing layer was connected in Wheatstone configuration. Moreover, low-pass filters also helped reduce noise in the sensor output.

5.3 Experimental methodology These specimens were mounted on MTS 810 for cyclic tensile loading as shown in Figure 5.2.

5 Structural health monitoring of glass fiber composite materials

65

Figure 5.1: Specimens with smart coating and conductive silver paint connections.

Figure 5.2: Specimen mounted on MTS 810 with extensometer and electrical connections.

A maximum load of 25% of the breaking load was applied in the cyclic configuration. The 25% breaking load applie, corresponds to 120 MPa testing load. Total number of cycles were kept as 20 for all the tests. The frequencies were adjusted to achieve a specific strain rate in the gauge length. Table 5.2 gives all the strain rates and the corresponding loading frequencies along with the initial force and amplitude of cyclic loading.

66

Zaffar M. Khan, Saad Nauman, M. Ali Nasir

Table 5.2: Testing parameters adopted for cyclic tests. Specimen no.

Strain rate (mm/min)

Frequency (Hz)

Initial force (MTS ) (kN)

Amplitude (mm)

No. of cycles





.

.

.







.





.





.





.





.

5.4 Results and discussion Since the specimens are made of viscoelastic material, high strain rates give smaller absolute strain values for the same load. It is thus seen that the sensor has a deformation limit up to which it gives a linear response. Beyond this limit, the dwell and noise start to appear. From these results, it can be inferred that the saturation level of the sensor changes with the increase in deformation rate (upper limit is reduced). The graph plotted in Figure 5.3 defines the limit of response for this smart sensing layer. The area lower than the curve represents the effective range of the sensor with respect to the applied strain rates. The loss of sensor range is of the order of 250% in the tested range of frequencies. The loading and unloading curves of the sensor represent another interesting characteristic. The rising and falling curves are more or less coincident, with better coincidence for higher strain rates. At lower strain rates, the difference between the two curves is more pronounced. However, the end points of the curves (max and min strain) match perfectly (Figure 5.3). The difference in loading and unloading does not seem to be maximum strain range dependent. The knee in the curves is due to the maximum strain saturation limit achieved at higher loads. The cyclic response and load–unload response leads us to believe that the max strain range limit is actually dependent on the material of the sensor. The viscoplastic behavior of the PS used for the sensor material will change with increase in deformation rate. Since the sensor works on the effect of tunneling and breakage of conductivity networks due to tensile loading, a difference in the deformation characteristics of the PS would strongly influence the sensor response. The first cycle is perfect with respect to sensor response. However, due to cycling, it cannot be assured that the PS will maintain a constant response to the applied load or strain. Cyclic

67

5 Structural health monitoring of glass fiber composite materials

1.60E–03 Sensor saturation limit

1.40E–03 1.20E–03 1.00E–03 8.00E–04 6.00E–04 4.00E–04 2.00E–04 0.00E+00 0

100

200

300

400

500

Strain rate Figure 5.3: Limit of response for the smart sensing layer under cyclic loading.

hardening or softening of the sensor material may modify the sensor response to a great degree. This is seen that at the last cycle, the sensor measurement range has changed considerably. At higher cycling rates, the response stabilizes more quickly and remains constant. The hysteresis curves indicate that the sensors show some hysteresis at all deformation rates. Higher noise in the cyclic response corresponds to the higher hysteresis in response.

5.5 Conclusions The results demonstrate that the smart sensing layer developed and applied on composite specimens can be used for monitoring structural vibrations, mechanical excitation and cyclic loads. The coating remained intact within a safe strain limit and showed no physical damage after 20 cycles. It is clear that the resistivity change is in adequate agreement with the strain. Further study of the large strain sensing ability of the smart sensing layer is focused at increasing the bandwidth of the dynamic response, minimization or correction of resistance drift and determination of the long term reliability of the sensor material. Funding sources: This work was not sponsored financially by any organization. Conflict of interest: Authors declare that there is no conflict of interest.

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References [1] [2]

[3]

[4] [5] [6] [7] [8] [9] [10] [11] [12] [13]

[14] [15]

[16]

[17] [18] [19] [20] [21]

Fu T, Liu Y, Li Q, et al. Fiber optic acoustic emission sensor and its applications in the structural health monitoring of CFRP materials. Opt Lasers Eng 2009, 47, 1056–62. Hamdi SE, Le Duff A, Simon L, et al. Acoustic emission pattern recognition approach based on Hilbert–Huang transform for structural health monitoring in polymer-composite materials. Appl Acoustics 2013, 74, 746–57. Naderi M, Kahirdeh A, Khonsari MM. Dissipated thermal energy and damage evolution of Glass/Epoxy using infrared thermography and acoustic emission. Compos Part B Eng 2012, 43, 1613–20. Panopoulou A, Loutas T, Roulias D, et al. Dynamic fiber Bragg gratings based health monitoring system of composite aerospace structures. Acta Astronautica 2011, 69, 445–57. Unnthorsson R, Runarsson TP, Jonsson MT. Acoustic emission based fatigue failure criterion for CFRP. Int J Fatigue 2008, 30, 11–20. Wang P, Takagi T, Takeno T, et al. Early fatigue damage detecting sensors – a review and prospects. Sens Actuators A Phys 2013, 198, 46–60. Swait TJ, Jones FR, Hayes SA. A practical structural health monitoring system for carbon fibre reinforced composite based on electrical resistance. Compos Sci Technol 2012, 72, 1515–23. Chung DDL. Carbon materials for structural self-sensing, electromagnetic shielding and thermal interfacing. Carbon 2012, 50, 3342–53. Ku-Herrera JJ, Avilés F. Cyclic tension and compression piezoresistivity of carbon nanotube/ vinyl ester composites in the elastic and plastic regimes. Carbon 2012, 50, 2592–98. Materazzi AL, Ubertini F, D’Alessandro A. Carbon nanotube cement-based transducers for dynamic sensing of strain. Cem Concr Compos 2013, 37, 2–11. Okuhara Y, Matsubara H. Carbon-matrix composites with continuous glass fiber and carbon black for maximum strain sensing. Carbon 2007, 45, 1152–59. Pham GT, Park Y-B, Liang Z, et al. Processing and modeling of conductive thermoplastic/ carbon nanotube films for strain sensing. Compos Part B Eng 2008, 39, 209–16. Sohi NJS, Bhadra S, Khastgir D. The effect of different carbon fillers on the electrical conductivity of ethylene vinyl acetate copolymer-based composites and the applicability of different conductivity models. Carbon 2011, 49, 1349–61. Knite M, Linarts A. Polymer/Nanographite Composites for Mechanical Impact Sensing. Graphene-Based Poly Nanocomposites Electron 2015, Springer, 223–52. Nasir MA, Akram H, Khan ZM, et al. Smart sensing layer for the detection of damage due to defects in a laminated composite structure. J Intell Mater Syst Struct 2014, 1045389X14554138. Nauman S, Cristian I, Koncar V. Simultaneous application of fibrous piezoresistive sensors for compression and traction detection in glass laminate composites. Sensors 2011a, 11, 9478–98. Nauman S, Cristian I, Koncar V. Intelligent carbon fibre composite based on 3D- interlock woven reinforcement. Text Res J 2012, 82, 931–44. Nauman S, Lapeyronnie P, Cristian I, et al. Online measurement of structural deformations in composites. Sens J IEEE 2011b, 11, 1329–36. Vertuccio L, Vittoria V, Guadagno L, et al. Strain and damage monitoring in carbon-nanotubebased composite under cyclic strain. Compos Part A Appl Sci Manuf 2015. Hierold C, Jungen A, Stampfer C, et al. Nano electromechanical sensors based on carbon nanotubes. Sens Actuators A Phys 2007, 136, 51–61. Hu N, Karube Y, Yan C, et al. Tunneling effect in a polymer/carbon nanotube nanocomposite strain sensor. Acta Mater 2008, 56, 2929–36.

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[22] Maaskant R, Alavie T, Measures R, et al. Fiber-optic Bragg grating sensors for bridge monitoring. Cem Concr Compos 1997, 19, 21–33. [23] Murukeshan V, Chan P, Ong L, et al. . Cure monitoring of smart composites using fiber Bragg grating based embedded sensors. Sens Actuators A: Phys 2000, 79, 153–61. [24] Takeda N, Okabe Y, Kuwahara J, et al. Development of smart composite structures with smalldiameter fiber Bragg grating sensors for damage detection: Quantitative evaluation of delamination length in CFRP laminates using Lamb wave sensing. Compos Sci Technol 2005, 65, 2575–87. [25] Zheng S, Deng J, Yang L, et al. Investigation on the piezoresistive behavior of high-density polyethylene/carbon black films in the elastic and plastic regimes. Compos Sci Technol 2014, 97, 34–40. [26] Zhao J, Dai K, Liu C, et al. A comparison between strain sensing behaviors of carbon black/ polypropylene and carbon nanotubes/polypropylene electrically conductive composites. Compos Part A Appl Sci Manuf 2013, 48, 129–36. [27] Cochrane C, Lewandowski M, Koncar V. A flexible strain sensor based on a conductive polymer composite for in situ measurement of parachute canopy deformation. Sensors 2010, 10, 8291–303.

Dragan Djurdjević, Vojkan Mitić, Miroslav Stevanović, Ljubiša Kocić

6 Fractal tools in combating terrorism and money laundering Abstract: Information society imposes globalization and universalization of values. In these circumstances, terrorism, as institutional political violence which attempts to spread morbid fear, becomes a threat not only to the nations but also to politics on the global level. Today, intelligence activities in combatting terrorism encompass financial investigations and money laundering for financing terrorism, which results in broadening of the scope of data to the level that is impossible for human logical evaluation. Technologies development increased the capacity of speed and the amount of data processing, which has enabled the computer experiments and simulations trying to get to more complex planning and forecasting to counterterrorism and “dirty” money transaction, as highly dangerous, complex and variable phenomena. This presentation aims at quotation the wide spectrum of mathematically founded fractal concepts suited to generate computer models of antiterrorist activities. In this sense, the logistic behind the items connected with detecting and recognizing the degree of terroristic threat by comparing fractal structure of people’s faces, fast search through the databases of faces and fingerprints. The speed of searching processes is of vital importance, which promotes the crucial importance of compression and data reduction with preservation of regularity. Especially important are analytic forecasting of missing visual data and forms, to supplement the empirical evidences and records. All these operations are possible with higher degree of knowledge utilization and adaptation of virtual reality in the fight against terrorism and different forms of money laundering. The results indicate that the achievements implementation of the concept of fractals depends on substantial prior knowledge, environmental influences, subsystem integration, decentralization and synchronization, and allows us to come up with similar high information technology models, but not necessarily to enable identification of the authentic features of the various anomalies that result in objectively asocial consequences. In this sense, we conclude that the application of information technology in the fight against terrorism, based on the concept of fractals has its place in the arsenal of antiterroristic prevention. Keywords: terrorism, money laundering, identification, fractal recognition, fractal compression

Dragan Djurdjević, Miroslav Stevanović, Academy of National Security Belgrade, Serbia Vojkan Mitić, Institute of Technical Sciences of SANU, Belgrade, Serbia Ljubiša Kocić, Faculty of Electronic Engineering, University of Niš, Serbia https://doi.org/10.1515/9783110627992-006

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6.1 Introduction Information society is characterized by intensified globalization and universalization of values. Operative politics and decision making on national and global levels, in these circumstances, face two challenges for the processes of globalization and universalization of values: terrorism and money laundering (ML). Terrorism, as an institutional political violence aimed at spreading fear within society, undermines the institutional order. On the other side, ML undermines foundation of globalization – the financial order. In 1996, the International Monetary Fund’s Interim Committee, its highest decision-making authority, estimated that 2–5% of the global gross domestic involved laundering money. These challenges have propelled a need for a new approach to national security, which now requires efforts to maintain the position of a state within global mechanisms. Every country is thus becoming engaged in combating terrorism (antiterrorism (AT)) and ML (antimoney laundering (AML)), perceived as transnational threats for “common values,” even if they are not directly threatened. Information age has enabled that agencies and institutions that are responsible for AT and AML at various phases have the capability to obtain and store vast number of data. Today, for example, intelligence activities in preventing and combatting terrorism include financial investigations of financing terrorism, resulting in broadening of the scope of data to the level which makes it impossible for human logical evaluation. Technologies development has enabled increasing capacity of speed, and the amount of data processing has enabled defining, analyzing and exploring more and more models. This led to evolution of computer experiments and simulations in an effort to achieve more complex planning and forecasting in countering terrorism and “dirty” money transaction, as highly dangerous, complex and variable phenomena. From the aspect of information technologies, since geometric shapes can be divided into parts that are miniature copies of the whole, fractals have emerged as suitable, in the sense that they provide visual projection of mathematical formulas. These transformation methods can be used to translate, scale, shear and rotate available data, creating an image. From the practical aspect, partitioned encoding of the total image will be smaller, but it will preserve the close resemblance to the characteristics of the whole. Thus, a fractal compressed image offers a form of interpolation, and its accuracy depends on resolution [1] (e.g., image in two resolutions, Figure 6.1).

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Figure 6.1: BaTiO3 ceramic grain from previous SEMs represented as numerical 3D surfaces in two resolutions.

6.2 Terrorism and ML as fractal concepts A fractal shape is geometry with scale. Applied on a phenomenon, it would be its middle ground. When faced with an occurrence that is based on a logic of growth and hierarchical scale (subsystems and networks), fractals should thus be suitable to create a model of such occurrence. The fact that fractals represent a middle ground implies that they necessarily involve a certain level of presumption. They, thus, also provide the ability to develop an educated guess about a phenomenon, though artificial to a degree (e.g., DNK model, Figure 6.2). Fractals are fabricated by the repetition of a geometric over a succession of hierarchical scale. The result is an image that describes the grid partitioning (the range blocks), on the one side, and that transforms per range block, on the other. This method of achieving an image of a subsystem from reality involves five basic issues: first, partitioning the image; second, forming the set of blocks; third, selecting the type of transformations that will be considered; fourth, selecting a distance metric between blocks; and fifth, specifying a method for pairing blocks. On the practical level, this requires that the coding process should provide for as precise as possible measure and quantification of errors in the compressed image. This is obtained through series of presumptions. Minimizing an error measure, as the practical application shows, may be of dubious value for recognition [2] (e.g., iterations of face, Figure 6.3). With respect to error measures, the scaling is fabricated through the mentioned repetition of a geometric act over a succession of hierarchical scale. The result obtained is an axis of scale symmetry. In scaling terrorism or ML wider image, coding

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C A G

G T

C

0.0

T 0.0 C

G A

T

G

C A

G A G

C T

NUCLEO BASE adenine cytosyne guanine thymine

–0.5

–1.0

DF < 2

T Phosphatedeoxyribose backbone

–1.5

–1

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Figure 6.2: Left: DNK chain segment of 104 pairs; right: geometric code forms a Brownian-like walk graph.

requires a computable error measure that would accurately capture impression of human viewers [3] (e.g., signature reconstruction, Figure 6.4). As per the model of the complex adaptive system (CAS), an organization that wants to cope with the accelerated rate of change can rebuild itself as a system. This quality provides for its independent functioning, in terms of the possibility to exploit the existing patterns for immediate, independent solutions (from bottom to top) [4]. The CAS model imitates the principles of a targeted natural system established on a decentralized deployment of autonomous cells (subsystems and fractals) acting independently in relation to environment. The effectiveness of the obtained model depends on two processes: first, on the capability of each fractal to independently carry out its assignment; and second, on the permanent integration of resources by transfer of relevant information among the fractals. From the aspect of computation, the important feature is that the specific knowledge of one cell is functional for all the other cells (fractals). The finding that is reached depends on five criteria: (1) definition of foci of system activities that have the potential for future growth; (2) relevant adaptation of organizational response to external events; (3) the integration between subsystems is brought about by dynamic work processes that enable coordination between the organization and its subsystems; (4) decision making on local level; and (5) adaptation of the organization’s ability to cope with changes in its environment, personal development and individual specialization of every participant.

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Figure 6.3: Sequence of images produced by random iteration on a superfractal, converging to a sequence of subtly different faces.

The way CAS operates, as studies show, has similarities with at least two patterns of behavior of terrorist organizations. Terrorist organizations operate as integrative networks of independent cells, and second, they are perceived as organizations with the ability to initiate actions even while the elements of certainty in their environment are changing [5]. Thus, by the analogy to CAS, the use of fractals can provide for the researcher of organized network of terrorism or ML, to overcome the following challenges: core competence, surrounding influence, recycling flow effect, decentralization and synchronization of knowledge resources.

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Figure 6.4: Examples of genuine signatures (left) and skilled forgeries (right) from the GPDS-160 dataset.

In the period since 9/11 attack in New York, the computational social science has recognized the practical aid of information technologies in combating terrorism, above all through the possibility of automation of visualizing of data available on the social networks, by their scaling or modeling. Computational social scientists argue that modeling and simulation techniques are uniquely suited to understanding the dynamics of emerging threats, at a time when national security decision makers are urgently looking for new frameworks, data sources and technologies for making sense. Computational social modeling and simulation have the capacity to enhance understanding of a wide range of national security problems, including terrorism and terrorist network detection.

6.3 Fractal tools against terrorism and ML A wide spectrum of mathematically founded fractal concepts is used to generate computer models of terrorist or ML activities. The logistics behind the items connected with detecting and recognizing the degree of threat involves comparing fractal structure of people’s faces, fast search through the databases of faces and fingerprints. In searching, the speed of processes is of vital importance, and the result depends on the ability of compression and reduction of data with preservation of regularity.

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Especially important is the analytic forecasting of missing visual data and forms, in addition to the empirical evidences and records.
 Let fw1 , w2 , . . ., wm g be a set of m contractive mappings of metric space Rk , d   in itself. Shortly, S = Rk ; w1 , w2 , . . ., wm will be called (hyperbolic) iterated function system (IFS). Let X be the bounded set from Rk and H ðÞ denotes the partitive set. To the IFS S, the Hutchinson operator W ðXÞ =

m [


 wi ð XÞ, X  Rk or X 2 H Rk

i=1

If s1, s2, . . ., sm, (|si| < 1) are respective Lipschitz factors of the mappings w1, w2, . . ., wm, and X, Y are arbitrary subsets of Rk , then hðWðXÞ, WðYÞÞ ≤ s hðX, YÞ where s = maxfs1 , s2 , . . . , sm g < 1 is now the Lipschitz factor of the whole IFS, endowed with Hausdorff metrics h. It follows that Hutchinson operator W is also a
 contraction in the metric space HðRk Þ, h . The Collage Theorem ([6, 7]). Let (X, d) be a complete metric space, and let
 X 2 H Rk and Ɛ > 0 be as given. Choose an IFS {X; wl, w2, . . ., wN} with contractivity factor 0 < s < 1, so that  [  N wn ðLÞ ≤ ε h L, n=1

where the Hausdorff metric h is induced by the Euclidean one. Then, hðL, AÞ ≤ ε=ð1 − sÞ where A is the attractor of the IFS. Example: Figure 6.5 shows the principle of construction of the IFS, and the associated Hutchinson operator W for fractal reconstruction of a handwritten letter h. It is found that six affine transformations were derived by decomposition of the linear structure of the letter, the set S 2 R2 , to seven parts (subsets).

Figure 6.5: Formation of IFS system for a handwritten letter “h.”

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The subset denoted by a (Figure 6.5, left) can be affinely transformed to other six parts, each associated with the transformation wi. The operations of generating computer models by mathematically founded fractal concepts are enabled through the higher degree of utilization of knowledge and adaptation of virtual reality in prevention of terrorism and ML. So, achievements in implementation of the concept of fractals depend on substantial prior knowledge, environmental influences, subsystem integration, decentralization and synchronization. It allows obtaining a similar high information technology models, but not necessarily the identification of the authentic features of the various anomalies that result in objectively asocial consequences. The development of computer technologies enabled wider scope of usefulness of fractals, as artistic field of mathematics (e.g., recreating the terrain and 3D iteration of parts), in creating virtual space like natural forms. Also, since fractals can be divided into miniature representations of the whole, compression and reduction of data provide the opportunity for anticipation of the wider processes, for the analysis of patterns, which has the application in the imitation of networks. Fractal structure does not have regularities and, in practice, it represents a supplement to experience and a higher level of use of knowledge and adaptability to reality. Computer forensics, which is aimed at collecting, identification, delivering and documenting computer for the need of a state, thus, also has a role in the work of intelligence services. Available and incoming data and their elements can be evaluated from the aspect of their complex patterns of spatial distribution, providing a fractal dimension, which introduces a tendency toward a more linear, and thus one-dimensional, structure [8]. That makes it suitable for automatized analytical and synthetic operations, based on programmed criteria, which would otherwise require lengthy logical or forensic procedures. This method has found its role in the analysis of potential scenarios, as simulation, forensics of scripts, evaluation of behavior, cognitive and psychological states (except emotional inflections and nuances), excluding information security (private massaging, digital money, online services, etc.). Fractal tools can be used in combating terrorism and ML, for at least five intelligence goals. First, the most acknowledged is the analysis of terrorist (money launderers) social networks. This includes three types of input: information intelligence on the intensive use of the Internet to communicate; human intelligence about the contacts of suspected terrorists; and technical intelligence about contacts of suspect terrorists [9]. The research is basically related to the structure of interconnections and interactions, and the analysis of possible bases for terrorist operations, with the aim of identifying recruiting, training and organizing. The input for these types of IT researching terrorism and ML are links between participants. The available links may be impossible to overview, or to comprehend with logical sense, which can be overcome by the algorithm models that provide a dimensional

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layout, based on the strength of association, and crossings – centering points and their locations, possible subgroups and their dispersion. Based on the types of relationship, the visualization is the output. The visualization is based on exclusion of most likely irrelevant data. Junctions with closest links can be filtered with fractal views because of stronger associations for those closer and more centered. This method provides a presentation suitable for observing and perception. The model can be simplified, focusing on fractal values: (a) probable core social structures of a network, (b) uncovering regional and indirect associations and even hierarchical order of on organization. This application of fractals is appropriate for spatial analysis, which in practice includes identifying possible terrorist leaders and their locations, or possible cells. For visualization to be effective it should respect certain requirements: (a) to fully utilize the space dimension, instead of a piled scale, the nodes should be separated by an optimal distance; (b) to reflect the strength of association among linked end nodes, the length of a link should appear closer if they are strongly associated; (c) in order that the user can clearly see the relationships between nodes, the crossing of edges should be minimized; and (d) the importance of the corresponding terrorist (money launderer) should be represented through a proportional size of a node [10]. Second, the fractal tools can be used for the analysis of resilience to terrorist threat [11]. This includes the estimation of two aspects related to threat: measuring ability: to resist, to absorb or to adapt, excluding the ability to function under stress; and measuring possible impact of damage of terrorism, as a criterion for estimation. The result of the analysis of resilience to terrorist (or ML) threats is an objective assessment of cascade ability, which can be further used for modeling scenarios and security requirements. Third, an analysis of shape and structure features involves searching for missing details in relation to the identification of persons and objects [12]. Fourth, the intelligence goal can be the analysis of psychological and behavioral aspects. This basically includes recognizing the temporal variabilities in actions of involved persons [13]. The analysis of psychological and behavioral aspects is practically data mining, since it involves active searching for understandable selfsimilarities to reproduce pattern of analogous behaviors [14]. Fifth, fractal tools can be applied in the analysis of linguistic markers. In practice, this involves searching for weak signals on the Internet, as input, their collection and analysis [15]. The aim of this type of application is to select and identify isolated terrorists. In general, fractal tools seem to be applicable as artificial reality modeling and scaling means for the research of terrorism and ML networks, as phenomena that are characterized by nonequilibrium stability, fractal dimensionality, selforganized criticality and spontaneous self-organization, “typically observed at the edge of chaos” [16].

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6.4 Assessment of methodological value of fractals for the AT and AML A fractal is a set of smaller subsets in some way similar to the larger set. The measure of its size and complexity is fractal dimension. A set is well ordered if it can be linearly ordered in a way that every subset has a smallest element in that ordering. Well ordering is equivalent to the axiom of choice – each implies the other. All natural shapes have fractality. One of its main characteristics is branching, which is applicable in researching parameters in the fields of terrorism and ML. That process seems chaotic and without scalable geometry. All connections relating to causes and consequences cannot be seen in the structure, and the achieved pictograph reproduces the essence of fractals – their similarity to the structure. This is obtained through a method that includes automated input of elements of appearance and details; automated informatics contour of an occurrence; conscious contour of an occurrence; selection of various elements that connected by specific links and conditions of specific elements of the occurrence. There is evidence against simplified or supposedly simplified approaches as a replacement for methods that achieve the best possible access to real life, language and philosophy [17]. Therefore, the researcher must apply culture and knowledge source-specific orientation. Redefining the boundaries between the different disciplines in the thought process includes reordering and reconnecting the ways of thinking outside of general. Though there were pictures, there was no definition [18]. The concept of fractional dimension, or fractals, was developed to describe the shapes of natural objects. A fundamental property of fractal objects is that as a figure is magnified, more details appear but the basic shape remains [19]. Thus, when faced with rough data, strongly nonlinear, irregular or displaying complex patterns that seem to defy statistical analysis, the fractal analysis offers a possibility to overcome these shortages and solve tasks, like identifying names, spaces, cases or situations. As a cognitive method, fractal tools provide graphs to facilitate an overview of complex time and space characteristics [20], saving time and manpower, drastically increasing general investigating capacities. Fractal views facilitate seeking, which aim at recognizing indicators of terrorism connected elements. In “war” against terrorism, the basic assumption is that there is a compulsive repetition of cycle of violence, but since the pattern is fractal, combating includes efforts to objectify the preconditions and subjectify potential perpetrators. The microscale replicates a certain aspect of macroscale [21]. It resembles reality, and visualization enables the reasonable assumption that the positioning of potential perpetrators is in real time [22]. As such it has more value for orienting capabilities, future resources structuring and concept exploration, that is, high-level decision making, but less so where its impact is confined to perception of possible prevention, that is, on the tactical level.

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Fractal tools have proven applicable. The data about global terrorist events from 1970 to 2014 have been analyzed by fractal dimension, which reflects the dynamics in time and space: first, the space–time characteristics from the available statistics; second, terrorism dynamics in a regional perspective; and third, complementary analysis on multidimensional scaling and clustering techniques [23]. They also trace ML, which is most often consensual and map chains of service providers, personnel and organizations used. There is no evidence that they have advanced the prevention, regarding recruitment or terrorist social activity (neither in ML), but they facilitate tactical initiative, in general, prevention, detection of associated activities and chains, and apprehending members [24]. Models and scales depend on the algorithmic construction of codes that result in form of signals, pieces, transformability, complexity and reduction. But software companies promote the impression that tools using fractals will by itself allow a real-time risk monitoring system, to detect potential ML activity across its transactions. The obvious problem causing the divergence between capability and expectation stems from the fact that most software projects have various stakeholders, including developers, funders and end users. In the software engineering, it is generally accepted that getting end users involved in the design and development of the tools they will use is critical if the software is to be usable, useful and relevant to real problems. Because the software projects are mostly commercial in nature, and begin, progress and end without much consideration of who will use the software or what they will do with it, end users have little influence in these projects. Computational models and simulations provide outputs, but predictions are forms of human judgments and reflect the state of knowledge at a moment in time. Focusing attention on the limitations of models and simulations as human tools, and investing what those limitations imply for decision making in the real world can advance in developing a broader understanding of how, where, when and why computational models and simulations can be useful to people working in highconsequence decision-making contexts [25]. Outside of that, similarly to application of approximative equation in highly automated high-frequency trading [26], fractal tools are not appropriate for precise results, but are useful for abstraction, approximation and reformulation [27].

6.5 Conclusion In the information age, planners and practitioners dealing with space, and asymmetric and irregular patterns of data analysis cannot be avoided to be receptive to nonlinear dynamic systems modeling, and fractal concept offers a suitable range of software opportunities.

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In combating terrorism and ML, which appear as such patterns, the application of information technology on the practical level requires the implementation of concept of fractals, thereby introducing mathematical methods in scaling and modeling of potential social anomalies. As the analysis demonstrates, even though there is computational prediction, IT models provide visual forecasting of missing data and supplement the empirical evidences and records, enabling higher degree of utilization of knowledge and adaptation in combating terrorism and various forms of ML. For this reason, application of information technologies based on the concept of fractals has its place in the analytic and strategic planning arsenal in combatting terrorism and ML.

References [1]

[2]

[3]

[4] [5]

[6] [7] [8]

[9]

Mitić V, Kocić L, Paunović V. Fractal modification of Curie-Weiss law based improved impedance of doped BaTiO3-ceramics. Paper presented at 6th International Congress on Ceramics (ICC6) August 21–25, 2016, Dresden, Germany, unpublished. Retrieved 17. June 2017, www.omicsgroup.com/conferences/ACS/conference/speaker_ppt/1607Keynote-ppt.pptx. Barnsley M, Hutchinson J, New methods in fractal imaging, Proceedings of the International Conference on Computer Graphics, Imaging and Visualisation, July 26–28, 2006, IEEE Society, Washington DC 296–301, Retrieved 17. June 2016. https://pdfs.semanticscholar. org/efb9/eb441a83227e14afa4213d08aef523f0daa0.pdf Yilmaz MB, Offline signature verification with user-based and global classifiers of local features, Ph.D. dissertation, Sabanc University, 2015, unpublished. Retrieved 7. June 2017. http://theses.eurasip.org/media/theses/documents/yilmaz-mustafa-berkay-offlinesignature-verification-with-user-based-and-global-classifiers-of-local-features.pdf Miller J, Page S. Complex Adaptive Systems: An Introduction to Computational Models of Social Life. New Jersey: Princeton University Press, 2007. Leary R, Thomas J. How Complexity Theory is Changing the Role of Analysis in Law Enforcement and National Security. In: Babak A, Yates S. (Eds), Intelligence Management: Knowledge Driven Frameworks for Combating Terrorism and Organized Crime. London: Springer-Verlag, 2011, 63, pp. 61–78. G. McIntosh, M. Lauren, Incorporating Fractal Concepts into Equations of Attrition for Military Conflicts, in: OR, Defence and Security, R. Forder, Ed., Basingstoke: Palgrave Macmillan, 2015, pp. 101–123. Barnsley MF. Fractals Everywhere. Orlando FL: Academic Press, 1988 & 1994. Kocić LM, Geometric Modelling, University of Niš, Electronic Faculty, 2009. Title of original. Geometrijsko modeliranje, Univerzitet u Nišu, Elektronski fakultet. McIntosh G, Lauren M. Incorporating Fractal Concepts into Equations of Attrition for Military Conflicts. In: Forder R. (Ed), OR, Defence and Security. Basingstoke: Palgrave Macmillan, 2015, 101–23. Yang C, Liu N, Sageman M, Analyzing the terrorist social networks with visualization tools, Intelligence and Security Informatics: IEEE International Conference on Intelligence and Security Informatics, ISI 2006, San Diego, CA, USA, May 23–24, 2006, Proceedings, S. Mehrotra, D. Zeng, H. Chen, B. Thuraisimgha, F-Y. Wang, Eds., Heidelberg: Springer, 2006, pp 331–342.

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[10] Yang C, M. Sageman M. Analysis of Terrorist Social Networks with Fractal Views. In: Vogt P. (Ed), SAGE Quantitative Research Methods: Volume 4 – Complex Designs for a Complex World. Sage Publications: London/Thousand Oaks/New Delhi/Singapore, 2011, 367–94. [11] Lewis T. Critical Infrastructure Protection in Homeland Security: Defending a Networked Nation. 2nd edition, John Wiley & Sons: New Jersey, 2015. [12] Obaidullah SM, Halder C, Das N, Roy K. An Approach for Automatic Indic Script Identification from Handwritten Document Images. In: Chaki R, Cortesi A, Saeed K, Chaki N, (Eds.), Advanced Computing and Systems for Security. Vol. 2, New Delhi: Springer, 2016, 37–51. [13] Wijnants M, Cox RFA, Hasselman F, Bosman AMT, Van Orden G. Does Simple Rate Introduce an Artifact in Spectral Analysis of Continuous Processes. In: Holden J, et al. (Eds), Fractal Analyses: Statistical and Methodological Innovations and Best Practices. Frontiers, 2003, 56–68. [14] Henderson T, Boje D. Organizational Development and Change Theory: Managing Fractal Organizing Processes. New York/London: Routledge, 2016. [15] Cohen K, Johansson F, Kaati L, Clausen Mork J. Detecting linguistic markers for radical violence in social media. Terror Polit Violenc 2014, 26(1), 253. 246–56. [16] Mesjasz C. Complex Systems Studies and Terrorism. In: Fellman V, Bar-Yam P, Yaneer MA. (Eds), Conflict and Complexity: Countering Terrorism, Insurgency, Ethnic and Regional Violence. New York: Springer, 2015, Vol. 38. 35–71. [17] Bangura AK. A pluridisciplinary treatise of the fractal complexity in John Mukum Mbaku’s Corruption in Africa: Causes, consequences and cleanups. African Soc Sci Rev 2014, 7(1). [18] Davis P. Spirals: From Theodorus to Chaos. Wellesley: A. K. Peters, 1993. [19] Russ J. The Image Processing Handbook. 6th edition, Boca Raton: CRC Press, 2011. [20] Akhgar B, Tabatabaei F, Bayerl PS, Nasserzadeh S, Staniforth A. Investigating Radicalized Individual Profiles through Fuzzy Cognitive Maps. In: Babak A, Arabnia H. (Eds), Emerging Trends in ICT Security. Waltham: Morgan Kaufmann, 2014, 559–74. [21] Blain M. Power, Discourse and Victimage Ritual in the War on Terror. 2nd edition, Oxon/ New York: Routledge, 2016. [22] Barlow M, Cox R. All Hazards Analysis; A Complex Perspective. In: Hussein A, Essam D. (Eds), Applications of Information Systems to Homeland Security and Defense. Hershey/London: Idea Group, 2006, 17–45. [23] Lopes A, Machado JT, Mata M. Analysis of global terrorism dynamics by means of entropy and state space portrait. Nonlinear Dyn 2016, 85(3), 1547–60. [24] Strang S. Network Analysis in Criminal Intelligence. In: Masys A. (Ed.), Networks and Network Analysis for Defence and Security. Cham: Springer, 2014, 1–26. [25] McNamara L, Why models Don’t forecast, Paper presented A Paper for the National Research Council’s “Unifying Social Frameworks” Workshop, Washington, DC, 16–17 August 2010, p. 23. Retrieved 05. June 2017. http://sites.nationalacademies.org/cs/groups/dbassesite/ documents/webpage/dbasse_071326.pdf [26] Aldridge I. High-Frequency Trading: A Practical Guide to Algorithmic Strategies and Trading Systems. 2nd edition, New Jersey: Wiley, 2013. [27] Saitta L, Zucker JD. Abstraction in Artificial Intelligence and Complex Systems. New York: Springer, 2013.

Rainer Gadow, Steffen Esslinger, Matthias Blum

7 Inkjet three-dimensional printing of bioceramics and bioglass Scaffolds for bone repair and regeneration Abstract: Modern surgery and health care have a strong demand for various prosthetic devices. One can separate between dense high strength permanent implants like superalloys and titanium, and in contrast to those the biodegradable porous bioceramics are partially or fully transformed to natural hard tissue structures by solution/reprecipitation mechanisms. Advanced manufacturing processes such as additive manufacturing technologies have the potential to ensure improved patient care with tailored or customized implants. In this context, bioceramics such as calcium phosphates and bioactive glasses are of particular importance because of their resorption behavior and interface biochemistry. These degradable materials allow a rapid ingrowth of the implant into the bone by the stimulation of osteoblast cells. The requirements for bone grafts are sometimes contradictory, for example, mechanical strength and high porosity. This study therefore explains the production of scaffolds using the inkjet three-dimensional (3D) printing process. The bioceramic raw materials were processed by spray dry granulation to get spherical granules with a suitable flowability for the 3D printing process. The powders were characterized using a scanning electron microscope and particle size distribution measurements, and the flowability was determined by calculation of the Hausner ratio. The porosity of the sintered structures, which was up to 70%, was measured by mercury porosimetry. Sintering curves were determined on the basis of differential thermal analysis/thermogravimetric analysis measurements. The surface characterization was carried out by white light interferometry. Keywords: calcium phosphate ceramic/bioglass scaffolds, inkjet printing, spray drying granulation, additive manufacturing

Rainer Gadow, Institute for Manufacturing Technologies of Ceramic Components and Composites; Graduate School of Excellence advanced Manufacturing Engineering GSaME, University of Stuttgart, Stuttgart, Germany, [email protected] Steffen Esslinger, Graduate School of Excellence advanced Manufacturing Engineering GSaME, University of Stuttgart, Stuttgart, Germany Matthias Blum, Institute for Manufacturing Technologies of Ceramic Components and Composites, University of Stuttgart, Stuttgart, Germany https://doi.org/10.1515/9783110627992-007

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7.1 Introduction Bone degradation and fractures represent a significant concern to human health and have a further impact on the increased population life expectancy. When such defects overcome a certain critical size, body-induced self-repair mechanisms cannot restore lost skeleton functionality. Medical treatment involves bone grafting, a common surgical procedure with a worldwide value of more than $2.7 mio in 2017. Autologous bone grafts are currently the gold standard treatment but are associated with donorsite complications, risk of infection and size limitations [1–3]. Artificial scaffolds with tailored porosity, architecture and composition present an alternative to autologous grafts and are excellent three-dimensional (3D) templates to provide structural support for the newly formed bone. The complex structure of a human bone is shown schematically in Figure 7.1 as well as the idea to replace a damaged part of the bone. But also the replacement of artificial joints, like knee and hip prosthesis, is strongly increasing. According to Health at a Glance [4] and Gradinger and Gollwitzer [5] more than 1 mio artificial joints have been inserted in 2010 worldwide. The expected course is shown in Figure 7.2. Progress in material science and the better understanding of bone-healing biology resulted in the development of numerous alternative bone graft substitutes, such as calcium phosphate ceramics and bioglass products [6, 7]. In Figure 7.3, the procedure is shown, which appears on the surface of hydroxyapatite after implantation [8]. Furthermore, constant developments of the additive manufacturing techniques in medicine enabled custom-made scaffolds of complex geometries. To support the ingrowth of the bone cells and the formation of new blood vessels, the porosity of the bone graft should be as high as possible (up to 90%) and the diameter of the interconnected pores should be in the range of 10–500 µm [9, 10]. The additive manufacturing technologies, like the powder-based inkjet printing or the fused deposition of ceramics, allow the proceeding of bioceramic materials to such filigree scaffolds. The binder jetting or also called inkjet 3D-printing technology was developed by the Massachusetts Institute of Technology in 1993. In 1995, a company named Z Corporation acquired an exclusive license. There are several modifications of the available machines, like a different amount of print heads or the possibility to cure/ evaporate the ink by infrared light immediately, but the printing process itself is always the same: the powder feedstock is filled into a powder feed chamber and a sliced file of the specimen you want to print is uploaded to the printer. In the first step of printing, a thin powder layer, typically about 50–100 µm layer thickness, is spread from the powder feed chamber to the build chamber by a roller or a coater blade. Then the print head emits a special ink at these areas, where the specimen shall be created to glue the powder particles together. Finally, the build chamber is lowered and the process starts again until the printed structure is finished layer by layer. The principle of the binder jetting process is shown in Figure 7.4. In Figure 7.5, we can see the process chain for the 3D printing of ceramics.

Figure 7.1: Bone replacement strategy: the damaged part of the bone is replaced by a 3D-printed scaffold. Pictures by Mallick et al. [3].

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Figure 7.2: Expected course of knee and hip replacements worldwide, based on [4].

Figure 7.3: The surface of hydroxyapatite after implantation [8].

In this study, the fabrication of scaffolds was carried out by the inkjet printing process with a commercial 3D inkjet printer. This low-temperature printing technique holds great promise in manufacturing bone scaffold substitutes with enhanced properties over traditional techniques and great flexibility in employed materials. The aim of this study is to investigate the processing and the possible biomedical use of 3D powder-printed calcium phosphate ceramic and bioglass scaffolds for the reconstruction of bone defects. The fabricated scaffolds were computer-aided design (CAD) with different geometries and pore interconnectivity. Powder feedstock requirements were optimized through the spray-drying granulation process. Control over the cocurrent spray-drying parameters yielded bioceramic feedstock with optimal granulometric and morphological characteristics. Characterization techniques utilized in this study included flowability tests, differential thermal analysis (DTA), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM).

7 Inkjet three-dimensional printing of bioceramics and bioglass

Figure 7.4: Principle of inkjet printing technology.

Figure 7.5: Process chain for powder-based 3D-printed ceramic components.

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7.2 Materials and methods 7.2.1 Materials The bioglass was received by Colorobbia SpA., Italy. The biomedical behavior of bioactive glasses strongly depends on the chemical composition (see Figure 7.6) [11]. The chemical composition of this glass was 47.3 wt% SiO2, 28.6 wt% CaO, 15.2 wt% P2O5, 4.9 wt% Na2O, 2.5 wt% MgO and 1.5 wt% F. The β-tricalcium phosphate (TCP) was obtained by Chemische Fabrik Budenheim, Germany.

Figure 7.6: Phase composition and biomedical behavior of bioactive glasses [11].

The measured particle size distribution of the powders as received by the manufacturers was the following: Bioglass: TCP:

d10 = 1.36 µm, d50 = 5.08 µm, d90 = 14.8 µm d10 = 2.27 µm, d50 = 6.09 µm, d90 = 17,4 µm.

To increase the sintering activity, the powders were milled in an attritor using 2 mm Y-TZP milling balls until the medium feedstock particle size was smaller than 1 µm. Therefore, the powders were dispersed in distilled water using 0.3 wt% based on the solid content DOLAPIX A 88 for the bioglass suspension and 0.3 wt% DOLAPIX CE 64 (both dispersing agents by Zschimmer and Schwarz GmbH, Germany) for composites that contained 90 wt% bioglass and 10 wt% TCP. The solid content of the slurries was 65 wt%. After the final particle size was reached, 1 wt% PVA (Fluka, Switzerland) was added into the slurry and finally the powders were spray granulated in a spray dryer Mobile Minor Spruehtrockner (GEA Niro, Germany) to receive spherical powders with a good flowability. The coarse granules fell in the drying chamber of the spray dryer, and the fine particles were trapped in the cyclone and could be recycled. The powders were sieved through a 100 µm mesh sieve. To

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improve the green density of the printed structures, coarse and fine granules were mixed to obtain a bimodal grain distribution with a volume ratio of 70% coarse and 30% fine powder. On top of that, 15 wt% Dextrin (Carl Roth, Germany) based on the solid content was added into the powder feedstock to glue the ceramic particles together after wetting by the injected ink.

7.2.2 CAD modeling The scaffolds were designed and converted into the .stl-format by using the CAD Software SolidWorks 2013 (Dassault Systemes, France); see Figure 7.7. The scaffolds had a cylindrical shape with a diameter of 11 mm, a height of 11 mm and radial and axial quadratic pores with a length of 1 mm. On top of that, three more geometries were designed to investigate the printability and the debindering behavior.

Figure 7.7: Slicing of the CAD files into single layers.

7.2.3 Inkjet printer For the printing of the scaffolds, a commercially available 3D-printer Z-Printer 310 Plus (Z Corporation, USA) was used. The binder in the printhead was the zb60 type (Z Corporation, USA). The layer thickness was 87.5 µm, and the binder volume ratio for the shell and the core was 0.4 and 0.2, respectively. The bleed compensation was turned off.

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7.2.4 Thermal analysis For the DTA/TGA a Netzsch STA 409 (Netzsch, Germany) was used with a heating rate of 5 K/min under air atmosphere with a sample mass of 28–30 mg.

7.2.5 Powder and scaffold characterization The particle size distribution was measured with a Mastersizer 3000 (Malvern, UK). For the SEM pictures, JEOL JSM-IT 300 (JEOL, Japan) was used. The flowability of the powder was estimated by calculating the Hausner ratio (HR) as follows: HR =

ρT ρB

(7:1)

where ρT is the tapped bulk density of the powder and ρB is the freely settled bulk density of the powder. The two kinds of densities are measured in accordance with DIN EN ISO 787-11. The measurements were carried out with a volumetric analyzer JEL STAV 2003 (J. Engelsmann AG, Germany). The porosity of the sintered structures was measured by a mercury porosimeter Pascal 140/440 (CE Instruments, UK). The surface roughness was measured with a white light interferometer ConturGT (Bruker, USA).

7.3 Results and discussion 7.3.1 Powder characterization After spray granulation, all powders had a medium particle size of more than 20 µm and a large particle size distribution, which is necessary for a good flowability of powders during the 3D printing process. These information are shown in Figure 7.8, and SEM pictures in Figure 7.9 show the spherical morphology of the spray-dried granules. The HR was calculated on the basis of three different measurements for each powder feedstock. The mean value for the bioglass powder was 1.45 ± 0.008; the mean value for the composite powder was 1.49 ± 0.060. Based on the literature, an HR of 1.0–1.25 indicates an excellent flow and an HR >1.4 indicates that the powder is nearly nonflowing [12]; nevertheless, the flowability of the used powder feedstocks was sufficient to form a homogeneous powder bed in the print chamber and every scaffold could be depowdered.

7 Inkjet three-dimensional printing of bioceramics and bioglass

Figure 7.8: Particle size distribution of the ceramic powder feedstocks.

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Figure 7.9: SEM pictures of the spray-granulated bioceramic powders.

7.3.2 Thermal analysis and sintering strategy The results of the DTA as well as the TGA are shown in Figure 7.10. You can tell that a weight loss up to 16% is caused by the evaporation of water and the debinding of the organic dextrin in the area between 20 and 450 °C. The degradation of the polymer started at about 250 °C and was finished at about 450 °C. This is the same for both types of powder feedstock. To avoid damaging the printed specimens by the evaporation of gases, the heating rate for the debinding process was chosen to be 30 K/h up to 450 °C with a dwell time of 1 h. This strategy worked for every scaffold geometries. The trend curve is identical for both powder feedstocks, and the different absolute values along the curve are probably due to the admixture of 10 wt% TCP within the composite feedstock. In both graphs, you can tell an endothermic reaction between 450 and 580 °C, which is probably caused by the quartz inversion of the glass. At about 800 °C, there is another endothermic peak that indicates the beginning crystallization of the glass. A similar thermal behavior was also reported in [13]. The glass starts melting when the temperature reaches values over 1,150 °C.

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Figure 7.10: DTA/TGA of the two different powder feedstocks used for 3D printing.

Both kinds of powders could be sintered with a heating rate of 70 K/h up to 1,000 °C with a dwell time of 2 h without damaging the specimens. Some impressions of the printed bioglass scaffolds as well as the corresponding CAD models are shown in Figure 7.11.

Figure 7.11: Successfully printed, depowdered and sintered bioglass scaffolds.

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7.3.3 Optical characterization and porosity In Figure 7.12, you can see the image of a scaffolds surface using white light interferometry. The surface is quite rough, which is characteristically for powder-based 3Dprinted parts and also a benefit for the colonization and the growth of bone cells on the surface. The medium surface roughness for this scaffold was 64.431 µm.

–109

8

–150 –200 6 –250

µm

mm

–300 4 –350 –400 2 –450 –500 0

–539 0

2

4 mm

6

8

Figure 7.12: Surface roughness of a 3D-printed bioglass scaffold after sintering.

The porosity of the sintered scaffolds was very different for the two powder feedstocks used. The porosity of the pure bioglass scaffolds was near 50%, while the porosity of the composite structures was more than 70%. This is caused by the TCP. While bioglass already exhibits a good densification at temperatures below 1,000 °C, higher temperatures are necessary for TCP, and a densification up to 86% of pure TCP at a maximum sintering temperature of 1,150 °C is reported in [14]. The pore size distribution is shown in Figure 7.13.

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Figure 7.13: Pore size distribution of 3D-printed cylinders.

7.4 Summary and outlook In this chapter, the inkjet printing technology was used to manufacture bioceramic scaffolds. The process chain started at the dispersion of the ceramic powders in water-based suspensions, followed by the spray-drying granulation. The powders had suitable flowability, so scaffolds of different geometries could be printed,

Figure 7.14: LDA of different composite scaffolds. Top: bioglass/TCP ratio = 50/50; bottom bioglass/TCP ratio = 70/30 [15].

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Figure 7.15: LDA on TCP and silver coating on titanium substrate, after (a) 3 days, (b) 7 days, (c) 14 days, (d) 21 days [17].

depowdered and sintered. The surfaces of the sintered structures have been characterized by optical measurements like SEM and white light interferometry. The porosity of the composite scaffolds reach values at about 70%, which is useful for the ingrowth of osteoblasts and blood vessels. In another study made by the authors of this chapter, the biomedical use could be investigated in cooperation with the University Hospital of Freiburg, Germany. In Figure 7.14, you can see the results of a life–dead assay (LDA) of composite scaffolds that were made similar to the scaffolds presented in this chapter [15]. The green fluorescence indicates a large amount of living cells on the surface of the scaffolds. A similar behavior can be observed on titanium-based implants that are coated with bioceramics [16, 17]. In Figure 7.15 you can see a similar result on such titanium prosthesis. Environmental SEM pictures in Figure 7.16 show the spreading of bone cells on coated implants [18].

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Figure 7.16: ESEM pictures of bioglass-coated titanium substrates [18].

References [1]

[2] [3]

[4] [5] [6] [7]

[8]

[9]

Sakkas A, Wilde F, Heufelder M, Winter K, Schramm A. Autogenous bone grafts in oral implantology-is it still a “gold standard”? A consecutive review of 279 patients with 456 clinical procedures. Int J Implant Dent 2017, 3(1), 23. Schildhauer TA, Gekle CJE, Muhr G. Neue Biomaterialien am Skelettsystem. Chirurg 1999, 70(8), 888–96. Mallick KK, Winnett J, van Grunsven W, Lapworth J, Reilly GC. Three-dimensional porous bioscaffolds for bone tissue regeneration: Fabrication via adaptive foam reticulation and freeze casting techniques, characterization, and cell study. J Biomed Mater Res A 2012, 100 (11), 2948–59. Health at a Glance: Europe 2016. OECD; 2016. Gradinger R, Gollwitzer H. Ossäre Integration; 2006. Chen QZ, Thompson ID, Boccaccini AR. 45S5 Bioglass-derived glass-ceramic scaffolds for bone tissue engineering. Biomaterials 2006, 27(11), 2414–25. Klammert U, Gbureck U, Vorndran E, Rödiger J, Meyer-Marcotty P, Kübler AC. 3D powder printed calcium phosphate implants for reconstruction of cranial and maxillofacial defects. J Craniomaxillofac Surg 2010, 38(8), 565–70. Bertazzo S, Zambuzzi WF, Campos DDP, Ogeda TL, Ferreira CV, Bertran CA. Hydroxyapatite surface solubility and effect on cell adhesion. Colloids Surf B Biointerfaces 2010, 78(2), 177–84. Karageorgiou V, Kaplan D. Porosity of 3D biomaterial scaffolds and osteogenesis. Biomaterials 2005, 26(27), 5474–91.

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[10] Chatzistavrou X, Newby P, Boccaccini AR. Bioactive glass and glass-ceramic scaffolds for bone tissue engineering. In: Ylänen HO (editor), Bioactive Glasses: Materials, Properties and Applications. Cambridge, UK: Woodhead Publishing; Philadelphia, PA, 107–28. [11] Wintermantel E, Ha S-W (eds.). Medizintechnik: Life Science Engineering; Interdisziplinarität, Biokompatibilität, Technologien, Implantate, Diagnostik, Werkstoffe, Zertifizierung, Business, 5th edition. Berlin: Springer, 2009. [12] Santomaso A, Lazzaro P, Canu P. Powder flowability and density ratios: The impact of granules packing. Chem Eng Sci 2003, 58(13), 2857–74. [13] ElBatal HA, Azooz MA, Khalil EMA, Soltan Monem A, Hamdy YM. Characterization of some bioglass–ceramics. Mater Chem Phys 2003, 80(3), 599–609. [14] Ryu H-S, Youn H-J, Sun Hong K, Chang B-S, Lee C-K, Chung -S-S. An improvement in sintering property of β-tricalcium phosphate by addition of calcium pyrophosphate. Biomaterials 2002, 23(3), 909–14. [15] Seidenstuecker M, Kerr L, Bernstein A, Mayr HO, Suedkamp NP, Gadow R, et al. 3D Powder Printed Bioglass and β-Tricalcium Phosphate Bone Scaffolds. Materials (Basel) 2017, 11, 1. [16] Bernstein A, Suedkamp N, Mayr HO, Gadow R, Burtscher S, Arhire I, et al. Thin Degradable Coatings for Optimization of Osseointegration Associated With Simultaneous Infection Prophylaxis. In: FICAI A (editor), Nanostructures for Antimicrobial Therapy. S.l: Elsevier, 2017, 117–37. [17] Krieg P, Killinger A, Gadow R, Burtscher S, Bernstein A. High velocity suspension flame spraying (HVSFS) of metal doped bioceramic coatings. Bioact Mater 2017, 2(3), 162–69. [18] Altomare L, Bellucci D, Bolelli G, Bonferroni B, Cannillo V, Nardo LD, et al. Microstructure and in vitro behaviour of 45S5 bioglass coatings deposited by high velocity suspension flame spraying (HVSFS). J Mater Sci Mater Med 2011, 22(5), 1303–19.

Jih Ru Hwu, Shwu-Chen Tsay, Shih Ching Hung, Ming-Hua Hsu, Ji-Yuan Ma, Vojislav V. Mitic, Goran Lazovic, Shang-Shing P. Chou

8 Identification of radicals responsible for DNA cleavage by photolysis of bis-oxime esters Abstract: Newly synthesized 9,10-anthraquinone and acenaphthene-1,2-dione derivatives exhibited high potency for DNA scission under photolytic conditions at concentrations of 37 and 6.5 μM, respectively. Results from electron paramagnetic resonance (EPR) experiments reveal that the benzoyloxy radicals and their degraded aryl radical intermediates (rather than bis-iminyl radicals) were mostly responsible for the DNA cleavage. Chemical compounds that can nick nucleic acids upon photoactivation would be of great value in photodynamic therapy [1–3] and gene therapy [4]. Well-known examples include porphyrins [5] and furocoumarins [6], which have been approved for clinical use globally. DNA scissions by organic compounds may proceed by various mechanisms [7]. Kanvah and Schuster developed a method [8] for the single-electron oxidation of DNA with 5-methylcytosine. Kawanishi’s [9] strategy involves a similar oxidation process, which uses benz[a]anthracene. Ito and Rokita [10] utilized aromatic amines to nick duplex DNA by a reductive electron injection method. Smith and Nicolaou [11] activated enediyne antibiotics by nucleophilic addition to cleave DNA. Frank et al. [12] achieved the same goal using a radical process that involves the drug

Acknowledgments: The authors thank the financial support provided by the Ministry of Science and Technology (MOST, Grant Nos. 109‐2113‐M‐007‐007 and 110‐2634‐F‐007‐023) and Ministry of Education (Grant Nos. 109QR001I5 and 110QR001I5) of R.O.C. Authors also thank the MOST in Taiwan to support The Featured Areas Research Center Program within the Framework of the Higher Education Sprout Project through the Frontier Research Center on Fundamental and Applied Sciences of Matters. †Electronic Supplementary Information (ESI) available: [details of any supplementary information available should be included here]. See DOI: 10.1039/b000000x/ Jih Ru Hwu, Shwu-Chen Tsay, Shih Ching Hung, Ming-Hua Hsu, Department of Chemistry, National Tsing Hua University & Frontier Research Center on Fundamental and Applied Sciences of Matters, Hsinchu 30013, Taiwan, Fax: 88635721594; Tel: 88635725813, [email protected] Shwu-Chen Tsay, Ji-Yuan Ma, Shang-Shing P. Chou, Department of Chemistry, Fu Jen Catholic University, New Taipei 24205, Taiwan, Fax: 886229023209; Tel: 886229052474, 002181@mail. fju.edu.tw Vojislav V. Mitic, Institute of Technical Sciences of the Serbian Academy of Sciences and Arts & Faculty of Electronic Engineering, University of Niš, Serbia, Belgrade, Serbia Goran Lazovic, University of Belgrade, Faculty of Mechanical Engineering, Belgrade, Serbia https://doi.org/10.1515/9783110627992-008

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neocarzinostatin. Cationic metalloporphyrins have also been applied as photo- and radiosensitizers in DNA scission [13]. Recently, some oxime esters have been reported to nick DNA when triggered by UV light [14]. These examples involve single-strand scission. The goal of this study is to identify the species that were responsible for DNA cleavage under the irradiation of oxime esters with UV light. Therefore, 18 bis-oxime ester conjugates that bore special intercalating moieties including 9,10-anthraquinone, acenaphthylene-1,2-dione and indane-1,3-dione were designed and synthesized by incorporation with various benzoyl moieties with different substituents such as H, F, Me and NO2. Their EPR signals and DNA-cleaving capacity were analyzed. This study presents evidence that the main DNA-cleaving species are related to the benzoyloxy and the aryl radicals, rather than the iminyl radicals.

8.1 Synthesis of conjugated bis-oxime esters In the synthesis of various bis-oxime esters 6, 9 and 12, oximations of bis-ketones 1, 7 and 10 were conducted with an excess (4.0 equivalents) of hydroxylamine hydrochloride in pyridine or ethanol at reflux (Scheme 8.1). The corresponding bis-oximes 5, 8 and 11 were then condensed with 3.5 equivalents of benzoyl chlorides 3 with various substituents in the presence of NaH (4.0 equivalents) or dimethylaminopyridine (DMAP, 3.0 equivalents) at 25 °C to generate the desired bis-oxime esters 6, 9 and 12 in good yields. A lack of sufficient hydroxylamine hydrochloride (1.1 equivalents) for oximation and sufficient benzoyl chlorides 3 (1.3 equivalents) for esterification resulted in the formation of monosubstituted compounds 2 and 4. The intercalating moieties in the final targets 6, 9 and 12 included 9,10-anthraquinone, acenaphthylene-1,2-dione and indane-1,3-dione. Benzoyl chloride 3a and para-substituted chlorides 3b–d (i.e., Me, F or NO2) were used to form oxime esters 6a–d, 9a–d and 12a–d. Additionally, 1- and 2-naphthoyl chlorides (i.e., 3e and 3 f) were used in oximation to form oxime esters 6e, 6 f, 9e, 9 f, 12e and 12f in good yields.

8.2 DNA scissions by oxime esters under irradiation with UV light To a sodium phosphate buffer solution (pH 6.0, 0.10 M) that contained supercoiled circular φX174 RFI DNA (form I, 50 μM/base pair) was added a bis-oxime ester (6, 9, or 12) to a concentration of 500 μM. The solution was irradiated by UV light (312 nm, 16 W) for 2.0 h under aerobic conditions at room temperature. The results of gel electrophoresis show that form II DNA was generated. Table 8.1 presents the ratios of (amount of form II)/(amount of form I).

8 Identification of radicals responsible for DNA cleavage by photolysis

Ar

O N

OH

O

N

(ii)

(i)

ArCOCl

O 2

O

O 4

3

Ar

O O 1

103

N

OH

O

N (iv)

(iii)

9,10-anthraquinone HO

3

N

N

O

5

O

Ar

O

OH O

N

(v)

O 7

8

Ar N O

(iv)

N

6

N O

3

Ar

OH

9

O

acenaphthylene-1,2-dione O N

O (iii)

indane-1,3-dione

N O (vi)

O 10

Ar

OH

N 11

3 OH

N O Ar 12

O

Ar = a) C6H5, b) p-Me-C6H4, c) p-F-C6H4, d) p-NO2-C6H4, e) 1-naphthyl, f) 2-naphthyl Scheme 8.1: Reagents: (i) NH2OH·HCl, EtOH; (ii) NaH, ArCOCl 3, THF; (iii) NH2OH·HCl, pyridine; (iv) NaH, ArCOCl 3, THF; (v) NH2OH·HCl, EtOH; (vi) ArCOCl 3, DMAP, THF.

All of these bis-oxime esters cleaved DNA; their (form II)/(form I) ratios ranged from 0.88 to >99 at a concentration of 500 μM. The conjugates 6d and 9d, containing an anthraquinone or an acenaphthylenedione intercalator, respectively, yielded the most appealing nicking results (>99). These two bis-oxime esters cleaved DNA at concentrations as low as 37 and 6.5 μM, respectively, when the (form II)/(form I) ratio was 1.0.

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Table 8.1: Ratios of (form II)/(form I)a,b for DNA cleavage, obtained by use of oxime esters 6, 9 and 12 with various intercalating moieties and aroyl groups. Intercalating moiety

,-Anthraquinone Acenaphthylene-,-dione Indane-,-dione (cf. ) (cf. ) (cf. )

Aroyl groups CHCO (cf. a)

.

.

.

p-Me-CHCO (cf. b)

.

.

.

p-F-CHCO (cf. c)

.

.

.

p-NO-CHCO (cf. d)

>

>

.

-CHCO (cf. e)

.

.

.

-CHCO (cf. f)

.

.

.

Cleavage of supercoiled circular φX174 RFI DNA (form I; 50 μM/base pair, molecular weight of 3.50 × 106, length of 5,386 base pairs) to form relaxed circular DNA (form II) under aerobic conditions and photolysis under 312 nm UV light at room temperature for 2.0 h. b Analyzed by gel electrophoresis with 1.0% agarose gel and ethidium bromide staining. a

8.3 Formation of radicals by photoinduced fragmentation of bis-oxime esters Trapping the intermediates that are formed by photolysis enables the mechanism of DNA cleavage to be elucidated. Therefore, oxime ester 6c in a phosphate buffer solution (pH 6.0, 0.10 M) was irradiated by 312 nm UV light. Unfortunately, no signal was detected directly by EPR. Alternatively, 5,5-dimethyl-1-pyrroline N-oxide (DMPO) was added to the reaction medium to trap any radical species that may have been formed in situ. In experiment with 6c as the starting material, EPR signals with intensities in the ratio 1:2:2:1 were obtained (Figure 8.1). The g value was 2.0061 and the hyperfine splitting constants were aN = aH = 14.5 G in Figure 8.1, which are highly consistent with structure 15. This radical species was formed by the addition of the p-fluorobenzoyloxy radical (13) to DMPO (Scheme 8.2). In a control experiment, a benzene solution of oxime ester 6c was irradiated with 312 nm UV light in the presence of 1,4-cyclohexadiene [15] at room temperature for 12 h (Scheme 8.2). Fluorobenzene (17) and anthraquinone (1) were isolated in

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Figure 8.1: EPR spectrum of the radical 15, formed by addition of the radical 13 to DMPO.

Me Me

N O

F

N

2 O C

O

hυ C6H6 O

N

Me

DMPO

O

O

O

Me N O

F

F N

CO2

F

16

17 NH

F

F

15

13

O 6c

O

O H2O

N 14 NH

O

18

1

Scheme 8.2: Fragmentation and spin-trapping reaction of bis-oxime ester 6 c after irradiation with UV light.

80% and 78% yields, respectively. These results reveal that the radical species 13 and 14 were formed during photolysis. The same reaction conditions were applied to the photo-fragmentation of bis-oxime esters 9a–f. 1,8-Dicyanonaphthalene 20 was isolated in 73–79% yields as shown in Scheme 8.3 with the representative bisoxime ester 9c. The same reactions of the related indane-1,3-dione oxime esters 12, however, did not yield any dicyano product.

8.4 Radical species responsible for DNA scission Photolysis of an O-benzoyl oxime ester gives a benzoyloxy radical, which may undergo the fragmentation to give an aryl radical as a secondary intermediate in situ. Ingold and coworkers [16] reported that a rapid decarboxylation takes place to the benzoyloxy

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radical [PhCOO.] to form a phenyl radical (Ph.). Davies and coworkers [17] also found a way to generate the 4-methoxyphenyl radical by reducing (4-methoxybenzene)diazonium tetrafluoroborate with FeII–EDTA or TiIII. In our EPR experiments, a set of signals from the adduct of DMPO and the pfluorobenzoyloxy radical were detected during the photolysis of oxime ester 6c (Figure 8.1). These data provide a direct evidence of the formation of the radical 13. Additionally, the formation of the p-fluorophenyl radical 16 was verified by the successful trapping of this species with 1,4-cyclohexadiene to yield fluorobenzene 17 (Scheme 8.2). Successful isolation of anthraquinone (1) in the same reaction reveals that the bis-iminyl radical 14 was also formed during the photolysis of the oxime ester 6c. Kensler et al. [18] as well as Theodorakis and Wilcoxen [19] individually found that benzoyloxy radicals can also damage DNA. Davies [17] and Murphy [20] found that aryl radicals could break strands of DNA. To determine potency of these radical species, Hazlewood and Davies [21] analyzed the reactions of benzoyloxy and phenyl radicals with sugars, nucleobases, nucleosides, and nucleotides. Their results support the claim that the benzoyloxy radicals are responsible for most of the observed DNA degradation. However, results from a systematic study show that arylhydrazones can nick DNA under UV irradiation [22]. In these photochemical reactions, iminyl and aminyl radicals are formed from hydrazones and both of these radicals participate in DNA scission. In the current method involving the photolysis of O-benzoyl oxime esters, all of the iminyl, the benzoyloxy and the aryl radicals were formed in situ. Which of these three species played a greater role than others must be identified. Our design for doing so involved the formation of bis-iminyl radicals 19 from bis-oxime esters 9a–f. These bis-iminyl radicals may undergo an intramolecular ring-opening reaction to afford dicyanonaphthalenes. Scheme 8.3 illustrates an example that involves acenaphthylene-1,2-dione bis-esters 9c. Indeed, the dicyano compound 20 was obtained in O F N O

N

hυ 312 nm

N O

N

F 9c

O F

2

19

O

CN F

O 13 DNA

DNA

DNA Cleavage

CN CO2

20

16

Scheme 8.3: Ring opening of acenaphthylene-1,2-dione bis-oximes after irradiation with UV light.

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good yield. In contrast, indane-1,3-dione bis-oxime esters 12a–f had one more methylene unit between the two oxime ester moieties than did acenaphthylene1,2-dione derivatives 9. Compounds 12a–f could not and did not undergo the same ring opening reaction. Additionally, dicyano compounds were not found in the photolysis of 9,10-anthraquinones 6a–f. Given these concerns, replacement of bis-oxime derivatives of 9,10-anthraquinone and indane-1,3-dione with those of acenaphthylene-1,2-dione should significantly reduce the contribution of bis-iminyl radicals to DNA cleavage. Nevertheless, the observation in Table 8.1 opposes this expectation. The data therein reveal that acenaphthylene-1,2-dione bis-oxime esters 9 commonly exhibited capacity of the same order as 9,10-anthraquinone bis-oxime esters 6 and indane-1,3-dione bis-oxime esters 12. With respect to the p-nitro derivatives, the capacity of acenaphthylene-1,2-dione 9d markedly exceeded that of indane-1,3-dione 12d. Therefore, the iminyl radicals are believed not to have played a crucial role in DNA-strand breakage; rather, the radicals that were formed from the benzoyloxy groups and their degradation radicals were essential to DNA scission.

Future works It has been experimentally determined that certain organic radicals participate significantly in DNA cleavage. The specificity of individual reactant movement, including its rate, affects the reaction. Radicals movement modeling become a topic of our future research. The stochastic movement of each radical may have certain specificity or regularity, which is associated with fractional Brownian motion. It could be characterized by its fractal dimension. Establishment of an ordering of radicals will be pursued, which could be related to their capacity in DNA cleavage.

References [1] [2] [3] [4]

[5] [6]

Photodynamic Therapy, ed. Gomer CJ, Pergamon, Oxford, 1987, Section V, VI. Wachter E, Heidary DK, Howerton BS, Parkin S, Glazer EC. J Chem Soc, Chem Commun 2012, 48, 9649–51. Poteet SA, Majewski MB, Breitbach ZS, Griffith CA, Singh S, Armstrong DW, Wolf MO, MacDonnell FM. J Am Chem Soc 2013, 135, 2419–22. (a) Zein N, Schroeder DR. Advances in DNA Sequence-Specific Agents, ed. Palumbo M, JAI, London, 1998, Vol. 3, 201–26, (b) Advances in DNA Sequence-Specific Agents, ed. Hurley LH, Chaires JB, JAI, London, 1996, Vol. 2, Part II; (c) Advances in DNA Sequence-Specific Agents, ed. Hurley LH, JAI, London, 1992, vol. 1, Part I. Jori G. J Photochem Photobiol B, 1996, 36, 87–93. Edelson RL. Yale J Biol Med 1989, 62, 565–77.

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[15] [16] [17] [18] [19] [20] [21] [22]

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Wolkenberg SE, Boger DL. Chem Rev 2002, 102, 2477–95. Kanvah S, Schuster GB. J Am Chem Soc 2004, 126, 7341–44. Seike K, Murata M, Oikawa S, Hiraku Y, Hirakawa K, Kawanishi S. Chem Res Toxicol 2003, 16, 1470–76. Ito T, Rokita SE. J Am Chem Soc 2004, 126, 15552–59. Smith AL, Nicolaou KC. J Med Chem 1996, 39, 2103–17. Frank BL, Worth L Jr., Christner DF, Kozarich JW, Stubbe J, Kappen LS, Goldberg IH. J Am Chem Soc 1991, 113, 2271–75. Ali H, van Lier JE. Chem Rev 1999, 99, 2379–450. (a) Hwu JR, Tasy S-C, Hong SC, Leu Y-J, Liu C-F, Chou SSP. Tetrahedron Lett 2003, 44, 2957–60. (b) Hwu JR, Yang JR, Tsay SC, Hsu MH, Chen YC, Chou SSP. Tetrahedron Lett 2008, 49, 3312–15. (c) Chou SSP, Juan JC, Tsay SC, Huang KP, Hwu JR. Molecules 2012, 17, 3370–82. Poloukhtine A, Popik VV. J Org Chem 2005, 70, 1297–305. Grossi L, Lusztyk J, Ingold KU. J Org Chem 1985, 50, 5882–85. Hazlewood C, Davies MJ, Gilbert BC, Packer JE. J Chem Soc, Perkin Trans 2, 1995, 12, 2167–74. Swauger JE, Dolan PM, Zweier JL, Kuppusamy P, Kensler TW. Chem Res Toxicol 1991, 4, 223–28. Theodorakis EA, Wilcoxen KM. J Chem Soc, Chem Commun 1996, 1927–28. Griffiths J, Murphy JA. J Chem Soc, Chem Commun 1992, 24–26. Hazlewood C, Davies MJ. Arch Biochem Biophys 1996, 332, 79–91. Hwu JR, Lin CC, Chuang SH, King KY, Su TR, Tsay SC. Bioorg Med Chem 2004, 12, 2509–15.

Wang Zhang, Qinlei Liu, Jiajun Gu, Di Zhang, Branislav Jelenković, Dejan V. Pantelić

9 Fabrication of hierarchical replicas with near-perfect microstructure using modified biotemplate method Abstract: We demonstrate here the successful fabrication of almost defect-free oxide replicas by refining the normal biotemplate preparation method templated from butterfly wings. By carefully tuning the experimental parameters, such as the choosing of proper precursor and calcinations process, the microstructure defects of the replicas were expected to be deduced to the minimum. These hierarchical microstructures properties of the butterfly wing replicas were characterized on field-emission scanning electron microscopy. To evaluate the characters of the structure properties semiquantitatively, a fast Fourier transform technique of image processing was adopted, which would assist us to identify and approve the accuracy of the fabrication process. In addition, the process could be popularized to other biotemplate materials’ fabrication and identification. Keywords: microstructure, sintering, biotemplate, butterfly

9.1 Introduction Biotemplate techniques in which biological materials are used directly as template for the synthesis of novel bioinspired microstructural inorganic materials, are an ideal concept for preparation of novel structural materials. It seeks to either replicate the microstructural characteristics of natural species or use a biological structure to guide the subsequent assembly of inorganic materials. The replication process is a wide concept, including either a negative, positive (or hollow) or exact copy of the

Acknowledgment: The authors wish to express their thanks to the financial support of the National Key Research and Development Program (number YS2017YFGH000385), the National Natural Science Foundation of China (number 51572169), the Shanghai Rising-Star Program (16QA1402400), the Shanghai Science and Technology Committee (18ZR1420900, 15ZR1422400, 14JC1403300 and 14520710100). Wang Zhang, State Key Lab of Metal Matrix Composites, Shanghai Jiao Tong University, 200240, Shanghai, P.R. China, [email protected] Qinlei Liu, Jiajun Gu, Di Zhang, State Key Lab of Metal Matrix Composites, Shanghai Jiao Tong University, 200240, Shanghai, P.R. China Branislav Jelenković, Dejan V. Pantelić, Institute of Physics Belgrade, University of Belgrade, Pregrevica 118, 11080 Zemun, Belgrade, Serbia https://doi.org/10.1515/9783110627992-009

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template. Recently, a large variety of biological species have been chose as templates, such as bacteria, textiles/paper, human/dog hair, cells, insect wings, spider silk, wool and wood; see reviews [1–3] and references therein. For most of the biological materials used in the replication process have subtle microstructures, and the level of precision in replicating into nanoscale morphologies and features is a great challenge. Nearly all the processing of the biotemplate materials’ fabrication in the current research are two-step methods. The first step is to compound the biotemplates with precursors by various means, such as wet chemistry, chemical vapor deposition or atomic layer deposition [4–7]. In this step, diverse interactions taken place between precursors and biotemplates. It is ubiquitously directed by chemical interactions and molecular recognition process in the chemistry method. Once the interactions taken place, the biotemplates will supply a useful platform for the precise synthesis. In this work, several potential precursors were through studied. After the combination, the second step is to wipe off the original biotemplates, such as burn off or dissolve off. In which, the calcination method can move the original templates easily and totally, though some thermal cracks will emerge during the heating process [3]. These cracks will destroy the microstructures integrity of the as-synthesized replicas without doubt that is the structure depended on properties (porosity distribution, optical properties, etc.) will be disturbed. Herein, we developed an effective three-step calcinations method to decrease the potential thermal defects. Also by choosing the proper precursors, the defects of the replicas microstructure could be deduced to the minimum, which will be convinced by fast Fourier transform (FFT) analysis on their corresponding field-emission scanning electron microscopy (FESEM) images. Compared with other widely researched biotemplates, such as bacterias, diatoms and woods, butterfly wings have more complicated periodical hierarchical architectures [8]. Due to the variety photonic properties of the butterfly wings, many research group’s [9] including us [10] done many previous works on replication the inner structures in the wings. The success achievement of the near-perfect replication of the butterfly wing scales will greatly prove the method we used effective.

9.2 Experimental details Wings taken from two species of the butterfly were used as bio-template in this work. One is Papilio paris (Linnaeus), the other one is Delias pasithoe (Linnaeus). Both were kindly supplied by Shanghai Natural Wild-Insect Kingdom Co., Ltd. Similar fabrication process was reported in our group’s former work, and the whole fabrication process can be divided into two steps. The first step is dipping the pretreated butterfly wings into the prepared precursor. Two zinc (II) and titanium (II) precursor solutions were prepared by dissolving the corresponding salts in alcohol water solution. After

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the soaked proper time, the butterfly wings were then drained, blotted to remove excess liquid, and dried in air. Then to calcine the treated biotemplates hybridization, an as-synthesized inorganic oxide replica could be obtained. The process is illustrated in Scheme 9.1.

Scheme 9.1: Schematic illustrations of the butterfly wing replicas fabrication process: step 1, dip the pretreated butterfly wings into the precursor; step 2, calcine the soaked butterfly wings and the as-synthesized replica can be obtained.

9.3 Results and discussion It is not feasible to choose the normal water solution as the precursor, because the butterfly wings surface is quite hydrophobic. To decrease the surface tension and improve the dipping effect, organic solution is a better choice in the precursor preparation. Therefore, the salt used in the precursor must be soluble in the organic solvent. Four zinc salts that are commonly used in our work and some other group’s work are listed in Table S1 (supplemental file) [11, 12], in which we can pick up the most suitable one by comparison. Three main properties of the salts that influenced the precursor solutions are listed in the supplemental table. The most important characters of the solvent are solubility, especially the solubility in the organic solution (here is alcohol). According to the table, it is obviously learned that zinc sulfate and zinc acetate have a very low dissolubility in the alcohol. Therefore, zinc chloride and zinc nitrate are two potential choices left. In the following process route, the soaked biotemplates will be burnt off. The reaction is usually endothermic as heat is required to break chemical bonds in the compound undergoing decomposition. Two main components will be decomposed in the soaked biotemplates: one is the biotemplate itself and the other one is the soaked precursor. The fewer differences between the two components the soaked biotemplates have, the better morphology properties will be obtained. In the following part, the influences of the thermal decomposition properties of the salts on the microstructures and performance of the final products are carefully studied. Zinc nitrate hexahydrate has six crystal waters in one molecular structure, which can be dissolved by itself crystal water above 37 °C. It will lose three water

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molecules to form trihydrate (Zn(NO3)2 · 3H2O) at 100 °C. Then it will become anhydrous variety at the temperature ranging from 105–131 °C as follows: Δ

8ZnðNO3 Þ2 · 3H2 O ! 2ZnðNO3 Þ2 · 3ZnðOHÞ2 + 18H2 O + 6NO2 " + 3O2 " Continue to heat to 317 °C, the Zn(NO3)2 decomposed into ZnO, NO2 and O2 as follows: Δ

2ZnðNO3 Þ2 ! 2ZnO + 4NO2 + O2 " Above 317 °C the zinc nitrate was decomposed to zinc oxide, which is much lower than the bio-templates’ (the main component of butterfly wings is chitin.) total decomposition point. Therefore, the zinc oxide microcrystal has enough time to connect together. It will be shown in the FESEM images that the as-synthesized replicas will have perfect microstructures with well crystallization. According to the TG-DTA analyses results of the original butterfly wings shown in Figure 9.1, the heat decomposition process can be divided into three steps. In the first step, from 60 to 230 °C, the butterfly wings started to lose water and decompose, and then chitin which is the main components of the butterfly wings quickly decomposed after 230 °C. The highest lost-weight peaks are around 293 °C. Some previous works confirmed that the chitin polysaccharide ring degradation takes place around 280 °C according to the FTIR spectra of thermally degraded residues [13]. At last, the decomposition process will be finished after 500 °C. The residual weight is less than 6%, which has less influence on the as-synthesized samples performance. As mentioned earlier, the chosen precursor salts’ heat decomposition discipline must match the ones of biotemplates. That is, all the salts must finish

Figure 9.1: TG/DTA curves tested from different butterfly wing templates.

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decomposition and crystallization before 500 °C; otherwise, the precursor did not have proper medium framework to adhere. Moreover, for the existence of the heat shrinkage, the precursor should decompose between 230 and 500 °C thoroughly. Based on the above consideration, zinc sulfate is not proper for the calcination process, while the decomposition temperature of zinc chloride and zinc acetate is lower than the biotemplate’s. Therefore, a three-step method shown in Figure 9.2a was developed to fabricate the replicas. In the first step, the aim is to get off the adsorption water in the soaked samples, so a rapid heat ratio could be adopted in this step, crystal water in the samples started to lose, for it was a decalescence reaction and much energy was needed, a relatively slow heat ratio was adopted in this process. The key step is step 3, in which the slowest heat ratio (1 °C/min) was chosen to decrease the proper heat (a) 500

Temperature (°C)

400

Step 3 Step 2

300 200

Step 1

100

2 °C/min

1 °C/min

0 100

0

200 300 Time (min)

400

500

(b) 600 Step 3

Temperature (°C)

500 Step 2

400 300 Step 1 200

1 °C/min 2 °C/min

100 0

0

50

100

150

200 250 Time (min)

300

350

400

Figure 9.2: Heating method of soaked butterfly wing templates with (a) zinc nitrate and (b) titanium sulfate.

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shrinkage and ensure the biotemplates burn off thoroughly. Once the temperature reached 500 °C, the temperature was held constant for more than 2 h to make the biotemplates completely burned off and the as-synthesized replica crystallized totally. A similar heating method was utilized in fabrication of the titania replicas, which was shown in Figure 9.2b. The same analysis about the fabrication of titania replicas were taken according to the parameters shown in Table S2 (supplemental file). With the above conclusion, two-tailored heating way was developed for the different precursors. The basic concept is designing special heating method for different decomposition zones. The first step is called the heating preparation period, in which both the precursor and the biotemplates lose some adhered water. Followed by the second step named rapid decomposition period, the precursor and biotemplates lose some small molecules or crystal water. The last step is the total decomposition period, in which the samples get decomposed and crystallized completely. Details of the heating method are shown in Figure 9.2. To evaluate the microstructures of the replicas, that is, the spatial distribution of the ridges and ribs, 2D FFT spectra of square areas selected from the FESEM images are shown in lower column of Figure 9.3. It is obvious that microstructure of the replicas fabricated using the optimized method are much more regular than others. The FFT patterns of the microstructures confirmed the results. Figure 9.3(a) and (c) shows nearly the same pattern, that is, a long diffraction line and two dividable diffraction cluster nearby. While the microstructures of the replicas heated at slower or faster heating rapid have inferior integrity. Diffraction line and two dividable clusters disappeared instead of a hazy diffraction ball in the FFT patterns.

Figure 9.3: FESEM images of as-synthesized zinc oxide using different calcination methods. (a) Original butterfly wings; (b) heat at slower heating rates; (c) calcine using optimizing heating method; and (d) heat at faster heating rates. The lower column shows the corresponding FFT images.

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9.4 Conclusion In conclusion, we summarized the fabrication of zinc oxide and titania replicas of butterfly wings. By analyzing the properties of butterfly wings and different potential precursors, we developed a whole method for the fabrication, especially the calcination method. Using the method, intact microstructures of the butterfly wings can be obtained and the characters of the patterns can be evaluated by the FFT method.

References [1]

Sotiropoulou S, Sierra-Sastre Y, Mark S, Batt C. Biotemplated nanostructured materials. Chem Mater 2008, 20, 821–34. [2] Caruso R. Micrometer to nanometer replication of hierarchical structures by using a surface sol-gel process. Angew Chem Int Ed 2004, 43, 2746–48. [3] Fan TX, Chow SK, Zhang D. Pro Mater Sci 2009, 54, 542. [4] Thibaud C, Roberta B, Fernand F, Jacques L. Bio-inorganic Hybrid Nanomaterials: Strategies, Syntheses, Characterization and Applications. Eduardo R, Katsuhiko A, Yuri L (Eds.). Letzte Änderung: Wiley-VCH, 2008, 159–83. [5] José LA, José IA, Maria SF. Handbook of Biomineralization: Biomimetic and bioinspired chemistry. Edmund B, Peter B (Eds.). Letzte Änderung: Wiley-VCH, 2009, 109–15. [6] Leila FD, Joshua DS, David WW. The Biomimetic Synthesis of Metal Oxide Nanomaterials Volume 2: Nanostructured Oxides. Challa KSSR (ed). Letzte Änderung: Wiley-VCH, 2009, 3–50. [7] He JH, Liu SX. Nanostructured Materials and Nanotechnology: Ceramic Engineering and Science Proceedings. DM Z, Singh M, Salem (Eds.). Letzte Änderung: Wiley-VCH, 2007, 31–39. [8] Ingram A. Butterfly photonics: Form and function. Funct Surf Bio 2009, 307–36. [9] a) Cook G, PL T, SC G. Angew Chem Int Edi 2003, 42, 557–59. b) Huang JY, Wang XD, Wang ZL, Nano lett 2006; 6; 2325-2331. [10] a) Zhang W, Zhang D, TX F, Ding J, QX G, Hiroshi O. Nanotechnology 2006, 17, 840–44. b) Zhang W, Zhang D, Fan TX, Ding J, Guo QX, Hiroshi O. Micropor Mesopor Mat 2006; 92: 227–233. c) Zhang W, Zhang D, Fan TX, Ding J, Guo QX, Hiroshi O. Bioinsp Biomim 2006; 1: 89–95. d) Zhang W, Zhang D, Fan TX, Gu JJ, Ding J, Wang H, et al. Chem Mater 2009; 21: 33–40. [11] Grushko YM. Handbook of Dangerous Properties of Inorganic and Organic Substances in Industrial Wastes. CRC Press, 1992, 138–45. [12] Raymond EK, Kirk O, et. al. Encyclopedia of Chemical Technology. Wiley, 1983, 131–94. [13] Pielichowski K, Njuguna J Thermal degradation of polymeric materials: Shawbury: Rapra Technology Limited; 2005.

Žarko Mitić, Sanja Stojanović, Stevo Najman, Mike Barbeck, Miroslav Trajanović

10 Analysis of the in vivo course of foreign body response to a phycogenic bone substitute using FTIR spectroscopy Abstract: Fourier transform infrared (FTIR) spectroscopy is one of the most common vibrational spectroscopic techniques used in biomaterials composition testing. In this chapter, we demonstrated how FTIR can be used for the analysis of the course of foreign body response (FBR) to a phycogenic bone substitute, in mice subcutaneous implantation model. We also examined how addition of blood to the bone substitute influences the FBR course. Natural apatite Algipore was analyzed prior to implantation, and 10 and 30 days after implantation using FTIR spectroscopy. Differences in the IR bands between different groups and time points were noticed in the FTIR spectra. Thirty days after implantation, the IR bands in the region approx. 3,600–1,300 cm−1 were assigned to newly generated protein collagen, which appeared to be more pronounced when biomaterial is combined with blood. Findings obtained by FTIR analysis correlate with our previous findings by other methods, which indicates that FTIR can be used in assessment of biomaterial-mediated tissue response and healing events. Keywords: FTIR, Algipore, collagen, in vivo

Acknowledgment: This work was partially supported by the Faculty of Medicine, University of Niš, Republic of Serbia (Grant no. 11-14629-4/16) and the Ministry for Science of the Republic of Serbia (Grant no. III 41017). Žarko Mitić, Faculty of Medicine, Department of Chemistry, University of Niš, Bul. Zorana Đinđića 81, RS-18000 Niš, Serbia, [email protected] Sanja Stojanović, Faculty of Medicine, Department for Cell and Tissue Engineering; Department of Biology and Human Genetics, University of Niš, Bul. Zorana Đinđića 81, RS-18000 Niš, Serbia, [email protected] Stevo Najman, Faculty of Medicine, Department for Cell and Tissue Engineering; Department of Biology and Human Genetics, University of Niš, Bul. Zorana Đinđića 81, RS-18000 Niš, Serbia, [email protected] Mike Barbeck, BerlinAnalytix GmbH, Ullsteinstrasse 108, D-12109 Berlin, Germany, [email protected] Miroslav Trajanović, Faculty of Mechanical Engineering, Laboratory for Intelligent Production Systems, University of Niš, Aleksandra Medvedeva 14, RS-18000 Niš, Serbia, [email protected] https://doi.org/10.1515/9783110627992-010

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10.1 Introduction Fourier transform infrared (FTIR) spectroscopy can be particularly applied in the field of biomedical sciences and is used a lot in biomaterial composition testing [1]. FTIR spectroscopy has also been used for analyzing secondary structure of collagen and other polypeptides, purified collagen cross-linked peptides and demineralized bovine bone collagen from animals of different ages [2–4]. Algipore® (DENTSPLY Implants Manufacturing GmbH, Mannheim, Germany) is a natural occurring hydroxyapatite (HAp) derived from red algae. It is prepared by the hydrothermal conversion of the original CaCO3 of the algae in the presence of (NH4)3PO4 at about 700 °C. It is available as granules with particle sizes of 0.3–2 mm and pores in the range of 5–10 μm and is widely used in implant dentistry for augmentation and for reconstruction of bone defects in maxillofacial surgery [5]. Algipore® has successfully been used as a bone grafting material, and after a lot of clinical experience, it has been demonstrated to enhance new bone formation in preclinical in vitro, in vivo as well as in clinical practice [5, 6]. Furthermore, Algipore® has shown good resorbable properties over time when used in animals as well as in humans since resorbed particles are being replaced by newly formed bone [5, 6]. Possible induction of a new connective tissue collagen by using Algipore® biomaterial, especially important from the point of view of the biomaterial activity mechanism, was investigated. During the process of foreign body response (FBR) in subcutaneous implantation model, formation of new chemical compounds within the implants was detected by FTIR spectroscopy.

10.2 Experimental 10.2.1 Animal experiments In our previously published paper, we have described in detail the implantation procedure of biomaterial Algipore® [6]. Briefly, biomaterial was implanted subcutaneously into the Balb/c mice. There were two experimental groups, Algipore plus saline solution (AS group) and Algipore plus blood (AB group). Biomaterial was explanted 10 and 30 days after implantation procedure, respectively. The effects of the addition of blood to a phycogenic bone substitute Algipore® on the severity of in vivo tissue reaction on the basis of specialized histochemical, immunohistochemical and histomorphometrical methods was explained in details previously [6].

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10.2.2 FTIR spectroscopy For FTIR sample preparation, the KBr pastille method was used. The dryness of the KBr pastille was controlled by the band at ca. 1,640 cm−1, which is associated with the deformation vibrations of the HOH bond from H2O molecules. In the experiment, 1.5 mg of the sample was mixed with 150 mg of KBr, so the sample concentration in relation to KBr was about 1%. When the mixture was well powdered in an agate mortar, it was pressed in a special mold by a hydraulic press that provides high pressure. The FTIR spectra as an average of 200 scans were recorded at room temperature on a BOMEM MB-100 spectrometer (Hartmann & Braun, Canada), equipped with a standard DTGS/KBr detector in the range of 4,000–400 cm−1 with a resolution of 2 cm−1. The spectrometer was purged with dry N2 gas. In the region all spectra were baselinecorrected and area-normalized. A Fourier self-deconvolution method was applied to enhance the resolution in a spectral region of 4,000–400 cm−1.

10.3 Results and discussion The IR spectrum of Algipore prior to implantation is presented in Figure 10.1a. The IR spectrum is characterized by IR bands arising from HAp, determined by analogy with the IR spectrum of pure HAp standard sample. IR bands with maxima at 1,095 cm−1, 1,046 cm−1, 604 cm−1 and 572 cm−1 arise from the PO43− groups of HAp [7, 8]. The wide IR band with centroid on the approx. 3,450 cm−1 is the result of stretching vibrations of all types of the hydrogen bound OH groups and H2O molecules [9]. Sharp IR band at 3,567 cm−1 needs attribute to ν(O–H) vibration of the free OH groups, which has not been included in the formation of hydrogen bonds. IR bands at 1,429 cm−1 and 630 cm−1 are attributed to the bending vibrations of OH group. The band on the approx. 1,634 cm−1 is the result of δ(HOH). Characteristic IR bands at about 2,925 cm−1 and 1,455 cm−1 are attributed to the stretching and the bending vibrations of the C–H group. In the area, 860–875 cm−1 carbonate band appears from CO32− substitution for OH− and PO43− groups in HAp [10]. The IR spectra of the group AS (b) and group AB (c) at day 10 are presented in Figure 10.1. The spectra show already mentioned IR bands arising from HAp (as illustrated in Figure 10.1a) and some new ones wide IR bands in the region from 2,850 cm−1 to 3,600 cm−1 and some sharp IR bands in the region from 1,450 to 1,750 cm−1. Beginning of the collagen phase formation is characterized by an increase in concentration of glucosamine-glucan (a secondary amine comprising NH group in its structure) [11]. Amide bands approx. 1,300–1,750 cm−1 are registered in the IR spectra due to the presence of proteins in the structure, primarily collagen [12]. IR band mostly originates from stretching ν(C=O) vibrations, so called amide I band at

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Figure 10.1: The FTIR spectra of Algipore® samples: (a) prior to implantation, and after implantation: (b) at day 10 (group AS), (c) at day 10 (group AB), (d) at day 30 (group AS) and (e) at day 30 (group AB).

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about 1,655 cm−1, amide II band mostly originates from bending δ(N–H) that is coupled with stretching ν(C–N) vibrations, and is at about 1,550 cm−1, while amide III band that mostly originates from stretching ν(C–N) vibrations that are coupled with bending vibrations of NH, occurs approx. 1,300 cm−1 [13, 14]. According to the given FTIR spectra analysis of the protein structures, it is first necessary to observe the IR bands arising from the amide bands [14]. The amide I band of approx. 1,655 cm−1 is shown in Figure 10.1b, c. No absorption IR bands in the region of 2,800 cm−1 to 1,800 cm−1 are evident, which is characteristic of biological molecules [15]. IR bands from 3,350–3,300 cm−1 originate most probably from the stretching vibration of the NH group of the secondary amines. IR bands in the spectral region of approx. 1,450–1,750 cm−1 (Figure 10.1b, c) arise most probably from the newly formed αamino acids taking part in protein collagen synthesis. Appearance of the IR bands of approx. 1,250–1,500 cm−1 (Figure 10.1b, c) may be attributed to the formed alkyl groups (CH2 and CH3) of the lipid base, which is characteristic of biological molecules [15]. The IR spectra of the group AS (d) and group AB (e) at day 30 are presented in Figure 10.1. The IR spectra are characterized by the presence of previously mentioned IR bands from HAp and a wide IR band with centroid at 3,430 cm−1, which dominates and corresponds to the IR spectrum of protein collagen [3, 4, 16]. The wide IR band with centroid at 3,430 cm−1 can be ascribed to the presence of stretching ν(N–H) vibrations as well as from the stretching ν(O–H) vibrations of aminoacids whose comprise protein collagen, that take part in formation of hydrogen bonds of different strength [2, 3, 17]. As can be seen at day 30, connective tissue was generated. Absence of the IR bands in the region of 2,800 cm−1 to 1,800 cm−1 can also be noticed thereby, is characteristic of biological molecules [16]. Comparing the FTIR spectra we can see that collagen generation found in the group AB at day 30 (Figure 10.1.e) is more prominent in comparison to the same biomaterial in saline solution (Figure 10.1.d).

10.4 Conclusion Ten days after implantation, in the FTIR spectra IR bands arising from newly formed functional groups of peptides and lipoproteins can be seen. This result seems to correlate with the early stage of the implants as it is well known that biomaterials are covered by different molecules even in this phase of the FBR. After 30 days, the FTIR spectra with pronounced IR bands in the region from 3,600 cm−1 to 1,300 cm−1 were assigned to newly generated collagen, which also correlates with the process of the FBR as the integration into connective tissue is most often proceeded at this time point after implantation. Altogether, the presented results showed that the analysis of tissue samples even in the field of biomedical research using FTIR spectroscopy allows having an insight in the biomaterial-mediated

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tissue response and healing events. Further studies have to show the usability of this method for analysis of the differences in the integration of different biomaterials comparably to the methods such as histology.

References [1]

[2]

[3] [4] [5] [6]

[7] [8]

[9] [10]

[11] [12] [13] [14]

[15] [16]

[17]

Ignjatović N, Vranješ Djurić S, Mitić Ž, Janković D, Uskoković D. Investigating an organtargeting platform based on hydroxyapatite nanoparticles using a novel in situ method of radioactive 125Iodine labeling. Mat Sci Eng C 2014, 43, 439–46. Mitić Ž, Najman S, Cakić M, Ajduković Z, Ignjatović N, Nikolić R, Nikolić G, Stojanović S, Vukelić M, Trajanović M. Spectroscopic characterization of bone tissue of experimental animals after glucocorticoid treatment and recovery period. J Mol Struct 2014, 1074, 315–20. Chang MC, Tanaka J. FT-IR study for hydroxyapatite/collagen nanocomposite, cross-linked by glutaraldehyde. Biomaterials 2002, 23, 4811–18. Paschalis E, Verdelis K, Doty S, Boskey A, Mendelsohn R, Yamauchi M. Spectroscopic characterization of collagen cross-links in bone. J Bone Miner Res 2001, 16, 1821–28. Tadic D, Epple M. A thorough physicochemical characterisation of 14 calcium phosphate-based bone substitution materials in comparison to natural bone. Biomaterials 2004, 25, 987–94. Barbeck M, Najman S, Stojanović S, Ž M, Živković J, Choukroun J, Kovačević P, Sader R, Kirkpatrick CJ, Ghanaati S. Addition of blood to a phycogenic bone substitute leads to increased in vivo vascularization. Biomed Mater 2015, 10, 055007. Fowler BO, Marković M, Brown WE. Octacalcium phosphate. 3. infrared and Raman vibrational spectra. Chem Mater 1993, 5, 1417–23. Marković S, Veselinović L, Lukić MJ, Karanović L, Bračko I, Ignjatović N, Uskoković D. Synthetical bone-like and biological hydroxyapatites: A comparative study of crystal structure and morphology. Biomed Mater 2011, 6, 045005. Ishikawa T, Wakamura M, Kondo S. Surface characterization of calcium hydroxylapatite by Fourier transform infrared spectroscopy. Langmuir 1989, 5, 140–44. Barralet J, Best S, Bonfield W. Carbonate substitution in precipitated hydroxyapatite: An investigation into the effects of reaction temperature and bicarbonate ion concentration. J Biomed Mater Res 1998, 41, 79–86. Lindner J. Bone healing. Clin Plast Surg 1977, 4, 425–37. Mantsch HH, McElhaney RN. Applications of infrared spectroscopy to biology and medicine. J Mol Struct 1990, 217, 347–62. Lazarev YA, Grishkovsky BA, Khromova TB. Amide I band spectrum and structure of collagen and related polypeptides. Biopolymers 1985, 24, 1449–78. Mitić Ž, Stolić A, Stojanović S, Najman S, Ignjatović N, Nikolić G, Trajanović M. Instrumental methods and techniques for structural and physicochemical characterization of biomaterials and bone tissue: A review. Mat Sci Eng C 2017, 79, 930–49. Mantsch H, Jackson M. Molecular spectroscopy in biodiagnostics. J Mol Struct 1995, 347, 187–206. Ficai A, Albu MG, Birsan M, Sonmez M, Ficai D, Trandafir V, Andronescu E. Collagen hydrolysate based collagen/hydroxyapatite composite materials. Collagen hydrolysate based collagen/hydroxyapatite composite materials. J Mol Struct 2013, 1037, 154–59. Cai S, Singh BR. Identification of β-turn and random coil amide III infrared bands for secondary structure estimation of proteins. Biophys Chem 1999, 80, 7–20.

Dragana Jugović

11 Synthesis and structural characterization of some cathode materials for lithium-ion batteries Abstract: Lithium-ion batteries are under intense scrutiny as alternative energy/power sources. Their electrochemistry is based on intercalation/deintercalation reactions of lithium ions within a crystal structure of an electrode material. Therefore, the structure itself determines both the electrode operating voltage and the transport pathways for lithium ions. Some oxide- and polyanion-based materials are synthesized by using ultrasonic spray pyrolysis method. The crystal structure refinement was based on the Rietveld full profile method. All relevant structural and microstructural crystal parameters that could be significant for electrochemical intercalation/deintercalation processes were determined. It was also shown that the structural and microstructural properties are significantly dependent on the synthesis condition. Electrochemical performances as cathode materials for lithium-ion batteries were examined through galvanostatic charge/discharge cycling. Galvanostatic cycling revealed variation in discharge curve profiles. It comes from different mechanism of lithium intercalation and also from the degree of structural order. Structural analyses revealed difference in the dimensionality of lithium-ion motion. Keywords: cathode, lithium-ion battery, crystal structure refinement, scanning electron microscopy, galvanostatic cycling

11.1 Introduction The lithium-ion rechargeable battery (LIB) has enabled the wireless revolution of mobile phones, digital cameras, computers and other handheld devices. There are several advantages of using lithium-ion batteries: Li is the third lightest element and has one of the smallest ionic radii of any single charged ion; and it has the lowest reduction potential. Therefore lithium-based batteries have high volumetric and gravimetric capacity and power density. A rechargeable battery is conceived as a transducer that transforms chemical energy into electrical energy and vice versa. It

Acknowledgment: This study was supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia under grant no. III45004. Dragana Jugović, Institute of Technical Sciences of SASA, Belgrade, Serbia, [email protected] https://doi.org/10.1515/9783110627992-011

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consists of a cathode, an anode and an electrolyte. In the case of lithium-ion battery, the anode is a source of lithium ions, the cathode is a sink for lithium ions, while the electrolyte separates the two electrodes enabling a transfer of lithium ions inside the cell (Figure 11.1). The overall chemical reaction that occurs at both electrodes (11.1) must be reversible on the application of charging current: Lix Hn + Hp $ Lix−y Hn + Liy Hp

(11:1)

where Hn and Hp refer to the negative and positive electrodes, respectively [1]. During discharge, y lithium ions are extracted from the negative electrode structure with a concomitant oxidation of the host Hn and inserted into the structure of the positive electrode Hp, which is reduced. Both negative electrode and positive electrode are intercalation materials, that is, a solid host grid that can store guest ions. The guest ions can be inserted into and be removed from the host structure reversibly. In a lithium-ion battery, Li+ is the guest ion while the host compounds are metal chalcogenides, transition metal oxides or polyanion compounds. These intercalation compounds belong to several crystal structures, among which the most common are layered, spinel and olivine (Figures 11.2–11.4) [2]. In current LIB technology the cathode material determines the cell voltage and capacities. Therefore, the developments of cathode materials become particularly crucial.

Figure 11.1: Schematic representation of working principles of lithium-ion battery.

11 Synthesis and structural characterization of some cathode materials

Figure 11.2: Layered structure of LiCoO2.

Figure 11.3: The structure of spinel LiMn2O4.

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Figure 11.4: The olivine structure.

11.1.1 Layered structure of LiMO2 The structure of the oxides with general formula LiMO2 (where is M = Co, V, Cr, Fe) takes the NaFeO2-type structure that can be viewed as a distorted rock salt superstructure [3]. In a cubic close-packed oxygen array the lithium and transition metal atoms are distributed in the octahedral interstitial sites. Transition metal edge-sharing [MO6] octahedra form MO2 layers. In between these layers lithium resides in octahedral [LiO6] coordination, leading to alternating (111) planes of the cubic rock salt structure (Figure 11.1). This (111) ordering induces a slight distortion of the lattice to hexagonal symmetry. On electrochemical cycling lithium ions are reversibly de/intercalated between these two-dimensional MO2 layers. After complete extraction of the lithium ions the structure takes layered CdCl2 structure type. Owing to the high electronegativity of oxygen that leads to a higher ionic character of the metal–oxygen bonds, the oxides are thermodynamically stable only in the intercalated state LiMO2. Repulsive interactions between adjacent layers, caused by the negative charge of the transition metal-oxygen layers, are compensated by intercalation of positively charged ions between the adjacent oxygen layers [3]. LiCoO2 is the first and the most commercially successful transition metal oxide cathode [4]. However, high cost, low thermal stability and fast capacity fade at high current rates are its major limitations.

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11.1.2 The structure of spinel LiMn2O4 The majority of spinel compounds AB2X4 (A and B are cations and X is an anion) belong to the space group Fd3m. There are Z = 8 formula units per cubic unit cell, consisting of 32 anions and 24 cations. While some spinels have almost-ideal cubic close-packed (ccp) anion sublattices, most of the anion sublattices are arranged in a pseudo-cubic close-packed spatial arrangement [5]. There are 96 interstices between the anions, but only 24 are occupied by cations, of which 8 are tetrahedral of the 64 tetrahedral interstices (one-eighth of the available tetrahedral voids) and 16 are octahedral of the 32 octahedral interstices (one-half of the available octahedral voids). Convention that is often used among chemists and physicists is that tetrahedral cation sites are called A-sites, whereas octahedral cation sites are called B-sites. A-site tetrahedra in spinel are isolated from each other and share corners with neighboring B-site octahedra. There is no edge sharing between A-site tetrahedra and other A- or B-site polyhedra. B-site octahedra share six edges with nearest-neighbor Bsite octahedra. Such connection enables short B-B distances that can facilitate electrical conductivity. In spinel-type LiMn2O4 lithium ions occupy A-sites, while manganese ions occupy B-sites within oxygen array (Figure 11.3). This arrangement allows three-dimensional network for lithium-ion transport during electrochemical cycling. Below room temperature, in the vicinity of 280 K, cubic spinel partly transforms to a tetragonal phase with space group symmetry of I4l/amd due to the Jahn-Teller distortion.

11.1.3 The structure of olivine LiFePO4 Natural occurrence of LiFePO4 is mineral triphylite that has the olivine-type structure and often contains some manganese ions Li(Mn,Fe)PO4 [6]. Olivine structure M2XO4 consists of M atoms in one-half of the available octahedral voids and X atoms in oneeighth of the available tetrahedral voids in a slightly distorted, hexagonal close-packed array of oxygen atoms [7]. It may be considered as hexagonal analog of the spinel structure. However, in olivine structure there are two types of octahedral sites that are energetically distinct, which commonly leads to an ordering of different cations between them. Such ordering happens in LiFePO4. The structure of LiFePO4 is usually described in the orthorhombic 62 space group Pnma (D16 2h ) [8]. Each unit cell contains four formula units of LiFePO4. Iron is positioned in the middle of a slightly distorted octahedron FeO6 (denoted as M(2) site, 4 c Wyckoff position with local symmetry m). Lithium occupies another set of octahedral positions (denoted as M(1), 4a Wyckoff position with local symmetry 1). None of the octahedra share faces in common. The important structural unit of olivine is the jagged chain of octahedra lying parallel to the b-axis: The M(1) sites form linear chains of edgeshared octahedra in alternate b-c planes, while the M(2) site forms zigzag planes

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of corner-shared octahedra in the other b-c planes. Phosphorous tetrahedra (PO4) bridge between alternate layers of FeO6 octahedra: PO4 tetrahedron shares one common edge with one FeO6 octahedron and two vertices with two FeO6 octahedra within one FeO6 layer and shares vertex with FeO6 octahedron from adjacent layer (Figure 11.4). Also, the PO4 tetrahedron connects the chains of LiO6 edge-shared octahedra through common vertex with two LiO6 octahedra within one chain and two common edges with two LiO6 octahedra from adjacent LiO6 chain. In that way PO4 tetrahedra constrain the volume in which the Li+ ions move. Lithium motion is happening through hopping between two neighboring octahedral M(1) sites along the Li chain. Therefore the lithium motion through olivine structure is one-dimensional along the b axis [9]. With such a tract, however, the long-range Li+ conduction can be easily blocked by ionic disorder, by foreign phases, or by stacking faults. For instance, atomic-scale simulations predict that the most favorable intrinsic defect is the Li–Fe “anti-site” pair in which a Li+ (on the M(1) site) and an Fe2+ (on the M (2) site) exchange their positions [10]. The average FeII–O distance is longer than expected for octahedral coordination of Fe2+ ion because of the change of the Fe–O covalency via the Fe–O–P inductive effect. Due to the fact that each FeO6 octahedron shares corners with four PO4 tetrahedra and one edge with one PO4 tetrahedron, the cation–cation repulsive forces distort the hexagonal close-packed anion array of olivine.

11.1.4 Synthesis methods Electrochemical performances of cathode materials are strongly correlated with the properties of synthesized powders such as: size, shape, morphology and distribution of particles and crystallite size. Therefore, various synthetic routes were probed in the synthesis of cathode materials. Conventional method for the synthesis of cathode materials is a solid-state reaction between proper salts of lithium and transition metal [11, 12]. It requires intensive grinding and mixing of the precursors and prolonged high-temperature treatment (usually above 600 °C) most often repeated several times, which are both time- and energy-consuming. Furthermore, throughout the solid state reaction it is hard to control particle growth and the stoichiometry. This can be overcome by introduction of a mechanochemical activation in the process prior to the high-temperature treatment [13]. During mechanochemical activation particles of the powders are intensively mixing, decreasing in size and melting. In that way better homogeneity can be achieved. However, the best homogeneity is accomplished in the solutions, where the components are mixed on molecular level, which is the base of the so-called wet chemical routes. Pechini method is based on the ability of some weak acids to form polybasic chelates with various cations [14]. These chelates on further heating in polyhydroxyl alcohol experience polyesterification reactions, due to which a solid polymeric resin

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is formed. In polymeric resin the cations are uniformly distributed. The calcination of these resins at adequate temperatures gives rise to phase-pure oxides [15]. Various combustion methods start from the nitrate solutions with the presence of the component that serves as a fuel. After the heating of the solution to the point of self-ignition the high temperature evolves, which varies with the oxidant to fuel ratio [16]. Thus obtained residue is additionally annealing in order to obtain phasepure powder of better crystallinity. In comparison to conventional ceramic methods the sol–gel processing enables higher purity and homogeneity of the precursors and works at lower temperatures [17]. Hydrothermal synthesis is also a low-temperature method and both cost- and energy-efficient. By varying the temperature, pressure and concentration fine particles can be obtained [18–20]. Ultrasonic spray pyrolysis method was also well explored and applied for the synthesis of cathode materials [21–23]. Here are presented some examples of the application of ultrasonic spray pyrolysis in the synthesis of LiMn2O4, metal-doped LiMn2O4 and LiFePO4 powders.

11.2 Experimental 11.2.1 Synthesis of LiMn2O4 powders The powders of LiMn2O4, LiCrxMn2–xO4 (x ≈ 0.175) and LiZnxMn2–xO4 (x ≈ 0.082) were synthesized by the ultrasonic spray pyrolysis. The starting solutions were 1 M aqueous solutions of LiNO3 (Laphoma), Mn(NO3)2 (Merck), Cr(NO3)3 (Merck) and Zn(NO3)2 (Merck), which were mixed in a proper ratio to achieve the desired stoichiometry. During a spray pyrolysis process, a starting solution atomizes into a mist that is then introduced to the reaction zone where each individual drop becomes a micro reactor. Each droplet experiences transformations that include solvent evaporation, precipitation of a solute, drying, high-temperature decomposition of precipitated particle and eventually sintering and formation of dense particle. The starting solution was sprayed at a frequency of 1.7 MHz by an ultrasonic nebulizer (Sonic profi, Prizma). The created mist was introduced to a horizontal electric furnace through a quartz tube by airflow with a rate of 0.5 dm3/min, effective reaction zone length of 0.6 m, and maximum temperature of 800 °C in the middle of the furnace. Considering that the rate of a carrying gas is equal to the rate of a droplet/particle, calculated retention time of a droplet/particle inside the furnace is 65 s, and 6 s in a zone of the highest temperature. Resulted powders were collected in two different manners: at the end of the reaction tube, where they were spontaneously cooled (denoted as SC LiMn2O4), and instantly cooled by quenching in water (denoted as Q LiMn2O4). Complexometric titrations and atomic absorption spectroscopy were used to analyze the concentration of precursor solution and the composition of the final powder,

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respectively. It is confirmed that the synthesized powders maintain basic chemical composition of the atomized solution.

11.2.2 Synthesis of LiFePO4 powders Ultrasonic spray pyrolysis was also used for the synthesis of the composite LiFePO4/C powder. The starting solution was made by mixing 1 M aqueous solutions of LiNO3 and FeSO4 · 7H2O with the Li:Fe molar ratio 1:1. Phosphoric acid and sucrose were added to the solution as phosphate and carbon source, respectively. The amount of added sucrose was 70 wt% of LiFePO4 to be formed. The starting solution was sprayed at a frequency of 1.7 MHz by an ultrasonic nebulizer (Sonic profi, Prizma). The created mist was carried to a horizontal electric furnace through a quartz tube by argon, at a flow rate of 0.3 dm3/min. The maximum temperature in the middle of the reaction zone was 800 °C, the calculated retention time of a droplet/particle inside the furnace was 97 s and the retention time in the zone of the highest temperature was 9 s. The as-synthesized powder, denoted as LFP-SP, was collected at the end of the reaction tube. The powder of pure LiFePO4 was synthesized by the solid state reaction between Li2CO3 (Merck), FeSO4 · 7H2O and (NH4)2HPO4. Starting compounds were mixed in the stoichiometric ratio, thoroughly grinded, pressed in a pellet and calcined at 700 °C in a slightly reductive atmosphere of 95% argon and 5% hydrogen. The synthesized sample is denoted as LFP-SS.

11.2.3 Materials characterization The synthesized powders were examined with X-ray Powder Diffraction (XRPD), using a Philips PW 1050 diffractometer with Cu-Kα1,2 radiation (Ni filter) at room temperature. Measurements were done in 2θ range of 10–100° with a scanning step width of 0.02° and 10 s time per step. Crystal structure refinement was based on the Rietveld full profile method [24] using the Koalariet computing program [25]. This program is suitable to handle the data obtained from the samples with dominant microstructural parameters. Scanning electron microscopy (JEOL JSM-5300) was used to study the morphology of the synthesized powders.

11.2.4 Electrochemical measurements Electrochemical measurements were performed in a closed, argon-filled two-electrode cell, with metallic lithium as a counter electrode. The electrolyte was 1 M solution of LiClO4 (p.a., Chemetall GmbH) in propylene carbonate (p.a., Honeywell). Working

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electrodes were made from the synthesized material, carbon black and polyvinylidene fluoride (PVdF, Aldrich) that were mixed and deposited on platinum foils from slurry prepared in N-methyl-2-pyrrolidone. The weight percent ratio of the mixture: synthesized material, carbon black and polyvinylidene fluoride was 90:5:5 for LiMn2O4 electrodes, respectively, while for the olivine LiFePO4 electrodes this ratio was 75:20:5, respectively. Because of the lower electronic conductivity of olivine phase more carbon black powder was added during the preparation of olivine electrodes. Subsequently, the electrodes were vacuum-dried overnight at 120 °C. Galvanostatic charging and discharging processes were done between 3.4 and 4.3 V for LiMn2O4 cathodes and between 2.3 and 4.1 V for LiFePO4 cathodes at different current rates by using Arbin BT 2042.

11.3 Results 11.3.1 XRD study 11.3.1.1 XRD analysis of LiMn2O4 X-ray powder diffraction data were used for the structural analysis of the synthesized powders. The structure of slowly cooled powder of LiMn2O4 has been refined in the space group Fd3m (Oh7) with following crystallographic positions: Li+ ions in special  crystallographic position 8a [0, 0, 0] with local symmetry 43m; both Mn3+ and Mn4+ ions in special crystallographic position 16d [5/8, 5/8, 5/8] with local symmetry 3m, and O2− ions in special crystallographic position 32e [u, u, u] with local symmetry 3m. The observed and calculated X-ray diffraction profiles for slowly cooled LiMn2O4 powder are given in Figure 11.5. During the refinement it was allowed for manganese ions to occupy both cation sites (tetrahedral (8a) and octahedral (16d)) owing to similar ionic radii of lithium and manganese ions. Due to the large difference in scattering factors of lithium and manganese ions, it is achievable to refine small occupancy of manganese ions in 8a crystallographic position with a rather high accuracy. The main results of the refinement, given in Table 11.1 [26], indicate that besides manganese ions, octahedral crystallographic sites are also occupied with some lithium ions (NLi(16d) = 0.0006(2)), and accordingly, in that same ratio manganese ions occupy tetrahedral crystallographic position (8a). In contrast to slowly cooled LiMn2O4 powder that crystallized in spinel structure, quenched LiMn2O4 powder crystallized in more unstable structure. The structure of quenched LiMn2O4 powder has been refined in the space group I41/amd (D4h19) in a structural type where cations are positioned in both special crystal lographic positions 4a [0, 1/4, 1/8] with local symmetry 42m and 8d [0, 1/2, 1/2] with 2− local symmetry 2/m, and O ions are positioned in special crystallographic positions

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Figure 11.5: The experimental (•), calculated (–), and divergence (bottom) X-ray diffraction data of slowly cooled LiMn2O4 at room temperature. Vertical indicators beneath the diffractograms indicate positions of plausible Bragg reflections.

Table 11.1: The final results of the Rietveld refinement for slowly cooled (SC) and quenched (Q) LiMn2O4 powders. SC LiMnO (e.g., Fdm)

Q LiMnO (I/amd)

LiCr.Mn.O LiZn.Mn.O (Fdm) (Fdm)

Lattice parameters (Å)

aC = .()

aT = .() cT = .()

a = .()

a = .()

Primitive cell volume (Å)

V = .

V = .

V = .

V = .

Mean crystallite size (Å)

()

()

()

()

Microstrains (%)

.

.()

.()

.()

Strain (%)

.()

–

.()

.()

Free coordinates O−, u

x=y=z= .()

x = .(), z = .()

x=y=z= .()

x=y=z= .()

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Table 11.1 (continued) SC LiMnO (e.g., Fdm)

Q LiMnO (I/amd)

LiCr.Mn.O LiZn.Mn.O (Fdm) (Fdm)

Li+ crystallographic position occupations

NLi(a) = –.()

NLi(a) = .()

NLi(a) = –.()

NLi(a) = –.()

R factors of the refinement (%)

RB = .

RB = .

RB = .

RB = .

16 h [0, x, z] with local symmetry m. The main results of the refinement are given in Table 11.1 [26], while the observed and calculated X-ray diffraction profiles are given in Figure 11.6. The refinement results show that lithium ions mostly occupy special crystallographic positions 4a (NLi (4a) = 0.72(5)), but there is also their significant presence in special crystallographic positions 8d (NLi (8d) = 0.28). It can be concluded that quenched LiMn2O4 powder did not accomplish to recline in spinel phase, where lithium and manganese ions occupy two different crystallographic sites.. Instead it crystallized in tetragonally distorted phase, where both lithium and manganese ions statistically occupy both tetragonal and octahedral crystallographic positions. In other

Figure 11.6: The experimental (◦), calculated (–), and divergence (bottom) X-ray diffraction data of quenched LiMn2O4 taken at room temperature. Vertical indicators beneath the diffractograms indicate positions of plausible Bragg reflection.

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words, the I41/amd phase of the lower symmetry represents a distorted state of the ordered state Fd3m. The value of this tetragonal distortion is c/a = 1.16 (the cubic lattice parameters are converted to the tetragonal lattice parameters using the equations aT = aC/√2 and cT = aC). The same tetragonal distortion was observed for other quenched powders of LiMn2O4 [27, 28], and for isothermally compressed LiMn2O4 powders when the structure was reduced from cubic (Fd3m) to tetragonal (F41/ddm) [29]. The tetragonal primitive cell volume is larger than the cubic (Table 11.1), meaning that the cubic phase is closely packed, which will probably affect its electrochemical properties. Chromium-doped LiMn2O4 powder crystallized in the space group Fd3m in the aforementioned spinel type with following crystallographic positions: Li+ ions in  special crystallographic position 8a [0, 0, 0] with local symmetry 43m; Mn3+, Mn4+, and Cr3+ ions in special crystallographic position 16d [5/8, 5/8, 5/8] with local symmetry 3m, and O2− ions in special crystallographic position 32e [u, u, u] with local symmetry 3m. Figure 11.7 gives comparative diffractograms of observed and calculated data, while the final results of the refinement are given in Table 11.1. During the refinement procedure, the probability that part of transition metal cations (both manganese and chromium) may also occupy tetrahedral 8a crystallographic position was considered as well. Due to the large difference in scattering factors of lithium and transition metal cations, it was plausible to refine small occupancy of transition metal ions in 8a site with a rather high accuracy (Table 11.1 [30]).

Figure 11.7: The experimental (◦), calculated (–), and divergence (bottom) X-ray diffraction data of LiCr0.175Mn1.825O4 taken at room temperature. Vertical indicators beneath the diffractograms indicate positions of plausible Bragg reflections.

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Consequently, for the stoichiometry reasons, the equivalent number of lithium ions occupy 16d site. However, owing to the similar scattering factors of manganese and chromium ions, it was impossible to differentiate between them and to determine which one more occupies 8a site. This can be resolved indirectly by comparing the results of the refinements of both the undoped LiMn2O4 powder and chromiumdoped LiMn2O4 powder (Table 11.1). In the case of the undoped LiMn2O4 powder the occupancy of the tetrahedral 8a crystallographic position by manganese ions is by two orders of magnitude lower than the occupancy of that position by transition metal ions (manganese and chromium) for chromium-doped LiMn2O4 powder. Therefore, it can be concluded that the tetrahedral 8a crystallographic position is rather occupied by chromium ions then manganese ions. It should be noted here that this occupancy is small and that transition metal ions prefer octahedral positions. The coordinates of oxygen ions at equipoint 32e are not special: they alter according to a single parameter, u. Anions in spinel usually are expounded away from their ideal cubic close-packed positions. The refinements results imply that anion parameter u is slightly larger for chromium-doped LiMn2O4 powder compared to the undoped LiMn2O4 powder (Table 11.1). This dilation, accomplished through chromium doping, has several important crystallographic implications such as elongation of Li–O bonds and concurrent shortening of M–O bonds (where M is manganese or chromium ion), which additionally stabilize spinel structure. The mean crystallite size is smaller for chromium-doped powder, as well as both microstrain and strain parameters. Zinc-doped LiMn2O4 powder is well crystallized as spinel in space group Fd3m. Two different approaches were applied in the refinement of zinc-doped LiMn2O4 powder. In the first model, Li+ ions were positioned in special crystallographic position 8a  [0, 0, 0] with local symmetry 43m; Mn3+, Mn4+ and Zn2+ ions were positioned in special crystallographic position 16d [5/8, 5/8, 5/8] with local symmetry 3m, and O2− ions in special crystallographic position 32e [u, u, u] with local symmetry 3m. In the second model, octahedral 16d sites were allowed to be occupied by manganese ions only, while tetrahedral 8a positions were allowed to be occupied by both lithium and zinc ions. The second model gave better agreement with experimental data and the final results of that refinement is given in Table 11.1, while comparative diffractograms of calculated and experimental data are given in Figure 11.8. Unlike undoped LiMn2O4 and chromium-doped LiMn2O4, which have similar anion parameter u (Table 11.1), anion parameter for zinc-doped LiMn2O4 is smaller, and closer to the u value for ideal anion close cubic packing (u = 0.375), which is strong evidence that zinc ions are positioned at tetrahedral sites. Similar results, obtained by neutron powder diffraction, were reported in the literature [31]. Occupation of tetrahedral sites by zinc ions is common for many spinel systems and is a consequence of zinc tendency to be surrounded by coordination number 4. Since tetrahedral sites are occupied by both lithium and zinc ions, compared to the undoped LiMn2O4, mean charge of tetrahedral sites is increased, with concurrent

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Figure 11.8: The experimental (◦), calculated (–), and divergence (bottom) X-ray diffraction data of LiZn0.082Mn1.918O4 taken at room temperature. Vertical indicators beneath the diffractograms indicate positions of plausible Bragg reflections.

mean charge decrease of octahedral sites. Regarding that, every oxygen ion is coordinated with one tetrahedrally coordinated cation and three octahedrally coordinated cations, thus forming distorted tetrahedron [5]. Mean charge modification at both tetrahedral and octahedral sites decreases both anionic polarization and distortion of oxygen tetrahedron, therefore additionally relaxing the lattice. Cation doping of LiMn2O4 caused a decrease of both microstrain and strain parameters (Table 11.1). Lattice strain is correlated with the Jahn-Teller distortion. Concerning that the Jahn-Teller distortion depends on the amount of Mn3+ ions, variations in lattice strains of the undoped LiMn2O4 and the doped LiMn2O4 may be linked with the mean valence of manganese ions therein. Manganese valences in undoped, chromium-doped and zinc-doped LiMn2O4 are 3.500, 3.548 and 3.564, respectively, which imply respective decrease of the amount of Mn3+ ions, and consequently the decrease of lattice strain that follows the same trend.

11.3.1.2 XRD analysis of LiFePO4 X-ray powder diffraction revealed the presence of LiFePO4 as the main component in powders LFP-SP and LFP-SS. The powder obtained by ultrasonic spray pyrolysis (LFP-SP), besides the olivine phase, also contained compounds of lithium/iron and carbon as minor impurity phases (Figure 11.9). There are no characteristic diffraction peaks that belong to carbon, so internal carbon, created as a result of the sucrose

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Figure 11.9: The experimental (◦), calculated (–), and divergence (bottom) X-ray diffraction data of LiFePO4 powder obtained by ultrasonic spray pyrolysis taken at room temperature. Vertical indicators beneath the diffractograms indicate positions of plausible Bragg reflections. The peaks that belong to impurity phases are marked with asterisks.

pyrolytic decomposition, can be treated as a contribution to the background. On the other hand, the solid state reaction gave monophased powder of olivine-type LiFePO4 (Figure 11.10) without the presence of any impurity phase. The structure of the powders was refined in the space group Pnma (D2h16) in the olivine type with the following crystallographic positions: Li+ ions at the crystallographic position 4a [0,0,0] with the local symmetry ī; Fe2+ and P5+ ions occupied two nonequivalent 4c crystallographic positions [x,0.25,z] with the local symmetry m. Oxygen O2− ions occupied three different crystallographic positions: additional two 4c positions and one general 8d position [x,y,z] with the local symmetry 1. The refinement results (Table 11.2 [32]) indicate that the structural parameters depend on the synthesis method: solid state reaction gave powder with larger lattice parameters, larger mean crystallite size and smaller microstrain. This is related with the rapid synthesis accomplished through the ultrasonic spray pyrolysis method. Upon fast heating and cooling, the crystallized particle had limited time to relax its structure and consequently strained structure of smaller volume is formed. In addition, there is a possibility of interstitial incorporation of carbon within the structure that could additionally cause the strain. All significant bond lengths and bond angles are calculated by using both refined and fixed fractional atomic coordinates. This allowed determination of the coordination

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Figure 11.10: The experimental (◦), calculated (–), and divergence (bottom) X-ray diffraction data of LiFePO4 powder obtained by solid state reaction taken at room temperature. Vertical indicators beneath the diffractograms indicate positions of plausible Bragg reflections. Table 11.2: The final results of the Rietveld refinement for LiFePO4 powders. SP LiFePO

SS LiFePO

Lattice parameters (Å)

a = .() b = .() c = .()

a = .() b = .() c = .()

Primitive cell volume (Å)

V = .

V = .

Mean crystallite size (Å)

()

()

Microstrains (%)

.()

.()

R factors of the refinement (%)

RB = .

RB = .

polyhedra, and examination of the geometry of lithium one-dimensional channel. An expected value of Fe–O bond length for octahedrally coordinated Fe2+ ion in oxides is 2.1405 Å. The mean Fe–O distances of the investigated powders deviate from the expected value (Table 11.3). Namely, FeO6 octahedron has common edge with PO4 tetrahedron and thus an Fe–O–P inductive effect is involved. The inductive effect is related with unequal electron distribution in chemical bond. The largest mean Fe–O distance is noticed for the powder obtained by ultrasonic spray pyrolysis. This

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Table 11.3: Selected bond lengths of LiFePO4 samples. M–O bond (Å)

SP LiFePO

SS LiFePO

Fe–O()

.

.

Fe–O()

.

.

Fe–O() × 

.

.

Fe–O()’ × 

.

.

(Fe–O)av.

.

.

Li–O() × 

.

.

Li–O() × 

.

.

Li–O() × 

.

.

(Li–O)av.

.

.

P–O()

.

.

P–O()

.

.

P–O() × 

.

.

(P–O)av.

.

.

O()–O()

.

.

Li–Li

.

.

implies weakening of Fe–O bond strength and shrinking of P–O bond. Significant distortion of PO4 tetrahedron of the LFP-SP powder in comparison with the LFP-SS sample (2.4 × 10−2 and 4.8 × 10−4, respectively) is an additional indicator of the disruptive structure obtained by ultrasonic spray pyrolysis. Evidently, additional high-temperature treatment of the powder prepared by spray pyrolysis is required in order to provide the conditions under which the structure can reorder in a more stable form. This is in accordance with the investigations reported in the literature [22, 33–35].

11.3.2 Morphology studies 11.3.2.1 The morphology of LiMn2O4 powders The morphology of the powders was investigated by scanning electron microscopy, whose representative images are given in Figures 11.11–11.14. Particles of slowly cooled LiMn2O4 powder are spherical in shape with rough surfaces, mostly individual, with sizes that vary from 0.5 to 1.2 μm (Figure 11.11). Quenched LiMn2O4 powder shows different morphology (Figure 11.12). Primary spherical particles that

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Figure 11.11: Scanning electron microscopy image of slowly cooled powder of LiMn2O4 obtained by ultrasonic spray pyrolysis.

Figure 11.12: Scanning electron microscopy image of quenched powder of LiMn2O4 obtained by ultrasonic spray pyrolysis.

are formed by solidification in the reaction tube are decomposed displaying inner substructure. This is demonstrated by the presence of agglomerates, albeit sole particles of different both shape and sizes can be observed too. Unlike rough surface that was observed for undoped LiMn2O4 particles, chromiumdoped LiMn2O4 powder consists of individual spherical particles with extremely smooth surface (Figure 11.13). Particle sizes lay in the range from 0.37 to 1.45 μm.

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Figure 11.13: Scanning electron microscopy image of LiCr0.175Mn1.825O4 obtained by ultrasonic spray pyrolysis.

Zinc-doped LiMn2O4 powder also consists of spherical individual particles of different sizes with microporous surface structure (Figure 11.14). A common feature for all LiMn2–xMxO4 (M = Mn, Cr, Zn) powders is spherical particle morphology that differs in surface appearance. Namely, the surface structure highly depends on precursor components: if metal nitrate melts before its decomposition and if this happens before an evaporation of a solvent, metal nitrate melt will inhibit removal of the trapped solvent and consequently porous particle will be formed [36]. This is the case for zinc-doped powder since Zn(NO3)2 melts at 45 °C, quite lower than water evaporates.

11.3.2.2 The morphology of LiFePO4 powders Scanning electron images of LiFePO4 powders disclose the differences in particle morphology. Solid state reaction (Figure 11.15) gave powder with puzzle-like morphology. There are no clearly observable boundaries between particles; instead, they are gathered and sintered. On the other hand, the particles obtained by ultrasonic spray pyrolysis are non-agglomerated and rounded (Figure 11.16). Taking into account mean crystallite sizes obtained by structural refinements (Table 11.2), it is obvious that the particles of both powders are polycrystalline, consisting numerous crystallites.

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Figure 11.14: Scanning electron microscopy image of LiZn0.082Mn1.918O4 obtained by ultrasonic spray pyrolysis.

Figure 11.15: SEM image of LiFePO4 powder obtained by solid state reaction.

11.3.3 Electrochemical properties Electrochemical performances of the samples used as cathodes for Li-ion batteries were investigated by galvanostatic charge–discharge tests.

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Figure 11.16: SEM image of LFP-SP powder.

11.3.3.1 Galvanostatic cycling of LiMn2O4 powders The energy of a Mn4+/Mn3+ redox couple in spinel LixMn2O4 is sensitive to the Li+ order on tetrahedral sites. There exist two voltage plateaus at 0 < x < 0.5 and 0.5 < x < 1 around 4 V vs. Li with a small voltage step between them. Sudden voltage drop from 4 to 3 V at x = 1 is related to Li+ shift from tetrahedral to octahedral sites [37]. This limits the capacity of the spinels to half a Li per framework cation. The second plateau, when occurs when the concentration of lithium (x) is 0.5 < x < 1, is no actual plateau; it corresponds to continual slow voltage decrease that can be ascribed to the solid-solution range. The discharge curves of the slowly cooled LiMn2O4 powder are presented in Figure 11.17. The initial discharge capacity of 115 mAh/g slightly decreases during early stages of cycling, similar to LiMn2O4 spinels obtained by other synthesis procedures [14]. Discharge curves of the first and the fifth cycles show two voltage plateaus, while the discharge curves of the second, the third and the fourth cycles show three voltage plateaus. Lower voltage plateau of the fifth discharging curve is moved to higher voltage in comparison with the same plateau of the first discharge. Actually, this plateau is developed during the second, the third and the fourth cycles and is most probably the consequence of the structural transformation inside spinels generated during deintercalation and intercalation of lithium ions. Contrary to the SC LiMn2O4, electrode composed of quenched LiMn2O4 powder had much lower initial capacity of 26 mAh/g and the absence of two voltage plateaus during cycling (Figure 11.18). It can be easily concluded that tetragonal LiMn2O4 is not an appropriate cathode material within the applied voltage range. Despite larger unit-

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Figure 11.17: Discharge curves of slowly cooled LiMn2O4 powder obtained by ultrasonic spray pyrolysis.

cell volume, the random distribution of lithium and manganese ions in both 4a and 8d crystallographic positions is detrimental for intercalation and deintercalation of lithium ions. Discharge curves of Cr-doped LiMn2O4 electrode show two distinct voltage plateaus (Figure 11.19), characteristic for spinel LiMn2O4 [37]. During first several cycles the capacity decreases, but then becomes stable (Figure 11.20). The initial capacity of 80 mAh/g in the given voltage range is smaller than the initial capacity derived from slowly cooled LiMn2O4 powder. This can be expected as LiCr0.175Mn1.825O4 contains a smaller amount of Mn3+ ions that can be oxidized, whereas the oxidation of Cr3+ ions occurs at higher voltages, beyond the applied voltage range. At a rough estimate, capacity can be calculated by taking the proportion of the Mn3+ ions decrease in doped spinel in comparison to the undoped spinel. The calculated value of 94.8 mAh/g matches the value of the first charging capacity of LiCr0.175Mn1.825O4 electrode, which implies that during the discharge process a smaller amount of lithium ions successfully intercalate into spinel lattice. The existence of irreversible capacity could be related with the tetrahedrally coordinated chromium ions. Namely, in compounds with large u values, for tetrahedral A-sites, a diffusion jump to a nearest-neighbor tetrahedral vacant site (48f ) can occur by a direct jump [5]. During the charging process lithium ions leave spinel structure and

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Figure 11.18: Discharge curves of quenched LiMn2O4 powder obtained by ultrasonic spray pyrolysis.

Figure 11.19: First charge and discharge curves of chromium-doped LiMn2O4 powder obtained by ultrasonic spray pyrolysis.

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Figure 11.20: The discharge capacity retention during cycling of chromium-doped LiMn2O4 powder obtained by ultrasonic spray pyrolysis.

subsequently tetrahedrally coordinated chromium ions are redistributed to other 48f positions which could be important for lithium-ion diffusion. It can be concluded that doping of spinel with chromium ions resulted in lower capacity, and that the capacity is more stable due to more rigid structure, namely, stronger M–O bond (M = Mn or Cr).

11.3.3.2 Galvanostatic cycling of LiFePO4 powders Electrochemical deintercalation and intercalation of lithium ions in olivine LiFePO4 are two-phased reactions. The two-phased mechanism that governs lithium intercalation/deintercalation is reflected in flat charge/discharge curves characterized by wide voltage plateau whose length varies with the applied current density. Such behavior is typical for a diffusion controlled process [38]. Also, the two-phase mechanism results in a poor electronic conductivity that is usually overcome by coating olivine particles with some conductive compound, i.e., carbon is the most often used. The performances of the investigated LiFePO4 cathodes differ from each other. Solid state reaction brought flat discharge curves (Figure 11.21) and the capacity close to 80 mAh/g, which represents 50% of the theoretical capacity. In addition,

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Figure 11.21: Charge and discharge curves of LiFePO4 powder obtained by solid state reaction.

due to low electronic conductivity in conjunction with large particle sizes, the capacity fades during the cycling. The appearance of large voltage divergence between charging and discharging curves indicates the increment of the electrode resistance. The source of this enlarged electrode resistance can be found in the slow kinetics of lithium ions due to large crystal size. Taking into account that the investigated powder is free of carbon it becomes apparent that carbon coating, which is widely used in the synthesis of LiFePO4 powders, is necessary to provide better electronic conductivity and to impede the growth of the particles. The powder of LiFePO4 obtained by ultrasonic spray pyrolysis method delivered a sloping discharge curve with a very short plateau and small initial capacity of only 17 mAh/g (Figure 11.22). During the cycling both the plateau length and the capacity increase, but still the overall electrochemical performances are poor. Having in mind the results of the Rietveld structural refinement it became once again obvious that the deformation of the structure unavoidably leads to poor electrochemical performances. The increase of a plateau length in every successive cycle implies that this structural deformation is partly mobile and that some structural rearrangements occur during cycling. Comparison of the obtained results with the literature data for LiFePO4 powders, prepared by ultrasonic spray pyrolysis method followed by annealing at high temperature (>600 °C) [34, 35], emphasizes the importance of additional hightemperature treatment on the structural and electrochemical properties. Namely, high-temperature treatment allows olivine structure to reduce both structural

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disorder and strain. On the other hand, good electrochemical performances were obtained for spinel structure without additional high-temperature treatment.

Figure 11.22: Discharge curves of LiFePO4 powder obtained by ultrasonic spray pyrolysis.

11.4 Discussion The investigation of electrochemical performances showed different mechanisms of lithium-ion transport through the bulk of the materials. Lithium transport in olivinetype LiFePO4 follows a two-phased mechanism that is characterized by the appearance of a voltage plateau in galvanostatic charge/discharge curves. Electrochemical reaction of LiMn2O4 is known to proceed in a topotactic manner. Within the applied voltage window (3.4–4.3 V) it can be divided in two parts: two-phased mechanism of lithium insertion/deinsertion characterized by voltage plateau around 4.1 V, and cubic one-phase reaction with plateau-like appearance at 3.94 V of midpoint voltage. There is also dissimilar effect of structural ordering on the electrochemical properties of spinel and olivine electrodes. Electrochemical performances of spinel structure are more independent of structural disorder than olivine structure. This is a consequence of different paths for lithium motion through olivine and spinel structures. Figure 11.22 shows LiMn2O4 layer of spinel structure perpendicular to [1, 2] direction, while Figure 11.23 shows the layer of the same structure viewed along [1–1 1] direction.

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Figure 11.23: The layer of spinel structure LiMn2O4 perpendicular to [1–1 1] direction.

These figures illustrate how spinel structure enables lithium motion in three directions, thus providing a three-dimensional network for lithium-ion transport. The only requirement for lithium release from the spinel structure is that lithium ion is positioned at the tetrahedral sites regardless of the cationic surrounding. This means that small impurities or cation disorder will have no significant impact on lithium-ion transport. Because of the tridimensional network, lithium ions can easily bypass any defect or impurity ion positioned on lithium site. On the other hand, lithium movement inside olivine structure is one-dimensional through channels along the b axis (illustrated in Figure 11.24), so lithium diffusion is more sensitive to any defect of the crystal structure (e.g., cation replacement, lattice distortion) that would influence the geometry of the lithium channel. Figure 11.24 represents the so called “antisite” defect that is its intrinsic property. These channels are not interconnected (Figure 11.25), so any defect or impurity ion positioned on lithium site will block the whole lithium channel and thus impede the lithium motion. Olivinetype LiFePO4 has only corner-connected Fe octahedra (Figure 11.4), which results in low electronic conductivity. In contrast, spinel-type LiMn2O4 has edge-connected Mn octahedra (Figure 11.3), which contribute to better electronic conductivity. Therefore, olivine-type LiFePO4 powder requires carbon coating to enhance its electrical conductivity, while for spinel-type LiMn2O4 powders there is no need for additional coating with some conductive compound.

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Figure 11.24: The layer of spinel structure LiMn2O4 perpendicular to [1 2 2] direction.

Figure 11.25: The edge-connected LiO6 octahedra within one chain with an illustration of “antisite” defect (when iron is positioned at lithium site).

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Figure 11.26: The structure of olivine-type LiFePO4 viewed along b axis. The one-dimensional chains of LiO6 octahedra are not interconnected.

11.5 Conclusion The structure is an essential parameter that determines lithium diffusion in cathode materials for lithium-ion batteries. Ultrasonic spray pyrolysis method was used for the synthesis of two cathode materials for lithium-ion batteries: spinel-type LiMn2O4 and olivine-type LiFePO4. It can be concluded that this method is a proper method for obtaining rounded particles, with surface appearance that can be attuned by varying the precursor solution. Fast heating and cooling, which is involved during the spray pyrolysis method, are suitable for the preparation of well-crystallized, ordered spinel powders of pure and transition metal-doped LiMn2O4. However, the synthesis of olivine LiFePO4 powder by ultrasonic spray pyrolysis resulted in the formation of a disruptive structure that requires additional annealing in order to obtain lattice relaxation. Crystal structure refinements confirmed successful doping of spinel structure by chromium or zinc ions. Different structures enable different pathways for lithium-ion motion: spinel structure defines a three-dimensional array for lithium-ion diffusion, unlike olivine structure where lithium transport is onedimensional. Electrochemical measurements, conducted on as-prepared powders, showed that doping with chromium derived lower, but more stable, capacity in comparison with the undoped LiMn2O4. Tetragonal phase of LiMn2O4 has been shown to be electrochemically almost inactive. This also stands for LiFePO4 powder obtained by ultrasonic spray pyrolysis method due to distorted structure.

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References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

[11] [12]

[13] [14] [15]

[16] [17]

[18] [19] [20]

[21]

Winter M, Brodd RJ. What are batteries, fuel cells, and supercapacitors? Chem Rev 2004, 104(10), 4245–69. Nitta GYN, Wu F, Lee J. Li-ion battery materials: Present and future. Materialstoday 2015, 18 (5), 252–64. Winter M, Besenhard JO, Spahr ME, Novák P. Insertion electrode materials for rechargeable lithium batteries. Adv Mater 1998, 10(10), 725–63. Whittingham MS. Lithium batteries and cathode materials. Chem Rev 2004, 104(10), 4271–302. Sickafus KE, Wills JM, Grimes NW. Structure of spinel. J Am Ceram Soc 1999, 82(12), 3279–92. Birle JD, Gibbs GV, Moore PB, Smith JV. Crystal structures of natural olivines. Am Mineral 1968, 53(5–6), 807–24. Padhi AK, Nanjundaswamy KS, Goodenough JB. Phospho-olivines as positive-electrode materials for rechargeable lithium batteries. J Electrochem Soc 1997, 144(4), 1188–93. Andersson AS, Kalska B, Haggstrom L, Thomas JO. Lithium extraction/insertion in LiFePO4: An X-ray diffraction and Mössbauer spectroscopy study. Solid State Ionics 2000, 130, 41–52. Morgan D, Van der Ven A, Ceder G. Li conductivity in LixMPO4 (M = Mn, Fe, Co, Ni) olivine materials. Electrochem Solid-State Lett 2004, 7(2), A30. Islam MS, Driscoll DJ, Fisher CAJ, Slater PR. Atomic-Scale Investigation of Defects, Dopants, and Lithium Transport in the LiFePO4 Olivine-Type Battery Material. Chem Mater Oct 2005, 17(20), 5085–92. Kozawa T, Yanagisawa K, Murakami T, Naito M. Growth behavior of LiMn2O4 particles formed by solid-state reactions in air and water vapor. J Solid State Chem 2016, 243, 241–46. Gim J, Song J, Nguyen D, Hilmy Alfaruqi M, Kim S, Kang J, Rai AK, Mathew V, Kim J. A two-step solid state synthesis of LiFePO4/C cathode with varying carbon contents for Li-ion batteries. Ceram Int 2014, 40(1), PART B, 1561–67. Kosova NV. Mechanochemical reactions and processing of nanostructured electrode materials for lithium-ion batteries. Mater Today Proc 2016, 3(2), 391–95. Han YS, Kim HG. Synthesis of LiMn2O4 by modified Pechini method and characterization as a cathode for rechargeable Li/LiMn2O4 cells. J Power Sources 2000, 88(2), 161–68. Bhaskar A, Mikhailova D, Kiziltas-yavuz N, Nikolowski K, Oswald S, Bramnik NN, Ehrenberg H. Progress in solid state chemistry 3d-transition metal doped spinels as high-voltage cathode materials for rechargeable lithium-ion batteries. Prog Solid State Chem 2014, 42, 128–48. Jugović D, Cvjetićanin N, Kusigerski V, Mentus S. Synthesis of LiMn2O4 by glycine-nitrate method. J Optoelectron Adv Mater 2003, 5(1), 343–46. Dominko R, Bele M, Gaberscek M, Remskar M, Hanzel D, Goupil JM, Pejovnik S, Jamnik J. Porous olivine composites synthesized by sol-gel technique. J Power Sources 2006, 153(2), 274–80. Zou BK, Ma XH, Tang ZF, Ding CX, Wen ZY, Chen CH. High rate LiMn2O4/carbon nanotube composite prepared by a two-step hydrothermal process. J Power Sources 2014, 268, 491–97. Azib T, Le Cras F, Porthault H. Direct fabrication of LiCoO2 thin–films in water–ethanol solutions by electrochemical–hydrothermal method. Electrochim Acta 2015, 160, 145–51. Bolloju S, Rohan R, Wu S-T, Yen H-X, Dwivedi GD, Lin YA, Lee J-T. A green and facile approach for hydrothermal synthesis of LiFePO4 using iron metal directly. Electrochim Acta 2016, 220, 164–68. Matsuda K, Taniguchi I. Relationship between the electrochemical and particle properties of LiMn2O4 prepared by ultrasonic spray pyrolysis. J Power Sources 2004, 132(1–2), 156–60.

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[22] Konarova M, Taniguchi I. Preparation of LiFePO4/C composite powders by ultrasonic spray pyrolysis followed by heat treatment and their electrochemical properties. Mater Res Bull 2008, 43(12), 3305–17. [23] Choi KY, Do Kim K, Yang JW. Optimization of the synthesis conditions of LiCoO2 for lithium secondary battery by ultrasonic spray pyrolysis process. J Mater Process Technol 2006, 171(1), 118–24. [24] Rietveld HM. A profile refinement method for nuclear and magnetic structures. J Appl Crystallogr 1969, 2(2), 65–71. [25] Cheary RW, Coelho A. A fundamental parameters approach to X-ray line-profile fitting. J Appl Crystallogr 1992. [26] Jugović D, Mitrić M, Cvjetićanin N, Miljković M, Jokanović V, Uskoković D. Properties of LiMn2O4 powders obtained by ultrasonic spray pyrolysis. Mater Sci Forum 2004, 453–454, 387–92. [27] Piszora P. Inequality of quenched and high temperature structure of lithium deficient LiMn2O4. J Alloys Compd 2005, 401(1–2), 34–40. [28] Yamada A, Tanaka M. Jahn-Teller structural phase transition around 280K in LiMn2O4. Mater Res Bull 1995, 715–21. [29] Darul J, Nowicki W, Lathe C, Piszora P. Observation of phase transformations in LiMn2O4 under high pressure and at high temperature by in situ X-ray diffraction measurements. Radiat Phys Chem 2011, 80(10), 1014–18. [30] Jugović D, Cvjetićanin N, Kusigerski V, Mitrić M, Miljković M, Makovec D, Uskoković D. Structural and magnetic characterization of LiMn1.825Cr0.175O4 spinel obtained by ultrasonic spray pyrolysis. Mater Res Bull 2007, 42(3), 515–22. [31] Bellitto C, Bauer EM, Righini G, Green MA, Branford WR, Antonini A, Pasquali M. The effect of doping LiMn2O4 spinel on its use as a cathode in Li-ion batteries: Neutron diffraction and electrochemical studies. J Phys Chem Solids 2004, 65(1), 29–37. [32] Jugović D, Cvjetićanin N, Mitrić M, Mentus S. Comparison between different LiFePO4 synthesis routes. Mater Sci Forum 2007, 555, 225–30. [33] Ju SH, Kang YC. LiFePO4/C cathode powders prepared by spray pyrolysis from the colloidal spray solution containing nano-sized carbon black. Mater Chem Phys 2008, 107(2–3), 328–33. [34] Konarova M, Taniguchi I. Preparation of carbon coated LiFePO4 by a combination of spray pyrolysis with planetary ball-milling followed by heat treatment and their electrochemical properties. Powder Technol 2009, 191(1–2), 111–16. [35] Yang M-R, Teng T-H, Wu S-H. LiFePO4/carbon cathode materials prepared by ultrasonic spray pyrolysis. J Power Sources 2006, 159(1), 307–11. [36] Messing GL, Zhang S-C, Jayanthi GV. Ceramic powder synthesis by spray pyrolysis. J Am Ceram Soc 1993, 76(11), 2707–26. [37] Guyomard D, Tarascon JM. The carbon/ Li1‒xMn2O4 system. Solid State Ionics 1994, 69, 222–37. [38] Goodenough JB. Evolution of strategies for modern rechargeable batteries. Acc Chem Res 2013, 46(5), 1053–61.

Aleksandar Radunovic, Zoran Popovic, Aleksandar Matic, Maja Vulovic

12 Application of ceramic components in knee arthroplasties Abstract: Total knee arthroplasty is currently a gold standard in surgical treatment of patients with degeneratively changed cartilage tissue of the knee gonarthrosis. Two major causes of total knee replacement failure are aseptic loosening caused by particle debris released by wear and nonoptimal positioning of endoprosthesis components. There is also an increase in the incidence of reported allergies on metal as a factor potentially causing failure of implant. Ceramic as a biomaterial has characteristics that could potentially make it a replacement for metal in endoprosthesis. First attempts were disappointing but following progress in endoprosthesis design and ceramics production make it look like a promising solution, at this moment exclusive option for the patients with confirmed allergies on metal. Keywords: knee, arthroplasty, biomaterials, ceramic

12.1 Introduction Osteoarthritis of the knee (gonarthrosis) is characterized by degenerative changes of cartilage tissue and, in final stages, serious disturbance of joint function. Total knee arthroplasty is considered as a gold standard in surgical treatment of patients with poor response on conservative therapy. Good orientation of endoprosthesis components and adequate soft tissue balancing are of essential importance for proper functioning and longevity of the implant. Thus, thorough knowledge of joints anatomy and biomechanics, surgical technique and implants characteristics are required.

Aleksandar Radunovic, Clinic for Orthopedic Surgery and Traumatology, Military Medical Academy, Belgrade, Serbia, [email protected] Zoran Popovic, Vozd clinic, Belgrade, Serbia Aleksandar Matic, Clinic for Orthopedic Surgery, Clinical Center Kragujevac, Kragujevac, Serbia Maja Vulovic, Department of Anatomy, Faculty of Medical Sciences, University of Kragujevac, Kragujevac, Serbia https://doi.org/10.1515/9783110627992-012

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12.2 Anatomy of the knee The knee joint is the largest one in the human body and has to withstand movements under body weight. Movements performed in knee joint are flexion, extension and rotational moves. The shape of the articular surfaces of femur and tibia does not provide bony stability of the joint, thus the ligaments of the knee and the joint capsule are stabilizing knee during motions under load. A very important role in stability of the knees is also of menisci (making flat articular surface of tibia slightly concave) [1].

Anterior cruciate ligament

Posterior cruciate ligament

Lateral collateral ligament

Lateral meniscus

Figure 12.1: Basic ligaments of knee (front side).

Figure 12.2: Ligaments of knee (back side).

Medial collateral ligament

Medial meniscus

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For understanding essentials of knee biomechanics and knee joint replacement surgery, it is important to mention just few of those ligaments. Cruciate knee ligaments (anterior and posterior cruciate ligaments) are the strongest knee ligaments. They are positioned in the joint central part, attaching proximally to intercondylar notch of femur and distally to tibial intercondylar area. These two ligaments provide mostly anteroposterior stability and partially rotational stability. Tibial and fibular collateral ligaments provide mediolateral stability of knee [2].

12.3 Biomechanics of the knee Knee flexion and extension are performed around axis that passes through lowest part of femoral bone with the range of motion from 0 to 130 degrees in active movements. It is important to mention that knee flexion is always combined with rolling of femur on tibia (during first 25 degrees of flexion especially) and rolling and gliding (after 25 degrees of flexion) [3]. Rotational movements are performed around longitudinal axis of the leg.

Figure 12.3: Rolling.

Figure 12.4: Gliding.

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12.4 History of knee arthroplasty The beginning of arthroplasties goes back to nineteenth century when surgeons tried to heal the knee with damaged cartilage tissue by interposing different animal tissues or synthetic materials between articular surfaces. These attempts were followed by implantation endoprosthesis made from ivory, performed by Temistocles Gluck in 1890. In the 1970s, few designs of endoprosthesis were developed that leaded to modern days of endoprosthesis design and materials used for fabrication [4]. As about materials, they were mostly based on the concept of low friction arthroplasty developed by Charnley for total hip arthroplasty. This concept implies that using metal on polyethylene (PE) articulation was most advanced coupling of articular surfaces with former technology. Follow-up of this prosthesis shows some problems of metal on PE coupling that raise interests in ceramics as a material for producing components of knee endoprosthesis.

12.5 Materials for producing endoprosthesis Biomaterials are the ones used to fabricate implants that substitute the function of body parts. There are some criteria that should be fulfilled for safe use of these materials: biocompatibility, strength for both compression and tensile forces, resistance to wear and corrosion, availability and economic efficiency. They also should not produce allergic reactions, toxicity, nor have carcinogenic properties. It is preferable for this materials to produce stimulant reaction of organism such as osteoinductivity, osteoconductivity or osteointegration. Today, the standard for total condylar knee arthroplasty is metal on PE articulation. In this type of knee endoprosthesis, there are metal femoral and tibial component, most frequently fixed to the bone with bone cement (PMAA – polymethyl methacrylate) with PE insert that is positioned on the tibial component. This PE insert can be locked (fixed bearing) or with possibility of movement in transverse plane on tibial plate (mobile bearing). Problems that occur while using this type of prosthesis are PE wear, aseptic loosening, metallosis, allergic reactions and infection.

12.5.1 PE wear and aseptic loosening When used for producing articulation surface in knee arthroplasty, PE is exposed to different stresses as a result of combination of movements: wheeling, sliding and rotatory moves. This can produce delamination, gapping and lassitude failure of the PE surface. Products of PE wear are small debris particles that induce foreign body

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Knee Femoral Component

Polyethylene Articulating Surface Stemmed Tibial Plate

Figure 12.5: Total condylar knee endoprosthesis metal on polyethylene.

inflammatory cascade (phagocytes–macrophages–osteoclasts activation) that activates many cellular mechanisms, and as a final product, there is an occurrence of osteolysis around implant that leads to aseptic loosening. There are many factors that can accelerate PE wear: some designs of endoprosthesis, type of PE, sterilization method, prosthesis components malalignment, patient-related factors (obesity and level of activity). Attempting to reduce PE wear, new PE types are developed: UHMWPE (ultrahigh-molecular-weight PE), HCL UHMWPE (highly cross-linked UHMWPE), X PE. There were also changes in sterilization methods, improvements in manufacturing and final processing of metal components (even minor scratches leads to dramatically increased wear of PE).

12.5.2 Allergic reactions Prevalence of metal hypersensitivity is approx. 10–15%. In contact with biological fluids, metals can undergo corrosion and wear, and metal ions or other molecules may induce allergic reactions. Nickel, cobalt and chromium are metals which have the highest potential for allergic reactions [5], but allergies to titanium and vanadium are also reported [6]. There are very few reports of PMMA as a sensitizer.

12.6 Ceramics in knee arthroplasties First modern design of knee endoprosthesis manufactured from ceramic and implanted has been reported by Langer in Germany in 1972. [7]. The first knee endoprosthesis was manufactured from modern ceramic. Alumina has been developed by the Kyocera

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Corp. (Kyoto, Japan) and implanted by Oonishi in the 1980s [8]. There were different kinds of ceramics used in knee arthroplasties, showing effort of engineers to improve material properties. 1. Al2O3 was introduced in the 1970s. First, ceramics failed because there were pits in the material that reduced the fracture toughness of the device. By improving manufacture processing, it became one of the most widely used ceramics in orthopedics today. Alumina is pronouncedly hard and only diamond has higher scratch resistance. It also has very high corrosion resistance in body fluids, weariness and fracture resistance. 2. ZrO2 (zirconia) was introduced in the 1980s. There were some attempts to enhance Zirconia: ZTA – zirconia toughened alumina (higher fracture strength and almost same wear as alumina). 3. Biolox forte (1990s) – alumina improved by reducing the grain size through a heat-pressing process. This reduced the porosity and improved the toughness. Biolox delta-alumina matrix composite (82% alumina with 17% stabilized zirconia and a bit of chromium and strontium) is the fourth generation of ceramics. This attempts to combine zirconia resistance and toughness with better wearing properties of alumina. 4. Trying to combine the best of both worlds, some manufacturers are using nitride coatings on metal, thus preventing potential allergic reactions and toxicity caused by metal. Si3N4 is in industrial use for 50 years. It is characterized with excellent toughness and wear resistance and can be manufactured as porous substrate and hard bearing surface. There are initial reports of even better results achieved by applying titanium nitride lining on metal, which protect the body from metallic ions that can harm the organism.

Biolox delta

Titanium nitride

Figure 12.6: Different ceramics in knee arthroplasties.

Silicone nitride

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12.7 Properties of ceramics in orthopedic surgery Ceramic has some properties that make it very desirable as the bearing surface in orthopedic surgery. It has very low wear rate and alumina ceramic bearings are shown to have lowest in vivo wear rate of any other combination of articulation surfaces [9]. Ceramics wettability is a feature that hugely improves lubrication of joint by uniform distribution of synovial film on articular surfaces due to strong hydrogen bonds between ceramic and synovial fluid. This feature is especially useful in hip arthroplasty causing gravitational effect that tends to leave articulating surfaces dry and ceramics hydrophilic resists tendency. Ceramic has greater hardness comparing to metal and during final processing it can be polished to a much smoother surface then metal. It is shown that ceramic has supreme biocompatibility comparing to metal. Cellular response is much lower for ceramic debris then for PE or metal [10], due to smaller size of ceramic particles and their biological inertness. There are some issues with ceramic components use in orthopedic surgery too. In first generation of ceramics, there was a lot of complication caused by brittleness. Improvements in materials as well as manufacturing advances made use of ceramics in hip arthroplasty routinely. There is completely a different situation when it comes to knee arthroplasties. At this moment, ceramic is mostly reserved for people with known allergic reactions on metal. Even then, the ceramic component is used by coupling with the PE liner and metal on tibial plate most frequently. There are few reasons for ceramic that enters the world of knee arthroplasties so slowly: There are many differences between the hip and knee joint in terms of motions and load stresses. There is also a problem of manufacturing components. In hip arthroplasty, there is very simple shape of articulating surfaces (axial symmetric structure – spheres and cones). Opposite to this in knee arthroplasties, components are of very complex shapes. Also, femoral component has to withstand significant stress forces at the angles of femoral resection (traction stress) and along the lines of contact with PE (contact stress under the surface). Until recently, mechanical properties of ceramics demanded massive components to hold out without breakage. This leads to more bone resection during preparation of bone. Consequently, bone stock for revision surgery is lowered compared to preparation for metal endoprosthesis. Also, joint line and whole biomechanics of knee can be affected with massive resection of bone. As mentioned earlier, ceramic hydrophilic and wettability are very favorable in hip arthroplasty to resist gravity that keeps fluid in the lowest part of joint. In knee arthroplasty, there is no such effect and this property of ceramics does not give it an advantage. There are also difficulties with implantation. During implantation of knee endoprosthesis components, it is necessary to handle them with special instruments.

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Femoral Component Overview of load situation Wedge Load oversize femoral cut 1 cycle 1 × BW Patella Load Patellar joint 20 Mio cycles 5 × BW

Condyle Load High step stumbling 1 Mio cycles 7 × BW

Frontal Load Walking 20 Mio cycles 4 × BW Figure 12.7: Loads on femoral component.

Very often, use of hammer is necessary. With ceramic components, there is a need for extremely precise cutting instruments during bone preparation. Additionally, no metal is handled, and ceramic contact is allowed during insertion of ceramic components and no hammering too.

12.8 Conclusion Nowadays, metal on PE articulation is still a gold standard in knee arthroplasties. Ceramic components are considered as an alternative suitable for patients with known allergic reactions to metals mentioned earlier. At this moment, there is limited number of studies of ceramic components in knee arthroplasty, especially with long-term follow-up. There is only one controlled clinical study of total knee prosthesis without metal (femoral and tibial component ceramics with PE liner) [11].

References [1] [2]

Бошковић М. (1982). Анатомија човека дескриптивна и функционална, Медицинска књига, Београд – Загреб Vaupel G, Dye S. Functional knee anatomy. In: Baker CL, Flandry F, Henderson JM (eds), The Hughston Clinic Sports Medicine Book. Baltimore: Williams & Wilkins, 1995, 403–15.

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[3]

163

Scholes SC, Bull AMJ, Unsworth A, Amis AA. Biomechanics of articulations and derangements in disease. In: Isenberg DA, Maddison PJ, Woo P, Glass D, Breedveld FC (Eds.), Oxford textbook of rheumatology. New York: Oxford University Press, 2004, 379–87. [4] Ranawat CS. History of total knee replacement. J South Orthop Assoc 2002, 11(4), 218–26. [5] Niki Y, Matsumoto H, Otani T, Yatabe T, Kondo M, Yoshimine F, et al. Screening for sintomatic metal sensitivity: a prospective study of 92 patients undergoing total knee arthroplasty. Biomaterials 2005, 26, 1019e26. [6] Lalor PA, Revell PA, Gray AB, Wright S, Railton GT, Freeman MA. Sensitivity to titanium. J Bone Joint Surg Br 1991, 73, 25e8. [7] Langer G. Ceramic Tibial Plateau of the 70s. Bioceramics in Joint Arthroplasty. Proceedings 7 th International BIOLOX Symposium; 2002 March 15, 16; Stuttgart: Thieme 2002. [8] Oonishi H, Aono M, Murata N, Kushitani S. Aluminia versus polyethylene in total knee arthroplasty. Clin Orthop 1992, 282, 95–104. [9] Boutin P, Christel P, Dorlot JM, et al. The use of dense Alumina-alumina ceramic combination in total hip replacement. J Biomed Mater Res 1988, 22, 1203–32. [10] Catelas I, Huk O, Petit A, et al. Flow cytometric analysis of macrophage response to ceramic andpolyethylen particles: Effects of size, concentration, and composition. J Biomed Mater Res 1998, 41, 600–07. [11] Meier E, et al. First clinical study of a novel complete metal-free ceramic total knee replacement system. J Orthop Surg Res 2016, 11, 21.

Pelemiš S., Mirjanić D. Lj., Mirjanić V., Mirjanić Dj., Vuković S.

13 Nanomaterials application in dentistry Abstract: Biomaterials in medicine and dentistry are a relatively new phenomenon dating back to the 1950s; yet, today, an estimated 20 million individuals have an implanted medical device. Nanotechnology is a matter at nanometer level and the application of the same to medicine is called nanomedicine. This technology, which deals with matter in nanodimensions, has widened our views of poorly understood health issues and provided novel means of diagnosis and treatment. Researchers in the field of dentistry have explored the potential of nanoparticles in existing therapeutic modalities with moderate success. In regard to biomaterials, nanotechnology has gained an increasing interest by researchers, particularly in case of dental implants. This is mainly due to the impact of nanoparticles on host responses at both cellular and tissue levels. The growing interest in the dental applications of nanotechnology is leading to the emergence of a new field called nanodentistry. Dentistry is frequently facing revolutions in order to provide a most reliable and comfortable therapeutic options for the patients. Recently, nanotechnology has emerged as a new science exploiting specific phenomena and direct manipulation of materials on nanoscale. Application of nanotechnology in dentistry holds a promise for the maintenance of comprehensive dental care by employing nanomaterials, including tissue engineering and ultimately nanorobots. Keywords: nanomaterials, dentistry, dental materials

13.1 Introduction Biomaterial science is in the midst of the largest transition in its history in terms of refocusing and embracing new and exciting technologies. True biological biomaterials are the ones that lead to natural tissue restoration. Science is presently undergoing a great evolution, taking humanity to a new era: the era of nanotechnology. The opportunity to witness the beginning of a pioneering development in technology is encountered rarely. The application of nanotechnology to dentistry and the time that will be required to implement the results of research into practice are the first questions that arise regarding nanotechnology in dentistry. Nanotechnology is

Pelemiš S., Vuković S., Faculty of Technology, University of East Sarajevo, Bosnia and Herzegovina Mirjanić D. Lj., Academy of Sciences and Arts of Republic of Srpska, Bosnia and Herzegovina Mirjanić V., Mirjanić Dj., Faculty of Medicine, Department of Dentistry, University of Banja Luka, Bosnia and Herzegovina, [email protected] https://doi.org/10.1515/9783110627992-013

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based on the concept that individual atoms and molecules can be used to obtain functional structures. It seeks to explain the ways in which complex structures such as crystals, polymers, proteins and drugs are built up at the nanoscale level (at the level of atoms and molecules). It also aims at exploring the ways in which we can modify the molecular arrangements of these complex structures in order to obtain the desirable macroscopic features. Nanotechnology will give us the ability to arrange atoms as we desire and subsequently to achieve effective, complete control of the structure of matter. The aims of nanotechnology are to enable the analysis of structures at the nanoscale, to understand the physical properties of structures at the nanoscale dimension, to manufacture nanoscale structures, to develop devices with nanoprecision and to establish a link between nanoscopic and macroscopic universes by inventing adequate methods. Similar to nanomedicine, the development of nanodentistry will allow nearly perfect oral health by the use of nanomaterials and biotechnologies, including tissue engineering and nanorobots. Nowadays, it is possible to produce complex systems composed of hundreds of millions precisely positioned nanostructures. Unexpected chemical, physical and biological properties may emerge in a material reduced to the nanoscale. These novel properties open up the possibilities for unique applications of the material. Size reduction leads to the increase in surface-to-volume ratio allowing for the occurrence of certain physical phenomena including statistical and quantum mechanical effects. Figure 13.1 presents the timeline of the recent past, near future and far future for the use of synthetic dental biomaterials versus truly biological materials. Biomaterials will be examined in terms of biological materials fabrication (tissue engineering, nanoengineering, self-assembling systems), leading edge synthetic biomaterials utilized in chairside dental applications (bonding, composites, curing, cements and

Figure 13.1: Timeline of the recent past, near future, and far future for the use of synthetic dental biomaterials versus truly biological materials [1].

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ceramics), and assessment of the performance outcomes of these strategies (longevity) [1, 2]. Any impact of truly biological materials depends on a combination of both technology and cost. If replacement teeth were available today from a hypothetical personal tissue bank, would this be a practical option for most restorative circumstances?

13.2 Nanomaterials and nanodentistry Nanostructures may occur in different forms: nanoparticles (NPs), nanopores, nanofibers, nanotubes, nanoshells, nanorods, nanospheres, dendrimers, and dendritic copolymers. There are a wide range of inorganic NPs – semiconductor NPs, metal NPs, metal oxide NPs, silica NPs, polyoxometalates, gold crystals and so on both in current use and under development. Nanodentistry includes nanorobotics, nanodiagnostics, and nanomaterials [3, 4]. Nanorobotics: local anesthesia, hypersensitivity cure, dental biomimetics, dental durability and cosmetics, orthodontic treatment, dentifrobots, renaturalization procedures and nanovectors. Local anesthesia: a colloid solution containing active analgesic dental robots (micron scale) is instilled on the gingiva of the patient. The nanorobots can reach the pulp through the gingival sulcus, lamina propria and dentinal tubules. The time necessary for the robots to reach the pulp from the surface of the tooth is approximately 100 s provided that the length of the path is approximately 10 mm in total and the travel speed is 100 µm/s [5]. Hypersensitivity cure: dentin hypersensitivity may be caused by changes in pressure transmitted hydrodynamically to the pulp. Dental nanorobots could selectively and precisely occlude selected tubules in minutes, using native biological materials, offering patients a quick and permanent cure [6]. Dental biomimetics: the most interesting venue for speculation on the nanorestoration of tooth structure is that of nanotechnology mimicking processes that occur in nature (biomimetics), such as the formation of dental enamel. Dental durability and cosmetics: durability and appearance of teeth can be improved using sapphire and diamond due to the fact that these materials are highly biocompatible and 20–100 times harder than natural tooth enamel or ceramic veneers used nowadays. Orthodontic treatment: it is possible to straighten, rotate and vertically position teeth for a relatively short period of time (minutes to hours) using orthodontic nanorobots which are able to directly manipulate periodontal tissues (gingivae, periodontal ligament, cementum and alveolar bone). Apart from being rapid, the procedure is also painless.

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Dentifrobots: it is possible to conduct a continuous calculus debridement and to convert trapped organic matter into harmless and odorless vapors using a mouthwash or toothpaste containing subocclusal nanorobotic dentifrice. The material can be used to search all supragingival and subgingival surfaces for pathogenic bacteria once a day or more frequently. Renaturalization procedures: Aesthetic dentistry can potentially benefit from novel treatment opportunities in the form of tooth renaturalization procedures as these methods become increasingly popular part of the standard dental practice. Nanovectors: nanovectors in the form of calcium phosphate NPs are a type of vehicle for gene targeted delivery to fibroblasts for the purpose of periodontal regeneration in vitro [7]. Nanodiagnostics: nanoscale cantilevers, nanopores, nanotubes, quantum dots, nanoelectromechanical systems (NEMS), oral fluid nanosensor test (OFNASET), optical nanobiosensor and lab-on-a-chip (LOC) methods. Dental caries and periodontal disease are the most common maladies affecting the human race. Methods to prevent and combat them have been devised, discussed, and implemented since ancient times. However, there is a constant need for improved tools and techniques. Nanoscale cantilevers: there are microscopic elastic beams that can be manipulated to bind specific substrates such as cancer-related molecules. Nanopores: DNA sequencing technologies are improved with the introduction of nanopores, or tiny holes capable of allowing DNA to be driven through one strand at a time. Nanotubes: these refer to tubular structures made of carbon. Due to their fibrous shape and the diameter half the size of a DNA molecule, they are considered a powerful vehicle for detecting altered genes and identifying the precise location of those changes. Quantum dots: these materials are capable of emitting light when illuminated by UV radiation. They are used in tumor labeling due to their ability to attach specifically to the molecules to be detected or to proteins unique to cancer cells. NEMS: these are a class of devices used as biosensors of extremely high sensitivity and specificity. These devices can change biochemical signals to electrical signals. Their exquisite sensing mechanisms are currently developed as a potent vehicle for analyte detection at the level of a single molecule. OFNASET: this technology is used in oral cancer detection due to its ability to detect salivary biomarkers with high sensitivity and specificity. The platform is based on a combination of different technologies such as self-assembled monolayers, bionanotechnology, cyclic enzymatic amplification and microfluidics. Optical nanobiosensor: the nanobiosensor is a unique fiberoptic-based tool which allows the minimally invasive analysis of intracellular components such as cytochrome C, an important protein involved in the production of cellular energy as well as in apoptosis, or programmed cell death.

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LOC methods: LOC is a device that integrates several laboratory functions on a single chip. LOCs deal with the handling of extremely small fluid volumes down to less than picoliters [4–8]. Nanomaterials in dentistry: nanocomposites, nanosolution, aesthetic materials, nano-optimized moldable ceramics, impression materials, nanoencapsulation, other products manufactured by SWRI, materials to induce bone growth, nanoneedles, self-assembly, nanomaterials for periodontal drug delivery, photodynamic therapy, implants. Nanocomposites: in nanocomposites, the resins or coatings are homogeneously reinforced with nonagglomerate discrete NPs. Nanosolution: nanosolutions produce unique and dispersible NPs, which can be added to various solvents, paints and polymers in which they are dispersed homogenously. Esthetic materials: a nano-based liquid polish is applied to give higher glossiness for resin composite restoration. Nano-optimized moldable ceramics: nanofillers, nanopigments and nanomodifiers. Impression materials: better flow, improved hydrophilic properties and enhanced detail precision. Nanoencapsulation: future specialized NPs could be engineered to target oral tissues, including cells derived from the periodontium. Other products manufactured by SWRI: protective clothing and filtration masks, using antipathogenic nanoemulsions and NPs. Medical appendages used for instantaneous healing: calcium phosphate-based biomaterial is an easily flowable, moldable paste that conforms to and interdigitates with the host bone supporting growth of cartilage and bone cells. It is possible to promote the growth of cartilage and bone cells using bioactive calcium phosphate material in the form of a paste which can be molded to conform to the host bone. Materials to induce bone growth: dentistry uses nanotechnology to imitate the natural nanostructures of bones based on the principle that reduction in particle size increases the surface area in volume. The loose microstructure of nanocrystallites with nanopores lying between the crystallites is imitated, meaning that the structure of the material is completed with micrometer-sized pores. Nanoneedles: stainless steel nanocrystals are integrated in suture needles. Self-assembly: a nanostructured fibrous scaffold can be constructed by pH-induced self-assembly of peptide amphiphile. The structural properties of the scaffold resemble those of the extracellular matrix. Nanomaterials for periodontal drug delivery: biodegradable polymer nanospheres can be used for timed release of drugs. The nanospheres degrade allowing for the drug to be delivered to a targeted specific site. Photodynamic therapy: a photosynthetizer and light of a specific wavelength are used for the removal of disease-carrying pathogens. The method is known as

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antimicrobial photodynamic therapy. The light commonly used for this purpose is toluidine blue with a wavelength of 600 nm [4, 9, 10]. Implants: To restore partial (enamel and dentin) or complete tooth loss, dental composite or implants are normally used. The retention of resin composite or dental implants is obtained mainly through micromechanical retention. The interface between resin composites and dental tissues or between dental implants and bone is therefore important for the success of these restorations. Looking at the structure of enamel, dentin and bone, they are composed of organic matrix, mainly collagen and noncollagenous proteins and hydroxyapatite (HA). The ratio of the organic to mineral phase varies according to the tissue. This section reviews the importance of resin composite–tooth as well as implant–bone interface and how nanotechnology has been employed to modify these interfaces to increase the longevity of resin composites and dental implants, respectively [11, 12]. There have been three types of nanostructured implant coatings developed recently: – Nanostructured diamond: these coatings are characterized by extreme hardness and toughness compared to conventional microcrystalline diamond. Another advantageous feature of this material is low friction and ability to adhere well to titanium alloys. – Nanostructured processing was applied to HA coatings. These coatings enable a gradual change from metallic to covalent bonding, which enhances adhesion to the substrate increasing the strength and toughness of the whole material. – Nanomaterials are well known to promote osteoblast adhesion and CA/phosphate mineral deposition. It has been suggested by a number of studies that nanophase ZnO and TiO2 are effective in reducing Staphylococcus epidermidis while increasing the osteoblast functions, which are the key advantages in the improvement of implants used in this field.

13.3 Conclusion Nanotechnology is a relatively novel field, which involves manipulation of matter at the molecular level, including individual molecules and the interactions among them. It focuses on achieving positional control with a high degree of specificity, thereby achieving the desired physical and chemical properties. When medicine, dentistry and healthcare are concerned, the advances made in nanotechnology and nanomaterials achieved recently prove to have much greater impact than any other developments. Although considerable progress has been made already, much work remains to develop biomaterials and biomolecular approaches that will provide effective repair and regeneration of the tooth tissue affected by caries. While there is a need

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for novel materials, it is equally important to facilitate the process of clinical translation, provided robust fabrication, scale-up methods and appropriate testing data are available.

References [1]

Bayne SC. Dental biomaterials: Where are we and where are we going? J Dent Educ 2005, 571–86. [2] Pelemiš S, Mirjanić D, Đeorđić D, Petrović O, Some of benefits nanomaterials applications in medicine Contemporary Materials, X−1 (2019); 28–34 [3] Ozak ST, Ozkan P. Nanotechnology and dentistry. Nanodentistry 2013, 7, 145–52. [4] Sree L. Balasubramanian, Deepa, nanotechnology in dentistry – a review. Int J Dent Sci Res 2013, 1(2), 40–44. [5] Deb S, (ed). Biomaterials for oral and craniomaxillofacial applications. Front Oral Biol Basel, Karger, 2015, 17, 1–12. DOI: 10.1159/000381686. [6] Freitas RA Jr. Nanodentistry. J Am Dent Assoc 2000, 131(11), 1559–66. [7] Elangovan S, Tsai PC, Jain S, Kwak SY, Margolis H, Amiji M. Calcium Phosphate based nano vectors for gene delivery in fibroblasts. J Periodontol Res 2013, 84(1), 117–25. [8] Song JM, Kasili PM, Griffin GD, Vo-Dinh T. Detection of cytochrome C in a single cell using an optical nanobiosensor. Anal Chem 2004, 76(9), 2591–94. [9] Saravana Kumar R, Vijayalakshmi R. Nanotechnology in Dentistry. Ind J Dent Res 2006, 17(2), 62–65. [10] Kanaparthy R, Kanaparthy A. The changing face of dentistry: nanotechnology. Int J Nanomedicine 2011, 6, 2799–804. [11] Colon G, Ward BC, Webster TJ. Increased osteoblast and decreased Staphylococcus epidermidis functions on nanophaseZnO and TiO2. J Biomedical Mater Res 2006, 78(3), 595–604. [12] Meyer U, Bühner M. Fast element mapping of titanium wear around implants of different surface structures. Clin Oral Implant Res 2006, 17(2), 206–11. [13] Ensanya AAN, Laurent B, Perez RA, Kim H-W, Knowles JC. Nanotechnology in dentistry: prevention, diagnosis, and therapy. Int J Nanomedicine 2015, 10, 6371–94.

Aleksandar Radunovic, Zoran Popovic, Ognjen Radunovic, Maja Vulovic

14 Complications of utilizing ceramic components in orthopedic surgery Abstract: There are a variety of biomaterials used in orthopedic surgery nowadays, with its own advantages and imperfections. Ceramics has its own place in manufacturing of endoprosthesis components due to its properties: low friction coefficient, scratch resistance, excellent biocompatibility. Principal disadvantage of ceramics is brittleness and inability for plastic deformation. These features are mitigated to a certain extent but remain the leading cause of ceramic components failure. Keywords: biomaterials, orthopedic surgery, complications, ceramic

14.1 Introduction During development of orthopedic implants, there was always a search for new materials that are capable to fulfill all demands for good long-term results such as biocompatibility, excellent mechanical properties (high compression, bending and torsional strength, fracture toughness, wear resistance at sliding surfaces, fatigue resistance under cyclic loading), properties that enable serial manufacturing and economical aspect. Biocompatibility is defined as the ability of a material to perform with an appropriate host response in a specific application. Implant materials must be nontoxic, nonirritant, nonallergenic and noncarcinogenic. For decades, metal and its alloys combined with polyethylene (PE) were almost exclusively used in big joint arthroplasties. Area of big joint arthroplasties suffered many problems while developing modern artificial joints. First, problems were not only about materials, but also about proper design of endoprosthesis. When long-term studies showed that biomechanical basis of few endoprosthesis designs are good one (Charnley low friction concept of hip endoprosthesis [1], anatomical and functional approach for total condylar knee endoprosthesis [2, 3]), scientists mostly focused on developing new materials.

Aleksandar Radunovic, Clinic for Orthopedic Surgery and Traumatology, Military Medical Academy, Belgrade, Serbia, [email protected] Zoran Popovic, Vozd Clinic, Belgrade, Serbia Ognjen Radunovic, Faculty of Medicine, University of Belgrade, Belgrade, Serbia Maja Vulovic, Department of Anatomy, Faculty of Medical Sciences, University of Kragujevac, Kragujevac, Serbia https://doi.org/10.1515/9783110627992-014

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Key problem with metal on polyethylene (MOP) articulation was aseptic loosening. For years it was considered as cement disease, because there was an established opinion that bone cement that was used for component fixation is the one that causes problem. After many investigations, it has been found that PE wear is the one that produces particular debris that activates inflammatory cascade (cellular response that ultimately leads to macrophagic and osteoclastic activation) and periprosthetic bone resorption resulting in implant failure. After identifying PE as a major problem there were many improvements in PE structure, manufacturing and sterilization, which dramatically decreased its wear rate and particle emission, but still PE is considered as the weakest part of the big joint endoprosthesis. This problem is of particular importance in hip and knee arthroplasties that are by far most frequently performed and those two joints have to withstand highest forces during everyday usage. There are a growing number of reports that deal with allergies on metal as a potential cause for implant failure. Metal and polymethyl methacrylate (bone cement) are considered to be source of particles that can induce delayed hypersensitivity reaction. This happens more frequently with metals, especially nickel, cobalt and chromium, but there are some reports of polymethyl methacrylate as immunogen [4, 5]. Problems with MOP concept produced new interest for ceramics. First generations of ceramics did not show good long-term results due to bad mechanical properties. There were many improvements in ceramic composition, manufacturing, final processing and implant designing. Nowadays, ceramic has many favorable characteristics (biocompatibility, hardness, high degree of wettability, low friction coefficient, scratch resistance, low biological activity of debris particles, small particle size and low allergic potential) but there are some problems while utilizing it in endoprosthesis. Ceramic brittleness, inability to withstand plastic deformation, low resistance to intense axial and traction forces are the major problems.

14.2 Fracture of ceramics articular surfaces Fracture of ceramic component that has been used as articular surface is associated with massive metallosis and consequently the reaction of local tissue and possibly systemic body reaction to metallic ions (titanium, cobalt, chrome and nickel alloys). First generation of ceramics showed unacceptable percentage of fractures. After improvements, in second generation of ceramics reported fracture rate was decreased to 0.014% and in third generation still reduced to 0.004% [6, 7]. Latest generation of ceramics (Biolox delta) underwent short-term investigations with no recorded fracture [8]. In those investigations, risk factors for fracture occurrence

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have been identified: excessive weight, dislocation, prosthetic impingement, altered joint biomechanic and advanced age. Biomechanic studies showed that improper positioning of endoprosthesis components gave rise to higher values of tensile stress if/when subluxation or impingement occurred [8].

Figure 14.1: Fractured ceramic femoral head in PE liner.

Figure 14.2: Fractured ceramic femoral head, damaged metal femoral stem and PE liner.

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Figure 14.3: Massive consequential tissue metallosis.

Another noticed problem with ceramic implants is that they can suffer breakage during insertion. It is not allowed for ceramic implants to be manipulated with metal handles (direct metal on ceramic contact). It is also not allowed to use hammer during insertion. While preparing femoral component of total condylar knee endoprosthesis, it is essential to have very precise tools for bony resection; otherwise, femoral component can undergo high wedge loading during implantation and possibly break. There were reports of such accidents [9].

Figure 14.4: No hammering during implantation.

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14.3 Stripe wear Stripe wear presents as elongated area of changed surface that can be observed in some alumina ceramic on ceramic bearing couples. This phenomenon was reported in first two generation of ceramics and less frequently in third generation [10, 11]. There were few biomechanical investigation about potential cause and few assumptions but all authors agreed that wear rate is very small, if particles are of small size and conclusion is that it is not related to osteolysis and bearing failure [12].

14.4 Squeaking Noises that arise from ceramic bearings are next concern with this material. Those are usually squeaking noises but there were few reports of clicking sounds. Reported rates vary from 0% to 33% [13, 14]. This sound very often annoys and worries patients. There are few theories about the origin of this noises but exact mechanism is not clear yet, although it is assumed its multifactoriarely caused. Some authors found the association of higher incidence of squeaking sounds in taller and heavier patients [15, 16]. Other authors noticed squeaking more frequently in certain endoprothesis designs, particularly one that enables neck impingement on metallic rim of the cup [17]. Another explanation offered for this phenomenon are localized stripe wear, changes of lubrication conditions and microseparation of femoral head [18, 19]. It has not been found that squeaking occurrence affects the long-term results of implant.

14.5 Conclusion Tribology properties of ceramics such as low friction, high wear resistance and excellent biocompatibility make them a very attractive option in joint replacement. Due to imperfections, at this moment in knee replacement surgery, they are used as a choice for patients with known allergies on metal. Specific concerns about ceramics, precisely fracture possibility, stripe wear and squeaking sounds are topics for discussion and area for future improvements.

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References [1] [2] [3] [4]

[5]

[6] [7] [8]

[9] [10]

[11]

[12] [13] [14] [15] [16]

[17] [18] [19]

Charnley J. Arthroplasty of the hip: A new operation. Lancet 1961, 1, 1129–32. Sledge CB, Ewald FC. Total knee arthroplasty experience at the Robert Breck Brigham Hospital. Clin Orthop Relat Res 1979, 145, 78–84. Insall J, Ranawat CS, Scott WN, Walker P. Total condylar knee replacement: Preliminary report. Clin Orthop Relat Res 1976, 120, 149–54. Niki Y, Matsumoto H, Otani T, Yatabe T, Kondo M, Yoshimine F, et al. Screening for symptomatic metal sensitivity: A prospective study of 92 patients undergoing total knee arthroplasty. Biomaterials 2005, 26, 1019e26. Haddad FS, Cobb AG, Bentley G, Levell NJ, Dowd PM. Hypersensitivity in aseptic loosening of total hip replacements. The role of constituents of bone cement. J Bone Joint Surg Br 1996, 78, 546e9. Inzerillo CV, Garino JP. Alternative bearing surfaces in total hip arthroplasty. J Southern Orthop Assoc 2003, 12, 106–11. Mehmood S, Riyaz JH, Pandit H. Review of ceramic-on- ceramic total hip arthroplasty. J Surg Ortho Adv 2008, 17, 45–50. Hamilton WG, McAuley JP, Dennis DA, Murphy JA, Blumenfeld TJ, Politi J. THA with Delta ceramic on ceramic: Results of a multicenter investigational device exemption trial. Clin Orthop Relat Res 2010, 468(2), 358–66. Bergschmidt P, et al. Ceramic Femoral Components in Total Knee Arthroplasty – Two Year FollowUp Results of an International Prospective Multi-Centre Study. Open Orthop J 2012, 6, 172. Nevelos JE, Prudhommeaux F, Hamadouche M, et al. Comparative analysis of two different types of alumina-alumina hip prosthesis retrieved for aseptic loosening. J Bone Joint Surg Br 2001, 83, 598. Nevelos J, Ingham E, Doyle C, et al. Microseparation of the centers of alumina-alumina artificial hip joints during simulator testing produces clinically relevant wear rates and patterns. J Arthroplasty 2000, 15, 793. Walter WL, Insley GM, Walter WK, et al. Edge Loading in Third Generation Alumina Ceramic-on -Ceramic Bearings. J Arthroplasty 2004, 19, 402–13. Restrepo C, Parvizi J, Kurtz SM, et al. The noisy ceramic hip: Is component malpositioning the cause? J Arthroplasty 2008, 23, 643–49. Keurentjes JC, Kuipers RM, Wever DJ, et al. High incidence of squeaking in THAs with alumina ceramic-on-ceramic bearings. Clin Orthop Relat Res 2008, 466, 1438–43. Walter WL, Waters TS, Gillies M, Donohoo S, Kurtz SM, Ranawat AS, Hozack WJ, Tuke MA. Squeaking hips. J Bone Joint Surg Am 2008, 90(Suppl 4), 102–11. Sexton SA, Yeung E, Jackson MP, Rajaratnam S, Martell JM, Walter WL, Zicat BA, Walter WK. The role of patient factors and implant position in squeaking of ceramic-on-ceramic total hip replacements. J Bone Joint Surg Br 2011, 93(4), 439–42. Parvizi J, Adeli B, Wong JC, Restrepo C, Rothman RH. A squeaky reputation: The problem may be design-dependent. Clin Orthop Relat Res 2011, 469(6), 1598–60. Taylor S, Manley MT, Sutton K. The role of stripe wear in causing acoustic emissions from alumina ceramic-on-ceramic bearings. J Arthroplasty 2007, 22(7 Suppl 3), 47–51. Glaser D, Komistek RD, Cates HE, Mahfouz MR. Clicking and squeaking: In vivo correlation of sound and separation for different bearing surfaces. J Bone Joint Surg Am 2008, 90(Suppl 4), 112–20.

Zorica Ž. Lazarević, Martina Gilić, Aleksandra Milutinović, Nebojša Romčević, Hana Ibrahim Elswie, Vesna Radojević, Dalibor L. Sekulić

15 Growth and characterization of calcium fluoride single crystals Abstract: The calcium fluoride (CaF2) single crystals were grown using the Bridgman technique. By optimizing growth conditions, -oriented CaF2, crystals up to 20 mm in diameter were grown. Number of dislocations in CaF2 crystals was 5 × 104–2 × 105 per cm2. Selected CaF2 single crystals is cut into several tile diamond saw. The plates were polished, first with the silicon carbide, then with the paraffin oil and finally with a diamond paste. The obtained crystals were studied by X-ray diffraction, Raman spectroscopy, far-IR reflectivity and by the measurement of transmission in the mid-IR range. The crystal structure is confirmed by XRD. One Raman and two IR optical modes predicted by group theory are observed. In the transmission spectra, except modes originated from vibration of -CH2 groups, hydroxyl groups -OH and KBr, is visible a peak at 671 cm−1 assigned to the Ca-F stretching vibrations. A low photoluminescence testifies that the concentration of oxygen defects within the host of CaF2 is small. The electrical and dielectric properties of CaF2 single crystal were studied. Keywords: goptical materials, CaF2, Raman spectroscopy, IR spectroscopy, photoluminescence

15.1 Introduction Crystals are the unacknowledged pillars of modern technology. Without crystals, there would be no electronic industry, no photonic industry, no fiber optic communications, which depend on materials/crystals such as semiconductors, superconductors, Acknowledgments: This research was financially supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia through Projects No. III45003 and TR34011. The results presented in this chapter are mainly from the doctoral thesis of Hana Ibrahim Elsvie which was under the supervision of Prof. Vesna Radojević and Zorica Lazarević. Zorica Ž. Lazarević, Martina Gilić, Aleksandra Milutinović, Nebojša Romčević, Institute of Physics, University of Belgrade, Belgrade, Serbia, [email protected] Hana Ibrahim Elswie, Vesna Radojević, Faculty of Technology and Metallurgy, University of Belgrade, Belgrade, Serbia, [email protected] Dalibor L. Sekulić, Faculty of Technical Sciences, University of Novi Sad, Novi Sad, Serbia, [email protected] https://doi.org/10.1515/9783110627992-015

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polarizers, transducers, radiation detectors, ultrasonic amplifiers, ferrites, magnetic garnets, solid state lasers, non-linear optics, piezo-electric, electro-optic, acousto-optic, photosensitive, refractory of different grades, crystalline films for microelectronics and computer industries [1]. Crystal growth is an interdisciplinary subject covering physics, chemistry, material science, chemical engineering, metallurgy, crystallography, mineralogy and others. In the past few decades, there has been a growing interest on crystal growth processes, particularly in view of the increasing demand of materials for technological applications. The materials can be grown in single crystal form from the melt provided they melt congruently without decomposition at the melting point and do not undergo any phase transformation between the melting point and room temperature. Depending on the thermal characteristics, the following techniques are employed: Bridgman, Czochralski, Kyropoulos, zone melting and Verneuil techniques. Schematics of the two Bridgman configurations and other crystal growth techniques are shown in Figures 15.1–15.6 [1, 2]. Czochralski method for obtain different optical materials and solid state lasers has been reviewed by several authors [3–7]. For most compound semiconductor materials, melt growth methods are the main methods of industrial manufacture as they provide a rapid growth of large single crystals.

Figure 15.1: Schematic diagram of a vertical Bridgman (VB) crystal growth process in a single-zone furnace: (a) at the beginning of the experiment and (b) with partially grown crystal.

Fluorides have attracted considerable research interest because they exhibit many unique properties that may increase their applications in optics and electronics. Among them, alkaline-earth fluorides are dielectric and have a wide transmission range, and therefore they are widely used in optical components, microelectronic and optoelectronic devices [8–10]. CaF2 is a kind of typical alkaline-earth fluorides.

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Figure 15.2: Schematic diagram of a horizontal Bridgman (HB) crystal growth process in a singlezone furnace: (a) at the beginning of the experiment and (b) with partially grown crystal.

It has a well-known fluorite structure, in which Ca2+ ions lie at the nodes in a facecentered lattice, while F− ions lie at the centers of the octants [11]. Furthermore, with an optically isotropic fluorite structure, the CaF2 crystal is suitable as a phosphor host because it exhibits outstanding transmission characteristics for a wide range of wavelength (0.3–8 mm) [12]. When CaF2 is doped with rare-earth (RE), some interesting luminescence properties can be expected. As a result, general attention has been drawn on this field recently. CaF2 doped with RE could be used as laser [13, 14] and fluorescent labeling material in biological applications [15–17]. Also, CaF2 crystals exhibit some excellent properties such as high transmittance in the far UV to mid IR range, low refractive index, high chemical resistance and high laser damage threshold. Such properties make this crystal very important

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Figure 15.3: Schematic of Czochralski growth equipment.

Figure 15.4: Schematic of Kyropoulos growth equipment. (a) The seed crystal contacts the melt, a small amount melts and then cooling is commenced to produce (b) and (c).

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Figure 15.5: Schematic of float-zone growth equipment.

for use in the manufacture of special lenses, and especially for use in the photolithography [18, 19]. Generally CaF2 single crystals are grown by the Bridgman method and the applications require large diameter CaF2 single crystals [20, 21]. But growing large-size single crystals has been very tough because of the grain boundaries during the growth and the cracks during the cooling process [22]. Recently ceramic laser technology is found to exhibit more advantages over the single crystal growth processes and in particular, the ceramics can be produced in large volumes and with the homogeneous doping of laser active ions in the host materials [23]. Polycrystalline CaF2 has been synthesized for the first time with dysprosium as an active ion [24]. Recently, thermal conductivity of the natural calcium fluoride ceramics has been investigated and compared with single crystals of CaF2 and are found to exhibit better mechanical properties over single crystals [25]. Also, it was confirmed that the grain boundaries are transparent to phonons as well as to photons in synthetic optical ceramics of CaF2. Calcium fluoride, fluorite, is a well-known face-centered cubic mineral [26]. The fluorite structure is shared with a wide variety of other compounds, for which CaF2 is considered the type compound. The structure of fluorite has eight fluorine

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Figure 15.6: Schematic of Verneuil growth equipment.

atoms arranged in a cube around the calcium atom, with the cubes of fluorine edge-connected in a face-centered cubic array. Conversely, the fluorine atom is surrounded by four calcium atoms arranged in an ideal tetrahedron, with the tetrahedra also edge-connected. Fluorite has a very simple structure (Figure 15.7). Calcium (green) atoms in a face-centered pattern contain a cube of fluorine atoms (purple). Darker shades are used to portray calcium atoms toward the rear of the unit cell. We can also view the structure as a simple cubic array of fluorine atoms with a calcium atom in the center of alternate cubes. Considered that way, there are obviously diagonal planes of cubes containing no cations. These planes will evidently be planes of weakness, accounting for fluorite’s excellent octahedral cleavage. Since each fluoride ion has four nearest-neighbor calcium ions, the coordination in this structure is described as (8:4). Although the radii of the two ions (F− = 117 pm, Ca2+ = 126 pm) do not allow true close packing, they are similar enough that one could

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Figure 15.7: Unit cell representation of CaF2 structure.

just as well describe the structure as a FCC lattice of fluoride ions with calcium ions in the octahedral holes [27]. The lattice dynamics of calcium fluoride crystal have been the subject of numerous investigations in the past. The phonon dispersion curves of calcium fluoride were observed by inelastic neutron scattering [28] and optical investigations. Raman scattering measurements [29, 30] and IR reflectivity measurements [31–33] have indicated pronounced phonon anharmonicity and defect induced scattering what must be included in oscillator model in order to estimate the lattice dynamical quantities properly. It may be noted that the Bridgman method is one of the most popular methods of crystal growth because it is very easy to perform in a vacuum and in an inert atmosphere [34, 35]. The entire melted batch of CaF2 in the crucible (which is of cylindrical shape with a conical bottom) is slowly lowered into the colder part of the furnace, so that the crystallization process begins at the bottom of the crucible at the top of the cone. Reviewing the literature it can be noted that the crucible can be made from spectroscopically pure graphite [22, 36–39] or platinum [40]. The aim of our work was to produce CaF2 single crystal. The structural and optical properties obtained crystals were characterized using XRD, Raman and IR spectroscopy and measurement of transmission. The photoluminescence (PL) emission spectrum of CaF2 has a broad band in the range of 320 nm to 475 nm. We have carried out a detailed study about electrical and dielectric properties of CaF2 single crystal over a relatively wide range of frequencies as a function of temperature.

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15.2 Experimental The BCG365 device was used to obtain single crystals of CaF2 by the Bridgman method [41, 42]. Initial samples of single crystals were mostly transparent, but some were cracked. Therefore, we had to make some changes in conditions of growth and construction of crucible. Experiments have been performed with CaF2 in the form of a powder. The CaF2 powder was compacted and sintered in the form of tablets. Crucible could easily be filled with such obtained tablets. Powder CaF2 (Rare Earth Products Limited) purity of 99.99% was used in the experiment. It was compacted under a pressure of 3,500 kg cm−2, and the sintering of the obtained tablets was carried out at 900 °C under an inert atmosphere of argon. We tried out combinations of various growth rates and generator powers with the aim to define the optimal growth conditions. Power generator was initially Pgen = 3.8 kW, and was later increased to Pgen = 3.94 kW. We tested different crystal growth rates. Crucible with the charge placed on the holder in the upper chamber furnace. Then the apparatus is sealed, and then put into operation a vacuum apparatus and cooling water. After establishing a vacuum, the generator gradually increases the heating power all the mass has melted. The maximum used power was 3.94 kW. Since the charge melted, the crucible slowly descends to the lower (cold) chamber of the furnace. At the top of the cone, which arrives first in a colder area, a germ of future crystallization is formed. Continued further lowering the crucible, and the power supply generators have been gradually decreasing. When lowered muffle up to 30 mm in length, the descent rate was R = 6.8 mm h−1. In a further descent we increased the speed at R = 12.7 mm h−1. In subsequent experiments, we used only the rate of descent crucible of R = 6.8 mm h−1 over the entire length of the chamber. During the growth of single crystals, a modified holder was used. His cooling fins at the upper end are slightly higher, while conventional brackets have all cooling fins of the same size. In Figure 15.8 shows a schematic representation of the apparatus, and Figure 15.9 gives the look and dimensions of the crucible that was used during the experiment. The observations relating to the dislocation were recorded by observing an etched surface of CaF2 crystal, using a Metaval of Carl Zeiss Java metallographic microscope with magnification of 270x. A selected CaF2 single crystal was cut into several tiles with the diamond saw. The plates were polished, first with the silicon carbide, then with the paraffin oil, and finally with a diamond paste. The obtained finely polished samples were used for the characterization by Raman, IR and luminescence spectroscopy. The crystal plane of cleavage of calcium fluoride crystal is . Thin panels for testing dislocations were obtained by splitting of individual pieces of crystal. Conc. H2SO4 was used as an etching solution. The samples were etched for 15 min. The crystal structure of CaF2 single crystal was approved using the X-ray diffractometer (XRD, Model Philips PW 1050 diffractometer) equipped with a PW 1730 generator, 40 kV × 20 mA, and using CuKα radiation of 1.540598 Å at the room temperature.

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Figure 15.8: A schematic view of an apparatus for Bridgman-grown CaF2 single crystals: 1) quartz tube; 2) ceramics; 3) line for cooling; 4) graphite crucible; 5) spiral for heating; 6) graphite crucible carrier and 7) spindle.

Figure 15.9: Schematic view – layout and dimensions of the crucibles used in the experiment for Bridgman-grown CaF2 single crystals.

Measurements were done in 2θ range of 10–90° with scanning step width of 0.05° and 10 s scanning time per step. The Raman scattering measurements of CaF2 crystal were performed in the backscattering geometry at room temperature in the air using a Jobin-Yvon T64000 triple spectrometer, equipped with a confocal microscope (100x) and a nitrogen-cooled charge coupled device detector (CCD). The spectra had been excited by a 514.5 nm line of Coherent Innova 99 Ar+ – ion laser with an output power of less than 20 mW to avoid local heating due to laser irradiation. Spectra were recorded in the range from 100 to 800 cm−1.

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The room temperature far-infrared reflectivity measurement was carried out with a BOMEM DA-8 FIR spectrometer. A DTGS pyroelectric detector was used to cover the wave number range from 50 to 600 cm−1. The transmission spectra of CaF2 samples (powdered and pressed in the discs with KBr) were obtained by transmission Fourier-transform infrared (FTIR) Hartmann&Braun spectrometer, MB-series. The FTIR spectra were recorded between 4,000 and 400 cm−1 with a resolution of 4 cm−1. Photoluminescence (PL) studies reported in this work were performed at room temperature using Optical Parametric Oscillator (Vibrant OPO) tuned at 350 nm as excitation source. The experimental setup used in this study consists of excitation and detection part (Figure 15.10). Pulsed excitation was provided by a tunable Nd: YAG laser system with pulse duration of about 5 ns and repetition rate of 10 Hz. Time resolved streak images of the emission spectrum excited by OPO system were collected by using a spectrograph (SpectraPro 2300i) and recorded with a Hamamatsu streak camera (model C4334). All streak camera operations were controlled by the HPD-TA (High Performance Digital Temporal Analyzer) software. The fundamental advantage of the streak camera is its two-dimensional nature, enabling the acquiring of the temporal evolution of laser-induced phenomena. The camera is equipped with image intensifier so single photons can be detected and counted, enabling the detection of even very small photoluminescence response of excited sample. The excitation and detection optical axes were aligned using the beam splitter, so it was possible to tune the angle of excitation beam regarding the surface of sample and to maintain the high sensitivity of detection. In order to study the electrical and dielectric properties of synthesized CaF2 single crystal, the plan-parallel plate with dimensions of 11 × 11 × 2 mm3 was coated with high-purity silver paste on adjacent faces as electrodes. AC (alternating current) parameters were measured using an impedance analyzer (Hewlett–Packard 4194A) at various temperatures between 25 °C and 175 °C in the frequency range 100 Hz to 1 MHz. For more details see Ref [43].

15.3 Results and discussion CaF2 single crystals are obtained by the vertical Bridgman method in vacuum. The best results were obtained with a crystal growth rate of 6.8 mm h−1. The obtained single crystal of CaF2 was 90 mm in length and 20 mm in diameter (Figure 15.11). Because of the low temperature gradient came to a sudden crystallization process with appearance of dendrites in the bottom of the crucible. This was the reason why change was made in the construction of crucible. The cone on the bottom of the crucible was extended into a narrow tube. This form avoid the appearance of dendrites. The crystals which were obtained from the thus-constructed crucible were of better quality.

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Figure 15.10: Experimental setup for photoluminescence measurements.

However, when grinding the upper surface of the crystal, due to impurities that have clung there, there have been cracks in crystals per plane cleavage . The general conclusion is that in all samples relatively high dislocation density (ranging from 60,000 to 140,000) was observed as a consequence of greater internal stresses, which have emerged in the process of cooling. From Figure 15.12 dislocations on CaF2 single crystal can be observed. Etch pits have the shape of a threesided pyramid. Number of dislocations in CaF2 crystals which were made by the Bridgman method was 5 × 104–2 × 105 per cm2 (Figure 15.6). After heating to 400 °C and gradual cooling, crystal etching was done with conc. H2SO4 and observation under a microscope. In places where there were the output of dislocations were not observed any major changes. The same was the case even after heating at a temperature of 600 °C. By observation under a microscope schedule dislocations remained unchanged. However, heating the crystals at 860 °C,

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Figure 15.11: Photographs of Bridgman-grown CaF2 single crystal.

Figure 15.12: The microscopic image of the surface CaF2 crystal plate in the direction < 111 > . Magnification of 270x.

after a gradual cooling, etching with conc. H2SO4 and observation under a microscope showed a different schedule point of exit of dislocations in the crystal surface. There was a movement of dislocations. It was seen that internal stress partially disappeared as a result of dislocation, with their stress fields partially reversed. In so doing, the concentration of the dislocations is not changed practically. After heating, it was noticed that the crystal on the surface was milky white. This layer was very thin,

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so it is assumed that there was a diffusion of oxygen and partial oxidation of CaF2, ie. formation of CaO. In order to eliminate stresses in the crystal, we made a crystal annealing. The process of annealing was carried out on the plate and bulk crystal CaF2. The temperature of annealing of the plate was at 1,000 °C for 3 h, and the temperature of annealing of the bulk crystal was at 1,000 °C and 1,080 °C for 1–3 h. Annealing was carried out under an inert atmosphere of argon. It was noticed that after annealing, plate CaF2 did not have enough stress. Annealing bulk single crystal CaF2 had less stress than non-annealing. During the annealing process there is a movement of dislocations. The leads to the formation of sub-boundaries, and, as a result, the internal stress in the crystal partially disappears. During the movement of dislocations their stress fields are partially reversed, but the dislocation density is practically not changed. XRD pattern (Figure 15.13) was indexed by using JCPDS database (card no. 870971). The sample of CaF2 single crystal was of cubic structure with the Fm3m space group [44]. The XRD pattern was found to match exactly with those reported in the literature [45–47]. The displayed peaks correspond to (h k l) values of (1 1 1), (2 2 0), (3 1 1), (4 0 0), (3 3 1) and (4 2 2). Using the (h k l) values of different peaks, the lattice constant (a) of the sample was calculated. Their lattice parameter was calculated from the equation of plane spacing for cubic crystal system and Bragg’s law for diffraction [48]. The lattice parameter was 5.460 ± 0.011 Å, calculated from the obtained XRD diagram, which was in good agreement with the literature [49]. The primitive cell of a fluorite structure contains three atoms that give nine fundamental vibrations in the center of Brilouin zone 6T1u(IR) + 3T2g(R). The first three of T1u are acoustic modes. At the Γ point, there are three distinct optic phonon modes: a doubly degenerate infrared-active TO T1u, an infrared-active nondegenerate LO T1u and a triply degenerate Raman-active mode T2g between them [50, 51]. The room-temperature first order T2g one-band spontaneous Raman scattering spectra of CaF2 crystal is shown in Figure 15.14. T2g mode originates from the stretching vibrations of F atoms around Ca. In this single triply degenerate Raman mode with frequency ω = 319.7 cm−1 Ca2+ cation remains stationary and the neighboring fluoride F−1 ions vibrate against each other [52–60]. The far-infrared reflectivity spectrum of the CaF2 substrate is shown in Figure 15.15a. The experimental data are presented with circles. The solid line in Figure 15.15a was obtained using the dielectric function in the factorized form given by eq. (15.1) [61, 62]: εðωÞ = ε∞

n ω2 − ω2 + iωγ Y jLo jLO j=1

ω2jTO − ω2 + iωγjTO

(15:1)

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calcium-fluoride CaF2

Intensity [arb. units]

(111)

(220)

(311) (400) (331) 20

40

60 2θ [°]

(422)

80

100

Figure 15.13: X-ray diffraction pattern of the CaF2 powdered sample.

T2g-vibration mode (T2g = 319.7)

Intensity [arb. units]

calcium-fluoride CaF2

100

200

300

400

500

600

700

Raman shift [cm-1] Figure 15.14: Raman spectrum of CaF2 single crystals, recorded at room temperature.

800

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ε∞ = 1.5

1,0 a) 0,8 Reflectivity [arb.units

193

0,6

ωTO

γTO

ωLO

γLO

272 323 414 129 197

31 67 66 65 73

319 399 475 139 203

46 67 52 65 53

0,4

0,2

0,0 100

200

300

400

500

600

b)

ε2, σ [arb.units]

ωTO = 272 cm-1

ωLO = 475 cm-1

0,4

ε2

0,2

σ

0,0 100

200

300 Wave number

400

500

600

[cm-1]

Figure 15.15: IR spectrum of CaF2 single crystals, recorded at room temperature.

The number of modes is n, ωjLO and ωjTO are the longitudinal and transverse optical frequencies, γjLO and γjTO denote longitudinal and transverse damping constants, respectively, and ε∞ is the dielectric constant (permittivity) at high frequency. As a result of the best fit we obtained the ωTO = 272 cm−1 and ωLO = 475 cm−1, somewhat higher than in Ref [63]. (TO/LO = 257/463). In pure CaF2, only two infrared active modes are allowed by the crystal symmetry (splitted TO-LO mode), but we see that the main reflectivity band of CaF2 exhibits a feature centered about 360 cm−1 as a result of a two-phonon combination. This feature has been observed in all stoichiometric fluorite-structured crystals [64]. There are two additional weak modes with relatively high dampings in the range of low energies. We suppose that mode about 130 cm−1 could be caused by impurities and about 200 cm−1 is a TO-mode from the X point . Kramers-Kröning analysis of far-IR reflectance data gives ωTO = 272 cm−1 and ωLO = 475 cm−1, in accordance with fitting procedure (Figure 15.15b).

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FTIR transmission was measured in order to check the purity of the obtained CaF2. As shown in Figure 15.16, the sharp peaks of the absorption at 2,854 cm−1 and 2,936 cm−1 are assigned to the symmetric and antisymmetric stretching vibration of -CH2 groups [65]. Also, the spectrum shows two broad IR absorption peaks at ∼3,432 cm−1 and 1,628 cm−1 are assigned to the symmetrically stretching vibration and antisymmetric stretching vibration of hydroxyl groups -OH, implying the presence of H2O molecules [66]. The peak at 671 cm−1 in the FTIR spectrum was assigned to the Ca-F stretching vibration of CaF2 [67]. The band at ∼2,357 cm−1 is due to KBr pellets used for recording FTIR spectrum [68].

CaF2

2854 2936

1628

Transmittance [%]

90 3432

671

60

4000

3500

3000

1500 Wavenumber [cm-1]

1000

500

Figure 15.16: FTIR spectrum of CaF2.

We have measured the photoluminescence response of the CaF2 crystal sample for various excitation wavelengths and different angles of excitation beam. The streak image of the fluorescence emission spectrum of CaF2 is presented in Figure 15.17a. The photoluminescence response was very small; see Figure 15.17a where a typical optical response of sample is presented. Although the streak images were acquired in photon counting mode using a very large number of expositions (20.000), very small number of photons were counted. The vertical axis in Figure 15.17a corresponds to the fluorescence development in time domain of 200 ns. The beginning of the vertical axis is cut off in order to avoid undesirable part of the spectra (excitation at 320 nm and second harmonic of Nd:YAG laser at 532 nm).

Time [ns]

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20 40 60 80 100 120 140 160 180 300

350

400 450 500 Wavelength [nm]

550

600

350

400 450 500 Wavelength [nm]

550

600

Intensity [a.u.]

40 30 20 10 0 300

Intensity [a.u.]

40 30 20 10 0 20

40

60

80 100 120 140 160 180 Time [ns]

Figure 15.17: (a) Streak image of the fluorescence spectra of CaF2 crystal. (b) Fluorescence spectra of CaF2 crystal as a function of wavelength (integrated profile). (c) Fluorescence spectra of CaF2 crystal as a function of time (integrated profile) and fitted curve.

Enlarged integrated profile of the fluorescence of CaF2 is presented in Figure 15.17b. Our pure sample of CaF2 crystal shows a broad band in 300–500 nm range. As pointed out in [69] this band might be induced due to the formation of color centers. These centers perhaps could be created by oxygen defects within the host of CaF2. However, the occurrence of defects in crystal is very rare compared to the nanostructures described in [69], so the luminescence of our sample is very weak compared to the luminescence of structure described in [69]. To obtain good luminescence response, the samples of CaF2 are doped with Ag, Eu, Tb, Cu or Dy [69, 70]. However, CaF2 crystal is usually used in applications where high optical transmission is needed and photoluminescence is not welcomed characteristics [71].

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Fluorescence line profile (fluorescence decay) from image Figure 15.17a is selected using the integration process in region from 340 nm to 460 nm. That profile is fitted using High Performance Digital Temporal Analyzer (HPD-TA) software, provided by Hamamatsu. Fluorescence decay and fitted curve are shown together in Figure 15.17c. The obtained lifetime is 33 ns (χ2 = 1.07). The properties of the crystal, such as density of dislocations, crystallinity and impurities concentrations, determine the optical quality. The frequency dependence of the AC electrical conductivity, that is, conductivity spectra for studied CaF2 single crystal at various temperatures is shown in Figure 15.18. These plots indicate the existence of two contributions inside our sample. Namely, DC conductivity contribution is predominant at low frequencies and high temperatures, whereas the frequency-dependent term dominates at high frequencies. Moreover, the observed dispersion in the conductivity spectrum is shifted toward the higher frequency side with the increase of temperature. This variation of AC conductivity with frequency at different temperatures obeys the power law given by the empirical formula (eq. (15.2)) proposed by Jonscher [72]: σAC ðωÞ = Aωs

(15:2)

where ω is the angular frequency of AC field. A and s (0 ≤ s ≤ 1) are the characteristic parameters which are temperature dependent. The Jonscher’s coefficient s represents the degree of interaction between mobile ions with the lattices around them, and the prefactor parameter A determines the strength of polarizability [73]. In general, the nature of the temperature dependence of frequency exponent s determines the AC conduction mechanism in the material [43].

Figure 15.18: Frequency dependence of AC conductivity for CaF2 single crystal at different temperatures.

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Changes in the real and imaginary part of complex impedance with frequency at different temperatures for CaF2 single crystal are shown in Figure 15.19. It can be noticed that the magnitude of part of complex impedance (Z') decreases with an increase in both applied frequency and temperature, indicating an increase in AC electrical conductivity of the CaF2 sample with increasing frequency and temperature. In addition, the temperature-dependent Z' shows a plateau on the low frequency side followed by a nearly negative slope on the high-frequency side, indicating a crossover from low-frequency relaxation behavior to high-frequency dispersion phenomenon.

Figure 15.19: The variation of real part (above) and imaginary part (below) of the complex impedance with frequency at measured temperatures for CaF2 single crystal.

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This segment of nearly constant real impedance becomes dominant with increasing temperature, suggesting strengthened relaxation behavior [74]. The imaginary part of complex impedance (Z'') initially increases, reaches a peak and then decreases continuously with increasing frequency at all temperatures. It is evident that the Z'' spectrum of CaF2 is characterized by the appearance of only one peak at a certain frequency that is called relaxation frequency. This suggests that a single relaxation process dominates over the conduction mechanism in synthesized CaF2. As the temperature rises the magnitude of observed peak in Z'' spectrum decreases considerably with the peak shift towards higher-frequency side. Such behavior indicates the presence of temperature-dependent electrical relaxation phenomenon and that the relaxation time decreases with increasing temperature. The representation of complex impedance data for CaF2 single crystal in Nyquist/Cole-Cole plot at different temperatures is illustrated in Figure 15.20. All these plots are characterized by the presence of a single semicircle, which corresponds to the bulk effects and indicates that the material is homogeneous. No residual semicircle at low frequencies attributed to the electrode effects has been noticed. Further, impedance spectra show depressed semicircles with their center below the real axis, which points to the non-Debye type of relaxation [75].

Figure 15.20: Impedance spectra of CaF2 single crystal at selected temperatures. Inset shows the proposed equivalent circuit model for analysis of the impedance data.

In addition, the radius of the semicircles, which corresponds to the resistance of the material, decreases as temperature increases, indicating a thermally activated conduction mechanism in studied CaF2. It is well known that in single crystal materials this kind of impedance response can be interpreted by means of an equivalent electrical circuit model consisting of one parallel RC element [76]. But taking into account the observed non-ideal Debye type behavior of sample, it is usual that the

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constant phase element (CPE) is used instead of ordinary capacitor as shown in the insertof Figure 15.20. The effect of applied electric field frequency on the dielectric constant of CaF2 single crystal at different temperatures is represented in Figure 15.21. It is clear from the analysis of the graph that dielectric constant decreases continuously with increasing frequency, exhibiting a normal dielectric behavior [77].

Figure 15.21: Frequency dependence of dielectric constant for CaF2 single crystal at different temperatures.

A more significant dispersion in a low-frequency region can be explained based on the fact that the dielectric constant, in general, is directly related to the dielectric polarization. It can be observed that the variation of dielectric constant with temperature at low frequencies is much more pronounced than at higher frequencies. This relatively insignificant variation of dielectric constant with temperature at higher frequencies can be ascribed to the atomic and electronic polarizations which are temperature independent.

15.4 Conclusions CaF2 single crystals in diameter of 20 mm are obtained by the vertical Bridgman method in vacuum. The crystal growth rate was 6.0 mm h−1. In order to eliminate stresses, crystals were annealed. The process of annealing was carried out on the plate and bulk crystal CaF2. The temperature of annealing of the plate was at 1,000 °C for 3 h, and the temperature of annealing of the bulk crystal was at 1,000 °C and 1,080 °C for 1–3 h. Number of dislocations is of the order of 5 × 104–2 × 105 per cm2. The Raman

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T2g optical mode at 319.7 cm−1 was observed. Kramers-Kröning analysis of the far-IR reflectance data for fluorite structure, as well as the fitting procedure, gave the same values for IR modes: ωTO = 272 cm−1 and ωLO = 475 cm−1. The FTIR transmission spectra indicate that there are some amounts of -CH2, -OH or water molecules and organic groups adhering to the surfaces. Photoluminescence intensity of the obtained crystal is very low, which is an advantage for applications where high optical transmission is needed. Based on our work and observations during the experiment, it could be concluded that the obtained transparent single crystal CaF2 is of good optical quality, which was the goal of our work. The variation of dielectric constant with temperature at higher frequencies can be ascribed to the atomic and electronic polarizations which are temperature independent.

References [1] [2]

Brice JC. Crystal Growth Processess. New York: John Wiley&Sons, 1986. Dhanaraj G, Byrappa K, Prasad V, Dudley M. Handbook of Crystal Growth. Berlin Haidelberg: Springer-Verlag, 2010. [3] Lazarević ZŽ, Kostić S, Romčević MJ, Trajić J, Hadžić B, Stojanović D, Romčević NŽ. Study of Bi12SiO20 single crystals obtained by Czochralski method. Optoelectr Adv Mat 2011, 5, 150–52. [4] Lazarević ZŽ, Mihailović P, Kostić S, Romčević MJ, Mitrić M, Petričević S, Radunović J, Petrović-Damjanović M, Gilić M, Romčević NŽ. Determination of magneto-optical quality and refractive index of bismuth germanium oxide single crystals grown by Czochralski technique. Opt Mater 2012, 34, 1849–59. [5] Petrović M, Romčević N, Romčević M, Stanišić G, Vasiljević-Radović D, Trajić J, Lazarević Z, Kostić S. Spectroscopy caracterization of MnDe nanoclasters randomly distributed in HgMnTe single crystal. J Cryst Growth 2012, 338, 75–79. [6] Lazarević ZŽ, Kostić S, Radojević V, Romčević M, Hadžić B, Trajić J, Romčević NŽ. Spectroscopy study of Bi12GeO20 single crystals. Optoelectr Adv Mat 2013, 7, 58–61. [7] Kostić S, Lazarević ZŽ, Radojević V, Milutinović A, Romčević M, Romčević NŽ, Valčić A. Study of structural and optical properties of YAG and Nd: YAGsingle crystals. Mater Res Bull 2015, 63, 80–87. [8] Tsai RY, Shiau SC, Lin D, Ho FC, Hua MY. Ion-assisted codeposition of CaF2-rich CaF2-TiO2 composites as infrared-transmitting films. Appl Opt 1999, 38, 5452–57. [9] Wang H, Liu R, Chen K, Shi X, Xu Z. Electrodeposition and characterization of CaF2 and rare earth doped CaF2 films. Thin Solid Films 2011, 519, 6438–42. [10] Fujihara S, Kadota Y, Kimura TJ. Role of organic additives in the sol-gel synthesis of porous CaF2 anti-reflective coatings. Sol-Gel Sci Technol 2002, 24, 147–51. [11] Hull AW. The crystal structure of calcium. Phys Rev 1921, 17, 42. [12] Sharonov MY, Zhmurova ZI, Krivandina EA, Bystrova AA, Buchinskaya II, Sobolev BP. Spectroscopic properties of nonstoichiometric multicomponent fluoride crystals with fluorite structure doped with Pr3+ ions. Opt Commun 1996, 124, 558–67. [13] Petit V, Doualan JL, Camy P, Menard V, Moncorge R. CW and tunable laser operation of Yb3+ doped CaF2. Appl Phys B 2004, 78, 681–84.

15 Growth and characterization of calcium fluoride single crystals

201

[14] Lucca A, Debourg G, Jacquemet M, Druon F, Balembois F, Georges P, Camy P, Doualn JL, Moncorge R. High-power diode-pumped Yb3+: CaF2femtosecond laser. Opt Lett 2004, 29, 2767–69. [15] Stouwdam JW, Raudsepp M, van Veggel FCJM. Colloidal nanoparticles of LaVO4: Energy transfer to visible and near-infrared emitting lanthanide ions. Langmuir 2005, 21, 7003–08. [16] Michalet X, Pinaud F, Bentolila L, Tsay J, Doose S, Li J, Sundaresan G, Wu A, Gambhir S, Weiss S. Quantum dots for live cells, in vivo imaging, and diagnostics. Science 2005, 307, 538–44. [17] Sivakumar S, Frank C, van Veggel JM, May PS. Bright white light through up-conversion of a single NIR source from sol-gel-derived thin film made with Ln3+-doped LaF3 nanoparticles. J Am Chem Soc 2007, 129, 620–25. [18] Xu X, Ling L, Wang R, Burgess JO. Formation and characterization of a novel fluoride-releasing dental composite. Dent Mater 2006, 22, 1014–23. [19] Samuel P, Ishizawa H, Ezura Y, Ueda KI, Moorthy Babu S. Spectroscopic analysis of Eu doped transparent CaF2 ceramics at different concentration. Opt Mater 2011, 33, 735–37. [20] Molchanova A, Friedricha J, Wehrhan G, Müller G. Study of the oxygen incorporation during growth of large CaF2-crystals. J Cryst Growth 2005, 273, 629–37. [21] Paraschiva M, Nicoara I, Stef M, Bunoiu OM. Distribution of Pb2+ ions in PbF2-doped CaF2 crystals. Acta Phys Pol A 2010, 117, 466–70. [22] Senguttuvan N, Aoshima M, Sumiya K, Ishibashi H. Oriented growth of large size calcium fluoride single crystals for optical lithography. J Cryst Growth 2005, 280, 462–66. [23] Ikesue A, Aung YL. Ceramic laser materials. Nat Photonics 2008, 2, 721–27. [24] Hatch SE, Parsons WF, Weagley RJ. Hot-pressed polycrystalline CaF2: Dy2+laser. Appl Phys Lett 1964, 5, 153–54. [25] Popov PA, Dykel'skii KV, Mironov IA, Smirnov AN, Smolyanskii PL, Fedorov PP, Osiko VV, Basiev TT. Thermal conductivity of CaF2 optical ceramic. Doklady Physics 2007, 52, 7–9. [26] Kotz J, Treichel P, Townsend J. Chemistry and Chemical Reactivity, Enhanced Edition. New York: Kluwer Academic/Plenum Publishers, Vol. 3, 2002. [27] Tilley RJD. Crystals and crystal Structures. England: John Wiley&Sons Ltd., 2006. [28] Elcombe MM, Pryor AW. The lattice dynamics of calcium fluoride. J Phys C: Solid State Phys 1970, 3, 492–99. [29] Elliott RJ, Hayes W W, Kleppmann WG, Rushworth AJ, Ryan JF. Experimental and theoretical studies of effects of anharmonicity and high-temperature disorder on Raman scattering in fluorite crystals. Proc R Soc A 1978, 360, 317–45. [30] Mead DG, Wilkinson GR. The temperature dependence of the Raman spectra of some alkaline earth crystals with the fluorite structure. J Phys C: Solid State Phys 1977, 10, 1063–70. [31] Kaiser W, Spitzer WG, Kaiser RH, Howarth LE. Infrared Properties of CaF2, SrF2, and BaF2. Phys Rev 1962, 127, 1950. [32] Lowndes RP. Anharmonicity in the alkaline earth fluorides. J Phys C 1971, 4, 3083. [33] Hisano K. Thermal emission spectra of CaF2 thin films. Infrared Phys 1985, 25, 415–21. [34] Luković D, Nikolić PM, Vujatović S, Savić S, Urošević D. Photoacoustic properties of single crystal PbTe(Ni). Sci Sinter 2007, 39, 161–67. [35] Nikolić PM, Vujatović SS, Ivetić T, Nikolić MV, Cvetković O, Aleksić OS, Blagojević V, Brankovic G, Nikolić N. Thermal diffusivity of single crystal Bi0.9Sb0.1. Sci Sinter 2010, 42, 45–50. [36] Xu J, Shi M, Lu B, Li X, Wu A. Bridgman growth and characterization of calcium fluoride crystals. J Crys Growth 2006, 292, 391–94. [37] Stepanov IV, Feofilov PP. Artificial fluorite. In: Rost Kristalov. Vol. I, Moscow, Russia: Akademia Nauk SSSR, 1957, 229. in Russian. [38] Molev GV, Bozhevolnov VE, Korobkov VI, Karelin VV. On the distribution of Sc3+ impurity in directed crystallization of fluorite from the melt. J Crys Growth 1973, 19, 117–21.

202

Zorica Ž. Lazarević et al.

[39] Recker K, Leckebusch R. Zur züchtung von CaF2-UND CaF2(U)-einkristallen aus der dampfphase. J Crys Growth 1971, 9, 274–80. [40] Guggenheim H. Growth of highly perfect fluoride single crystals for optical masers. J Appl Phys 1963, 34, 2482–85. [41] Elswie HI, Kostić S, Radojević V, Romčević NŽ, Hadžić B, Trajić J, Lazarević ZŽ. Growth, characterization and optical quality of calcium fluoride single crystals grown by the Bridgman method. Optoelectr Adv Mat 2016, 10, 522–25. [42] Elswie HI, Lazarević ZŽ, Radojević V, Gilić M, Rabasović M, Šević D, Romčević NŽ. The Bridgman method growth and spectroscopic characterization of calcium fluoride single crystals. Sci Sinter 2016, 48, 333–41. [43] Čajko KO, Sekulić DL, Lukić-Petrović S, Šiljegović MV, Petrović DM. Temperature-dependent electrical properties and impedance response of amorphous Agx(As40S30Se30)100-x chalcogenide glasses. J Mater Sci – Mater El 2017, 28, 120–28. [44] Gerward L, Olsen JS, Steenstrup S, Malinowski M, Åsbrink S, Waskowska A. X-ray diffraction investigations of CaF2 at high pressure. J Appl Crystallogr 1992, 25, 578–81. [45] Hong B-C, Kawano K. Luminescence studies of the rare earth ions-doped CaF2 and MgF2 films for wavelength conversion. J Alloys Compd 2006, 408-412, 838–41. [46] Alharbi ND. Size controlled CaF2 nanocubes and their dosimetric properties using photoluminescence technique. J Nanomaterials 2015, 16, 302–10. [47] Fujihara S, Kadota Y, Kimura T. Role of organic additives in the sol-gel synthesis of porous CaF2 anti-reflective coatings. J Sol-Gel Sci Technol 2002, 24, 147–54. [48] Biswas S, Kar S, Chaudhuri S. Growth of different morphological features of micro and nanocrystalline manganese sulfide via solvothermal process. J Cryst Growth 2007, 299, 94–102. [49] Scholz G, Dörfel I, Heidemann D, Feist M, Stösser R. Nanocrystalline CaF2 particles obtained by high-energy ball milling. J Solid State Chem 2006, 179, 1119–28. [50] Wang Y, Zhang LA, Shang S, Kui Z, Liu, Chen LQ. Accurate calculations of phonon dispersion in CaF2 and CeO2. Phys Rev B 2013, 88, 024304. [51] Schmalzl K, Strauch D, Schober H. Lattice-dynamical and ground-state properties of CaF2 studied by inelastic neutron scattering and density-functional methods. Phys Rev B 2003, 68, 144301. [52] Chang RK, Lacina B, Pershan PS. Raman scattering from mixed crystals (CaxSr1−x)F2 and (SrxBa1−x)F2. Phys Rev Lett 1966, 17, 755–58. [53] Ferraro JR, Horan H, Quattrochi A. Pressure dependence of the infrared‐active optical phonon modes in alkaline‐earth fluorides. J Chem Phys 1971, 55, 664–66. [54] Oostra DJ, den Hartog HW. Raman spectroscopy of superionic solid solutions of alkaline-earth and rare-earth halides. Phys Rev B 1984, 29, 2423–32. [55] Ricci PC, Casu A, de Giudici G, Scardi P, Anedda A. Phonon confinement effect in calcium fluoride nanoparticles. Chem Phys Let 2007, 444, 145–48. [56] Kaminskii AA, Bagayev SN, Eichler HJ, Rhee H, Ueda K, Takaichi K, Oka K, Shibata H, Hatanaka Y, Matsumoto Y. Steady-state picosecond stimulated Raman scattering in two host-crystals for Ln3+ and Ln2+ lasants. Laser Phys Lett 2006, 8, 385–91. [57] Tu J, FitzGerald SA, Campbell JA, Sievers AJ. Glass-like properties observed in low-frequency Raman scattering of mixed fluorite crystals. J Non-Cryst Solids 1996, 203, 153–58. [58] Su L, Xu J, Yang W, Jiang X, Dong Y. Raman spectra of undoped and uranium doped CaF2 single crystals. Chinese Optics Letters 2005, 3, 219–21. [59] Russell JP, The Raman spectrum of calcium fluoride, Proceedings of the Physical Society, vol. 85, pp. 194–96, 1965. [60] Russell JP. Raman spectroscopy using a gas laser. J Phys France 1965, 26, 620–26. [61] Gervais F. Infrared and Millimeter Waves. Vol. 8, New York: Academic, 1983, 279–339.

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[62] Kadlec F, Simon P, Raimboux N. Vibrational spectra of superionic crystals (BaF2)1−x (LaF3)x. J Phy Chem Solids 1999, 60, 861–66. [63] Ganesan S, Burstein E. Selection rules for second order infrared and raman processes. II. Fluorite structure and the interpretation of the second order infrared and Raman spectra of CaF2. Journal de Physique 1965, 26, 645–48. [64] Kaiser W, Spitzer WG, Kaiser RH, Howarth LE. Infrared Properties of CaF2, SrF2, and BaF2. Phys Rev 1962, 127, 1950–54. [65] Song J, Zhi G, Zhang Y, Mei B. Synthesis and characterization of CaF2 nanoparticles with different doping concentrations of Er3+. Nano-Micro Lett 2011, 3, 73–78. [66] Zhou L, Chen D, Luo W, Wang Y, Yu Y, Liu F. Transparent glass ceramic containing Er3+: CaF2nano-crystals prepared by sol-gel method. Mater Lett 2007, 61, 3988–90. [67] Tahvildari K, Esmaeilipour M, Ghammamy S, Nabipour H. CaF2 nanoparticles: synthesis and characterization. Int J Nano Dim 2012, 2, 269–73. [68] Pandurangappa C, Lakshminarasappa BN, Nagabhushana BM. Synthesis and characterization of CaF2 nanocrystals. J Alloys Compd 2010, 489, 592–95. [69] Singh VS, Joshi CP, Moharil SV, Muthalc PL, Dhopte SM. Modification of luminescence spectra of CaF2:Eu2+. Luminescence 2015, 30, 1101–05. [70] Salah N, Alharbi ND, Habib SS, Lochab SP. Luminescence properties of CaF2 nanostructure activated by different elements. J Nanomaterials 2015, 16, 136402. DOI: http://dx.doi.org/ 10.1155/2015/136402. [71] Fairfield Crystal Technology, http://www.fairfieldcrystal.com. [72] Jonscher AK. The “universal” dielectric response. Nature 1977, 267, 673–79. [73] Ben Said R, Louati B, Guidara K. AC conduction mechanism of the zinc potassium diphosphate. Ionics 2017, 23, 2397–404. [74] Chen W, Zhu W, Tan OK, Chen XF. Frequency and temperature dependent impedance spectroscopy of cobalt ferrite composite thick films. J Appl Phys 2010, 108, 034101-034101-7. [75] Jlassi I, Sdiri N, Elhouichet H, Ferid M. Raman and impedance spectroscopy methods of P2O5–Li2O–Al2O3 glass system doped with MgO. J Alloys Compd 2015, 645, 125–30. [76] Mirsaneh M, Furman E, Ryan JV, Lanagan MT, Pantano CG. Frequency dependent electrical measurements of amorphous GeSbSe chalcogenide thin films. Appl Phys Lett 2010, 96, 112907. [77] Wanga J, Wanga CC, Li QJ, Yu Y, Zhang J, Zheng J, Cheng C, Li YD, Wang H, Huang SG. High-temperature relaxations in CaF2 single crystals. Mater Sci Eng B 2014, 188, 31–34.

Marija Stojmenović, Vladimir Dodevski

16 Ceramic electrolytes for solid oxide fuel cells (SOFCs) as alternative energy sources Abstract: Alternative energetic systems of the new generation conceptually differ from conventional energy systems, and among them one of the most perspective technologies is the technology of solid oxide fuel cells (SOFCs). Based on their characteristics SOFC are considered third-generation devices and occupy a leading position compared to the other fuel cell types. One of the most important components of the SOFC from an operational aspect is the solid electrolyte and its characteristics. Today, as the electrolyte for SOFC, cerium-oxide (CeO2) doped with rare earth ions is increasingly used due to better properties at lower temperatures in the range of 500–700 °C, which is the working temperatures for intermediate temperature solid oxide fuel cells (IT-SOFC). As an example application of CeO2 as solid electrolyte, in this paper the three different oxides in the form of solid solutions doped ceria (Ce0.80Re0.20O2–δ; Re = Yb3+, Y3+, Sm3+) were successfully synthesized by using self-propagating reaction at room temperature (SPRT method). This method was enabled to obtain very precisely, the targeted stoichiometry of the final products. The influence of different sized ionic radius on the properties synthesized nanopowders was investigated by using XRDP, Raman spectroscopy and TEM methods. According to XRPD and Raman spectroscopy results, single phase solid solutions of the fluorite structure were evidenced regardless of the type of dopants. Nanometric dimensions of the crystallites of the synthetized powders were confirmed by XRPD and TEM methods. A part of the obtained powdery samples was densified in ambiental air for 2 h at 1,550 °C. The sintering process did not lead to loss of the mole fraction (20%) of dopants in final compositions. Techniques such as XRPD, SEM and electrochemical impedance spectroscopy (EIS) were used for microstructural and electrical characterization of the sintered samples. The highest electrical conductivity (2.19 × 10−2 Ω−1 cm−1) was found for the sample with the composition Ce0.80Y0.20O2–δ, at 700 °C. For the intermediate temperature range, the value of conductivity activation energy for this sample was 0.28 eV. The results of electrical conductivity and high thermal stability for solid electrolytes based

Acknowledgment: The research was funded by the Ministry of Education, Science and Technological Development of the Republic of Serbia. Marija Stojmenović, Vladimir Dodevski, Department of materials science, “VINČA” Institute of Nuclear Sciences – National Institute of the Republic of Serbia, University of Belgrade, Belgrade, Serbia https://doi.org/10.1515/9783110627992-016

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on rare earth doped CeO2 promote this type of material as a good candidate for application in IT-SOFC. Keywords: nanostructures, chemical synthesis, X-ray diffraction, impedance spectroscopy, ionic conductivity

16.1 Introduction Production processes, as well as life on the Earth, depend on energy sources and the degree to which they can be efficiently utilized. As a consequence, there is a constant interest in finding new energy sources. Today, in the focus of interest are materials used in energetics, especially those that provide small resistance in energy transmission. The necessity of the production of new energy sources, as well as the fulfillment of the conditions of their exploitation; makes these materials necessary for all who strive for civilization’s progress and faster development of the society. Since for them this is a major source of income, particular attention has been given to this goal by countries which are manufacturers of energy components [1]. The basic forms of energy that enable the functioning of today’s civilization are heat and electricity. By applying technological processes and appropriate converters, their conversion into other forms of energy is possible, and the form of energy depends on further purposes. Today, thermal and electrical energy represent the biggest part of non-renewable energy sources. The term “nonrenewable energy” as a source means all potential carriers of any type of energy that once created but cannot be renewed. Such energy carriers are fossil fuels: coal, oil and oil derivatives, natural gas, as well as fission and fusion fuels [2]. The beginning of the development of manufacturing and industry was the invention of the steam engine in the eighteenth century (James Watt 1763), and changes caused by its application were called the first industrial revolution. Coal burning became dominant at that time, but despite the large reserves of coal and the constant improvement of steam engines, the need for other types of fuel (liquid and solid) has been steadily growing. At the end of the nineteenth and the beginning of the twentieth centuries, fossil fuels became particularly interesting because of the possibility of using in the car industry. Internal combustion engines (Etienne Lenoir – the development of gas engines, Nikolaus Otto and Karl Benz – the development of liquid fuel engines) gave the greatest contribution to the development of the oil industry and enabled them to become the dominant drivers of economic development in the mid-twentieth century. The first problems that have arisen with non-renewable energy sources are their quantity and distribution. Fossil fuel reserves are limited, quickly disappearing, and, due to the concentration of energy resources in only a few areas in the world, the use of non-renewable fuels has created a system of interdependence, so countries that depend on imported fossil fuels are in a subordinate position.

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Another problem is the environmental pollution as a result of combustion of fossil fuels, especially those based on oil and coal. The burning process is considered to be the most important for global warming, that is, for occurrence of the greenhouse effect due to carbon dioxide emissions, sulfur and nitrogen compounds. The change in climatic conditions that results from global warming is one of the most serious threats to the Earth’s ecological system. All of these factors have an impact on food production and key processes that ensure the natural productivity of the environment. On the other hand, new sources of energy, such as fission and fusion processes [2] in the mid-twentieth century, have been greeted as sources of unlimited possibilities. The use of nuclear energy was considered as conditionally pure technology, but it was established (the case of the disaster in Chernobyl, Ukraine, in 1986, and the last in Fukushima, Japan, 2011) that it could lead to extremely large pollution, with terrible consequences for humans and the environment. On this basis, it was found that there are also limitations of these sources of energy. In addition, in both cases, limitations are also related to the disposal of nuclear waste and spent fuel. Although it is practically impossible to exclude non-renewable energy sources, the use of renewable energy sources can greatly reduce the emissions of harmful gases. The term “renewable energy sources” refer to sources that are in nature and might be renewed in whole or in part. Since the potential energy from renewable sources is in a form that is very often not possible to be used directly, its conversion is necessary. Due to the periodicity of the work of environmentally friendly energy converters (wind generators, photovoltaic cells, solar collectors), and their dependence on the weather conditions, the season in the year, time in the day, it is necessary to accumulate the obtained energy (storage) [3–5] in order to allow its consumption even under unfavorable conditions. The conversion and storage of electrical energy [3–5], (as well as thermal energy) are especially important if the converters are used in specific conditions, where there is no possibility of connecting to the electro distribution network. Biorenewable energy sources are an inexhaustible form of energy that is recycled periodically due to the process of photosynthesis. The simplest use of biorenewable sources is the process of combustion of bio-fuels (wood, wood waste, corn, straw, hay, etc.), which gives heat energy, which can be translated into all other forms of energy. Different types of biomass can be converted into biodiesel (oilseed rape, sunflower, corn, etc.) and directly used as motor fuel. In addition, bio-alcohols and biogas can also be obtained in the fermentation process of biomass (sugar, starch, etc.), which also may be directly used for the operation of engines with internal combustion. This modified biomass can be directly applied as fuel in fuel cells or after decomposition in the form of hydrogen (Figure 16.1) [3–6]. Wind energy (using an electric current generator) or solar radiation energy (using photovoltaic cells) can be converted to electrical energy. This type of electrical energy

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Figure 16.1: Possible technological procedures for the conversion and accumulation of energy of renewable energy sources for the car industry [6].

can be accumulated in electrochemical sources [3–6] and later be used for work of the electromobiles (Figure 16.1) [3–6]. Another method of accumulation is the water electrolysis [7], where gaseous hydrogen may be obtained and which can be stored, compressed and used as a fuel in fuel galvanic combinations. In Figure 16.1, possible technological processes of conversion and accumulation of energy from some renewable sources used in the car industry are presented. Considering that around 50,000,000 cars are produced annually in the world, the importance of renewable resources can be clearly seen in order to reduce environmental pollution. From above examples, it can be seen that the conversion and accumulation of energy from renewable energy sources provide unlimited possibilities of application, as well as the reason for further improvement of the technologies of the mentioned processes. New materials for the production, conversion and transmission of energy are becoming more and more important [7–19], especially in the field of fuel cells. Fuel cell technology is thought to be one of the key technologies nowadays that enables direct conversion of chemical energy into electrical energy [7–19].

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16.1.1 Types of fuel cells Alternative energy systems of the new generation conceptually differ from conventional energy systems, and among them the most perspective technology is the technology of fuel cells [7–19]. Fuel cells are energetic devices that, based on chemical reactions, allow direct conversion of chemical into electrical energy. Due to their specificity it is possible to achieve significantly higher theoretical and practical efficiency for obtaining energy than conventional methods [13]. From the constructional aspect, the fuel cells contain several key components: anode (where fuel is brought), cathodes (where the oxidation substance is brought – oxygen), semipermeable membranes, catalyst and electrolyte (which allow the ion flow from the anode to the cathode; not of electrons and reactants) [13–15]. The chemical reaction that takes place in fuel cells is equivalent to the combustion process, but as the reactants are spatially separated, the flow of electrons that spontaneously tend to move from the fuel to the oxidation substance is stopped and directed through the outer circuit (Figure 16.2). Solid Oxide Fuel Cell Fuel H2 + CO Permeable Anode Impermeable Electrolyte Permeable Cathode

Air

CO + H2O H2

H2

H2O + CO2 Heat

H2 + CO2 H2

H2

– + 2H2O H2O e H2O 2H2 + = = = O O O O= O= O= O= O2 + 4e– 2O= e–

2O=

4e–

O=

O2

O2 Oxidant

O2

e– e– e– e–

O2 Depleted O2 Heat

Figure 16.2: Schematic overview of the operation of the SOFC [20].

Although there is a similarity, the fundamental difference between fuel cells and batteries [8, 9, 13–15] is that neither fuel nor oxidizing substances are integral parts of fuel cells. Their supplying takes place according to the needs and requirements of consumers, while the waste products are constantly removed. With hydrogen (H2) as the typical fuel in the fuel cells, and oxygen supplied to the cathode (O2), in most cases the waste product is pure water (H2O), which makes fuel cells ecofriendly source of energy. In addition to hydrogen, petroleum, natural gas, coal or methanol (CH3OH) can be used as a fuel in fuel cells [16–19]. The only difference is that these types of fuels must be transformed first into an appropriate chemical state and then used as fuels.

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As fuel cell produces a voltage of about 1 V, in order to obtain higher voltage, the cells can be connected in series. The heat released during the reaction can be used for different processes, which gives fuel cells the possibility of combining with generators of electricity and heat in industry or residential buildings [13–15]. All of these indicate that fuel cells have extraordinary advantages and that their further development, as well as improvement is of great importance for humanity. The advantages of fuel cells in relation to other energy sources are as follows: – High energy efficiency (efficiency is about 60%) – Ease of packaging – Large number of cells can be grouped into packages of different dimensions – They can easily be installed due to practically negligible impact on the environ ment – Very small amount of waste gases and heat – The possibility of using different fuels, which can be changed easily and quickly – Require minimum maintenance requirements There are also secondary benefits such as current—voltage reactive control, quick start of the system, work that does not require monitoring and the absence of moving parts in the reactor. Fuel cells also have defects, such as high investment costs, incompatibility with the industry and lack of infrastructure. The classification of fuel cells is mainly done based on the type of electrolyte. Thus, there are several basic types of fuel cells: – Fuel cells with polymer electrolyte (PEFC) – Direct methanol fuel cells (DMFC) – Alkaline fuel cells (AFC) – Phosphorus fuel cells (PAFC) – Fuel cells with melted carbonates as electrolytes (MCFC) – Solid oxide fuel cells (SOFC)

16.2 Solid oxide fuel cells (SOFCs) Based on their characteristics SOFC are considered third-generation devices and occupy a leading position compared to the five above-mentioned fuel cell types. Today, as the electrolyte of SOFC, cerium-oxide (CeO2) doped with lanthanides (Ln) [8–12] is increasingly used due to better properties in lower temperatures. In addition, the electrolytes thus obtained show significantly higher conductivity compared to commercial yttrium (Y) stabilized zirconium oxide (ZrO2)-YSZ, which is one of the most important characteristics. Such doped CeO2 is increasingly the object of interest and research, which is why the next chapters are devoted to SOFC, CeO2 characteristics and application of doped CeO2 as an electrolyte in SOFC.

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16.2.1 Structural properties of SOFCs The basic characteristic of SOFC is an attractive direct conversion of energy of fuel into electricity, which favors them as a unique type of fuel cell [20]. This also represents the fundamental difference in relation to conventional energetic devices which convert chemical energy to heat, then to mechanical and finally to electrical. The technology of solid electrolyte applications requires significant changes in the structure of fuel cells. A rigid electrolyte is a solid oxide that can be made on the basis of ceramic materials [8–12] so it does not require refilling or filling during the operating period. This greatly simplifies the construction, operation and maintenance, but also reduces the cost of production. In addition, the construction of solid materials makes it possible to achieve higher operating temperatures ensuring good ionic conductivity of the electrolyte. Low ionic conductivity was one of the main problems which limited development of this type of fuel cells, but thanks to research and continuous improvement of solid electrolytes, this problem has been overcome [9–12]. The operating temperature of the SOFCs is up to 1,000 °C, and the utilization rate is 60–65%. However, todayʼs focus of research SOFCs is to decrease the working temperature in the limits of intermediate values (500–700 °C) [9–12], even below 500 °C [8], with the possibility of achieving good ionic conductivity (order to 10−2 S/m) and the utilization rate above 65%. Regarding the historical development aspects of SOFC, the focus is on exploring the bell-shaped and tubular design of fuel cells [21], on the basis of which the division into planar (PSOFC) and tubular (TSOFC) fuel cells was carried out. The difference between them is in the construction, and the geometry of the system depends on the needs and uses of fuel cells. In addition to the above research, tubular design was often used in the United States [22], as well as in Swiss companies [23]. Also, in the development and demonstration of the application of the monolithic fuel cell design, the work was carried out in the national laboratory Argona (Argonne) [24, 25], while several different organizations worked on the development of the planar design of fuel cells [26]. Another way to distinguish the SOFC is by the way the ceramic material is applied: or whether it is applied on the cathode, on an anode, or used as an electrolyte. The most common material for making electrodes is a mixture of CeO2 doped with samarium (Sm) or gadolinium (Gd) with nickel oxide (NiO/GDC; NiO/SDC), whereby it is necessary that anode material contains about 40 vol% of Ni after reducing of NiO to Ni [13–15, 27]. The electrolyte and interconnector should have high density to prevent mixing of gases on electrodes, while the anode and cathode must be porous in order to facilitate gas transport to the reaction site. When applying ceramic material on the cathode or anode, the thickness of the layer should be from 250 μm to 2 mm with the purpose to achieve satisfactory ionic conductivity. The development directions of this technology were aimed in reducing the thickness of the electrolyte layer aiming to reduce the operating temperature of the fuel cell,

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increase efficiency and reduce the consumption of materials [27]. However, today are more and more working on the research and application of ceramic material as an independent electrolyte without application on cathode or anode [27–29]. Limitations occur at high temperatures (900 °C) in terms of expensive ceramic materials and the production of a carrier (interconnector due to transmission of electrons) of chromium steel. The possibility of reducing of working temperature (500–700 °C) using doped CeO2 as an electrolyte may overcome that problem [8–12]. Nanopowders CeO2 represent very good conductors compared to other types of electrolytes PEFC, PAFC, AFC and MCFC fuel cells because they conduct oxygen (O2−) ions well [8–12]. Based on this, in addition to being used in SOFCs, these ceramic materials can be used as gas sensors for O2, oxygen pumps and catalysts [30–34]. The principle of operation of SOFC (Figure 16.2) [20] is similar to the principle of battery operation, with the difference that fuel cells cannot be discharged and do not require recharging [13–15, 25–27]. As long as there is a gas supply from external sources (reactants) and gas flow on electrodes, SOFC produces energy. During the work of this fuel cell type, fuel is introduced to the anode where it is oxidized, the electrons are released and an external electric circuit is formed, while the oxidant (oxygen or air) is reduced to the cathode by accepting electrons from an external electric circuit (Figure 16.2). The basic reactions in SOFCs are given as shown in Figure 16.2 by eqs. (16.1) and (16.2): On anode:

−

2H2 + 2O2 = 2H2 O + 4e −

On cathode: O2 + 4e − = 2O2

−

(16:1) (16:2)

while the total reaction in the system is defined by eq. (16.3): 2H2 + O2 = 2H2 O

(16:3)

The corresponding Nernst expression for these reactions is [35] E = Eo + RT=2F lnðPH2 PO2 =PH2 OÞ

(16:4)

where E is the energy of the system, E° is the standard energy, R is the universal gas constant, T is the operating temperature, F is the Faraday constant, PH2 is the partial pressure of hydrogen, PO2 is the partial pressure of the oxygen and PH2O is the partial pressure of the water vapor. The electrochemical transformation of the fuel and the oxidant is isomeric, which means that the fuel cell directly uses the available energy at operating temperature. For SOFC a thermodynamic equation is given in the form: Qr = TΔS = ΔH − ΔG

(16:5)

where Qr is energy at the operating temperature, T is the temperature of the system, ΔS represents changes in entropy, ΔH the change in enthalpy and ΔG the change in

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Gibbs free energy. If the enthalpy change is negative (ΔH < 0), the cell is heated and its operating temperature increases. At the same time, losses due to increased operating temperature are eliminated by cooling the fuel cells [36]. Fuels that use SOFC are different [16–18]. Tolerance to impurities in fuel allows the use of H2 and CO obtained by the coal gasification process. In addition, natural gas, carbon monoxide and methane (CH4) can also be used [16–18]. The thermodynamic efficiency of SOFC is lower than the efficiency of MCFC and PAFC due to less free energy and higher operating temperature. However, a higher operating temperature is an advantage, since it allows less polarization resistance [37].

16.2.2 Electrolytes in SOFCs–ZrO2 as electrolyte in SOFCs Stabilized ZrO2 is commonly known [38] and has been used as a solid electrolyte in SOFC due to its stability in the reduction and oxidation atmosphere [39, 40]. As such, it is one of the rare solid electrolytes that are commercially produced for use in SOFC. At the room temperature zirconium dioxide has a monoclinic crystal structure and at temperatures higher than 1,170 °C this crystal structure is changed to tetragonal. With an increase in temperature up to 2,370 °C, ZrO2 exhibits a cubic fluorite structure, which remains up to the melting point 2,680 °C. Doping with ions with the lower oxidation states than Zr4+ ions could stabilize the cubic crystal structure of zirconium dioxide in the temperature range from ambiental to melting point. The ions of Zr4+ have too small radius to maintain thermal stability of a cubic fluorite crystal structure of ZrO2. In this structure there are eight oxygen ions O2−, while in a monoclinic there are only six. Adding the ions of rare-earth elements leads to the stabilization of the cubic crystal structure, allowing the formation of oxygen vacancies that are concentrated over the ion dopant, rather than around the Zr4+ ions. In this way there is an efficient formation of oxygen ions with coordination number 6 or 7. It has been established [41] that non-stoichiometric oxygen leads to the appearance of electrons whose concentration is directly proportional to the oxygen vacancy in the ratio of 2:1. Based on that, it may be concluded that pure ZrO2 is rather an electronic conductor than an electrolyte, since the diffusion of the electrons is several order of magnitude larger than the diffusion of ion defects. Nevertheless, doping ZrO2 with metallic ions of an appropriate size whose valence is less than +4, ZrO2 may result in stable structures and properties characteristic for solid electrolytes (ZrO2 doped with 15% CaO)—CaSZ [41]. In addition, ZrO2 can also be stabilized with yttrium-oxide (Y2O3), achieving higher ionic conductivity, but in the narrow area partial pressure of oxygen [41]. The highest value of ionic conductivity show systems with 11% scandium oxide (Sc2O3) stabilized ZrO2-SZZ (0.15 Scm−1 at 800 °C), which is similar to the ionic conductivity values for CaSZ at 1,000 °C [42]. Such high values are due to a small distortion which comes from replacement of Zr4+ ions (0.84 Å) with ions Sc3+ (0.87 Å) within the crystal lattice [42, 43], since the

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increase in the ionic radius stabilizes the fluorite structure of ZrO2. However, the application of Sc2O3 leads to the several a lacks such as the high prices of this material, the appearance of high-temperature aging at concentrations greater than 10%, as well as the difficulty in obtaining appropriate densities during sintering [44, 45]. Improvement of the ionic conductivity of the electrolytes based on ZrO2 can be achieved using two ways. The first approach requires the further development of the production technique of thin, vacuumed ZrO2–CaO layers [46], while the second requires changes in the ZrO2 microstructure adding a small quantity of Al2O3 (aluminum oxide) modifies the grain boundary, smooths the sintering progression and increase the electrical conductivity of the electrolyte [47]. Benefits such as good mechanical properties can be attributed to doped ZrO2. However, the increase in electrolyte density involves high firmness, and the thickness of electrolyte layer should be not less than 100 μm thick. This condition increases the electrical resistance of the fuel cell and reduces the ionic conductivity at a temperature range of 600–700 °C, which is the main disadvantage of these electrolytes.

16.2.3 Electrolytes in SOFCs–Bi2O3 as electrolyte in SOFCs In addition to doped ZrO2, the δ phase of bismuth oxide (Bi2O3) was shown as a very characteristic electrolyte [41, 48]. It is one of the electrolytes that show the highest ionic conductivity values in relation to all materials that have been tested so far, but in a very narrow temperature range (729–825 °C). The disadvantages of the δ phase Bi2O3 such as the existence in a narrow temperature interval and the susceptibility of reduction in a non-oxygen atmosphere to metal bismuth caused the limited application of the unmodified Bi2O3 as an electrolyte for high-temperature fuel cells.

16.2.4 Electrolytes in SOFCs–LaGaO3 as electrolyte in SOFCs Perovskite materials based on lanthanum–gallium–oxide (LaGaO3) have potential to be electrolytes due to their extremely high ionic conductivity [49]. As concrete example, La0.9Sr0.1Ga0.8Mg0.2O3–δ (LSGM) possesses ionic conductivity value several times larger compared to YSZ. But, effective application of LaGaO3 for marketable purposes requires additional upgrading toward chemically more stable system. The possibility of interaction at the boundary between the electrolyte and anodic material containing nickel–LaGaO3 may lower the performance of the cell [35, 50], what is undesirable effect for this type of electrolytic material. Another limitation in the application is the LaGaO3 decomposition in a reduction atmosphere at temperatures above 800 °C due to the high volatility of Ga2O3 [51]. Although some disadvantages occur, by application LaGaO3 in SOFCs, it is possible to produce a power up

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to 3.5 Wcm−2. In order to improve performance of this type of fuel cell, a layer of LSGM covered with Sm-CeO2 (SDC) thin film could be used as composite electrolyte [52]. Based on that, it may be concluded that CeO2 doped with rare-earth ions enables the performance of electrolytes based on oxides of other metals. This provides the possibility of further investigation of the characteristics of the electrolytes obtained on the basis of CeO2, which is the basis of this research, which will be explained in the following chapters.

16.2.5 Electrolytes in SOFCs – structural characteristics of CeO2 as electrolyte in SOFCs Cerium (Ce) as an element with atomic number 58 belongs to a group of lanthanides or rare elements characterized by the successive filling of 4f orbital by electrons, and with electronic configuration 4f1 5d1 6s2. Since the energy of the inner 4f level is slightly different from the energy of the external levels, Ce occurs in oxides with an oxidation numbers of +2, +3 and +4, where oxides with oxidation number of cerium +4 are more stable than oxides where Ce is +3 form. Regarding effective ionic radius of the Ce3+ and Ce4+ it depends on their coordination number with other ions [53–55]. CeO2 is the most stable cerium oxide in the air, but with increasing temperature, it is transformed into non-stoichiometric oxides with defective crystalline structure due to loss of oxygen that is accompanied by the formation of anionic vacancy and the partial reduction of the Ce4+ ions in Ce3+ ions, depending on the partial pressure of the oxygen. Based on that, it may be concluded that CeO2 belongs to real crystals, in contrast to ideal crystals in which all atoms are located at the appropriate positions of the crystal lattice, and electrons at the lowest energy levels, and various irregularities and deviations from the ideal structure are known as defects [56, 57]. Many properties such as electrical conductivity [8–12, 48], optical properties and color [58] are caused both by the type and by the concentration of defects in the crystal structure [57]. It is known that CeO2 has a crystalline structure of calcium fluorite type (CaF2) (Figure 16.3) [59], spatial groups Fm3m, with the unit cell parameter a = 5.411 (1) Å [60]. In this type of crystalline structure, cerium atoms form dense-packed layers that are placed together and form a surface-centered cubic (FCC, face-centered cubic) lattice of cerium atom. Within this grid there are tetrahedral and octahedron cavities, where is the number of octahedral holes equal to the number of cerium atoms, while the number of tetrahedral holes is twice higher. Oxygen atoms fill the tetrahedral cavities of the sublattice of cerium atoms, thereby achieving the stoichiometric ratio of cerium to oxygen, as in CeO2. Each cerium atom is coordinated with 8 oxygen atoms; that is, the coordination polyhedron is a cube, while oxygen atoms in coordination with 4 cerium atoms form a tetrahedron as a coordination polyhedral, where the ionic radius of the O2− ion for the coordination number 4 is 1.38 Å [55]. Coordinating polymers, cubes and tetrahedron, are interconnected over the edges [59].

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– O2– – Ce4+

Figure 16.3: Fluorite structure of CeO2 [59].

Measurements of electrical conductivity showed that electronic and ionic conductivity is present in CeO2, whereby electronic conductivity can be n-type and p-type [61]. In the case of the CeO2–x oxide, the electronic conductivity of the n-type is dominant and proportional to x, and is carried out by thermally activated transport of the small polarone, Ce’Ce, as the carrier of the electron, together with the transport of dislocations caused by the displacement of adjacent ions in the formation of the Ce3+ defect. The ionic conductivity of CeO2 significantly increases by doping of the oxides of bivalent or trivalent metals due to the formation of oxide ions vacancies [8–12]. Transport of O2− ions through vacancies, that is, ionic conductivity, exceeds the electronic air conductivity in the temperate range (500–700 °C), and the material becomes an excellent electrolyte [9–11]. The parameter a of the unit cell of the non-stoichiometric oxide CeO2–x calculated in the relation to the pseudocubic fluorite structure shows the linear dependence on the composition (Figure 16.4) [62]. With the rise in temperature, linear expansion of the unit cell CeO2–x also occurs [62]. Kim’s (Kim) empirical relationship, which gives a link between the parameter of the doped oxide and the fluorite structure, the differences in the ionic radius of the metal ion, the differences in cation valence and molar dopant concentration, can also be applied to CeO2–x oxides [63]. By adding the values of the ionic radius for Ce3+ and Ce4+ the dependence of the parameters of the unit cell and of the composition x is given in the form: a = 5.413 + 0.4612xðÅÞ

(16:6)

Since the CeO2 radius of the oxygen vacancies (1.164 Å) is considerably smaller than the O2− ion radius (1.38 Å) [53], the reason for the expansion of CeO2 during reduction is the difference in Ce3+ and Ce4+ ions. The connection between the lattice parameter and the CeO2-x composition also gives the ionic-based equation based on fluorite structures of type MO2-M′O1.5 [64]: n pffiffiffi o pffiffiffi (16:7) a = 0.9971 4= 3 ½rM′ − rCe − 0.25ro + 0.25rV  O u + 4= 3 ½rCe + ro 

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Figure 16.4: The parameter а pseudocubic unit cell CeO2–x in the function of the composition 2–x [63].

where rM′, rCe and ro are radius of Ce3+, Ce4+ and O2− ions, respectively, rVo•• is radius of the oxygen vacancies, and u is molar fraction of dopants (in this case Ce3+ ions). The introduction of vacancies of oxygen and Ce3+ ions in the CeO2 structure during reduction leads to a disturbance of local symmetry due to changes in the oxygen sub-surface, while the cationic subsurface does not change. The ions of O2− around vacancies occupy new equilibrium positions by reducing the distance between the oxygen atoms that are in octahedral coordinate with the vacancies in relation to these distances in the coordination octahedron around the ion O2− (Figure 16.5) [65].

3.8 Å

3.3 Å

Figure 16.5: Reduction of octahedron oxygen around the oxygen vacancies [65].

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Recent research is increasingly focused on methods for obtaining nanostructured CeO2, because it has been shown that nanometer particle size and crystallite, as well as large specific powder surfaces, can improve the properties of CeO2-based materials. The most common methods are: deposition of oxide from cerium salt [66], solid state reaction [67], mechanochemical synthesis [68], self-inflammation synthesis [69], synthesis by modified combustion process of glycine nitrate gel [8–12], self-propagating reaction at room and elevated temperatures [8–12], solgel method [70], and others. In nanocrystalline materials, the proportion of grain boundaries is significantly higher in relation to the grains themselves. The grain boundaries, however, have a higher density and higher mobility of defects compared to microcrystalline materials, which leads to an increase in ionic conductivity [8–12, 28, 29, 48]. The diffusion of ions is in principle slower through volume, but over the surface and through the grain boundary, and smaller crystals and a higher proportion of grain boundaries mean a short path of ions and increased mass transport [8–12, 48, 57]. The ability to reduce nanocrystalline CeO2 increases due to the extremely large surface on which the release of oxygen is taking place [8–12, 48, 57]. At the same time, the reduction accelerates the mass transport in sintering and densification due to the increase in the concentration of vacancies of the slower type, which contributes to the better properties of the material [8–12, 48, 57]. Thanks to the ability to improve electrical conductivity, CeO2 is a candidate for electrolyte, but also for anode material in SOFCs [8–12]. Application of CeO2 as a catalyst for purification of automotive exhaust gases, catalysts for oil cracking, oxygen sensor and aluminum protection coatings depends of its oxide-reduction ability. It is also used in optoelectronics, because it has high transparency in the visible part of the spectrum and near infrared, as well as good electro-optical characteristics [58]. Ceramic materials in form of color pigments [58] and glass polishing agents are common additives, and since they are low-cost and not toxic, they are in agreement with reqirements in order to environmental protection.

16.2.6 Properties of rare earth oxides used to doping CeO2 Thanks to its fluorite structure and capability of doping with ions of rare earths (neodymium – Nd3+, samarium – Sm3+, gadolinium – Gd3+, dysprosium – Dy3+, yttrium – Y3+ and ytterbium – Yb3+), the CeO2 nanometer powders have become a very current ceramic as electrolytes for application in SOFCs [8–12]. By applying the ultra-fine CeO2 powder to rare-earth ions, higher ion-conduction values than the conductivity value shown by YSZ in the oxidation atmosphere [41] are achieved. The possibility of achieving high ionic conductivity at lower temperatures (500–700 °C) [8–12, 48] is attributed to the formation of oxygen vectors in the cerium lattice, which result from the replacement of four-valent cerium ions (Ce4+) with trivalent ions of rare countries [8–12, 48]. In addition to vacancies, the attainment of high ionic conductivity values

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can be attributed to distortions of the cerium lattice due to the difference in ionic radius dopant (Nd3+ – 1.109 Å, Sm3+ – 1.079 Å, Gd3+ – 1.053 Å, Dy3+ – 1.027 Å, Y3+ – 1.019 Å and Yb3+ – 0.985 Å) and Ce4+ ions (0.97 Å) [53]. Additionally, from literature it is known that the conductivity of nanocrystalline electrolyte materials increases when the grains size decrease, while their distribution is uniform [8–12, 48, 57]. Based on the above facts, it can be concluded that the characteristics of ions, such as ionic radius and valence, are decisive when determining the dopant role. In addition, the amount of dopants that can be introduced into the CeO2 grid is also very important. The total dopamine concentration varied, but [8–12, 48, 57] showed that for concentrations of 10 to 20%, they reached the highest values of ionic conductivity. Further increase in concentration of dopants causes reducing of oxygen vacancies mobility, and as a consequence, the values ionic conductivity decreases. In order to achieve the highest value of ionic conductivity, the combination and at the same time the introduction of one or more dopants into the CeO2 crystal grating were performed. The most common dopants are rare earth oxides [8–12], yttrium oxide (Y2O3) [8–12], as well as alkaline (Li2O and Cs2O) [71] and earth metal alkaline oxides (MgO, CaO, SrO, BaO) [72]. In addition, the individual introduction of different oxides (Sb2O3, Ga2O3, In2O3, AlCl3, Bi2O3 and Sm2O3) [48, 73] was performed in order to increase the ionic conductivity, where it was found that the highest conductivity shows CeO2 doped with antimony ions (Bi3+) at a certain temperature. In addition to the above-mentioned research, the introduction of a small quantity (5 mol%) of manganese oxide (MnO2) in the CeO2-doped Ga3+ ion-doped [74] gene tended to increase the concentration of oxygen vans and, therefore, ionic conductivity. However, it has been found that manganese is not as effective an acceptor as it has been assumed and does not affect the increase in ionic conductivity. A certain increase in conductivity compared to pure CeO2 was achieved by simultaneous doping with two, three, four, but five ions such as Sm3+, Y3+, Gd3+, Y3+ and Dy3+ [8–12]. Generally, all of these facts are an important prerequisite for significantly reducing the temperature of sintering, but also energy savings in the process of producing fuel cells. The characteristics of SOFCs such as low cost of the technological process of obtaining ceramics without pollutants, low operating temperature, and high efficiency make doped CeO2 as a focus of interest, which is presented in detail in the next chapter.

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16.3 Nanocrystalline materials based on CeO2 as solid electrolytes for IT-SOFC Nanocrystalline materials based on CeO2 represent a very important group of materials in novel technologies. CeO2 found many versatile applications in various fields, such as automotive industry (catalyst for exhaust system), photocatalysis, biomedicine, optics, water splitting and dopant for IT-SOFC [8–12, 30–34, 61–75]. From this point of view, materials based on nanometric CeO2 are of increased interest for researchers worldwide as electrolytes of the new generation of SOFCs with a high ionic conductivity at lower temperatures compared to commercial ones, especially by using diversity fuels, such as natural gas, hydrogen, methane and biogas [16– 19]. Many of researchers are familiar with the fact that ionic conductivity of CeO2based electrolytes is highly dependent on the composition, nanostructure as well as crystal structure parameters and microstructure [8–12, 48, 61–75]. Thanks to its crystal structure, which is fluorite type, large amounts of cations of IIA group or rare earth metals (Er3+, Gd3+, Sr2+, Ca2+, La3+, Yb3+, Sm3+, Eu3+, Nd3+, Y3+, Dy3+, Ho3+) could be accommodated in the crystal lattice of CeO2, which could change its ionic conductivity [8–12, 57, 76–78]. Many of investigation confirm that the substitution of low-valence cations with Ce4+ creates oxygen vacancies as a result of charge compensation [8–12, 48, 57]. Due to presence of vacancies, the mobility of oxygen anions is allowed, i.e., their transport in direction from cathode to anode in SOFCs. Besides increasing concentration of vacancies, doped cations with the ionic radius larger than Ce4+ also make an unavoidable distortion in ceria crystal lattice. This crystal lattice distortion, which is also anticipated to change the conductivity [8–12, 48, 57], can be maintained by adding cations with different ionic radius, as well as the simultaneous doping of different cations [8–12, 48, 57]. So, CeO2-eletrolyte ionic conductivity is highly dependent on concentration, ionic size and formal charge of dopant [8–12, 48, 57]. Additionally, microstructure features like grain size and grain boundaries fraction play an important role in the ionic conductivity. The conductivity in the regions of nanocrystalline grain boundary is greater than for grains of larger dimensions, and increases with decreases grains size and increasing of the uniformity of distribution [8–12, 48, 57]. That is an important precondition for considerable decrease of temperature during sintering process and lower energy consumption in the SOFC production process. That is why high-quality powders with particle size in the nanometric range are a crucial and essential condition for sintering and achieving fast densification with inhibited grain growth. In such a way, nanocrystalline ceramics with good quality could be produced and may be suitable for SOFC application as an electrolyte, due to high electrical conductivity as well as better mechanical properties. Nowadays, one of the most perspective and most fruitful methods for synthesis of various nanopowders is the self-propagating room temperature method (SPRT)

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[8–12, 48, 57]. The main advantage of this method is synthesis of nanoparticles with precise stoichiometry at room temperature in comparison with nominal composition. This method is based on solid state exothermic reaction and has better economic efficiency compared to the other methods [66–70]. In this research results of preparation and properties of the obtained nanocrystalline powders of doped ceria (Ce0.80Re0.20O2–δ; Re = Yb3+, Y3+, Sm3+) by using SPRT method were presented. Yb3+, Y3+ and Sm3+ were chosen as candidates for doping and research of ion conductivity of CeO2-based electrolyte, due to their valence state which is lower than Ce4+ and also due to different ionic radius in comparison with Ce4+ (Ce4+–0.970 Å, Yb3+–0.985 Å, Y3+–1.019 Å, Sm3+–1.079 Å [53]). Having in mind differences in valence state and cationic ionic radius we expected significant changes of the properties of CeO2 as a consequence of doping. In order to estimate usability of the obtained nanopowders in solid oxide fuel cells (IT-SOFCs) in intermediate temperatures (500–700 °C), the process of sintering and electrical conductivity of sintered samples were examined. The aim of application of above-mentioned electrolytes with high ionic conductivity is to increase efficiency of SOFCs and decrease operating temperatures including reducing the production costs without harmful environmental impacts. In addition, application of electrolytes based on CeO2 with high ionic conductivity indicates the direction of development of a new-generation electrolyte for IT-SOFCs.

16.4 Synthesis and characterization materials based on CeO2 16.4.1 Synthesis procedure and sintering process Experimental procedure included the synthesis of nanopowders compositions Ce0.80Re0.20O2–δ (Re = Yb3+, Y3+, Sm3+) by using self-propagating reaction at room temperature (SPRT) [8–12, 48]. In this procedure metal nitrates react with sodium hydroxide through fast and spontaneous reaction. Precursors were Ce(NO3)3 · 6H2O (Aldrich, 99.999%), Re(NO3)3 · 6H2O (Aldrich, 99.999%) and NaOH (p.a. Fluka). The compositions of the desired solid solutions were calculated using ion-packing model [64]. The compositions of the starting mixtures were adjusted according to desired composition of the final reaction product. The overall reaction of the synthesis is 2½ð1 − xÞCeðNO3 Þ3 · 6H2 O + xReðNO3 Þ3 · 6H2 O + 6NaOH + ð1=2 − δÞO2 ! 2Ce1−x Rex O2 −δ + 6NaNO3 + 15H2 O

(16:8)

The mixture of precursors was milled in an alumina mortar for 15 min at ambient temperature in air, allowing a rapid development of the reaction. Then the mixture was kept in air atmosphere for 3 h. The advantage of this technique is a solid state

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exothermic reaction, yielding the ceramic powders without a significant increasing of temperature during reaction. The resulted powder was then moved in distilled water and centrifuged at 3,000 rpm, for 10 min by using Centurion 1020D centrifuge. A centrifuged sample was rinsed four times with water and two times with ethanol. Then the synthesized nanopowders were dried at 100 °C. This method is pronouncedly cost-effective compared to the other methods reported in the literature [66–70]. The obtained powders were pressed, first, uniaxially and then isostatically at 225 MPa. The sintering of pressed pellets was performed in an air atmosphere at 1,550 °C for 2 h, at a heating rate of 5 °C/min. The result densities of sintered samples were determined by Archimedes’ method.

16.4.2 Characterization The synthesized powders and/or sintered samples were analyzed using the following methods: X-ray powder diffraction (XRPD), Raman spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). For Roentgen X-ray diffraction analysis (XRD) the diffractometer Ultima IV Rigaku with Cu Kα1,2 radiation, equipped with a voltage at 40.0 kV and current at 40.0 mA generators was used. The samples were analyzed in a continuous scan mode in the °2θ range 20–80, a scanning step was 0.02°, while a scan rate was of 2°/min. The spectrometer DXR Raman microscope (Thermo Scientific, USA), equipped with an Olympus optical microscope and a CCD detector excited with a diode pumped solid state high-brightness laser (532 nm) was used for investigation of the structural properties of the samples. The spectra were recorded at room temperature in the spectral range 200–800 cm−1. The powdered samples were placed on X–Y motorized sample holder. For focusing of the laser beam on the sample an objective magnification of 10 × was used. The spectrograph with a grating 900 lines/mm was applied for the analysis of the scattered light. Laser power was 1 mW. TEM analysis was performed on JEOL 400 FX instrument. The values of particle size were measured on micrographs directly by using the existing computer program Digital Micrograph. The micrographs with maximal possible separated particles were chosen for measurements. The diameters of particles were measured manually, and these results were recalculated by digital micrograph program into particle size. For each sample, approximately 40 particles were measured and about 7 photos taken. Mean value was taken as the particle size of the investigated powder. Investigation of surface properties of the sintered samples was performed by scanning electron microscopy (SEM) using the instrument FE–SEM Jeol JSM 6330F (Japan). The samples were pre-coated with a several nanometers’ thick layer of gold prior analysis. For coating procedure, a device JEOL Fine Coat JFC–1100 ION SPUTTER was used. All images were taken in SEI mode (magnification ×10,000) with the

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accelerating voltage of 10 kV and maximal resolution at 0.4 nm. The EDS analysis was carried out at the invasive electron energy of 30 keV by using QX 2000S device (Oxford Microanalysis Group). The electrical characterization of sintered samples was performed using electrochemical complex impedance method, in a range of frequencies 10 µHz to 1 MHz, using Interface 1000 Potentiostat/Galvanostat/ZRA and EIS300 Electrochemical Impedance Spectroscopy software. The measurements were conducted in an air atmosphere, in the temperature range from 500 °C to 700 °C, with an increment of 50 °C. The applied sinusoidal voltage signal was 20 mV. In order to provide a good electrical contact between electrolyte and electrodes, onto both sides of the sample pellets, a thin layer of high-conductivity silver paste was applied. The samples were placed between the silver plates in a ceramic holder, which was heated by vertical oven. For temperature monitoring the Pt–Rh thermocouple was used and located just below the bottom silver plate. The impedance plots obtained experimentally were fitted by means of the software ZViews for Windows (Version 3.2b). The values of were calculated from the impedance graphs recorded at various temperatures.

16.5 Results and discussion A detailed characterization of the pure CeO2 [8, 57] and doped Ce0.80Re0.20O2–δ (Re = Yb3+, Y3+, Sm3+) [10, 65] synthesized by SPRT method, as well as after sintering process was done with the purpose to determine modifications in microstructural and morphological properties, since it was shown that size of ionic radius has a strong influence on the above-mentioned properties. Results of characterizations of pure and doped CeO2 samples (Ce0.80Yb0.20O2–δ, Ce0.80Sm0.20O2–δ) synthesized by SPRT method were published previously [10, 57], and in this paper were presented in order to compare properties of sintered samples with composition of Ce0.80Y0.20O2–δ.

16.5.1 Structure details of nanopowders Figure 16.6 displays the typical X-ray diffraction patterns for all synthesized nanopowders obtained by the SPRT method [10, 57, 65]. According to the XRPD analysis, all peaks of the nanopowders showed the presence of single phase ceria with the cubic fluorite structure (space group Fm3m) without any other traces. They demonstrate that the CeO2 was fully stabilized and incorporated with Yb3+, Y3+ and Sm3+ ions in the form of oxides. This means that dopant ions were easily replaced the Ce4+ ions in the crystal lattice, even though dopants in 3+ oxidation state have the slightly larger ionic radius in comparison with Ce4+ ion (0.97 Å) [53]. In addition, all peaks of

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Figure 16.6: X-ray diffraction patterns of pure CeO2 and Ce0.80Re0.20O2–δ (Re = Yb3+, Y3+, Sm3+) nanopowders obtained by the SPRT method.

each powder was significantly expanded, which indicated a small crystallite size (DXRPD) and/or microstrain (eXRPD) (Table 16.1). Additionally, due to pronounced broadening of diffraction lines hkl: 222, 400, 331, 420 for obtained powders of crystal planes remains unnoticeable. Table 16.1: Lattice parameters (aXRPD), average ionic radius (rd(XRPD)), crystallite size (DXRPD) and microstraine (EXRPD) determined by XRPD method, and particle size determined by TEM method for pure CeO2 and doped CeO2 nanopowders obtained by SPRT method. Composition

aXRPD (Å)

rd(XRPD) (Å)

DXRPD (nm)

eXRPD (%)

TEM (nm)

CeO []

.

.

.

.

.

Ce.Yb.O–δ []

.

.

.

.

.

Ce.Y.O–δ

.

.

.

.

.

Ce.Sm.O–δ []

.

.

.

.

.

Table 16.1 summarizes the values of lattice parameters of investigated nanopowders obtained by XRPD analysis. The results are in agreement with literature data concerning anomaly of relatively strong increase of ceria lattice parameter with decreasing particle size below 10 nm [79]. The values of microstrain (Table 16.1) are significantly higher in comparison with value for pure CeO2. Thus, the larger

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particles are most likely composed of considerable number of crystallites, which are non-coherently oriented within the particle and thus creating higher microstrains upon each other. On the other hand, smaller particles are composed of just few crystallites because their dimensions less that 2 nm and their values of microstrain are slightly less. The values of lattice parameter (aXRPD), crystallite size (DXRPD) and microstrain (eXRPD) determined by XRPD analysis are presented in Table 16.1. From the literature it is known that fluorite structure of CeO2 is characterized with a single first-order Raman mode which is localized at frequency 465 cm−1 [57], which originates from the symmetric F2g mode of the O atoms around each cation. Raman spectra of pure and doped nanopowders of CeO2 presented in Figure 16.7 and showed the shift to lower energies of the F2g mode from 465 cm–1 [57] to 449 cm–1 (doped CeO2 sample). Its asymmetrical broadening was consistent with a decrease in particle size of below 10 nm.

Figure 16.7: Raman spectra of pure CeO2 and Ce0.80Re0.20O2–δ (Re = Yb3+, Y3+, Sm3+) nanopowders obtained by the SPRT method.

The broad Raman mode at about 550 cm−1 is the special feature of the doped CeO2 spectrum, what confirms the presence of vacancies of oxygen in doped solid solutions (Figure 16.7). The appearance of this Raman mode in doped samples is due to the extrinsic O2− vacancies in fluorite structures in order to keep charge neutrality when Ce4+ ions are partly replaced with dopants (Re = Yb3+, Y3+, Sm3+) ions. The intensity of this peak depends on the concentration of vacancies. Since the dopant concentration in all investigated samples was the same, one possible explanation for differences in

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magnitude of modes is the size of the vacancies, which increased with the effective radius (rd(XRPD); Table 16.1) of the dopant [77]. It may introduce additional incoherent scattering terms to mode because of the polarizability changes [77]. Beside Raman mode localized at about 550 cm−1, additional Raman mode appears at about 600 cm−1 originating from intrinsic oxygen vacancies due to nonstoichiometry of powder. Based on the results obtained by Raman spectroscopy it can be concluded that we are not dealing with simple mechanical mixtures of oxides and that the lattice parameters depend on the type dopants. Figure 16.8 presents results obtained by TEM analysis for doped Ce0.80Re0.20O2–δ nanopowders (Re = Yb3+, Y3+, Sm3+).

Figure 16.8: TEM micrographs of Ce0.80Ye0.20O2–δ synthesized by SPRT method.

All results show that crystallites form agglomerates and aggregates as could be found in literature [80]. This trend has been confirmed by decreasing of specific surface area values [10, 57, 65]. From an energetic point of view, the agglomeration process is a more stable configuration that allows crystallite growth and nanoparticles have a natural propensity to agglomerate. The sizes of particles are nanometric (Table 16.1), which corresponds to results determined by XRPD.

16.5.2 Densification and microstructure of sintered samples After sintering process of pressed Ce0.80Re0.20O2–δ nanopowders (Re = Yb3+, Y3+, Sm3+) at temperature 1,550 °C for 2 h, densification between ∼86 and 90% occurs (Table 16.2) [81]. In comparison to values of theoretical density [81], maximum density was achieved for the sample Ce0.80Y0.20O2–δ (90%). In this context, parameters like the green structure with pore size distribution and particle size [50, 83], have a key role

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Table 16.2: Theoretical and Archimedes’s densities of sintered samples at temperature 1,550 °C for 2 h in air atmoshere of doped CeO2 nanopowders obtained by sprt method. ρteor. [g/cm]

ρexp. [g/cm]

TD %

CeO []

.

.



Ce.Yb.O–δ []

.

.



Ce.Y.O–δ

.

.



Ce.Sm.O–δ []

.

.



COMPOSITION

in attaining high density values. Thus, since nanopowder Ce0.80Y0.20O2–δ possesses micro and mesopores [10, 57, 65], and smallest particles size, it was expected that sintering process achieves the highest density (Table 16.2). Figure 16.9 shows micrographs of sintered sample with the highest value of density Ce0.80Y0.20O2–δ. The grain size is in the range of 1–2 µm.

Figure 16.9: SEM micrographs of Ce0.80Y0.20O2–δ sintered sample at temperature 1,550 °C for 2 h in ambiental atmosphere.

The presence of larger grains surrounded by smaller grains indicated that the grain growth was gained mostly by mechanism of Ostwald ripening. On the other hand, the presence of curved grain boundaries is telling that the process of sintering is still not finished in some part of microstructure [50, 83]. This confirmed the presence of porosity and cracks at surface of the sample, which is in accordance with the obtained relative density. Thus, it can be concluded that different particle morphologies may lead to different packing densities in the sample during sintering process [50, 81, 83, 84].

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16.5.3 Electrical Properties of Sintered Samples The electrochemical impedance spectroscopy is a method for electrical characterization of solid electrolytes, especially for the measurement of bulk and grain boundary resistance, different electrode process, and electronic and ionic conductivity [8–12, 48, 50, 77, 78, 83, 84]. The spectra obtained by using electrochemical impedance spectroscopy are usually present in the form of Nyquist plots. Typical Nyquist plots are most often presented as negative of imaginary component of impedance (–Zimag) in a function of real component of impedance (Zreal). Additionally, a typical Nyquist plot of the solid electrolyte consists of three semicircles: the first and second semicircles are positioned in range of high and intermediate frequency and are attributed to bulk and grain boundary [50, 83, 84]. The third semicircle, positioned in a lower frequency range, belongs to the processes at the electrode [42]. The processes that occur in the measured samples could be presented using equivalent circuits, usually with resistive, capacitive and constant phase elements. Present equivalent circuits with both constant [8–12, 48] and distributed capacitive elements [8–12, 48] were widely applied for characterization of electrical properties of sintered ceramics. Thus, semicircles in a high-frequency range could be characteristic of the bulk resistance of crystallite grains (Rb) with the corresponding geometric capacitance (Cg) of the sample [8–12, 48]. When the impedance semicircles were clearly separated (RbCg≪RgbCgb), the values of resistance of bulk and grain boundary may be read separately, where low-frequency semicircles intercept the real axis [8–12, 48]. The geometric capacitance (ωmax,b) can be calculated based on values corresponding to maximum of frequency of high-frequency semicircle according to the equation: ωmax, b = 1=Rb · Cb

(16:9)

In the case of low frequency semicircle, it could be described by using equivalent circuit which consists of parallel connection of the resistance of grain boundary (Rgb) and the intergranular capacitance (Cgb), and frequency can be calculated by using the following equation: ωmax, gb = 1=Rgb · Cgb

(16:10)

By increasing the operation temperature the resistance elements Rb and Rgb decrease with increasing ωmax, gb and the Nyquist graphs shift towards the low-frequency semicircle [8–12, 48]. In this case, with increase of temperatures instead separate values of Rb and Rgb in the corresponding frequency range, it was possible to read only the sum of Rb + Rgb [8–12, 48]. In this paper was examined ionic conductivity of the sintered samples with different dopants Ce0.80Re0.20O2–δ (Re = Yb3+, Y3+, Sm3+), as solid electrolyte for the future

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application in IT-SOFC systems. All values of ionic conductivity were measured in a temperature range from 500 °C to 700 °C, with the corresponding step of 50 °C. The recorded Nyquist plots of Ce0.80Y0.20O2–δ solid electrolyte, which shows the highest ionic conductivity, are presented in Figure 16.10.

Figure 16.10: Complex impedance plots of the sintered samples Ce0.80Y0.20O2–δ recorded in the temperature range 500–700 °C in ambient atmosphere (at each diagrams are present temperatures of measurements; arrows presented the points of intersections with the real axis and readinged values of Rb + Rig).

In Figure 16.10, in the frequency range of 1.0 Hz–0.1 MHz, the recorded high- and intermediate-frequency semicircles slowly disappear with increasing temperature and only a single semicircle [8–12, 48] was recorded. In this case, the values of total

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resistance were obtained from the cross section of semicircles with the Zreal, and were presented as sum of the Rb + Rgb (marked by arrows in Figure 16.10) [8–12, 48]. In available temperature from 600 to 700 °C (Figure 16.10), in area of low frequencies, new semicircles were observed, whose presence can be attributed to reactions of oxygen electrode in the form of O2/O2− [8–12, 48]. The values of total ionic conductivity of sintered samples Ce0.80Re0.20O2–δ (Re = Yb3+, Y3+, Sm3+) at different temperatures (Table 16.3) were calculated from values of measured resistances. Based on detailed analysis of the obtained results it can be concluded that the highest value of ionic conductivity showed sample Ce0.80Y0.20O2–δ at 700 °C (2.19 × 10−2 Ω−1cm−1). In comparison with values for conductivity obtained in this paper, with conductivities of other ion oxygen conductors [77, 78], it can be said that values are very similar to each other. However, due to a lot of advantages of the SPRT method (spontaneity at ambient temperature, very fast terminates of reaction, final product was very precisely stoichiometric, method was much cheaper than other methods) we can suggest that SPRT is one of the most promising methods for synthesis of solid electrolytes. Table 16.3: The temperature dependence of total ionic conductivity (κ) of the sintered samples composition Ce0.80Re0.20O2–δ (Re = Yb3+, Y3+, Sm3+). COMPOSITION

κ × − κ × − κ × − κ × − κ × − Ea − − − − − − − − (Ω cm ) (Ω cm ) (Ω cm ) (Ω cm ) (Ω−cm−) (eV)  °C  °C  °C  °C  °C

CeO []

.

.

.

.

. .

Ce.Yb.O–δ []

.

.

.

.

. .

Ce.Y.O–δ

.

.

.

.

. .

Ce.Sm.O–δ []

.

.

.

.

. .

Based on the results listed in Table 16.3, the dependence logκ = f(1/T) for the sintered sample Ce0.80Y0.20O2–δ is shown in Figure 16.11. Energy activation value (Ea) was determined from Arrhenius plots based on equation: lnðσ · TÞ = ln A − ðEa =kÞ · ð1=T Þ

(16:11)

where parameters σ, T, A and k presents the conductivity, the absolute temperature, the pre-exponential factor and the Boltzmann constant, respectively. Obtained results showed that activation energy for the total conductivity of sintered sample Ce0.80Y0.20O2–δ was 0.28 eV. Based on literature data, it can be noted that value of Ea determined in this paper was significantly lower compared to the activation energy of other doped CeO2 [77, 78, 81]. The reason for that may be the easier processing of SPRT nanopowders and the forming of a well-ordered structure

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Figure 16.11: The plot of dependence logκ = f(1/T) of the sintered sample Ce0.80Y0.20O2–δ measured at intermediate temperatures from 500 °C to 700 °C in ambient atmosphere.

during sintering process, which allows faster and easier activation carriers of conductivity, and thus decrease of Ea.

16.6 Conclusions Today, SOFCs as third-generation devices occupy a leading position compared to the other fuel cell types. Doped CeO2 with ions of rare earth as solid electrolyte is increasingly used due to its better electrical properties at intermediate temperature range from 500 °C to 700 °C (IT-SOFCs). Nanostructured solid solutions in the form of oxides Ce0.80Re0.20O2–δ (Re = Yb3+, Y3+, Sm3+) were successfully synthesized by self-propagating room temperature method. XRPD and Raman spectroscopy confirmed fluorite structures like cerium-oxide (space group Fm3m) for all samples. XRPD and TEM analysis revealed the particle size less than 5 nm. After sintering process at 1,550 °C during 2 h, the density of fine crystalline powders reached 90% of theoretical density. SEM analysis confirmed that the sintered samples have grain size distribution in the range of 1–2 µm. The maximal determined value of ionic conductivity was found at 700 °C (2.19 × 10−2 Ω−1cm−1) for the sample cerium-oxide

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doped with Y3+ ions. Based on presented results together with very easy and inexpensive method for obtaining nanopowders doped CeO2, it can be said that this material has potential for application as an electrolyte for fuel cells while working at intermediate temperature.

References [1] [2]

[3] [4]

[5]

[6] [7]

[8] [9] [10]

[11]

[12]

[13] [14] [15]

IRENA (2018), Global Energy Transformation: A roadmap to 2050, International Renewable Energy. This report is available for download from www.irena.org/publications. Zucchetti M, Candido L, Khripunov V, Kolbasov B, Testoni R, Fusion power plants, fission and conventional power plants. Radioactivity, radiotoxicity, radioactive waste, https://doi.org/ 10.1016/j.fusengdes.2018.05.049. Shahsavari A, Akbari M. Potential of solar energy in developing countries for reducing energyrelated emissions. Renewable Sustainable Energy Rev 2018, 90, 275–91. Stojmenović M, Vujković M, Matović L, Krstić J, Đukić A, Dodevski V, Živković SM, Mentus S. Complex investigation of charge storage behavior of microporous carbon synthesized by zeolite template. Micro Meso Materials 2016, 228, 94–106. Dodevski V, Stojmenović M, Vujković M, Krstić J, Krstić S, Bajuk–Bogdanović D, Kuzmanović B, Kaluđerović B, Menus S. Complex insight into the charge storage behavior of active carbons obtained by carbonization of the plane tree seed. Electrochim Acta 2016, 222, 156–71. Zhou1 M, Xu1 Y, Lei Y. Heterogeneous nanostructure array for electrochemical energy conversion and storage. Nano Today 2018, 20, 33–57. Marceta Kaninski MP, Saponjic DP, Perovic IM, Maksic AD, Nikolic VM. Electrochemical characterization of the Ni–W catalyst formed in situ during alkaline electrolytic hydrogen production – Part II. Appl Catal A Gen 2011, 405, 29–35. Stojmenović M, Bosković S, Bučevac D, Prekajski M, Babić B, Matović B, Mentus S. Electrical characterization of multidoped ceria ceramics. Ceram Int 2013, 39, 1249–55. Stojmenović M, Bošković S, Žunić M, Varela JA, Prekajski M, Matović B, Mentus S. Electrical properties of multidoped ceria. Ceram Int 2014, 40, 9285–92. Stojmenović M, Žunić M, Gulicovski J, Bajuk–Bogdanović D, Holclajtner–Antunović I, Dodevski V, Menus S. Structural, morphological, and electrical properties of doped ceria as a solid electrolyte for intermediate–temperature solid oxide fuel cells. J Mater Sci 2015, 50, 3781–94. Stojmenović M, Bošković S, Milan Žunić M, Babić B, Matović B, Bajuk-Bogdanović D, Menus S. Studies on structural, morphological and electrical properties of Ce1-xErxO2–δ (x = 0.05–0.20) as solid electrolyte for IT–SOFC. Mater Chem Phys 2015, 153, 422–31. Stojmenović M, Žunić M, Gulicovski J, Dodevski V, Prekajski M, Radulović A, Menus S. Structural, morphological and electrical properties of Ce1−xRuxO2−δ (x=0.005–0.02) solid solutions. Ceram Int 2016, 42, 14011–20. Appleby AJ, Foulkes FR. Fuel Cell Handbook. New York: Van Nostrand Reinhold, 1989. Republished by Krieger Publishing Company, Melborne, FL, 1993. Wang CY. Fundamental models for fuel cell engineering. Chem Rev 2004, 104, 4727–66. Winter M, Brodd RJ. What are batteries, fuel cell and supercapacitors?. Chem Rev 2004, 104, 4245–69.

16 Ceramic electrolytes for solid oxide fuel cells (SOFCs)

233

[16] Alves HJ, Junior CB, Niklevicz RR, Frigo EP, Frigo MS, Coimbra-Araújo CH. Overview of hydrogen production technologies from biogas and the applications in fuel cells. Int J Hydrogen Energy 2013, 38, 5215–25. [17] Galvagno A, Chiodo V, Urbani F, Freni F. Biogas as hydrogen source for fuel cell applications. Int J Hydrogen Energy 2013, 38, 3913–20. [18] Liu J, Zhang S, Wang W, Gao J, Liu W, Chen C. Partial oxidation of methane in a Zr0.84Y0.16O1.92eLa0.8Sr0.2Cr0.5Fe0.5O3-δ hollow fiber membrane reactor targeting solid oxide fuel cell applications. J Power Sources 2012, 217, 287–90. [19] Takagi Y, Kerman K, Ko C, Ramanathan S. Operational characteristics of thin film solid oxide fuel cells with ruthenium anode in natural gas. J Power Sources 243(201), 1–9. [20] http://hr.scribd.com/doc/12886440/Gorivne-celije, https://www.slideshare.net/iuslu/sofc [21] Aylward JR, Whitener EM. Dissolution of Zirconium in HCl ‐ Methanol. J Electrochem Soc 1962, 109, 87–91. [22] Isenberg AO. Electrode Materials on Processes for Energy Conversionand Storage. McIntyre JDE, Srinivasan S, Will FG (edited by), Pennington: Electrochem. Soc. Inc., NJ 77-6, 1977, 682. [23] Fischer W, Rohr FJ, U.S. Patent #3, 718, 506 (Feb. 27, 1973). [24] Srinivasan S, Dave BB, Murugesamoorthi KA, Parthasarathy A, Appleby AJ. in Fuel Cell Systems. Blomen LJMJ, Mugerwa MN (edited by), New York: Plenum Press, 1993, 37. [25] Myles KM, McPheeters CC. Monolithic solid oxide fuel cell development. J Power Sources 1990, 29, 311–19. [26] Khandkar AC, Elangovan S, Hartvigsen JJ. Ceramic Transactions 1996, 65, 263–77. [27] Stevenson JW, Singh P, Low Cost Modular SOFC Development, Technical Progress Report, Part 1: Development of Advanced Materials and Fabrication Techniques for SOFC Components, March 2002. [28] Mirković M, Dosen A, Erić S, Stojmenović M, Matović B, Rosić A. Structural, Morphological and Electrical Properties of Multi-Doped Calcium Phosphate Materials as Solid Electrolytes for Intermediate Temperature Solid Oxide Fuel Cells. Science of Sintering 2018, 50, 95–109. [29] Egelja A, Pašalić S, Dodevski V, Kragović M, Stojković-Simatović I, Radovanović Ž, Stojmenović M, Structural, morphological and electrical properties of alumina/YAG composites as solid electrolyte for IT – SOFC, Science of Sintering, UDK: 692.533.1; 546.62, Accepted Manuscripts, Published: 2018-07-26. [30] Panagiotopoulou P, Papavasiliou J, Avgouropoulos G, Ioannides T, Kondarides DI. Water–gas shift activity of doped Pt/CeO2 catalysts. Chem Eng Jour 2007, 134, 16–22. [31] Li H, Lu G, Wang Y, Guo Y, Guo Y. Synthesis of flower-like La or Pr-doped mesoporous ceria microspheres and their catalytic activities for methane combustion. Catalysis Comm 2010, 11, 946–50. [32] Chen H-T. First-principles study of CO adsorption and oxidation on Ru-Doped CeO2(111) surface. J Phys Chem C 2012, 116, 6239–46. [33] Ma X, Feng X, He X, Guo H, Lv L, Guo J, Cao H, Zhou T. Mesoporous CuO/CeO2 bimetal oxides: One-pot synthesis, characterization and their application in catalytic destruction of 1,2dichlorobenzene. Micro Meso Mat 2012, 158, 214–18. [34] Li C, Zhang X, Dong W, Liu Y. High photocatalytic activity material based on high‐porosity ZnO/CeO2 nanofibers. Mater Letters 2012, 80, 145–47. [35] Zhang X, Ohara S, Maric R, Okawa H, Fukui T, Yoshida H, Inagaki T, Miura K. Interface reactions in the NiO–SDC–LSGM system. Solid State Ionic 2000, 133, 153–60. [36] Buckkremer HP, Diekmann U, de Haart LGJ, Kabs H, Stimming U, Stöver D, Solis oxide fuel cell V: Advances in the anode-supported planar SOFC technology, edited by Stimming U, Singhal SC, Tagawa H, Lehnert W, Electrochemical Proceedings, 97-18 (1997) 160–70.

234

Marija Stojmenović, Vladimir Dodevski

[37] Bloom I, Krumpelt M, Intermediate temperature electrolytes for SOFC, proceedings of the Fourth Annual Fuel Cells Contractors Review Meeting, U.S. DOE/METC, July, 1992. [38] Worrell WL. Topics in Applied Physics: Solid Electrolytes. Geller S (edited by), Berlin Heidelberg New York: Springer-Verlag, Vol. 21, 1977, 143–68. [39] Minh NQ. Ceramic fuel cells. J Am Ceram Soc 1993, 76, 563–88. [40] Ivers-Tiffee E, Weber A, Herbstritt D. Materials and technologies for SOFC-components. J Eur Ceram Soc 2001, 21, 1805–11. [41] Molenda J, Świerczek K, Zając W. Functional materials for the IT-SOFC. J Powder Sources 2007, 173, 657–70. [42] Arachi Y, Sakai H, Yamamoto O, Takeda Y, Imanishai N. Electrical conductivity of the ZrO2– Ln2O3 (Ln=lanthanides) system. Solid State Ionics 1999, 121, 133–39. [43] Etsell TH, Flengas SN. The electrical properties of solid oxide electrolytes. Chem Rev 1970, 70, 339–76. [44] Haering C, Roosen A, Schichl H, Schnfller M. Degradation of the electrical conductivity in stabilised zirconia system: Part II: Scandia-stabilised zirconia. Solid State Ionics 2005, 176, 261–68. [45] Badwal SPS, Ciacchi FT, Rajendran S, Drennan J. An investigation of conductivity, microstructure and stability of electrolyte compositions in the system 9 mol% (Sc2O3–Y2O3)– ZrO2(Al2O3). Solid State Ionics 1998, 109, 167–86. [46] Pederson LR, Singh P, Zhou XD. Application of vacuum deposition methods to solid oxide fuel cells. Vacuum 2006, 80, 1066–83. [47] Ji Y, Liu J, Lu Z, Zhao X, He T, Su W. Study on the properties of Al2O3-doped (ZrO2)0.92(Y2O3)0.08 electrolyt. Solis State Ionic 1999, 126, 277–83. [48] Prekajski M, Stojmenović M, Radojković A, Branković G, Oraon H, Subasri R, Matović B. Sintering and electrical properties of Ce1-xBixO2–δ solid solution. J Alloy Compd 2014, 617, 563–68. [49] Thangadurai V, Weppner W. Studies on Electrical Properties of La0.8Sr0.2Ga0.8Mg0.2O2.80 (LSGM) and LSGMSrSn1-xFexO3 (x = 0.8; 0.9) Composites and Their Chemical Reactivity. Electrochem Acta 2005, 50, 1871–77. [50] Mitic VV, Paunovic V, Purenovic J, Jankovic S, Kocic L, Antolovic I, Rancic D. The contribution of fractal nature to BaTiO3-ceramics microstructure analysis. Ceram Int 2012, 38, 1295–301. [51] Yamaji K, Horita T, Ishikawa M, Sakai N, Yokokawa H. Chemical stability of the La0.9Sr0.1Ga0.8Mg0.2O2.85 electrolyte in a reducing atmosphere. Solid State Ionics 1999, 121, 217–24. [52] Yan JW, Matsumoto H, Enoki M, Ishihara T. High-power SOFC using La0.9Sr0.1Ga0.8Mg0.2O3-d composite film. Electrochem Solid-State Lett 2005, 8, A389-391. [53] Shannon RD. Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides. Acta Crystallogr 1976, A32, 751–67. [54] Lide DR. CRC Handbook of Chemistry and Physics. 73rd edition, Boca Raton: CRC Press, 1993, 4–121. [55] Chiang Y-M, Birnie DP, Kingery WD. Physical Ceramics. USA: John Wiley & Sons Inc., 1997, 16, 72, 84, 263-350. [56] Kofstad P. Nonstoichiometry, Diffusion, and Electrical Conductivity in Binary Metal Oxides. USA: JohnWiley & Sons, 1972, 1–21. [57] Stojmenović M, Bošković S, Zec S, Babić B, Matović B, Bučevac D, Dohčević Mitrović Z, Aldinger F. Characterization of nanometric multidoped ceria powders. J Alloy Compd 2010, 507, 279–85. [58] Stojmenović M, Milenković MC, Banković PT, Žunić M, Gulicovski JJ, Pantić JR, Bošković SB. Influence of temperature and dopant concentration on structural, morphological and optical

16 Ceramic electrolytes for solid oxide fuel cells (SOFCs)

[59] [60] [61] [62] [63] [64] [65] [66]

[67] [68] [69] [70] [71] [72]

[73] [74] [75] [76]

[77]

[78]

[79]

235

properties of nanometric Ce1-xErxO2–δ (x = 0.05–0.20) as a pigment. Dyes and Pigments 2015, 123, 116–24. http://www.uwgb.edu/dutchs/PETROLGY/Fluorite%20Structure.HT. Bailar JC, Emeleus HJ, Nyholm R, Trotman-Dickenson AF. Comprehensive Inorganic Chemistry. New York: Pergamon Press, 1973, 99. Qi X, Lin YS, Swartz CT. Electric conductivity and oxygen permeability of modified cerium oxides. J Mat Science 2003, 38, 1073–79. Kümmerle EA, Heger G. The Structures of C-Ce2O3+δ, Ce7O12, and Ce11O20, J. Solid State Chem 1999, 147, 485–500. Kim DJ. Lattice parameters, ionic conductivities, and solubility limits in fluorite-structure MO2 oxide (M = Hf4+, Zr4+, Ce4+, Th4+, U4+) solid solutions. J Am Ceram Soc 1989, 72, 1415–21. Hong SJ, Virkar AV. Lattice parameters and densities of rare-earth oxide doped ceria electrolytes. J Am Ceram Soc 1995, 78, 433–39. Gotte A, Hermansson K, Baudin M. Molecular dynamics simulations of reduced CeO2: Bulk and surfaces. Surf Sci 2004, 552, 273–80. Terribile D, Trovarelli A, Llorca J, de Leitenburg C, Dolcetti G. The synthesis and characterization of mesoporous high-surface area ceria prepared using a hybrid organic/ inorganic route. J Catal 1998, 178, 299–308. Yu X, Li F, Ye X, Xin X, Xue Z. Synthesis of cerium(IV) oxide ultrafine particles by solid-state reactions. J Am Ceram Soc 2000, 83, 964–66. Tsuzki T, McCormik PG. Synthesis of ultrafine ceria powders by mechanochemical processing. J Am Ceram Soc 2001, 84, 1453–58. Mokkelbost T, Kaus I, Grande T, Einarsrud M. Combustion synthesis and characterization of nanocrystalline CeO2-based powders. Chem Mater 2004, 16, 5489–94. Gnanam S, Rajendran V. Synthesis of CeO2 or α–Mn2O3 nanoparticles via sol–gel process and their optical properties. J Sol-Gel Sci Tech 2011, 58, 62–69. Mori T, Ikegami T, Yamamura H. Application of a Crystallographic Index for Improvement of the Electrolytic Properties of the CeO2‐ Sm2O3 System. J Electrochem Soc 1999, 146, 4380–85. Shing OP, Ping TY, Hin TYY. Mechanochemical synthesis and characterization of calciumdoped ceria oxide ion conductor. IOP Conf Series: Mater Sci Eng 2011, 17, 012017, DOI: 10.1088/1757-899X/17/1/012017. Zhang H, Wang J, Wang S, Li Z. Conductivity of cerium oxides doped by trivalent cations. Trans Nonferrous Met Soc China 2007, 17, s565-s569. Park SH, Yoo HI. Defect-chemical role of Mn in Gd-doped CeO2. Solid State Ionics 2005, 176, 1485–90. Aguirre M, Paulis M, Leiza JR. UV screening clear coats based on encapsulated CeO2 hybrid latexes. J Mater Chem A 2013, 1, 3155–62. Siqueira Júnior JM, Brum Malta LF, Garrido FMS, Ogasawara T, Medeiros ME. Raman and rietveld structural characterization of sintered alkaline earth doped ceria. Mater Chem Phys 2012, 135, 957–64. Yu E, Pikalova AA, Murashkina VI, Maragou AK, Demin VN, Strekalovsky PE. Tsiakaras, CeO2 based materials doped with lanthanides for applications in intermediate temperature electrochemical devices. Int J Hydrogen Energy 2011, 36, 6175–83. Kahlaoui M, Chefi S, Inoubli A, Madani A, Chefi C. Synthesis and electrical properties of codoping with La3+, Nd3+, Y3+, and Eu3+ citric acid-nitrate prepared samarium-doped ceria ceramics. Ceram Int 2013, 39, 3873–79. Tsunekawa S, Wang J-T, Kawazoe Y. Lattice constants and electron gap energies of nano- and subnano-sized cerium oxides from the experiments and first-principles calculations. J Alloy Compd 2006, 408–412, 1145–48.

236

Marija Stojmenović, Vladimir Dodevski

[80] Phoka S, Laokul P, Swatsitang E, Promarack V. Mater. Synthesis, structural and optical properties of CeO2 nanoparticles synthesized by a simple polyvinyl pyrrolidone (PVP) solution route. Chem Phys 2009, 115, 423–28. [81] Doroftei C, Popa PD, Iacomi F, Leontie L. The influence of Zn2+ ions on the microstructure, electrical and gassensing properties of La0.8Pb0.2FeO3 perovskite. Sensors Actuators B 2014, 191, 239–45. [83] Mitic VV, Kocic L, Paunovic V, Bastić F, Sirmić D. The fractal nature materials microstructure influence on electrochemical energy sources. Science of Sintering 2015, 47, 195–204. [84] Mitić VV, Kocić LM, Tidrow S, Fecht H-J. Structures, fractals and energy. In: Raj B, Van de Vorde M, Mahajan Y (eds.), Nanotechnology for Energy Sustainability. Vol. 2, Weinheim, Germany: Wiley-VCH Verlag GmbH&Co KgaA, 2017, 781–808.

Silvana B. Dimitrijević, Stevan P. Dimitrijević

17 E-scrap processing: theory and practice Abstract: The importance of recycling the waste electrical and electronic equipment (WEEE), in recent years, has been taken into increasing concern and consideration not only by the government, but also by their hazardous material contents. Electronic waste can be defined as a mixture of various metals, particularly copper, aluminum and steel, with various types of plastics and ceramics. Recycling of electronic waste is an important subject not only from the point of waste treatment, but also from the recovery aspect of valuable materials. Pyrometallurgical processing has been a traditional technology for recovery of the precious metals from waste electronic equipment. In the past two decades, the most active research area on recovery of metals from electronic scraps is recovering the precious metals using the hydrometallurgical techniques. Compared with the pyrometallurgical processing, the hydrometallurgical method is more exact, more predictable and more easily controlled. In the last decade, the recovery of metals by biotechnology has been one of the most promising technologies. Biometallurgy has the potential for a major technology breakthrough for the materials and minerals industry due to a great interest shown by the major international companies for this new technology. Understanding the biochemical processes, involved in treatments of metals, has been the subject to growing investigations for the last 20 years. At present, the research and development are in progress for a number of metals such as copper, nickel, cobalt, zinc, gold and silver. However, the activity of leaching bacteria is applied for recovery of gold and silver only to remove the interfering metal sulfides from ore bearing the precious metals prior to the cyanidation treatment. Recent research trend is to use the combined methods for optimal results. Keywords: E-scrap processing, pyrometallurgy, hydrometallurgy, biometallurgy, gold, silver, recycling

Acknowledgment: This work has resulted from the projects funded by the Ministry of Education, Science and Technological Development of the Republic of Serbia, No. 34024: “Development of Technologies for Recycling of Precious, Rare and Associated Metals from Solid Waste in Serbia to High Purity Products” and No. 34033: “Innovative Synergy of By-products, Waste Minimization and Clean Technologies in Metallurgy” for which the authors would like to thank on this occasion. Silvana B. Dimitrijević, Mining and Metallurgy Institute Bor, Bor, Serbia, [email protected] Stevan P. Dimitrijević, Innovation center of the TMF Faculty, Belgrade, Serbia, University of Belgrade, Belgrade, [email protected] https://doi.org/10.1515/9783110627992-017

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17.1 Introduction E-scrap processing has been actualized from the last few decades of the twentieth century since the amount of e-waste is growing, which was caused by the shorter useful lifespan of devices and products. The importance of these technologies is reflected in recovering the valuable materials and solving the environmental problems caused by hazardous materials contained in the e-waste [1]. Waste printed circuit boards (WPCBs) are the most worthy and most common type of the e-waste, after its disassembling. They contain mostly plastics (nearly 40%), about 30% are the metals and remaining are, other than plastics non-metals, like glass, ceramics and similar. Technologies for the process usually include a combination of methods due to the complexity of processed materials. This includes disassembling, shredding, mechanical and magnetic separation, and different chemical and metallurgical processes. Metal recovery always includes different extractive metallurgy methods, often all types of it, pyrometallurgy, hydrometallurgy and electrometallurgy [2–4]. Pyrometallurgy is often used as the start of the processing after the mechanical route. But the incineration is often connected by the emission of the hazardous materials. Some of the toxic metals (Cd, Pb) were the components in the soldering and brazing alloys, used in electronics, till recently and easily fumed during the melting of the metallic phase. Furthermore, the resin components during the combustion and/or partial pyrolysis produce brominated hydrocarbons, benzenes and phenols [5]. These are the reasons for the more sophisticated use of pyrometallurgy. Modification of the pyrometallurgical route was proposed, including low-temperature melting followed by centrifugation separation and [6], a two-step process that included oxidation of metallic granulate followed by pyrometallurgical refining in a DC arc-furnace [7], and vacuum metallurgy [8]. The most active research area on recovery of metals from electronic scraps is recovering the precious metals using the hydrometallurgical techniques [9–11]. Hydrometallurgy has a lot of advantages in comparison to pyrometallurgy. It does not produce gaseous emissions; is more energy-efficient; has a higher recovery rate, higher selectivity; and is comparatively easier to operate and control [12–14]. Furthermore, it has a relatively low capital cost and suitability for small-scale applications [15]. The leaching agents are commonly mineral acids or their combinations. The alkaline leach is also used, especially in the pre-treatment phase [16]. Recovery of metals is further proceeded with the various physical–chemistry methods, from simple precipitation to modern procedures like solvent extraction, use of organics solvents, ultra/ nanofiltration/RO, and ion-exchange [17–19]. However, hydrometallurgy has several disadvantages that limit its application on the industrial scale. They are related to the low rate of the processes, a highly corrosive environment with special requirements for the equipment and high costs of purifying waste solutions to fitful modern environmental standards. Because of this, hydrometallurgy cannot be used alone, and thus it is almost always combined with pyrometallurgy, followed by

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electrometallurgical (electrochemical) processes (electrorefining or electrowinning) for full metal separation and recovery [20, 21]. The integration of biotechnology into the hydrometallurgy has evolved into an alternate metallurgical area collectively known as biohydrometallurgy or biometallurgy (bioleaching) and is excessively used for e-waste recycling [22]. Biological metal recovery is based on the same mechanism of the hydrometallurgical processes with the use of microorganisms for the production of reagents for metals extraction [23]. In the last decades, biohydrometallurgical strategies have gained increasing prominence in this field. It is due to high efficiency and high sustainability treatment for metal extraction from PCBs [24]. Biotechnologies alone or in combination with other hydro- or electro-metallurgy processes are proven in the recovery of a large number of non-ferrous metals, and especially copper and gold [25–27]. E-scrap processing for non-ferrous and precious metals production in the Mining and Metallurgy Institute Bor, Serbia, and Innovation Centre of Faculty of Technology and Metallurgy, University of Belgrade, Serbia, was investigated by a group of authors [28–42] based on the actual trends in related technology and economy fields. These investigations included the recycling of various secondary raw materials with the primary goal to obtain silver, gold and platinum group of metals (PGMs), of which primarily Pt, Pd and Rh [28–31]. It should be noted that copper was a significant product of recycling. Economy of copper recovery is based on high content of copper in the e-waste, and the ease of obtaining high grade by electrorefining [32]. Even the possibility of obtaining lead and tin was studied, with partial results of the high yield but satisfactory for very precise economic calculation of the whole process of the e-scrap recycling [33]. Selective metal recovery was an important realized objective of the research [34]. Supplementary products obtained in the recycling process were rare-earth elements (In, Ga) [35] and even components from the non-metallic fraction of the e-waste [36, 37]. The additional goal of research was to obtain the materials of higher value than pure metals, such as the microsized silver powder for electrical contacts [38], cadmium-free, environmentally friendly silver brazing alloys [39–41] and gold organic complex for electroplating [42].

17.2 Recent developments of e-scrap processing in practice at large scale 17.2.1 Pyrometallurgical recovery of metals from e-scrap In practice, pyrometallurgy represents a dominant processing method for waste PCBs. Processing is performed through the black copper route. This route means that the waste is processed together with the primary copper sources by main technologies for that purpose [43].

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Black copper name is derived from the black color of the Cu(I)-oxide, which is oxidized through the process and then reacts with the more easily oxidizing elements/metals (Si, Al, Ca, Cr, Mg) and consequently converts into copper by the reduction reaction in the melt. Oxidized elements (practically impurities in the system) are transferred in oxides and make the slag. This route uses the metals with lower oxidation-reduction potential for copper conversion and leaves the precious metals in the melt. Since the majority of the metals are toxic or have a low price, it is beneficial to the process. Technologically, it is not perfect since some of the metals are valuable (Ni, Sn) and distribute in both melt and slag, which is even more important. To this group belong Pb, Co, Bi, Pb, Ni, and Sn. Most of them are the constituent of the WPCBs. The main copper production processes are autogenic, where the most present is the flash-melting process developed by the Outokumpu company. Distribution of the PCBs materials through the flash-melting process is studied in detail, although the process is fully optimized just for copper and the precious metals [44]. The limitation of the input feed is around 10–15%, which constraints possibilities for e-waste recycling by this process. Several commercial smelting operations charge e-waste into a copper flashsmelting furnace as a secondary copper-bearing material; several large smelters in Europe process a few hundred kilotons of WPCBs per year [43], and another example is the Horne smelter in Canada [45]. Noranda process, as a similar autogenic pyrometallurgy process, is also suitable for the recycling of the used electronics. In Quebec, Canada, about 100 kt of this material is used annually [1]. Besides the technologies for copper production from primary sources, zinc and lead recovery processes are also very suitable for the recovery of e-waste in general. With an increasing focus on the sustainable use of resources, in the last decades, interest in the processing of secondary feed material sources, in these facilities, has substantially increased. Ausmelt Technology has proven to the economic recovery of values from such sources. Whyalla Zinc facility for the treatment of zinc bearing secondary feeds in Australia is a good example [46]. Umicore’s integrated metal (Pb–Cu–Zn) smelter and refinery facilities in Hoboken use advanced smelting processes at the start for “low-grade” e-waste (with lower content of precious metals) and direct feeds of high content of Au waste such as PCBs for following separate metals recycling plant. With the use of mainly pyrometallurgical processes, in combination with hydrometallurgical processes followed by electrorefining, recover 17 precious and specialty metals with a high recovery rate (over 75% for IT waste) and with full compliance with regulations on environmental protection of the EU [47]. In total 250 kt of feed-materials were treated annually in the middle of the first decade of the century, and capacity was expanded to 500 kt per year, recently, using over 200 complex input streams, making it as one of the world’s largest precious metals recycling facilities [47, 48].

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Despite promising results, vacuum pyrometallurgy is still not applied at an industry scale [8]. Similar is for other proposals for the improvements of the black copper route, which is complicated and consists of many phases [7, 32]. Nonmetallic fractions of the e-waste, in these processes, are used as both, fuels and reducing agents, and are their advantage [21]. Despite confirmed use in practice at a large scale, the pyrometallurgical approach has substantial disadvantages, of which the most important are [15, 21, 49, 50]: 1) It is time-consuming, and requires a long term for the full process (several weeks at least). 2) It has a minimum of three pyro-processes (in three furnaces), reduction (from where black copper originated), oxidation and fire refining. Usually, it consists of four pyrometallurgy phases (last one in the process of precious metals refining). 3) It causes air pollution; high costs for just fitful legislation, which is not even close to the high environmental considerations. 4) It has significant loss of noble metals; it (again) fitful just legislation/recommendations (of EU), and is close to 20%. 5) It is not an independent; it has to be complemented with several hydrometallurgy phases and electrorefining processes. Finally, it is important to stress that calculation showed that the minimum plant capacity for the process is 30 kt/year, for the economic viability and even facilities with higher (100 kt per annum) capacity, and higher benefit/cost rate, are very sensitive on the variation of the raw material cost [51].

17.2.2 Hydrometallurgical recovery of metals from e-scrap The use of hydrometallurgy (HM) at the largest scale, connected to the e-waste, is still the treatment of the anodic slime after the electrorefining of the copper [51]. However, it is not a pure HM route and does not use all the advantages of it. Hydrometallurgy route is characterized by the wide use of pre-treatments. They can be mechanical and chemical, and both are critical for the high selectivity and high recovery rates [16]. The stricter classification of the e-waste, before the processing, is more important than for the pyrometallurgical route. Generally, hydrometallurgy is more selective, has a higher recovery of metals and is more environmentally friendly [21]. Basically, this route consists of two major phases, leaching and further processing of the leachate.

17.2.2.1 Leaching Three hydrometallurgical process options for recycling of copper and precious metals from waste PCBs are in use today [34]:

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a) conventional leaching (use of sulfuric acid, chlorides (halides generally, including the acids, cyanides), b) Recovery of high-purity metals by selective leaching agents (fluoroboric and fluoric acid, ammonia and ammonium salt solutions), c) application of eco-friendly reagents for leaching (formic acid, potassium persulfate, thiourea, and thiosulfates). 17.2.2.1.1 Conventional leaching Gold cyanide leaching has been used in the mining industries from the last decade of the nineteenth century, and the process itself was proposed and patented in 1887 [52]. Besides gold, silver and some PGMs (Pt, Pd) are also suitable for the process, but with lower recovery rates due to the less stable complexes. Cyanides, sodium or potassium, are used in the alkaline environments, with pH between 10 and 11, where they are the most active and the possibility for hydrogen cyanide, as gas, realized is minimum. Environmental issues including (even in near history, Baia Mare, Romania, in 2000) large-scale accidents at different gold/non-ferrous mines that caused severe contamination of water sources have been the reason for abandoning the cyanidation process [53]. Consequently, use of cyanide for e-waste recycling, starting almost 50 years ago with the aim of silver and gold recovery, is very rare, although studies with a new approach and for new material (cell phones) are still performed, even recently [54]. The very high recovery rate (97.5%) for gold was reported for leaching by iodine from PCBs. 17.2.2.1.2 Use of mineral acids and/or chlorides/halogenides Sulfuric acid is used in mining and e-waste processing with the aim to leach copper in the first place and for selective leaching for further recovery of precious metals. Nitric acid is often used for Ag selective leaching after H2SO4 or aqua regia; aqua regia is commonly used for wastes with a high content of precious metals [54]. Leaching with the use of chalcogenides of non-ferrous and precious metals has a major problem with materials for tanks and equipment due to the highly corrosive environment. Hydrochloride acid and halogenic gases are highly toxic and have to be controlled in the process for the working environment and treated to avoid air/ water/soil pollution. Proof for the high popularity of chloride solutions for the leaching of the e-waste in practice is the numerous studies that investigate the recovery of precious metals from chloride leaching solutions of electronic waste, which are discussed in subsequent text. The very high recovery rate (97.5%) for gold was reported for leaching by iodine from PCBs [55]. A novel approach is the use of the organic halide complexes for leaching of precious metals from e-waste [56].

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17.2.2.1.3 Nonconventional leaching Thiourea and thiosulfate were the first replacement for the cyanidation process respect to lower environmental risk and higher safety at work. Thiosulfate leaching is performed in mild alkaline environment (pH = 8–10) and thiourea leaching in strong acid environment (pH = 1–2). Stability constants of the gold complexes, Au(S2O3)23− and Au(CS(NH2)2)+ are substantially high, log K = 28.7 and log K = 22, respectively. However, analog silver, Ag(I), complexes have logK value of only 13 for both ligands [57]. This directly influences the recovery rates. For thiosulfate, 91% for the gold was reported [58], and with the use of thiourea, 89.7% and 48.3% were achieved for gold and silver, respectively [59]. As previously referred to in laboratory conditions, it is clear why these cyanide substitutes are only used for smaller recycling facilities. Organic acids, like acetic and citric, were tested for the recycling of PCBs, but with less than 1% recovery of Au and Pd and only 13.2% and 4.2% of silver, respectively. Pure sulfuric acid also performed badly, with virtually no leach of Au and Pd, and with about one-third of the recovered silver [60]. Thus, with all efforts, these green alternatives did not find an application on a large scale. Developments of new innovative processes with the low environmental impact have been encouraged in the last decades but without real industrial applications. One of the many promising ideas is to enhance leaching by using a deep eutectic solvent, a form of ionic liquid, and additionally improve the process by ultrasonic agitation. However, the study has shown good results only for copper recovery [61].

17.2.2.2 Recovery of precious metals from leachate At least one of the leaching phases is not fully selective, and the metals from the solution are often recovered by selective methods, or separated and then recovered. Metals are usually preconcentrated in the first phase of the process. To obtain valuable metals (copper and precious) from leaching solutions, different methods are in use: Physicochemical methods that do not include adsorption (precipitation, cementation and crystallization), solvent extraction (liquid–liquid extraction in general), ion-exchange (generally, solid-phase extraction) and adsorption (chemical or biological) [60]. Cementation was the most used as the process for copper recovery from solutions with the low concentration (mine waste waters) but is rarely used nowadays, especially for e-waste recycling, although is still present, and useful in some special cases [50]. Solvent extraction is the most used in the high-capacity industry, in hydrometallurgy from primary sources and secondary sources, often combined [52]. However, solid-phase extraction has advantages over liquid–liquid separation, since it has higher recovery efficiency, simpler adsorption–desorption mechanism, better regeneration process, and avoids organic pollution [60].

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Well-known separation processes by use of membranes (reverse osmose or more selective nanofiltration) have been innovated through the last decade with polymer inclusion membranes, which proved successful for the recovery of cupric ions [62]. Another innovative membrane technology for selective recovery of metals from PCB recycling developed recently is the use of liquid membranes [63]. Recovery of precious metals from chloride (halogenide) solutions has been studied intensively in the last decade, with many applied novelties. Among the most prominent research of this kind were: extraction of Ag and Au from chloride electronic waste leach solutions using ionic liquids [64], recovery of gold from hydrometallurgical leaching solution of e-waste via reduction by organic reagents like polyaniline [65], the use of biotechnology with the application of modified persimmon tannin as the new sustainable material for selective recovery of precious metals from acidic chloride solution [66].

17.2.3 Biometallurgical recovery of metals from e-waste 17.2.3.1 Bioleaching of metals from electronic waste From the beginning of the twenty-first century, biotechnology has shown one of the highest potentials as breakthrough technologies for recovering metals from primary and secondary resources. Bioleaching offers numerous advantages compared to conventional processes. These include lower operating costs and investments, better scalability from the small plants to industrial facilities and lower environmental impact [67]. Bioleaching processes use the capabilities of microorganisms such as bacteria or fungi to oxidize or reduce the natural minerals or synthetic compounds and convert them into soluble metal complexes [68]. These can leach various non-ferrous metal sources, but it is massively used only for copper and gold, the former mostly for primary sources (sulfide ores) and later for both primary and secondary sources, such as e-waste [52]. Biological cyanide produced by the cyanogenic micro-organisms is a newly introduced and ecologically friendly process which can be considered as an appropriate alternative for the chemical cyanidation process. With glycine as the source which cyanogenic bacteria species use to transform to cyanide by oxidative decarboxylation substantially high recovery rate (~80%) from gold ore has been reported [69]. Similarly, from the e-waste as the metal source, and the use of different microorganisms, very high recovery rates for copper (85–99%) were presented in several studies, higher than 80% of many non-ferrous metals (Ni, Zn, Al), and even >90% for gold; only low recoveries for the silver (up to 12.1%) were obtained, probably due to its high antimicrobial activity [22].

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17.2.3.2 Biosorption Biosorption can be a metabolism-independent process, and rarely related to the metabolic processes. It takes place in the cell wall of microorganisms: bacteria, fungi, yeast, algae and biowaste. Later enable the researchers to work on biosorption with conditions that are not ideal for the living world, such as high temperature, low pH, low or high oxygenation, and their combinations [70]. In the present time, biosorption can be defined as the second stage in the biomining concept that combines it with the first stage (bioleaching) of this biotechnology. Together these biological processes have the aim to extract and recover the metals from primary and secondary sources such as ore, industrial and mining waste, and e-waste. Despite numerous bio-/hydrometallurgical (bioleaching and biosorption) studies, in the last two decades, this concept is essentially limited to lab-scale tests. This is the reason that current researches often focus on the development of a combined process with the bio-/hydrometallurgical aspect. Further, they are not only limited to copper and precious metals but also investigate possibilities for the recovery of the rare earths elements which belong to the group of technologically critical raw materials and have high economic potential [71].

17.3 Experimental investigation Experimental investigation by two groups of authors (from Mining and Metallurgy Institute Bor, Bor and Innovation center of the TMF Faculty, Belgrade) was performed using: I: Hydrometallurgical process. II: A combination of pyrometallurgical, electrometallurgical and chemical process. III: Obtaining fine (micro-sized) silver powder, silver brazing alloys and electrolytic gold bath based on mercaptotriazole (cyanide-free), in all cases from recycled materials. The first stage in all investigations was the manual disassembling of computers, the liberation of PCB (Figure 17.1), and the removal of batteries and capacitors. Preparation was done by a mechanical processing, that is, by rejecting the parts without gold, for the purpose of less acid consumption required for dissolution. The parts of the PCB after manual disassembling are shown in Figure 17.2. The weight and percentage of the PCB parts are given in Table 17.1. Research is done on 10 PCBs with full and detailed analyses, but for practical reasons, in this chapter, the average values for all PCBs are given.

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Figure 17.1: Printed circuit board (PCB).

Figure 17.2: Parts of PCB after manual disassembling.

Content of metallic and nonmetallic components of PCB determined using a Roentgen Thermo Scientific Niton XL3t-900 (Producer: Niton, Palomar, Model: Niton XL3t – 900 Series) is shown in Figure 17.4. Component analysis of PCB used in these experiments determined the metal component to be 37% by weight, and this has consisted of the base metals (Cu 17.0%,

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247

Table 17.1: Weight and percentage of the PCB parts. No. Part of PCB

Weight (g)

Black plastic

.

Vitroplast board with printed connections

.

.

.

.

Metal contacts

.

.

.

.

Metal solder

.

.

.

.

Others

.

.

.

.

Technological losses

.

.

.

.

.

.

.

Weight of parts after dissolving in aqua regia (g)

.

Σ

.

Wt (%) of PCB

.

Fe 5.0%, Ni 0.5%, Sn 5.0%, Pb 0.8%, Al 0.2% and Zn 8.0%), and precious metals (Au 0.001% and silver 0.005%). Plastic materials were 60% by weight. Also, silicon oxide and the metal oxides (alkaline, alkaline earth, alumina and other) were determined. In terms of weight, plastic and steel tend to dominate, but in terms of value, the lower part of PCB, gold and the other precious metals dominate. Gold and other precious metals make more than 80% of the value in PCB. Copper is next in terms of value.

Figure 17.3: Percentage of the PCB components.

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I: Hydrometallurgical process In the first stages of research, the previous disassembled computer components are leached in three different ways [30]: – direct leaching in aqua regia, – two-phase leaching (nitric acid/aqua regia) and – three-phase leaching (hydrochloric acid/nitric acid/aqua regia). Direct leaching in aqua regia of the PCB in aqua regia was performed at temperature: 85 ± 2 °C. The present metals are dissolved in aqua regia according to the following reactions: AuðsÞ + 4HClðaqÞ + HNO3ðaqÞ ! HAuCl4 ðaqÞ + 2H2 OðaqÞ + NOðgÞ

(17:1)

3AgðsÞ + 3HClðaqÞ + HNO3 ðaqÞ ! 3AgClðsÞ + 3H2 OðaqÞ + NOðgÞ

(17:2)

MeðsÞ + 3HClðaqÞ + HNO3 ðaqÞ ! MeCl2ðaqÞ + NOClðaqÞ + 2H2 OðaqÞ

(17:3)

Me = Cu, Ni, Sn Generally, most of the metals were dissolved in aqua regia. Silver is relatively stable in this solution due to the formation of the surface AgCl film. Two-phase leaching (nitric acid/aqua regia) was performed with the aim to prove to be the best in terms of silver leaching since silver is relatively stable in aqua regia. The following reactions take place in the nitric acid leaching process: 3AgðsÞ + 4HNO3ðaqÞ ! 3AgNO3 ðaqÞ + 2H2 OðaqÞ + NOðgÞ

(17:4)

FeðsÞ + 4HNO3ðaqÞ ! 3FeðNO3 Þ2ðaqÞ + 2H2 OðaqÞ + NOðgÞ

(17:5)

3MeðsÞ + 8HNO3ðaqÞ ! 3MeðNO3 Þ2ðaqÞ + 4H2 OðaqÞ + 2NOðgÞ

(17:6)

Me = Cu, Zn, Ni, Pb After leaching with nitric acid, silver was precipitated with the solution of sodium chloride, with lead as following reactions: AgNO3 ðaqÞ + NaClðaqÞ ! AgClðsÞ + NaNO3 ðaqÞ

(17:7)

PbNO3 ðaqÞ + NaClðaqÞ ! PbClðsÞ + NaNO3 ðaqÞ

(17:8)

Silver with an AgCl layer can be recovered to pure silver by the conventional purification process (first dissolving in ammonia solution, and reduction with hydrazine hydrate):

(17:9) AgClðsÞ + 2NH4 OHðaqÞ ! AgðNH3 Þ2 ClðaqÞ + 2H2 OðaqÞ

 (17:10) AgðNH3 Þ2 ClðaqÞ + N2 H4 · H2 OðaqÞ ! AgðsÞ + 1 2 N2ðgÞ + H2 OðaqÞ

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The recovered silver powder had a quality of 99.95%. It is possible to get the purity of 99.99% with one more consecutive precipitation. Three-phase leaching (hydrochloric acid/nitric acid/aqua regia) was performed in order to solve a problem of formation of β-tin acid. In the course of (tin II) – chloride hydrolysis, β-tin acid is formed and separated in the form of voluminous deposit, as per the following reaction: SnCl4 ðaqÞ + 2H2 OðaqÞ ! SnO2ðaqÞ + 4HClðgÞ

(17:11)

In the first phase, the samples were leached in hydrochloric acid (in order to remove tin), and then in nitric acid (dissolution of silver and copper reactions: (17.4)–(17.6)). This method proved to be good in terms of tin removal. The degree of leaching for three ways of leaching is shown in Table 17.2. Table 17.2: Metal extraction efficiency for the three-phase leaching. Element

Direct leaching in aqua regia

Two-phase leaching (nitric acid/aqua regia)

Three-phase leaching (hydrochloric acid/nitric acid/aqua regia)

Au

.

.

.

Ag

.

.

.

Cu

.

.

.

Ni

.

.

.

Sn

.

.

.

Mn

.

.

.

Sb

.

.

.

Mg

.

.

.

Si

.

.

.

V

.

.

.

Cr

.

.

.

Mo

.

.

.

Se

.

.

.

Ti

.

.

.

Al

.

.

.

The selective gold reduction has been performed so that a part of a dissolved tin and all quantity of copper and nickel remain in the solution in the form of chlorides.

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The gold reduction is done as follows:  HAuCl4 ðaqÞ + Na2 SO3 ðsÞ + H2 OðaqÞ ! Au + Na2 SO4 ðaqÞ + 3HClðgÞ + 1 2 Cl2ðgÞ  HAuCl4 ðaqÞ + NaNO2ðsÞ + H2 OðaqÞ ! Au + NaNO3 ðaqÞ + 3HClðgÞ + 1 2 Cl2ðgÞ  HAuCl4 ðaqÞ + SO2ðgÞ + H2 OðaqÞ ! Au + H2 SO4 ðaqÞ + 3HClðgÞ + 1 2 ClðgÞ

(17:12) (17:13) (17:14)

The reduced gold in the form of powder is separated by filtering, washed, dried and measured. The recovered gold powder was of 99.95% quality, but it is possible to obtain the purity of 99.99% with another consecutive precipitation.

II: Combination of pyrometallurgical, electrometallurgical and chemical process Results from the first stages of the investigation were a base for the second stages of investigation in a pilot plant for pyrometallurgical, electrometallurgical and chemical methods. All tests were carried out in a pilot plant presented in Figure 17.4. Printed Circuit Board (PCB) as the basic row for the special metal production was analyzed first. The chemical composition of the PCB is shown in Table 17.3. Investigations [38–41] of seven types of PCBs have led to the following conclusion: the average metal part of the PCB content is 28.6%, with the dominant copper content of 22.6%. Precious metal content, considered as the most important for their share in the market value of the metal production, was estimated to be 65–80%. In the first phase, the capacitors with very harmful and toxic materials were removed. After grinding to the required grain size and separation of plastic, first follows the magnetic separation, and then the separation of aluminum parts. Since chips, microprocessors, resistors, transistors and capacitors are produced from ferromagnetic materials, they, except Fe and Ni, contain a significant amount of metals such as Ag, In, Ga, Ge, Ta and Ti and make the magnetic fraction attractive for recycling [33]. Technologies for recycling metals from PCB magnetic fractions are poorly developed. Mainly research deals with the distribution of these metals in the melting process rather than methods for their valorization. Experimental investigation of these problems was performed by a group of authors from the Innovation Center of the TMF Faculty, Belgrade, Serbia, through pyrometallurgical laboratory tests [33, 37]. Lead and tin in solder are very harmful to further processing, especially in the electrolytic refining of copper. These metals must be removed by a low-temperature heating process (320–350 °C). Melting and casting of copper anode containing collected

17 E-scrap processing: theory and practice

a)

251

b)

c)

Figure 17.4: Pilot plant equipment: a) Electrolytic arc furnace; b) Plant for electrolytic refining of copper; c) Glass reactor for dissolving.

precious metals were performed in an Electric arc furnace-Birlac (Figure 17.4a) using the conventional techniques for copper. Electrolytic refining of anodes, obtained by e-scrap melting, was performed in two cathode periods in a new pilot plant for electrolytic refining of the anode with a non-standard chemical composition (Figure 17.4b) with the aim to obtain the copper cathodes of commercial quality (99.99% Cu). The anode sludge is subjected to further hydrometallurgical processes to obtain the precious metals of commercial quality. The anode slime, obtained by the electrolytic refinement of the copper anodes with a high content of precious metals, was processed in the Laboratory for refining

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Table 17.3: Chemical composition of PCB. Element

%

Element

%

Element

%

Ag

.

Cr

.

Mg

.

Cu

.

Ba

.

Cd

.×−

Sn

.

Si

.

As

.

Pb

.

Mo

.

Ag

.

Ni

.

Zr

.

Ti

.

Au

.

Sr

.

Se

.

Mn

.

Co

.

Fe

.

Sb

.

Al

.

Zn

.

Cr

.

Mg

.

Ca

.

Ba

.

Cd

−

.×

Insoluble residue

.

of precious metals in the special 100 dm3 glass reactors (Figure 1c). The first phase of refinement is the process of decopperization [72] of anode slime by leaching with diluted sulfuric acid in the presence of oxygen as the oxidant. After the process of decopperization, the anode slime contains max. 2% of copper. Anode slime without copper is a raw material for the next stages of processes with the aim to obtain gold, silver and palladium. Figure 17.5 shows the technology proposed by the Mining and Metallurgy Institute Bor.

17.3.1 Obtaining the high-value products from recycled metals 17.3.1.1 High-quality copper and fine silver powder with 5N purity Recycling of silver-plated contacts has some specific issues when compared with the conventional e-waste processing. The aim of recovery is to obtain and separate the three main metals in material: copper, zinc and silver. In this process, the additional aim was to obtain materials of higher value and to lower the cost of processing. In this report, an improved process for recycling the silver-plated electric contacts is presented. Copper and silver are standardly recovered with a purity of 99.90% and 99.99%, respectively. Improvements in the process with the same equipment lead to obtaining the new materials of higher value. The novel approach with subsequent electrorefining yields copper of 99.99% purity with BS EN 1978:1998 (Cu-CATH-1) quality, and is referred to as the LME grade A. The additional processing of silver

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Figure 17.5: E-scrap processing and metal production-technology in the Mining and Metallurgy Institute Bor.

results in a superfine, micro-sized Ag powder with particle size from 0.1 to 1.0 µm, and purity of 99.999% [29–32]. Synthesis of fine silver powder was performed from silver nitrate solution with hydrazine hydrate (HH) and ascorbic acid (AA) as a reducing agent. The research included testing polyvinylpyrrolidone (PVP) and sodium dodecyl sulfate (SDS) as dispersants. The experiments were adapted to the conditions without the necessity for special equipment [32]. The PVP as dispersant has shown very similar performance for both reducing agents. The average sizes of particles were very similar and about 0.70 µm, but the size distribution for the AA was narrower. The PVP could be a very useful dispersant for the production of silver powder with the average particle size of about 1–2 µm without a special requirement for the process. Adjustment of hydrodynamic and other mechanical conditions could improve the size distribution that is not the stronger side of the reactant. The SDS performed better, especially when the AA was a reducing agent. That powder had a fair distribution of size, and their size was smaller with more than 50% of particles below 500 nm, and mostly in the range of 300 to 700 nm. The SDS

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is a promising surfactant for the simple mass technology for the powders with particles less than 1.0 µm. The results of optimal parameters and reactants are shown in Figure 17.6 and Table 17.4.

Figure 17.6: SEM image of silver powder obtained by ascorbic acid reduction in the presence of SDS. Table 17.4: Statistical analysis of the particle sizes obtained by ascorbic acid reduction in the presence of SDS, given in Figure 17.6. Reduction agent/ dispersant

Ascorbic acid, SDS

Average particle size (µm)

.

Standard deviation (µm)

.

Particle size (µm)

.–.

Particle size distribution (µm)

Silver purity (%)

D

D

D

.

.

.

. (. ppm impurities)

17.3.1.2 Obtaining the cadmium-free silver brazing alloys with less than 100 ppm of total impurities Silver brazing alloys of the system Ag–Cu–Zn are environmentally friendly, and used in various industries such as construction, food, power electronics, automotive and aerospace. High-purity materials (99.99% or more) of the recycling processes are used for obtaining the extremely high purity brazing filler metals for special use. They have an order of magnitude greater purity of the standard requirements (less than 0.15%, EN 1044:1999) [30–32].

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The silver brazing alloys Ag60Cu26Zn14, Ag43Cu37Zn20, Ag40Cu30Zn30 and Ag25 Cu52.5Zn22.5 were obtained. Technology is based on the use of pure metals and two consecutive melting and casting phases of ingot metallurgy. Induction melting paired with the vacuum casting is an optimal procedure. Figure 17.7a shows the surface of the Ag25Cu52.5Zn22.5 alloy after the first phase of processing. It had the following composition (all in wt. %): 51.48 Ag, 28.57 Cu and 19.94 Zn. The porous structure can be seen in Figure 17.7. It is caused by zinc vapor. Figure 17.7b shows the final alloy surface after the second melting-casting process and homogenization annealing (600 °C, 24 h). The homogenous structure is clearly visible in Figure 17.7b. The precise composition is obtained with deviations that are far less than the allowed by the standard (SRPS EN 1044:2008; ±1% for Ag and Cu, and ±2%). a)

b)

Figure 17.7: (a) Surface of the Ag25Cu52.5Zn22.5 alloy after the first phase of processing and (b) final alloy surface after the second melting-casting process and homogenization annealing (600 °C, 24 h).

17.3.1.3 Gold coatings obtained from electrolyte based on mercaptotriazole In the Mining and Metallurgy Institute Bor, an electrolyte based on the gold complex with mercaptotriazole was synthesized in a wide pH range from acid to alkaline (pH = 2–12). After synthesis of electrolyte, a detailed characterization the complex in liquid and solid states in the whole range of its stability was performed in order to determine the optimum conditions for obtaining the quality decorative gold plating from this electrolyte and to compare it with the quality of gold plating, obtained from the classic electrolyte [42–45]. Physicochemical characterization of electrolyte, performed by ultraviolet–visible spectroscopy (UV–vis), indicated that the coordination of Au to MT at pH = 9 is realized through a sulfur atom. For comparative toxicity study of electrolytes based on the mercaptotriazole gold complex (pH = 2, 4, 7, 9 and 12), and the classic alkaline cyanide electrolyte

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(pH = 9), “in vitro” method on the culture of K562 cells of human leukemia was applied. Results show that the toxicity of organic complex of gold at pH values of 4, 7 and 12, is lower than alkaline cyanide electrolyte but higher at pH = 2, while at pH = 9, the relative cell viability is almost equal. Electrochemical characterization of the gold complex based on mercaptotriazole was performed by the open circuit potential measurement, cycling voltammetry method and recording the polarization curves, with pH values and conductivity of the electrolyte measurement, before and after each electrochemical experiment. These tests were performed for a period of 12 months at different pH values: 2, 4, 7, 9 and 12 at an optimal concentration of gold in the electrolyte of 2.5 g/dm3, and an optimal pH value of 9 and in the period of 4 mounts at the concentrations of gold in the electrolyte of 1.5; 2.0; 2.5; 3.0 and 3.5 g/dm3. For electrolytes with pH = 4, 7 and 12 the first visible signs of decomposition of the complex appeared three months after synthesis. The electrochemical characteristics of mercaptotriazole gold complex at a pH value of 2 and nine remained unchanged for a period of one year. In that period, any visual changes did not appear. Synthesized solutions of the gold complex based on mercaptotriazole are vaporized at room temperature to dry in order to obtain and characterize Au-MT in the crystalline form. The optical microscopy showed that the crystals obtained from solutions of different pH values are different in color, size and homogeneity. The most homogeneous (according to size and color), and the smallest crystals were obtained from the electrolyte with pH = 9. Figure 17.8 shows crystals obtained from electrolyte with pH = 9.

Figure 17.8: Crystals obtained from electrolyte with pH = 9.

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a)

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b)

Figure 17.9: Macrophoto of gold coatings obtained from (a) classical gold cyanide electrolyte and (b) gold complex based on mercaptotriazole.

Based on the experimental investigations, it could be concluded that the quality of decorative gold plating, obtained from a gold complex based on mercaptotriazole, satisfies all requirements of decorative gold plating. The most important advantage of this electrolyte is ecological, as gold could be regenerated by simply settling with hydrogen peroxide in which sulfur is precipitated [42–48].

17.4 Conclusion Recycling is an important industrial activity for economic and environmental reasons. The chapter presents a literature review of e-scrap processing and results of its own research on the recovery of metals from e-scrap. Using pyrometallurgical, hydrometallurgical and electrometallurgy processes, highly pure metals and the materials of higher value than pure metals were obtained, such as the microsized silver powder, cadmium-free silver brazing alloys and gold organic complex for electroplating.

References [1] [2]

Cui J, Zhang L. Metallurgical recovery of metals from electronic waste: A review. J Hazard Mater 2008, 158, 228–56. Ding Y, Zhang S, Liu B, Li B. Integrated process for recycling copper anode slime from electronic waste smelting. J Clean Prod 2017, 165, 48–56.

258

[3]

[4] [5] [6]

[7]

[8] [9]

[10]

[11] [12]

[13]

[14] [15] [16]

[17]

[18]

[19]

[20]

Silvana B. Dimitrijević, Stevan P. Dimitrijević

Ilankoon IMSK, Ghorbani Y, Chong MN, Herath G, Moyo T, Petersen J. E-waste in the international context – A review of trade flows, regulations, hazards, waste management strategies and technologies for value recovery. Waste Manage 2018, 82, 258–75. Robinson BH. E-waste: An assessment of global production and environmental impacts. Sci Total Environ 2009, 408, 183–91. Qiu R, Lin M, Ruan J, Fu Y, Hu J, Deng M, Tang Y, Qiu R. Recovering full metallic resources from waste printed circuit boards: A refined review. J Clean Prod 2020, 244, 118690. Meng L, Zhong Y, Wang Z, Chen K, Guo Z. Low-temperature melting and centrifugation of lead and tin from metal-rich particles of crushed waste printed circuit boards. Chem Eng Process 2018, 130, 192–200. Kamberović Ž, Ranitović M, Korać M, Jovanović N, Tomović B, Gajić N. Pyro-refining of mechanically treated waste printed circuit boards in a DC Arc-furnace. J Sustain Metall 2018, 4, 251–59. Zhan L, Xu Z. Separating and recycling metals from mixed metallic particles of crushed electronic wastes by vacuum metallurgy. Environ Sci Technol 2009, 43, 7074–78. Li H, Eksteen J, Oraby E. Hydrometallurgical recovery of metals from waste printed circuit boards (WPCBs): Current status and perspectives – A review. Resour Conserv Recy 2018, 139, 122–39. Sethurajan M, van Hullebusch ED, Fontana D, Akcil A, Deveci H, Batinic B, Leal JP, Gasche TA, Kucuker MA, Kuchta K, Neto IFF, Soares HMVM, Chmielarz A. Recent advances on hydrometallurgical recovery of critical and precious elements from end of life electronic wastes – a review. Crit Rev Env Sci Tec 2019, 49, 212–75. Duttaab D, Pandab R, Kumarib A, Goela S, Jha MK. Sustainable recycling process for metals recovery from used printed circuit boards (PCBs). 2018, 17, e00066. Tue NM, Takahashi S, Subramanian A, Sakai S, Tanabe S. Environmental contamination and human exposure to dioxin-related compounds in e-waste recycling sites of developing countries. Environ Sci Process Impact 2013, 15, 1326–31. Wu Z, Yuan W, Li J, Wang X, Liu L, Wang J. A critical review on the recycling of copper and precious metals from waste printed circuit boards using hydrometallurgy. Front Environ Sci Eng China 2017, 11, 8–21. Kaya M. Recovery of metals and nonmetals from electronic waste by physical and chemical recycling processes. Waste Manage 2016, 57, 64–90. Ghosh B, Ghosh MK, Parhi P, Mukherjee PS, Mishra BK. Waste printed circuit boards recycling: an extensive assessment of current status. J Clean Prod 2015, 94, 5–19. Moyo T, Chirume BH, Petersen J. Assessing alternative pre-treatment methods to promote metal recovery in the leaching of printed circuit boards. Resour, Conserv Recycl 2020, 152, 104545. Yousef S, Tatariants M, Tichonovas M, Bendikiene R, Denafas G. Recycling of bare waste printed circuit boards as received using an organic solvent technique at a low temperature. J Clean Prod 2018, 187, 780–88. Nekouei RK, Pahlevani F, Assefi M, Maroufi S, Sahajwalla V. Selective isolation of heavy metals from spent electronic waste solution by macroporous ion-exchange resins. J Hazard Mater 2019, 371, 389–96. Lawler W, Bradford-Hartke Z, Cran MJ, Duke M, Leslie G, Ladewig BP, Le-Clech P. Towards new opportunities for reuse, recycling and disposal of used reverse osmosis membranes. Desalination 2012, 299, 103–12. Awasthi AK, Li J. An overview of the potential of eco-friendly hybrid strategy for metal recycling from WEEE. Resour Conserv Recycl 2017, 126, 228–39.

17 E-scrap processing: theory and practice

259

[21] Khaliq A, Rhamdahani MA, Brooks G, Masood S. Metal Extraction processes for electronic waste and existing industrial routes: a review and australian perspective. Resources 2014, 3, 152–79. [22] Priya A, Hait S. Comparative assessment of metallurgical recovery of metals from electronic waste with special emphasis on bioleaching. Environ Sci Pollut Res 2017, 24, 6989–7008. [23] Baniasadi M, Vakilchap F, Bahaloo-Horeh N, Mousavi SM, Farnaud S. Advances in bioleaching as a sustainable method for metal recovery from e-waste: A review. J Ind Eng Chem (Amsterdam, Neth) 2019, 76, 75–90. [24] Becci A, Amato A, Fonti V, Karaj D, Beolchini F. An innovative biotechnology for metal recovery from printed circuit boards. Resour, Conserv Recycl 2020, 153, 104549. [25] Andrzejewska-Górecka DA, Poniatowska A, Macherzyński B, Wojewódka D, Wszelaka-Rylik ME. Comparison of the effectiveness of biological and chemical leaching of copper, nickel and zinc from circuit boards. J Ecol Eng 2019, 20, 62–69. [26] Wei X, Liu D, Huang W, Huang W, Lei Z. Simultaneously enhanced Cu bioleaching from E-wastes and recovered Cu ions by direct current electric field in a bioelectrical reactor. Bioresour Technol 2020, 298, 122566. [27] Zhou G, Yhang H, Yang W, Wu Z, Liu W, Yang C. Bioleaching assisted foam fractionation for recovery of gold fromthe printed circuit boards of discarded cellphone. Waste Manage 2020, 101, 200–09. [28] Dragulović S, Ljubomirović Z, Stanojević-Šimšić Z, Conić V, Dimitrijević S, Cvetkovski V, Trujić V. Recovery of rhodium from secondary raw materials for usage in electronic devices. Optoelectron Adv Mater Rapid Commun 2011, 5(12), 1370–75. [29] Ivanović A, Dimitrijević S, Dimitrijević S, Trumić B, Marjanović V, Petrović J, Vuković N. Electrodeposition of silver powder from nitrate electrolyte for usage in electronic. Optoelectron Adv Mater Rapid Commun 2012, 6(3–4), 1454–64. [30] Dimitrijević SB, Mirić M, Trujić V, Ivanović A, Dimitrijević SP. Recycling of Precious Metals from E–scrap. Iran J Chemistry & Chem Eng 2013, 32(4), 17–23. [31] Dimitrijević SB, Mirić MB, Trujić VK, Madić BN, Dimitrijević SP. Recovery of Precious (Au, Ag, Pd, Pt) and Other Metals by E–Scrap Processing. Bulg Chem Commun 2014, 46(2), 417–22. [32] Dimitrijević SP, Anđić ZN, Kamberović Ž, Dimitrijević SB, Vuković N. Recycling of silver plated brass for production оf high purity cathode copper аnd ultrafine silver powder for electric contacts. Bulg Chem Commun 2014, 46(4), 814–24. [33] Ranitović M, Kamberović Ž, Korać M, Jovanović N, Mihjalović A. Hydrometallurgical recovery of tin and lead from waste printed circuit boards (Wpcbs): Limitations and opportunities. Metalurgija 2016, 55, 153–56. [34] Kamberović Ž, Ranitović M, Korać M, Andjić Z, Gajić N, Đokić J, Jevtić S. Hydrometallurgical Process for Selective Metals Recovery from Waste-Printed Circuit Boards. Metals 2018, 8, 441. [35] Ranitović M, Đokić J, Korać M, Gajić N, Dimitrijević S. Recyclability of technology metals from e-waste: case study of in and ga recovery from magnetic fraction. Metall Mater Eng 2019, 25, 183–94. [36] Ranitović M, Kamberović Ž, Korać M, Gavrilovski M, Issa H, Anđić Z. Investigation of possibility for stabilization and valorization of electric ARC furnace dust and glass from electronic waste. Sci Sintering 2014, 46, 83–93. [37] Vučinić A, Kamberović Ž, Ranitović M, Kovačević T, Najčević I. Analysis of the treatment of plastic from electrical and electronic waste in the Republic of Serbia and the testing of the recycling potential of non-metallic fractions of printed circuit boards. Hem Ind 2017, 71, 271–79. [38] Dimitrijević SP, Kamberović ŽJ, Korać MS, Anđić ZM, Dimitrijević SB, Vuković NS. Influence of reducing agents and surfactants on size and shape of silver fine powder particles. Metall Mater Eng 2014, 20, 73–87.

260

Silvana B. Dimitrijević, Stevan P. Dimitrijević

[39] Dimitrijević SP, Rajčić-Vujasinović M, Kamberović Ž, Dimitrijević SB, Grekulović V, Trumić B, Ivanović A. Corrosion behavior of the Ag43Cu37Zn20 alloy in the natural seawaters. Mater Transac 2015, 56(12), 2088–91. [40] Dimitrijević SP, Manasijević D, Kamberović Ž, Dimitrijević SB, Mitrić M, Gorgievski M, Mladenović S. Experimental investigation of microstructure and phase transitions in Ag-Cu-Zn brazing alloys. J Mater Eng Perform 2018, 27, 1570–79. [41] Dimitrijević SP, Parežanin V, Kamberović Ž, Ranitović M, Korać M, Dimitrijević SB. Design of anti-tarnish sterling silver Ag-Cu-Zn alloy and investigation of silicon addition influence on mechanical and corrosion characteristics. Chem Ind Chem Eng Q 2018, 24, 267–74. [42] Dimitrijević S, Rajčić-Vujasinović M, Alagić S, Grekulović V, Trujić V. Formulation and characterization of electrolyte for decorative gold plating based on mercaptotriazole. Electrochim Acta 2013, 104, 330–36. [43] Kamberović Ž, Ranitović M, Korać M, Jovanović N, Tomović B, Gajić N. Pyro-refining of mechanically treated waste printed circuit boards in a DC arc-furnace. J Sustain Metall 2018, 4, 251–59. [44] Wan X, Fellman J, Jokilaakso A, Klemettinen L, Marjakoski M. Behavior of waste printed circuit board (WPCB) materials in the copper matte smelting process. Metals 2018, 8, 887. [45] Wood J, Creedy S, Matusewicz R, Reuter M, Secondary copper processing using Outotec Ausmelt TSL Technology, in proceedings of the MetPlant 2011, Perth, Australia, 8–9 August 2011; pp. 460–67. [46] Hughes S, Reuter MA, Baxter R, Kaye A, Ausmelt technology for lead and zinc processing, Proceedings Lead and Zinc 2008, 25–29th February 2008, South African Institute of Mining and Metallurgy (SAIMM), South Africa, 147–62. [47] Hagelüken C. Recycling of Electronic Scrap at Umicore’s Integrated Metals Smelter and Refinery. World of Metallurgy – Erzmetall 2006, 59, 152–61. [48] https://www.umicore.com/en/cases/hoboken, accessed in April 2020. [49] Ghodrat M, Rhamdhani MA, Brooks G, Rashidi M, Samali B. A thermodynamic-based life cycle assessment of precious metal recycling out of waste printed circuit board through secondary copper smelting. Environ Dev 2017, 24, 39–49. [50] Lee J, Song HT, Yoo J. Present status of the recycling of waste electrical and electronic equipment in Korea. Resour, Conserv Recycl 2007, 50, 380–97. [51] Ghodrat M, Rhamdhani MA, Brooks G, Masood S, Corder G. Techno economic analysis of electronic waste processing through black copper smelting route. J Clean Prod 2016, 126, 178–90. [52] Habashi F. A short history of hydrometallurgy. Hydrometallurgy 2005, 79, 15–22. [53] Bud I, Duma S, Gusat D, Pasca II, Bud A, Controversial history of cyanide utilization in mining industry. Romanian specific issues, (conference paper), International Multidisciplinary Scientific GeoConference Surveying Geology and Mining Ecology Management, SGEM, 18–24 June 2015 in Albena, Bulgaria, vol. 3, pp. 149–54, 2015. [54] Petter PMH, Veit HM, Bernardes AM. Evaluation of gold and silver leaching from printed circuit board of cellphones. Waste Manage 2014, 34, 475–82. [55] Xu Q, Chen DH, Huang MH. Iodine leaching process for recovery of gold from waste PCB. Chinese J Environ Eng 2009, 5, 911–14. [56] Isaia F, Aragoni MC, Arca M, Caltagirone C, Castellano C, Filippo GD, Garau A, Lippolis V, Pivetta T. Gold and palladium oxidation/complexation in water by a thioamide–iodine leaching system. Green Chem 2017, 19, 4591–99. [57] Tuncuk A, Stazi V, Akcil A, Yazici E, Deveci H. Aqueous metal recovery techniques from e-scrap: hydrometallurgy in recycling. Miner Eng 2012, 25, 28–37.

17 E-scrap processing: theory and practice

261

[58] Ha VH, Lee J, Huynh TH, Jeong J, Pandey BD. Optimizing the thiosulfate leaching of gold from printed circuit boards of discarded mobile phone. Hydrometallurgy 2014, 149, 118–26. [59] Li J, Xu X, Liu W. Thiourea leaching gold and silver from the printed circuit boards of waste mobile phones. Waste Manage 2012, 32, 1209–12. [60] Ding Y, Zhang S, Liu B, Yheng H, Chang CC, Ekberg C. Recovery of precious metals from electronic waste and spent catalysts: A review. Resour, Conserv Recycl 2019, 141, 284–98. [61] Doche ML, Mandoryan A, Mahmoud MM, Mautarlier V, Hihn JY. An ultrasonic-assisted process for copper recovery in a des solvent: Leaching and re-deposition. Chem Eng Process 2017, 121, 90–96. [62] Kavitha N, Palanivelu K. Recovery of copper(II) through polymer inclusion membrane with di (2-ethylhexyl) phosphoric acid as carrier from e-waste. J Membr Sci 2012, 415–416, 663–69. [63] Lende AB, Kulkarn PS. Selective recovery of tungsten from printed circuit board recycling unit wastewater by using emulsion liquid membrane process. J Water Proces Eng 2015, 8, 75–81. [64] Masilela M, Ndlovu S. Extraction of Ag and Au from chloride electronic waste leach solutions using ionic liquids. J Environ Chem Eng 2019, 7, 102810. [65] Wu Y, Fang Q, Yi X, Liu G, Li RW. Recovery of gold from hydrometallurgical leaching solution of electronic waste via spontaneous reduction by polyaniline. Prog Nat Sci 2017, 27, 514–19. [66] Gurung M, Adhikari BB, Morisada S, Kawakita H, Ohto K, Inoue K, Alam S. N-aminoguanidine modified persimmon tannin: A new sustainable material for selective adsorption, preconcentration and recovery of precious metals from acidic chloride solution. Bioresour Technol 2013, 129, 108–17. [67] Ilyas S, Lee J, Chi R. Bioleaching of metals from electronic scrap and its potential for commercial exploitation. Hydrometallurgy 2013, 131–132, 138–43. [68] Liu R, Li J, Ge Z. Review on Chromobacterium violaceum for gold bioleaching from e-waste. Procedia Environ Sci 2016, 3, 947–53. [69] Gorji M, Hosseini MR, Ahmadi A. Comparison and optimization of the bio-cyanidation potentials of B. megaterium and P. aeruginosa for extracting gold from an oxidized copper-gold ore in the presence of residual glycine. Hydrometallurgy 2020, 191, 105218. [70] Das N. Recovery of precious metals through biosorptio – a review. Hydrometallurgy 2010, 103, 180–89. [71] Kucuker MA, Kuchta K. Biomining – biotechnological systems for the extraction and recovery of metals from secondary sources. Global Nest J 2018, 20, 737–42. [72] Dimitrijević SB, Stević ZM, Trumić BT, Ivanović AT, Dimitrijević SP, Energy efficient recycling of precious metals from computer waste by hydrometallurgical processing, The 4th ICREPS 16, Belgrade, pp. 149–54, 2016. [73] Sisamoutha L, Hamdia L, Arigab T. Investigation of gap filling ability of Ag–Cu–In brazing filler metals. J Alloys Compd 2010, 504, 325–29. [74] He P, Feng JC, Zhou H. Microstructure and strength of brazed joints of Ti3Al-base alloy with different filler metals. Mater Charact 2005, 54, 338–46. [75] Huijie L, Jicai F. Vacuum brazing TiAl-based alloy to 40Cr steel using Ag-Cu-Zn filler metal. J Mater Sci Lett 2002, 21(1), 9–10. [76] Zhang L, Feng J, Li Z, Liu H. Evaluation of corrosion and wear resistance of friction stir welded ZK60 alloy. Sci Technol Weld Joi 2004, 9, 280–82.

Mirjanić D. Lj., Pelemiš S.

18 Intelligent nanomaterials for medicine diagnostic and therapy application Abstract: Application of nanomaterials in biomedicine has an important place in research of nanomaterials. Nanomedical approaches are a major transforming factor in medical diagnosis and therapies. The great advantages of using nanomaterials in biomedical areas lie in their ability to operate on the same small scale as all the intimate biochemical functions involved in the growth, development and aging of the human body. Achieving full potential of nanomedicine may be years or even decades away; however, potential advances in drug delivery, diagnosis and development of nanotechnology-related drugs start to change the landscape of medicine. One of the main issues is certainly related to long-term safety of nanomaterials, both developed for in vitro and in vivo applications [1].

18.1 Introduction Today, biological and medical research focuses on finding materials suitable for the application of contrast agents and therapy applications for treating different diseases. Bearing in mind that the size of nanomaterial particles is similar to the size of biological molecules and structures, a conclusion can be drawn that the application of nanomaterials in in vivo and in vitro biomedical researches is possible [2]. During the last decade, nanotechnology has had a steadily increasing impact on preclinical development in medicine, shaping the emerging scientific field of nanomedicine. Today, many of these developments are entering the clinical domain. An important topic is the development of composite nanosystems for diagnosis and therapy within the body. Such systems often consist of (i) a carrier platform, (ii) a payload for imaging, sensing, or therapy and (iii) optional targeting ligands [3]. Many critical issues in nanostructured materials, particularly their applications in biomedicine, must be addressed before clinical applications. Some of the key issues in biomedicine deal with bioactivity, compatibility, toxicity and nano-bio interfacial properties. In the biomedical applications, traditional materials science and engineering face new challenges in the synthesis and microstructure development since the requirements for general materials must be based on special medical needs [4].

Mirjanić D. Lj., Academy of Sciences and Arts of Republic of Srpska, B&H, [email protected] Pelemiš S., Faculty of Technology, University of East Sarajevo, B&H https://doi.org/10.1515/9783110627992-018

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Figure 18.1: Schematic illustration, showing established therapeutic nanocarrier platforms (NPs) in preclinical development [3].

18.2 Diagnostic – nanoimaging (some of the methods) Inorganic nanomaterials are used in various imaging modalities: computed tomography, MRI (magnetic resonance imaging), positron emission tomography, single photon emission computed tomography, gold nanocage, QDs (quantum dots), quantum rods, CNTs (carbon nanotubes), mesoporous silica nanoparticles and gold nanoparticles [5]. Magnetic nanoparticles have become important tools for the imaging of prevalent diseases, such as cancer, atherosclerosis and diabetes. While first-generation nanoparticles were fairly nonspecific, newer generations have been targeted to specific cell types and molecular targets via affinity ligands. The most common methods of diagnostics are based on fluorescent microscopy that in nondestructive manner monitors labeled nanoparticles in the body of a patient in real time, thereby providing information about the spatial distribution of the test compound in different cell compartments [6].

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Figure 18.2: Nanoimaging methods [5].

Superparamagnetic iron oxide nanoparticles (SPIONs) are used to enhance the contrast of MRI. MRI labeling can be done by attaching the nanoparticles to the stem cell surface or causing uptake of the particle by the stem cell through endocytosis or phagocytosis. Resulting nanocomposite have a high relaxivity under a clinical MRI scanner. Nanomaterials have attracted considerable interest in analytical chemistry (e.g., sample preconcentration, molecular probes and biological and electrochemical sensing). Applications of nanomaterials in analytical atomic spectrometry include: – improvement of the sensitivity and the selectivity, – broadening the application range to biological-molecule detection and – characterization and determination of nanomaterials themselves [7]. Simple and automated inorganic chromium speciation analysis method uses flow injection nano-TiO2 minicolumn separation and electrothermal atomic absorption spectrometric detection. Without any additional oxidizing/reducing process, Cr(VI) or Cr(III) species were, respectively, mixed with HCl or NH3·H2O solutions and passed through the minicolumn where the chromium species were selectively preconcentrated and separated [8].

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Figure 18.3: Cells labelled with nanoparticles [6].

Figure 18.4: Nanomaterials in analytical atomic spectrometry [8].

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18.3 Nanotechnology carrier platforms suited for switch functionality In recent years, major efforts have been devoted to develop suitable nanotechnological platforms to improve drug delivery to tumor tissue. For the development of such platforms, several challenges need to be mastered: (i) the control of the particle size, which can have influence on the NP distribution, clearance by kidney or liver and payload uptake; (ii) biocompatibility, to achieve an optimal benefit/risk relation; (iii) stealth properties, to escape immunological recognition and serum protein interactions; (iv) optimal blood circulation time for a specific application; (v) high target specificity for delivery of drugs or advanced functionality; (vi) controlled release mechanisms, for example, endosomal escape; and (vii) further functionality control through stimuli responsiveness [3].

Micelles and liposomes Micelles are nanosized structures characterized by a hydrophobic core and a hydrophilic coat and form spontaneously from amphiphilic molecules in aqueous environments. Liposomes are self-assembling structures with a spherical shape, composed of a lipid bilayer, which entirely surrounds an aqueous core, able to deliver different kinds of biomolecules. Depending on the assembly technique used, the size of the vesicles can range from tens of nanometers to micrometers. Under specific conditions, liposomes of ~100 nm in diameter have been successfully used to deliver chemotherapeutic agents to tumors. Drug delivery of poorly soluble molecules can be achieved through micelles using lipid moieties as hydrophobic blocks linked to hydrophilic polymers [9, 10]. Liposomes are interesting carrier candidates for delivery of intelligent switches at the nanoscale because the inner aqueous core offers a “nanocompartment” where processes that require protection from the surrounding body fluids when injected into an organism take place. Liposomes have already been converted into intelligent nanosystems by incorporating a wide variety of stimuli response functionalities such as temperature, light, pH, ultrasound, enzymatic response or even as drug delivery system for radiation-sensitive nanoparticles highlighting that liposomes are simple, but effective carriers for multimodal nanoscale trigger and effector functionalities [3].

Polymeric systems Polymeric and polymeric-biologic hybrid nanomaterials have gained increasing attention as modifiers of pharmacokinetics of “biologicals” (pharmaceutical products

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originating from biomacromolecules), as carriers of hydrophobic drugs and in particular as nonviral vectors for nucleic acid delivery. A structurally simple approach is to couple a polymer (typically polyethylene glycol) with a protein, a strategy that allows the control of pharmacokinetics while maintaining the biological properties of the protein. Self-assembly to nanoparticles is not exploited here. Different types of polymers, biodegradable or nondegradable, synthetic and natural are being used for the formation of polymeric micelles and polymersomes (polymeric vesicles) as drug delivery systems [3, 11].

Dendrimers Dendrimers are large and complex molecules with very regular chemical structure, which were pioneered in the early 1980s. They are nearly perfect monodisperse macromolecules with a regular and highly branched tree like architecture. Dendrimers are constructed through a repeating sequence of chemical reaction steps, leading to predictable alterations in their size determined by each generation. In typically used chemical syntheses, dendrimers are structures with a size of 1–10 nm and a hydrophobic interior, which enables drug delivery of hydrophobic compounds such as cancer drugs [3, 11].

Carbon nanotubes CNTs are a distinct molecular form of carbon atoms, yielding a hexagonal arrangement. CNTs exist as single-walled and multiwalled variants [1]. Their structure, formed from layered graphite sheets, gives them extreme physical strength, ten times as strong as steel, and unusual heat and conductivity properties. Recently, CNTs have attracted attention due to their use in controlled drug release as well as delivery of nucleic acids, peptides and antibodies. Their inner core and their outer surface allow the insertion of specific payload into the small inner core, while the outer surface can be modified to achieve the necessary biocompatibility within the body or to attach targeting ligands or drug payloads Clinically, however, CNTs have not overcome phase I trials [3].

Metallic nanoparticles Metallic nanoparticles such as iron oxide, gold and silver have been developed and modified for use in drug delivery, magnetic separation and diagnostic imaging. SPION built from oxide nanoparticles, such as magnetite (Fe3O4) and maghemite (Fe2O3), exhibit particular features like ultrafine size, biocompatibility and magnetic

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properties. The superparamagnetic properties become manifest when a magnetic moment is induced through the application of a magnetic field. A potential concern of metallic nanoparticles using heavy metals is their release into the environment in a potentially nonrecyclable form; a mass balance in the body and an estimation of the environmental mass balance of such materials seems prudent when industrial products are developed [3].

Quantum dots QDs are small-sized (1–10 nm) semiconductor nanocrystals that were developed in the early 1980s by Alexei Ekimov and Louis E. Brus. They are composed of an inorganic elemental core (e.g., Cd and Se) surrounded by a metallic shell (ZnS), which constitutes a barrier between the optically active core and the surrounding medium. QDs can be modified by ligand attachment or encapsulated with amphiphilic polymers to improve solubility, specificity, size and visualization properties in tissue [11].

18.4 Conclusion Nanomedicine is a very important global business enterprise impacting universities, startups and boardrooms of multinational corporations alike. Industry and governments clearly are beginning to envision nanomedicine’s enormous potential. Owing to their size-dependent effects, nanomaterials exhibit new physical and chemical properties compared with conventional bulk and molecular materials. In general, nanomaterials include inorganic, organic and inorganic/organic composite nanostructures, such as nanoparticles, nanowires and nanopatterns. The emerging field of intelligent nanomaterials for medical diagnosis, therapy and their combination “theragnostics” is based on a range of well-studied carrier platforms, a number of targeting strategies each offering advantages and challenges and a “smart” payload. Nanoimaging has a very important role. Insights into the complex biological properties of a diseased area may be exploited to enhance specific drug release within the diseased area or the cytoplasm of a key cell type involved in pathophysiology, by taking advantage of unique patterns or multimodal factors of the microenvironment. The design of such intelligent, stimuli-responsive nanoplatforms also promises diagnostic opportunities with increased disease specificity [12]. For nanomedicine (and nanotechnology) to truly become a global mega trend, the hype must be separated from reality. In addition, societal, environmental and ethical concerns will need to be addressed as scientific advances occur [11].

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References [1]

Fornara A. Multifunctional nanomaterials for diagnostic and therapeutic applications. Doctoral thesis, Stockholm: School of Information and Communication Technology Royal Institute of Technology, 2010. [2] Mirjanić DL, Pelemiš S. Nanotechnological materials in biomedicine. Contemporary Mater 2011, II, 68–74. [3] Lehner R, Wang X, Marsch S, Hunziker P. Intelligent nanomaterials for medicine: Carrier platforms and targeting strategies in the context of clinical application. Nanomed: Nanotechnol Biol Med 2013, 9, 742–57. [4] DongluShi HG. Editorial nanostructured materials for biomedical applications, Hindawi Publishing Corporation. J Nanomater 2008, Article ID529890, 2, DOI: 10.1155/2008/529890. [5] Yang F, et al. Cancer Treat Rev 2012, 38, 566–79. [6] http://www.kurzweilai.net/nanoparticles-could-lead-to-stronger-drugs-fewer-side-effects-forcancer-patients [7] Jiang X, et al. Trends Anal Chem 2012, 39. [8] Wu P, Chen H, Cheng G, Hou X. J Anal At Spectrom 2009, 24, 1098. [9] Cukierman E, Khan DR. The benefits and challenges associated with the use of drug delivery systems in cancer therapy. Biochem Pharmacol 2010, 80, 762–70. [10] Sawant RR, Torchilin VP. Multifunctionality of lipid-core micelles for drug delivery and tumour targeting. Mol Membr Biol 2010, 27, 232–46. [11] Mirjanić DL, Pelemiš SS, Hut I, Application of nanomaterials in biomedicine International Scientific Conference UNITECH –Gabrovo, (IV)- 336-340, (2014) [12] Hu X, Liu S, Huang Y, Chen X, Jing X. Biodegradable block copolymer doxorubicin conjugates via different linkages: Preparation, characterization, and in vitro evaluation. Biomacromolecules 2010, 11, 2094–102.

S. Petrović, N. Starčević, M. Ćosić, N. Nešković

19 On the doughnut effect and the rainbow proton–silicon interaction potential Abstract: This work shows how recent experimental results of angular distributions of 2 MeV protons channeled in a 55-nm-thick (001) silicon crystal tilted away from the [001] direction can be explained by the very accurate rainbow ion–atom interaction potential. The obtained results are compared with the ones applying universal ZBL interaction ion–atom potential, which is mainly used in the literature. Keywords: ion channeling, rainbows, interaction potential, doughnut scattering

19.1 Introduction An axial ion crystal channeling effect is the process of ion motion through the axial crystal channels, which is explained as the result of the series of its correlated collisions with the atoms of the strings defining the channel [1]. The rainbows in the axial channeling through very thin crystal were predicted by Nešković [2]. Theory of the crystal rainbows was formulated by Petrović et al. [3]. This theory will be applied in the work presented here. Recently, the group from Center for Ion Beam Applications in Singapore performed high-resolution ion channeling experiments with 0.7–2 MeV proton beams and an ultrathin (001) silicon crystal. The thickness of the crystal was 55 nm [4–6]. After that, the morphological approach based on the theory of crystal rainbows was applied to explain the doughnut effect [7]. It occurs after an ion beam is tilted away from a major crystallographic direction. Theory of the crystal rainbows is based on analysis of the mapping of the impact parameter (IP) plane to the transmission angle (TA) plane determine by the scattering/channeling process: θx = θx ðx0 , y0 Þ and θy = θy ðx0 , y0 Þ

(19:1)

where x0 and y0 are the transverse components of initial ion position vector, that is, the components of its impact parameter vector, θx and θy are the components of final ion channeling angle, that is, the components of its transmission angle. It

Acknowledgments: The authors acknowledge the support by the Ministry of Education, Science and Technological Development of Serbia. S. Petrović, N. Starčević, M. Ćosić, N. Nešković, Laboratory of Physics, Vinča Institute of nuclear sciences, University of Belgrade, Belgrade, P. O. Box 522, Belgrade, Serbia https://doi.org/10.1515/9783110627992-019

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should be noted that the mapping (19.1) depends on the ion’s energy, crystal channel, its thickness, as well as on the crystal tilt angle φ. Since the components of ion channeling angle are small (smaller than the critical angle for channeling) the ion differential transmission cross section is given by σðx0 , y0 Þ =

1 jJθ ðx0 , y0 Þj

(19:2)

where Jθ ðx0 , y0 Þ = ∂x0 θx ∂y0 θy − ∂y0 θx ∂x0 θy is the Jacobian of the mapping (19.1). Thus, the following equation Jθ ðx0 , y0 Þ = 0

(19:3)

gives the rainbow lines in the IP plane. The images of these lines determined by functions θx ðx0 , y0 Þ and θy ðx0 , y0 Þ (19.1) are the rainbow lines in the TA plane.

19.2 Results In this work, the ZBL ion–atom interaction potential [8] will be applied together with the recently obtained rainbow ion–atom interaction potential [9]. The ZBL potential reads   4 Z1 Z2 e2 X βi (19:4) αi exp VZBL = R i=1 RaZBL where Z1 and Z2 are atomic numbers of ion and atom, respectively, R is the distance −1 1=3
between ion and atom, aZBL = ð9π3 =128Þ Z1p + Z2p a0 is the ZBL screening radius, a0 is the Bohr radius, and αi = (0.1818, 0.5099, 0.2802, 0.02817), βi = (3.2, 0.9423, 0.4028, 0.2016) and p = 0.23 are the fitting parameters. The Molière’s ion–atom interaction potential is given by   3 Z1 Z2 e2 X δi VM = γi exp R i=1 RaTF

(19:5)

 1=3 − 1=3 where aTF = ð9π3 128Þ Z2 a0 is the Thomas–Fermi screening radius, and γi = (0.10, 0.55, 0.35) and δi = (6, 1.2, 0.3) are the fitting parameters [10]. In the case of the Molière’s potential it is also commonly used the Firsov screening radius aF = ð9π3 =128Þ1=3 ðZ1 + Z2 Þ− 2=3 a0 . Then, one can designate the potential VMF , by using Firsov instead of Thomas–Fermi screening radius. 1=2

1=2

The potentials V ZBL and VMF were dominantly applied for small-distance ion–atom scattering processes. However, Krause et al. [10], in analyzing their channeling experiments through a very thin silicon crystal, concluded that they were better reproduced

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by the VM interaction potentials, taking into account that they recorded the angular distributions generated by the ions moving far from the atomic strings of the crystal defining the channel. Recently, Petrović et al. [9] have been able to merge VZBL and VM interaction potentials by changing the fitting parameters δi to δri = (5.124, 1.828, 0.2562) F interaction potential to be accuin the VMF potential obtaining so called the rainbow VMr rate for all the impact parameters. They have used the morphological method in order to well approximate for small impact parameters the rainbow lines in the TA plane and the rainbow lines generated by the VZBL interaction potential and for large impact parameters the rainbow lines in the TA plane and the rainbow lines generated by VM interaction potential.

Figure 19.1: The rainbow lines in the impact parameter plane for 2 MeV protons channeled in a 55-nm-thick (001) silicon crystal tilted away from the [001] direction for tilted angles equal to 0, 0.05, 0.06, 0.07, 0.09 and 0.15 deg; the rainbow potential – red lines; ZBL potential – blue lines.

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Figure 19.1. shows rainbow lines in the IP plane for 2 MeV protons channeled in a 55-nm-thick (001) silicon crystal tilted away from the [001] direction. Tilted angles φ are equal to 0, 0.05, 0.06, 0.07, 0.09 and 0.15 deg. The red lines designate the F while the blue lines designate the ones obtained by the VZBL ones obtained by VMr interaction potential. It is clear that these lines very well match those close to the atomic strings, for small-impact parameters, and differ for large-impact parameters. It is also clear that two separate lines for the straight case (φ = 0), around the channel center and close to the atomic strings, for titled angle larger than around 0.05 max (a)

φ = 0 deg

(b)

0.2

–0.2

φ = 0.05 deg

0.2

0

–0.2 –0.2

0

(c)

φ = 0.06 deg

(d)

0.2

–0.2

φ = 0.09 deg

(f)

0

min max

0.2 φ = 0.07 deg

θx (deg)

0.2

0

–0.2 –0.2

0

(e)

0

min

0.2

max

φ = 0.15 deg

0.2

0

–0.2 –0.2

0

0.2

0.4 θy (deg)

0

0.2

0.4

min

Figure 19.2: The rainbow lines in the scattering angle corresponding to Figure 19.1, the rainbow potential – red lines; ZBL potential – blue lines.

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deg “interact” with each other being separated after. For larger tiled angles the one line is located around the atomic strings and in between them while the other one is located around the channel center and in between them. Rainbow lines in the SA plane that correspond to the rainbow lines presented in Figure 19.1 are shown in Figure 19.2. In this figure the corresponding experimental patterns are also shown. For the straight case, the rainbow interaction potential clearly better reproduces the experimental result, especially for the inner line around the channel center. It is also clear that the outer rainbow F interaction potential better reproduce the experimental lines obtained by the VMr pattern, which is particularly well visible for φ = 0.05. It is interesting to note that both potentials give qualitatively the same way how the doughnut has been formed. Namely, after the interaction of the above-mentioned two rainbow lines, the inner rainbow line experiences self-evolution from four cusp-like closed lines to the circle. This fact can be attributed to well-known structural stability of the singularities of the mapping [12]. Further, one can claim that it is the circular rainbow.

19.3 Results It is shown here that the rainbow proton–silicon interaction potential very well approximates the doughnut formation observed in the experimental angular patterns for 2 MeV protons channeled in a 55-nm-thick (001) silicon crystal tilted away from the [001] direction. The obtained results are compared with the ones applying the ZBL proton–silicon interaction potential.

References [1] [2] [3]

[4] [5]

[6]

Gemmell DS. Channeling and related effects in the motion of charged particles through crystals. Rev Mod Phys 1974, 46, 129. Nešković N. Rainbow effect in ion channeling. Phys Rev B 1986, 33, 6030. Petrović S, Miletić L, Nešković N. Theory of rainbows in thin crystals: The explanation of ion channeling applied to Ne10+ ions transmitted through a Si thin crystal. Phys Rev B 2000, 61, 184. Dang ZY, Motapothula M, Ow YS, Venkatesan T, Breese MBH, Rana MA, Osman A. Fabrication of large-area ultra-thin single crystal silicon membranes. Appl Phys Lett 2011, 99, 223105. Motapothula M, Dang ZY, Venkatesan T, Breese MBH, Rana MA, Osman A. Axial ion channeling patterns from ultra-thin silicon membranes. Nucl Instrum Meth Phys Res B 2012, 283, 29. Motapothula M, Dang ZY, Venkatesan T, Breese MBH, Rana MA, Osman A. Influence of the narrow {111} planes on axial and planar ion channeling. Phys Rev Lett 2012, 108, 195502.

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Motapothula M, Petrović S, Nešković N, Dang ZY, Breese MBH, Rana MA, Osman A. Origin of ringlike angular distributions observed in rainbow channeling in ultrathin crystals. Phys Rev B 2012, 86, 205426. [8] Ziegler JF, Biersack JP, Ziegler MD. SRIM – The Stopping and Range of Ions in Matter. Annapolis: SRIM, 2008. [9] Petrović S, Nešković N, Ćosić M, Motapothula M, Breese MBH. Proton-silicon interaction potential extracted from high-resolution measurements of crystal rainbows. Nucl Instrum Methods Phys Res B 2015, 360, 23. [10] Molière G. Theorie der Streuung schneller geladener Teilchen I: Einzelstreuung am abgeschirmten Coulomb-Feld. Z Naturforsch A 1947, 2, 133, in German. [11] Krause HF, Barrett JH, Datz S, Dittner PF, Jones NL, Gomez Del Campo J, Vane CR. Angular distribution of ions axially channeled in a very thin crystal: Experimental and theoretical results. Phys Rev A 1994, 49, 283. [12] Thom R, Structural Stability and Morphogenesis (Benjamin, Reading, 1975).

Ana Radosavljević-Mihajlović, Vojislav Mitic

20 The methods of safe storage of spent nuclear fuel and waste Abstract: The current problem is the issue of safe storage of nuclear waste, especially materials generated as waste in nuclear power plants. In the nuclear fuel cycle, in the fuel, a large amount of artificial radionuclides are created (most of them are much more active than uranium), so radioactivity in the normal reactor operation is about a billion times greater than before entering the reactor (1021 Bq observed for 100 tons). Radionuclides are the most important part of the nuclear waste and their safe storage and removal from the natural environment is very important. For now, utilized nuclear fuel (high radio-co-active waste which remains after its transformation) is temporarily stored in special storages in order to exploit a rapid decline initial period of its radioactivity and thus simplify further operation with it. In this paper the literature data of different methods of disposal of nuclear waste are presented. Keywords: waste storage, method of safe storage, storage area

20.1 Introduction The safe storage of spent nuclear fuel and waste, especially materials observing from nuclear reactors, represents a significant technological and security challenge [1]. Waste nuclear is material formed in the nuclear reactors, as a by-product in controlled chain nuclear reactions [2]. It is well known, in the nuclear fuel cycle, fuel is produced with a large amount of synthetic radionuclide whose radioactivity in the normal reactor operation is about one billion times higher than before entering the reactor (1,021 Bq/100 t). This synthetic radionuclide, used in nuclear fuel, represents the largest part of radioactive waste. The label for spent nuclear fuel is SNF (Spent Magnox fuel) [3]. The uranium oxides (UOx) and mixtures of uranium and plutonium oxide (MOX fuel) are also present in SNF.

Acknowledgment: The authors thank the Ministry of Education, Science and Technological Development of the Republic of Serbia for supporting this investigation through project III-45012. Ana Radosavljević-Mihajlović, Institute for Technology of Nuclear and Other Mineral Raw Materials,P.O. Box 390,Franche d’Epere Street 86, 11000 Belgrade, Serbia Vojislav Mitic, Institute of Technical Science, Serbian Academy of Science and Arts, Knez Mihailova 35/IV; Electronic Faculty, University of Niš,Aleksandra Medvedeva 14, Niš 180000 https://doi.org/10.1515/9783110627992-020

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A very important parameter for the deposit of SNF is the factor of heat energy, that is, the values of the heat capacity. Depending on that, spent nuclear fuel will be deposited. The spent nuclear fuel and the radioactive waste are temporarily stored in special storehouses, in order to take advantage of the initial period of rapid deterioration of its radioactivity and thus simplify its further handling. Based on the presence of oxides and radionuclide in SNF is divided into: – Fuel with a low level of radiation of 5 × 106 − 5 × 109 Bq (low-level waste – LLW). – Fuel with a mean level of radiation of 5 × 109 to 5 × 1014 Bq (international-level waste – ILW). – Expensive fuel with a high level of radiation of 5 × 1014 Bq (high-level waste – HLW). LLW − due to less danger to the environment it can be deposited in surface. LLW is sealed in concrete containers, which are disposed of in concrete basins and are closed with concrete slabs or buried in the ground. ILW − storage depends on the aggregate state. Gaseous waste is collected, and afterward the process of segregation and decontamination of waste (waste recycling treatment and cutting for easier packaging) is carried out. The solid ILW is placed in metal barrels and poured with concrete for immobilization. At the selected location, tunnels (similar to mining tunnels) are struck, and metal barrels are placed in tunnels. After that, tunnels filled with waterproof material. HLW – presents the mixture of short- and long-lived radionuclide [4, 5]. This nuclear waste contains approximately 94% of uranium, 1.3% of plutonium, 0.14% of actinide elements and 5.2% of fission products [4]. HLW waste also contains long-lived isotope 79Se, 93Zr, 99Te, 107Pd, 126Sn, 129I, 135Cs and short-life isotope 89Sr, 90 Sr, 106Ru, 125Sn, 134Cs, 137Cs and 147Pm. This type of waste must be so well stored, that the radioactive isotopes are never released into the environment (atmosphere, hydrosphere, biosphere and lithosphere). Storage of nuclear waste for a longer period involves the use of materials with specific physical and chemical properties that are resistant to corrosion, radiation and weather conditions. The International Atomic Energy Agency (IAEA) in Vienna has defined methods for the disposal of nuclear waste [6]. The objects are located on or below the surface of the earth, where the protective cover is up to several meters. Waste containers are located in built storehouses, which have the appropriate drainage and ventilation system. Nuclear waste can also be disposed of in caves below ground level, or in geologically favorable environments. The basic conditions for the selection and storage of spent nuclear waste are: 1. Stable and sufficiently large geological formation 2. A stable social community (without armed or civil conflicts over the past 100 years)

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The US Department of Energy (DOE) and the US Environmental Protection Agency (EPA) have established public health and environmental health measures in the processes of building, operating and disposing of spent nuclear fuel with high–low radiation [7, 8]. The storage of nuclear waste is done in two phases: – Wet storage is the temporary disposal and holding of spent nuclear materials in water basins within nuclear power plants. – Dry storage is the disposal of nuclear material in concrete or steel containers in the appropriate geological environment.

20.2 The storage areas The safety sustainable storage is based on the principle of disposing nuclear waste at great depths to the interior of the Earth’s crust. The International Panel on Fissile Materials (IPFM Group of Independent Nuclear Scientists from 16 countries established in 2006) made certain recommendations – “Spent Nuclear Fuel (HLW-type) and recycled fuel require a well-designed space for the storage period from several tens of thousands to one million years. The selected space should have the least possible environmental impact, be well-insured and safe” [6]. There is a general consensus that placing spent nuclear fuel in storage hundreds of meters below the surface is safer than storage of spent fuel on the surface. The basic parameter is the level of its thermal energy. In the process of construction of the landfill, the possibility of controlling temperature is very important. The waste that has a low heat capacity can be placed in large cells with a larger number of packages.

20.2.1 Disposal in a geological environment 20.2.1.1 Storage on the Earth’s surface Surface storage is a temporary measure for the disposal of radioactive waste, but can be considered an effective option. The proposals for long-term storage above the ground can be classified into two categories: facilities currently used for temporary storage and which would require replacement and reclaiming waste every 200 years. These structures have the name “Monolith” or “Mausoleums” (mausoleum). Another type of object is the one that represents a long-term storage method, where future generations will be able to monitor and monitor stored waste. Both proposals lead to the question of the stability of a future society, and it is very important to establish good monitoring and supervision. So far, no government has planned to implement a long-term plan for the storage of nuclear waste above the surface of the earth.

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20.2.1.2 Deep geological storage The basic goal of deep storage is the removal of nuclear waste, with radionuclide with a short lifespan, because their isolation from the biosphere and the prevention of their migration is very important. For this method of disposal, it is necessary to have knowledge of the selected area (the geological and structural data and data of stability and good ecological protection selected area). The geological environment must be adequate to prevent the migration of isotopes over a longer period of time. The following mineralogical rocks are suitable: magmatic rock (basalts and granites), deposit of sedimentary origin, as well as volcanic tuff. 20.2.1.2.1 Deposit of salt Based on the proposals and reports from 1957, by NAS (National Academy of Sciences, United States of America) scientists, it has been suggested that there is a possibility of storing nuclear material in salt deposits. Salt deposits are genetically related to evaporite formations and belong to hemogenic sediments. The accessory minerals in deposit of salt are anhydrite (CaSO4), dolomite (CaCO3·MgCO3) and potassium chloride (KCl). These formations can move through large areas of land, where deposits are formed whose thickness ranges from 200 to 600 m. Based on its physical chemical properties, it has a high degree of thermal conductivity, expressed viscosity, low permeability and porosity. These deposits can provide quite a good space for the storage of nuclear material, and it is also advantageous in the areas that are tectonically stable. These deposits provide a suitable place for nuclear material storage. The mobility of solid salt solutions is a disadvantage that must be considered. 20.2.1.2.2 Deposit of clay Clay deposits are genetically and spatially associated with marine and lake sediments. Minerals of clay such as kaolinite (Al2Si2O5(OH)), smectite (Al2Si4O10(OH)2xH2O), ilite (K0.75Al1.3Mg0.25Fe0.25Si3.7Al0.3 10(OH)2) or bentonite (M+0.3Al2Si3.7Al0.3O10(OH)2) have exceptional physical–chemical properties: high viscosity degree and high degree of absorption of radionuclides. Deposits of clay minerals are found in zones of tectonically stable regions. Since the mid-1980s, Belgium, France and Switzerland have launched research programs in Europe to test the possibility of storing nuclear material in areas where clay deposits are located. Based on research by Hansen et al. [7] it has been established that new methods can provide greater precision in characterization, in the design of landfills and in the assessment of landfill efficiency. A new approach is needed among governments using clay deposit sites for the disposal of nuclear materials.

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20.2.1.2.3 Deposit of carbonate and shalk In the United State of America, in 1984 the Department of Energy initiated a project aimed at evaluating common types of sedimentary deposit, to determine the probability and ability to store nuclear material in the deposit of this genetic type. According to the research, carbonate and shalk deposits are acceptable environment for the safe storage of nuclear waste. The carbonate deposits, limestone, dolomites and magnesites, also have a fairly good geological and mineralogical basis to be used as places for disposal and permanent storage of nuclear waste [8]. The limited amount of seismic activity in these deposits makes them suitable for use [9]. The problem that is present in carbonate deposits is low thermal resistance because at temperatures above 150 °C there is a cracking of the rock; therefore, a nuclear material that can be deposited must not have a high thermal capacity [10]. 20.2.1.2.4 Granite massives Granite is a deep-walled magma rock from a group of acidic magma rock. They have great hardness and resistance to extreme physical and chemical conditions. In the 1970s, the US Geological Survey Department of the United States Department of Geosciences (USGSD) and the DOE examined the possibility of granite rocks being places for storing and permanently disposing of nuclear material [11]. Canada (Lac du Bonnet area), Switzerland (Grimsel tunnel region) and Japan also examined the possibility of granite rocks being used as warehouses. Sweden and Finland have selected granite rocks and are in preparation to receive license. The basic features that enable the use of granite rocks as storage spaces are: – their great power in their expansion; – their resistance to heat changes and processes of mineral alteration; – their low permeability, low water content and often quite dry area; – their moderate homogeneity; – there is no possibility of adsorption of radionuclide; and – their chemical stability and location in areas of stable tectonic regions. 20.2.1.2.5 Basalt rock Basalt is a rock formed from an outflowing magma by decompression melting of earthen coating. Basaltic rocks have relatively high power in their spans, are resistant to mineral alterations and have low thermal conductivity. Basalt is stable in the natural environment and is not a typical area for economic use. However, except in Hanford in the United States, the basalt is not considered a potential site for the storage of nuclear waste [12].

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20.2.1.2.6 Volcanic tuff Volcanic tuffs deposits are spatially and genetically associated with volcanic-sedimentary rocks. These deposits were formed in marine and lake environments of the Neogene age, originated mostly by devitrification of volcanic glass. Since 1976, intensive research has been carried out in the United States about the possibility of storing nuclear material in the volcanic tuff [13]. The basic properties of volcanic tuffs that can be used in storage processes of nuclear materials are their relatively high power, resistance to chemical alteration processes, relatively stable thermal conductivity (except zeolite) and expressed radionuclide adsorption power.

20.3 The method of nuclear storage 20.3.1 Method for storage by injection process The process of direct injection involves the insertion of liquid waste under pressure into the deep layer of stones, mostly porous stones (sandstone, limestone or surface layer of the earth), Figure 20.1 [14, 15].

izvorište P projektovani pritisak

priliv P

površina

sveža voda talog

ubrizgavanje

injektirana zona

Figure 20.1: The projection of injection hole (image taken from http://www.pollutionissues.com/ Ho-Li/Injection-Well.html).

This concept implies the placement of nuclear waste in geological formations of the “hole” at depths of 10,000 m (or 6 miles), in zones of sedimentary or magma-

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metamorphic rock, where a stable geological zone is located [16]. Based on research, it has been shown that granite rocks are the most favorable because they are chemically stable, are resistant to processes of alteration and have a moderate thermal conductivity that decreases with depth. Waste that is inserted into the “holes” is mostly in the liquid state, mostly waste or saline water – or water with chemicals. In the United States, injection and its activities are regulated by the EPA [17]. Wastewater or treated water is injected into the ground between impermeable stone layers, where the injection wells are pre-stressed from the solid wall so as not to interfere with the environment. In this way, the land is used as a filter for further cleaning and purification of wastewater. The problem that is present is the occurrence of possible mixing of drinking water with wastewater, unless a detailed protection procedure is carried out. Based on the EPA, six types of injection holes have been defined [18]: – Injection holes for injection of municipal waste underground sources – Injection holes for injecting liquids produced as by-products after the production of oil and gas – Injection holes for injection of tailings in places below the site where freshwater sources are used, which are used for drinking – Injection holes for injection of hazardous waste under natural sources – Injection holes for injection of waste under atmospheric drainage wells and septic systems of leaching in the fields – Injection holes for injection of CO2 for storage The injection methods and activities are regulated and controlled by the EPA and the European Agency for Environmental Protection.

20.3.2 Method of lying below the seabed There are two ways to postpone nuclear waste on the seabed [19]: – The disposal of containers with nuclear waste to the seabed. In places where a favorable geological environment exists, containers with radioactive waste bury underneath the sea or ocean floor. – By injection into the seabed, solid waste containers have the shape of a projectile and are discharged from ships and enter several meters below seabed sediments [20]. Permanent disposal of nuclear waste involves at least three options: shallow burial in the sea or ocean floor; deep storage of nuclear waste through drilling processes; processes of subduction into the tectonic plates.

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The shallow disposal of nuclear waste implies the disposal of a container a few meters below sea of sediments [21]. The protective layers of containers could not endanger the marine or oceanic environment. Deep storage through drilling has advantages, due to sedimentary rocks that contain clay components at the bottom of the ocean, and have the power to absorb radioactive material. Disposal in subduction zones is a place of permanent disposal of nuclear waste to the interior of the earth’s crust. The subduction zones remain geographically limited in terms of access. The Cascadia subduction zone, located on the west coast of the United States, may be a zone for the disposal of nuclear waste [22]. In the period from 1946 to 1993, a large number of countries used the oceans as a site for the disposal of nuclear waste. The ban on the disposal of nuclear waste on the marine and ocean floor was introduced on the basis of the London Convention – the Convention on the Prevention of Pollution by the Wastes and Other Substances [23]; Basel Convention on the Border Control of Hazardous Waste and Its Disposal [24]; MARPOL 73/78 – International Convention for the Prevention of Pollution from Ships of 1973 year and Modified Protocol of 1978 year [25].

20.3.3 Method of lying in ice cover Philberth [26] was the first to propose the concept of nuclear waste storage in Antarctica as a means to provide safe disposal. Greenland is a territory belonging to the Kingdom of Denmark with populated areas, so there is no possibility of permanent disposal in that area. The storing of nuclear material in ice cover can be problem. The heat generated by nuclear materials could lead to the melting of the glaciers. So this method is forbidden under the International Convention. The main principles of the usage of Antarctica were adopted on the basis of the Treaty – The Antarctic Treaty – (which was signed in Washington on December 1, 1959 by the twelve countries whose scientists had been engaged in and around Antarctica). A new protocol, The Protocol on Environmental Protection of Antarctica, was signed in 1998, designating this region as a “natural reserve, devoted to peace and science” (Art. 2). The Environment Protocol’s Article 3 lays out the fundamental principles that apply to human activity in Antarctica, while Article 7 restricts all activity involving Antarctic mineral resources, with the exception of scientific research. Only after 2048 may this protocol be changed.

20.3.4 Method of separation and transmutation of nuclear waste In nuclear technology, with chemical processes, it is possible to extract plutonium from spent nuclear fuel [27]. In this process, the goal is to extract Pu239 and U235 that

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are used in the military industry, or to produce MOX fuel. The fuel is stored in lead and steel drums and then dissolved in HNO3, while the separated gases are retained. Three types of products are obtained: – U235 and Pu239 – Highly active liquid waste – Low active solid and liquid waste and gases From 100 t of spent fuel, it is possible to separate 3.5 t of fission products, 94.3 t U238, 0.8 t U235, 0.8 t Pu239 and 0.5 t of transuranic elements [28, 29]. Reprocessing and separation represents only the reorganization of waste, but not the reduction of its quantity or toxicity. Radioactive elements can be transformed into non-radioactive through nuclear reactions, transmutation. These processes reduce the volume of high levels of waste, but do not reduce radioactivity or heat generation, therefore, it is necessary to store it. Problems can arise due to the misuse and spread of nuclear weapons. There are a number of separation technologies plutonium and uranium recovery by extraction, uranium extraction, transuranic extraction, diamide extraction, selective actinide extraction and universal extraction [30].

20.3.5 Methods of disposal in the universe The proposal for the disposal of nuclear waste in space was considered in the 1970s and 1980s. From 1970 to 1989, NASA researchers investigated the potential of storing nuclear waste in space. There are a number of factors that influence the possibility of disposing nuclear waste in the space: the sun’s winds, the corona, the effect of the moon and solar on the movement of the earth’s orbit. So these parameters show that it is very dangerous for nuclear waste to remain in orbit. The possibility of solar burning ensures that the waste is permanently destroyed, but the problem is the large amount of energy needed to send. The likelihood of waste returning to the Earth’s surface is a downside of these space deposition procedures. Also, there are difficulties in monitoring such materials in Earth’s orbit. Following the disastrous launches of the shuttles in 1986 and 1991, the projected project to store nuclear waste in orbit was shelved [31].

20.4 Containers for waste disposal Nuclear waste is deposited in containers designed to provide permanent packaging safety during the handling, disposal and transport process. The material for the

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construction of the container must be resistant to corrosion and the formation of cracks and other deformations. Materials must have the ability to persevere a longer time period (from 1,000 to 100,000 years). Most common types of alloys, which must possess specific physical chemical properties, are used for the construction of containers. These are mainly materials based on different types of concrete and metals, copper and nickel alloys, and various types of steel [32] (Figure 20.2).

prednja strana ublažavanje udara poklopca

ventil za pražnjenje smola

drugi poklopac 2 koncentrični zaptivak osnovni poklopac

Korpa za 37 PWR montažu

2 koncentrični zaptivak

ležajevi kovana čelična školjka smola toplotni provodnik

spoljašni čelik bočni granični udari

zadnji absorbujući poklopac

Figure 20.2: Appearance of a container in which nuclear waste is stored.

The size of packages for storing waste is very important; larger packages allow for storage of larger quantities, but it is more difficult to handle. The shape of the container is usually cylindrical or cubic. The weight and size of the waste packages vary in the range of 1 t/1.3 m/0.4 m to 70 t/6 m/2.1 m in diameter. Dry storage in containers is a method of keeping highly radioactive waste for at least a year and often for 10 years. There is presently no long-term method for storing bottles of fuel that are stacked vertically. A very important thing is that after storage of nuclear waste, there is constant motoring over the warehouses and places where nuclear waste is located.

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Surveillance systems can be placed near the facility or in the building itself [32]. It is necessary to constantly observe: 1. The mechanical and hydrogeological conditions in the environment, where nuclear waste is stored. 2. Constant monitoring of temperature, pressure and possible presence of hazardous gases. 3. Continuous supervision of mechanical and electrical installations, control of machines used to purify nuclear waste. Sweden proposed the KBS-3 concept of storage of nuclear waste, by depositing them in copper containers, which are stored in depots at depths of about 500 m in a stone surface (Figure 20.3) [33].

tuba za odlaganje

istrošeno nuklearno gorivo

bentonitski sloj

površina

300 m

gorivo UO2

bakarni kanister

stenska masa

podzemne prostonje

Figure 20.3:The KBS-3 project (image taken from [36]).

Storage can be done before closing the hole or after closing it. In the first case, the canister will be surrounded by bentonite (which does not absorb water), which means it can be lifted from the landfill using an installation canister. In the second case, the storage will be done after the tunnel is closed; checking is done due to the increase in temperature in the environment of the stored material. Conditions in the tunnel must be returned to the appropriate level, through natural ventilation. The reinforced concrete barrier at the entrance to the tunnel must be demolished and the material removed from the tunnel. The most common method of removing material from tunnels is to pump it to the surface. The Swiss Warehouse Concept [33] is also in use, where technological processes relate to operations that depend on the site and the appearance of the tunnel.

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20.5 Transport of nuclear material Preparing of the nuclear material for transport takes place on the basis of classified material [34]. The waste can be classified as: 1. Excluded waste (waste without radioactive substance). 2. Industrial waste (used containers for low radioactive activity, such as uranium oxide concentrate). 3. Type A waste (containers for the transport of relatively small amounts of radioactive material of medical origin or isotopes used in medicine). 4. Type B waste (containers used for the transport of dangerous chemical substances, such as UF6. Containers are type 48Y with a diameter of 122 cm and each can contain 12.5 t of UF6, or HLW, used fuel or MOX fuel. Containers must be gamma- and neutron-resistant materials, even under extreme conditions. The price of one container is up to $ 1.6 million). 5. Type C waste (small quantity material including plutonium). Transportation of nuclear material depends on the type of material. Pallets can be used to store uranium fuel that is produced as a by-product of production procedures (sintered at high temperatures). This pallet formed in process of sintering oxide of uranium at high temperatures. In Western Europe, Asia and America, the most common way of transporting these assemblies is by road traffic. Railway transport is commonly used in Russia and Eastern Europe. Transportation of spent waste with low level of radiation (LLW and ILW materials) is done with barrels up to 200 l. Transport can be carried out by road, rail or international waters. The spent nuclear fuel, with a high level of radiation, before transport, must be stored in water basins, where it is stored for at least five months prior to transport. After that time, it can be transported by road, rail or sea transport. The containers are a combination of steel and lead; when they are empty they can be up to 110 t. Since 1971, there have been over 7,000 fuel deliveries (over 80,000 tons) transported over one million kilometers without any damage or accident.

20.6 Conclusion The storage of spent nuclear fuel and waste, especially materials generated by commercial reactors or state-controlled reactors, presents a technological and security challenge today. A large number of activities are related to radioactive materials that arise as a by-product in nuclear reactors, creating waste nuclear material: in the civil nuclear program (nuclear power plants for the production of electricity),

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the military nuclear program (nuclear weapons, marine reactors), industrial and scientific activities (scientific research, medical research). Depending on the presence of oxides and radionuclides, spent nuclear fuel is divided into worn fuel with a low level of radiation of 5 × 106 to 5 × 109 Bq (LLW), spent fuel with a mean level of radiation of 5 × 109 to 5 × 1014 Bq (ILW), spent fuel with a high level of radiation of 5 × 1014 Bq (HLW). The basic conditions for the selection and storage of spent nuclear waste are a stable and sufficiently large geological formation and stable social community (without armed or civil conflicts over the past 100 years). US DOE and US EPA 36, 37 reference have established public health protection measures for the population and environment in the processes of building, operating and disposing of spent nuclear fuel with high-low radiation. The safety sustainable storage is based on the principle of disposing nuclear waste at great depths to the interior of the Earth’s crust. The basic parameter is the level of its thermal energy. In Temperature is the most important factor in ensuring their safe preservation. As a result, the ability to manage the temperature in a given facility is a critical aspect in nuclear waste storage systems. The nuclear waste is deposited in containers designed to provide permanent packaging safety during the handling, disposal and transport process. The material for the construction of the container must be resistant to corrosion and the formation of cracks and other deformations. Transportation of the nuclear material depends on the type of material.

References [1] [2] [3] [4] [5] [6] [7]

[8]

Fusco AM, Winfrey L, Bourhan AM. Sheilding properties of protective thin film coatings and blended concrete compositions for high level waste storage packages. Ann Nucl Energy 2016, 89, 63–69. Yim K, Man-Sung M, Linga K. Materials Issues in Nuclear-Waste Management. JOM 2000, 52(9), pp 26–29. Geological Disposal of Radioactive Waste (Vienna 2009): Technological Implications for Retrievability – IAEA Nuclear Energy Series NO. NW – T – 1–19, International Atomic Energy Agency. Nuclear Science Division. Retrieved 2009-01-05 from Environmental Surveillance, Education and Research Program.2009. Department of Energy & Climate Change., Implementing Geological Disposal – a framework for the long-term management of higher activity radioactive waste. 2014. International Panel on Fissile Materials, from http://fissilematerials.org/ipfm/about.html Hansen FD, Hardin EL, Rechard RP, Freeze GA, Sassani DC, Brady PV, Stone CM, Martinez MJ, Holland JF, Dewers T, Gaither KN, Sobolik SR, Cygan RT. Shale Disposal of U.S. High-Level Radioactive Waste. SAND2010-2843. Albuquerque, NM: Sandia National Laboratories.2010 a. Lomenick TF,. The Sitting Record: An Account of the Programs of Federal Agencies and Events That Have Led to the Selection of a Potential Site for a Geologic Repository for High-Level Radioactive Waste. ORNLTM- 12940. Oak Ridge, TN: Oak Ridge National Laboratory. 1996.

290

[9] [10] [11]

[12] [13] [14] [15]

[16] [17] [18]

[19] [20]

[21] [22]

[23] [24] [25] [26] [27] [28] [29] [30]

[31] [32]

Ana Radosavljević-Mihajlović, Vojislav Mitic

Gonzales S, Johnson KS, Shale and Other Argillaceous Strata in the United States. ORNL/ Sub/84-64794/1. Oak Ridge, TN: Oak Ridge National Laboratory.1984. Yavuz HS, Demirdag S, Cara S. Thermal Effect on the Physical Properties of Carbonate Rock. Int J Rock Mech Min Sci Geomech Abstr 2010, 47, 94–103. Smedes HW, Rationale for Geologic Isolation of High-Level Radioactive Waste and Assessment of the Suitability of Crystalline Rocks. Open-File Report 80–1065. Reston, VA: US Geological Survey.1980 Chapman NA. Geological Disposal of Radioactive Wastes – Concept, Status and Trends. J Iber Geol 2006, 32, 7–14. Winograd IJ. Radioactive waste storage in the arid zone. EOS 1974, 55, 884–94, 1974. EPA. Updated 2015-10-05 from “Underground Injection Control Regulations.”. Brady PV, Arnold BW, Freeze GA, Swift PN, Bauer SJ, Kanney JL, Rechard RP, Stein JS. Deep Borehole Disposal of High-Level Radioactive Waste. SAND 2009–4401, Albuquerque, NM: Sandia National Laboratories, 2009. Nuclear Waste Policy Act of 1982. 96 Statutes at large 2201, 42 U.S. Code 10101 et seq. EPA. (July 2001). From “Technical Program Overview: Underground Injection Control Regulations.” Document no. EPA 816-R–02–025. Bala A, Sub-seabed burial of nuclear waste: if the disposal method could succeed technically, could it also succeed legally Editor in Chief, Boston College Environmental affairs law review, 2013–2014. From http://ealr.bclawreview.org/files/2014/04/05_bala.pdf IAEA retrieved 2011-12-4, from TECDOC-1105 Inventory of radioactive waste disposals at sea” August 1999. Nadis SS, “The Sub Seabed Solution, Atlantic Monthly, from http://www.theatlantic.com/ magazine/archive/1996/10/the-sub-seabed-solution/308434 and http://perma.cc/S2U6SR9B (describing sub-seabed disposal as possibly the best solution yet advanced to the nuclear-waste problem” despite setbacks from “a series of political blunders”), 1996. Cascadia Subduction Zone, U.S. GEOLOGICAL SURV., http://earthquake.usgs.gov/research/ structure/crust/cascadia.php (last updated Aug. 17, 2012), from http://perma.cc/D87X-7B9B. London Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter, from https://en.wikipedia.org/wiki/London_Convention_on_the_Prevention_of_ Marine_Pollution_by_Dumping_of_Wastes_and_Other_Matter Basel Convention, from https://en.wikipedia.org/wiki/Basel_Convention MARPOL 73/78 is the International Convention for the Prevention of Pollution from Ships, 1973 as modified by the Protocol of 1978, from https://en.wikipedia.org/wiki/MARPOL_73/78. Secrtériate du Traité sur l’Antarqtique, from ATS.aq. Philberth B. Beseitigung radioaktiver Abfallsubstan- zen in den Eiskappen der Erde. Schweizerische Zeits f Hydrologie, Fasc. 1, 1961, 262–84. “Supply of Uranium” World Nuclear Association 2010. World Nuclear Association Fast Neutron Reactors”.2012. Maxwell. I. Nuclear power: a very short introduction. Oxford: Oxford University Press, Vol. 55, 2011. Rechard RP, Goldstein B. B, Brush LH, Blink J. A. JA, Sutton M, Perry FV. “Prepared for U. S. Department of Energy Used Fuel Disposition Campaign, Basis for Identification Disposal Options for Research and Development for Spent Nuclear Fuel and High-Level”.2011. Youn-Myoung L, Heui-Joo C, Kyungsu K. A preliminary comparison study of two options for disposal of high-level waste. Prog Nucl Energy 2016, 90, 229–39. IAEA Nuclear Energy Series No. NW-T-1.19, Geological disposal of radioactive waste: technological implications for retrievability, IAEA Vienna. from http://www-pub.iaea.org/ MTCD/publications/PDF/Pub1378_web.pdf. 2009.

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[33] IAEA Safety standards for protecting people and the environment – regulations for the safe transport of radioactive material 2012 Edition specific safety requirements NA SSR-6 IAEA 2012 Vienna. [34] Vandenbosch R, Vandenbosch SE. Nuclear waste stalemate: Politicila and scientific controversies. Salt Lake City: University of Utha Press, 2007. [35] https://radwasteplanning.ca/sites/default/files/lilw_white_paper_final.pdf [36] Andrews A, Nuclear Fuel Reprocessing: U.S. Policy. CRS Report For Congress, 2008. [37] U.S. Environmental Protection Agency (EPA) (2015-10-08). Washington, DC. From “General Information About Injection Wells”.

Zoran B. Vosika, Vojislav V. Mitić, Goran Lazović, Vesna Paunović, Ljubiša Kocić

21 Fractal corrected Schottky potential and Heywang model Abstract: As a material with high dielectric constant, barium titanate has attractive electrical properties that have been extensively studied and reported. On the valencecompensated semiconduction papers led to the positive temperature coefficient (PTC) of the resistance effect found in doped BaTiO3. Also, this material have a strong porosity and his fractal nature influenced on microelectronic properties of material. The framework of this chapter describes the fractal correction of Schottky potential barriers within Heywang’s model. For it is used Tarasov’s fractional calculus with the concept of mass fractal dimension. Also, we involved the complex fractal correction in Schottky potential through relative dielectric permittivity εr and working temperature. This is confirmed by appropriate experimental conditions and the analysis of the fractal surface construction. Keywords: BaTiO3 ceramics, Schottky potential, Heywang model, fractals

21.1 Introduction BaTiO3-based materials are one important group of materials with positive temperature coefficient (PTC) effect. At room temperature, he which as a monocrystal, is an insulator after predominantly doping with trivalent donors (e.g., cations La3+,Y3+, Sb3+, Ho3+, Er3+ and Dy3+) which substitute for the Ba2+ or with pentavalent or higher donors (atoms Sb, Nb, Ta) which substitute for Ti4+ that get semiconductive properties [1–4]. In addition, the substitution of Ho3+ or Er3+ on Ba2+ sites requires the formations of negatively charged defects acceptor sites [5, 6]. At this moment three possible compensation mechanisms are known: titanium vacancies (VTi’’’’),

Acknowledgments: This research is a part of the project “Directed synthesis, structure and properties of multifunctional materials” (172057). The authors gratefully acknowledge the financial support of Serbian Ministry of Education, Science and Technological Development for this work. Zoran B. Vosika, Vesna Paunović, Ljubiša Kocić, University of Niš, Faculty of Electronic Engineering, Aleksandra Medvedeva 14, Niš, Serbia Vojislav V. Mitić, University of Niš, Faculty of Electronic Engineering, Aleksandra Medvedeva 14, Niš, Serbia; Institute of Technical Sciences of SASA, Belgrade, Knez Mihailova 35/IV, Serbia, [email protected] Goran Lazović, University of Belgrade, Faculty of Mechanical Engineering, Belgrade, Serbia https://doi.org/10.1515/9783110627992-021

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barium vacancies (VBa’’), and electrons (e’). When properly processed, semiconductive BaTiO3 polycrystals show a PTC effect. The temperature at which the PTC normally occurs can be altered by adjusting the Curie point, Tc (the transition temperature from the ferroelectric tetragonal phase to the paraelectric cubic phase). The PTC behavior of donor doped polycrystalline BaTiO3 ceramics depends on process of sintering, microstructural aspects such as grain size, domain orientation, phase profile and porosity. The PTC effect in BaTiO3-type compounds is a very important research topic, because of its technical importance and the difficulty of explaining the behavior thoroughly. The principal doping mechanism for samples sintered in air atmosphere, opposite to the above, which are the electrical insulators, is the ionic compensation mechanism. Between two grains, double quadratic BaTiO3 ceramics Schottky potential according to Heywang model which explains PTC effect [7–11], near the grain boundary, with the corresponding effective barrier width y0 is φðyÞ =

eNd ðy − y0 Þ2 , 0 ≤ y ≤ y0 2ε0 εr

(21:1)

where Nd is the charge carrier concentration, ε0 is the dielectric permittivity of free space and εr is the relative dielectric permittivity of the grain boundary region, y is the normal distance from the contact, y0 is the width of space-charge region. Heywang proposed a model based on two resistive layers in the equilibrium to arise as a result of the presence of deep electron traps (acceptor or donor states) at the grain surfaces, developing Schottky-like potential barriers between the grains. For example, acceptors attract electrons from the bulk, resulting in an electron depletion layer with a width of y0: y0 =

NS 2Nd

(21:2)

NS is the density of the acceptor states at the grain boundaries and Nd is the density of the donor states. The depletion layer results in a grain boundary potential barrier φ0 = φ(0): φ0 =

eNS2 8ε0 εr ðT ÞNd

(21:3)

The temperature dependence of the active acceptor state density, NS, is described by equation N S ðT Þ =

NS 0

E + eφ − E 1 + exp F k T0 S B

(21:4)

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ES is the energy gap between the energy levels of the acceptor states and kB is the Boltzmann constant. The Fermi energy is given by the formula   NC (21:5) EF = kB T ln Nd where NC is the effective density of the states in the conduction band  3 me kB T 2 NC = 2 2πh2

(21:6)

Constants me and h are effective electron mass and Dirac constant. For the Fermi– Dirac integral [7], 2 Fn ðxÞ = pffiffiffi π

∞ ð

dy · 0

yn 1 + expðy − xÞ

(21:7)

the free-carrier densities, for the conduction energy level EC can be written as   EF − EC (21:8) n = NC F1=2 kB T where F1/2 is the Fermi–Dirac integral of order 1/2. The charge carrier concentration Nd described by equation Nd =

2 · exp

N D

EF − Ed kB T

+1

(21:9)

where ND is the total donor concentration at the donor energy level Ed. The additives that affect on the dielelectric properties below the Curie pointthen for the many cases valid Curie–Weiss law [12] εr =

C T − Tc

(21:10)

C ~ 105 is the Curie constant, for BaTiO3 ceramics. Tc are the usual temperatures about 100 °C. The corresponding Poisson equation, in the full depletion approximation, is ∂2 ϕðyÞ eNd = ε0 εr ∂y2

(21:11)

For T > Tc the specific electrical resistance of the BaTiO3 ceramics is described by the term   eφ0 (21:12) ρ = ρV · exp kB T And ρV is a constant, which describes the monocrystalline state of BaTiO3.

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More detailed, in his model, Heywang [8, 9] made three assumptions. a) Grain-boundary effect is the cause of the PTC. b) The permittivity of a single crystal equals the grain-boundary permittivity and follows the Curie–Weiss law. c) Along the grain boundaries exist at least two-dimensional electron-trap layers. The formation of an electrical potential barrier is presented as a contact phenomenon in the air of two identical BaTiO3 grains an with interlayer of material that represents the grain boundary. According to Heywang’s model, the grain boundary is made of the same semiconductor but also contains dopants, impurities or defects. Heywang’s model proposed that the existence of grain boundaries leads to a significant change in the periodicity of the structural lattice, resulting in formation of surface electronic states of the acceptor or donor type. The existence of surface electronic states of the acceptor or donor type at the grain boundaries leads to enrichment or depletion of these surfaces’ free charge carriers. Thus, doping of barium titanate can affect oxidation processes in the grain boundaries. During these processes, oxygen from air is adsorbed by the grain boundary taking over the electrons from the area near the grain boundary, thereby creating the so-called trap for electrons. Forming trapping points for electrons leads to a decrease in the concentration of the electrons inside depletion region layer, effective width y0, located at the energy level Es below the conductive zone. It results in the creation of a dual Schottky barrier potential with height φ0. In Heywang’s model the formation of these states is not explained in detail, whereas according to Daniels, this is the consequence of different distributions of defects per sample [13]. Daniels et al., with his model, could explain Heywang’s model’s unanswered questions. Daniels and Wernicke claimed that the VA act as accepters and trap electrons from the bulk, creating a potential barrier. As the semiconductive BaTiO3 generated by reduction contains oxygen vacancies only, there is no PTC in this type of material. The PTC effect, according to Daniels and Wernicke, depends largely on the thickness of the VBa rich grain boundary layer. A wider layer will form for the slower cooling greater VBa concentration. If the cooling rate is sufficiently slow, the doped BaTiO3 will become an insulator, and the effect will vanish. The PTC conductivity anomaly is explained by Daniels’ model as follows. It is known that high dopant concentrations (or adequately slow cooling rate) lead to small grain sizes, generally, maximum, a several micrometers in size. At realistic cooling rates, thickness of the insulating grain boundary layers is approximately about 1 µm. The smallest grained materials become an insulator. However, the low resistance of a PTC device at room temperature – below the Curie point – cannot be explained by either the Heywang model or the Daniels model. Jonker’s model [14], which describes the resistivity below Tc, is a refinement of the Daniels’ or Heywang’s model. Jonker’s model is based upon the ferroelectric behavior of BaTiO3 below the Curie point, that is, BaTiO3 becomes ferroelectric with its polarization axis aligned with the tetragonal crystal axis. Then, the polarization, as

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expected, changes direction from domain to domain. As adjacent grains have different crystal orientations, the polarization direction is also different from grain to grain. The difference in polarization direction causes a net polarization perpendicular to the grain boundaries and creates surface charges at the grain boundaries as additional surface effect, which significantly affects the grain boundary potential barrier height. Jonker’s model is usually used in combination with Heywang’s or Daniels’ models. Lastly, fractals [15–18] represents a relatively new approach to modeling and describing mentioned the porosity, dynamics, grain’s shapes and relations between BaTiO3 ceramic structure and electrical properties [19–21]. It gives more natural approximation to the motion of particles or grain’s boundaries in a construction that uses recursive random algorithms. In the fractal analysis estimation of the main parameter, the Hausdorff or fractal dimension is relevant for all morphologies that occur in the sintering process. If its variant is accepted – a mass fractal dimension – it is possible to make new predictions about the shape and properties of the Schottky barrier, using the Tarasov’s fractional calculus [22–26]. Based on the above, bearing in mind the connection between the Heywang model and other models, fractal nature of the surface of the grains, assuming that the fractal distribution of charged particles in the grain and using the Tarasov’s calculus, in this chapter it is considered complex fractal correction of the Schottky potential, through relative dielectric permittivity εr and working temperature. This is confirmed by appropriate experimental conditions and the analysis of the fractal surface (the fractional Brownian field) construction through the tensor product of two curves that are fractional Brownian motions [27].

21.2 Results and discussion Ceramic grain contacts are essential for understanding complex electrodynamics properties of sintered materials. Microstructures of sintered BaTiO3 ceramics obtained by SEM method are characteristic examples of complex-shaped geometry, which cannot easily be described or modeled. A possible approach for describing contact phenomena is establishing the grain shape or grains contact models. Our new approach includes fractal geometry in describing complexity of the spatial distribution of electroceramic grains [19–21], now including Schottky potential.

21.2.1 Experimental BaTiO3 ceramics prepared by a conventional solid state were used for our investigation. Sintering procedure were starting from reagent grade powder BaTiO3. Different

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additives like as MnCO3, CaZr2O3, Er2O3, Yb2O3, Ho2O3 were used for doping BaTiO3ceramics. The additive content ranged from 0.01 to 2.0 wt%. Starting powders were ball milled in ethyl alcohol 24 h, and pressed into pellets 2 mm thick and 7 mm in diameter at a pressure of 120 MPa. The pellets were sintered in air from 1,320 °C to 1,380 °C for 4 hours. Scanning electron microscope, JEOL, SEM-5300 equipped by EDS (Energy Dispersive Spectrometer) system, was used for the investigation of the microstructure of BaTiO3 doped samples. Most of microstructures have been done with selection of some grains and pores with minimum five magnifications, which is important because microstructure fractal nature analysis. Based on experimental results and samples we continued to analyze microstructure fractality by theoretical experiment.

21.2.2 Theoretical experiment Based on the several consolidated BaTiO3 ceramic samples, within real sintering processes, we continued the real technological experiment via theoretical experiment, where theoretical experiment represents part of real experiment and an introduction to it, which are a subject of our scientific research reporting by this chapter. To understand the processes on the grain boundary and especially between the grain boundaries on the better and more precise way, we applied here important advanced knowledge to respect on this matter. One is the Minkowsky–Hull double layer approach [20], and he has already opened new frontiers precisely enlightening spaces near the grain boundary, analyzing the electrons space processes. We found that nature of these processes could be explained best by fractional Brownian (particles) motion, which is also characterized by fractal nature. This way we can easily apply the mathematical fractional calculus explaining the real picture of physical processes more precisely. On the other side, it is very important for Schottky barrier phenomena to analyze the trapping centers and the grain boundaries. In previous scientific papers [28, 29], the effects of electrons collisions and associated relaxation time are described already, so we continue to enrich and upgrade the knowledge and understanding of all these processes. In that sense, we demonstrated and explained here the particle trajectories as a fractal curvature. Also, by our intention to explain these processes within the surfaces between the grains where trapping centers reside, we extended the analysis by the fractal curvature’s tensor product in a way to get a real figure about sub-micro processes and particles’ motions in the area near grain boundaries or between the grain boundaries. Further, we develop this physical mathematical apparatus in details as a tool toward completing the picture of sub-microstructure processes.

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In addition, many different approaches exist to the problem of Descartes or tensors products of Cantor’s sets C. Optimal sets C × C: their diameters, measures, symmetries and the shapes are investigated in [17]. Basic results in [30, 31] are examples of compact sets showing that the dimension of the product of metric spaces E × F may attain any of the values permitted by these inequalities: dimH E + dimH F ≤ dimH ðE × F Þ ≤ dimH E + dimP F dimH E + dimP F ≤ dimP ðE × F Þ ≤ dimP E + dimP F

(21:13)

dimB E + dimB F ≤ dimB ðE × FÞ ≤ dimB E + dimB F In the mathematical literature, from point of view theoretically and algorithmically, there is a method of construction of fractional Brownian field by the tensor product of two curves as a part of Brownian motion [27]. These mathematical models are practically arranged patterns at the measurements, as application for data spatial processes. For these data spatial processes, collection and analysis are very important in sciences and engineering, including the earth fields, design of materials, astronomy and urban planning. The possibilities of availability of fast computers applied at Monte Carlo simulations methods what is high importance for better spatial processes knowledge. These processes is practically random variables {Xt, t ∈ T } collection where is T is just subset of the d-dimensional space Rd –space; Xt is a random quantity related with a special parameter t in geometric or time space. Xt is the possible values set which we call the spatial process state space. One-dimensional Wiener process {Wt, t ≥ 0} is a stochastic process. Its features are: (1) Wt increments are stationary and normally distributed (Wt − Ws ~ N(0, t − s) for all t > s > 0) with respect to the parameter t; that is, (2) for t1 < t2 ≤ t3 < t4, random variables Wt4 − Wt3 and Wt2 − Wt1 are independents-autonomous; (3) Wt − Ws, t > s is autonomous of the previous history of {Wu, 0 ≤ u ≤ s}); (4) all paths of {Wt} are continuous with respect to t, with the initial condition W0 = 0. A continuous zero-mean Gaussian process {Wt, t ≥ 0} called fractional Brownian motion (fBm) with roughness parameter αB ∈ (0, 2) is he fulfills the relation-covariance function 1 CovðWt , Ws Þ = ½jtjαB + jsjαB − jt − sjαB , 2

t, s ≥ 0

(21:14)

This process is often parameterized with respect to the Hurst or self-similarity parameter H = αB/2. Of course, H ∈ (0, 1). Process fBm has a feature rescaled processes {c−H Wct, t ≥ 0} has the same distribution as {Wt, t ≥ 0} for all c > 0, and, as conclusion, this trajectories are a random and self-similar.

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The uniformly spaced grid generated on the fBm 0 = t0 < t1 < t2 < . . . < tn = 1 can be achieved by first generating the increment process {X1, X2,. . ., Xn} (Figure 21.1). Where Xi = Wi − Wi −1. Then the cumulative sum is Wti = cH

i X

Xk ,

c=

i = 1, 2, 3, . . . , n,

k=1

1 n

(21:15)

Then fractional Gaussian noise is a set {X1, X2,. . ., Xn}. 0.4 0.35 0.3

W(t)

0.25 0.2 0.15 0.1 0.05 0 –0.05

0

0.1

0.2

0.3

0.4

0.5 t

0.6

0.7

0.8

0.9

1

Figure 21.1: Fractional Brownian fractal nature motion for space coordinate W(t), t = k/n, with Hurst parameter H = 0.6, n = 500, k = 0,1, . . ., n.

This is a discrete zero-mean stationary Gaussian process characterized with covariance 1 CovðXi , Xi + k Þ = ½jk + 1jαB + jk − 1jαB − 2jkjαB , 2

k = 0, 1, 2, . . .

(21:16)

In two dimensions, the Wiener sheet (field) is a spatial generalization of the fractional Brownian motion. The continuous zero-mean Gaussian process {Wt, t ∈ [0, 1]2} is the Wiener field process on the unit square characterized byproduct for covariance function form extension of (21.14) CovðWt , Ws Þ =

1 ½js1 jαB + jt1 jαB − js1 − t1 jαB  ½js2 jαB + jt2 jαB − js2 − t2 jαB  4

(21:17)

301

21 Fractal corrected Schottky potential and Heywang model

The fractal Brownian motion field obtained as a Kronecker product as a independent two fBm (Figure 21.2). (a)

(b)

2

1 0

0

Z

Z

1 –1

–1 –2 2

1.5 t2

1

0.5

0 0

1

0.5

1.5

–2 2

2

1.5 t2

1

0.5

1.5

2

t1

(d)

1.5

0.5

1 0.5

0 W

W

(c)

0 –0.5 –1 2

0.5

t1

1

–0.5 –1

1.5

1 t2

0.5

0 0

0.5

1

1.5

2

–1.5 2

1.5

1

0.5

0 0

0.5

1 t1

1.5

2

Figure 21.2: Tensor product of two fractional Brownian fractal nature motions Z = Z(t1, t2)-space distribution of the Brownian motions, t1,2 = k1,2/n, with Hurst parameter H = 0.6, n = 500, k1,2 = 0, 1, . . ., n; (a) Only fractional Brownian field; (b) Fractional Brownian field with 30 levels in the plane t1Ot2; (c) FBm W(t1); (d) FBm W(t2).

Each of these fractal curves is defined on the unit intervals and can easily be scaled to any scale from the real experimental microstructure. The dimensions of t1, t2, Z (these variables are space coordinates) correspond to real geometry dimensions. Also, t1, t2, in another research could be used as time coordinates. In that case time could be involved as a fourth dimension. The surface total fractal dimension of satisfies the relations (13) and especially within the contour representation in Figure 21.3. In this chapter, we adapted approach in view of [27], considering a precisely Kronecker tensor product and ceramics technological preparation geometry, which could be applicable on any surface structure in real sample microstructures. From the other point of view, this is very interesting tool to be applied on the starting the powders particles before, during the process of consolidation exactly before pressing pressure or before sintering phase cooling. By this way that solution is a very powerful application for controlling microstructure (grains and pores) from the beginning samples consolidation processes up to the end.

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Figure 21.3: Contour graph for fractional Brownian field Z = Z(t1, t2), t1,2 = k1,2/l, the Hurst parameter is H = 0.6, l = 500, k1,2 = 0, 1, . . . , l, with n = 30 levels in the plane t1Ot2.

With Figure 21.3. we presented the new method applicably within the many perspectives for fractal microelectronic topology, what is a new light toward directions of high level of microelectronics integration by fractal nature analysis. The levels on the fractal surface roughness on one grain boundary, together with another similar structure on the other grain boundary contact, practically defining the base for the superfine fractal microstructure.

21.2.3 Tarasov’s approach By Tarasov’s original approach [22, 26], fractal media can be characterized by the relation between the mass MD(W) of a ball region W, and the radius R of this ball in the form MD(W) = M0(R/R0)D, R0 ≫ 1, where R0 is the characteristic size of fractal medium such as a minimal scale of similarity for a considered fractal medium (fractal atom with the mass M0), positive or zero constant D is called the mass fractal dimension. Then, fractal materials can be considered as a continuous media with non-negative mass dimensions. By using the integration over non-integer dimensional space, the power law MD(W) ∼ RD can be naturally derived where the space dimension is equal to the mass dimension of fractal media. It is convenient to work in the dimensionless space variables x/R0 → x, y/R0 → x, z/R0 → x, r/R0 → r, in the continuum models of fractal media that yield dimensionless integration and dimensionless differentiation in non-integer dimensional space. Then, the physical quantities of fractal media have correct physical dimensions. Concepts of density of states cn(D, r) and distribution function ρ(r) should be used in order to describe fractal media by continuum models. In the space region where the fractal medium is distributed, the density of states describes how closely

21 Fractal corrected Schottky potential and Heywang model

303

permitted places (states) in the space Rn are packed. For example, the expression cn(D, r)dVn (dVn is a hypervolume) is equal to the number of permitted states between Vn and Vn + dVn in Rn. For spatial, surface and line fractals and their fractal hypervolumes are: dVD = c3 ðD, rÞdV3 ,

dSd = c2 ðd, rÞdS2 ,

dlβ = c1 ðβ, rÞdl1

(21:18)

Then, for line fractals valid formula: β

π2 c1 ðβ, xÞ = · j xjβ − 1 , Γð0.5 · βÞ

(21:19)

β 2 ð0, 1

For surface fractals is 22 − d c2 ðd, rÞ =
d jrjd − 2 , Γ 2

1