Nanotechnology in Space 9814877549, 9789814877541

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NANOTECHNOLOGY IN SPACE

NANOTECHNOLOGY IN SPACE

edited by

Maria Letizia Terranova Emanuela Tamburri

Published by Jenny Stanford Publishing Pte. Ltd. Level 34, Centennial Tower 3 Temasek Avenue Singapore 039190

Email: [email protected] Web: www.jennystanford.com

British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library.

Nanotechnology in Space Copyright © 2022 by Jenny Stanford Publishing Pte. Ltd. All rights reserved. This book, or parts thereof, may not be reproduced in any form or by any means, electronic or mechanical, including photocopying, recording or any information storage and retrieval system now known or to be invented, without written permission from the publisher.

For photocopying of material in this volume, please pay a copying fee through the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, USA. In this case permission to photocopy is not required from the publisher. ISBN 978-981-4877-54-1 (Hardcover) ISBN 978-1-003-13191-5 (eBook) DOI: 10.1201/9781003131915

Contents

Trends in Space Nanotechnologies 1. Nanotechnology for Space Power Devices Ryne P. Raffaelle 1.1 Introduction 1.2 Engineered Materials and Structures 1.3 Power Generation, Storage, and Distribution 1.3.1 Carbon Nanotube Wires 1.3.2 Lithium-Ion Batteries 1.3.3 Quantum Dot Solar Cells 1.4 Propulsion and Propellants 1.5 Future Nanotech Approaches to Space Power

2. Nanocomposite and Micro-Nanostructured Materials with Applications of MEMS/Nano Devices for Aerospace Rodolfo Guzzi, Francesco Marra, and Giovanni Pulci 2.1 Introduction 2.2 Ablative Nanocomposite Materials 2.3 Nanostructured Thermal Barrier Coatings 2.4 Additive Manufacturing of Nanocomposite Materials for Aerospace Applications 2.4.1 Materials 2.4.2 Techniques 2.4.3 Aerospace Applications 2.5 Space Sensors for Gas Detection and Microthruster 2.5.1 Technology of Lithium Niobate 2.5.2 Microinterferometer 2.5.3 Nanothruster 2.6 Conclusion

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3. Advanced Polymer Composites for Use on Earth and in Space Konchits Andrey, Yeriomina Yekaterina, Tomina Anna-Mariia, Lysenko Oleksandr, Krasnovyd Serhii, and Morozov Olexander 3.1 Introduction 3.2 Technology of Preparation of Polymer Composites Based on Aromatic Polyamides 3.2.1 Components for Manufacture of CMs 3.2.2 Preparation of Polymeric CMs in Rotating Electromagnetic Field 3.3 Results 3.3.1 CMs with Nanofillers 3.3.1.1 Electronic properties 3.3.1.2 Tribotechnical characteristics 3.3.2 Composites with Micro-dispersed Fillers 3.3.2.1 Electronic properties 3.3.2.2 Tribotechnical characteristics 3.3.3 Examples of Application of Developed CMs

4. Printable Materials for Additive Manufacturing in Harsh Earth and Space Environments Amanda M. Schrand, Manoj Kolel-Veetil, Edwin Elston, Clayton Neff, Tosin Ajayi, and Cheryl Xu 4.1 Introduction 4.2 What Makes the Space Environment Harsh? 4.3 Considerations for Printable Inks in Harsh Environments 4.3.1 Studies on Material Properties of 3D Printable Inks 4.4 Considerations for Printable Ceramics in Harsh Environments 4.4.1 Additive Manufacturing (3D) for Ceramic Materials: Slurry-Based Technique 4.4.2 Major Stereolithography Processing Parameters

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4.4.3 Stereolithography Manufacturing via Polymer-Derived Ceramic Process 4.4.4 Additive Manufacturing (3D) for Ceramic Materials: Solid-Based Technique 4.4.5 Filament Selection for Fused Deposition of Ceramics 4.4.6 Some Examples of Additive Manufactured Components for Harsh Environments Future Directions for AM in Harsh Environments 4.5.1 Resilient Hybrid Electronics 4.5.2 Food Printing 4.5.3 Space Garments Conclusionary Statement

5. Nano-Based Coating for Spacecraft: Antibacterial Film for Manned Application Antonia Simone and Cristina Balagna 5.1 5.2 5.3 5.4 5.5

5.6 5.7 5.8 5.9

Introduction Biofilm Formation Antibacterial Surfaces Nanostructured Layers Complete Characterization of Coated Materials 5.5.1 Case of Textiles Antibacterial Test in Broth Toxicological Behavior Mechanical Characterization Conclusion

6. Nanotechnology in Space Economy Tanya Scalia and Lucia Bonventre 6.1 Introduction 6.1.1 Space Economy 6.1.1.1 Public actors 6.1.1.2 New approaches to space economy 6.1.2 Space Economy and Nanotechnology

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6.2 Methodology 6.3 Nanotechnologies for Space Sector 6.3.1 Nanotechnologies for Engineered Materials and Structures 6.3.2 Nanotechnologies for Sensors, Electronics, and Devices 6.3.3 Nanotechnologies for Energy Storage, Power Generation, and Power Distribution 6.3.4 Nanotechnologies for Life Support Systems 6.3.5 Nanotechnologies for Payload/ Satellites 6.3.6 Nanotechnologies for Space Transportation and Propulsion Systems 6.4 Conclusion and Perspectives Index

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Trends in Space Nanotechnologies

Under the broad theme “Nanotechnology in Space,” this book highlights some selected topics related to nanotech applications in the strategic sector of space. The expanding field of “space” encompasses a lot of items, from spatial stations to satellites, from manned/unmanned vehicles to deep-space vessels and future lunar habitat. The ambitious vision of an enlarged exploration of the solar system as well as of Moon and Mars colonization in the decades to come needs now to realize in a practical context many of the fanciful paradigms cultivated at the beginning of the nanotechnological era. In this regard one must note that the rational engineering of complex nanostructures has already enabled to achieve outstanding results in many “on-the-earth” applications. However, in comparison with on-the-earth applications, the space, in view of the peculiar characteristics of the out-of-earth environment, poses additional challenges that must be considered. Beyond the severe shocks due to cycling variations of both temperature and pressure, the materials experience extreme changes in gravitational forces. Moreover, several uncommon effects occur in the outer space. Galactic cosmic radiations, solar particles and neutrons generated by secondary nuclear processes represent hazards not only for the humans but also for the structural components and the electronic systems of the spacecrafts. Corona discharges and gas condensation are produced by invacuum outgassing and gas clouding, with consequent modification of optical, thermal, and electrical properties of materials. Other limits of performances are due to impacts from debris and micrometeoroids that produce damages in the outer layers of the spacecrafts, or to the corrosion induced by atomic oxygen for lowearth orbits. Beyond designing nanomaterials with on-demand combinations of tunable properties and with architectures able to avoid premature systems failure, the instruments and components that constitute the payloads of space missions must match further requirements. Whereas some demands, such as a net reduction in weight, mass

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footprint, and power consumption, are common to all the spacerelated uses, others are almost specific. As an example, speaking about the mechanical properties, for each nanomaterial/system and for the reliability of each operation, the main requirement could be, in turn, hardness, toughness, resilience, or a combination of them. The working at the frontier of chemical physics and of materials engineering is giving an unprecedent control of matter on the nanoscale and will enable, in perspective, to withstand the very unique space environment increasing safety and reliability of all the space-related activities. To make this happen, design of multifunctional nanomaterials, innovations in manufacturing processes, creation of new products, and realization of advanced devices represent the fundamental building blocks of the value chain that got started. The “NASA Technology Roadmaps - TA 10: Nanotechnology,” released by NASA in 2015, identified four key topics to be developed during 2015–2035. The planning, further confirmed in the recently released “NASA-2020 Technology Taxonometry,” was to cover the four areas of propulsion, materials/structures engineering, energy generation/storage/distribution, and devices. The last topic was subdivided into sensors/actuators, nanoelectronics, and miniaturized instruments/components. The awareness about the objectives to be attained, jointly with remarkable studies and stimulating debates, is leading the scientific community toward encouraging advancements in almost every area, facilitating the goals to produce faster, lighter, cheaper, more reliable/versatile, and less energy-consuming objects. This book features six chapters that showcase some present activities combining creativity with a multidisciplinary approach and, moreover, identify future efforts needed to further expand the mega trend of nanotechnology in space. More specifically, the first five chapters provide an up-to-date look at the ongoing experimental activities in such rapidly progressing research field and elucidate with concrete examples the many aspects of nanomaterials and nanotech tools advantageous for the space sector. But we should not forget that the space is a strategic sector in the global economy, with an even increasing worldwide related businesses. In this light, the sixth chapter is dedicated to the analysis of the current and future markets for space-related nanotech products and applications.

Trends in Space Nanotechnologies

Chapter 1, “Nanotechnology for Space Power Devices” by Dr Ryne P. Raffaelle, focuses on carbon nanotubes (CNTs), the outstanding class of nanocarbons that can find place in a variety of aircraft structures and components, from payloads, instrumentation, and devices to propulsion and power systems. The chapter reviews the current state of the art of space power devices used to provide electrical power to aerospace vehicles. The adaptive use of CNT is now allowing fabrication of innovative quantum dot solar cells, highly efficient rechargeable Li-ion batteries and thermionic devices for energy conversion, as well as supercapacitors for energy storage. Moreover, CNTs in the form of electrical wires are being tested for power management and distribution in spacecrafts and platforms. The engineering of CNT shows tremendous promises also in the last-generation propulsion systems, such as the alternative concept of electric propulsion (EP), where the propellant is accelerated by electromagnetic fields. The high efficiency of EP in converting energy to thrust requires a very small mass of propellants to accelerate a spacecraft and makes, therefore, possible a decrease in the loaded weight. As indicated in the NASA studies cited in this chapter, a decrease in the overall vehicle mass by up to 50% could be obtained by employing properly engineered CNTs in the assembling of both primary and secondary structures. The achievement of such a goal would mean a reduction in launch costs, a more affordable access to space, and, at the same time, an increase in functionality, safety, and reliability of the missions. Under the title “Nanocomposite and Nanostructured Materials: Applications and Devices for Aerospace,” Chapter 2 by Dr Rodolfo Guzzi et al. presents a scenario of current studies focused on materials/devices for applications in avionics, satellites, space vehicles and platforms, communication, and radar technologies. Here the reader can find a selection of technologies that represent very important opportunities for the aerospace industry. Starting from nanocomposite materials and techniques for their assembling into defined architectures, this chapter illustrates the state of the art of the thermal protection systems (TPS) designed for atmospheric re-entry, as well as of the technologies adopted for thermal barrier and wear-resistant coatings. Several examples of polymer-based ablative nanocomposite materials are presented, along with their mechanical and thermal properties and the results of the tests performed under working conditions.

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As regards the nanotech-based devices, this chapter reports on currently available or foreseen set of miniaturized sensors and lab-on-a-chip biosensors able to control and monitor the physical, chemical, and biological conditions inside and outside the space vehicle. The next generation of sensors, in some cases based on non-traditional materials, is expected to manage at the best the issues to detect and measure in continuous a series of very different parameters. Among the multitude of tasks that sensors will be called to do during space and planetary explorations, there are indeed the inspection of astronaut health, the control of the structure reliability, and the analysis of the instrumentation functionality. For the spectral analysis of radiations, Guzzi et al. proposed an innovative highly performant scanning micro-interferometer. The most peculiar characteristic of such optical device is the lack of moving parts, which enables better efficiency and a longer working life. Moreover, the small size and the negligible weight of the device allow the packaging of several similar items, each of them optimized for a specific narrow spectral range. Based on the same technology, an optical gyroscope has also been fabricated, which can find application as valuable attitude sensors. Such devices, with performances improved by CNT, can work coupled with a chemical monopropellant micro-thruster obtained via nanotechnological fabrication steps.

Chapter 3, “Advanced Polymer Composites for Use on the Earth and in Space” by Dr Konchits Andrey et al., focuses on the outstanding matter of dual-use nanotechnologies and deeply illustrates the mutual benefits of key-enabling materials that can be used successfully both on earth and in space. Joining all aspects of science and technology in a highly adaptive manner is a fundamental concept for managing, at the best, the human and economic resources and for reaching in a short time many challenging goals. Here the attention is focused on innovative nanocomposites based on “phenylone” polyamide polymer. A series of low-cost/low-weight hybrid nanomaterials are obtained by combining the aromatic polyamide with various classes of materials, such as graphites, metals, organic compounds, nanocarbons, and more. The chapter showcases manufacturing schemes, structural analysis, and applications in many technological areas of such last-generation nanomaterials characterized by a number of unrivalled properties, going from the thermophysical to the magnetic and tribological ones. The combination of outstanding

Trends in Space Nanotechnologies

properties is a fundamental requirement for long life-time missions, when materials used to assembly components must provide solutions to complex problems, such as resistance to thermal cycling coupled with high stiffness/strength.

Chapter 4, “Printable Materials for Additive Manufacturing in Harsh Earth and Space Environments” by Dr Amanda M. Schrand et al., faces the topic of “on-site” in-space fabrication and repair of equipment and infrastructures using additive manufacturing (AD) techniques. The use of 3D printing can allow production/replacement of tools during the missions, avoiding the need for a re-supply from earth and reducing launch costs. In this context, the emphasis is on the choice of materials able to globally withstand the critical conditions of harsh environments. The contribution by Schrand et al. illustrates a series of polymer-based nanocomposites and ceramics formulations able to behave as extrudable and printable inks for AD. The results of materials exposures and degradation experiments carried out under extreme conditions demonstrate the maintenance of the structural and functional properties and the prolonged service life of the parts/systems assembled with the polymer- and silicon-based nanocomposite inks. The chapter discusses the feasibility of 3D printing in microgravity and at zero gravity and reports on the 3D printing experiments performed on board the International Space Station. Such experiments represent a fundamental proof of concept to assess the feasibility of future AD manufacturing in deep-space missions. Another interesting topic addressed in this contribution is that of the feasibility to use the “local” soils of Moon or Mars for manufacturing the items that will be needed for colonization. In this context, the chapter discusses if the chemical composition and properties of the Lunar and Martian regolith could allow their use as feedstock material for 3D technologies.

Chapter 5, “Nano-Based Coating for Spacecraft: Antibacterial Film for Manned Application” by Dr Antonia Simone and Dr Cristina Balagna, deals with effective strategies offered by nanotechnologies to generate antibacterial surfaces. The antifungal and antibacterial protection of the human crew represents indeed an outstanding bio-related application of the nanotechnology for space. In spatial manned missions, a very critical concern is the formation of resistant biofilms produced by bacterial and fungal species on surfaces. Highly adherent biofilms are found deposited on all the materials

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present inside the close environment of spacecrafts. The effect is even more critical for life-supporting regenerative equipment, such as the systems for water regeneration from air condensation, where bacterial/fungal associations and lipoprotein complexes produce compact and well-adherent biofilms on the inner surfaces of pipes. The potential effects of such microbiological populations on the safe living and working of crewmembers need the implementation of effective countermeasures. In this context, nanomaterials offer great potentialities for the design of surfaces able to control the attachment of living cells. The properties of some traditional antifungal and antibacterial materials are indeed found strongly enhanced by the process of size nanoscaling, which allows a better interaction with cell surface and induces a more likely rupture of cellular membranes. The chapter discusses solutions to minimize hazards for manned spaceflights and presents an overview of the advanced methodologies nowadays proposed to engineer nanomaterials and to enhance the biocide efficiency of nanostructured surface layers. The book also expands to describe the current market and future directions of nanotechnology in the space sector. This topic is discussed by Dr Tanya Scalia and Dr Lucia Bonventre, who in Chapter 6, “Nanotechnology in Space Economy,” present an exhaustive market analysis encompassing the whole area of strategic applications: materials and structures; sensors, electronics, and devices; energy storage, power generation, and power distribution; life support systems; payload/satellites; and space transportation and propulsion systems. As explained in the chapter, space economy is a concept not limited to the traditional “upstream” space sector, but rather a long value-added chain, starting with research and development and ending with the final users. Such “downstream” segment of the value chain leads to benefits for the global economy and explains the growing interest in space technology of governments, public institutions, and also private investors around the world. In this context, Drs Scalia and Bonventre also discuss the impact that the space-related nanotechnologies and products already have and will have on the terrestrial markets. This important aspect is explored by deeply analyzing the strategic possibilities offered by such “bidirectional” applications in both the sectors and presenting an analysis of the enormous numbers of patents related to space nanotechnology, released worldwide during 2010–2019.

Trends in Space Nanotechnologies

In view of these numbers, one can well understand that the objective of the present book is not, of course, to present an exhaustive review of all the aspects of space-related nanotechnologies. This selected collection of contributions from high-level authors gives rather the opportunity, for those seeking to enter this fascinating field, to look at a scenario where “nanotech” routes and innovative solutions are in a continuous evolution. Some of the themes illustrated here are presently mature for practical implementations, whereas others are beyond the immediate horizon, but it should be considered that scientific/technological developments can make what seems impossible today commonplace tomorrow. The research continues! Maria Letizia Terranova Emanuela Tamburri April 2021

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Nanotechnology for Space Power Devices

Ryne P. Raffaelle Physics Department, Rochester Institute of Technology, 1 Lomb Memorial Drive, Rochester, NY 14623, USA [email protected]

The exploration of space has always been synonymous with the development of technology. This is most certainly the case for space power systems or the systems that have been used to provide electrical power and even propulsion for the spacecraft. Since Vanguard 1 was launched on March 17, 1958 (the American satellite that was the fourth artificial Earth-orbiting satellite to be successfully launched following Sputnik 1, Sputnik 2, and Explorer, and the first spacecraft to utilize photovoltaic solar cells), space power needs have been the major driving force in the development of new and more efficient solar cells, batteries, and other components. These developments have been driven by the challenges and costs associated with space exploration that have put a premium on power devices. It is therefore no surprise that the developers of space power systems Nanotechnology in Space Edited by Maria Letizia Terranova and Emanuela Tamburri Copyright © 2022 Jenny Stanford Publishing Pte. Ltd. ISBN 978-981-4877-54-1 (Hardcover), 978-1-003-13191-5 (eBook) www.jennystanford.com

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have embraced the nanotechnological revolution. In this chapter, we will explore some of the ways that nanotechnology is being used to develop new and better space power components.

1.1

Introduction

In 1974, Norio Taniguchi of Tokyo Science University used the term nanotechnology to describe semiconductor processes such as thinfilm deposition that deal with control on the order of nanometers. His definition still stands today: Nanotechnology mainly consists of the processing of separation, consolidation, and deformation of materials by one atom or one molecule [1]. Although this terminology could be considered somewhat new at the time, the concept most certainly was not. The idea of manipulating matter on the nanoscale had been around for some time. One could argue that it goes back to the origins of the development quantum mechanics and the many discoveries and breakthroughs associated with “modern physics” of the early 20th century. It can certainly be argued that when Richard Feynman threw down the gauntlet with his grand challenges outlined in his 1959: There’s Plenty of Room at the Bottom—An Invitation to Enter a New Field of Physics, he was certainly planting the seeds for the later nanotechnological revolution [2]. The nanotechnological revolution was most certainly upon us by the turn of the 21st century. In some ways the United States set the pace for nanotechnology innovation worldwide with the activities that preceded it and ultimately with the advent of their National Nanotechnology Initiative (NNI) in 2000 [3]. The NNI consists of the individual and cooperative nanotechnology-related activities of Federal agencies with a range of research and regulatory roles and responsibilities. Funding support for nanotechnology research and development or R&D stems directly from NNI member agencies. As an interagency effort, the NNI informs and influences the federal budget and planning processes through its member agencies and through the National Science and Technology Council (NSTC). In 2016, the United States published its National Nanotechnology Initiative Strategic Plan [4]. This was an update of the previous plan released in 2014. This update was to satisfy the requirement set forth

Introduction

in the 21st Century Nanotechnology Research and Development Act of 2003. This updated plan represented a consensus of the NNI member agencies on the high-level goals and priorities for NNI. The plan provided the framework under which individual agencies would conduct their own mission-specific nanotechnology programs and how these programs would be shared between agencies. There are 29 different agencies that participate in the U. S. NNI. Example agencies include the Department of Energy, National Institutes of Health, National Science Foundation, and most importantly in view of this chapter the National Aeronautics and Space Administration (NASA). In case one might think that the focus on nanotechnology has somewhat faded at this point, the 2020 federal budget provides more than $1.4 billion for the NNI, affirming the role that nanotechnology continues to play [5]. As nanotechnology efforts were spinning up at the turn of the 21st century, one of the primary drivers was that it offered the promise of developing multifunctional materials that would contribute to building and maintaining lighter, safer, smarter, and more efficient vehicles, aircraft, and spacecraft. Low-cost access to space was often used as one of the primary justifications for the investments that were being made in nanotechnology across the globe. It was argued that there would be “game changing” benefits from the use of nanotechnology-enabled lightweight, high-strength materials for the use in space. In the Technology Area (TA) 10: Nanotechnology, one of the 16 sections of the 2015 NASA Roadmap, it was indicated that the areas where nanotechnologies have the greatest potential to impact NASA mission needs included (a) engineered materials and structures, (b) power generation, energy storage, and power distribution, (c) propulsion and propellants, and (d) sensors, electronics, and devices [6]. In these applications, nanotechnologies were projected to replace state-of-the-art materials used in aerospace vehicle components, including primary and secondary structures, propulsion systems, power systems, avionics, propellant, payloads, instrumentation, and devices. It was proposed that these benefits could possibly reduce overall vehicle mass by up to 50 percent. Not only could this save a significant amount of energy needed to launch spacecraft into orbit, but it would also enable the development of single stage to orbit launch vehicles, further reducing launch costs,

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increasing mission reliability, and opening the door to alternative propulsion concepts. These types of improvement could make access to space much more affordable.

1.2

Engineered Materials and Structures

An area that has received considerable attention from the spacerelated research community is the use of nanomaterials to improve engineered materials and structures used for space power applications. The use of nanoscale or nanostructured materials to make things stronger, lighter, or more radiation tolerant would provide tremendous benefit to future spacecraft. There have been a wide variety of materials studied in this regard, but perhaps none more so than carbon nanotubes. Carbon nanotubes are less a material unto themselves as they are a class of materials. Carbon nanotubes can come in an infinite variety of lengths, diameters, chiralities, purities, etc. and are rarely used as a single nanoscale tube. They are more often used in bulk form or in a composite material. In considering carbon nanotubes, one generally is referring to single-wall carbon nanotubes (SWCNTs) with diameters in the range of a nanometer. They were discovered independently by Iijima and Ichihashi [7] and Bethune et al. [8] in carbon arc chambers similar to those used to produce fullerenes. SWCNTs are just one of the allotropes of carbon that fall somewhere in between fullerene cages and flat graphene sheets [9]. An SWCNT can be thought of a two-dimensional hexagonal lattice of carbon atoms rolled up along one of the Bravais lattice vectors of the hexagonal lattice to form a hollow cylinder [10]. The chirality of a particular tube is determined by which the lattice vector tube is “rolled-up” upon. This chirality will determine the optoelectronic properties of the tube which can range from metallic to semiconducting. Carbon nanotubes can also refer to multi-wall carbon nanotubes (MWCNTs) consisting of nested single-wall carbon nanotubes. Intrinsically carbon nanotubes exhibit ballistic conduction and can support remarkably high current densities [11, 12]. They also have been shown to exhibit exceptional tensile strength [13]

Engineered Materials and Structures

and good thermal conductivity [14, 15]. In addition, they can be chemically modified after they are synthesized to dramatically alter their basic properties [16]. The remarkable properties of carbon nanotubes make them a very desirable candidate for additives in a host of different composite materials used in space, such as lightweight, radiation shielding, high thermal conductivity matrices and coatings, and structural matrix systems [17, 18].

Figure 1.1 MISSE on the International Space Station (courtesy of NASA).

Carbon nanotube have been used in industrial epoxy to augment their electrical or thermal properties [19]. Since carbon nanotubes can have incredible aspect ratios of length (microns) to diameter (nanometers), they can reach a percolation threshold in composite epoxies at very low weight-percent doping and still have a dramatic effect on their thermal and electrical properties. In addition, the introduction of the nanotubes can also serve to improve the strength of the epoxy. The Materials International Space Station Experiment (MISSE-8) tested a variety of different carbon nanotube containing materials, including carbon nanotube yarn, on the surface of the International Space State, or ISS. As the ISS operates in low Earth orbit (LEO) environment, it offers a very important set of space conditions [i.e., vacuum, UV radiation, ionizing particle radiation in the form of high energy protons and electrons, thermal cycling with temperatures

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varying from –175 to +160°C, and atomic oxygen (AO)]. While all of these can induce chemical reactions in these orbits, its AO and UV radiation primarily cause the degradation seen in many organic materials. Although some changes were observed in the materials properties, the carbon nanotube yarns exhibited good resiliency in the 2.14 year long flight [20]. In 2017, NASA demonstrated that a carbon nanotube composite could be used for a Composite Overwrapped Pressure Vessels (COPVs), which are designed to hold fluid under pressure and are used in many capacities including propellant tanks [21]. A carbon nanotube wrapped COPV flew as part of the SubTec-7 mission using a 56-foot tall Black Brant IX rocket launched from NASA’s Wallops Flight Facility in Virginia. NASA computer modelling analysis has shown that composites using carbon nanotube reinforcements could lead to a 30% reduction in the total mass of a launch vehicle compared to conventional carbon fiber epoxy composites [21].

Figure 1.2 A demonstration carbon nanotube Composite Overwrap Pressure Vessel (COPV) flight article is wound with carbon nanotube composites (courtesy of NASA).

Power Generation, Storage, and Distribution

1.3

Power Generation, Storage, and Distribution

In addition to the potential use as a structural material, carbon nanotubes are showing tremendous promise in improving other areas of the performance of space power systems. Examples include energy conversion devices such as solar cells [22], fuel cells [23], thermionic devices [24], for energy storage in batteries and capacitors [25], and even in the form of electrical wires for power management and distribution [26]. The control of the fundamental nature of carbon nanotubes used (i.e., diameter distributions, dispersion, purity, etc.) is key to optimizing the device performance in many of the aforementioned applications [27].

1.3.1 Carbon Nanotube Wires

Used in a wire format, carbon nanotubes are being considered for a variety of applications including power and data transmission applications in space [28–30]. Applications that exploit the superior flexure tolerance, tensile strength to weight, and corrosion resistance over conventional metal wires are particularly attractive. Wires produced from carbon nanotubes have already been used as replacements in RG-402 and RG-58 coaxial data transmission cables [31].

Figure 1.3 SEM micrograph of high-purity single-wall carbon nanotube and resulting carbon nanotube data cables [28].

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Carbon nanotube wires are yet to achieve the specific conductivity associated with individual single-wall carbon nanotube or that of bulk metals due to a variety of practical concerns [32–35]. Current approaches have tended to focus on the use of chemical treatments and processing methods to increase the intrinsic conductivity of carbon nanotubes and their extended networks [36–38].

1.3.2 Lithium-Ion Batteries

In 2019, the Nobel Prize in Chemistry was awarded to John B. Goodenough, M. Stanley Whittingham, and Akira Yoshino, “for the development of lithium-ion batteries” [39]. Because these batteries were based on lithium ions moving between anodes and cathodes, rather than chemical reactions, they had the potential to be recharged many times before degrading. In addition, they had a higher specific energy and energy efficiency than the nickel–metal–hydride batteries that were the mainstay of space power systems at the time. There were initial concerns over their potential reliability, self-discharge, thermal characteristics, and safety, but time and development proved that in fact they could be superior to their predecessors in all of these aspects. This made them particularly attractive for a whole number of different space applications, and in particular the storage for the main power bus in earth-orbiting satellites. When coupled with solar arrays, satellites could both operate and store energy in their batteries while on the sun side of their orbit and then rely upon the batteries while in the Earth’s shade. This, along with their attractive energy and power densities, allowed lithium-ion batteries to very quickly supplant other chemistries very shortly after they were first introduced into space in the early 2000s. The European Space Agency flew one of the very first lithium-ion batteries in space back in 2001, for the experimental Proba-1 Earth-observing mission, which still remains operational to this day [40]. The remarkable performance offered by lithium-ion batteries caused them to not only be of interest to the space community, but also for a host of terrestrial applications ranging from portable electronics to electric vehicles. Today they are even being deployed at scale in electrical grid storage systems across the globe. This interest accelerated the development of lithium-ion batteries and has now gone far beyond that of any other rechargeable battery chemistries [41, 42].

Power Generation, Storage, and Distribution

The use of nanoscale materials in the composite anodes and cathodes in lithium-ion batteries is very common. Providing intimate contact between the various active elements in such batteries is key, so the use of nanoscale to provide high surface area, porosity, low percolation thresholds, etc. is quite common [43]. One of the most interesting materials being utilized, due to its unique set of electrochemical and mechanical properties as well as its unprecedented geometry (i.e., aspect ratio), are once again carbon nanotubes. The incorporation of CNTs as a conductive additive to replace conventional carbon black and/or graphite offers the ability to establish an electrical percolation network at dramatically reduced weight percent dopings, similar to their use in the aforementioned epoxies. This allows more of the weight of the battery to be used by the lithium storage materials, improving the energy density and the ability to produce thicker electrodes without sacrificing the charge/ discharge or C-rate of the batteries. In addition, carbon nanotubes can be produced as a free-standing sheet or paper to serve as a support for other active materials, or in other words to serve both as a lithium storage material and as a replacement for the conventional metal electrode. This can be accomplished without the need to introduce any binder as in a conventional composite electrode, therefore reducing the wasted mass of non-active elements in the battery. Reversible lithium-ion capacities for CNT-based anodes have exceeded 1000 mAh g−1, which is a 3× improvement over conventional graphite anodes [44].

1.3.3 Quantum Dot Solar Cells

From the time between the launching of Vanguard 1 to the early 1990s, when the terrestrial deployment of solar cells really started to take off, the driving force behind the development of photovoltaics was primarily the space industry. Even today, in terms of producing the most efficient and highest mass specific power cells, it is still the space industry leading the charge. This is simply due to the trade-offs for terrestrial deployment and space deployment being so dramatically different. It is true that both regimes appreciate higher efficiency solar cells and producing solar cells at a lower cost is always attractive, but the premiums put on these things is quite different. That is why silicon solar cells that can be produced

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at a relatively low cost at scale continue to dominate the terrestrial marketplace, and the much higher efficient, albeit much more expensive, III-V based solar cells have totally displaced almost any use of silicon solar cells in space. At this point, multi-junction III-V solar cells have exceeded 39% efficiency under illumination from an air-mass 1.5 spectrum with a 1 Sun intensity, and over 47% under concentration (see Fig. 1.4). The world-record efficiencies of III-V multi-junction cells continue to be set by the addition of more junctions (i.e., dual to triple to quads to 5J and even 6J) [45]. The addition of more junctions allows the cell to be better “tuned” to the solar spectrum and to lose less incoming solar energy to thermalization. This is mediated by the ability to grow additional composition layers epitaxially within the device and the inevitable defects that will occur at each incremental interface. As researchers have continued to seek out new ways of continuing to improve the efficiency of solar cells, their attention has been drawn toward the use of nanostructures [46]. Several of these approaches attempt to exploit the fundamental quantum mechanical behavior of nanoscale crystals, also known as quantum dots, which alter the way in which these materials will absorb light and conduct electrons. The electrical, optical, mechanical and even thermal properties of nanomaterials can be controlled by changing the particle size, making them highly useful in photovoltaic device development. Exploiting the quantum confinement effects associated with nanoscale or nanostructured materials provides a new means of breaking out of the normal constraints associated with conventional crystalline device growth. Some of the approaches using nanoscale or nanostructured materials approaches to achieve higher efficiency photovoltaic devices include the use of bandgap engineering using multiple quantum wells (MQW) for multijunction tuning and quantum dot arrays to produce an “intermediate band” solar cell [46–48]. In these approaches, one attempts to “tune” the absorption and photovoltaic conversion behavior of a junction or that of the entire device by the mini-band formation associated with the nanostructured dimensions of the semiconductor layers used in these devices. The theoretical improvements possible by adopting these approaches are very significant, even potentially exceeding the Shockley–Queisser limit, and thus have driven considerable research in this area.

1980

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National Renewable Energy world-record solar cell charge (courtesy of the U.S. Department of Energy).

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Figure 1.4

0

4

8

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Cell Efficiency (%)

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Power Generation, Storage, and Distribution 11

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Nanotechnology for Space Power Devices

The intermediate band solar cell, first proposed by Luque and Marti [49], is a novel extension of a bandgap engineering approach. It uses a QD superlattice to form a thermally isolated intermediate band (IB) within the bandgap of a standard single-junction solar cell. A photon whose energy is less than the host bandgap can be absorbed and can promote an electron from the host valence band to this intermediate band, followed by the promoted electron in the IB absorbing a second photon for promotion to the conduction band. Thus, photons which would normally not contribute to the photocurrent can be converted. The trick of course is that the states in the conduction band and IM must remain thermally isolated (i.e., the so-called phonon bottleneck) and the quantum dot array must be introduced into the normal device structure in such a way as to not comprise any of the normal conversion processes of the host cell. Luque and Marti derived a theoretical limit for an intermediate band device using detailed balance [49]. They assumed no carriers recombined at the intermediate band and the device was under full concentration. They found the maximum efficiency to be 63.2%, for a bandgap of 1.95 eV with the IB 0.71 eV from either the valence or conduction band. This equated to a limiting efficiency of 47% under a 1 Sun illumination [50]. Several experiments have demonstrated the key operating principles of the IB solar cell using both indium arsenide and gallium antimonide quantum dot arrays in a gallium arsenide host material [5154]. In addition, it has been shown that the contributions of the quantum dots to subgap conversion can be improved with the use of concentration [55]. A quantum dot solar cell, along with several other advanced photovoltaic technologies, was tested aboard the eighth Materials International Space Station Experiment (MISSE-8) as part of the third Forward Technology Solar Cell Experiment (FTSCE-III) over a period of approximately 26 months [56]. The U. S. Air Force Research Laboratory Space Vehicles Directorate in collaboration with the U. S. Naval Research Laboratory flew a myriad of experiments to evaluate advanced photovoltaic cells and material technologies, including the aforementioned quantum dot cell. From the perspective of the use in space, one of the most attractive features of these quantum dot cells is the enhanced radiation tolerance that is achievable [57]. The effects of radiation on a quantum dot array is less pronounced than what would normally be seen in a minority

Propulsion and propellants

carrier limited bulk semiconductor material. This is at least partially true to the increased knock-on energy required to create defects in the strained nanoscale elements [57].

1.4

Propulsion and Propellants

Traditionally, the majority spacecraft have relied upon chemical propulsion to achieve both orbit and attitude control (i.e., the control of the angular position and rotation of the spacecraft relative to the object that it is orbiting, or relative to the celestial sphere). Whether solid, liquid, or gas these are the types of propulsion systems we are most accustomed to seeing. However, since the turn of the century there has been tremendous improvement in the electric propulsion (EP) systems [58]. EP systems use electrical power to accelerate a propellant using electromagnetic fields [59]. These systems can be extraordinarily efficient at converting energy to thrust and unlike chemical systems require very little mass to accelerate a spacecraft. The ejection velocities of the propellant can be far greater in EP systems than traditional chemical propulsion systems, and can, therefore, deliver an extremely high specific impulse. Specific impulse (which directly relates how efficiently the propellant is being used) means that an EP system can develop thrust at a very low propellant mass-flow rate, and thus the mass of propellant required for the entire mission can be redued. EP systems are limited by the electrical power on-board the spacecraft, and thus are normally constrained to low thrust (i.e., mN levels or below). However, these can be extremely useful very long duration applications. At this stage, EP is already considered to be a well-established technology and has been used on a number of missions (i.e., Artemis, SMART-1, GOCE, AlphaSat, Bepi Colombo, SmallGeo, NEOSat, Electra, Deep Space 1, HAYABUSA) [60]. These systems are nanotechnological by nature due to the fact that what they eject are ionized nanoscale elements ranging from the atomic to molecular level. There are a very large number of designs that have been explored, including gridded ion engine (GIE), Hall effect thruster (HET), high-efficiency multistage plasma thruster (HEMPT), pulsed plasma thruster (PPT), magneto plasma dynamic (MPD) thruster, quad confinement thruster (QCT), and

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field-emission electric propulsion (FEEP) thruster, amongst others [61]. The types of propellant used varies with the type of thruster and is typically a rare earth gas, metal, or more or in some cases a more complex molecule [62]. There is tremendous potential surrounding the use of other nanomaterials in future EP systems. Applications range from the use of graphene for cold emission or magnetic control, or the use of carbon nanotubes for strong light-weight structures or emitters, to the use of boron nitride nanotubes for self-healing structures and use in the acceleration channels [58]. Researchers at the University of Michigan have developed ion thrusters that use MEMS devices to accelerate charged nanoparticles [63]. This nanoparticle field extraction thruster, or NanoFET, is designed to allow it to last longer than other types of ion thrusters and allow multiple NanoFETs to be clustered together. This could simplify the job of spacecraft engineers by allowing the same thruster design to be used on spacecraft over many different missions just by changing the number of NanoFETs mounted on the spacecraft.

1.5 Future Nanotech Approaches to Space Power

A variety of nanomaterials and other nanotechnologies have already found their way into space power systems. However, there are still some approaches that most likely won’t be realized for years to come. One notable example is the use of carbon nanotubes for solar sails [64]. Solar sails are spacecraft propulsion systems that produce thrust through the radiation pressure applied by the sun, or alternatively with the use of a laser, onto a reflective surface or “sail” (see Fig. 1.5). An example of such a system was developed by the Japanese Aerospace Exploration Agency (JAXA) and was called IKAROS, or Interplanetary Kite-craft Accelerated by Radiation Of the Sun [65]. It was launched on May 20th, 2010, aboard an H-IIA rocket, together with the Akatsuki (Venus Climate Orbiter) probe and four other small spacecraft. IKAROS was the first spacecraft to successfully demonstrate solar sail technology in interplanetary space. On December 8th, 2010, IKAROS passed by Venus at about 80,800 km (50,200 mi) distance, completing its planned mission [66].

Future Nanotech Approaches to Space Power

Figure 1.5 A 1:64 scale model of the IKAROS developed by the Japanese Aerospace Exploration Agency (JAXA) (picture courtesy of JAXA).

The promise of the solar sail relies on the constant radiation pressure provided by the sun, the vacuum of space, and the light mass of the craft, to reach incredibly high speeds approaching significant fractions of the speed of light. At these speeds, exploration beyond that of our solar system start to become realistic and we could reach Pluto in days and even our nearest star in a couple of decades [67]. Typical materials that have been used to date include aluminized Mylar and Kapton, which are both commercially available materials with areal density of approximately 7 g/m2. The promise of carbon nanotube solar sails lies in the fact that they can be produced with dramatically lower areal densities and still be able to withstand the rigors of space flight [68, 69]. One project that could possibly use such a material is the Starshot project. It is an interesting concept based on using thin sails, to travel at 15%−20% of the speed of light [70]. The project plans to get to Alpha Centauri in 20 years. The project is funded by Yuri Milner, a Russian internet entrepreneur, and was supported by late Stephen Hawking, the English cosmologist.

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30. Jarosz, P. R., Shaukat, A., Schauerman, C. M., Cress, C. D., Kladitis, P. E., Ridgley, R. D., Landi, B. J. (2012) High-performance, lightweight coaxial cable from carbon nanotube conductors, ACS Appl Mater Inter, 4, pp. 1103–1109. 31. Hemond, J., Martens, R., Loyd, A. (2012) In evaluation of crimping as a termination technique for carbon nanotube macro-structures, 2012 IEEE 58th Holm Conference on Electrical Contacts, 23–26 Sept. 2012, 2012, pp 1– 8.

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34. Barnes, T. M., Blackburn, J. L., van de Lagemaat, J., Coutts, T. J., Heben, M. J. (2008) Reversibility, dopant desorption, and tunneling in the temperature-dependent conductivity of type-separated, conductive carbon nanotube networks, ACS Nano, 2, pp. 1968–1976.

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36. Nirmalraj, P. N., Lyons, P. E., De, S., Coleman, J. N., Boland, J. J. (2009) Electrical connectivity in single-walled carbon nanotube networks. Nano Lett., 9, pp. 3890–3895. 37. Zhao, Y., Wei, J., Vajtai, R., Ajayan, P. M., Barrera, E. V. (2011) Iodine doped carbon nanotube cables exceeding specific electrical conductivity of metals, Sci. Rep, 1, pp. 1–5.

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44. Landi, B. J., Ganter, M. J., Cress, C. D., DiLeo, R. A., Raffaelle, R. P. (2009) Carbon nanotubes for lithium ion batteries, Energy Environ. Sci., 2, pp. 638–654.

45. Jones, R. K., Ermer, J. H., Fetzer, C. M., King, R. R. (2012) Evolution of multijunction solar cell technology for concentrating photovoltaics, Jpn. J. Appl. Phys., 51, 10, Part 2, 10ND01.

46. Soga, T. (Ed.) (2006) Nanostructured Materials for Solar Energy Conversion (Elsevier, Oxford, UK). 47. Sharps, P., Cornfeld, A., Stan, M., Korostyshevsky, A., Ley, V., Cho, B. Varghese, T., Diaz, J., Aiken, D. (2008) The future of high-efficiency, multi-junction space solar cells, Proc. 33rd IEEE Photovolt. Spec. Conf. 1, pp. 1–6.

48. Hubbard, S. M., Bailey, C., Polly, S. Cress, C., Andersen, J., Forbes, D., Raffaelle, R. (2009) Nanostructured photovoltaics for space power, J. Nanophoton., 3, 1, pp. 031880–031816.

49. Luque, A., Marti, A. (1997) Increasing the efficiency of ideal solar cells by photon induced transitions at intermediate levels, Phys. Rev. Lett., 78, pp. 5014–5017.

50. Okada, Y., Sogabe, T., Shoji, Y. (2014) Chapter 13: Intermediate band solar cells, In: Advanced Concepts in Photovoltaics, Nozik, A. J., Conibeer, G., Beard, M. C. (Eds.), (Royal Society of Chemistry, Cambridge, UK), pp. 425–454.

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Chapter 2

Nanocomposite and MicroNanostructured Materials with Applications of MEMS/Nano Devices for Aerospace

Rodolfo Guzzi,a Francesco Marra,b and Giovanni Pulcib aOptical Society of America Emeritus and Systems Biology Group Lab, Sapienza University of Rome, via Antonio Scarpa 16, 00161 Rome, Italy bDepartment of Chemical Engineering Materials Environment, Sapienza University of Rome; INSTM Reference Laboratory for Engineering of Surface Treatment; via Eudossiana 18, 00184 Rome, Italy [email protected]

Recent developments in nanotechnology materials and micro-/ nanotechnology have allowed new applications based on microelectromechanical systems (MEMS) and nanotechnology sensors and devices. Nanotechnology can be used not only for surface protection, but also for new sensors and devices suited for communication, medical diagnosis, commercial, military, aerospace, and satellite applications. Integration with MEMS will improve the overall sensor or device performance, reducing the sensor weight, Nanotechnology in Space Edited by Maria Letizia Terranova and Emanuela Tamburri Copyright © 2022 Jenny Stanford Publishing Pte. Ltd. ISBN 978-981-4877-54-1 (Hardcover), 978-1-003-13191-5 (eBook) www.jennystanford.com

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size, power consumption, and production costs. It offers unlimited opportunities in designing and developing, among others, of various electro-optics emitter and/or sensors like lasers, RF/mmwave components such as phase shifters, switches, tunable filters, and micromechanical (MM) resonators, acoustic and infrared (IR) sensors, photonic devices, accelerometers, gyros, automobilebased control and safety devices, unmanned aerial vehicle (UAV) sensors able to provide missions equipped with intelligence for the reconnaissance, and surveillance of the target. This chapter dealing with nanotechnology and MEMS provides a wide-lens perspective of the field. It starts with basic design principles, current technologies, and applications with a look toward the integration of nanotechnology materials that enable special purposes of MEMS.

2.1 Introduction

Nanocomposite materials can be defined as polymer, metal, or ceramic matrices containing fillers with one dimension smaller than 100 nm (Fig. 2.1). In the last 20 years, polymer nanocomposites have attracted considerable interest because they show outstanding improvement in materials properties. For example, the properties modification induced by the addition of a low volume fraction (1–5%) of nanofillers, in some cases, can be comparable to those obtained with a 15–40% volume fraction of conventional microfillers. These enhancements include increased elastic modulus [1–6], improved strength and thermal stability [7], decreased gas permeability [8–12], and flammability [13–17] and modified thermal and electrical conductivity. The vast extent of the nanofillers surface area leads to a large volume of an interfacial matrix having completely different thermal, mechanical, and electrical properties if compared to the bulk polymer. Nanocomposites are expanding their applications in the aerospace industry. They are promising candidates for the thermal protection of spacecraft and rockets and the electromagnetic shielding and lightning strike protection of the aircraft structures. In the aerospace industry, there is a great need for new materials that exhibit improved mechanical properties. Materials possessing high strength at a reduced mass and size make lighter aircraft with lower fuel consumption. The development of new materials with

Introduction

tailored property is a primary goal of today’s materials science and engineering. The extraordinary stiffness, higher than that of a diamond (ten times higher than that of any other available material), high toughness, changeable conductivity, and the specific tensile strength of carbon nanotubes (CNTs) makes them eminently suited as reinforcing elements in macroscopic composites. a

100nm

b

100nm

c

500 nm

Figure 2.1 Different type of nanofillers: (a) nanoparticles, (b) nanowires, (c) nanoplatelets [18, 19].

With a potential high strength-to-weight ratio and multifunctionality, carbon nanotube reinforced polymer composites may provide a unique option for the aviation industry. Their use can enhance a material’s ability to resist vibration and fire. Functionalization and irradiation of polymer-embedded nanotubes and nanotube fibers also have been shown to improve the dispersion and strengthen nanotube-matrix interactions, allowing for further improvement of the mechanical properties of CNT-reinforced composites. The impressive properties of CNTs have led to investigations of various applications. The most critical aerospace application is a high strength, low weight composites. However, other uses for CNTs include electronic components, logic and memory chips, sensors, catalyst support, adsorption media, actuators, optical devices, etc. The opportunities for the aerospace industry are through the thermal barrier and wear-resistant coatings. Recent advancements in nanotechnology (NT) materials mainly used on surface protection and growth of micro-/nanotechnology have allowed the development of potential applications of MEMS and NT-based sensors, devices. MEMS are not nanotechnology, but while some MEMS devices have features that are measured in nanometers, MEMS and

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nanotechnology are fundamentally different. MEMS devices operate with dynamics that are determined by modeling matter as a continuum, while nanotechnology deals with matter’s quantum mechanical behavior. However, coupling MEMS and NTs it is possible to design and development various electro-optics sensors, among the other, lasers, RF/mm-wave components such as phase shifters, switches, tunable filters, and micromechanical (MM) resonators, acoustic and infrared (IR) sensors, photonic devices, accelerometers, gyros, automobile-based control, and safety devices, unmanned aerial vehicles (UAVs) sensors. For these reasons, MEMS- and NTbased sensors will be most attractive for aerospace, military, and space applications, where weight, size, power consumption, and reliability are the critical design requirements. This chapter deals with the current studies on nanocomposite materials, additive manufacturing technology, aerospace applications. Miniaturized (MEMS-based) optical space sensors and microthrusters for the attitude of space vehicles are also presented with a look at the future integration between the two technologies.

2.2 Ablative Nanocomposite Materials

During atmospheric reentry, the hypersonic vehicles experience extreme aerothermal conditions. Consequently, very high temperatures are reached on the spacecraft structures [20]. For this reason, reentry vehicles have to be protected by a properly designed thermal protection system (TPS). Several TPS technologies have been developed in the past: (i) reusable TPS, adopted for lifting hypersonic vehicles, based on ceramics or ceramic matrix composite materials [21–25]; (ii) ablative thermal shields, for very high entry speeds, typical of ballistic capsules, and interplanetary entry probes [20, 26]. Polymer-based ablative materials represent state of the art for TPS in several aerospace applications: not only spacecraft thermal shields during atmospheric reentry, but also thermal protection of missile-launching systems, and insulation in solid rocket motors (SRMs). Ablative materials are usually reinforced with polymer matrix composites. These materials can dissipate a considerable amount

Ablative Nanocomposite Materials

of heat through endothermic phenomena such as pyrolysis of the organic matrix, vaporization, and sublimation. The incident heat flux leading to a fast temperature rise of the ablator surface induces the pyrolysis reactions and the consequent production of decomposition gases and solid carbonaceous char residue. The sketch of the pyrolysis and ablation phenomena is shown in Fig. 2.2. Pyrolysis Gas

Incoming Heat Flux

Mechanical Erosion Chemical Reactions Transpirational Cooling Chemical Species Diffusion Radiation Heat Convection Conduction Char

Backup Pyrolysis Virgin Material Material Zone

Figure 2.2 Schematic diagram illustrating the different ablation mechanisms and different zones of an ablator under thermal attack [27].

Conventional ablative materials are usually thermosetting polymer matrix composites. They are composed of layers of woven carbon, quartz, silica, glass fibers, or felt preforms impregnated with a resin matrix: phenolic resin is the most commonly adopted polymer matrix. Micron-scale structured constituents reinforce the conventional ablative composites. Nanocomposites contain ultrafine phases, typically with one dimension smaller than 100 nm [28]. They can exhibit unique combinations of specific properties that cannot be found in traditional composites. Nanocomposite ablative materials can be produced starting from thermosetting, thermoplastic, or elastomeric matrices. They are modified by different nanofillers such as: (i) nanoclays

27

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Nanocomposite and Micro-Nanostructured Materials

(e.g., montmorillonite, MMT), (ii) carbon nanofibers (CNFs), (iii) polyhedral oligomeric silsesquioxanes (POSS), (iv) ceramic nanoparticles (e.g., SiO2, Al2O3, ZrO2, SiC), (iv) carbon black, and (vi) carbon nanotubes (CNTs). Furthermore, they are reinforced by conventional fibers such as carbon, silica, glass, or asbestos [29, 30]. Polymer layered silicate nanocomposites are an important class of ablative material. They are obtained by modifying a polymeric matrix with layered silicate reinforcements such as nanoclays [30] that are primarily composed of stacked planes of aluminosilicate layers with a thickness of about 1 nm [29]. Polymer chains can penetrate the stacked structures of the layered silicates, and the properties of the nanocomposite depend on the degree of polymer penetration. Extensive delamination of the silicate layers produced by the polymer penetration generates an exfoliated morphology with individual layers dispersed in the polymer matrix. A finite expansion of the aluminosilicate sheets, produced by partial polymer penetration, generates an intercalated morphology. It consists of ordered alternating polymer/silicate layers with a thickness of a few nanometers [30]. Organically modified layered silicate (e.g., modified montmorillonite) is produced by introducing organic molecules in the interlayer spaces to promote the polymer penetration and interaction with the layered structure. Nanocomposite ablative materials can be designed for TPSs operating both in mild and severe combinations of heat flux and mechanical stress. For example, polymer layered silicate nanocomposites are studied and developed to increase the thermal insulation effectiveness of different ablative thermal protections such as elastomeric heat-shielding materials for solid rocket motor liners [31]. Vaia et al. proposed pioneering researches [32] on the ablative properties of nylon 6 modified by the addition of 2 wt% and 5 wt% of an exfoliated layered silicate (an organically modified montmorillonite) compared with the response of the neat matrix. A reduction in the recession rate was highlighted even with limited nanofiller content (2 wt% – 0.8 vol.%) of exfoliated montmorillonite. The improved ablation performance is related to the microstructure and composition of the char layer: the presence of

Ablative Nanocomposite Materials

the layered silicate nanofillers leads to the formation of a submicron lamellar structure resulting in a tougher char layer exhibiting a lower recession rate [32]. Koo et al. [29] modified a commercial carbon/phenolic ablative composite (Cytec MX-4926) by the dispersion of 5 wt% organically modified montmorillonite into the resole phenolic resin matrix [33]. These researches showed that the presence of a micron-scale structure (the carbon woven fabric) leads to the formation during the high-enthalpy tests of a compact and homogeneous thermal barrier (Fig. 2.3a) induced by the ablative reassembly of the nanoclay platelets and enhanced by the exposure at high heat flux levels promoting the sintering of nanoclay sheets (Fig. 2.3b). Severe hyperthermal environment

Sintered platelets

(b)

Char

Nanoclay platelets

Fiber tows

Ablative re-assembly

Moderate hyperthermal environment (below 10 W/cm2)

(a)

Figure 2.3 Response of a fiber-reinforced polymer ablator modified by layered silicate nanofillers under a moderate (a) and a severe (b) hyperthermal environment [34].

29

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Nanocomposite and Micro-Nanostructured Materials

Thermoplastic polyurethane elastomer (TPU) matrices can also be modified by the addition of different nanofillers [35–39] to evaluate potential alternative composite materials for the heat shielding of solid rocket motors (at present the standard solution is an aramid/EPDM composite). TPU was modified with different amounts of nanoparticles (MMT, CNFs, and MWNTs) and processed using a twin-screw extruder. In Fig. 2.4, several TEM images of the TPU-based nanocomposites are reported. The thermal insulation effectiveness and the ablation resistance were assessed by the exposure to an oxyacetylene torch with a heat flux of 5 MW/m2. All the investigated TPU-based nanocomposites exhibit a similar trend in terms of mass loss during the exposure tests: a reduction up to a certain weight percent. They show about 8% for the MMT/MWNTTPU and about 18% for the CNF-TPU and then a slight increase for a higher amount of nanofiller content. (a)

(b)

(c)

(d)

(e)

(f)

Figure 2.4 TEM images of montmorillonite (MMT) clay dispersion in the TPU formulations with 2.5 (a), 5.0 (b), and 10.0 (c) wt%. TEM images of multiwalled carbon nanotubes (MWNT) dispersion in the thermoplastic polyurethane elastomer nanocomposite (TPU) formulations with 2.5 (d), 5.0 (e), and 10.0 (f) wt% [40].

MMT-TPU nanocomposites overcome the other TPU-based materials showing the higher ablation resistance. The results indicate that the nanoclay platelets embedded in the matrix tend

Ablative Nanocomposite Materials

to modify the char morphology by creating a hybrid external carbon/ceramic layer composed by sintered and aligned platelets (ablative reassembly phenomenon) and characterized by increased mechanical properties [32]. Lightweight ceramic ablators (LCAs) are the state of the art for the thermal protection of space vehicles during the hypersonic flight through planets or earth atmosphere. These low-density ablative materials are nonconventional composites having a density lower than 0.5 g/cm3 and manufactured starting from low-density carbon felts partially impregnated with an organic resin. Phenolic impregnated carbon ablators (PICAs) are a class of lightweight materials developed by NASA beginning from the 1990s and successfully adopted for the heat shield of the Stardust sample return capsule (2006), for the Genesis probe (2004), and the Mars Science Laboratory (2012). PICA-X, a modified version of PICA, is currently adopted for the TPS of the spacecraft Dragon, developed by the SpaceX company. Several works report the attempt to modify standard LCAs by the addition of specific nanofillers. Pulci et al. [41, 42] described the manufacturing process and the properties of carbon/phenolic lightweight ablators modified by the addition of a different amount of ceramic nanoparticles to improve the thermal insulation and the mechanical properties of the char layer generated by the severe heat flux exposure. Various degrees of ZrO2 nanoparticle dispersion in phenolic resin are shown in Fig. 2.5.

2 mm

EHT = 1200 kV WO = 7.7 nm

Signal A = NTS 050 Mag = 10.00 KX

200 nm

EHT = 1200 kV WO = 17 nm

Signal A = plans Mag = 10000 K X

2 mm

EHT = 15.00 kV WO = 9.0 nm

Signal A = NTS 050 Mag = 10.00 K X

200 nm

EHT = 1200 kV WO = 8.0 nm

Signal A = plans Mag = 10000 K X

2 mm

EHT = 15.00 kV WO = 5.6 nm

Signal A = NTS 050 Mag = 10.00 K X

200 nm

EHT = 1200 kV WO = 7.0 nm

Signal A = plans Mag = 10000 K X

Figure 2.5 SEM images of ZrO2 nanoparticles modified by different functionalization treatments and dispersed in phenolic resin [42].

31

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Nanocomposite and Micro-Nanostructured Materials

The performance of the nanocomposite ablators was evaluated in terms of mechanical properties and thermal insulation effectiveness. Compression tests confirmed the possibility of strongly improving the mechanical properties both for the virgin and for the charred lightweight carbon-phenolic ablative material by the addition of ZrO2 nanoparticles (5 wt%) [42]. Moreover, the modified ablators were tested by the exposure to an oxyacetylene torch and in a plasma wind tunnel facility able to better reproduce the thermochemical conditions of atmospheric reentry (Plasmatron, Von Karman Institute). Both the tests were performed with a heat flux of 4 MW/m2, and the samples modified by the addition of ZrO2 nanoparticles exhibited better thermal insulation and a reduced ablation rate concerning the conventional lightweight carbon-phenolic ablative material [42]. SEM analysis also confirmed in this case that the homogeneously dispersed ceramic nanoparticles promote the formation of a tougher char layer and a carbon/ceramic external shell (Fig. 2.6). It increases the thermal insulation and the ablation resistance of the nanocomposite ablative material.

1 mm

EHT = 10.00 kV

Signal A = SE2

WD = 14.8 mm

Mag = 10.00 K X

Figure 2.6 Carbon-phenolic ablative sample modified by 5 wt% of ZrO2 nanoparticles (a) after plasma wind tunnel test. (b) Particular (SEM image) of the external shell. Unpublished image - Credit: Sapienza University of Rome.

2.3 Nanostructured Thermal Barrier Coatings Thermal barrier coatings (TBCs) are protective multilayer systems deposited on the surface of thermally stressed components of gas turbine engines (e.g., turbine blades or combustor liners). One of the main application fields of TBCs is aircraft propulsion. The production of aviation gas turbine engines for 2016–30 has been

Nanostructured Thermal Barrier Coatings

estimated to be higher than 220,000 units with a market value higher than $1.2 trillion [43]; for this reason, the development of more efficient protective coating technologies for aircraft engines can be considered a critical challenge both from a technological and economic point of view. Conventional TBC systems consist of a metallic bond coat directly deposited on the component surface, a thermally grown oxide (TGO) layer that is the result of the hightemperature oxidation of the aluminum-rich bond coat, and a ceramic topcoat mainly providing the thermal insulation. Zirconium oxide stabilized with 6–8 wt% of yttria (7-YSZ) is the material of choice for the ceramic topcoats, because of its high fracture toughness, high melting point (about 2700°C), low thermal conductivity, and high coefficient of thermal expansion (CTE) close to that of the superalloy substrate [44]. Figure 2.7 shows a typical TBC multilayer architecture.

Top Coat (ZrO2–6-8%Y2O3)

TGO (a-Al2O3) Bond Coat (Ni/Co-CrAlY) Substrate (Ni–base superalloy)

Acc.V Spot Magn 27.0 kV 5.0 250x

Det WD BSE 7.2

200 mm

Figure 2.7 Typical TBC multilayer architecture. Unpublished image - Credit: Sapienza University of Rome.

Bond coat and ceramic topcoat are typically deposited by thermal spray processes, consisting of injecting feedstock powders having an average particle size ranging from 10 to 100 µm into a highenthalpy flow. These particles are accelerated, molten during the in-flight time, and projected toward the surface of the component to be coated. The high-speed impact against the substrate leads to

33

Nanocomposite and Micro-Nanostructured Materials

the spreading and flattening of the molten or semi-molten particles that solidify in the form of lamellae (the so-called “splats”) of a few micrometers in thickness—the coating results from the stacking of this lamellar microstructure [45–47]. The atmospheric plasma spray (APS) process is a thermal spray technique often selected for the deposition of the ceramic topcoat: an electric arc generated between the anode and cathode of a deposition torch ionizes the flowing process gases (Ar, H2, N2, or He) into the plasma state, thus reaching local flow temperature exceeding 10,000 K because of the ionization and recombination effects in the gases. The extreme heat of the plasma plume permits to melt or partially melt also ceramic or refractory powders with a very high melting point. The sketch of a plasma spray torch with powder injection is reported in Fig. 2.8. Powder Injection + Carrier Gas

Plasma Gas

34

Coating

Powder Trajectory

Cathode Anode Plasma Torch

Plasma Jet

Substrate

Stand-off Distance

Figure 2.8 Sketch of a plasma spray torch with powder injection [48].

In the last 20 years, there was an intense interest in developing and studying nanostructured coatings (i.e., with microstructural features size smaller than 100 nm) obtained by thermal spraying techniques [49] mainly because of the possible enhanced properties that can be obtained by reducing the microstructure scale down to the nanometer level: improved toughness and strength, reduced apparent elastic modulus and thermal conductivity, increased CTE, and other numerous potential enhancements [50]. There are different ways to obtain nanostructured thermally sprayed coatings. The most straightforward idea could be the use of nanosized feedstock particles, but unfortunately, such

Nanostructured Thermal Barrier Coatings

high fine powders are difficult to handle in a dry state, tend not to be free-flowing, and cannot be easily managed by the powder feeders adopted in thermal spraying equipment. Then individual nanometric particles do not exhibit the inertia and momentum required to penetrate the thermal spray jets [51]. A possible solution is to agglomerate the starting nanoparticles into micrometric agglomerates using a spray-drying process and to inject them using a conventional feeding system based on a carrier gas [51]. In the spray-drying process, a slurry consisting of the starting nanoparticles finely dispersed in a solution of an organic binder and water is atomized in microscopic droplets and dried by a hot air flux to obtain nanostructured spherical agglomerates with a micrometric size finally. Figure 2.9 shows a nanostructured agglomerated YSZ particle for TBC systems (Nanox S4007, Inframat Corp.): it is possible to observe that the powder is formed by the agglomeration of YSZ nanoparticles with diameters ranging from 30 to 130 nm [52].

Figure 2.9 (a) Spray-dried agglomerated YSZ particle. (b) Higher magnification view showing the nanostructured features of the agglomerate [52].

To obtain nanostructured thermal spray coatings, starting from nanostructured agglomerated powders, it is necessary to avoid full melting of the material to maintain part of the nanostructured features. At the same time, an utterly molten fraction of particles must be present to guarantee the coating cohesion. For this reason, the final coating microstructure will be formed by semi-molten particles retaining the nanostructured features (called “nanozones”) surrounded by fully molten particles acting as a binder and thus providing the coating integrity. Several authors define this particular mixture of fully and semi-molten particles as

35

36

Nanocomposite and Micro-Nanostructured Materials

a “bimodal microstructure.” A schematic is presented in Fig. 2.10, while a SEM image of a nanostructured YSZ topcoat is shown in Fig. 2.11. Fully molten particle

Semi molten particle

Individual nanostructured particle

Splat

Semi-molten particle

Pore

SUBSTRATE Figure 2.10 Typical schematic (cross section) of the bimodal microstructure of thermal spray coatings formed by fully molten and semi-molten nanostructured agglomerated particles. From Ref. [51].

10 mm

EHT = 8.00 kV WD = 8.1 mm

Signal A = SE2 Date :3 Nov 2014 Mag = 3.00 K X Sample ID =

Figure 2.11 Particular (SEM image) of a nanostructured YSZ topcoat in a TBC system [53].

It is essential to highlight that the nanozones exhibit entirely different properties if compared with the molten splats (e.g., a higher porosity), and thus, it is possible to design coatings with very

Nanostructured Thermal Barrier Coatings

different mechanical or physical properties by controlling the size, shape, and distribution of the bimodal microstructure. For example, in nanostructured YSZ topcoat for TBC systems, the porous nanozones can mitigate the densification effects induced by the elevated working temperature using a differential sintering mechanism that reduces the increase in the elastic modulus and thermal conductivity significantly during the service life of the TBC system. At the service temperatures, the sintering rate of the nanostructured zones is much higher than the denser coating matrix because of the pronounced thermodynamic tendency to densify and reduce the excess of interfacial energy typical of nanostructured materials. Sintering phenomena in conventional TBC systems typically lead to a porosity reduction and an increase in the thermal conductivity and elastic modulus, thus reducing the thermal insulation capability and the strain tolerance of the ceramic topcoat [54]. On the contrary, in nanostructured TBC systems, the differential sintering rate leads to faster densification of the nanozones, increasing the overall coating porosity and thus limiting the increase in thermal conductivity and elastic modulus and improving the durability of the system. In addition to the increased sintering resistance, several authors [55–57] reported an improved thermal cycling resistance (number of cycles to failure 2–4 times higher) for nanostructured TBCs concerning YSZ topcoats deposited starting from conventional powders. The higher thermal shock resistance of the nano TBCs could be associated with the enhancement of the fracture toughness of the nanostructured coatings due to the presence of the nanozones that are hypothesized to promote phenomena of cracks entrapment, deflection, and arrest. In Fig. 2.11, the deflection of a crack induced by the presence of a nanozone is visible. Another strategy to obtain nanostructured/ultrafine TBCs, alternative to the use of nanostructured agglomerated feedstock powders, is the direct injection of nanosized particles in the plasma jet by using a liquid carrier instead of a gas [58–63]. This route, known as suspension plasma spraying (SPS), is a relatively new technique able to deposit highly porous TBC topcoats (with low thermal conductivity, typical of the APS TBCs) characterized by a columnar (strain tolerant) microstructure [64].

37

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Nanocomposite and Micro-Nanostructured Materials

The suspension is typically composed of nanoparticles or ultrafine particles, usually suspended in water or alcohol. The suspension stream is injected in the plasma jet and undergoes fragmentation phenomena leading to the formation of extremely fine droplets and, after the in-flight liquid evaporation, tiny particles that are projected and deposited on the bond coat surface [65, 66]. Column formation in SPS is reported to be correlated to suspension properties, plasma spray parameters, and bond coat roughness, with a higher column density, observed on smoother bond coat surfaces [66]. SPS YSZ coatings with a porous and columnar microstructure are promising candidates for new-generation TBCs with improved functional properties such as lower thermal conductivity [67], enhanced thermal cyclic fatigue, and thermal shock resistance [68]. In Fig. 2.12, the columnar microstructure of an SPS YSZ topcoat is shown, and its nano- and ultrafine microstructural features are highlighted. (a)

(b)

(c)

(d)

Figure 2.12 Different micrographs showing the top view of a fractured SPS YSZ column (a); a fractured cross section (b), a magnified fracture surface within the column (c), and within the inter-columnar spacing (d). Several features are highlighted: columns (C in blue), inter-columnar spacing (IC in violet), molten splats (in black), spherical particles (S in orange), nanopores (NP in red), submicron pores (SP in green), and micron pores (MP in white) [69].

Additive Manufacturing of Nanocomposite Materials for Aerospace Applications

2.4 Additive Manufacturing of Nanocomposite Materials for Aerospace Applications The explosion of studies and research on additive manufacturing (AM) techniques was also addressed to the aerospace sector in recent years. The ultimate design freedom, the capacity to obtain lighter components by mean of topologic optimization, and the low production volume with high intrinsic value and performances (and cost) for parts produced meet the aerospace industry characteristics with the peculiarity of AM family techniques. After a fast growth in the past two decades, now the AM technology approaches to the maturity age. Several applications start to be transferred from the research field to the industry field, requesting increased reliability for the realized component, a more controlled production process, an increased interest on economic, logistic, and health aspects of the AM processes, to be plausible on the industrial point of view. In the first phase, almost completed, the evolution of this technology was devoted to the development of improved techniques and the setup of entirely new ones. Now increased attention and research efforts are allocated for the development, design, and setup of materials, alloys, and composites systems specially designed for AM applications. At the end of this technology development process, an increase in real components and applications for these techniques is the expected goal. Another aspect of being considered is the presence, in the aerospace sector, of some “rigid” regulations that must be fulfilled. These can use a newly developed component on the market, leading to the necessity to have a set of requirements for process management, e.g., the quality control for raw materials and the monitoring of the production defects for realized components, especially for those mission critical.

2.4.1 Materials

The exploitation of AM potentiality is strongly connected with the availability of materials suitable to be processed by AM and selected or designed to improve the expected performance of the final components [70, 71]. Also, a proper design of the material could

39

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Nanocomposite and Micro-Nanostructured Materials

lead to introducing new features and capabilities; this is typically the case of composites (and nanocomposites) where the introduction of a small (and smaller for nanocomposites) quantity of reinforcement could lead to obtaining a dramatic improvement in performance or added functionality [72–74]. Material Extrusion

(a) Fused Filament Fabrication

Other Approaches Prepreg composite filament

In-situ coating with liquid resin To extruder Liquid resin Dry fiber

Impregnated fiber

In-situ fusion with molten thermoplastic Dry fiber

Molten thermoplastics

(b) Liquid Deposition Modeling Randomly oriented short fibers in paste or liquid

Cross-section view Fiber

Matrix

Aligned fibers

Inter-layer boundaries Voids

Figure 2.13 Material extrusion process: (a) Three different ways to produce composites by FFF are shown: extrusion of prepreg composite filament, in situ coatings of fiber with liquid resin, and in situ fusion of fiber with molten thermoplastics. (b) Shear forces obtained extrusion of short fibers (or powders) in paste-in LDM process, alignment of fiber. The nozzle could be heated. The final cure is required after deposition. Reproduced/adapted with permission from Ref. [72].

Additive Manufacturing of Nanocomposite Materials for Aerospace Applications

The design of a nanocomposite system for AM is challenging because the effect of the process has to be taken into account to guarantee the surviving and the desired dispersion of nanofillers during the manufacturing [75, 76]. Also, the introduction of nanofillers in an existing AM raw material could induce a modification in the material behavior during the process, requesting an accurate study, setup, and/or modeling of the manufacturing process [77, 78]. The more developed field of application and research on nanocomposites for aerospace applications (structural and related to sensor development/microelectronics) involves the polymeric systems, attractive because the relatively low process temperatures used is less disruptive for heat-sensitive nanofillers [72]. Development of materials for fused filament fabrication (FFF) concerns the realization of composite filaments adding nanofillers (CNT, ceramic nanoparticles) to a standard matrix polymer (ABS, Nylon, PEI) [73, 79], usually made by a screw mixer/extruder. The main manufacturing issues are the realization of a continuous and homogeneous filament with a sufficient level of reinforcement, and the facing of extrusion problems (clogging, nozzle wear, modified rheology, etc.) due to the presence of hard particles in the melt flow. The other most used way for the preparation of polymer-based nanocomposites is based on the dispersion of nanofillers on polymer solution (LDM), sharply reducing the preparation problems, also leading to a reduction in raw materials preparation costs (no need of screw extruders and mechanical mixing of polymer and filler). The AM process could be different, depending on the specific technique used to deposit the precursor solution/paste and the curing/consolidation process (Polyjet, UV curing [80], direct writing, temperature consolidation [81]). For aerospace applications, some efforts are devoted to study and develop metallic alloys suitable for AM, typically obtained with laser-based techniques (e.g., SLS, SLM). For the production of metal matrix composites (MMCs), and more for nanocomposites (MMnC), these techniques involving a high quantity of localized heat flux on the powder beds request a careful design of raw powders and process parameters [77], to avoid losing the nanofillers during the manufacturing process. Usually, at the laboratory research level, the nanocomposite powders are obtained by milling of matrix and nanofiller components, in an inert atmosphere.

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Nanocomposite and Micro-Nanostructured Materials

Vat Photopolymerization (a)

Laser source

Mirror

Elevator

Cross-section view UV radiation Scattered radiation

Wiper Fiber

Liquid resin

UV penetration

Fiber

Polymerized resin

Platform

(b)

(1) Deposition

(2) Coating

(3) Selective curing

(4) Moves down for next layer

Figure 2.14  (a)  Vat  photopolymerization  process  and  detail  of  UV  curing  of  FRPC in SLA. A laser source in the UV spectrum is used. Powders and short fibers are typically premixed with the liquid resin. The addition of fibers reduces the UV penetration, which requires modification of printing parameters. (b) The procedure of modified SLA in which a new layer is deposited on top to prevent the sedimentation of fibers. Reproduced/adapted with permission from Ref. [72].

The most used metallic matrix is Ti-Al-based alloys for hightemperature applications, modified adding ceramic nanoparticles [82] or inducing in situ intermetallic nanostructures nucleation during the consolidation phase [83]. For structural applications, to obtain lighter and stiffer structures, the primary research efforts are devoted to Al matrix-based nanocomposites. Also, in this case consolidation process is typically the SLM, and composite powder

Additive Manufacturing of Nanocomposite Materials for Aerospace Applications

is obtained by milling of Al alloy with CNT [84] or nano-ceramic particles [85]. Powder Bed Fusion

Selective Laser Sintering Types of composite powder

Laser source

Composite powder delivery system

Mirror Roller

Reinforcement Matrix Reinforcement coated with matrix

Figure 2.15 Powder bed fusion using composite powders. Two approaches are shown: (1) Using a blend of reinforcement and matrix powders and (2) using a modified reinforcement powder precoated with a matrix. The laser is used as a heat source to melt the composite powder selectively. Reproduced/adapted with permission from Ref. [72].

2.4.2 Techniques Some AM techniques are proven to produce micro-nanocomposites, with some adjustments for the experimental setup. Typically, some problems arise moving from homogeneous material to composites: differential heating, clogging of nozzles and distribution systems, segregation of reinforcements, leading to a poorly densified microstructure with nonuniform reinforcement distribution, formation of macro defects (cracks, bubbles) due to solvent evaporation and filler agglomeration or non-homogenous shrinkage during cooling and consolidation phase. For polymer-based nanocomposites, several techniques were employed [72, 73, 75, 80, 86], demonstrating the possibility to fabricate nanocomposites. To increase reliability and deepen the knowledge on the behavior of the material during the printing process, some researches are addressed on the modeling of AM process [78, 86]. This approach is promising in nanocomposite preparation, leading to a reduction in the overall experimental activity to assess

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Nanocomposite and Micro-Nanostructured Materials

the optimal process parameters. Metal matrix nanocomposites (MMnCs) are less common with respect to the polymer counterparts because the high energy level involved could affect the survival of nano reinforcement. Nevertheless, some research shows promising results on the preparation of MMnC by laser processes [82, 87]. For this last class of nanocomposites, direct energy deposition [83, 88, 89] techniques are quite developed. It has been derived from the thermal spray, laser cladding and welding technologies, exploiting the possibility to select the most appropriate feed rate and to tune the heat transferred to the material, and, in turn, the capability to obtain a fully dense structure avoiding the heat transfer problem typical of powder bed techniques. Also, the DED approach simplifies the preparation of the composite feedstock, allowing the use of blended and composite powders/wires. Powder, carrier gas (Ar, He)

Processing head with powder nozzles Laser beam, shielding gas (Ar)

Scanning direction Welded powder (deposit) Welded substrate Heat affected zone

Melt pool Substrate

Figure 2.16 DED process principle. Reproduced/adapted from Ref. [89].

Also, in the case of MMnCs, a modeling approach is really useful to reduce the experimental cost during the process optimization phase [77]. The following table resumes the more critical characteristics of AM techniques suitable for nanocomposites preparation [70, 72].

Table 2.1

AM techniques suitable for nanocomposites preparation Material Extrusion (FFF, LDM)

Vat Photopolymerization (SLA)

Powder Bed Fusion (SLS, SLM)

Direct Energy Deposition (DED)

Materials

FFF Continuous filaments of thermoplastic polymers Continuous fiberreinforced polymers LDM A concentrated dispersion of particles in a liquid (ink or paste) or epoxy resin

A resin with photoactive monomers Hybrid polymerceramics

Compacted fine powders Metals, alloys, and limited polymers (SLS or SLM)

Metals and alloys in powder or wire form Ceramics and polymers Composites by powder mixing

Biomedical Electronics Aerospace Lightweight structures (lattices)

Aerospace Retrofitting Repair Cladding Biomedical

Applications

Biomedical Rapid prototyping Advanced composite parts Prototyping Biomedical Electronics Aerospace Lightweight structures (lattices)

(Continued)

Additive Manufacturing of Nanocomposite Materials for Aerospace Applications

Technique

45

Table 2.1

(Continued) Vat Photopolymerization (SLA)

Powder Bed Fusion (SLS, SLM)

Direct Energy Deposition (DED)

Benefits

Low cost Easy fabrication Able to modify print-head for laying fibers Multi-material capability

Fine resolution High quality Random alignment of discontinuous fibers for isotropic mechanical property

Fine resolution High quality Easy to remove support material Unused powder can be reused High loading of reinforcement

Drawbacks

Obvious layer-by-layer effect Nozzle degradation Nozzle clogging at high fiber volume

Very limited materials Slow printing Expensive Adding fiber increases viscosity, thus making handling difficult Fiber sedimentation in resin Need for additional feeding device for deposition UV penetration issue Bubble formation causing pores to form and leading to crack initiation

Slow printing Expensive High porosity in the binder method Rough surface finish

Reduced manufacturing time and cost Excellent mechanical properties Controlled microstructure Accurate composition control Excellent for repair and retrofitting Low accuracy Low surface quality Need for a dense support structure Limitation in printing complex shapes with fine details

Nanocomposite and Micro-Nanostructured Materials

Material Extrusion (FFF, LDM)

46

Technique

Material Extrusion (FFF, LDM)

Special Properties for Composites

Electrically conductive Graded dielectricity Electrocaloric deformation

Resolution Filler Orientation

50–200 μm

Along printing direction

Vat Photopolymerization (SLA)

Powder Bed Fusion (SLS, SLM)

Direct Energy Deposition (DED)

Electrically conductive 10 μm

Along electric field direction Along magnetic field direction Along laying direction According to fiber pattern of the mat Random orientation

80–250 μm

Random orientation

250 μm

Random orientation

Additive Manufacturing of Nanocomposite Materials for Aerospace Applications

Technique

47

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Nanocomposite and Micro-Nanostructured Materials

2.4.3 Aerospace Applications Aerospace is one of the most attractive and demanding industry sectors for AM. Currently, hundreds of different applications of AM components are used and flight proven, on earth and also in space [90]. With respect to other industries in the aerospace field, the certification rules are rigid about the introduction of novel materials and manufacturing processes, needing a considerable time to transfer lab technologies on the real applications. Testing and safety standards for AM in aerospace are still under development. Also, it is not easy to identify a set of certification rules given that different AM technologies are still on their way to being fully matured. One condition about AM composites and, more, nanocomposites is that besides the technical issues, we need an additional effort to overcome the regulation limits, proving the reliability and the quality of the manufacturing process. Nevertheless, the full exploitation of potential advantages of the introduction of nano-/microcomposites is pursued by research labs and industry partners, based on their possible performance in terms of mechanical and electromagnetic properties (PMnC with CNT or graphene), high-temperature strength (for MMnC with ceramic nanofillers). AM techniques are ideal for aerospace components as they have the following peculiar characteristics [70]:



∑ Complex geometry. Complex shapes are necessary for integrated functions, i.e., structural, heat dissipation, and airflow. For example, GE Aviation is developing fan blade edges with optimized airflow. Moreover, it is possible to simplify parts by combining multiple components, such as GE fuel nozzles. Finally, functional electronics can be implemented (or printed) easily as AM parts. ∑ Difficult-to-machine materials and high buy-to-fly ratio. The aerospace industry uses advanced and costly materials, such as titanium alloys, nickel-based superalloys, highstrength steel alloys, or ultrahigh-temperature ceramics that are very difficult to manufacture and create a large number of waste materials (up to 95%). AM reduces waste (down to around 10–20%) and provides complex shapes.

Space Sensors for Gas Detection and Microthruster







∑ Customized production. The aerospace industry is characterized by the production of small batches of parts. AM is more convenient economically than conventional techniques for small batches as it does not require expensive equipment such as molds or dies. ∑ On-demand manufacturing. Airplanes have a long working life of up to 30 years. Keeping old parts incurs a notable cost of inventory, but AM is capable of manufacturing parts on demand, thereby reducing the maintenance time. ∑ High performance to weight ratio. Aerospace components need to be lightweight and present high strength- and stiffness-to-weight ratios to reduce costs and emissions.

The Oak Ridge National Laboratory in Tennessee has also developed a way to infuse reinforcing carbon fibers into polymer raw material to print parts that can carry loads. In general, polymer parts are of low strength and are not suitable as load-carrying components. Tethers Unlimited, Inc., of Bothell, Washington, has been working since 2012 under a NASA Innovative Advanced Concepts contract to develop a technique for making multifunctional spacecraft structures in an open orbit. As part of the company’s plan to launch selffabricating satellites, it has proposed a device called “Trusselator.” This device would automatically extrude layers of material to form lightweight carbon-fiber truss structures that would be robotically assembled into solar arrays, antennas, or other components [90].

2.5 Space Sensors for Gas Detection and Microthruster

One of the requirements in optical instruments (from UV to FIR) for EOS and interplanetary missions is to have high precision and light spectral instruments with no moving parts. In the past, these requirements were partially fulfilled. For example, current satellites that are flying in the frame of EOS missions, mount payloads like Global Ozone Monitoring Experiment GOME I and GOME II (onboard ERS 2 and METOP, respectively), Infrared Atmospheric Sounding

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Interferometer IASI (onboard Meteorological Operational satellite METOP). These instruments have been mounted onboard a small satellite of 300–400 kg in weight or have been integrated into the payload of higher satellite as ENVISAT or METOP or TERRA or similar. However, their weights prevent both to be mounted on satellites designed to make studies of planetary atmospheres and to be installed onboard the commercial aircraft (as it is planned, for instance, by the MOSAIC project) or micro-nano satellites. In the recent years, with the advent of MEMS/nanotechnology, however, the size of satellites and materials they are made of and accordingly the onboard instruments are changing, and new sensors based on the MEMS/nanotechnology have been built to substitute the previous one. The miniaturization obtained by MEMS/ nanotechnology can recover a significant number of applications previously done by traditional instruments. This miniaturization means not only to change the size of conventional instruments devoted to the measurements of earth or universe but also to introduce new devices to control and monitor the physical and chemical properties of the space vehicle. Beyond the traditional ones as germanium and silicon, other materials are currently used. A non-exhaustive list is reported in Table 2.2. Table 2.2

Non-exhaustive list of materials and related applications for space

Material

Application

Silicon

Electronics, sensors

Indium oxide

Chemical sensors, biosensors

Germanium Tin oxide

Indium tin oxide Zinc oxide

Copper oxide

Electronics, IR detector Chemical sensors

Transparent conductive film in display electrodes, solar cells, organic light-emitting diodes UV laser, field emission device, chemical sensors Field emission device

Space Sensors for Gas Detection and Microthruster

Material

Application

Wide band gap nitrides (GaN)

High-temperature electronics, UV detectors and laser, automotive electronics and sensors

Boron nitride

Indium phosphate Zinc selenide

Copper, tungsten Lithium niobate

Insulator

Electronics, optoelectronics Photonics (Q-switch, blue– green laser diode, blue–UV photodector) Electrical interconnects Amplifier, microinterferometer

The objective of nanotechnology is to obtain optical, chemical, and biological sensors for detecting gas and protein or other components and to develop autonomous sensor platforms with high sensitivity and selectivity. Independent sensor platforms have broad applications in integrated vehicle health management (IVHM), astronaut health management, and earth and planetary exploration. NASA has used carbon nanotube (CNT) sensors for trace gas detection on the International Space Station (ISS) and toxic emissions. Carbon nanofiber (CNF) sensors with integrated microfluidics for biomarker detections (troponin, myoglobin, cardiac reactive protein) have been also developed

2.5.1 Technology of Lithium Niobate

Lithium niobate crystals were grown for the first time by the Czochralski method in 1965 [91], and Abrahams investigated their structure in the series of works [92]. The distance of Li+ to the nearest oxygen plane is 0.37 Å. The lattice asymmetry makes lithium niobate the polar material, and as shown in Fig. 2.17, oxygen atoms reside in the oxygen triangles. The Li+ ion has to be displaced to the other side of the nearest oxygen triangle, whereas the Nb5+ ion can only move within the oxygen cages. Two stable positions (before and after reversal) define two possible directions of the spontaneous polarization. The unit cell can be either rhombohedral (trigonal, а = 5.4944 Å, α = 55°52¢) or

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Nanocomposite and Micro-Nanostructured Materials

hexagonal (а H = 5.1483 Å, c H = 13.8631 Å, c/a = 2.693) with six formula units per unit cell. The stacking sequence of cations in these octahedral sites is Nb, Li, vacancy, Nb, Li, vacancy, and so on [95]. The octahedral interstices formed in this structure are one-third filled by lithium atoms, one-third filled by niobium atoms, and one-third is vacant. From this point of view, bulk crystals with a stoichiometric composition (R = Li/Nb = 1) have a nearly ideal structure. In lithiumreduced crystals, along with congruent crystals (R = 0.946), a cation sublattice is considerably disordered. It was demonstrated [96] that excessive niobium ions substitute lithium ions at their positions, and, at the same time, a quite loose cation sublattice allows various ions to be introduced into the structure. LiNbO3 is a material with variable composition demonstrating a wide range of solutions. Specifically, there are areas consisting of both LiNbO3 oxide and either Li3NbO4 or LiNb3O8, which are centrosymmetric and hence non-ferroelectric phases. Therefore, LiNbO3 single crystals are grown with special care at low temperatures, because a small deviation results in the formation of Li3NbO4, or LiNb3O8 oxides provoking degradation of ferroelectric properties [96]. +C axis

- Li

- Nb

-O

Figure 2.17  Positions of the lithium atoms and niobium atoms with respect to  oxygen octahedra in the ferroelectric phase of lithium niobate. The positions of lithium atoms are equally probable to be either above or below the oxygen. The horizontal lines in the diagram on the right represent the oxygen layers [93, 94]. Reprinted with permission by IOP Science.

Space Sensors for Gas Detection and Microthruster

Several waveguide fabrication processes were developed to

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Nanocomposite and Micro-Nanostructured Materials

ne

(a) Extraordinary Index Profile Model

2.25

Wave Guide

End of Range Damage Substrate

2.67mm

2.20

ng = 2.2329 ns = 2.203

Neff = 2.2188

2.15

nd = 2.1643

2.10 0 no

1

3 2 Depth (mm)

5

(b) Ordinary Index Profile Model End of Range Damage

2.30

Wave Guide 2.25

Substrate

ns = 2.286

2.67mm ng = 2.2614

2.20

2.15

4

Neff = 2.2299

0

1

2

nd = 2.1928 3

4

5

Depth (mm)

Figure 2.18  Schematized  refractive  index  profile  of  the  2×1014 O/cm2 implanted sample obtained under the hypothesis of a step-like trend (a) extraordinary refractive index ne; (b) ordinary refractive index no. Source: JAP [101].

model, fitting the de-channeling with a multiple scattering function. It was assumed that the de-channeling zone was independent of the different kinds of defects present in the sample. Ion implantation and RBS experiments were performed in a clean cryo-pumped vacuum in the 10-7 hPa range. These processes gave rise to planar

Space Sensors for Gas Detection and Microthruster

optical waveguides in the different samples. As a result, one can obtain a refractive index variation of LiNbO3, induced by the defect profile generated by high-energy oxygen implantation that was used for the fabrication of good quality optical planar waveguides. As a first approximation, from an optics point of view, the effect produced by ion implantation can be schematized by a step refractive index distribution (see Fig. 2.18a,b). Au SiO

LiNbq

Displaced Atoms (%)

0.025 0.020 0.015 0.010 0.005 0.000 0.0

0.5

1.0

1.5 Depth (mm)

2.0

2.5

Figure 2.19 Damage profile used for obtaining the channel waveguide.

To obtain the simplified refractive index model, we used the following hypotheses: (i) The refractive index profile has a steplike shape; (ii) the turning point of the waveguide is placed at the same depth at which the end-of-range damage peak was detected by the RBS technique (~2.7 microns); and (iii) the turning point of the guide is the same for all the modes observed. The width of the optical barrier corresponds approximately to the half-width at halfmaximum of the end-of-range damage profile peak as calculated by Stopping and Range of Ions in Matter (SRIM). Computer programs calculate the interaction of ions with matter; (iv) ng (mean refractive index of the guiding region) and nd (mean refractive index at the end of the damaged region range) were then adjusted to best fit the observed neff (effective refractive index).

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The damage produced in regions where electronic stopping is dominant depends on implant dose and can be correlated to lithium and oxygen migration. The damage is highly stable and does not depend on room temperature. At the end of the process, we obtained the damage profile shown in Fig. 2.19. In Fig. 2.20 we show waveguide inside the lithium niobate slab and the related optical loss measurement.

2.0 1.9 1.8 log[ I ] 1.7 1.6 1.5

32 34 36 38 40 42 44 46 48 distance (mm)

Figure 2.20 Slab waveguide, about 3 inches long, obtained by implantation at 2 × 1014 O/cm2, annealed for 30 min at 235°C in dry oxygen atmosphere and optical loss measurement of the slab waveguide (below).

2.5.2 Microinterferometer Recent advances in MEMS techniques have made it possible to produce low-cost devices using batch-processing techniques. MEMS can be monolithically integrated on a single chip and compared with macroscale optomechanical devices; they are smaller, lighter, faster, and more rugged. Very efficient light modulators, switches, tunable lasers, detector filters, and now spectrometers and interferometer

Space Sensors for Gas Detection and Microthruster

can be realized. MEMS offers many advantages over conventional optical systems. Instead of developing a new process for each optical system, different optical functions can be realized by rearranging and resizing the basic building blocks of the MEMS device, enabling fast prototyping of new optical system and shortens the product development cycle. Since micro-optical bench uses photolithography processes to make micro-optical elements and optomechanical at the same time, the interconnections among the optical elements can be pre-aligned during the layout of the photomask. The entire optics system can be monolithically integrated on a single chip MEMS­ fiberoptic switch. MEMS technology offers a potential solution for reducing the size, weight, and cost of optical switches providing the advantage to scale up to large switches arrays. A large number of optical switches can be monolithically integrated on the same silicon substrate. With the technology previously proposed, we built up a microinterferometer, based on the well-known Mach–Zehnder geometry. This device, which was made the preliminary CAD design, was planned to be realized on a hybrid chip containing the integrated interferometer and the signal detection integrated circuit. The device is designed to perform a spectral analysis of the incoming radiation with the technique of the Fourier spectroscopy. The device is made on an LiNbO3 wafer and is designed to use the electro-optic properties of this material to obtain a scanning interferometer without moving parts. The change in the optical path typically got moving an optical component of the interferometer (e.g., a mirror) was obtained modifying the refractive index of one of the waveguides, forming the arm of the device (Fig. 2.21), through the application of an electric field. The device performances allow spanning a spectral resolution ranging between 0.1 nm and 1 nm, as a function of both the geometrical size of the device and the applied electric field. The length of the waveguides, defining the interferometer arms, should range between 1 cm and 2 cm, whereas the width of each arm should be of the order of a few microns. The total thickness of the device is determined by the depth of the LiNbO3 wafer (500 µm). Wafer-bonding techniques will be used to join the integrated optics chip with the silicon chip containing the detection system and the relatively integrated logic. Considering that LiNbO3

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Nanocomposite and Micro-Nanostructured Materials

1.5

l(nm) (a)

1.0

1 Voltage (V) (b)

2

770

760 l(nm) (d)

5 Voltage (V) (e)

10

1.0

0 55.0

460

l(nm) (g)

480

0.0

55.5 56.0 Time (s) (c) 770 l(nm) 760

0 55.0

55.5 56.0 Time (s) (f) 460 l(nm) 480

Amplitude

1.5

1.5

1.5

3

Amplitude

0

Relative density

0.0

Interference Pattern

Input Spectrum

1

1.5

1.0

0.0

0

1.0

1.5

0.0

0.0

760 Relative density

770

Relative density

0.0

1.5

Voltage Ramp

LiNbO

Amplitude

1.0

1.0

770 l(nm) 760

1

Relative density

Relative density

has a transmissivity curve covering a spectral interval ranging from 0.45 µm to 4.5 µm and taking into account the reduced size and the negligible weight of a device, it is convenient to package together some devices, each of them designed to give optimum performances on a relatively narrow spectral range.

Relative density

58

0

10 5 Voltage (V) (h)

15

0.0

92

Time (s) (i)

88

Figure 2.21 The design of the microinterferometer (to the right) with NO2 spectrum as a function of voltage. Looking down from above, the resolution of the spectral range performed by interferometer is highly dependent on the voltage, as appears comparing the Fourier transform at right. Along the electrically polarized waveguide is applied a voltage inducing the variation of refractive index in a branch. Two optical fibers obtain the Y junction (on right). The instrument weight is of the order of a few grams. In the present drawing, we have also included an array of microinterferometer with SPADs.

Electronic board with drive Control

Photodiode

LiNbO3 Mach-Zehnder

Figure 2.22 Electronic board with drive control and photodiode has been packed with Mach–Zehnder resulting in a very compact device.

Space Sensors for Gas Detection and Microthruster

The present MEMS technology for this device cannot be implemented with NT due to reasons related to physics. However, some additive improvements can be made on the collateral devices using NTs, for example, on high-speed optical sensors as single photon avalanche diode. As a further application of Mach–Zehnder, there is an optical gyroscope that can be used as attitude sensors. It is made on Sagnac effect where the phase shift between two light beams propagating in opposite directions along the fiber coil is measured through interferometry, thus translating one component of the angular velocity into a shift of the interference pattern, which is measured photometrically [104–106]. Also, such devices can be improved using NTs as in the most recent single photon avalanche diode [107].

Figure 2.23 Schematic top view of the microthruster with details of the precombustion chamber and nozzle throat. Source: CANEUS2600-11020 France [110].

2.5.3 Nanothruster MEMS-based chemical monopropellant thruster has been widely reported in the literature [108–110]. The nanothruster based on H2O2 monopropellant has been developed by Chiarini et al. [111] and typically works using a highly exothermic chemical decomposition

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of the propellant itself. The reaction is induced by a suitable catalyst, which produces energetic gaseous reactants that expand and then exit through a micronozzle, providing the required thrust. Liquid hydrogen peroxide of high concentration (~90%) is fed through a zigzag injector into the catalytic chamber where the liquid propellant undergoes chemical decomposition and produces gaseous products of reaction at the catalytic chamber outlet (Fig. 2.23). The nozzle has been designed to have a three-dimensional convergent structure. It is approximately two times thicker than the catalyst chamber. The fabrication of the thruster has been made by using both standard silicon micromachining based on photolithography associated with deep reactive ion etching (D-RIE) technology and ultrasound micro-drilling to allow the threedimensional converging part of the nozzle. The smallest structures are on the order of 20–40 µm (Fig. 2.24).

Figure 2.24 Detail of the thruster showing the three-dimensional convergent part of the nozzle and the control system between injector and propeller. The thruster has been built by silicon micromachining based on photolithography.

Table 2.3 shows the performances of the supersonic micronozzles. The performance of the system could be improved by the thermal insulation of the reaction chamber with nanomaterial [112].

Conclusion

Table 2.3

Performance of microthruster Parameter

Design values

Thrust

10 mN

Mass flow rate

~5.5 × 10-3 g/s

Specific impulse Throat diameter Inlet pressure

Exit Mach number

2.6 Conclusion

120 s ÷ 150 s 150 µm

~2.8 bar 5.4

The impressive properties of CNTs have led to various applications. Investigation of MMC and MMnC has shown that the most critical aerospace application is due to high strength and low weight composites. The opportunities for the relative industry are through the thermal barrier and wear-resistant coatings, for future commercial aircraft, military aircraft, UAVs, MAVs, space vehicles, satellites, aerostats, and HAPS. The benefits of CNT implementation in aerospace engineering for terrestrial and space applications are very high. Despite the limited existing applications of CNTs in aerospace sciences, the rationale for future applications of these materials in aerospace engineering will be realized with both a short-term and a long-term perspective. New concepts in nanotechnology will facilitate this implementation procedure despite current existing scientific challenges. In such a frame, there is the realization of sensors that can perform at high temperature and other physical and chemical sensors that can play safety inspection cost effectively, quickly, and efficiently than the present procedures, as new composites, wear-resistant tires, improved avionics, satellite, communication systems, optical and radar technologies. Then the applications shown here indicate that further research is needed on new aerospace applications and sensors and also on the merging of technologies developing intelligent materials that control themselves. The integration of NT with MEMS improves mostly the performance of devices and materials, reducing the sensor weight, size, power consumption, and production costs and also taking advantage of the different technological scales.

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49. Fauchais, P., Montavon, G., Lima, R. S., and Marple, B.R. (2011). Engineering a new class of thermal spray nano-based microstructures from agglomerated nanostructured particles, suspensions and solutions: An invited review. J. Phys. D. Appl. Phys., 44. 50. Gell, M. (1995). Application opportunities for nanostructured materials and coatings. Mater. Sci. Eng. A, 204, 246–251.

51. Lima, R. S. and Marple, B. R. (2007). Thermal spray coatings engineered from nanostructured ceramic agglomerated powders for structural, thermal barrier and biomedical applications: A review. J. Therm. Spray Technol., 16(1), 40–63.

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52. Lima, R. S. and Marple, B. R. (2008). Nanostructured YSZ thermal barrier coatings engineered to counteract sintering effects. Mater. Sci. Eng. A, 485, 182–193.

53. Baiamonte, L., Marra, F., Pulci, G., Tirillò, J., Sarasini, F., Bartuli, C., and Valente, T. (2015). High temperature mechanical characterization of plasma-sprayed zirconia-yttria from conventional and nanostructured powders. Surf. Coatings Technol., 277.

54. Lima, R. S. and Marple, B. R. (2008). Toward highly sintering-resistant nanostructured ZrO2-7 wt.%Y2O3 coatings for TBC applications by employing differential sintering. J. Thermal Spray Technol., 17(5–6), 846–852.

55. Wang, W. Q., Sha, C. K., Sun, D. Q., and Gu, X. Y., (2006). Microstructural feature, thermal shock resistance and isothermal oxidation resistance of nanostructured zirconia coating. Mater. Sci. Eng. A, 424, 1–5.

56. Zhou, C., Wang, N., and Xu, H. (2007). Comparison of thermal cycling behavior of plasma-sprayed nanostructured and traditional thermal barrier coatings. Mater. Sci. Eng. A, 452–453, 569–574.

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58. Fauchais, P., Etchart-Salas, R., Rat, V., Coudert, J. F., Caron, N., and Wittmann-Ténèze, K. (2008). Parameters controlling liquid plasma spraying: Solutions, sols, or suspensions. J. Therm. Spray Technol., 17, 31–59. 59. Fauchais, P., Montavon, G., Vardelle, M., and Cedelle, J. (2006). Developments in direct current plasma spraying. Surf. Coatings Technol., 201, 1908–1921.

60. Pawlowski, L. (2009). Suspension and solution thermal spray coatings Surf. Coat. Technol., 203, 2807–2829.

61. Shaw, L. L., Goberman, D., Ren, R., Gell, M., Jiang, S., Wang, Y., Xiao, T. D., and Strutt, P. R. (2000). The dependency of microstructure and properties of nanostructured coatings on plasma spray conditions. Surf. Coatings Technol., 130, 1–8.

62. Cipri, F., Marra, F., Pulci, G., Tirillò, J., Bartuli, C., and Valente, T. (2009). Plasma sprayed composite coatings obtained by liquid injection of secondary phases. Surf. Coatings Technol., 203, 2116–2124. 63. Karthikeyan, J., Berndt, C. C., Tikkanen, J., Wang, J. Y., King, A. H., and Herman, H. (1997). Preparation of nanophase materials by thermal spray processing of liquid precursors. Nanostructured Mater., 9, 137– 140.

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79. Kyratsis, P. and Tzetzis, D. (2018). Investigation of the mechanical properties of acrylonitrile butadiene styrene (ABS): Nanosilica reinforced nanocomposites for fused filament fabrication 3D printing. IOP Conf. Series Mater. Sci. Eng., 416(1), 0–6.

80. Gouzman, I., Grossman, E., Verker, R., Atar, N., Bolker, A., and Eliaz, N. (2019). Advances in polyimide-based materials for space applications. Adv. Mater., 31(18), 1–15. 81. Hmeidat, N. S., Kemp, J. W., and Compton, B. G. (2018). High-strength epoxy nanocomposites for 3D printing. Compos. Sci. Technol., 160, 9–20.

82. Rittinghaus, S. K. and Wilms, M. B. (2019). Oxide dispersion strengthening of γ-TiAl by laser additive manufacturing. J. Alloys Compd., 804, 457–460.

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Chapter 3

Advanced Polymer Composites for Use on Earth and in Space

Konchits Andrey,a Yeriomina Yekaterina,b Tomina Anna-Mariia,b Lysenko Oleksandr,b Krasnovyd Serhii,a and Morozov Olexanderc aDepartment

of Optics and Spectroscopy, V. Lashkaryov Institute of Semiconductor Physics NASU, Prospect Nauky, 41, Kyiv 03028, Ukraine bDepartment of Condensed Matter Physics, Dniprovsk State Technical University, Dneprostroevskaya str., 2, Kamenskoe, Ukraine cNational University of Life and Environmental Sciences of Ukraine, Heroiv Oborony Str. 15, Kyiv 03041, Ukraine [email protected] Dedicated to Alexander Burya (1950–2019)

3.1 Introduction Carbon-based materials such as carbon fiber (CF)-reinforced carbon, CF-reinforced silicon carbide, CF-reinforced plastic, ceramic matrix composites, and others are widely used in space technology for the thermal protection of spacecraft [1, 2]. On the other hand, the use of Nanotechnology in Space Edited by Maria Letizia Terranova and Emanuela Tamburri Copyright © 2022 Jenny Stanford Publishing Pte. Ltd. ISBN 978-981-4877-54-1 (Hardcover), 978-1-003-13191-5 (eBook) www.jennystanford.com

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composite materials (CMs) in devices on earth and in space allows both to increase the lifetime of space technology [3] and to reduce the weight of apparatus construction by 25–35% and production cost by ~50% [4]. Nowadays, CMs based on thermoplastic and ceramic binders [5, 6] reinforced with nanofillers, wire made of heat-resistant and refractory alloys and metals [7], carbon nanotubes (CNTs) [8], long [9] and short [11] CFs, etc., are commonly used. The use of parts from composites based on thermoplastic and ceramic matrix while manufacturing fuel tanks, fairing allows to reach high thermal and erosion stability and less destruction of space technology parts under the influence of dynamic and fatigue loading [10]. Composites that contain CFs, CNTs, and so on redistribute internal stresses and block expansion of small cracks [11, 12]. Thus, parts with CMs based on thermoplastic matrix are used for manufacturing new solid rocket motors by the Design Bureau of “Pivdenne” State Enterprise instead of traditional aluminum and titanium parts [13]. However, there are factors that hold their widespread introduction back: high production cost [14] and anisotropy of properties [15]. That is why searching for new CMs is an actual task for using them both on the earth and in space. Electronic and tribological properties of the developed composites based on heatresistant aromatic polyamide phenylone (APP), which is analogous to Nomex, and different nano- or micro-fillers are considered in this section. The examples of their usage and their high efficiency are provided in the final part of the section.

3.2 Technology of Preparation of Polymer Composites Based on Aromatic Polyamides

The technology for polymer CMs based on thermoplastic binders is quiet important since operational characteristics of the products depend on the uniformity of distribution of filler in the polymer matrix. It is known [16] that it is possible to reach a qualitative mix of dry bulk materials in the vortex layer of ferromagnetic particles for a short period of time. An apparatus with a weighted layer of ferromagnetic particles is effective for uniform mixing of both nanoand micro-fillers with polymer and reinforcing fibers. Reacting substances that go through the vortex layer of ferromagnetic particles are influenced by various physical effects such as magnetic

Technology of Preparation of Polymer Composites Based on Aromatic Polyamides

treatment, acoustic oscillation, electrolyzing, electrical spark discharge, blow and mechanical mixing. Thanks to that their surface is activated, and physical and chemical properties are accelerated.

3.2.1 Components for Manufacture of CMs

Great attention is paid to the initial components, which are matrix and fillers. Aromatic polyamides are different from other thermoplastic binders in the stability of their sizes, high fatigue strength, fire resistance, and ability to stand significant static and dynamic loads under high temperatures (up to 523 K), radiation, and aggressive environment [17, 18]. Thereby, based on these polymers, it is possible to create composite materials that can operate both on earth and in space. APP is a linear hetero-chain copolymer. Its macromolecules are built from aromatic fragments with different structure and are connected by amide bonds [19]. The creation of CMs based on APP allows to expand the areas of using the products that are made from them in machinery, medicine, and space technology (including stealth technologies). The modified C-1 APP has high thermal and mechanical resistance: O

O

H

H

O

O

H

H

C

C

N

N

C

C

N

N

n

m

Where n = 0.75; m = 0.25. Another representative of APP is the modification of C-2, which contains the –HNCO– amide group connected by phenyl fragments [20] from each side in the main chain of macromolecules. It is described by the chemical formula: H2N

H

O

N

C

CO



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In order to get predefined properties of CMs, a great amount of nano- and micro-dispersed fillers or discrete CFs were used as fillers. CNTs, fullerene С60, fullerene soot (FS) and fullerene black (FB), silver and thermally split graphite, powders of dispersed metals are an interesting group of fillers due to their unusual chemical, thermal, and physical properties. CNT “Taunit” (Fig. 3.1) are one-dimensional nanoscale threadlike formations of polycrystalline cylindrical graphite with external and internal diameters of 20–70 nm and 5–10 nm, respectively, length of 2–10 mcm, with thermal resistance in air up to 873 K.

4-3-04 100nm

Figure 3.1 Microstructure of carbon nanotubes received in the industrial reactor.

Ultra-dispersed diamonds (UDDs) are a product of explosive decomposition of the mix of explosives with negative oxygen balance and following chemical cleaning of detonation products (diamondcontaining charge) by strong oxidizers, for example, by nitrate acid. The average size of diamond microcrystals is 3–6 nm. UDD particles are characterized by round shape without a pronounced crystal cut. Fullerene С60 (99.9% fullerene content) and FS (11% fullerene content) are the products that are received by the arc evaporation of graphite. FB (fullerene content not higher than 0.1%) is soot after extraction of fullerene substances by nonpolar organic solvents and

Technology of Preparation of Polymer Composites Based on Aromatic Polyamides

then steamed for the removal of organic solvent [21, 22]. The size of particles of this group is 40–50 nm. CFs that contain highly dispersed cuprum (Cu) have been received in the National Academy of Science of Belarus [23] (Fig. 3.2). In order to get cuprum-containing CFs, Ural T-24 hydrate-cellulosed fiber is impregnated with copper chlorides, after which it is carbonized in inert gas flow [24]. High heat resistance and strength that exceeds two–three times the strength of usual chemical fibers are among the main advantages [25].

2 mm

EHT=20.00 kV WD=3 mm

Signal A=3 WLans Photo No.=2539

Date 23 Sep 2000 Time: 12:27:19

Figure 3.2 Electron microscopic image of copper-containing carbon fiber.

GL-2 thermally split graphite (TSG) and silver graphite allow increasing mechanical properties of graphitoplastics (GP) in comparison with colloidal graphite. Carbonyl nickel (PNK-2K10), cuprum (PMC-1), aluminum (PA–1), titanium (PTK–1 (2)), and bronze (BrО5Ts5S5), which are characterized by high indicators of thermophysical and physicomechanical properties, have been used as powders of dispersed metals [26].

3.2.2 Preparation of Polymeric CMs in Rotating Electromagnetic Field

CMs based on C-1 and C-2 APP were prepared by the method of dry mixing in an apparatus (Fig. 3.3) with a rotating electromagnetic

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field (0.12 T) with the help of ferromagnetic particles extracted from ready composition by magnetic separation [16, 22, 23, 26]. Reinforcement technology in the rotating electromagnetic field, in contrast to the famous method of getting CMs in the sulfuric acid solution, allows to receive composites with equal distribution of the filler in the polymer matrix (Figs. 3.4 and 3.5); the process duration decreases with the activation of fillers’ surface at the same time. Environmental safety increases, too [27]. A B C 1 2

3

Figure 3.3 The scheme of experimental plant for mixing polymer binders and fillers: 1 is magnetic induction meter, 2 is electromagnetic apparatus, 3 is threephase transformer.

Figure 3.4 The character of distribution of cuprum-containing CF in polymer binder (×150).

Results

Figures 3.4 and 3.5 demonstrate the uniform distribution of fillers in the polymer obtained on the experimental setup.

Figure 3.5 The character of distribution of carbonyl nickel powder in polymer binder (×150).

3.3 Results The modern machinery and aircraft-building industry needs to expand the range of polymer CMs with high tribotechnical characteristics. For both terrestrial and space applications, composites with high wear resistance and low friction coefficient are of great interest. Such CMs allow increasing the resource and reliability of friction units, saving scarce and expensive materials, and, in general, improving the operational characteristics of machines and apparatuses [28].

3.3.1 CMs with Nanofillers 3.3.1.1 Electronic properties

Purposeful synthesis of new CMs is impossible without information of their structure as well as electronic and magnetic properties at

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the atomic-molecular level. In particular, it is important to control the electronic properties of both base polymers and their fillers, dispersity level of fillers in composites, and mechanisms of their interaction with the polymer matrix. It seems especially important in the case of using hybrid matrixes or hybrid fillers, namely, those containing several components simultaneously. For instance, CFs covered with metal micro- or nanoparticles. One of the most efficient methods for the investigation of electronic or magnetic properties of substances is the method of electron paramagnetic resonance (EPR), which is based on the universal property of electrons—availability of their spin. The method of EPR enables to directly determine both the total concentration of paramagnetic centers in composites and electronic properties of the latter in whole, and separately magnetic and electronic properties of individual components. Since both the polymer matrix APP and practically all the fillers that were used for developing these composites possessed paramagnetic or ferromagnetic properties; the EPR investigations contributed essentially to the elaboration of new nanocomposites. The efficiency of magnetic resonance study for reaching topical practical purposes was proved by us earlier, when developing optimal diamond-like composite films for thin-layer coatings of hard discs for information storage. This work was performed in cooperation with the American

EPR signal, arb. units

78

750

C-2 APP

1000

1

0 -750 330

333

336

339

0 2 1

-1000 ν = 9350 MHz 0

200 400 Magnetic induction, mT

600

Figure 3.6 Magnetic resonance spectrum in a sample of C-2 APP. Lines 1 and 2 are caused by paramagnetic defects in the polymer chains of C-2 APP molecules, and superparamagnetic iron oxide nanoparticles, respectively.

Results

firm VEECO Instruments. As a result, the relation between the structure, hardness, and degree of internal stresses in these films was ascertained as well as the characteristics of spin systems inherent to the studied paramagnetic defects [29]. The acquired experience provided a good start for further investigations of polymer materials and their composites. In the initial polymer C-2 APP, at the temperature Т = 300 K, we revealed two types of signals: the narrow line 1 (g ª 2.004, DBpp ª 1 mT) and the broad line 2 (g ª 2.23, DBpp ª 100 mT) (Fig. 3.6). The narrow line 1 is conditioned by paramagnetic defects inside the polymeric chains of C-2 APP molecules, while the broad line 2 is conditioned by the presence of superparamagnetic nanoparticles of ferric oxide [30, 31]. In the case of С-2 APP + MWCNT (multiwalled carbon nanotube, material “Taunit”) composite, signals of the superparamagnetic nature (g ª 2.0, DBpp ª 130 mT) caused by the presence of metal nanoparticles related to the catalyst were also revealed (Fig. 3.7, curve 1). The intensity of these signals depends on the separation efficiency of the material “Taunit” after its synthesis. In our experiments, it was lowered by approximately two orders (Fig. 3.7, curve 2). EPR signal, arb. units

800

1 2 (gain х100)

0

-800

0

200

400

600

Magnetic induction, mT

Figure 3.7 Magnetic resonance spectra of MWCNT “Taunit” (curve 1) and composite C-2 APP+10 wt.% purified MWCNT (curve 2).

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Advanced Polymer Composites for Use on Earth and in Space

The availability of intense superparamagnetic signals is not a property inherent exclusively to MWCNTs, since we also observed this property in single-walled carbon nanotubes (SWCNTs), when in the role of catalyst for their synthesis nickel nanoparticles were used. EPR/FMR signals in SWCNT bundles were investigated within the temperature range Т =10–300 K both for initial samples and for those diluted in the nonmagnetic matrix [32]. 350

300 B res , mT

80

250

200

150 0

100

200

300

T, K

Figure 3.8 Temperature dependence of the resonant magnetic field Bres of the sample SWCNT/Ni nanoparticles dispersed in paraffin.

The magnetic response of samples can be of the ferromagnetic nature or of the superparamagnetic one in dependence on the temperature and distribution of Ni nanoparticles in the sample. The behavior of the spectra shows that nondispersed materials keep the ferromagnetic nature of nanoparticles ensemble even at room temperature. It is explained by dipole–dipole interactions and macroscopic demagnetizing fields in the powder-like samples. For the samples dispersed in paraffin, one can observe the superparamagnetic signal only at room temperature. With decreasing temperature, there is a transition from the case of freely rotating magnetic moments (superparamagnetic state) to moments aligned along the easy magnetization axis (ferromagnetic state). In this case, the value of the resonant magnetic field can be determined by the way described in Refs. [32, 33]: Hres = wres/g –HA–HD–Hi,

(3.1)

Results

Here wres is the resonance frequency, g is the electron gyromagnetic ratio, HA and HD represent a magnetocrystalline anisotropy field and the demagnetizing one, respectively, and Hi is the intensity of the mean dipolar magnetic field acting on a particle due to all others particles (Fig. 3.8). Temperature dependence of the linewidth DBpp for the sample SWCNTs/Ni diluted in paraffin is shown in Fig. 3.9. The solid line in Fig. 3.9 represents the predicted anisotropy contribution to the linewidth based on Eq. (3.2) [33]:

∆Bpp , mT

50

DHpp ª 1.15DHo + C·(HAeff)2/DHo

(3.2)

experiment theory

40

30

20 0

100

200

300

T, K

Figure 3.9 Temperature dependence of the EPR linewidth DBpp of the same sample as in Fig. 3.8. Solid line — theory according to Eq. (3.2).

In Eq. (3.2), the first term comes from the intrinsic linewidth, and the second one corresponds to the random easy-axis contribution; C is approximately 3. Assuming DH0 as constant in the high-T limit, the observed DBpp is determined by the temperature dependence of HAeff. The solid curve in Fig. 3.9 is calculated by fitting Eq. (3.2) with the parameters DH0 = 12.6 mT and C = 2.9. Generally, the results obtained for SWCNT/Ni are indicative of the availability to use the system “CNT/Ni nanoparticles” for further fundamental investigations and creation of nanomaterials with magnetic properties capable of satisfying specific functional requirements to nanoscale electronics, for example, spintronics. It is worth to note that poor accordance between the theory and

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experimental data at low temperatures in Fig. 3.9 is related, as it was ascertained, with uncontrolled contribution of ferric oxide particles. It was checked up in special experiments by studying the magnetic response of the composite C-2 APP/Fe3O4 nanoparticles. Shown in Fig. 3.10 is the temperature dependence of the magnetic resonance linewidth in the samples C-2 APP and the natural corrosion layer (rust) on the iron surface [34]. The great similarity of these dependencies is noticeable. 50

40 ∆ B pp , mT

82

1

30

2

20 100

Т, К

200

300

Figure 3.10 Temperature dependence of the width of the magnetic resonance lines in samples C-2 APP (curve 1) and the natural corrosion layer (rust) on the iron surface (curve 2). Dotted lines are a guide for the eyes.

As seen from Fig. 3.10, within the range of temperatures around 120 K, one can observe the clear minimum of the linewidth that can be unequivocally related to the Verwey transition that takes place in magnetite at this temperature [35]. In this case, we deal with the transition from cubic to monoclinic symmetry, which is accompanied by the transition from the conducting state to the dielectric one [36]. Near the transition temperature TV, the charge-orbital ordering of the system disappears [37], and all the anisotropic contributions, including those to the EPR linewidth, are minimized. And it is observed in our experiments as considerable lowering of the linewidth near TV. Magnetic resonance properties of fullerene-derived fillers in FCbased nanocomposites were studied in Refs. [38–41]. EPR signals

Results

EPR signal, arb.units

caused by the presence of filling compound were registered. In Fig. 3.11, the EPR spectra of fullerene C60, FS, and FB are presented. In the limits of the experiment, the entire spectrum is characterized by g-factor g = 2.0024±2×10–4. The values of g-factors inherent to the EPR lines observed in composites coincide entirely with those for the initial fillers, g = 2.0024–2.0027. 200 1 (gain х5) 0 2 -200

3 ν = 9412.5 MHz 333.0

334.5

336.0

337.5

339.0

Magnetic induction, mT

Figure 3.11 EPR spectra of composites C-2 APP+3% fillers, notably fullerene C60 (curve1), FB (curve 2), and FS (curve 3). An additional broader line in spectrum 1 belongs to C-2 APP (see also Fig. 3.6).

The EPR line shape is Lorentzian for the C60 spectrum, and for FS and FB, it is the sum of two Lorentzian lines. The contribution of individual components to the total intensity of the EPR spectrum depends on the type of samples and their interaction with the surrounding oxygen. The properties of fillers and composites were also studied when pumping samples at temperatures T = 293–573 K. Figure 3.12 shows the EPR spectra of FS under pumping out. It is seen that when pumping out at T = 300 K, the intensity of the spectrum increases significantly with the increase in vacuum. Pumping out at higher temperatures results in a dramatic increase in the signal intensity of more than 30 times relative to the initial signal, mainly due to the formation of broad wings of the EPR spectrum. A similar effect, although not as strong, is observed in composites C-2 APP/FS, FB when pumping samples at elevated temperatures.

83

Fullerene soot

2000

*

30 20 I/I 0

EPR signal, arb. units

Advanced Polymer Composites for Use on Earth and in Space

10 0

0.01

0

-2000

0.1 P, atm.

1

* Pump. 0.5 h at 160 C ν = 9350 MHz 332

333

334

335

Magnetic induction, mT

Figure 3.12 EPR spectra of fullerene soot at various oxygen content. The magnitude of the pressure of residual atmospheres (from the small to the larger amplitudes) at room temperatures of pumping out: 1; 0.8; 0.61; 0.42; 0.21; 0.1; 0.043; 0.02; 0.001 atm.; dash lines — fitting by 3 Lorentzian. Insert: the dependence of the total intensity of the EPR spectrum on the oxygen pressure.

Figure 3.13 shows the decrease in signal intensity for the sample C-2 APP + 3% FS (d~1.5×3×3 mm3) after pumping out at T = 160°C and subsequently bringing the sample in contact with air. C-2 APP+3% FS

2nd pump.

2

1st pump.

3 EPR signal, I/I ini.

84

1

initial 0

10

20 t, hours

30

40

Figure 3.13 Decline in the EPR signal of bulk composite sample C-2 APP + 3% FS (~1.5×3×3 mm3) after evacuation during 1 h at T = 160°C. The contact of the sample was set with the environment after evacuation. Dash and dotted lines are a guide for the eyes.

Results

So FS and FB actively interact with gas molecules from the environment. This leads to an almost complete (about 95%) suppression of EPR signals from carbon defects, which can be restored after pumping out the samples in the temperature range of 20 to 300°C. Under these conditions, a complex EPR spectrum consisting of three components, each of which originated from the specific elements of the sample structure, is clearly manifested (Fig. 3.14).

EPR signal, a.u.

600

Fullerene black

L1

300

L2

0 L3

-300 -600

ν = 9375 MHz

3330

3340

3350 -1

Magnetic induction, 10 mT

Figure 3.14 The separation of the EPR spectrum of fullerene black into components. The sample FB after pumping out during 0.5 h at 300°C. L1, L2, and L3 represent components of the spectrum with DB = 0.09, 0.3, and 2.4 mT, respectively. The solid white line is the envelope of spectrum. L3 component was calculated taking into account subsystem of 2D electrons.

The most powerful contribution L3 comes from the 2D electron spin subsystem at the surface of the carbon flakes. The L1 and L2 components belong to defects of fullerene (or fullerene-like) molecules and edge carbon atoms at the carbon flakes. Theoretical calculations of the L3 signal line shape were carried out, and a good agreement with experiment has been obtained. The decay rate of the L1, L2, and L3 components in the total EPR signal (the restoration of equilibrium), after bringing the sample in contact with the ambient air, was obtained from comparison with the experiment. As mentioned earlier, these phenomena occur also in the bulk of composite samples C-2 APP/FS, FB. However, they are observed not so clearly, which is possibly due to the apparent low gas permeability of composites at RT.

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As for the EPR signal in C60 fullerene (Fig. 3.11, curve 1), it has a different nature. It is known [42] that this signal belongs to C120-O defects, whose concentration sharply increases upon annealing the samples at temperatures of T = 100–200°C, which is the case in our experiments. Paramagnetic molecular oxygen of the air does not practically affect the EPR linewidth of these defects in C60. A somewhat different situation takes place in nanocomposites Si/diamond (Fig. 3.15) [43]. 3000

EPR signal, arb. units

86

ν = 9412,8 MHz 2000

1

1000

0

2

333

3

336

339

Magnetic induction, mT

Figure 3.15 EPR spectra for nanocomposite Si/diamond film at T = 300 K. Full lines: (1) derivative dc¢¢/dB curve; (2) susceptibility c¢¢(B) of integrated curve. The dashed curve (3) is a fit with three Lorentzian curves with different linewidths.

In Ref. [43], the visible-light-emitting nanocomposite Si/diamond polycrystalline layers have been investigated. The important role of paramagnetic defects in the light-emitting properties has been established. The ESR results suggest that the active centers originate from the dangling bonds with g = 2.0025 induced in sp3-coordinated carbon atoms by insertion of the Si nanoparticles. Depending on the porosity of the film and the uniformity of the distribution of defects, the EPR line can be described as a single Lorentz curve [29], or their sum, as can be seen in Fig. 3.15. In APP-based composites with UDD nanofillers, the maximal Ns~1020 cm–3 caused by carbon dangling bonds is observed (Fig. 3.16). It is due to the small sizes of crystallites (d~4 nm [44]) and large “diamond” surface in the sample.

Results

The observed linewidth DBpp~1 mT is formed by dipole and exchange interactions in paramagnetic system, i.e., depends on Ns. The integral intensity of EPR signals in the composites is proportional to the mass of the entered filler (Fig. 3.16) and, therefore, allows quantitative estimation of its content in a composite. EPR signal, arb. units

1000

3

Ref. sample 3+

Cr : MgO

2 0 1

-1000

3300

3350

3400

Magnetic induction, mT

Figure 3.16 EPR spectra of APP/ultra-dispersed diamond (UDD) composite. UDD content is 0.5% (1), 1.5% (2), and 3 wt.% (3). T = 300 K.

The EPR linewidth DBpp slightly increases from 0.82 mT in the UDD to 0.93 mT in the composite due to interaction between matrix and filler. The intensity of the spectra in Fig. 3.16 is a proportional concentration of the introduced filler, which serves as a good test of the condition and properties of the filler in the composite. One of the most widely used composites is carbon-filled plastic, in which CFs are used as fillers [45]. The specific feature of its structure is the availability of the so-called “turbostrat structure,” when adjacent graphite layers in the CF are turned by some angle around the normal to this layer. This angle depends inclusively on the type of initial raw materials and processing temperature [46]. Crystallites of turbostratic graphite are usually packed in such a manner that they can form the layers with the length of several micrometers and the thickness of the order of a few nanometers. Thus, although the filaments of CFs have the diameter close to several micrometers, it could be expected that their electronic as well as mechanical properties should be observable even at the nanometer scale.

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Figure 3.17 shows the EPR spectra of CFs URAL-24 (Russia) and Toray (Japan). The spectra have an asymmetric shape, so-called Dyson shape, characteristic of conductive samples [47–49]. This shows that the nature of paramagnetic signals in these samples is due to free electrons, which does not contradict the known semiconductor properties of CF. 1000 EPR signal, arb. units

88

1

2

0

330

335

340

Magnetic induction, mT

Figure 3.17 EPR spectra of CF URAL-24 (curve 1) and Toray (curve 2). Both spectra exhibit the Dyson shape, which indicates significant conductivity of CF.

Table 3.1 shows, for comparison, the EPR linewidths of CFs of four different types and their mechanical properties known in the literature (see, for example, Ref. [50]).

Table 3.1

Comparison of the mechanical and EPR properties of various types of CF

Fiber Type

Evlon

Concor

URAL-24

Toray

DBpp, mT (filaments)

3.7

3

1.8

0.18

DBpp, mT (dispersed)

Module elasticity, GPa

The tensile strength at compression, MPa

3.7

100–140 2900

2.9

150–220 —

1.7

90

1500

0.17

230

4900

As can be seen from Table 3.1, there is a perceptible correlation between the mechanical and paramagnetic properties of CFs. Namely,

Results

the most durable fibers have the smallest EPR linewidth. The value of the g-factor for all measured fibers was g = 2.0028±2×10–4. For its precise determination, a special procedure was used for conductive samples [47–49]. The samples of CFs ground and dispersed in paraffin showed symmetrical EPR lines with the same g-factors and linewidths (Table 3.1). This means that for dispersed fibers, their minimum sizes are smaller than the thickness of the skin layer. Note that CF samples have high microwave conductivity, which greatly degrades the quality factor of the resonator of the EPR spectrometer and leads to the need for using a small amount of sample for measurements. This circumstance is especially pronounced in experiments with powders of APP/CF composites. The quality factor of a resonator with a dense powder in a quartz tube is so low that it does not allow measurements, and this possibility appears only when the sample is specially fluffed, while its visible volume increases by about two times. This fact is illustrated in Fig. 3.18, where the spectra of one sample are given in fluffy and slightly compressed states with a small effort. 1000

EPR signal, arb. units

C2 APP+40% CF 1

0

-1000

2

0

150

300

450

600

Magnetic induction, mT

Figure 3.18 EPR signals in the powder of the composite C-2 APP/40% CF. (1) as is initial powder; (2) slightly compressed sample. EPR measurements are not possible in highly compressed powder due to a drop in the Q-factor of the resonator owing to strong nonresonant microwave absorption.

It should be noted that the only part of the spectrum in Fig. 3.18, namely, the narrow line at the center, is caused by CFs. The rest part

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Advanced Polymer Composites for Use on Earth and in Space

of the spectrum—broad intense lines—belongs to ferromagnetic and superparamagnetic signals related with the availability of technologically conditioned impurities of ferric oxides. These signals are especially strong in composites with CF, since in view of the high strength inherent to CFs, their electromagnetic mixing in the mixture results in additional creation of ferric oxide nanoparticles. In composites without CF, this effect is pronounced several times weaker. The value of the effect of nonresonant microwave absorption in composites with CFs is not the same in all the samples but depends on CF concentration, in fact, on the degree of their dispersion in this composite. After lowering the concentration of CF, slight compression of the composite powder has no further effect on the value of nonresonant microwave absorption (as seen in Fig. 3.19). Besides, this figure shows that the central part of the spectrum consists of not one but two lines with the same g-factor g = 2.0037, while their linewidths are different: DB (L1) = 9.2 mT, DB (L2) = 1 mT. Line L1 differs from EPR spectrum of micrographite (see Section 3.3.2.1) due to the structural features of CFs [50]. 1000

as is compressed

C-2 APP +30% CF L1

EPR signal, arb. units

90

3+

MgO: Cr

0

L2

-1000 320

340

360

Magnetic induction, mT

Figure 3.19 Central part of the spectrum of the composite C2 APP + 30% CF. The effect of small compression on the value of nonresonant microwave absorption is absent, in contrast to Fig. 3.18.

CFs reinforced with nickel or copper are very promising for tribological applications [51]. Figure 3.20 shows the EPR spectra in samples of composites C-2 APP + 30% CF “URAL-24,” metalized with Ni (curve 1) or Cu (curve 2 in the inset).

EPR signal, arb. units

C-2 APP + CF+ Ni 1000

EPR signal, a.u.

Results

C-2 APP +CF+Cu

200

2

0

-200 315 330 345 Magnetic induction, mT

0 1 -1000

0

200

400

600

Magnetic induction, mT

Figure 3.20 EPR spectra in samples of composites C-2 APP + 30% CF “URAL24,” metallized with Ni (curve 1) or Cu (curve 2 in the inset).

In these composites, new magnetic resonance signals appear due to the presence of metallic nickel or copper. In the case of Ni (Fig. 3.20, curve 1), the signal is characterized by g = 2.0015, DBpp= 70 mT, and its behavior as a function of temperature indicates the superparamagnetic nature of the signal. This is easy to understand, given the small thickness of the nickel deposited on CFs. If copper is deposited instead of nickel on the CFs, a new EPR signal with g = 2.000 and DBpp= 4.1 mT is detected in the composite, due to the manifestation of the paramagnetic properties of copper (insert in Fig. 3.20, curve 2).

3.3.1.2 Tribotechnical characteristics

The influence of CNT “Taunit” on tribological properties of C-2 APP was studied by the authors [52]. The results of research on the tribotechnical properties of PCM filled with CNTs in the conditions of friction without lubrication according to the “disk–shoe” scheme (load (Р) 1 MPa, sliding speed (υ) 1.3 m/s, and distance covered (L) 1000 m) are shown in Fig. 3.21. It can be seen that introduction of 3–5 wt.% of the filler leads to a decrease in the friction coefficient and mass wear of initial C-2 APP by 1.5–1.85 and 1.2–3 times, respectively. The highest efficiency can be reached when the content of CNT is 5 wt.%.

91

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Dm, mg/km

f coefficient of friction weight wear

1.0

100

0.8

80

0.6

60

0.4

40

0.2

20

0

0

3

5 10 the content of the filler, C, %

0

Figure 3.21  Influence of carbon nanotubes on friction coefficient and mass  wear of composites based on APP.

As for the influence of UDD on the tribological properties of the APP, it was determined [53] that under the same operating conditions, the proposed CM surpasses the base polymer in terms of the relative abrasion resistance Kn by 2.8 times at the content of UDD is 0.5 wt% (Fig. 3.22). KH

1.0 0.8 0.6 0.4 0.2 0

0 0.1 0.2 0.5 1.0 1.1 the content of the filler, C, mas.%

Figure 3.22  Influence of UDD on related abrasive wears resistance of APP.

CF-reinforced plastic with cuprum-containing CFs “Ural T-24-Cu” is a bright representative of composites of tribotechnical purpose.

Results

As it is shown in Ref. [21], the introduction of cuprum-containing CF to polymer significantly increases the wear resistance of C-2 APP up to 40 times (Fig. 3.23) with simultaneous reduction in friction coefficient by 2.2–3.4 times (Fig. 3.24). Dm, g 0.10 1 0.06

0.02 2

2 4

6

8

P, MPa

Figure 3.23 Dependence of mass loss Dm  of  С-2  APP  (curve  1)  and  CFreinforced APP with Cu on CF (curve 2) on the loads at sliding speed of 1 m/s.

f 0.4

1

0.3

2

0.2 0.1 2

4

6

8

P, MPa

Figure 3.24 Dependence of friction coefficient f of С-2 APP (curve 1) and CFreinforced APP with Cu on CF (curve 2) on the loads at sliding speed of 1 m/s.

It is shown in Ref. [54] that such significant improvement in tribological properties can be reached due to the chemical interaction between Cu and APP. Thus, the developed CF-reinforced plastic based on phenylone reinforced with 17 wt.% of cuprum Ural Т-24-Сu fiber is characterized by high indicators of tribological properties and can be used in the

93

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Advanced Polymer Composites for Use on Earth and in Space

conditions of friction without lubrication at the criterion value of Рυ £ 1.0 MPa·m/s; at the same time, exploitation of non-modified C-2 APP is possible only at Рυ £ 0.5 MPa·m/s. CF-reinforced plastics reinforced by FS, FB, and fullerene С60 [24] proved themselves as antifriction CMs. Since friction coefficient is one of the determining indicators that are used while making technical calculations and making decisions about choosing materials, these composites have become widely used. It is shown in Ref. [24] that the use of fullerene С60 decreases the APP friction coefficient by 1.6–2.0 times (Fig. 3.25), and if filled with FS and FB, it decreases by 1.1–2.2 and 1.2–2.1 times, respectively (Figs. 3.26 and 3.27). At the same time, concentration dependencies of this indicator go through minimum at 1.5 wt.% of the content of filler. The correlation of the friction coefficient with the strength characteristic of composites is also found [24]. I, mg/sm2 23

f 0.4 1

18

2

0.3

13 8

0.2 0.1

3 0

1 2 the content of fullerene C60, mas.%

3

Figure 3.25 Dependence of friction coefficient (f, 1) and wear (I, 2) on the content of fullerene C60 at the sliding speed of 1.3 m/s and load of 1.0 MPa.

The same character of concentration dependence is marked for the wear of composites, too. Minimal values of the indicator can be observed at 1.5 wt.% of filling. At the same time, wear decreases by 2.8–4.8 times for the composite that contains С60 fullerene. The use of FS and FB allows creating more wear-resistant materials: wear decreases by 4.4–10.1 and 3.0–8.1 times, respectively.

Results

I, mg/sm2 23

f 0.4

18 1

0.3

2

13 8

0.2 0.1

3 0

1

2

3

the content of fullerene black, mas.%

Figure 3.26 Dependence of friction coefficient (f, 1) and wear (I, 2) on the content of fullerene black at the sliding speed of 1.3 m/s and load of 1.0 MPa.

I, mg/sm2

f

21

0.4

1

2

16

0.3

11

0.2 0.1

6 0

1

2

1 3

the content of fullerene soot, mas.%

Figure 3.27 Dependence of friction coefficient (f, 1) and wear (I, 2) on the content of fullerene soot at the sliding speed of 1.3 m/s and load of 1.0 MPa.

Typically, tribotechnical characteristics change symbiotically regardless of concentration. The composite that contains 1.5 wt.% of FB is characterized by the smallest value of mass loss (3.0 mg/ cm2) and the lowest friction coefficient (0.19). It proves the stability of its properties, and low cost of the filler promotes the fact that it is appropriate to make parts for agricultural machines that work in the conditions of limited lubrication or without it from this material [24, 55]. At the same time, it is shown in Ref. [24] that C-2 APP wears according to adhesive mechanism [55]. It is proven by the setting areas on the friction surface of polymer sample.

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3.3.2 Composites with Micro-dispersed Fillers 3.3.2.1 Electronic properties In Section 3.3.1.1, we considered, in particular, the paramagnetic properties of CFs whose surface is reinforced with a thin layer of nickel or copper. Of interest are also composites in which dispersed microparticles of metals, namely, Ni, Al, Ti, Cu, bronze, are used as fillers. Their magnetic properties and dispersity of distribution in the polymer matrix can also be tested by the EPR method. It can be illustrated using the samples of composites with bronze and nickel microparticles used as fillers [56]. Figure 3.28 shows the EPR spectrum of the composite C-1 APP/bronze. 1000

EPR signal, arb. units

96

0

-1000 0

200

400

600

Magnetic induction, mT

Figure 3.28 EPR spectrum of the composite C-1 APP + 15 wt.% bronze.

This EPR spectrum is actually a high-field part of the magnetic resonance spectrum of the C-1 APP/bronze composite, the width of which can be estimated as DBpp ª 160 mT. Such a wide and intense line can be explained solely by the presence of ferromagnetic impurities, the nature of which in this case cannot be clearly identified. The magnetic properties of the composite with nickel can be described more confidently, since it can be expected that ferromagnetic nickel will make the predominant contribution to the magnetic properties. C-1 APP/Ni magnetic resonance spectra are shown in Fig. 3.29.

Results

B

EPR signal, arb. units

1500

ϑ

750

Axis of easy magnetization

2 0

1

-750 0

150

300

450

600

Magnetic induction, mT

Figure 3.29 EPR spectra of oriented Ni microparticles. (1) J = 0°; (2) J = 90°, where J is the angle between the magnetic field and the axis of easy magnetization of nickel microparticles. In each set 1 and 2, several curves are presented, which differ in the initial conditions for recording the spectrum [56].

To verify that nickel microparticles are responsible for the observed spectrum, measurements were made with aligned particles. For this, Ni powder was poured into a quartz ampoule with molten paraffin, after which the ampoule was placed in a magnetic field of B = 600 mT. In this field, nickel particles line up along the axis of easy magnetization and then “freeze” in this state with the paraffin gradually solidifying. After that, the magnetic resonance spectra were measured. Figure 3.29 shows that the spectra differ significantly for the orientations J = 0° and J = 90° (the orientation of the Ni particles is parallel and perpendicular to the axis of easy magnetization, respectively). For J = 0°, we have Bres = 93 mT, DBpp = 227 mT. For J = 90°, we have Bres = 233 mT, DBpp = 363 mT. The reason for the difference is related to the different contributions of magnetic anisotropy energy and demagnetizing factors to the total interaction energy in the orientations J = 0° and J = 90°. The presence of hysteresis shows that the microparticles of nickel are in a ferromagnetic but not superparamagnetic state, which is natural to expect for micron-sized magnetic particles. Currently, it seems topical to develop hybrid composites simultaneously containing several matrixes or several types of fillers. In these composites, one can realize the so-called “synergetic effect” when deficiencies of one component will be compensated by the advantages of another component, while their positive properties

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will be summed. In this relation, the interest of researchers is attracted by the composites with fillers of the type “graphite + CFs.” Let us consider their electronic properties in detail. Among the variety of allotropic forms of carbon, graphite is a unique layered material with strongly anisotropic properties. It possesses good electricity- and heat-conducting properties within the plane of each layer due to the metallic type of bonding, but these properties are considerably worse along the direction normal to these layers, as a consequence of weak van der Waals bonds between the layers [57]. The unique property of graphite is its record high diamagnetic susceptibility and anisotropy of the latter, which is related with the features of graphite band structure [58]. The paramagnetic resonance of conduction electrons (CE) in graphite was first studied in Refs. [59, 60]. It was ascertained that the g-factor of CE is strongly anisotropic: g = 2.05, g^ = 2.0026. The main contribution to the CE g-factor anisotropy is by orbital susceptibility. In this situation, the orbital contribution to g^ from valence electrons is very low, while the contribution to g is considerable, which leads to this strong anisotropy in observed g-factor of CE. We studied powder-like samples of graphite with the apparent density of 1800 kg/m3 and the size of particles close to 150 mm. Figure 3.30 shows the EPR spectrum of the tested composite graphite/paraffin. 1000

EPR signal, arb. units

98

g=2.0026

0 g=2.05 -1000 ν = 9374 MHz 322.5

330.0

337.5

Magnetic induction, mT

Figure 3.30 EPR spectrum of graphite/paraffin composition.

The spectrum in Fig. 3.30 is a “classical” spectrum of powdered graphite with two peaks at magnetic fields corresponding to g= 2.05

Results

and g^= 2.0026 [59, 60]. Unexpectedly, the spectrum of powder freely poured into a quartz tube showed one peak only, corresponding to g = 2.0026 (Fig. 3.31). EPR signal, arb. units

750

g =2.0026 0

-750

325

330

335

340

Magnetic induction, mT

Figure 3.31 Spectrum of graphite powder freely poured into a quartz tube.

An analysis of the entire complex of data showed that the main factor in the orientation of graphite microparticles in a magnetic field is the strong diamagnetism of graphite. The behavior of thermally expanded graphite (TEG) differs significantly from ordinary graphite. It is known that the morphology of TEG at the macroscale is realized in a specific “worm-like” structure [61, 62]. Figure 3.32 shows, for example, the morphology of the TEG samples used in our experiments.

Figure 3.32  View of individual TEG flakes (gain ×20).

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Since the distance between the planes in the TEG increases by tens or even hundreds of times, the material is extremely light, and the absence of interaction between the planes leads to the fact that the anisotropy of the EPR spectrum disappears and the spectrum (Fig. 3.33) becomes similar to that observed in graphene. 100

EPR signal, arb. units

100

0

-100

-200

g =2.003

324

330

336

Magnetic induction, mT

Figure 3.33 EPR signal of a “compressed” TEG powder sample. n = 9374 MHz, g = 2.003, DBpp = 0.8 mT.

It is noteworthy that the nonresonant microwave absorption of freely filled TEG powder is weaker, as compared with the powder slightly or strongly compressed, by analogy of that taking place in CFs and composites based on them (see Fig. 3.18). It shows that by changing the concentration of CFs or TEG in the composites, one can control not only their mechanical properties but also the efficiency of screening the microwaves with these materials. In recent times, a great interest has been shown in the so-called hybrid CMs, in which one can purposefully realize the synergetic effect allowing enhancement of composite useful properties and weakening their undesired ones. Figure 3.34 shows the spectrum of composite C-1 APP + 40% CFs “URAL-24” + 15% graphite. The most intense part of the spectrum in Fig. 3.34 belongs to ferromagnetic and superparamagnetic inclusions of technological origin, and the central part of the spectrum is caused by contributions both of graphite and CFs. The insert in Fig. 3.34 shows that the left

Results

EPR signal, arb. units

part of the spectrum has a “blurred” character, which indicates the spread of orientations inherent to graphite particles and/or CFs. The spectrum in Fig. 3.34 does not enable to exactly separate the contribution of each component due to the strong overlap of the spectra from the graphite and CFs “URAL-24,” because the latter have the large width of EPR line DBpp= 1.8 mT. The situation can become clearer if one uses in this composite Toray fibers characterized by the very narrow EPR line with DBpp = 0.18 mT (see Table 3.1 and Fig. 3.35).

0

-1500 ν = 9375 MHz 0

200

3200

400

3300 3400 B

600

Magnetic induction, mT

Figure 3.34 EPR spectrum of composite C-1 APP + 40% CFs (URAL-24) + 15% graphite. Insert: part of the spectrum due to the total contribution of graphite and CFs.

It is interesting to note that under a low content of graphite in the composite (10–30%), its EPR spectrum is close to that observed for the free filled powder (Fig. 3.31). With the growth of graphite content up to 60%, its spectrum changes the shape toward the “classical” powder spectrum with two peaks (see Figs. 3.30 and 3.35, curve 1). The same powder dispersed and “frozen” in paraffin, when the directions of particles are distributed chaotically, demonstrates the EPR spectrum (Fig. 3.35, curve 2) fully corresponding to Fig. 3.30. The EPR line of dispersed CFs Torrey (Fig. 3.35, curve 3) loses the Dyson shape and becomes symmetrical, as a result of which the depth of skin layer at the microwave frequency exceeds the thickness of single fibers. Besides, the EPR line of free carriers

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Advanced Polymer Composites for Use on Earth and in Space

becomes isotropic, and its g-factor value (g = 2.0027) coincides with that of graphite particles oriented along the normal to the external magnetic field [59, 60]. 1000 EPR signal, arb. units

102

1

2

3

MgO: Cr

3+

0

-1000 ν = 9374 MHz

-2000

325

330

335

340

Magnetic induction, mT

Figure 3.35 Central part of the EPR spectrum of the composite C-1APP + 60% graphite. (1) powder freely poured into a quartz tube; (2) same powder dispersed and “frozen” in paraffin; (3) EPR spectrum of CFs “Toray,” recorded with a modulation amplitude reduced by 100 times.

I

f 0.4 0.2 0

5

15

C,%

2

3

5

10

15

20 P, MPa

II f 0.4 0.2 0

5

15

C,%

2

3

5

10

15

20 P, MPa

Figure 3.36  Influence  of  the  content  of  GL  (І)  and  S  (ІІ)  TSG,  and  load  on  friction coefficient (f) of GP based on C-2 APP.

Results

3.3.2.2 Tribotechnical characteristics It is shown in Ref. [16] that in order to increase the tribotechnical characteristics of graphitoplastics based on heat-resistant APP, it is appropriate to use thermally split GL-2 and S (silver) graphites (TSG) as filler [33, 34]. The analysis of the results of the tribological properties of GP proves that if load increases up to 10 MPa, the friction coefficient falls from 0.35 to 0.04 and from 0.4 to 0.07 (see Fig. 3.36), respectively. After that if Р = 25 MPa, the friction coefficient of the studied materials is stable in the limits of 0.04–0.06 [16, 63]. Dh, mkm 350 275 200 125 50 4 3 2 1 0

I

5

15

2

C,%

5

3

10

15

Dh, mkm 350 275 200 125 50 9 8 7 6 5 4 3 2 1

0

20 P, MPa

II

5

15

C,%

2

3

5

15

20

P, MPa

10 working Pu catastrophic wear

Figure 3.37  Influence of the content of GL (І) and S (ІІ) TSG, and load (Δh) on the friction coefficient (f) of GP based on C-2 APP.

Regarding GP wear (Fig. 3.37), the minimal load wear of GP containing 15 wt.% of TSG is twice higher in comparison with GP

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with 25 wt.% of TSG. At the same time, this difference is only 5–10% in the range of 20–25 MPa. It is explained by the fact that in the first case, the speed of appearing transfer film is higher for the sample that contains a huge amount of graphite. When the load increases, the amount of graphite on the counterbody balances out due to the high intensity of wear. That leads to equivalent indicators. The comparison of the tribotechnical characteristics of composites that contain 5, 15, and 25 wt.% of the filler gives an opportunity to give preference to materials that contain 15 wt.% of S-type TSG. Exactly for this material, there is the best ratio of the properties at high wear resistance [63, 64]. Interesting results can be obtained if different metal particles are introduced to the volume of heat-resistant APP. It is shown in Ref. [64] that the tribotechnical characteristics of metalopolymers (MP) are determined by the degree of filling [16], and the intensity of wear decreases with increased content of the filler and reaches its minimum when the content is 15 wt.% (Fig. 3.38). This is explained by the better complex of the physicomechanical properties of MP in comparison with unfilled APP. Ih, x10-8

3 1

2

2 3 4

1

5

0

10

C, %

Figure 3.38 Dependence of wear intensity MP on the content of the filler: (1) Cu; (2) bronze; (3) Ti; (4) Al; (5) Ni.

Table 3.2 shows that the efficiency of wear resistance improves in the following order: nickel, aluminum, titanium, bronze, and cuprum. The introduction of finely dispersed carbonyl nickel powder to APP improves the wear resistance of the polymer matrix by about 11 times and 2 times if copper is introduced [16].

Results

Table 3.2

Tribological properties of metalopolymers [37]

Properties Wear intensity,

·10–8

The coefficient of friction

APP

Al

Bronze

Cu

Ti

Ni

3.95

0.92

1.9

2.08

1.3

0.35

0.52

0.35

0.27

0.39

0.25

0.43

Since the wear resistance of materials depends on hardness, elastic properties, operating mode, external conditions, and construction features of friction unit [65], significant difference in the tribological properties of MP is connected, first of all, with difference in the strength of both fillers and CMs. It is shown in Ref. [66] that the antifriction properties of developed metalopolymers obey Ratner’s law that connects the frictional properties of the materials with other ones. As it is shown in Ref. [67], the appearance of metal fillers in the polymer matrix increases the polymer thermal conductivity that leads to increase in the wear resistance of composite due to the better heat dissipation from friction area. Table 3.3

Intensity of wear and the coefficient of friction of metal polymers when lubricating with oil

Properties

APP

Al

Bronze Cu

Ti

Ni

Wear intensity, ·10–8

0.8

0.16

0.03

0.22

0.48

0.73

Temperature in contact area, K

368

335

331

353

333

346

The coefficient of friction

0.1

0.055 0.038

0.078

0.050

0.060

Table 3.3 shows that the composition, which contains bronze as filler, is characterized by much lower wear intensity in comparison with other compositions that cannot be explained only by higher heat conductivity. It is known that the porosity of the APP/bronze composite increases at the polymer-filler interface, which leads to the formation of free volumes. These volumes are filled with oil, which provides easier sliding in a pair of friction. They also play the role of dampers that provide long wear resistance of the composite. Thus, the

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introduction of bronze significantly increases the wear resistance of APP at friction with lubrication (almost 27 times) (Fig. 3.39) [68, 69]. I ◊ 10-8 1.6

0.8

0

10 Cu

Al filler

Ti

bronze

6

Pa

M P,

Figure 3.39 Dependence of wear intensity (I) on the load, and filler nature. Friction path is 3 km.

Another promising way of developing KM tribotechnical purpose is the introduction of hybrid fillers in the polymer matrix. Thus, in Ref. [25], the effect of graphite, CFs, and their mixture content on the tribological properties of CFs based on phenylone is shown. Analyzing the results of researches (Figs. 3.40 and 3.41) on the influence of the percentage of fillers on tribological properties of CMs based on phenylone, we can say it is evidently that filling polymer matrix with 20–30 wt.% of CFs leads to the sharp decrease in friction coefficient and intensity of linear wear by 2.8–3 and 10.2– 24.7 times, respectively, in comparison with initial polymer (f = 0.54, Іh = 8.9×10–8). The only one possible explanation for it can be the fact that finely dispersed wear debris, which fill microcavities on the surface of the counter body, appear in the process of carbon plastic (CP) wear. In addition, friction is carried out on the wear debris, but not on the steel. While studying the friction surface of initial polymer and developed composites, it was detected that the deep furrows of ploughing appear on the surface of APP. This testifies to the adhesion mechanism of wear, the distinguishing feature of which is frictional transference of ribbons of binder on the surface of counterbody, which is conditioned by the presence of local connections between contacting surfaces.

Results

During the wear of CF-reinforced plastic, a smooth glassy surface appears. There are clearly visible chaotically distributed fibers and ribbons (furrows) of ploughing, which testifies to the pseudoelastic mechanism of detrition of CP. This provides the longest service life for movable joints [25].

f 0.3 0.2

0

0.1 0 0 Gr ap h

t,

ite

10 con

40 ten 20 t, w t. %

30

ten 20 on c , r ibe nf

.% wt

rbo

Ca

Figure 3.40 Dependence of the coefficient of friction on the content of fillers.

With further increase in the number of CFs to 40 wt.%, we observe an increase in the coefficient of friction and intensity of wear, which is conditioned, on one hand, by crumbling of solid fiber particulates [25], and, on the other hand, by fluffing of CP on the boundaries of “polymer binder – CF.” It is better to use graphite as filler in terms of improvement in antifriction properties and wear resistance. The comparison of tribotechnical characteristics of CP and GP, which contain 20 wt.% of filler, shows that clearly. So the wear resistance and coefficient of friction of graphitoplastics with such content of filler are 2 and 1.5 times better than the analogical indexes for CF-reinforced plastic. It can be explained by the fact that in the process of maintenance, graphite [69] forms a structure on the surface of friction similar to the structure of liquid crystals that carry out the role of dry grease and characterized by low movable supports and high loading ability. Both CP and graphitoplastics are characterized by the pseudoelastic mechanism of detritions: a smooth glassy surface appears [25].

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Ih×10-9

8 6 4

Gr

2

ap 0 hit 10 ec on 20 ten t, w t

40 %

30 n rbo

20 er

fib

t,

ten

n co

0 .% wt

Ca

Figure 3.41 Linear wear rate depending on filler content.

An improvement in the tribotechnical properties of the polymer matrix occurs while using a hybrid filler; the coefficient of friction and wear decrease by 2.85–4 and 22–32 times, respectively. The results can be explained by the fact that CF and graphite have high heat conductivity, which encourages dispersion of vibration energy that reduces the self-warming of material in the zone of friction due to the decline in internal friction force and shear stresses.

3.3.3 Examples of Application of Developed CMs

The use of polymer materials for manufacturing parts of agricultural machines solves several important tasks: improving the manufacturability of parts, introduction of non-waste production technology, release of production area and equipment, reduction in the mass of machines, increase in the resource of constriction work, etc. CMs are appropriate for manufacturing parts of agricultural machines where one is required to reduce the moment of mass inertia, increase in chemical resistance, ability of vibration absorption, and low friction coefficient in contact with agricultural materials [16]. The advantage of these materials in comparison with traditional ones is the ability to process them with or without cutting. The cost of manufacturing the same parts of developed CMs is lower by

Results

10–15% in comparison with metal alloys. When the products are formed from CMs, they are 90–95% used compared to 60–80% for metal ones. In addition, plastic part can be recycled after failure. The replacement of serial parts by composite ones allowed significant economic effects due to increase in the durability of friction units (due to the increase in wear resistance by 3–5 times), saving oils, and reduction in labor costs on the maintenance of machines and mechanisms. Until now, the most common are threshing drums include steel beaters (65G steel). Their disadvantage is the high injury to grain, which is unacceptable when harvesting seed plots of grain crops. To overcome this problem we have developed and manufactured beaters with V-shaped profiles from composite APP/metal containing carbon fibers, which provided the necessary elasticity, as well as higher strength and wear resistance of the product [16, 21]. Such beaters are widely used in Ukraine when harvesting from seed plots of grain crops. It allowed reducing grain injury significantly. Beaters based on developed compositions (Fig. 3.42) can be used during the whole harvesting campaign and not only on seed areas. Moreover, reduction in grain injury increases food properties, germination rate, and growth energy. It can have a huge economic impact on the national scale.

Figure 3.42 Beaters of beater drums made of CF-reinforced plastic.

Composites reinforced with metal-containing CFs are used in the metallurgical industry as parts of moving joints that work in extreme conditions (high dustiness and huge dynamic loads). This requires the qualities that provide reliability and durability of constructions. Parts passed industrial inspection in friction units of pilgrim pipe mills (pipe plants). Developed bearings were set on the roller tables of excretory chute of rolling mills (Fig. 3.43) in

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the most extreme conditions of insufficient lubrication and high temperatures up 473 K. Bearings from CFRP that were set in friction units of first drive rollers near the work stand of rolling mill were working during 7 months. This exceeds the lifetime of bronze details by three times on the average. Composite bushings that are set on the lamellar chain of transfers (Mariupol research and experimental plant) worked without remarks for 1050–1100 h.

Figure 3.43 Tractor chain.

Research and industrial tests of metal-polymer kingpin bushings in passenger electric transport were carried out. Experimental parts made of MP, which were used in usual production conditions after that, were set on ZiU-9, YuMZт-2 trolley buses. The parts that had the greatest amount of disabilities, difficulties in operation, maintenance and repair, bushings of the kingpin of front axle (Fig. 3.44) were chosen for replacement. The parts were greased with plastic oil before the test. They were not greased further. There was no failure of experimental parts during the tests. Exploitation was in accordance with the regulations. The mileage of trolley buses equipped with experimental parts was in the limits from 21,179 km to 23,298 km, which is 6–7 times higher than the maximum allowable mileage of bronze bushings. On the day when technical condition was checked, it was determined that experimental bushings have a slight wear: Backlashes in the kingpins were insignificant and in allowable limits (less than 0.3 mm). Due to

Results

the technical suitability of operation, experimental bushings were left for further tests.

1 2

3

Figure 3.44 Front axle of the trolley bus: (1) the upper pin bush, (2) the pin, (3) the lower pin bush.

Taking into account significant increase in the durability of metal-polymer kingpin bushings, their introduction can save of current asset of trolley bus depot minimum twice. The replacement of bronze parts on trolley buses, buses, and trucks just in the Dnipropetrovsk region saved $8000 per year, because it is necessary to have at least 2000 kg of parts from BRAJ94 bronze ($16000) to provide these automobiles with bronze parts (running, brake, and pneumatic systems) [70]. Taking into account the specifics of military techniques (load, speed, dustiness, high temperatures, long-term work, and aggressive environment) and the necessity of operating reliability on which human life depends, there are some decisions based on CMs [16]. Thus, the parts (see Fig. 3.45) made of hybrid composite were set to МB10-1 microblower, which is released by the “Iskra” Research and Production Enterprise in Zaporizhzhia. Microblower is destined for providing circulation in closed loop in the system of shell tightness control. The working environment (argon gas) through the suction port goes to suction cavity, then through the hole to working chamber, where it is caught by rotor and transferred to the blowing side. The more load should blow such block, the greater difference of pressures in adjacent compression chambers, and the greater centered force should be for preventing air flow. In turn,

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the more centered force, the greater friction force in the moment of start/stop, and the thinner oil film during the work. Since the oil film between the plates and stators is just a few microns, any dust or solid particles that are bigger are like abrasive that scratches stator and wears the plates. This leads to bypass of compressed air from one chamber to another, and the productivity drops markedly [16].

Figure 3.45  МB10-1 microblower and its component parts.

The proposed technical decision increased the operating reliability of МB10-1 microblower due to the increase in thermal and wearing resistance and reduction in friction coefficient. Industrial resource tests of experimental details worked without interruptions. This allowed recommendation of CMs based on APP to be introduced in manufacturing [70, 71]. Armored personnel carriers (APCs) are tracked vehicles that have armament, armor protection, and high maneuverability. APCs (Fig. 3.46) are meant to provide increased mobility, armament, and security to infantry operating on battlefields [16]. In such machines, human life directly depends on the reliability of all aggregates. One of them is the APC tower. Positioning accuracy and fail-free operation depend on ball-frame carriage, i.e., from the ball of radial-thrust ballbearing.

References

Figure 3.46 Armored personnel carrier and ball-bearings.

Ball-bearings (ball Ø 25.4+02) from developed CFRP based on phenylone were also sent to Zhitomyr armored plant for carrying out tests in the rotary device of APC tower and possible replacement of serial parts. Experimental parts of CFRP passed four cycles of bench factory tests successfully. For this, they were recommended for further introduction [71]. Taking into account the above-mentioned facts, the use of developed CMs in the friction units of modern machines provided significant economic benefits due to increase in the durability of tribological joints, savings in oils, and reduction in maintenance cost. These materials are prospective for usage both on earth and in space due to their wonderful properties.

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52. Burya, O. I., Gayun, N. S., Redchuk, A. S., and Tkachev, A. G. (2010). Development and study of the properties of composites based on phenylone C-2 filled with carbon nanotubes, Proceedings of 10th Anniversary International Industrial Conference Effectiveness of the Realization of Scientific, Resource and Industrial Potential in Modern Conditions, pp. 370–373 (in Russian).

53. Burya, O. I., Sherstyuk, A. I., Ivashchenko, V. M., and Borodin, V. G. (2010). Patent Ukraine 46895 (in Ukrainian). 54. Buryak, A. V., Rula, I. V., and Burya, O. I. (2016). IR-spectral studies of the structure of CFRPs, Proceedings of 11th All-Ukrainian Conference on Young Scientists and Students on Topical Chemistry, p. 84 (in Ukrainian). 55. Kargin, V. A. and Slonimsky, G. L. (1967). Brief Essays on the Physical Chemistry of Polymers, Chemistry Press, Russia (in Russian).

56. Burya, A. I., Yeriomina, Ye. A., Konchits, A. A., Krasnovid, S. V., and Tverdostup, N. I. (2016). The study of electrical and magnetic properties of metal polymers based on phenylone C-1, Composite Mater., 9., 2, pp. 68–76 (in Russian).

57. Chung, D. D. L. (2002). Review graphite, J. Mater. Sci., 37, pp. 1475– 1489. 58. Slonczewski, J. C. and Weiss, P. R. (1958). Band structure of graphite, Phys. Rev., 109, 2, pp. 272–279.

59. Wagoner, G. (1960). Spin resonance of charge carriers in graphite, Phys. Rev., 118, 3, pp. 647–653. 60. Singer, L. S. and Wagoner, G. (1962). Electron spin resonance in polycrystalline graphite, J. Chem. Phys., 37, pp. 1812–1817, doi: 10.1063/1.1733373.

References

61. Strativnov, E. V. (2015). Design of modern reactors for synthesis of thermally expanded graphite, Nanoscale Res. Lett., 10, 245, doi 10.1186/s11671-015-0919-y.

62. Yakovlev, A. V., Finaenov, A. I., Zabud’kov, S. L., and Yakovleva, E. V. (2006). Thermally expanded graphite: Synthesis, properties, and prospects for use. Russian J. Appl. Chem., 79, 11, pp. 1741–1751.

63. Burya, O. I., Skoropanov, A. V., Ilyushonok, V. V., and Smolyanoy, V. I. (1991). Wear resistance of graphitoplasts based on aromatic polyamide phenylone and thermally split graphites, Proceedings of the All-Union Scientific and Technical Conference, pp. 143–144 (in Russian).

64. Burya, O. I. (2002). Friction and wear of aromatic polyamide filled with thermally split graphite, J. Friction Wear, 3, pp. 296–299 (in Russian).

65. Burya, O. I. and Yeriomina, Ye. A. (2015). The effect of bronze on the wear resistance of aromatic polyamide phenylone, J. Chernihiv State Technological University, 2, pp. 27–32 (in Russian).

66. Yeriomina, Ye. (2017). Development, investigation of properties and application of metal polymers on the basis of heat-resistant aromatic phenyl polyamide, Diss. Degree Cand. Tech. Sci. 05.02.01. Kherson (in Ukrainian).

67. Frolov, K. V., Popov, S. A., Musatov, A. K., and Frolov, K. V. (1987). Theory of Mechanisms and Machines, Higher. Shk Press, Russia (in Russian).

68. Kozlov, P. M. (1966). The Use of Polymeric Materials in Structures Operating Under Load, Chemistry Press, Russia (in Russian).

69. Burya, O. I., Dudin, V. Yu., and Burmister, M. V. (2003). Friction and wear of graphitoplastics based on phenylone polyamide, J. Mechanics Tribology Transport Systems, pp. 163–167 (in Russian). 70. Naberezhnaya, O. (2017). Development and research of self-reinforced organoplastic properties based on heat-resistant aromatic polyamides, Diss. Degree Cand. Tech. Sci., 05.02.01. Lutsk (in Ukrainian). 71. Burya, O. I., Naberezhnaya, O. O., Morozov, O. F., and Komisar, O. A. Patent Ukraine 118300 (in Ukrainian).

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Chapter 4

Printable Materials for Additive Manufacturing in Harsh Earth and Space Environments

Amanda M. Schrand,a Manoj Kolel-Veetil,b Edwin Elston,c Clayton Neff,d Tosin Ajayi,e and Cheryl Xue aAir Force Research Laboratory, Fuzes Branch, Munitions Directorate, Eglin AFB, FL 32578, USA bNaval Research Laboratory, Chemistry Division, Washington, DC 20375, USA cAir Force Research Laboratory/University of Dayton, Fuzes Branch, Munitions Directorate, Eglin AFB, FL 32578, USA dAir Force Research Laboratory/National Research Council, Fuzes Branch, Munitions Directorate, Eglin AFB, FL 32578, USA eDepartment of Mechanical and Aerospace Engineering, North Carolina State University, USA [email protected]

4.1

Introduction

Nanotechnology, as a field, has contributed a host of technologies for diverse fields with some of the most outstanding achievements in the areas of materials development and biomedical devices. Early Nanotechnology in Space Edited by Maria Letizia Terranova and Emanuela Tamburri Copyright © 2022 Jenny Stanford Publishing Pte. Ltd. ISBN 978-981-4877-54-1 (Hardcover), 978-1-003-13191-5 (eBook) www.jennystanford.com

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successes in the area of epoxy nanocomposites [1] demonstrated improved mechanical, electrical, and thermal properties, to name a few. From a lifecycle perspective, carbon nanoparticles of various forms were extensively evaluated for safety prior to widespread adoption [2–7]. However, biocompatibility and environmental aspects of nanomaterials are still a very active area of research and many research communities and companies have accepted the risks while exploiting advances in manufacturing. Additive manufacturing (AM), is one type of technology that is being pursued to enable a range of benefits compared to traditional subtractive techniques. By and large, the greatest benefits of AM include reductions in time and cost to rapidly produce immediately functional parts [8]. BENEFITS

Time & Novelty Cost Complexity & Customization

CHALLENGES

Quality

Trust

Workforce Development

Figure 4.1 Opportunities and challenges for additive manufacturing. Image courtesy of DSIAC [8].

Further, the production of novel, extremely complex and customized parts are some of the other significant advantages to AM. On the flip side, innovative processes often come with challenges in the adoption or even trust of the AM parts by the end users who may rightly question the quality of the newly made parts compared to original equipment manufacturer (OEM) parts. Many benefits of AM apply to the harsh defense environments and include: small production/procurement volumes, ability to decrease mass through design methods (such as topology optimization), complex geometries, potential for repair or maintenance in the field, and accelerated, small-scale availability of tailored traditional materials/alloys. Another aspect of the AM design process is to optimize the shape and tailor properties such as thermal, mechanical, and electrical

Introduction

outputs for specific applications. Since the constraints of traditional subtractive manufacturing are removed, this can lead to drastically different products that are lightweight, mechanically stronger in strategic areas, and incorporate additional functionality like thermal dissipation as part of the design [9]. For example, the morphing of a metal part for reduced weight and strategic reinforcement is shown in Fig. 4.2a. An artistic rendering of a moon base is also shown as a futuristic example of how AM could be applied in space (Fig. 4.2b). (a)

(b)

Figure 4.2 Use of additive manufacturing in space design. (a) Metal part that was morphed via topology optimization to meet part requirements resulting in a very different product appearance. (b) Artistic rendering of Moon base for manufacturing [10].

With regards to nanomaterials and AM, there is an intersection in the area of polymer nanocomposites. These can be either thermoplastic or thermoset polymers, which have both been ‘printed’. The resulting parts may be slated for high-temperature applications [11, 12] including clay nanofillers [13]. Other applications of AM include printed electronics utilizing composite conductive inks to fabricate hybrid COTS/AM electronics [14–23]. The latter conductive ‘inks’ typically contain carbon and/ or silver-based nanoparticles (Fig. 4.3). Many other extrudable materials formulations for AM are characterized as ‘printable’ and can be custom formulated to contain a variety of additives, including nanoparticles, to impart strength, toughness, color, conductivity, etc. Indeed, several recent patents have been filed on the use of novel pre-ceramic polymer precursors with or without additional additives [24]. This technology includes the adaptation of open source printers that can extrude polymers that convert to ceramic upon high-temperature pyrolysis.

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CB028

CB028

CB028

(mm) 20 15 10

25 kV

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KA801

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0

Figure 4.3 “As printed” sample characterization for dimensions and particle size. (a) CB028 surface morphology, (b) CB028 cross section, (c) CB028 3D optical profilometry profile, (d) KA801 surface morphology, (e) KA801 cross section, and (f) KA801 3D optical profilometry profile [14].

In-space manufacturing, i.e. manufacturing ‘on-site’ in space, is necessary for the greater advancement of future space missions. This will obviate the need to resupply from Earth thereby reducing launch costs by providing on-demand and on-site tools for long duration self-sustainable missions. Further, in-space manufacturing requires alternative uses for materials at the end of their lifecycle. Therefore, all aspects of waste are considered before launch, and potential recycling options studied. This follows recent concept work by the Army to utilize in-the-field or in situ resources utilization in manufacturing. A combination of recycled materials and indigenous resources are proposed for on-demand manufacturing and repair of equipment/infrastructure to enable mission sustainability even with degraded or suboptimal materials properties [10, 25]. One such ‘on-site’ example on earth is shown in Fig. 4.4. The goal of the study was to determine whether indigenous sand from deserts or beaches, for example, could be used in sand printers along with the appropriate binder to manufacture parts in the field. The molds were made as CAD drawings and used to cast molten metal alloy (Aluminum A356) to make the part. The indigenous desert sand contained a larger size distribution of particles and compositions compared to beach or OEM sand. Of course, OEM sand was sieved, washed, etc. to maintain a greater purity and consistency. Therefore,

Introduction

additional steps that could improve the indigenous sand molds include purification and the use of chemical hardeners to increase curing profiles. (A)

(B)

Figure 4.4 Examples of 2 parts produced via sand-printed molds. (A) Cast aluminum A356 part manufactured with an AM mold manufactured from OEM sand and (B) same part made with AM printed mold made from Mojave Desert sand. Note the rougher surface compared to the part made with OEM sand [25].

Further research into AM ‘on-site’ will help to develop and promote green technologies. This is a direct result of a huge reduction in waste in AM compared to conventional manufacturing methods, along with a reduction of manufacturing steps, energy consumption and overall environmental footprint. In this regard, the immediate focus to enable AM in space should be on 3D printing plastics and metals, and the recyclability of such printed parts [26]. Typically, in spacecraft materials, composites account for around 17% of the total mass, and metallic materials around 63%, thus metallic materials show the biggest potential for reuse, especially aluminum alloys which can be optimized for AM. Recently, the printing of acrylonitrile butadiene styrene (ABS) was conducted on board the International Space Station (ISS), thereby demonstrating the feasibility of 3D printing in microgravity [26]. While detailed analysis of how ABS and other thermoplastics behave in microgravity with long term exposure is yet to be conducted, zerogravity 3D printing on board the ISS is a proof-of-concept for AM and future deep space missions. It provides the first step in in-space manufacturing for future materials and more complex structures involving metals. In-house recycling of feedstock material for 3D printing is needed to achieve this, which might include, for example, multi-material 3D printing of small satellites consisting of metallic and electronic parts. Another objective would be to use a planetary

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body or asteroid’s available resources for additive construction (vide supra). With regard to specific materials that are used for in-space AM, the requirements for materials in the space environment are substantial. A commonly used polymer coating to protect spacecraft surfaces from environmental effects in low earth orbit (LEO) is Kapton, a high-temperature polyimide. Kapton is a polyimide formed by the condensation of dianhydride and a diamine monomer [27]. It exemplifies good resistance to UV radiation and is stable between –269 to 400°C. Due to this thermal stability, Kapton is used as flexible film substrate for solar arrays, thermal insulation, and spacecraft inflatable structures. However, after long exposure (ca. six years) in LEO, Kapton has the potential to degrade significantly due to the harsh environment. The main causes of such material degradation are the high energy vacuum UV radiation of wavelengths from 100 to 200 nm, temperature extremes from –175 to 160°C, collisional impacts from space debris and micrometeoroids, ionizing radiation and atomic oxygen (ATOX) [28, 29]. In LEO, ATOX is said to be the prime cause of material degradation. ATOX is generated by photodissociation of molecular oxygen by intense UV light. The collisions with a material will cause oxidation and erosion, unless they are already in their highest oxidation state. The collisions with polymers like Kapton can break their C–C and C–H bonds and cause oxidation, which results in the loss of mass and ejection of gases, such as CO2 and CO [27]. Carbon fiber reinforced plastics tend to be used for rigid structural members such as a space reflector. For these designs the possible use of tensegrity structures, i.e. stable 3D structures consisting of members under tension that are contiguous and members under compression that are not, becomes favorable, where no mechanical joints are present. This creates a compression system that can be more accurately predicted than conventional hinged systems. Such tensegrity structures are ideal for space applications since the mass of materials can be reduced by placing some members in compression and the others in tension, in which the members in tension can have smaller cross-sectional areas. With careful design, a ‘form finding’ property is enabled. Utilizing the spatial freedom of the bars, and flexibility of the cables, some bars contain a fixed length whilst others are variable.

Introduction

PEEK is a high-strength thermoplastic used for demanding applications, due to its high thermal and mechanical stability, and low levels of outgassing in a vacuum. Few thermoplastics are present in spacecraft materials, although PEEK is showing great promise, and becoming increasingly popular in replacing thermoset composites [26]. For example, a high-strength engineering-grade thermoplastic version of PEEK was used for NASA’s COSMIC-2 project. The high-grade thermoplastic passed all qualification tests for the exterior of a satellite. All that was needed was a protective space-resilient paint to protect it against atomic oxygen and UV [26]. Such protective coatings can include SiO2, which has previously been applied as a coating on Kapton and such coated surfaces were found to be relatively unreactive to atomic oxygen. Also, the atomic layer deposition of Al2O3 and TiO2 onto polymer surfaces can shield the substrate against atomic oxygen erosion and vacuum-UV-induced degradation [26]. For colonizing the moon or Mars, AM that uses “local” soils for manufacturing needed items will be more efficient than having to manufacture them on earth followed by subsequent transport. Such a system will only require that the tools for AM or 3D Printing be brought to space, moon or Mars. While the lunar soil is comparatively richer in Al2O3 and CaO, the Martian soil is richer in FeO, Na2O, K2O, P2O5, MnO, and SO3 [30]. Binders that connect such disparate metal oxides provide a material solution to explore the possibilities of future 3D printing endeavor in lunar and Martian missions. Such binders and glazing materials include compounds such as boric acid, soda ash, whiting, flint, and kaolin clay. In this regard, ferrosilicon metallic alloy derived from lunar and Martian regolith has been used as a candidate feedstock material for wirebased 3D printers designed for in-space manufacturing. The alloys were found to primarily consist of the ferrosilicon phases of various silicon concentration such as 3wt% Si, 9wt% Si, and 12 wt% Si. It was determined that samples above 3wt% Si were too brittle to be pulled into wire and was observed to rupture at low strain values [31]. In-space manufacturing of materials can also utilize 3D printing in producing triboelectric nanogenerator (TENG) which can be used for producing consistent and reliable power supply that is critical for interplanetary exploration missions and realizing habitats on Mars. Sources of mechanical energy such as abundant wind, strong dust

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storms, and surface vibrations on Mars can be utilized to produce electric energy by the triboelectric effect, i.e. contact electrification and subsequent electrostatic induction phenomenon. Polymers such as polytetrafluroethylene (PTFE or Teflon) and polydimethylsiloxane (PDMS) are known to provide the highest triboelectric charge density among all materials with inherent triboelectric properties [32]. However, the printer technologies, materials and software are not yet optimized for printing in harsh environments, including space, and would need to include certain aspects such as antigravity and best practices for materials handling, to name a few. This is not the same as realizing exceptional material properties for space-application materials to survive prolonged exposure to space environment, rather include addressing issues with the printer technology in space. Furthermore, mass production and storage of space-application materials for an extended time are becoming less desirable due to the inability to predict/detect damage to such materials and structures with conventional inspectional methods.

4.2

What Makes the Space Environment Harsh?

Space missions require materials that can preserve functional integrity under extreme conditions of heat, impact, and radiation [10]. Beginning with the ground activities of a space mission, the as-assembled parts will experience stress during static, acoustic, and dynamic qualification testing (Fig. 4.5). During any storage or transport, the materials are also at risk for contamination and corrosion. During the actual lift-off and launch, the materials experience vibration, acoustic and shock waves, thermal fluxes, and the potential for lightning and bird strikes. Once in orbit, materials can experience adverse effects due to exposure to solar ultra-violet flux, solar wind, atomic oxygen, space vacuum, galactic cosmic radiation, plasma charging, micrometeoroid/space debris, and spacecraft-induced environment and contamination [10, 33]. The result is materials’ degradation manifesting as water desorption, outgassing, condensation, cracking, delamination, oxidation, short circuits, and loss of optical transmission, to name a few.

Vacuum/zero gravity violent temperature High-energy change electron

Electrostatic charge/discharge

Outer radiation belt

High-energy electron

Inner radiation belt

Energetic proton

Lightning strike Birds strike

Atmosphere

Atomic oxygen

Vibration and shock during launch phase

Figure 4.5 Starting from the launch phase, spacecraft face high vibrations, acoustic and shock levels, and lightning and bird strikes. Once in orbit, space materials and structures are exposed to vacuum, atomic oxygen, high solar and cosmic radiations, as well as hyper velocity impact collisions with micrometeoroids and orbital debris. For planetary exploration, re-entry aerothermodynamics effects and specific planet environment are acting on the vehicles [10].

Ultraviolet ray

Solar proton

Magnetosphere

What Makes the Space Environment Harsh? 129

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During orbital phases around the Earth, spacecraft materials may experience extremely cold and hot temperatures ranging from –180°C to +180°C. Other planets such as Jupiter can experience temperatures as low as –200°C and closer to the Sun such temperatures can be upwards of 520°C. By comparison to the fuze testing environment, the thermal fluxes experienced in the space environment are even greater than the −54°C to +71°C (–65F to 160F) prescribed in MIL STD 331C Test C6 Extreme Temperature criteria. For the reader’s clarity, the fuze, or fuzing system, is defined as a physical system designed to sense a target or respond to one or more prescribed conditions, such as elapsed time, pressure, or command, and initiate a train of fire or detonation in a munition. Safety and arming are primary roles performed by a fuze to preclude ignition of the munition before the desired position or time. This particular MIL STD 331C was recently adapted for laboratory testing of AM printed electronic materials [14]. The particular types of erosion in space may mimic gun launched conditions. For example, in low earth orbit, atomic oxygen can degrade both metals and polymers [10]. Another similarity between space vehicles and munitions is dynamic pressure experienced by the materials. For example, spacecraft or landing vehicles experience this dynamic pressure upon entry or re-entry to a planet. Overall, the materials degradation risks upon entry are erosion/corrosion due to extreme temperatures and atmospheric friction. NASA and the ESA have compiled databases with recommendation for materials and processes in space to combat material degradation. In the following sections of this chapter, a selection of examples of additively manufactured material compositions and applications for harsh environments will be discussed, including inks and ceramics.

4.3 Considerations for Printable Inks in Harsh Environments

In AM applications, nanoparticle ‘inks’ can be defined as material compositions with appropriate rheological properties that enable ‘printing’ from a device, such as an extrusion or aerosol head. The individual components (i.e. nanoparticles such as silver flakes, carbon black, carbon nanotubes, etc.), as well as inter-component

Considerations for Printable Inks in Harsh Environments

interactions of the various ink components, are optimized for aspects such as particle-to-particle interconnectivity and interfacial adhesion to a substrate, for example. The interconnectivity of the conducting component/particles can be obtained by crossing the percolation threshold and retaining that structure in the final printed product. In harsh environments, the material interfaces between ink/substrate or mixed/graded materials, for example, must withstand external stimuli such as temperature, pressure (exerted as mechanical forces due to gravity, thrust, and such), radiation, ablation, etc. For space applications, in particular, the severity of forces exerted at material interfaces due to changes in gravitational and ablative forces is expected to be substantial in addition to extremes in temperature and other environmental factors. This section will explore some of the materials (i.e. Kapton, PEEK, CB028 ink, etc.) and products (i.e. antennas, nanosatellites, sensors, etc.) that are additively manufactured to be resilient in harsh environments.

4.3.1 Studies on Material Properties of 3D Printable Inks

As alluded above, the gravity environment in space varies from 3 to 6 g during launch and re-entry for both the space craft and astronauts in contrast to reduced gravity environments while in space. This results in a broad variation in the mechanical forces exerted on spacecraft material interfaces. Recently, a study was conducted to examine 3D printed ink resiliency in harsh mechanical and thermal environments, specifically exposure to high g force and temperature cycling [14]. Conductive patterns were printed on a radar transparent polymer such as poly ether ether ketone (or PEEK) using commercial silver inks and their resiliency was tested to extreme thermal and mechanical stresses. CB028 and KA801, i.e. Ag-flake containing conductive inks from DuPont, Inc., were used in the study. The intent was to determine what effect the material composition of each of the ink had on the fidelity in performance of the 3D printed conductive patterns. While CB028 contained a polyether component as the resin component, KA801 contained the polymeric component Kapton, also from DuPont.

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The quality of ink adhesion, a factor found to directly correlate with antenna performance, was examined using adhesion testing after exposure to high accelerations up to 20,000 g and temperature cycling from –54°C to +71°C. As expected, it was observed that the composition of the inks had a direct influence on the survivability of such printed patterns. It was observed that conductive patterns obtained with CB028 had greater stability (i.e. less sensitive to environmental shocks) than the ones obtained with KA801 ink. We are continuing research efforts on a systematic study of how individual factors ultimately affect material performance, such as the molecular weight of organic/polymer component, morphology and size of the silver nanoparticles, and properties of composition modifiers used to manipulate the flow characteristics of the composition. Ultimately, the resiliency of the inks to extreme gravitational forces and temperature cycling presented in this study far surpass the conditions experienced by space components and thus can be used as an exaggerated upper limit of interfacial material property under extreme gravitational pull. In this section, a few other related studies on inks suitable for 3D printing originating from our group are discussed below (Figs. 4.6–4.8).

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

Figure 4.6 Example binary images of samples after adhesion testing: (a) CB028 as-printed, (b) CB028 thermal, (c) CB028 high g, (d) thermal then high g, (e) KA801 as-printed, (f) KA801 thermal, (g) KA801 high g, and (h) KA801 thermal then high g [14].

5 -5

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Considerations for Printable Inks in Harsh Environments

-60 (f)

Figure 4.7 (a) Reflection coefficient: CB028, (b) reflection coefficient: KA801, (c) transmission coefficient: CB028, (d) transmission coefficient: KA801, (e) spread of reflection coefficient, and (f) spread of transmission coefficient [14].

In the context of AM printed electronics, there is a diverse set of materials utilized including COTS parts connected to printed materials and other materials that are composite or nanocomposite inks. Therefore, thermal stresses deserve attention since the materials have varying coefficients of thermal expansion. With temperature cycling, it is anticipated that the thermal stresses can lead to cracking, delamination, and spalling of the inks thereby degrading performance or failure. However, a more representative combination of effects to include thermal and high g (red triangles,

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Fig. 4.8) leads to the greatest change in resistance of printed serpentine patterns [14]. In this case, 2 different inks (CB028 and KA801) were printed onto poly-ether-ether-ketone (PEEK) sheets and exposed to the aforementioned thermal cycling regime (−54°C to +71°C) for 4 hours at a time for the thermal treatment and impacted at 20,000 g’s for the high g treatment. The thermal cycling alone did not produce degradation, rather the conductivity was improved. This is likely due to additional curing of the inks during the hightemperature portion of the thermal cycling. Therefore, this study highlights the importance of material types, combination of effects and secondary effects of the treatment. 150 125 100 75 50 25 0 -25 -50 -75

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Figure 4.8 Average resistance changes (ΔR) plotted in mOhms (left) and percentage (right). Below: image of serpentine pattern printed in Dupont CB028 ink utilized for resistivity testing. Conductor length from ad to pad is 200 mm [14].

To study the electromechanical, adhesive, and viscoelastic properties of polymer nanocomposites (PNC) usable in AM, we investigated the material properties of free standing films of a thermoplastic polyurethane (TPU) polymer and a Ag-carbon black

Considerations for Printable Inks in Harsh Environments

(Ag-CB) TPU PNC in a lightly loaded low strain compression contact as a rough measure of their suitability for AM [20]. The TPU was seen to exhibit high hysteresis, and a large viscoelastic response. It was determined that sufficient time was needed for polymer chain relaxation and measurable adhesion and, as a new discovery, that a ‘large enough contact area’ was needed to allow ‘longer time constant polymer ordering’ in the contact that led to higher adhesion and better performance and reliability (Figs. 4.9–4.11). Such in-depth evaluation of the rheological properties of polymer/ oligomer components in a 3D printing ink is absolutely necessary and critical to ensure the success of printing AM constructs for space applications. Neat TPU Compression With Au Electrodes

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Figure 4.9 Contact force versus RD for the neat TPU polymer during a localized compression experiment. Hysteresis, adhesion, and necking are observed in the experiment [20].

Two other studies from our group specifically focused on the effect of carbon fibers or carbon nanotubes on the electrical conductivity of composites that contain either of them. In the first study, a theoretical derivation for aligning discontinuous carbon fiber in an applied electrical field was developed and was compared

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with experimental evaluation [34]. It was determined that a direct current (DC) electrical field of 20.12 V/mm was required to align short carbon fibers (0.15 mm in length) in the liquid thermosetting resin, Kion® Ceraset polysilazane, containing repeating units of silicon and nitrogen atoms bonded in an alternating sequence. A mathematical expression was also derived to include weight percentage of the carbon fibers in the composites as means for controlling pearl-chain formation by concatenation of the carbon fibers that led to the control of the composites’ electrical conductivity (Figs. 4.12–4.15). Initial contact force ~ 13 mN

Initial contact force ~ 9 mN Initial contact force ~ 3.5 mN Adhesion force ~ 2.5 mN 3 10-8 Dwell time = 350 s

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Figure 4.10 Contact area versus adhesion force at various initial contact force and dwell time. Data are initial contact force. At the highest initial contact force and contact area, adhesion increases even more dramatically at higher dwell times [20].

In the second study, polysilazane (PSZ, KiON Defense Technologies, Inc. USA) was utilized to produce silicon carbonitride (SiCN)-reinforced aligned carbon nanotube (CNT) sheets. The sheets

Considerations for Printable Inks in Harsh Environments Polymer chain segment relaxation Short t, entanglement hinders electrode contact

(a)

Polymer chains

Dwell time

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Au electrode

Polymer chain reorientation/disentanglement, diffusion, and ordering/crystallization Long t, higher polymer chain areal density – high adhesion, needs large enough contact area for ordering Dwell time

(b)

Au electrode

Au electrode

Figure 4.11 Proposed mechanisms responsible for adhesion behavior: (a) polymer chain relaxation is operative with a short time constant and entanglement hinders electrode contact; and (b) polymer chain ordering is operative with a long time constant and requires large contact area. This leads to high adhesion due to high packing density of polymer chains [20].

Z

E

4. Pearl chain formation (approaching)

q X

j

Y 2. Aligned fiber pairs (rotation)

1. Random placed fiber pairs

d

3. Dielectrophoretic motion (translation)

Figure 4.12 Stages of alignment for carbon fiber [34].

were formed by infiltrating liquid polysilazane into mechanically stretched CNTs followed by conversion of this matrix into a solid preceramic state by thermal crosslinking at 140oC in air atmosphere for 24 h [35]. Subsequently, this solid preceramic was converted to the final ceramic nanocomposites by repeated cycles of impregnation and pyrolysis at 1000°C for 1 h in a N2 atmosphere (Figs. 4.16– 4.18). The nanocomposites averaged to contain a high-volume

137

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Printable Materials for Additive Manufacturing in Harsh Earth and Space Environments

Electrodes

Randomly dispersed carbon fiber (black lines)

200 mm

Liquid resin (grey)

Figure 4.13 Randomly dispersed carbon fiber [34].

200 mm

200 mm

30 sec

0 sec

200 mm

200 mm

120 sec

200 mm

60 sec

180 sec

200 mm

240 sec

Figure 4.14 Alignment process of carbon fiber in polymer precursor [34].

fraction of CNTs (up to 60 vol%) and an electrical conductivity of up to 2.2 ¥ 105 Sm–1. The electrical conductivity was found to have a significant dependence on the extent of alignment of CNTs in the nanocomposites and was found to increase by three-fold upon an isotropic alignment of the CNTs upon pyrolysis. Such high electrical conductivity of the nanocomposites bodes well for the application of these nanocomposites in electromagnetic interference shielding. Also, as can be discerned from such evaluations, the alignment of

Considerations for Printable Inks in Harsh Environments

various functional nanomaterials within a 3D printable ink has as much of an impact on the final product obtained as the morphology of such materials during printing. 0.5 wt. %

40 30 20 10 0

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Potential Field (V)

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(a) 0.5 wt. % CF

Potential Field (V)

Potential Field (V)

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400

41 40.5 40 39.5 39

500

0

400

200

600

Time(s)

(c) 0.1 wt. % CF

(d) 0.05 wt. % CF

Figure 4.15 Various weight percentages: 0.5%, 0.1%, 0.25%, and 0.05% of carbon fiber (CF) solutions were submitted to an electrical field. (Voltage was recorded vs. time) [34]. (a)

(b)

Alignment direction 1 mm

1 mm

Figure 4.16 SEM images of random and aligned CNTs sheet. (a) Random, (b) aligned [35].

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Printable Materials for Additive Manufacturing in Harsh Earth and Space Environments

2.0×105 1.5×105

sI

1.0×105

2.5×104 2.0×104 1.5×104

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5.0×103

0.0

0.0

1 2 Z eet Sh PS /SiCN SiCN / Ts Ts/ s N C CN CNT CNTs 12

sII/s

9 6 3 0

t 1 Z 2 hee s/PS SiCN SiCN / T / sS T CN CNTs CNTs CN

s^

1.0×104

(d)

CNTs Volume Fraction/%

(c)

(b)

2.5×105

s^/(S◊m-1)

(a) sII/(S◊m-1)

140

eet /PSZ iCN1 iCN2 Sh Ts CNTs NTs/S NTs/S CN C C 100

80 60 40 20

This study CNT/ceramic

our material CNT/MgAl2O4 CNT/Al2O3 CNT/Al2O3

0 100 101 102 103 104 105 106 Electrical Conductivity/(S◊m-1)

Figure 4.17 Electrical conductivity characterization of ceramic matrix nanocomposites. (a) Electrical conductivity along the CNT alignment direction, (b) Electrical conductivity measurements vertical to the CNT alignment direction, (c) The ratio of σ|| to σ⊥, and (d) Comparison of the aligned CNTreinforced silicon carbonitride nanocomposites with other representative CNTreinforced ceramic nanocomposites [35].

Another critical aspect in the overall stability and viability of structures obtained for space applications with AM or 3D printing is the stability of interfaces made during ‘nanojoining’ of line-toline, line-to-layer, and layer-to-layer nanostructures during their fabrication [36]. In this aspect, an important feature that will enable formation of functionally enhanced 3D printed structures would be the formation of printed structures with gradient properties. Such complex functionally graded 3D printed objects can possess spatially non-linearly varying material properties such as color, concentration and mechanical properties. Failure of components often transpires at the interfaces of various materials as sharp changes in geometry or material can induce stress concentrations. Therefore, a process with the ability to gradually vary material properties spatially can obviate stress concentrations and enhance robustness of a component without a sharp interface. The strength of 3D printing lies in the facility to achieve such graded material production, which is typically impossible in a conventional

250 nm

CNTs covered by PSZ

30 nm

Exposed CNTs

250 nm

100 nm

(b)

1 mm

(f)

1 mm

(c) CNTs covered by PSZ

100 nm

180 nm

1 mm

(d)

145 nm

Exposed CNTs

Figure 4.18 AFM and SEM analysis of CNT/PSZ and CNT/SiCN1. (a) AFM of CNT/PSZ, (b) AFM of CNT/SiCN1, (c) SEM of CNT/PSZ, (d) SEM of CNT/SiCN1, (e) the cross-sectional SEM of CNT/PSZ, and (f) the cross-sectional SEM of CNT/SiCN1 [35].

1 mm

(e)

(a)

Considerations for Printable Inks in Harsh Environments 141

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Printable Materials for Additive Manufacturing in Harsh Earth and Space Environments

manufacturing setup. The effectiveness of such advanced printing technology was demonstrated recently by the successful printing of a diverse range of objects with complex spatial variations in color and Al2O3 concentration. Polyurethane objects with various gradient patterns in material mechanical properties were also fabricated in this study, Figs. 4.19 and 4.20 [37]. The inclusion of a gradient in the material construct will obviate any deleterious effects on material properties that occur at sharp interfaces. Such gradient formation will also rely heavily on the features of the computer-aided design (CAD) process that ultimately drive the 3D printing endeavor. (a)

Computer

G-code

Active mixer

Three-axis motion gantry

6-axis controller

V U W Z Digital material feeding Y

(b) Function modeling & gray-scale representation

f(x,y,z)=x+y+z

Control codes generation

Digital feeding & 3D printing

15mm

10mm

Figure 4.19 Gradient 3D printing system. (a) Schematics of the gradient 3D printing mechanical setup and printing control system. (b) Process of gradient 3D printing [37].

CubeSats are nanosatellites typically weighing between 2 and 20 lbs (Figs. 4.21) [26]. Specifically, for X-ray shielding purposes in space-based applications, material extrusion 3D-printing technology has been used for “on-the-go” rapid creation of space-based devices such as cube satellites [38]. Composites comprising tungstenloaded polycarbonate 3D printing filaments were found to be highly amenable to printing and resulted in marked improvement of X-ray

Considerations for Printable Inks in Harsh Environments

(b)

(a)

10 mm (d)

(c)

XY

10 mm

XZ 10 mm

Z Y (0,0,0) X

10 mm

YZ 10 mm

Figure 4.20 Printing of objects with 3D graded nano-Al2O3 concentration. (a) Multi-layer gray scale images showing the 3D diagonal concentration distribution. (b) The printed object with 3D diagonal concentration gradient. (c) 3D reconstruction of the printed object using CT scans. (d) Representative cross sections perpendicular to the direction of X, Y, and Z axis, respectively, from the reconstructed 3D objects. The color depth on different sections indicates the concentration distribution of nano-Al2O3 particles [37].

shielding (~10%) even with small loadings of tungsten (~0.3% by volume). Furthermore, because of the low-volume loading, the electromagnetic properties of the polycarbonate composite were not found to be degraded, i.e. there was no significant increase in loss tangent or change in permittivity in the GHz frequency range. The same group has also further reported investigation into anisotropy in thermal conductivity in 3D printed polymer matrix composites (PMCs) for space based cube satellites [39]. They studied thermally conductive polymer matrix composites comprising graphite, carbon fiber, and silver in an acrylonitrile-butadiene-styrene copolymer matrix. Specifically, the effect of the anisotropic nature of the composite materials, as well as filler loading percentage, that is

143

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required to successfully transfer heat to active cooling structures was studied to enhance the anisotropy in thermal conductivity. Such enhancement was expected to improve thermal profile orientation, thermal load, radiative element performance, and integrated electronic performance within the 3D printed CubeSat. Eventually these CubeSats could be 3D printed in space. ESA has 3D printed CubeSat structures incorporating their own electrical lines. These can be printed using PEEK and other high-grade thermoplastics, as they are recyclable and biocompatible [40].

Figure 4.21 CubeSats being launched from the International Space Station’s Kibo laboratory in 2014 [26].

Inkjet-printed flexible sensors fabricated on paper have been reported for making flexible antennas, RF electronics and sensors. Polyaminobenzene sulfonic acid-SWNT solution in DMF and NH3 was used to print thin films and traces on paper substrates to produce assemblies with electromagnetic properties especially for use as “smart skins” in space-wearable applications. The study investigated various challenges of RF packaging, and power sources integration in terms of ruggedness, accuracy, and reliability/flexing performance for applications up to 6 GHz [41].

4.4 Considerations for Printable Ceramics in Harsh Environments

Ceramic materials have many excellent properties such as high strength and good resistance to wear, oxidation, and corrosion. Ceramics are considered high performance structural materials because of their superior high-temperature stability and ultrahigh-

Considerations for Printable Ceramics in Harsh Environments

temperature ceramics are of particular interest to the aerospace and aeronautics industries, which require chemical and structural stability under extremely high-temperature operating conditions. Aerospace components, such as wing leading edges, fuel combustors, and thermal protection systems, require materials that can withstand conditions of high thermal, mechanical, and shock-wave loading. Figure 4.22 compares the melting temperatures of different high-temperature materials. Notice that the ceramic-based carbides have the highest melting temperatures out of the different classes represented. Therefore, combining the robust properties of ceramics with AM processes for complex shapes opens multiple opportunities for the fabrication of high-temperature materials for the harsh environments presented by space and munitions, for example, to include a range of technologies from microelectromechanical systems (MEMS) to macro-scale thermal protection systems (TPS). Below, the most common techniques to additively manufacture ceramics are discussed (i.e. slurry-based stereolithography and solid-based fused deposition of ceramics, FDC) followed by several examples of printed ceramic parts.

TaN HfN TiN ZrN

TiC

NbB2 TaB2

NbN

2800

Os Mo

3000

MgO HfO2 UO2 ZrO2

Ta

3200

ThO2

3400

HfB2 ZrB2 TiB2

W

3600

Re

Melting Temperature (°C)

3800

NbC

ZrC

TaC HfC

4000

2600 2400

Metals

Oxides

Borides

Carbides

Nitrides

Material Family

Figure 4.22 Comparison of melting temperatures of different materials. Notice that the ceramic-based carbides have the highest melting temperatures out of the different classes represented [47].

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4.4.1 Additive Manufacturing (3D) for Ceramic Materials: Slurry-Based Technique There are many types of slurry-based AM techniques, with the most common one being the stereolithography process. Stereolithography is an additive manufacturing process that allows the fabrication of parts using a computer-aided design (CAD) software [42–44]. The manufacturing of 3D objects by stereolithography is based on the spatially controlled solidification of a liquid or semi-liquid resin systems by photopolymerization such as the use of ultraviolet laser to selectively cure the liquid [45]. For ceramic materials, the resin system, with the aid of surfactants, is usually dispersed with fine ceramic particles to form micro-/nanocomposite inks or pastes. The process described here, then, takes advantage of a fillercontaining polymer technique. After a layer has been “printed,” the polymer phase is exposed under light irradiation, which causes it to polymerize and thereby uniformly form a cross-linked organic network around the ceramic particles. This process is repeated until the entire 3D part is built up. The cured product is further treated at high temperature in a process known as sintering or pyrolysis to densify the material, a process similar to conventional ceramic processing routes [46]. A condensed ceramic fabrication process is shown in Fig. 4.23.

4.4.2 Major Stereolithography Processing Parameters

The rheological behavior such as viscosity and shear rate of the photo-polymerizable suspension is also very important for the deposition of new layers, which must be uniform to get accurate builds. For instance, when a fresh layer is being applied, the shear rate can vary as the printing device passes from a thick uncured area to a thin liquid layer on a solid cured area [50] thereby generating a change in shear stress by a factor of 1000 or even more. Scalera et al. [51] addressed the rheological challenges in terms of reactivity and stability associated with a ceramic stereolithography process through the fitting of viscosity curve as a function of time after powder dispersion. The curves were fitted with Ellis model as: h=

h0

1 + ( lg )m

(4.1)

Figure 4.23

Z

X

CAD model Image projection

Paste tank

Blade

Generator

Slicing

Layer information

Z axis

UV laser

Brown part

Workpiece

De-binding

XY Mirror

Green part

Workbench

Sintering

Ceramic part

Schematic illustration of (a) a typical ceramic stereolithography process and (b) stereolithography set-up [48, 49].

Y

(b)

(a)

Considerations for Printable Ceramics in Harsh Environments 147

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Printable Materials for Additive Manufacturing in Harsh Earth and Space Environments

where h0 is the viscosity at zero shear rate, l and m are the model parameters, and g is the shear rate. g in particular, is the reciprocal of the shear rate at which the calculated value of h is equal to h0. Also, it is important to know the cure depth of the polymer resin during photopolymerization and the expression is given as [50]: Ê Eˆ Cd = Dp ln Á ˜ Ë EC ¯

(4.2)

where Dp is the penetration depth (a characteristic that depends on the initiator concentration and efficiency and on the presence of dispersed particles). EC represents the critical energy (minimum energy required to gel the resin) and E is the energy dose. Furthermore, the penetration depth can be computed based on the ceramic volume fraction (F), the particle size and the refractive index between the ceramic particles and the photopolymerizable medium [50]: 1 = S + (1 - F )(e pcp - e DcD ) Dp

(4.3)

where cp and ep represent the concentrations of the photoinitiator and cD and eD are the concentration and molar extinction coefficient of the dye. S represents the light scattering effects and can be obtained by empirical fitting [50, 52]: Ê b ˆ 2 S(F ) = b(F ) - Á F Ë 2F m ˜¯

(4.4)

where β is a fitting parameter that depends strongly on the refractive index difference between the ceramic particles and the liquid. Figure 4.24 shows the practical representation of the equation above. As seen in the curve, the polymerization rate decreases with increase in index ratio as a result of high scattering and absorption, which is not palatable for larger particle sizes. As shown in the figure, the stereolithography of SiO2 and Al2O3 are easier than that of ZrO2 and SiC. This means, smaller ceramic particles having better light-scattering properties are preferred in stereolithography.

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Figure 4.24 (a) Conversion rate with respect to particle size and (b) and effect of refractive index (SiO2 < Al3O3 < ZrO2 < SiC) on conversion rate of ceramic filler containing acrylate [53, 54].

Conversion (%)

80

0.5 mm 1.4 mm 2.3 mm

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(a) 85

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4.4.3 Stereolithography Manufacturing via PolymerDerived Ceramic Process It should be noted that preceramic polymer approach to obtain polymer-derived ceramics (PDCs) also offer excellent alternative to the ceramic filler-containing polymer technique. PDCs are made from silicon-based organic polymer precursor and is converted to inorganic ceramic material upon pyrolysis. The pyrolysis process requires gradually heating up the precursor as the material transforms to a ceramic under a controlled environment [55]. The main advantage of PDC for stereolithography process is the ability to fabricate components from relatively simple processing from polymeric precursors. Hence, this process is well suited for technologies involving polymers such as stereolithography. Recently, some researches have been conducted using PDCs in conjunction with stereolithography method. An example of stereolithography of polymer derived ceramic process is presented in Fig. 4.25. One major limitation of the PDC technology is after pyrolysis, cracks and pores are developed in the material. This is because during pyrolytic conversion, some organic functional groups such as CH4, C6H6, and CH3NH2 present in the precursor are released [56]. To tackle this challenge, inert or active filler is added to the precursor to produce denser parts, although this still remains a problem. The main effects of the active fillers are to form a stabilizing network of the filler reaction products, increase ceramic yield of the polymer, and to provide an internal surface for material transport during polymer decomposition reactions [57]. On the other hand, inert fillers do not react with the precursor but rather help to fill in the pores by acting as substitute elements. An example of this can be seen in Fig. 4.26 where SiC whiskers are added into a siloxane precursor (precursor for SiOC) to reduce the shrinkage of the final product. The SiC-reinforced ceramic endures 37% shrinkage while unreinforced parts endures 42% shrinkage.

n

R2

R2 H

n

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F

1 cm

G

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Stereolithography or self-propagating photo-polymerization

Resin

UV Laser

3cm

1 cm

1000C

Pyrolysis

Pre-ceramic polymer

C

H

D

2 cm

Polymer-derived ceramic

Figure 4.25 Stereolithography process for PDCs. (A) UV-curable preceramic monomers mixed with photoinitiator, (B) resin mixture is exposed to UV light in a stereolithography 3D printer, (C) cured product formed, and (D) pyrolysis converts material to ceramics. Examples (E) stereolithography printer cork screw, (F and G) microlattice structure, (H) honeycomb structure [58].

0.5 mm

Examples: E

UV curable monomers & UV photo initiator

Si O

Si C

n

R1

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H Si N

R1

R1 H

A

Considerations for Printable Ceramics in Harsh Environments 151

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Printable Materials for Additive Manufacturing in Harsh Earth and Space Environments (b) Pyrolysis (a)

1000°C 2 mm (c)

(d)

4 mm

20 mm

Figure 4.26 Examples of (a) PDC parts fabricated through stereolithography process at high resolution (zoomed image) and (b) printed sample before and after pyrolysis, scanning electron micrographs (c) of fractured surface of showing dispersion of SiC whiskers in the ceramic and (d) and higher magnification of a single SIC whicker embedded in the ceramic structure [59].

4.4.4 Additive Manufacturing (3D) for Ceramic Materials: Solid-Based Technique Fused deposition modelling (FDM) is an example of bulk solid-based AM technique which was developed and commercialized by Stratasys Inc. in Eden Prairie, Minnesota [60]. This solid freeform fabrication method is done by building a 3D object from a filament fed into an extruder head capable of moving in the X-Y-Z direction, where the filament material is selectively extruded through heated nozzles. This method is generally used to fabricate polymeric components but the technology has since been extended to the fabrication of ceramic components. To do this, a dried surfactant pre-coated ceramic powder mixed with appropriate volume of binder agent is thoroughly mixed with thermoplastic polymers. The product is then extruded to form filaments via a pair of counter-rotating rollers [61, 62]. The filament is then fed into the heated extrusion (resistive heater) system and extruded through a nozzle. The molten feedstock is then deposited in the X–Y plane in cross-sectional layers. After each layer is completed, the part is lowered by one layer thickness in the Z direction and the process repeats to obtain a ceramic green part. Afterwards, the green product is exposed to high temperature for sintering to remove the binder and densify the

Considerations for Printable Ceramics in Harsh Environments

component. The method of modifying the FDM method to produce ceramic components is sometimes termed as fused deposition of ceramics (FDC). The schematic representation of the FDM process is presented in Fig. 4.27. Generally, the FDC development process can be categorized into four stages [64]: Optimization of thermoplastic binder composition, Fabrication of the filament, Process fabrication (systematic printing of layers), and Binder removal and sintering of the green body. FDM head

PCL filament rollers liquefier

temperature control

x-y axes

nozzle tip PCL extrudate

scaffold

platform z-axis

Figure 4.27 Schematic diagram of the FDM extrusion and deposition process [63].

4.4.5 Filament Selection for Fused Deposition of Ceramics In selecting the filament material feedstock, careful consideration has to be given to some important requirements. For instance, fine ceramic particles with wide size distributions are required to improve the filament by decreasing the overall viscosity of the binder and powder. Likewise, the binder system should possess properties such as high mechanical strength, low viscosity, and high strain.

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For example, low binder viscosity helps in preventing the return of the molten metal. Another important requirement is the selection of adequate nozzle size and type for the extrusion of the filament in order to ensure proper flow. The layer thickness and vertical dimensional accuracy are determined by the extruder die diameter which ranges from 0.013 to 0.005 inches [65]. An example of a ceramic-filled thermoplastic filament called a “Lay-ceramic” from a company named Kai Parthy is shown in Fig. 4.28 [66]. It contains 3.0 mm diameter filaments printable at about 250–280°C. After the part has been printed, the green ceramic can undergo sintering up to 1200°C.

Figure 4.28 “Lay-ceramic” (3.0 mm) filament and some example of parts printed with the filament [66].

4.4.6 Some Examples of Additive Manufactured Components for Harsh Environments Based upon the outstanding thermal, mechanical, and electrical properties of ceramics in harsh environments, and their ability to be manufactured into complex shapes via AM, several examples of products produced are described below. Ref. [58] reported the fabrication of silicon oxycarbide (SiOC) microlattices and honeycomb cellular structures from a preceramic polymer for harsh-environment applications. The preceramic polymer was cured with ultraviolet light in a stereolithography 3D printer and the green body pyrolyzed at 1000°C to obtain a dense SiOC ceramic product. The cellular structure displayed 10 times more strength than commercially available ceramic foams of similar density and could survive temperatures in air up to 1700°C with only minimal surface oxidation. From the results shown in Fig. 4.29, there is an

0

Foam Duoce Foam

SiC

AISiO

SiC

Amorphous

Foam

SiOC

(B)

SiOC (HRL)

SiOC

SiC

Si3N4

ZrB2+SiC

ZrB2

Ta

in air Nb

0.01 1300 1400 1500 1600 1700 Temperature (°C)

0.1

1

10

100

10 nm

(D)

Microlattice

SiOC

Mass Change D mg/cm2/h

Compressive Strength (MPa)

Figure 4.29 (a) Compressive strength of polymer SiOC PDC, high-temperature oxidation of SiOC microlattice, (b) mass change compared with other ceramics, (c) TEM micrograph of SiOC region, and (d) TEM micrograph of SiO2 region [58].

Graphite

0.5

(A)

0.1 0.2 0.3 0.4 Density (g/cm2)

SiOC Honeycomb

(C)

50 45 40 35 30 25 20 15 10 5 0

Considerations for Printable Ceramics in Harsh Environments 155

Printable Materials for Additive Manufacturing in Harsh Earth and Space Environments

indication that such cellular ceramic material can be used as load bearing ceramic sandwich panels for high-temperature applications such as space vehicles. Another example of a high-performance ceramic material for harsh environments is hafnium diboride (HfB2). HfB2 belongs to a class of ultrahigh-temperature ceramic (UHTC) materials that exist in hexagonal crystal structures of AlB2 prototype with layers of B atoms in 2D graphite-like rings alternating the Hf layers in hexagonally close-packed array [67]. This makes HfB2 one of the best candidate materials for applications where thermal stress response is important. An example of this application is in rocket nozzles where temperature rises up to 2000°C in less than 0.15 seconds on the inside wall, while the outer wall remains at room temperature [67]. (a)

(d)

(c)

(b)

600

Wuchina et al. [24] Sciti et al. [27] Kafish et al. [28] Rhodes et al. [29] IC [2013] Coarse Grained (This Work) Fine Grained (This Work)

500 Strength (MPa)

156

400 300 200 100 0

0

200

400

600

800 1000 1200 1400 1600 1800 2000 2200 Temperature (°C)

Figure 4.30 (a–c) Examples of parts fabricated with robocasting 3D method and (d) HfB2 bending strength compared with the literature for a range of temperatures [68].

Future Directions for AM in Harsh Environments

Feilden et al. [68] has recently fabricated HfB2 ceramic through an AM process called robocasting. This process is very similar to the FDM process, but the major difference is the immediate solidification of the molten feedstock (filament) after extrusion. In this work, very highly densified parts were achieved via pressure-less sintering and they exhibited bending strength of 364 ± 31 MPa at room temperature, and maintained strengths of 196 ± 5 MPa up to 1950°C, which is comparable to UHTC parts produced by traditional means (Fig. 4.30). According to the report, this was the highest temperature a 3D printed part has ever withstood during mechanical tests. Although AM of ceramics is still a fairly new research area, it is growing and demonstrating many promising applications. Fabricating high performance ceramic materials through AM for advanced applications and harsh environments creates an avenue of great potential in extending the scope of applicable ceramics for highly demanding aerospace applications.

4.5 Future Directions for AM in Harsh Environments

The future of AM for space spans a diverse range of disciplines including resilient hybrid electronics, food, garments, and even transition to 4D printing. These topics will be covered in the sections below.

4.5.1 Resilient Hybrid Electronics

The field of AM electronics has approached device production in a hybridized manner by incorporating printed components and interconnects and COTS components. This is due to both printer technology and materials’ limitations where components such as batteries, LEDs, capacitors, switches, etc. can be ‘picked and placed’ into the printed structures and connected by a combination of traditional or novel adhesives and conductive inks. Although COTS components such as low-voltage circuits may be widely available (Custer 2011), there are no commercial market forces to drive improvements in the manufacture of specialized (non-COTS)

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electronics for defense applications. Therefore, the prototyping and development of unique defense-worthy components is one area that AM of electronics is addressing. By combining both the hybridized COTS-AM concept and the mechanical/electrical/thermal stability demanded by defense applications, the specialty area of ‘resilient hybrid electronics’ (RHE) was [8]. Resiliency relates to the ability of the material to maintain performance in the harsh environment; that it is tough, durable, strong, reliable, etc. The goal of RHE is to exploit complex designs not possible with traditional manufacturing, to deviate from rigid circuit boards, increase functionality and implement an on-demand concept of use. In contrast to a 30-year inventory of a stock item, it is envisioned that AM can revolutionize innovative improvements through iterative rapid prototyping, prolong part service life via effective repair and avoid obsolescence and long lead times for hard-to-source parts. Overall, an ‘as-needed’ mindset leads to reduced lifecycle costs by avoiding large production runs and the associated storage, aging, and disposal requirements. Although AM electronics is a maturing field, it is worth considering the results of studies where resiliency to harsh environments have been reported. These may provide an underlying understanding for the parameters and thresholds of printed materials. With this knowledge, there is the potential to extrapolate the results to conditions that would be encountered during launch, assent (heat, vibration), and orbiting in space (heat, cold, vacuum, UV, etc.).

4.5.2 Food Printing

Additive manufacturing of food in space is being explored to meet the requirements of food safety, nutritional stability and acceptability of meals for long space missions, while using the least amount of spacecraft resources. The current food system of NASA for space travel is not able to meet the nutritional and five-year shelf life requirements for long missions, as the individual packaged foods processed with traditional cooking methods lose nutritional value due to degradation over time. Also, the refrigeration equipment that is required for preserving such food resources takes up excessive spacecraft resources [70–73]. NASA has recently funded Systems and Materials Research Corporation (SMRC) to investigate the possibility and application of

Future Directions for AM in Harsh Environments

3D printing for producing food during long space missions [72, 73]. In order to design a food system to meet nutritional and personalized requirements for individual astronaut during long space missions, the SMRC has proposed that 3D/inkjet printing be employed to deliver micro-/macronutrients containing carbohydrate, protein, and fat, structure and texture, and components responsible for flavor and smell. Dry sterile containers will be used to store the micro-/macronutrient stocks and sterile packs to store flavors as liquids, aqueous solutions or dispersions. During the production of food, the micro-/macronutrient stocks will be fed directly to the printer by combining with water or oil and blending with flavors and texture modifiers at the print head. Then the mixtures will be extruded into desired structures and shapes. The three main aspects taken into consideration to realize an accurate and precise printing of food items include: material properties, process parameters, and post-processing methods. The desired materials properties include rheological properties, binding mechanisms, and thermodynamic properties of food components during pre-treatment and postprocessing methods. Fine tuning the rheological properties of the mixtures could be used to produce food products of different consistencies and nutritional values. This technology could not only solve the long-term storage, sustenance, and micro-nutrition issues, but also could meet the personalized dietary needs and improve the pleasure of eating.

4.5.3 Space Garments

Garments that can withstand high compressive forces are required for space medicine and for activity outside of the space vehicle with extremely different g conditions. For such applications, shape changing materials that also possess shape memory properties are desirable. Some of the efforts in this area include the integration of shape changing materials such as NiTi shape memory alloy coil actuators formed into modular, 3D-printed cartridges into compression garments resulting in garments capable of constricting on demand [74]. Such NiTi shape memory alloy has been used previously for developing artificial muscles that employ voltage, magnetic field, light, or temperature-driven dimensional changes to produce forces and displacements within such materials [75]. Such

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3D-printed hierarchical elastomer-derived ceramics are currently being utilized for 4D-printing by following the step of 3D-printing with a shape-morphing step, in which an external stimulus activates a response in the material that produces autonomous morphing structures for use in space exploration, aerospace propulsion components, etc. [76]. In a similar vein, shape memory polymers used in applications such as space structures, self-assembling robots, etc. that can sequentially self-fold into targeted structures by thermal activation of 3D printed spatially variable patterns have been reported. The study utilized two base shape memory polymer mixtures, viz. VeroWhite and TangoBlack for jet spraying followed by UV curing. VeroWhite and TangoBlack are rigid and compliant polymers at room temperature that have the ability to create tensegrity [77]. In this area, tensegrity structures with detached struts suitable for deployable applications such as outer-space structures have been 3D-printed with stimulus responsive polymers. One of the polymers used in this study also happens to be VeroWhite [76]. The emergence of ‘4D printing’, i.e. 3D-printed ‘responsive’ materials, and smart materials will also further fuel future deep space exploration and self-sustainability. In fact, the future of 3D printing in all applications, including space applications, will be the adaptation of 3D-printed articles that can respond in a programmed manner to an external stimulus; i.e. 3D-printed ‘smart materials’ [26]. For example, life support for human habitat, producing a closed artificial eco-system, recycling of water, O2, and CO2. Several studies have already demonstrated novel proof-of-concepts for 4D printing structures and medical parts, such as stents, and new drug delivery mechanisms using carbon-fiber reinforced polyetheretherketone thermoplastics (CF/PEEK) [26]. With such in-orbit manufacturing pultrusion system, large carbon composite structures have been produced in space. The pultrusion process has been scaled down such that the equipment can be accommodated into a spacecraft. Most conventional deployable devices are highly complex, containing numerous linkages, hinges and motors, which ultimately accumulates high cost and heavy structures. Recent developments in functional materials, give rise to lightweight, inexpensive materials capable of multiple deformations without degradation. The functionality of 4D printing allows materials to interact and adapt to changing

References

environments. Materials which can transform and adapt to variable stiffness applications have potential for deployable structures, such that it is possible to withstand deformations with low stiffness areas and retain their structure with high stiffness areas [26].

4.6 Conclusionary Statement

Nanotechnology in space will surely rely upon advanced materials and technologies such as composite additive manufacturing.

Acknowledgments

Special thanks for funding from the National Research Council (NRC) for C. Neff and funding from the Joint Fuze Technology Program (JFTP) for A. Schrand, M. Kolel-Veetil, and E. Elston.

References

1. Schrand, A. M. and Benson-Tolle T. (2006). Chapter 18: Carbon nanotube and epoxy composites for military applications, in Carbon Nanotechnology: Recent Developments in Chemistry, Physics, Materials Science, and Device Applications, Liming Dai (Ed.), Elsevier Publishers.

2. Schrand, A. M. (2016). Chapter 1: Perspectives on carbon nanomaterials in medicine based upon physicochemical properties: nanotubes, nanodiamonds and carbon nanobombs, in Carbon Nanomaterials for Biomedical Applications, pp. 3–29, Prof. Liming Dai, Dr. Rajesh Naik, and Prof. Mei Zhang (Eds.), Springer Publishers. DOI: 10.1007/978-3319-22861-7

3. Schrand, A. M. and Lin, J. B. (2012). Chapter 16: Characterization of detonation nanodiamonds biocompatibility, in Ultrananocrystalline Diamond (2nd Edition), Olga Shenderova and Dieter Gruen, Eds. 4. Schrand, A. M., Lin, J. B., and Hussain, S. M. (2012). Chapter 32: Cytotoxicity assessment of carbon-based nanomaterials with the MTS assay, in Nanoparticles in Biology and Medicine, Mikhail Soloviev (Ed.), Springer Science+Business Media, LLC (Humana Press).

5. Schrand, A. M., Ciftan Hens, S. A., Shenderova, O. A. (2012). Chapter 26: Nanodiamond particles: Properties and perspectives for bioapplications, in Handbook of Nanoscience, Engineering, and Technology (Third Edition), Taylor and Francis, LLC.

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6. Schrand, A. M., Dai, L., Schlager, J. J., and Hussain, S. M. (2012). Chapter 5: Toxicity testing of nanomaterials, in New Technologies for Toxicity Testing, N. Bhoghal (Ed.), Landes Bioscience.

7. Schrand, A. M., Johnson, J., Dai, L., Hussain, S. M., Schlager, J. J., Zhu, L., Hong, Y., and Osawa, E. (2010). Chapter 8: Cytotoxicity and genotoxicity of carbon nanomaterials, in Safety of Nanoparticles: From Manufacturing to Clinical Applications, Prof. T. Webster (Ed.), Springer Publishing.

8. Schrand, A. (2018). Additive manufacturing in the DoD, DSIAC, 5(4), pp. 31–39.

9. Hillman, C. (2019). Thermal degradation of electronics: How hot is too hot?, Engineering Simulation & 3D Design Software, ANSYS Inc., www. ansys.com/blog/thermal-degradation-electronics.

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11. Koerner, H., Strong, R. J., Smith, M. L., Wang, D. H., Tan, L. S., Lee, K. M., White, T. J., and Vaia, R. A. (2013). Polymer design for high temperature shape memory: Low crosslink density polyimides.

12. Johnson, K. J., Wiegart, L., Abbott, A. C., Johnson, E. B., Baur, J. W., and Koerner, H. (2019). In operando monitoring of dynamic recovery in 3D-Printed thermoset nanocomposites by XPCS, Langmuir, doi: 10.1021/acs.langmuir.9b00766 13. Pierson, H. A., Celik, E., Abbott, A., Jarnette, H. D., Gutierrez, L. S., Johnson, K., Koerner, H., and Baur, J. W. (2019). Mechanical properties of printed epoxy-carbon fiber composites, Exp Mech, https://doi. org/10.1007/s11340-019-00498-z

14. Neff, C., Elston, E., Burfeindt, M., Crane, N., and Schrand, A., (2018). A fundamental study of printed ink resiliency for harsh mechanical and thermal environmental applications, Additive Manufacturing, 20, pp. 156–163, doi: 10.1016/j.addma.2018.01.009 15. Neff, C., Nussbaum, J., Gardiner, C., Crane, N. B., Zunino III, J., and Newton, M. (2019). Mechanical and temperature resilience of multimaterial systems for printed electronics packaging, Flexible and Printed Electronics, https://doi.org/10.1088/2058-8585/ab38e9

16. Neff, C., Rojas-Nastrucci, E. A., Nussbaum, J., Griffin, D., Weller, T. M., and Crane, N. B. (2019). Thermal and vapor smoothing of thermoplastic for reduced surface roughness of additive manufactured RF electronics, IEEE Transactions on Components, Packaging and Manufacturing Technology, 9(6), pp. 1151–1160, doi: 10.1109/TCPMT.2019.2910791

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35. Yang, J., Downes, R., Schrand, A., Park, J. G., Liang, R., and Xu, C. (2016). High electrical conductivity and anisotropy of aligned carbon nanotube nanocomposites reinforced by silicon carbonitride, Scripta Materialia, 124, pp. 21–25.

36. Ma, Y., Li, H., Bridges, D., Peng, P., Lawrie, B., Feng, Z., and Hu, A. (2016). Zero-dimensional to three-dimensional nanojoining: current status and potential applications, RSC Adv., 6, pp. 75916–75936. 37. Ren, L., Song, Z., Liu, H., Han, Q., Zhao, C., Derby, B., Liu, Q., and Ren, L. (2018). 3D printing of materials with spatially non-linearly varying properties, Materials and Design, 156, pp. 470–479.

38. Shemelya, C. M., Rivera, A., Perez, A. T., Rocha, C., Liang, M., Yu, X., Kief, C., Alexander, D., Stegeman, J., Xin, H., Wicker, R. B., MacDonald, E., and Roberson, D. A. (2015). Mechanical, electromagnetic, and X-ray shielding characterization of a 3D printable tungsten-polycarbonate polymer matrix composite for space-based applications, J. Electronic Mater., 44(8), pp. 2598–2607. 39. Shemelya, C. M., Rosa, A. D. L., Torrado, A. R., Yu, K., Domanowski, J., Bonacuse, P. J., Martin, R. E., Juhasz, M., Hurwitz, F., Wicker, R. B., Conner, R. B., MacDonald, E., and Roberson, D. A. (2017). Anisotropy of thermal conductivity in 3D printed polymer matrix composites for space based cube satellites, Additive Manufacturing, 16, pp. 186–196.

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44. Chartier, T., Chaput, C., Doreau, F., and Loiseau, M. (2002). Stereolithography of structural complex ceramic parts, Journal of materials Science, 37(15), pp. 3141–3147. 45. Arcurate, K., Mann, B., and Wicker, R. (2010). Stereolithography of spatially controlled multi-materials bioactive poly(ethylene glycol) scaffolds, Acta Biomaterialia, 6, pp. 1047–1054.

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47. Fahrenholtz, W. G., Hilmas, G. E., Talmy, I. G., and Zaykoski, J. A. (2007). Refractory diborides of zirconium and hafnium, Journal of American Ceramic Society, 90(5), pp. 1347–1364. 48. Hwa, L. C., Rajoo, S., Noor, A. M., Ahmad, N., and Uday, M. B. (2017). Recent advances in 3D printing of porous ceramics: a review, Current Opinion in Solid State & Materials Science, 21, pp. 323–347.

49. He, L., Fei, F., Wang, W., and Song, X. (2019). Support-free ceramic stereolithography of complex overhanging structures based on elastoviscoplastic suspension feedstock, ACS Applied Materials & Interfaces, 11, pp. 18849–18857.

50. Halloran, J. W. (2016). Ceramic stereolithography: Additive manufacturing for ceramics by photopolymerization, Annual Revision of Materials Research, 46, pp. 19–40.

51. Scalera, F., Corcione, C. E., Montagna, F., Sannino, A., and Maffezzoli, A. (2014). Development and characterization of UV curable epoxy/ hydroxyapatite suspensions for stereolithography applied to bone tissue engineering, Ceramics International, 40, pp. 15455–15462.

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Chapter 5

Nano-Based Coating for Spacecraft: Antibacterial Film for Manned Application

Antonia Simonea and Cristina Balagnab aThales Alenia Space Italia S.da Antica di Collegno, 253 10100 - Torino, Italy bInstitute of Materials Physics and Engineering, Applied Science and Technology Department, Politecnico di Torino, Torino, Italy

[email protected]

The microbiological contamination onboard spacecraft and orbital stations is a relevant problem in prolonged space explorations. Microorganisms can be introduced into the spacecraft through several avenues. Crew members will be a primary source of microorganisms in confined space habitats, as a healthy human body can host at least 50 microbial species. The microorganisms in the surrounding environment, on the other hand, may contaminate the life-supporting systems, such as air recirculation, water containers, and systems for biological waste recycle and may colonize the internal structures of space modules. In particular, the contamination of textile and polymeric materials can easily form on Nanotechnology in Space Edited by Maria Letizia Terranova and Emanuela Tamburri Copyright © 2022 Jenny Stanford Publishing Pte. Ltd. ISBN 978-981-4877-54-1 (Hardcover), 978-1-003-13191-5 (eBook) www.jennystanford.com

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the surfaces a bacterial biofilm capable of progressively damaging the materials. As a matter of fact, the biofilm can cause not just health hazard but also safety problems. Hence, there is a need to provide antibacterial protections to technical textiles whenever they are used for a long time in closed volumes with high probability of diffusion of pathogenic agents, such as in inflatable space modules. The antimicrobial behavior of the nanocluster composite coating has been tested against several bacterial and fungal species discovered into the International Space Station (ISS). The compatibility with humans has been assessed by percutaneous absorption, and the mechanical behavior has been deeply checked.

5.1 Introduction

The human exploration programs include priorities for addressing crew health and environmental design related to microorganisms and focus on ensuring a safe living and working environment for crew members, as well as design elements that minimize the potential for microbial growth in and on the spacecraft. The presence of microorganisms and their potential effects have been a source of study since the advent of manned spaceflight, showing as a general tendency toward increased cell growth, biomass production, and growth rate. In addition, the aggressiveness of fungi population could be higher than on earth as demonstrated during several flight experiment [1–3]. Surface-associated bacterial communities, known as biofilms, were abundant on the Mir Space Station and continue to be a challenge on the ISS impacting flight hardware and decreasing lifetime and efficiency. In particular, long exposure missions need effective countermeasures to be implemented for the reduction of microbiological material surface susceptibility by dedicated preflight screening phase. Estimates indicate that 90% of the bacteria in cooling systems is on system surfaces since generally microbial organisms form colonies at points of low water velocity. In fact, the problem of microbial colonization of materials is even more critical when regenerative life support systems are involved, for example the systems of water regeneration from air condensate. In water pipes of these systems, specific biofilms can appear by the

Biofilm Formation

way of adhesion and consist of bacteria proper or bacteria fungal associations and the lipoprotein complex (glycocalix) produced by the associations with the inclusion of organic and inorganic water components. As ESA prepares for the longer duration spaceflights necessary to enter the era of manned planetary exploration, it is critical that countermeasures will be developed avoiding undesirable microbial interactions with the spacecraft and crewmembers. Consequently, the microbial quality control of the atmosphere, surfaces, water, food, and waste reservoirs has to be reinforced. Since the large species diversity that was obtained from the environmental samples was more pronounced in the surface samples than in the air samples, a promising countermeasure could be represented by antibacterial layers on the spacecraft’s internal surface that is in contact with human presence by an antimicrobial bulk material.

5.2 Biofilm Formation

As mentioned before, biofilm formation characterizes the totality of surfaces in contact with water; in particular, considering water intended for human consumption, pathogenic microorganisms as well as environmental biota should be considered (a). Pathogens are the most hazardous and undesired species, but it should be considered that these microorganisms are less stable in the environment in which the temperature and nutrient conditions are disadvantageous for their proliferation. On the other hand, the “protection” of such microorganisms that could be exerted by the biofilm itself should be considered a factor affecting their natural decay in water, suggesting the possibility to include in the panel of microorganisms also a thermotolerant indicator to investigate also this aspect of the problem (b). Finally, the literature reports results obtained only on specific microorganisms studied for very short contact time and neglects the simultaneous copresence of different microorganisms (c). Many studies demonstrated the formation of an indigenous population within the closed environment of the spacecraft; the bacterial and fungal species and their relative quantities changed significantly in their location. For example, in the case of Mir Space

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Station, Penicillium was initially the predominant organism in air and on surface samples, while Aspergillus was most abundant in air. % of the number of samples 60

Surface Air Water

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Figure 5.1 Occurrence of various bacterial and fungi species detected on Mir Space Station [1].

5.3 Antibacterial Surfaces The antibacterial surfaces can reduce the extent of attachment and proliferation of bacteria. They provide antibiofouling when the mechanism is based on the repulsion of bacteria from the surfaces

Antibacterial Surfaces

or act as a bactericidal if they inactivate the bacterial cells. Biofilm development involves complex processes affected by several variables such as inoculation sources, nutrient sources, flow rate, pH, and temperature. In general, attachment will occur most readily on surfaces that are rougher, more hydrophobic, and coated by surface conditioning films [6]. The presence of a water film is considered a key step in the biofilm formation. As outlined, the basic stages of bacterial adhesion are generally described by a two-stage kinetic binding model: an initial, rapid, and easily reversible interaction between the bacteria cell surface and the material surface, followed by a second stage that includes specific and nonspecific interactions between so-called adhesin proteins expressed on bacterial surface structures (fimbriae or pilli) and binding molecules on the material surface; this step is slowly reversible and often termed irreversible [7]. The biocide agents are an essential tool to control undesired biofilms, as reported in several reviews. They can be generally ascribed to three chief strategies for antibacterial surface design: Table 5.1

Biofilm formation mechanism and biocide surface

Proliferation Mechanisms Adhesion resistance by reducing the capacity of bacteria to achieve stage I and/or stage II adhesion

Antimicrobial Surfaces Newer strategies to achieve this adhesion resistance have focused on superhydrophobic surfaces (in this case, aqueous suspensions of bacteria have limited contact with the surface) [6]. Nanostructured surfaces that manifest superhydrophobic properties during water condensation are made using a variety of synthetic methods as chemical etching method. Surface modification to control bacteria colonization by means of topography, patterning, self-assembly as for bio-surface repellent topography as the spinner shark. Conditioning the surfaces by pre-adsorption of molecules claimed to increase apolar hydrophilicity, hydrophobicity or to compete with host adhesins adsorption. Heparin coatings have long been used to reduce bacterial adhesion to catheters.

(Continued)

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Table 5.1

(Continued)

Proliferation Mechanisms Biocide leaching, in which cytotoxic compounds are released and diffuse over time from a material surface, inducing death either of nearby (but nonadhered) bacteria or of adhered bacteria

Contact killing by induced death (e.g., via cell lysis) of bacteria that have adhered stably to a surface

Antimicrobial Surfaces Metals: It is well known that several metals such as silver, copper, and zinc have antibacterial properties and they can confer to materials antimicrobial properties in the form of metallic film/coating, nanoparticles, and ions. Silver ions can bind to specific chemical sites with thiol group causing cell inactivation or death, to proteins altering the structure and breaking the cell walls, to enzymes preventing their function, or to DNA interfering with cell division and replication. Silver nanoparticles, whose antimicrobial potential is mainly due to the reduced dimensions, shape, and high available surface, directly interact with the surface of the cell, inducing membrane rupture [4]. Also zinc and copper, less known than silver, are characterized by antibacterial properties, especially in the form of ions. Nano- and microstructured polymeric materials play an increasing role in the design and creation of surfaces capable of controlling systematically the attachment of living cells.

This has generally been approached via conjugation of a material surface with antibiotic functional groups. These include antimicrobial peptides, which are constrained by species and strain specificity or compounds that penetrate the cell membrane inducing cell lysis. These compounds include quaternary ammonium salts, guanidine polymers, and phosphonium salts.

Thales Alenia Space Italia, in collaboration with different partners and under internal and co-funded R&D projects, evaluated the nanostructured layers as antimicrobial surfaces and applied to: ∑ ∑ ∑ ∑

Aluminum alloys Engineering polymer, e.g., aramid-based fabric Multilayered polymer sheet Bulk polymers

Antibacterial Surfaces

In this section, more details will be provided on engineering polymers such as aramid, which are widely used for secondary elements or expandable structures in spacecraft. The biocide efficiency has been assessed by means of the following methods: ∑ Inhibition halo (contact test), with the evaluation of inhibition halo against strains, is considered a suitable method to screen the effects of an antimicrobial surface. The evaluation of inhibition halo is performed toward fungal species (see case of Candida albicans) in accordance with standards of the National Committee for Clinical Laboratory (NCCLS). As observed in Fig. 5.2, a material (L side) is not able to express an antifungal behavior, and the fungi proliferate. The other sample produces an inhibition halo in almost the whole agar.

Bacteria on Mueller-Hinton agar

Sample

Inhibition halo

Figure 5.2 Contact test for Candida albicans case of microbial sensitive material (L) and antimicrobial surface, courtesy TAS-I.

∑ Bacterial viability plate counts or colony-forming units (CFUs) to determine how many live bacteria are actually in a sample, especially when measuring growth rates or determining disinfectant effectiveness. This involves the serial dilution of bacteria samples and plating them on suitable growth media. The plates are incubated until you see visible

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colonies, usually 18–24 h. The colonies you see growing on the plate are considered to have started from one viable bacterial unit. The results are reported as CFUs. Resulting colonies are then counted, and the number of CFUs per mL was calculated. The number of CFUs is assumed to be equivalent to the number of live cells in suspension.

Figure 5.3 Example of CFU for Staphylococcus aureus, courtesy POLITO.

∑ Bio-damage: The immersion test in containing strains broths could be a viable method, even if a qualitative one to assess biodegradation. The fungal proliferation is controlled by observation of the broth conditions and turbidity after 24 h up to TBD days. After exposure, samples are removed from the broth, vortexed into physiological solution, and washed into acetone in an ultrasonic bath in order to detach fungal residue on the surface. Figure 5.4 reports the case of samples after the immersion into a broth containing C. albicans after 24 h up to 7 days. C. albicans proliferates, depositing at the bottom of the test tube, already after 24 h only in the broth. The amount of deposited fungi increases with the increase in immersion time, as showed on the left side of Fig. 5.4, while on the right is reported the case of a polymer not sensitive to fungi growth. ∑ Field emission scanning electron microscopy (FESEM) equipped with energy dispersion spectroscopy (EDS) could also be used to verify eventual damage occurring to the material for fungal adhesion after the test. ∑ Leaching test (toxicological impact on the environment) to be conducted on samples immersed in distilled water at

Nanostructured Layers

24 h 7 days

7 days

24 h

room temperature and/or artificial sweat or representative medium, picking up 1 ml of solution each time up to fixed time.

Figure 5.4 Immersion test toward Candida albicans case of microbial sensitive material (L) and antimicrobial surface (R).

5.4 Nanostructured Layers The coating composed of metallic particles, such as silver, dispersed in an inert matrix, such as silica, was studied, developed, and patented by Prof. Ferraris’s group from Politecnico di Torino in order to confer antibacterial properties to glasses, ceramics, metals, and polymers. It is deposited onto the substrates by means of the radiofrequency (RF) co-sputtering technique using simultaneously one silica target and one silver target. More details are reported in Ref. [9]. Thales Alenia Space Italia in collaboration with Politecnico di Torino participated to several co-funded projects as NABLA, STEPS and more recently MARTe. The projects aimed to validate an antibacterial coating based on nanostructured composites. The coating has been developed as application for Inflatable Manned module and well characterized by means of mechanical, thermal, morphological and antimicrobial testing.

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The use of silver nanocluster silica composite coating offers the following advantages: ∑ A porous sputtered matrix morphology, enough to promote the release of antibacterial ions, but also able to retain the nanoclusters, which are well embedded into the matrix, much more than with other coatings (usually polymeric) present in the market. Moreover, the presence of the matrix allows the decrease in the amount of silver in equal antibacterial properties, with a reduction in risk of toxicity. ∑ A high biocide effect in broad strains spectrum such as Gram positive and Gram negative bacteria, fungi.

S. aureus

As Dep

1 settimana

2 settimane

As Dep

1 settimana

2 settimane

As Dep

1 settimana

2 settimane

1 mese

3 mesi

As Dep

1 settimana

2 settimane

1 mese

3 mesi

1 settimana

2 settimane

1 mese

3 mesi

Bacllus cereus

Morganella

Klebsiella

E. coli

As Dep

1 mese

1 mese

3 mesi

3 mesi

Figure 5.5 Halo test up to 3 months (case of polymeric bulk substrates) NABLA project.

∑ High adhesion and mechanical strength also suitable for the most flexible substrates. The presence of a matrix material

Nanostructured Layers



such as silica does not induce rigidity to the substrate, and the coating thickness can be modulated from a few to a few hundred nanometers. ∑ Thermal and dimensional stability, difficult to reach with other deposition techniques. ∑ Deposition on all substrates through a simple and easy process with short deposition times. On bulk polymers

On fabric

On metals (AA2219)

On ceramic (silica glass)

Figure 5.6 Coated substrates (NABLA project).

Kev_40

S. Aureus Adhesion 2.50E+07 2.00E+07 CFU/cm2

ADHESION

Kev

1.50E+07

PROLIFERATION

1.00E+07 5.00E+06

0.00E+00

Kev

Kev_40

Figure 5.7 CFU test results; see the different behaviors from uncoated (label Kev) and coated (label Kev_40) MARTe project.

∑ The coating can withstand thermal treatment up to 450°C without changing its antibacterial properties. ∑ Antibacterial behavior has been validated after 100 cycles (up to 85% RH) and after >75% RH 3 months exposure. ∑ Leaching test conducted on distilled water/artificial sweat showed about 0.4 µg/L of silver leached medium when the limit of toxicity is less than 10 mg/L as maximum concentration for human cells.

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∑ Test of permeation into skin for 24 h demonstrated an ion release of about 1.5 µg/L when the limit of toxicity is less than 500 µg/L. In addition, the amount is concentrated on epidermis and not on dermis.

FRANZ CELL

Donor chamber

Sampling outport

OUT Skin IN

Medium Jacket

32°C water

Receptor chamber Magnet

Figure 5.8 Percutaneous adsorption test by means of Franz cell (MARTe project).

Complete Characterization of Coated Materials

5.5 Complete Characterization of Coated Materials 5.5.1 Case of Textiles In the research projects, different types of materials (metals, polymers, ceramics, etc.) have been coated with a silver nanocluster/ silica composite. Hereafter, the complete characterization on the aramid fibers will be discussed. Several pretreatments, such as thermal, washing, and plasma treatment, before coating deposition have been evaluated for improving the adhesion of the coating to the textile substrates. A thermal treatment at low temperature and a washing treatment before deposition could clean the textile material from some chemical elements used during the fiber production or weaving. On the other hand, the most favorable plasma treatment allows the activation of the fiber surfaces besides cleaning them from chemical compounds. Then all the samples were coated and analyzed by means of leaching test into water and antibacterial inhibition halo test toward Staphylococcus aureus. The solutions of the silver release (in triplicate) were analyzed by graphite furnace atomic absorption spectroscopy. Figure 5.9 shows the trend of the silver release of the samples with and without the pretreatments (washing or thermal treatment). The washing or the thermal pretreatment on textiles did not significantly influence the silver release. KEV_40

Ag release (mg/mm2)

0.006 0.005

as dep

0.004 0.003

TT+dep

0.002

wash+dep

0.001 0

0

0.5

1

1.5 days

2

2.5

3

Figure 5.9 Silver release of coated Kevlar (40 min) with and without prewashed and thermal treatment (analyzed by MARTe-partner).

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The antibacterial behavior of the Kevlar samples is evaluated by means of inhibition halo toward S. aureus. The pretreatment does not affect the antibacterial behavior of the coating. Also the behavior after 3 days of immersion in water for the release test is not significantly changed. No release

After release

TT

As dep

Kev

Washed

182

Figure 5.10 Comparison of the antibacterial halo of Kevlar samples (40 min) with and without pretreatment and after 3 days of release in water.

The coating deposited on Kevlar with the plasma pretreatment seems to not form a halo around sample (anyway, bacteria do not grow under the sample), and after the release test the halo is very small compared with that formed by the correspondent sample without plasma treatment. (a)

(b)

(c)

1cm

Figure 5.11 Inhibition halo toward Staphylococcus aureus of Kev_40 samples: (a) without plasma pretreatment, (b) with plasma pretreatment, and (c) with plasma pretreatment after 3 days of release test.

Figure 5.12 reports the photographs of inhibition halo test toward Escherichia coli (Gram negative bacterial strain) and C. albicans. Toward these two microbial strains, the effect of silver is less evident

Antibacterial Test in Broth

because some colonies also grew within the inhibition zone, making it relatively less transparent as compared to the inhibition zones observed in the case of S. aureus. Kev

40

Uncoated

Kev

Figure 5.12 Inhibition halo test toward Escherichia coli of (L) and Candida.

The antibacterial effect of the coating deposited for 40 min toward S. aureus has also been verified after 3 days of release. On the contrary, the halo formed around Kev_40 is about 0.5 mm, more pronounced than that visible for the sample before leaching test. No release

After 3 days release

Kev_40

Sample

Figure 5.13 Comparison of the inhibition halo of coated samples (deposition time 40 min) before and after 3 days of release test.

5.6 Antibacterial Test in Broth The broth dilution test has been performed only for the Kev_40 sample, and the data were compared with the uncoated textile. After 24 h of incubation for the broth dilution test, the McFarland index of the broth containing the Kev_40 sample results less than that of the uncoated sample. This indicates relatively less turbidity of the solution due to less bacterial suspension. The number of CFUs of bacteria counted both in the adhesion and in the proliferation tests is shown at the bottom of Fig. 5.14. Agar photographs are taken

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after several dilutions (six dilutions for adhesion and eight dilutions for broth). The number of CFUs for coated Kevlar® specimen is one order of magnitude less than that of uncoated samples in the adhesion test. It is worth noting that the samples were coated only on one side of the Kevlar fabric; therefore, bacterial adhesion on the uncoated side is expected. With coating on both sides of the samples, even better result is expected in the reduction in the number of CFUs in bacterial adhesion test. On the other hand, the number of CFUs in the proliferation test is approximately the same for coated and uncoated samples. This means that the coating does not prohibit the proliferation of the bacteria in the broths; however, it is able to limit the bacterial adhesion on the surface of the coated samples, which allows relatively less bacterial growth on the sample surface compared to that of uncoated samples. Kev_40

PROLIFERATION

ADHESION

Kev

S. Aureus proliferation

S. Aureus Adhesion 2.50E+07

6.00E+09

2.00E+07

5.00E+09 CFU/cm2

CFU/cm2

184

1.50E+07 1.00E+07

4.00E+09 3.00E+09 2.00E+09

5.00E+06

1.00E+09

0.00E+00

0.00E+00

Kev

Kev_40

Kev

Kev_40

Figure 5.14 Broth dilution tests: agar with colonies after dilutions and histogram of CFU regarding bacterial adhesion on the sample surface and bacterial proliferation in the broth.

Toxicological Behavior

5.7 Toxicological Behavior The skin is one of the larger organs of the human body and an important route for the uptake of many chemicals. Since nanoparticles have dimensions compatible with the dermal route, it is important to evaluate the possibility of skin permeation of silver nanoparticles (enabling a large release of silver ions responsible for a broad spectrum of antimicrobial activity) on coated textiles since they are in contact with the human skin. The aim of toxicological characterization is determining the in vitro percutaneous penetration of silver and characterizing the silver species released from textiles loaded with nano Ag in layers of full-thickness human skin by using Franz’s cell where the coated textile is in contact with human skin in the presence of sweat. The ICP-MS measures the amount of silver in the receptor phase. The samples are collected at selected time intervals: 0, 2, 4, 8, 12, 20, 24 h. At the end, epidermis and dermis of each skin sample will be also analyzed. Figure 5.15 reports all the data collected for the tested samples. Permeation profile: all tissues

Permeation (mg cm-2)

3.50

Time

Mean (mg/cm2)

2.50

0

0.00

2.00

4

0.89

8

1.07

16

1.53

20

1.71

24

3.02

3.00

1.50 1.00 0.50 0.00 0

5

10

15 Time (h)

Figure 5.15 Permeation profile.

20

25

30

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Silver permeates the skin without significant differences among textiles and is revealed in the epidermis (µg/cm2) and in the dermis (µg/cm2) at the end of the experiments without significant differences among textiles. It should be underlined that for all the samples, the silver percutaneous absorption, being at the µg level, is several orders of magnitude lower than the cytotoxicity threshold, assessed at the mg level. In addition, the small amount is concentrated on epidermis instead of derma.

5.8 Mechanical Characterization

Mechanical characterization has been performed by tensile, tear, abrasion, puncture, and flame tests before and after UV light exposure simulating indoor conditions, thermal cycling, and RH% exposure as environmental ageing.

Figure 5.16 Kevlar and Kevlar-coated samples: particular of breaking after abrasion test.

As evidenced in Fig. 5.17, the UV and TT treatments on Kevlar (not coated UT) affect the behavior, in particular, on tensile and puncture resistance, while tear does not affect at all. Mechanical characterization shows that the coating does not affect the properties even if, as expected, more susceptibility is experienced after UV exposure.

Conclusion 2000 1800 1600 1400 1200 1000 800 600 400 200 0 a

Gr

G

ON

t-L

es bt

ab Gr

Kevlar UT

R

t-T

tes

NG

LO

ar-

Te

Kevlar UT aged TT

TR

ar-

Te

Kevlar UT aged RH

e

tur

nc

Pu

Kevlar UT aged UV

Figure 5.17 Comparison of Kevlar properties before and after ageing.

5.9 Conclusion As discussed earlier, the biocide strategy to be adopted in space application is more linked to identifying materials that do not promote or can even suppress biofilm formation instead of cleaning and disinfecting regularly before bacteria attach firmly to surfaces that are largely used for food production or in water reservoirs where the use of dissolved biocide is preferred since the effect of disinfection is easily controlled by means of routine analyses performed on drinking water. On the other hand, for space application, the (limited) extension of the water distribution networks and of the exposed surfaces onto which water condenses makes the investment costs for new materials sustainable for preserving water quality and facilitating its treatment for reuse. It has been recognized that microorganism biology in space environment is different from that experienced on earth. The effects of spaceflight on biofilm development and physiology remain unclear even if planktonic cultures of microbes have indicated that spaceflight can lead to increase in growth and virulence. In addition, the characteristics of a bacterial culture in microgravity are different from those experienced on earth (e.g., absence of physical stresses, longer log phase growth, and increased resistance to antibiotics). So

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as remarked earlier, the approach is more linked to the prevention of biofilm by means of suitable non-sensitive material selected by:

∑ Longevity evaluation, in particular, considering that the observed bacteriofungal associations responsible of biofilm are more aggressive and resistant different from natural properties of individual member species [4]; ∑ Participation of human pathogens—fungi (Aspergillus niger and others) and bacilli (Pseudomonas aeruginosa)—in the biodegradation of materials can gravely impact the situation by also adding medical risks. Stenotrophomonas maltophilia, Ralstonia paucula, C. guilliermondii, and C. krusei have been identified from condensate accumulated on panels onboard the Mir Space Station.

Silver nanocluster/silica composite coatings with different thicknesses were successfully deposited on several substrates, imparting a brown color to the substrate due to the presence of silver. The morphology of the coating is similar for all the substrates with the porous and globular silica well embedding the silver nanoclusters. The EDS and XPS analysis confirm the presence of silica and silver (in the metallic state). The silver ion released into artificial sweat is low and acceptably higher than the minimum concentration required for antimicrobial efficacy (0.1 µg/L) and less than the maximum toxic concentration (10 mg/L) for human cells. The antibacterial behavior of the coated textiles is verified toward Gram positive S. aureus, Gram negative E. coli, and fungal strain C. albicans even on environmental aged substrates. The effect is more pronounced with the increase in coating thickness and toward S. aureus. Silver permeation profiles revealed in synthetic sweat in a Franz diffusion showed that for the all the coated samples and aged coated textile, the concentration detected in the soaking solution is several orders of magnitude inferior to the cytotoxic value. Release of heavy metal nanoparticles (silver, zinc, and copper) into the environment, which could affect both human safety and environment for prolonged exposure, has been taken into account. On the other hand, few and limited data are available about the waste management of silver-containing products, but a relevant effect on the environmental in the long term could be supposed. In general, wet chemical treatments have the following potential disadvantages:

References

uneven application or aggregation of Ag nanoparticles; use of reducing agents that can be toxic and undesirable; and poor control over the size of nanoparticles depending on weaker or stronger reducing agents. The physical processes such as sputtering are considered a more sustainable and reliable approach to form a composite coating of nanoclusters of silver and inert matrix. Relevant tests [10, 11] for evaluating the bacterial contamination as MARS 500, concerning the simulation of a travel to Mars (samples remained in a close environment for 520 days with the presence of crew members and with typical conditions of a space mission) and VIABLE ISS (4 years on ISS with conditions suitable for the microbial film formation) have been performed on metallic substrates (Al 2219). The results of the bacterial biofilm formation and proliferation are very promising and report a higher biocide efficacy. The idea for future developments is the evaluation of the effectiveness of Zn and Cu or a mixture of Zn, Cu, and Ag as antibacterial elements in the layer in order to reduce water susceptibility. In order to tailor the antibacterial properties of the films, the Zn, Cu, and Ag concentrations should be strictly controlled and the deposition rates of each element or compound need to be measured.

References

1. Novikova, N., De Boever, P., Poddubko, S., Deshevaya, E., Polikarpov, N., Rakova, N., Coninx, I., and Mergeay, M. (2006). Survey of environmental biocontamination on board the International Space Station, Res. Microbiol., 157: 5–12. 2. Klintworth, R., Reher, H. J., Viktorov, A. N., and Bohle, D. (1999). Biological induced corrosion of materials II: New test methods and experiences from mir station, Acta Astronaut., 44: 569–578.

3. Gu, J., Roman, M., Esselman, T., and Mitchell, R. (1998). The role of microbial biofilms in deterioration of space station candidate materials, Int. Biodeterior. Biodegrad., 41: 25–33. 4. Mendez-Vilus, A. (Ed.) (2011). Science Against Microbial Pathogens: Communicating Current Research and Technological Advances. Formatex Research Center, pp. 211–218.

5. www.innocua.net/web/download-1051/simoes-lwt.pdf.

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6. Lichter, J. A., van Vliet, K. J., and Rubner, M. F. (2009). Design of antibacterial surfaces and interfaces: Polyelectrolyte multilayers as a multifunctional platform, Macromolecules, 42: 8573–8586. 7. www.particleandfibretoxicology.com/content/7/1/8.

8. Ilyin, V. K. (2005). Microbiological status of cosmonauts during orbital space-flights on Salyut and Mir orbital stations, Acta Astronaut, 56: 839–850 9. Balagna, C., Ferraris, S., Perero, S., Miola, M., Baino, F., Battiato, A., Manfredotti, C., Vittone, E., Vernè, E., and Ferraris, M. (2015). Sputtered silver nanocluster/silica composite coatings for antibacterial applications. In: Comprehensive Guide for Nanocoatings Technology. Volume 4: Application and Commercialization, Nova Science Publishers.

10. Canganella, F., Bianconi, G., Di Mattia, E., Rettberg, P., Fani, R., Lobascio, C., Perero, S., and Poddubko, S. (2012). Microbial ecology of space confined habitats and biofilm development on space materials: The project MARS500–MICHA. In: 63rd International Astronautical Congress 2012, Naples, Italy.

11. Canganella, F., Bianconi, G., Di Mattia, E., Lobascio, C., Perero, S., and Castagnolo, D. (2012). VIABLE: A current flight experiment on ISS to investigate biocontamination and human life support in space. In 63rd International Astronautical Congress 2012, Naples, Italy.

Chapter 6

Nanotechnology in Space Economy

Tanya Scalia and Lucia Bonventre ASI – Italian Space Agency, Via del Politecnico snc, 00133 Rome, Italy [email protected]

The global nanotechnology market is expected to exceed a net value of approximately $124 billion by 2024 and to have a CAGR of around 17% between 2018 and 2025. Nanotechnologies are typically considered emerging systems with performance payoffs in the far future; however, several of these technologies have already proven to be beneficial in applications relevant to the space sector. Thanks to their significant transversal impact, nanotechnologies can be widely applied and could have a disruptive impact across many space segments such as launchers, satellite manufacturing and services, ground segment, etc. For these reasons, in this chapter, we would like to explore in more detail the synergies between nanotechnologies and the space domain. Starting from the results of a previous study on nanotechnologies in space applications, Nanotechnology in Space Edited by Maria Letizia Terranova and Emanuela Tamburri Copyright © 2022 Jenny Stanford Publishing Pte. Ltd. ISBN 978-981-4877-54-1 (Hardcover), 978-1-003-13191-5 (eBook) www.jennystanford.com

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concluded in 2010, we here explore the additional and most recent evolutions with a specific focus on patents and market trends. This type of data is useful to assess the technological trends and maturity reached.

6.1 Introduction

6.1.1 Space Economy Although there is not a universally agreed definition, we can refer to space economy as “the full range of activities and the use of the resources that create and provide value and benefits to human beings in the course of exploring, understanding, managing and utilising space” [1]. In detail, we can define space economy as “All public and private actors involved in developing and providing space-enabled products and services. It comprises a long value-added chain, starting with research and development actors and manufacturers of space hardware (e.g. launch vehicles, satellites, ground stations) and ending with the providers of space-enabled products (e.g. navigation equipment, satellite phones) and services (e.g. satellite-based meteorological services or direct-to-home video services) to final users. Thus, the space economy is larger than the traditional space sector (e.g. rockets and launchers); and it involves more and more new services and product providers (e.g. geographic information systems developers, navigation equipment sellers) who are using space systems’ capacities to create new products” [3]. The long value chain of space economy is traditionally composed of two activity streams [1]. The “upstream” segment comprises space technology, products and services, and, generally speaking, all the activities related to the exploration and the production, development, and supply of space systems, ground systems, launch activities, and related activities. “Downstream” means “all those activities based on space technology, or using a space-derived system in a space or non-space environment, that may result in an application,

Introduction

product or service to the benefit of the European economy or society” [2]. Space-technology/ product/service

Upstream space sector

Downstream sector

Space-related activities

Specific to the space sectorastronomy research, satellite, sub system, ...

Space-enabled product/ service

Which WOULD not function without satellite capacity

Activities/products/ services utilising space technology e.g. ad-hoc spin-offs, technology transfers to non-space sectors...

Figure 6.1 Upstream and downstream segments (OECD Space Forum segmentation of the space sector, 2017).

According to a recent research conducted by Bryce-Space and Technology, the global space economy was worth an estimated $360 billion in 2018 [5], having considered both revenue-generating commercial space activities and government investments in space. This is a growing trend, if compared to the estimated budget of $345 billion in 2016 [5]. According to some authoritative forecasters, space economy will continue to grow considerably in the coming decades. Goldman Sachs predicted the sector would grow to about $1 trillion. Analysts from the Bank of America Merrill Lynch predicted that the sector would surpass $3 trillion over the same period. According to the U.S. Chamber of Commerce, the space economy will reach $1.5 trillion by 2040 [7]. Several national space budgets exceeded $1 billion in 2018: among them include the United States, Europe (collectively considered), People’s Republic of China, Russian Federation, Japan, and India. The United States leads in government space spending, with an estimated $50.1 billion. Europe follows with a $11.5 billion budget, while China’s budget has been reduced to $8.5 billion. At long distance are Russia with a $3.9 billion budget, Japan with a $1.78 billion budget, and India with a $1.6 billion budget.

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The top-tier space powers—the United States, Europe, People’s Republic of China, and Russian Federation—are the world’s top geopolitical and, with the exception of Russia, economic powers [5].

Figure 6.2 Global space economy in 2018 (Bryce Space & Technology, 2018 [5]).

According to another recent report from Bryce, State of the Space Industry 2019 [6], around 87.8% of the global space economy revenues—estimated in $277 billion—are generated by activities based on satellite capacity. Indeed, commercial satellite services represent the largest share, valued at $126.5 billion, i.e., 45.6% of the estimated total revenues, split in satellite fixed services representing $17.9 billion, mobile satellite services $4 billion, satellite radio $5.8 billion, satellite broadband $2.4 billion, commercial remote sensing $2.1 billion, and satellite television services $94.2 billion. The second largest share, valued at $125.2 billion, i.e., 45% of the estimated total revenues, derives from devices and chipsets to receive positioning, navigation, and timing signals with $93.3 billion, consumer equipment such as satellite television dishes, with $18.1 billion, and other network equipment, such as very small aperture terminals and gateways, with $13.8 billion [6]. Manufacturing of space systems represents $19.5 billion, i.e., 7% of the total, while commercial launch industry represents $6.2 billion, i.e., 2.2%. These two activities form the basis for all

Introduction

other activities and are strongly affected by the digitalization of new market trends, such as the growing competition from newcomers [8].

6.1.1.1 Public actors

Although public space budgets shift over time, because of national priorities and strategies, governments have been—and still are— the main contributors of space activities, providing significant budget to public agencies and organizations, universities, research institutes, and private entities [3]. Indeed, according to Euroconsult’s Government Space Programs 2019 report, global institutional expenditures for space activities reached $70.9 billion in 2018, with a forecasted growth of $84.6 billion by 2025 [9]. In 2018, the U.S. Government confirmed its supremacy with the highest budget in absolute terms of $40.9 billion, i.e., 58% of the global market. The People’s Republic of China confirmed its secondplace ranking, with an estimated $5.83 billion budget, followed by Russian Federation with an estimated budget of $4.17 billion, France (the largest investor in Europe, with a budget of $3.15 billion), and Japan, with a budget of $3.05 billion.

6.1.1.2 New approaches to space economy

In the last two decades, however, the global landscape of space economy has evolved and, in addition to the investments of governments and public institutions, more than 400 private investors around the world—mainly venture capital firms and business angels—have started to invest in space activities, with a result of EUR14.789 billion invested in space ventures from 2000 to 2017, including EUR3.3 billion in debt financing. Around 66% of them are based in the United States. In much smaller percentages, investors come from the United Kingdom, Japan, Israel, Canada, Spain, India, and People’s Republic of China. Venture capital firms (46%) and business angels (25%) comprise two-thirds of the investors in space activities. Private equity firms (6%), corporations (19%), and lenders (4%) represent the remaining third [8].

195

40,996 United States**

Figure 6.3

Euroc nsult

3,056 Japan

PROFILES OF GOVERNMENT SPACE PROGRAMS

© Euroconsult 2019 - Authorized for release

205 272 Indonesia Australia

35 593 Taiwan South 17 Korea Laos 70 Bangladesh 45 Vietnam 30 10 Thailand Malaysia 29 Singapore

World government expenditures in 2018 for space programs—total $70.8 billion (Euroconsult, 2019 [9]).

** The United States is undersized (80%)

* Only countries with a budget of at least $10 milion appear on the map.

their contributions to ESA and Eumetsat:

61 Pakistan 77 80 276 75 Israel Morocco Algeria Turkey 48 142 177 1,493 Nigeria Egypt Iran 165 India Saudi Arabia 42 Angola 36 Qatar UAE South Africa

2,115 European Union

127 125 Sweden Norway 58 28 4,170 143 Finland Belarus 25 Netherlands47 Russia Ireland 894 Denmark 90 28 Belgium 247 United Poland Ukraine Kingdom Slovenia 73 2,151 59 50 13 Azerbaijan Kazakhstan Germany Czech Rep. 12 88 Hungary 76 3,158 Austria 62 Luxembourg France ESA & Romania 202 Eumetsat Switzerland 5,279 28 5,833 399 22 Portugal Spain Greece China

33 10 Mexico Venezuela 122 83 Nicaragua Brazil 44 Bolivia 110 Argentina Budgets indicated for European countries include

315 Canada

196

Nanotechnology in Space Economy

Introduction

Table 6.1

Volume and types of investment into space ventures Investment into space ventures [m EUR]

Investment type 2000–2005

Total 2006–2011 2012–2017 (2000–2017)

Seed Prize/ Grant

615

220

1,123

1,957

Venture Capital

228

306

4,680

5,214

Private Equity

224

946

185

1,354

Acquisition Public Offering

0 0

429

2,488

2,916

Total investment

1,067

1,900

8,494

11,461

0

3,007

321

3,328

Total with Debt

1,067

4,907

8,815

14,789

Debt Financing

0

Source: European Investment Bank [10]

19

19

In the last few years, a growing number of space-faring nations and new countries have started investing in space programs and supporting private initiatives. United Arab Emirates and Israel planned missions to Mars and to the Moon, respectively; New Zealand started to launch small satellites, and the United Kingdom allowed the launch of small satellites and suborbital activities directly from national territory with the Space Industry Act 2018. More than 80 countries have a registered satellite in orbit, launched independently or via a third party between 1957 and 2018. Among them, several African countries, such as Algeria, Angola, Egypt, Ghana, Kenya, Morocco, Nigeria, and South Africa [8].

197

Figure 6.4

0

10

20

30

40

50

60

70

80

First satellite in orbit 1st independent orbital launch

More than 80 countries with a registered satellite in orbit (OECD, 2019 [8]).

Number of countries 90

19 5 1 7 9 5 19 8 6 19 2 6 1 4 9 6 19 5 6 1 7 9 6 19 9 7 1 0 9 1971 7 19 3 7 1 4 9 7 19 5 7 1 6 9 7 1 8 9 7 19 9 8 1 0 9 8 19 1 8 1 5 9 8 1 6 9 8 19 8 9 1 0 9 9 1 2 9 9 19 3 9 19 4 9 19 5 9 1 6 9 9 19 7 9 19 8 9 2 9 0 0 20 0 0 20 1 0 2 2 0 0 20 3 0 2 5 0 0 20 6 0 20 7 0 20 8 0 20 9 1 20 0 1 2 1 0 1 20 2 1 2 3 0 1 2 4 0 1 20 5 1 20 6 1 20 7 18

198

Nanotechnology in Space Economy

Introduction

6.1.2 Space Economy and Nanotechnology

100 90 80 70 60 50 40 30 20 10 0

Growth Rate

2017

2018

Market Size 10 9 8 7 6 5 4 3 2 1 0 2023 2024

Growth Rate (%)

Market Size (RMB 100 Million)

As reported by the 2019 European Investment Bank’s report, the overall global space economy “grew by 6,7% on average per year between 2005 and 2017, almost twice the 3,5% average yearly growth of the global economy.” A significant contribution to this growing trend is due to technology advancements and innovations, such as artificial intelligence, additive manufacturing, reusable launch systems, miniaturization, nanotechnologies, etc., which allow consistent cost and time reduction for access and use of space [10]. Focusing on the nanotechnologies area, we can expect that by 2024, the global nanotechnology market will exceed a net value of approximately $124 billion [39]. As the applications of this area of science continue to increase within the electronics, energy, biomedicine, defense, automotive, and agricultural industries, the rise in government support and private-sector funding to improve this technology is also expected [39]. In addition, according to the estimates made by ENRICH [56], the global nanotechnology market is expected to have a “CAGR of around 17% between 2018 and 2025. This market trend is also reflected at the policy level between the EU and the US, which includes nanotechnologies one of the main thematic collaboration priorities.”

2019

2020

2021

2022

Figure 6.5 Global nanotechnology market (Nanotechnology Expo 2020 Market Analysis, 2019 [39]).

199

200

Nanotechnology in Space Economy

In this chapter, we would like to explore in more detail the synergies between nanotechnologies and the space sector, considering that the significant transversal nature of nanotechnologies makes them potentially applicable in any industrial sector. Although nanotechnology may seem a simple extension of miniaturization, this statement could not be more wrong. As reported by ESA [11] and The Royal Society [12], “nanotechnologies are defined by the Royal Society as the design, characterisation, production and application of structures, devices and systems by controlling shape and size at nanometre scale while nanoscience is the study of phenomena and manipulation of materials at atomic, molecular and macromolecular scales, where properties differ significantly from those at a larger scale.” This means that nanoscale science is a discipline involving different competences, such as chemistry (synthesis of purposely designed molecules), physics (e.g., quantum effects), and biology (e.g., use of DNA as template molecules or linking bridges). As such, although nanomaterials are typically considered emerging systems with performance payoffs in the far future, several of these technologies have already proven to be beneficial in applications relevant to aerospace needs. In fact, ASI has already identified the potential relevance of nanotechnology in space, identifying its potential contribution to the reduction in costs and masses of space transportation systems, increasing reliability at the same time. On this regard, ASI launched a dedicated study (I/006/10/0) specifically to “Nanotechnologies in Space Transport Systems,” which was concluded in 2010 [13]. Nanotechnology could pave the way to more compact, integrated systems and incorporate high-end sensors in spacecraft. The science of the very small material components, such as atoms and molecules, and the science of materials in their bulk configuration have been objects of study since the development of quantum mechanics. In addition, nanotechnology can offer great advantages and solutions to many engineering problems in space science. The progress made in nanotechnology opens new possibilities also for designing devices.

Introduction

Nanotechnology, in conjunction with available microelectronic techniques, offers new possibilities of system integration [13]. The space technological areas that can be directly involved by nanorelated capabilities are many and include, for example, quantum dots, which can provide novel optical behaviors, depending on their material and shape [14]. Nanoscale texturing of surfaces can lead to self-healing adhesives and self-cleaning surfaces. The unusual combination of superior mechanical, electrical, electronic, and thermal properties of carbon-based nanostructured materials can change the design paradigm of future aerospace systems by enabling lightweight, multifunctional structures. As reported by the European Investment Bank [10], intense effect “could come from nanomaterials, such as carbon nanotubes and nanoballs, graphene providing failure free structures with superior material strength characteristics to such an extent that it may be possible to build a space elevator ranging from the Earth’s surface to geostationary orbit at 36,000 km altitude and beyond. In this respect, nanotechnology takes the promise of advanced materials (e.g. super-alloys such as gamma-titanium-aluminide or metal–ceramic matrices, carbon fibre reinforced plastics, as well as combinations of CFRP and other resin materials with metals) further, to unprecedented levels”. Nanotechnologies could be used for nano-medicine as well, “to support the immune system such that it will augment the natural repair mechanism to an extent that astronauts will be able to survive radiation doses far beyond levels where today health risks start to emerge. Nano-based computers and robotics will allow faster and more robust computer and robot systems, supporting swarm intelligence and behaviour”. As reported in Table 6.2 [10], nanotechnologies are among those technologies with a significant transversal impact across the segments considered (launcher industry, satellite manufacturing, satellite services, ground equipment, national security, crewed and robotic space science and exploration, space tourism, energy, mining, processing, and assembly) and among those with the highest potential disruption.

201

Nanotechnology in Space Economy

Satellite Services

Ground Equipment

National Security

Crewed and Robotic Space Science and Exploration

Space Tourism (incl. Habitation)

Energy, Mining, Processing and Assembly

Trends impacting business model segments

Satellite Manufacturing

Table 6.2

Launcher Industry

202

Acceleration of generation change/ obsolescence

∑

∑

∑

∑

∑

∑

∑

∑

Advanced manufacturing technologies/3D printing

∑

∑

∑

∑

∑

∑

∑

∑

Micro- and nanoelectronics/ advanced telemetry and telecommand

∑

∑

∑

∑

∑

∑

∑

∑

Agile development and industrial standard implementation

∑

∑

∑

∑

∑

∑

∑

∑

Artificial intelligence (AI)/man-machine interface (MMI)

∑

∑

∑

∑

∑

∑

∑

∑

Change detection and data fusion

∑

∑

∑

∑

∑

∑

∑

∑

Digital transformation and convergence

∑

∑

∑

∑

∑

∑

∑

∑

Evolved expendable/ reusable launcher systems

∑

∑

∑

∑

∑

∑

∑

∑

Miniaturisation and nanotechnology

∑

∑

∑

∑

∑

∑

∑

∑

Optical and ubiquitous communications

∑

∑

∑

∑

∑

∑

∑

∑

Source: European Investment Bank, 2019 [10]

Methodology

6.2 Methodology In our analysis, we would like to explore the possibilities of nanotechnologies in both directions, in terms of their value in relation to the space sector and how the space-related products, enabled by nanotechnology, have an impact on terrestrial markets. Although the number of patents is not, in itself, a sufficiently accurate indicator of the capability of producing new knowledge, data on patents publications are very useful to characterize the technological profiles of the industries and to try identifying possible knowledge spillovers [58]. This is why, following the results already obtained in a previous study on the impact of nanotechnologies in space systems [13] and was funded by the ASI, we here carry on and present the results of an update of the analyses of patents that were performed in such study. The patent analysis made use of the Orbit Intelligence Patent Database tool by Questel [62] with the aim of extracting information from the patents titles, abstracts, claims, descriptions, and concepts to identify: ∑ ∑ ∑ ∑ ∑ ∑ ∑ ∑ ∑ ∑

Classifications (IPC; IPC4) Technology domains Assignees Publication numbers Publication dates (2010–19) Legal state Assignee country Family patent number Cited patents Cited literature

For our analysis, we identified possible links between the two areas, starting from the aforementioned study [13] that was funded by the ASI and concluded in 2010. Without the aim of being exhaustive, the present work has begun the process of updating the results of this study following a systematic approach. In this paper, we explore the new patents trends for the period 2010–19, since the previous study searches ended in 2010. In order to provide a systematic approach to the identification of the most recent IPR evolution in nanotechnology areas related to the space sector, we worked on

203

204

Nanotechnology in Space Economy

various combinations of keywords, using standardized taxonomies as much as possible. For what the space keywords are concerned, the reference taxonomy is the official ESA Technology Tree v3.0 [15], while the reference six (6) space domains were derived from the previous study [13]. The resulting combination of space domain keywords is reported in Table 6.3. It is interesting to notice how most of these domains were also explored in NASA’s roadmaps on nanotechnologies [16], thus providing further confirmation on the transversal impact of nanotechnologies in the space environment. Table 6.3

Space domain keywords for IPR analysis

Space Domain Main Space Keywords Engineered Materials and Structures

Spacecraft structure Inflatable structure

Deployable structure

EVA (Extra-Vehicular Activity) Pyrotechnic technology

Spacecraft (S/C) Material and Processing S/C ceramic structure Sensors, Electronics, and Devices

S/C metallic structure

On-board data system

GNC (Guidance, Navigation, and Control) Electromagnetic technology

Antenna/reflector and lens antenna/array antenna/ millimeter-wave antenna Ground data system

Automation, telepresence, and robotics Optics, MOEMS, MEMS

Optoelectronics/laser technology/detector technology/photonics

EEE components (electrical, electronic, and electromechanical)

Methodology

Space Domain Main Space Keywords Energy Storage, Power Generation, and Power Distribution

S/C electrical power Fuel cell technology

Energy storage technology

Power conditioning and distribution Thermal power

Heat transport technology

Cryogenics and refrigeration Life Support Systems

Thermal protection/insulation Heat storage and rejection Life and physical sciences

Cultivation and bioprocessing

Environmental control life support (ECLS) In-situ resource and utilization (ISRU) Biodiversity/bioburden monitoring

Payload and Satellites

Bio-barrier

Dry heat sterilization

Telemetry, tracking, and commanding (TT&C) Radio navigation

Telecommunication system

Global navigation satellite system (GNSS) Synthetic aperture radar (SAR)

Space environment Space Transportation Space weather and Propulsion S/C flight dynamics Systems Mechanisms and tribology

Actuator/damper technology Speed regulators Force sensors

Aerothermodynamics Chemical propulsion Electric propulsion Propellant

205

206

Nanotechnology in Space Economy

Similar to what has been done for the space domain, for the nanotechnology area, a systematic process was carried out, even though a specific dedicated taxonomy was not identified. However, still basing on the analysis and results of the previous study performed under ASI funding [13], the following keywords were identified and combined with those from the space domain reported in Table 6.3. Table 6.4 shows the main keywords used for the nanotechnology domain. Table 6.4

Nanotechnology domain keywords for IPR analysis

Domain

Main “Nano” Keywords

Nanotechnology

Nanostructured coating

Nanostructured material

Nanofluid

Nanodispersion Nanosensor

Nanomachine NEMS

Nanoelectronic

Nanostructured photonic device

The following paragraphs present the results obtained for the patent analysis worldwide, for the period 2010–19.

6.3 Nanotechnologies for Space Sector

6.3.1 Nanotechnologies for Engineered Materials and Structures As anticipated in the previous paragraphs, the use of nanomaterials in the space sector may significantly contribute to the improvement in performances and reduction in costs. For example, the mechanical properties of nanomaterials allow for innovative design solutions for many space structures, with enhanced optical and thermal features that may withstand the harsh environmental conditions

Nanotechnologies for Space Sector

(e.g., radiation exposure and thermal variations) to which space structures are exposed [13]. Although there is not an agreed definition of nanomaterials, according to the definition provided by the European Commission, “‘Nanomaterial’ means a natural, incidental or manufactured material containing particles, in an unbound state or as an aggregate or as an agglomerate and where, for 50 % or more of the particles in the number size distribution, one or more external dimensions is in the size range 1 nanometre (nm) to 100 nm…. A material should be considered as (a nanomaterial) where the specific surface area by volume is greater than 60 m2 /cm3 .” “…. fullerenes, graphene flakes and single wall carbon nanotubes with one or more external dimensions below 1 nm should be considered as nanomaterials” [40]. This specific domain is dedicated to materials, coatings, and structures. Such a wide range of technologies includes different nanomaterials, such as composite material with polymeric matrix, or nanostructured metals or metal matrix composites filled with nanotubes or nanofillers able to provide specific features (e.g., high Young modules, high thermal conductivity, resistance to fatigue, and to micro-cracking, etc.) [13]. In this space domain, we also considered technologies such as spacecraft structures, inflatable structures, deployable structures, extra-vehicular activity (EVA), pyrotechnic technologies, spacecraft (S/C) materials and processing, and S/C ceramic or metallic structures. In this regard, we can mention that ESA is intending to launch a dedicated tender on the topic “surface nano-texturing of materials for adhesive bonding improvement in metal/CFRP and metal/ metal structural joining” with the aim of demonstrating superior performances of adhesive bonded joints of adherents treated with plasma technology compared to adherents treated with conventional technologies. Such development still needs to be matured up to TRL 5 for space applications, i.e., adhesive bonded joint critical function verification in a relevant space environment [17]. From a European perspective, it is also worth mentioning the third stage of the EC-funded part of the Graphene (as basic structural element for CNT and fullerenes) Flagship program. It builds upon the results achieved in the ramp-up phase (2013–16) and the first core project (2016–18), and covers the period from April 2018 to March

207

Nanotechnology in Space Economy

2020 [18]. Such an initiative aims at bringing together academic and industrial researchers to take graphene from the realm of academic laboratories to the European society in the space of 10 years, thus generating economic growth, new jobs, and new opportunities [18]. In our analysis, without the aim of being exhaustive, we retrieved the previous analysis carried out in 2010 and updated it with results taking into consideration the period 2010–19, as better detailed in the following figures. According to Statista [19], the global nanotechnology market value for 2010–20 has been growing since 2010 (Fig. 6.6). It is expected to grow even more in the next period, as reported by a recent report on the smart nanomaterial market, expected to reach $3.210 million by 2025, actuating at an estimated CAGR of 67.3% from 2019 to 2025 [20]. 100

Market value in billion U.S. dollars

208

80

75.8 64.2

60 48.9 40

20

0

15.7

2010

20.1

20.7

2011

2012

22.9

2013

26

27

2014

2015

2017

2019*

2020*

© Statista 2020

Figure 6.6 Market value of nanotechnology worldwide from 2010 to 2020 (in billion USD) (Statista, 2020 [19]).

Figure 6.7 shows the results of the patent analysis carried out on the application of nanotechnologies for engineered materials and structures. The figure shows the patents trend (2010–19) and the related legal state. Please note that 2019 represents a partial picture since patents are still veiled in secrecy for 18 months before been published.

Nanotechnologies for Space Sector

120 100 80 60 40 20 0

2010

2011

2012

2013

2014

2015

2016

2017

2018

2019

(a) Publication Trend 2010–2019

19% DEAD

ALIVE

81% (b) Patents Legal State

39

11

10

10

A62C

B64C

11

Figure 6.8 Engineered materials and structures main IPC4.

B01J

C08L

16 11 A61K

G02B

16 G01N

18

21

20 F42B

A61F

21 B32B

A61M

23

22 H01M

A61B

C01B

27 H01L

C06B

C04B

27

33 B64G

42

39 C07D

Figure 6.7 Engineered materials and structures publication trend and legal state.

209

Figure 6.9

0 5

Engineered materials and structures top assignees.

Lockheed Martin

Zeon

Zogenix

Beijing University of Technology

ArianeGroup

Gear Box

Nitto Denko

Syngenta Crop Protection

North University of China

Procter & Gamble

Brilliant Light Power

Harbin Institute of Technology

Nanjing University of Science & Technology

Boeing

Ningbo University

Syngenta Participations

10

15

20

25

30

210

Nanotechnology in Space Economy

Nanotechnologies for Space Sector

Figure 6.8 shows the most relevant IPC4 for this space domain. Please refer to Annex I (Par. 5.1) for the detailed description of the relevant codes. The most frequent IPC4 in this area are related to ceramics, compounds, and spacecrafts. The most active assignees are reported in Fig. 6.9. Since this area is quite transversal to different technological domains, it is worth noticing that not only traditionally aerospace-related companies are present (e.g., Boeing, ArianeGroup, Lockheed Martin) but also companies from other industrial sectors (e.g., Procter & Gamble), and academies working on advanced materials are deeply involved. The distribution of countries for this patent segment is reported in Fig. 6.10, confirming the strong role played by the United States and People’s Republic of China. Please refer to Annex II (Par. 5.2) for the detailed description of country codes.

AU 3%

JP KR 3% GB 3% 3%

EP 3%

FR Other RU DE 2% 3% 2% 2%

CN 28%

CA 11%

US 20% WO 17%

Figure 6.10 Engineered materials and structures top countries.

Figure 6.11 shows the relation between the most frequent technology domains addressed in this space area divided by their publication country.

211

Basic materials chemistry

IN IT

Electrical machinery, apparatus, energy

US UY WO

Medical Basic materials technology chemistry Pharmaceuticals Organic fine chemistry Pharmaceuticals

JP KR PT RU SE TW

Other special machines

FR GB IL

Basic materials chemistry Organic fine chemistry

BR CA CN DE EP FI

Medical technology Transport

AU

Engineered materials and structures main technological domains by country.

Materials metallurgy

Figure 6.11

0

10

20

30

40

50

60

70

Environmental technology

212

Nanotechnology in Space Economy

Nanotechnologies for Space Sector

6.3.2 Nanotechnologies for Sensors, Electronics, and Devices For what concerns the domain of nanoelectronics, it is well known how the innovative properties of nanotubes and nanofillers can contribute to the development of innovative sensors. This also involves new semiconductor materials able to increase the performances in data storage, data processing, and data transmission [13]. This domain is considered strategic by the European Commission, which recognized nanoelectronics as a KET, “to start growing again in Europe toward a share comparable with the EU share in the world GDP” [21]. In order to translate the foreseen actions into an executable plan, the commission established “an electronics Leaders Group that proposed in 2014 to take a wider view to the value chain, include electronic system houses servicing and users and generate growth by balancing technology push and market pull” in order to drive technology progress in this area [21]. The group also recommended establishing the ECSEL JU as an essential element in implementing the European strategy in nanoelectronics. ECSEL JU represents the actors from the areas of micro- and nanoelectronics, smart integrated systems, and embedded/cyber-physical systems [22]. In this space domain, we also considered technologies such as onboard data system; electromagnetic technology; antenna/reflector and lens antenna/array antenna/millimeter-wave antenna; ground data system; automation, telepresence, and robotics; optics, MOEMS, MEMS; optoelectronics/laser technology/detector technology/ photonics, and EEE components. In this regard, we can mention that ESA has recently launched a tender dedicated to MEMS-based nanoparticle storage and release system for quantum physics platform. This activity aims at demonstrating feasibility of the concept for the mission needs of quantum physics payload platform (QPPF). This activity aims at increasing the TRL concentrating on aspects such as vacuum operation; positioning of a nanoparticle in the desired location; characterization of the adsorption forces and potentially surface treatment/engineering to reduce it; and development of diagnostics

213

214

Nanotechnology in Space Economy

to image the system, and verify the particle ejection and direction. A characterization in the space environment is also expected to evaluate the device survival and functional stability after typical launch shock and vibration levels; furthermore, a scalable loading method, appropriate for loading the order of 100,000 nanoparticles, is also expected [23]. Besides the already mentioned ECSEL initiative, it is also worth mentioning the recently ended CSA, funded under the H2020 framework, called “Nanoarchitectronics” (NTX). This CSA aims at denoting a new interdisciplinary research area at the crossroads of electromagnetics and nanoelectronics. NTX is a new technology aimed at conceiving, designing, and developing reconfigurable, adaptive, and cognitive structures, sensorial surfaces, and functional “skins” with unique physical properties and engineering applications in the whole electromagnetic spectrum, through assembling building blocks at nanoscale in hierarchical architectures [24]. Such project responds to the need of unifying concepts, methodologies, and technologies in communications, environment sensing systems, safety and security, biosensing systems, and imaging nanosystems, within a wide frequency range. The expected impact of this initiative includes the space sector specifically (Fig. 6.12). Autonomous Vehicles

Connected People

Smart Phones

Internet on Train

Drones

Biosensing

Artistic cities

Cloaking

Airplanes

Industry 4.0

Smart cities

Flexible Electronics

Energy Satellites Radar monitoring Harvesting

Health

Robotics

Radar absorbing materials

Nanoelectronics Reconfigurable antennas

Figure 6.12 Impact sectors of NTX research (NTX Nanoarchitetronics [25]).

Nanotechnologies for Space Sector

In our analysis, without the aim of being exhaustive, we retrieved the previous analysis carried out in 2010 and updated it with results taking into consideration the period 2010–19, as better detailed in the following figures. According to Allied Market Research [26], only the global sensor market was valued at $138,965 million in 2017 and is projected to reach $287,002 million by 2025, growing at a CAGR of 9.5% from 2018 to 2025. This amount is only a part of the relevant applications for nanoelectronic devices. Globally, the long-term market trend for electronic components is expected to exceed $1000 billion by 2030. In Europe, the semiconductor ecosystem employs about 250,000 people, with 2.5 million in the overall value chain of equipment, materials, semiconductors components, system integration, applications, and services, mostly in jobs requiring a high level of education [27]. The following figures show the results of the patent analysis carried out on the application of nanotechnologies for engineered materials and structures. Figure 6.13 shows the patents trend (2010–19) and the related legal state. Please note that 2019 represents a partial picture since patents are still veiled in secrecy for 18 months before been published. 300

250

200

150

100

50

0

2010

2011

2012

2013

2014

2015

2016

(a) Publication trend 2010–2019

19% DEAD

ALIVE

2017

2018

2019

215

50

0

2010

2011

2012

2013

2014

Nanotechnology in Space Economy

2015

2016

2017

2018

2019

(a) Publication trend 2010–2019

19% DEAD

ALIVE

81%

(b) Patents legal state

Figure 6.13 Sensors, electronics, and devices publication trend and legal state.

30 G06F

36 H04W

30

37 H01S

Figure 6.14 Sensors, electronics, and devices main IPC4.

H01F

37

64 G02F

C09K

65 G01S

38

67 H04B

A61B

70 G01N

G02B

H01Q

104

129

208

Figure 6.14 shows the most relevant IPC4 for this space domain. Please refer to Annex I (Par. 5.1) for the detailed description of the relevant codes. The most frequent IPC4 in this area are related to semiconductor devices, electric solid-state devices, antennas, and optics.

H01L

216

Figure 6.15

0

Sensors, electronics, and devices top assignees.

BASF

Raytheon

Korea Advanced Institute of Science & Technology

CEA-Commissariat al Energie Atomique & Aux Energies Alternatives Hangzhou Dianzi University

Sabic Global Technologies

Beijing University of Technology

Merck

MC10

Samsung Electronics

California Institute of Technology

Avago Technologies

Boeing

AT&T

University of California

Energous

5

10

15

20

25

Nanotechnologies for Space Sector 217

218

Nanotechnology in Space Economy

The most active assignees are reported in Fig. 6.15. Since this area is quite transversal to different technological domains, it is worth noticing that not only traditionally aerospace-related companies (e.g., Boeing) are present but also very large enterprises operating in the electronic sector (e.g., Samsung). The distribution of countries for this patent segment is reported in Fig. 6.16, confirming the strong role played by the United States and People’s Republic of China. Please refer to Annex II (Par. 5.2) for the detailed description of country codes. EP 3%

JP 3%

TW GB AU FR 0%Other DE 2% 1% 2% KR 2% 2% 3%

US 28%

CA 8%

CN 23%

WO 23%

Figure 6.16 Sensors, electronics, and devices top countries.

Figure 6.17 shows the relation between the most frequent technology domains addressed in this space area divided by their publication country. The general balance of the technology domains of interest, especially in the area of semiconductors, is worth noticing.

6.3.3 Nanotechnologies for Energy Storage, Power Generation, and Power Distribution

Nanotechnologies provide the potential to enhance energy efficiency across all branches of industry and to economically leverage renewable energy production through new technological solutions and optimized production technologies [63].

Figure 6.17

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80

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100

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120

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Sensors, electronics, and devices main technological domains by country.

ns

pt

ea

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140

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CA

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Nanotechnologies for Space Sector

219

220

Nanotechnology in Space Economy

In the last decades, advances in the area of nanotechnology have developed materials and techniques that could significantly improve the performance, mass, and volume of energy conversion/ storage devices. Carbon nanotubes have exhibited many interesting properties, including electrical properties that range from conducting to insulating, exceptionally high mechanical strength, and a potential to store large amounts of hydrogen and other atoms and molecules within the tubes and tube bundles. Because of these unique properties, energy conversion/storage devices incorporating nanotubes have the potential to display significant improvements in performance and energy density over the current state of the art [64]. In this space domain, we considered technologies such as cryogenics and refrigeration, electrical power, energy storage, fuel cell, heat storage and rejection, heat transport, power conditioning and distribution, thermal insulation and protection, and thermal power. Already in 2010, the ESA Working Group on MNT identified, through two nanotechnology surveys [41, 42], where the contributions of nanotechnology developments to energy storage for space transportation and satellites were clearly identified as a priority. For example, batteries could benefit from CNT electrodes to improve the energy-to-mass ratio, and in addition, some roadmaps were established where the topic of energy storage (battery) and thermal control was considered top priorities by both Thales Alenia Space and Astrium SAS [41]. Also in the nanotechnology survey carried out in 2010 by NPL [42], among the seven technologies that could have a significant impact on space applications, two were related to energy systems: (a) nano-thermoelectric materials for energy generation and (b) improved energy storage. In particular, the following areas were already identified as basis for the investigation of the improvements that nanomaterials can offer for the energy space domain: ∑ Thermal management: properties that enable control of the thermal environment of the spacecraft and need to be improved: o Thermal capacity, e.g., heat storage; o Thermal conductivity, including the ability to vary it;

Nanotechnologies for Space Sector

o Thermoelectric devices.

∑ Electric power generation:

o Energy storage properties:  Improved energy density;  Increased lifetime;  Improved efficiency of storage devices;  Increased power output over long or short periods. o Conversion system properties:  Conversion efficiency;  Improved power-to-mass ratio;  Reduced mass of the conversion system.

Based on the aforementioned roadmaps [41, 42], ESA activities have been ongoing to increase the TRL levels of the nanotechnologies identified in the energy domain. More details on the ongoing activities are available in Ref. [38]. The EU promotes different types of platforms, networks, or joint initiatives, which are relevant also to energy. Different ETPs are dedicated to such topic (e.g., biofuels, EU PV TP, TP Ocean; RHC; Smartgrids; SNETP; ETPWind; ZEP, etc.). Also within the H2020 Programme, many projects have been funded regarding the use of nanotechnologies in the energy space domain. For example, without the aim of being exhaustive, we can mention some recent initiatives such as the project ECLIPSE, coordinated by Airbus Defence & Space, which aims at focusing research activities in Europe to ensure that the harsh environmental constraints in space are taken into account for the further improvements of lithium–sulfur technology. The expected outcomes of ECLIPSE [43, 44] include the mass reduction in batteries by a factor two, cost reduction at all levels: subsystem, system, and launching costs and the maturation of the technology (TRL 5 expected at the end of the project). Another project funded in H2020, MONBASA (Monolithic Batteries for Spaceship Applications), set out to develop an energy storage solution, compliant with existing standards and regulations, reliable, with high energy efficiency, while remaining light and compact. The researchers designed new thin-film components, crucial for the next generation of high-voltage all-solid-state Li-ion rechargeable batteries [45].

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CAGR

33.9%

∑ The battery energy storage system market is expected to be valued at USD 2.0 billion in 2018 and is likely to reach USD 8.5 billion by 2023.

USD 2.0 Billion

2018

USD 8.5 Billion

∑ The increasing demand for grid flexibility, and declining prices of lithiumion batteries are driving the growth of the battery energy storage system market. ∑ Utilities is expected to hold a major share of the battery energy storage system market during the forecast period.

2023

∑ Lucrative markets such as China and India offer several growth opportunities to battery energy storage system manufacturers and providers.

(a) Battery market forecast CAGR

25.4% ∑ The Global Fuel Cell Technology Market is projected to reach USD 1,059 million by 2024 from an estimated size of USD 342 million in 2019. ∑ Effective utilization of clean energy resources is projected drive the growth of the advances in fuel cell technology market.

USD 342 Million 2019-e

USD 1,059 Million

2024-p

∑ Fuel cells are used as a substitute for natural gas-powered distributed generation end-use, which is one of the major opportunities in the advances in fuel cell technology market. ∑ Asia Pacific is projected to account for the largest share in the advances in fuel cell technology market due to the increasing application in energy generation and vehicle propulsion based on fuel cells.

(b) Fuel cells market forecast

Figure 6.18 Global battery and (MarketsandMarkets, 2019 [46, 47]).

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Just to give an idea of the relevance of the battery and fuel cell markets for terrestrial applications, we can mention the MarketsandMarkets forecasts for the battery energy storage system, which is expected to grow from $2.0 billion in 2018 to reach $8.5 billion by 2023, at a CAGR of 33.9% between 2018 and 2023. Increasing demand for grid-connected solutions is one of the major factors driving the growth of the market. Moreover, high demand for the lithium-ion technology in the renewable energy industry and declining prices of lithium-ion batteries are expected to considerably boost the market in the coming years [46].

Nanotechnologies for Space Sector

Similarly, the size of the global fuel cells market is projected to reach $1059 million by 2024 from an estimated value of $342 million in 2019, growing at a CAGR of 25.4% during the forecast period. The growth is attributed to the rising demand for clean energy generation in developed regions, increased use of fuel-cell-based vehicles, booming power sector, and augmented power generation capacities globally. The following figures show the results of the patent analysis carried out on the application of nanotechnologies for energy storage, power generation, and power distribution. Figure 6.19 shows the patents trend (2010–19) and the related legal state. Please note that 2019 represents a partial picture since patents are still veiled in secrecy for 18 months before been published. 160 140 120 100 80 60 40 20 0

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(a) Publication trend 2010–2019

15% DEAD

ALIVE

85% (b) Patents legal state

Figure 6.19 Energy storage, power generation, and power distribution publication trend and legal state.

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Nanotechnology in Space Economy

21

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123

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Figure 6.20 shows the most relevant IPC4 for this space domain. Please refer to Annex I (Par. 5.1) for the detailed description of the relevant codes. The most frequent IPC4 in this area are related to processes for the direct conversion of chemical energy into electrical energy (H01M) and semiconductor devices (H01L).

H01M

224

Figure 6.20 Energy storage, power generation, and power distribution main IPC4.

Semiconductor Energy Laboratory Boeing Aerospace Research Institute of Special Material & Process Technology California Institute of Technology Sz Dji Technology Toray Industries

BASF Harbin Institute of Technology University of Tokyo 0

20

40

60

80

100

120

Figure 6.21 Energy storage, power generation, and power distribution top assignees.

Nanotechnologies for Space Sector

The most active assignees are reported in Fig. 6.21. Since this area is quite transversal to different technological domains, it is worth noticing that not only traditionally aerospace-related companies (e.g., Boeing) are present but also very large enterprises operating in other industrial sectors (e.g., Semiconductor Energy Laboratory Co., Ltd). The distribution of countries for this patent segment is reported in Fig. 6.22, confirming the strong role played by the United States and People’s Republic of China. Please refer to Annex II (Par. 5.2) for the detailed description of country codes. CA 6%

GB Other EP RU AU KR 2% 2% 1%1% 3% DE 2% 2%

US 29%

JP 11%

WO 16%

CN 25%

Figure 6.22 Energy storage, power generation, and power distribution top countries.

Figure 6.23 shows the relation between the most frequent technology domains addressed in this space area divided by their publication country. It is worth noticing the general prevalence of the technology domains of interest, such as electrical machinery and energy, engines, pumps and turbines, materials and metallurgy, and semiconductors. In particular, we note the significant Japanese presence in the energy technology domain related to engines, pumps, and turbines.

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Nanotechnology in Space Economy

Nanotechnologies for Space Sector

6.3.4 Nanotechnologies for Life Support Systems In the domain of life support systems, already in the previous ASI study [13], the topic of how nanotechnologies could contribute in improving water treatment, wastewater, filtering, and air purification in space stations was explored. Besides the removal of toxic gases and water treatment, another important area, within the life support systems, to which nanotechnologies could significantly contribute, is related to astronauts’ health, particularly referring to long-term missions. In this regard, already since 2008, the NASA AMES Centre has been working on (a) ultra-sensitive electronic biochips based on nanoelectrode arrays made of CNT; (b) thermoelectric components implantable on humans; and (c) solid-state nanopores for genetic sequencing [13, 28]. The Institute of Space Systems at the University of Stuttgart began research on microalgae for space applications back in 2008 and started work on a photobioreactor in 2014, together with the German Aerospace Centre (DLR) and Airbus [29]. Earlier this year, the first synthetic biology experiments were carried out in space. The experiments aimed to test how well bacteria in space take in synthetic DNA inserted into their genome and how well the bacteria produce proteins, while being spun to simulate microgravity (what astronauts in the ISS encounter), lunar gravity, and Martian gravity levels. The experiments took place on the PowerCell payload aboard the German satellite mission Eu:CROPIS (Euglena and Combined Regenerative Organic-Food Production in Space) [30]. In this space domain, we considered also technologies such as life and physical sciences; cultivation and bioprocessing; ECLS; ISRU; biodiversity/bioburden monitoring; bio-barrier; and dry heat sterilization. In this regard, we can mention that ESA intends to launch a dedicated tender on the topic of biodegradable packaging material, waste inhibition and compaction technology for life support systems [31]. The topic of waste management is a critical component of manned space exploration particularly for life support systems, and in this area, as already previously highlighted, nanotechnologies could play a key role. Currently, no waste management practice has been implemented in space other than sealing organic waste materials into plastic bags, mixing with other waste items, followed

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by manual compaction and temporary storage into visiting cargo vehicles [31]. In general, accumulated wastes are discarded either as part of returning cargos (minimal amount) or incinerated during re-entry. Waste materials mainly include human metabolic wastes, organic wastes as well as packaging/padding materials used for transportation of cargo items. Today, it is estimated that 50% of pressurized cargo uploaded mass is mostly composed of packaging/ padding material, which are not and cannot be reused/recycled/ transformed into resources and become ultimate mission wastes. Furthermore, waste management does not prevent microbial proliferation, nor the growth of potentially harmful microbial pathogens and, therefore, represents biosafety risks for the crew, and a significant part of uploaded mass is wasted and waste volume reduction is very limited [31]. In order to address these issues, the identification of adequate technologies is required for inhibition and compaction of wastes generated during the mission, in view of safe, temporary storage, and which allow further processing and recovery of resources by life support systems. In addition, the EC H2020 space projects, funded under the Space COMPET call, identified this topic as an important area for European non-dependence. It is worth mentioning the results of the TIME SCALE (Technology and Innovation for development of Modular Equipment in SCalable Advanced Life support systems for space Explorations) project [32] to which the University of Stuttgart also contributed, following the experience gained in the aforementioned photobioreactor. Another interesting initiative was funded under the COMPET-Space exploration—life support program—and is coordinated by DLR on the Ground Demonstration of Plant Cultivation Technologies and Operation in Space for Safe Food Production on-board ISS and Future Human Space Exploration Vehicles and Planetary Outposts [48]. It is worth mentioning that also the ESA Life Support System Working Group confirmed the relevance of nanofiltration for the Grey Water Treatment Unit life support technology. This technology is dedicated to water recovery and recycling, aiming at producing water meeting ESA quality standards (hygiene and potentially potable) from all sources of grey waters (showers, hand wash, even kitchen water, laundry waters) and cabin condensates also making use of nanofiltration. Test bed for future lab testing includes fully

Nanotechnologies for Space Sector

automated unit available with four stages of membrane filtration (ultrafiltration/nanofiltration/two stages of reverse osmosis), using oxonia for microbial stabilization, sized for treatment of 20 l/h, aiming at recovering 95% of the water [33]. In our analysis, without the aim of being exhaustive, we retrieved the previous analysis carried out in 2010 and updated it with results taking into consideration the period 2010–19, as better detailed in the following figures, which show the results of the patent analysis carried out on the application of nanotechnologies for life support systems. Figure 6.24 shows the patents trend (2010–19) and the related legal state. Please note that 2019 represents a partial picture since patents are still veiled in secrecy for 18 months before been published. 140 120 100 80 60 40 20 0

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(a) Publication trend 2010–2019

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Figure 6.24 Life support systems publication trend and legal state.

2019

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Nanotechnology in Space Economy

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C07K

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Figure 6.25 shows the most relevant IPC4 for this space domain. Please refer to Annex I (Par. 5.1) for the detailed description of the relevant codes. The most frequent IPC4 in this area are related to preparations for medical, dental, or toilet purposes; treatment of water, wastewater, sewage, or sludge and microorganisms, or enzymes; compositions thereof; propagating, preserving, or maintaining microorganisms; mutation or genetic engineering and culture media.

A61K

230

Figure 6.25 Life support systems main IPC4.

The most active assignees are reported in Fig. 6.26. Since this area is quite transversal to different technological domains, it is worth noticing that the US company Otonomy Inc. was also founded in 2008 by the chief of otolaryngology and by the head and neck surgery at the University of California San Diego, which therefore results as a highly active area in this specific field. The distribution of countries for this patent segment is reported in Fig. 6.27, confirming the strong role played by the United States and People’s Republic of China and have a very significant role played by Canada. Please refer to Annex II (Par. 5.2) for the detailed description of country codes.

Nanotechnologies for Space Sector

Figure 6.28 shows the relation between the most frequent technology domains addressed in this space area divided by their publication country. It is worth confirming the significant participation of Canada in this field and the general worldwide distribution of most technological domains. Otonomy Xyleco University of California Tsinghua University Fujifilm Suzhou BEC Biological Technology Tego Joule Unlimited Becton Dickinson & Company Zhejiang Kanglaite Wang Hui Zhejiang University

0

5

10

20

15

25

30

Figure 6.26 Life support systems top assignees.

AU 4%

JP 3%

EP Other GB KR 2% 2% 2% 2% CN 40%

US 15%

WO 15% CA 15%

Figure 6.27 Life support systems top countries.

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Nanotechnologies for Space Sector

6.3.5 Nanotechnologies for Payload/Satellites Already in 1996, the ESA Working Group on Micro/NanoTechnologies recommended holding a Round Table on Micro/ Nano-Technologies for Space together with Industry. It was agreed that micro/nanotechnologies should be seen as a key factor within the cost reduction and miniaturization efforts. “These technologies could be a means to produce very small payloads and spacecraft with all the related benefits” [37]. As defined, micro/nanotechnologies are suitable for building distributed systems consisting of several similar or identical small units, whose combined effect would be equivalent to that of one large system unit. This type of concept is the basis, among others, of very long baseline interferometry, synthetic aperture radar, and phased arrays. Any reduction in mass, volume, and power requirements is thus desirable and will have a significant effect on cost [37]. Micro- and nanotechnologies (MNT) allow the creation of functional devices, as reported by ESCIES “extremely small dimensions; up to less than one-hundredth of the width of a human hair for nanotechnologies. The incorporation of MNT’s into spacecraft design has a number of benefits including possible reduction in mass, low power consumption, low volume, high reliability and low cost and it is anticipated that these technologies will form an integral part of space systems. A major attraction of MNT is its ability to produce devices of significantly improved performance such as accuracy, operating speed and complexity. This is true, particularly for micromechanical devices when associated with embedded analogue and/or digital circuitry” [38]. The satellite payloads (GEO, MEO, and LEO) market is estimated to be $11.84 billion in 2017 and is projected to reach $18.15 billion by 2022, at a CAGR of 8.92% during the forecast period [34]. At the same time, we are witnessing a significant increase in the demand for nano/microsatellites, as confirmed by most market researches. For example, as it can be seen in Fig. 6.29, SpaceWorks’ [35] 2019 market forecast report on nano/microsatellites confirms the following: “SpaceWorks’, 2019 projections have been revised to reflect the changing attitudes of civil and military operators, as well as the rapid progress of commercial satellite IoT ventures Increasing global demand in down-stream data analytics and communications

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markets continues to drive growth in the nano /microsatellite segment, but concerns remain about how many operators demand can realistically support SpaceWorks predicts 294 nano /microsatellites will be launched in 2019 representing a 17 increase from 2018” [35]. 100%

Civil operators Military operators Commercial operators

Percentage of satellites

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Future (2019–2023)

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FCARS

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2%

Communications 27% 27%

41% Historical (2014–2018)

10% Scientific

Future (2019–2023)

57%

Technology

(b) Satellite application trends

20% 10% Scientific

Figure 6.29 Nano-/microsatellites (1–50 kg) (SpaceWorks [35]).

Confirming the relevant interest on satellite payload market, we can mention the initiative of the Aerospace Corporation’s AeroCube-14 CubeSats, launched in November 2019 and loaded with nanotechnology payloads to conduct modular experiments and other research. AeroCube-14’s experiments include nanotechnology payloads that will test new and emerging materials, including structural materials and thermal straps, in a space environment [36].

Nanotechnologies for Space Sector

Based on payload segment, the recent advent of smallsats, spacecraft that weigh anywhere from an ounce to as much as a few hundred pounds, has upended that status quo. The same advances in electronics and communications technologies are allowing scientists and engineers to design smallsats and coordinated networks of multiple smallsats (known as smallsat constellations). These satellites typically weighing anything between 1 and 10 kg are made of off-the-shelf parts, and manufactured in just a matter of days, thus lowering the barrier to entry for commercial entities from complexity, timing, and cost perspective. Increasing the intelligence of satellites and concepts such as space data highway, machine learning, and blockchain are revolutionizing the industry. SSL is working with NASA and DARPA for the development of satelliteservicing technologies to provide operators with flexibility to inspect, augment, refuel, and repair satellites in GEO and LEO orbits. Shared satellite platform arrangements such as CondoSats, PODS (Payload Orbital Delivery System), and hosted payloads are providing more frequent and cost-effective access to space, and companies [53]. In this space domain, we also considered technologies such as TT&C, radio navigation, telecommunication system, GNSS, and SAR. Nanotechnology has been recognized by the EC as a KET and has great potential for addressing societal challenges, including energy supply and health care, not only space needs. Nonetheless, the use of nanomaterials also raises safety concerns, which need to be addressed in a Europe-wide regulatory context. EU regulations on consumer products such as food, cosmetics, and biocides have specific provisions for nanomaterials. Such provisions for nanomaterials, e.g., ingredient labelling, have to be based on a regular definition of the term “nanomaterial” [49]. Details on how nanomaterials are covered by EU legislation such as the chemicals legislation (REACH Regulation) are described in the Commission’s Second Regulatory Review on Nanomaterials [50]. In our analysis, without the aim of being exhaustive, we retrieved the previous analysis carried out in 2010 and updated it with results taking into consideration the period 2010–19, as better detailed in the following figures, which show the results of the patent analysis carried out on the application of nanotechnologies for satellite payloads.

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Figure 6.30 shows the patents trend (2010–19) and the related legal state. Please note that 2019 represents a partial picture since patents are still veiled in secrecy for 18 months before been published. 100 90 80 70 60 50 40 30 20 10 0

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(a) Publication trend 2010–2019

17% DEAD

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Figure 6.30 Payload/satellites publication trend and legal state.

Figure 6.31 shows the most relevant IPC4 for this space domain. Please refer to Annex I (Par. 5.1) for the detailed description of the relevant codes. The most frequent IPC4 in this area are related to radio direction finding, radio navigation, and the capability of determining distance or velocity by the use of radio waves; locating or presence-detecting by the use of the reflection or re-radiation of radio waves; analogous arrangements using other waves and wireless communication networks.

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Nanotechnologies for Space Sector

Figure 6.31 Payload/satellites main IPC4.

The most active assignees are reported in Fig. 6.32. Considering that this area has keywords related to communication systems, it is not surprising that the resulting assignees include worldwide players such as Qualcomm, Samsung, and AT&T Mobility. Qualcomm Samsung Electronics AT&T Mobility Tego Locata Texas Instruments Mitsubishi Electric GM Global Technology Operations Skyhook Holding Ericsson Intel Intuitive Surgical Henan Zhilian Huanyu IP Operation Iceberg Luxembourg Microsoft Technology Licensing AT&T Sony Nextnav

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Figure 6.32 Payload/satellites top assignees.

The distribution of countries for this patent segment is reported in Fig. 6.33, confirming the strong role played by the United States and People’s Republic of China and with a significant role played by Canada. Please refer to Annex II (Par. 5.2) for the detailed description of country codes.

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EP 5%

JP KR DE 3% 2% GB 3% AU 3% 3%

Other 6% US 35%

CA 10%

CN 12%

WO 18%

Figure 6.33 Payload/satellites top countries.

Figure 6.34 shows the relation between the most frequent technology domains addressed in this space area divided by their publication country. It is worth confirming the significant participation of Canada in this field and the well distributed presence in the topics of tele and digital communication.

6.3.6 Nanotechnologies for Space Transportation and Propulsion Systems

The opportunities brought by nanotechnologies to space transportation systems have been identified as soon as nanotechnologies were started to be explored. In fact, the nanotechnology survey carried out for ESA [41] identified application in thermal barrier and wear-resistant coatings, sensors that can perform at high temperature and other physical and chemical sensors, sensors that can perform safety inspection more cost effectively, quickly, and efficiently than the present procedures, composites, wear-resistant tires, and improved avionics. For launchers, the main application where these improvements could be of great interest in coming years (short term) are electrical conductivity; damage detection and tolerance; thermal protection systems (C/C and C/phenolic); structural composites (thermoplastic- and thermoset-based composites); and nanosensors [41].

BR

CA CN

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Measurement Digital Digital Computer Telecommunication technology communications Telecommunications communication Telecommunications

AU

Payload/satellites main technological domains by country.

Measurement

Figure 6.34

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Nanotechnologies for Space Sector 239

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It is also worth noticing how nanopropellants have the potential to reach higher combustion efficiency. The use of nanopropellants is game changing because they can provide a 15% to 40% increase in efficiency, resulting in a decrease in system weight. In addition, nanopropellants can be multifunctional, i.e., the propellant can act as a structural component that is consumed, as well as providing energy storage for in-space power [51]. Also the EC promoted the development of advanced solid rocket propellants making use of nanoparticles, such as Al nanoparticles, as was started in the EC FP7 funded project HISP (High Performance Solid Propellants for In-Space Propulsion) [52], coordinated by FOI. Among others, the project had the objective of developing a highperformance solid propellant by using the new high energy density oxidizer ammonium dinitramide (and), an energetic binder based on glycidyl azide polymer (GAP), and high energy density fuels such as nano-aluminum. Also the ESA has supported this approach to innovative propellants based on nanoparticles, as shown in the Experimental Modelling of Alumina Particulates in Solid Booster project [55, 56]. The research carried out showed that by replacing the currently used micrometric Al powders (30–50 mum nominal size) with nanometric powders (0.1–0.2 mum), the burning rate increases (up to 100%), different aluminum agglomeration modified the flame structure, and the condensed combustion products featured different aluminum oxidation histories. The condensed combustion products were investigated, and the results obtained point out that the high reactivity of nano-aluminum powders offers an efficient way to increase rocket propellant performance [54]. In this space domain, we also considered technologies such as space environment; space weather; S/C flight dynamics; mechanisms and tribology; actuator/damper technology; speed regulators; force sensors; aerothermodynamics; chemical and electric propulsion and propellant. The market for space launch services was valued at $8.67 billion in 2016 and is projected to reach $27.18 billion by 2025, at a CAGR of 15.01% during the forecast period, according to MarketsandMarkets. The base year considered for the study is 2016, and the forecast period is from 2017 to 2025.

Nanotechnologies for Space Sector

According to ResearchandMarkets [53], the global market for space launch services is accounted for $9.68 billion in 2017 and expected to grow at a CAGR of 16% to reach $36.99 billion by 2026. The demand for Commercial Non-Geostationary Satellite Orbit (NGSO) launches, small satellites, advancements in Reusable Launch Vehicle (RLV) technology, increase in space exploration missions are a few factors impacting the market growth. In addition, “the trend toward manufacturers forming consolidated service companies are also involved in the emergence of new international satellite communications services along with changing regulatory framework, demand for micro-launcher compatible payload delivery, new entrants in the satellite business want quick access to space as well as institutions are backing the development of micro-launchers which will greatly impact the market.” This aspect is also highlighted in Section 6.3.5 (see Fig. 6.29). “The limited availability of appropriate launch systems will curb the deployment pace of small satellites. However, lack of operational measures for the disposal of orbital debris and limited intellectual resources and lack of skilled workforce pose challenge for industry” [53]. The following figures show the results of the patent analysis carried out on the application of nanotechnologies for engineered materials and structures. Figure 6.35 shows the patents trend (2010–19) and the related legal state. Please note that 2019 represents a partial picture since patents are still veiled in secrecy for 18 months before been published. 140 120 100 80 60 40 20 0

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Nanotechnology in Space Economy

18% DEAD

ALIVE

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Figure 6.35 Space transportation and propulsion systems publication trend and legal state.

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Figure 6.36 shows the most relevant IPC4 for this space domain. Please refer to Annex I (Par. 5.1) for the detailed description of the relevant codes. The most frequent IPC4 in this area are related to spacecrafts and vehicles and to equipment producing a reactive propulsive thrust.

B64G

242

Figure 6.36 Space transportation and propulsion systems main IPC4.

The most active assignees are reported in Fig. 6.37. Considering that this area has quite specific keywords, it is not surprising to find worldwide large organizations such as Boeing and NASA. The distribution of countries for this patent segment is reported in Fig. 6.38, strongly dominated by the United States and People’s Republic of China. Please refer to Annex II (Par. 5.2) for the detailed description of country codes.

Nanotechnologies for Space Sector

Boeing BASF Beihang University of Aeronautics & Astronautics GM Global Technology Operations Northwestern Polytechnical University Southwest State University Nanjing University of Aeronautics & Astronautics (NUAA) NASA-National Aeronautics & Space Administration Nanjing University of Science & Technology Harbin Institute of Technology Tego Changzhou Feiman Biotechnology Beijing Institute of Control Engineering Semiconductor Energy Laboratory US Navy National University of Defense Technology 0

5

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30

Figure 6.37 Space transportation and propulsion systems top assignees.

DE 3%

FR Other KR AU GB EP 2% 2% 1%1% 3% RU 3% 3%

CN 30%

JP 8%

CA 8%

WO 16%

US 20%

Figure 6.38 Space transportation and propulsion systems top countries.

Figure 6.39 shows the relation between the most frequent technology domains addressed in this space area divided by their publication country. It is worth confirming the significant impact of China and the United States on most of the technological domains examined.

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Nanotechnology in Space Economy

Conclusion and Perspectives

6.4 Conclusion and Perspectives Nanotechnologies cover a wide range of scientific knowledge since their applications may include nanoparticles, nanocomposites, nanostructures, etc. and may be applied in life science and health, in energy conversion, storage systems, in environmental applications, chemistry (agro-food, biotechnology, and consumer goods), textiles (fabrics and fibers), and security, just to mention a few [13]. It is worth noticing that the global nanotechnology market is expected to have a “CAGR of around 17% between 2018 and 2025. This market trend is also reflected at the policy level between the EU and the US, which includes nanotechnologies one of the main thematic collaboration priorities” [57]. According to the EC, it was estimated that nanotechnologies in 2015 was worth more than $1 trillion (EUR 900 billion) and is still growing [57]. Although the number of patents is not in itself a sufficiently accurate indicator of the capability of producing new knowledge, data on publications of patents are very useful to characterize the technological profiles of the industries and to identify possible knowledge spillovers [58]. It is rather difficult to forecast emerging technologies when there is little or no historical data available. In such cases, the use of bibliometrics and patent analysis has provided useful data. This type of data has been often used and demonstrated to be useful to identify the trends of emerging technologies, especially when integrating the use of bibliometrics and patent analysis into wellknown technology forecasting tools such as scenario planning, growth curves, and analogies [59]. System dynamics is also used to be able to model the dynamic ecosystem of the technologies and their diffusion. This kind of methodology has also been used since such data might signal the kinds of product and processes foreign companies are planning to introduce in a specific country, as for example highlighted in Ref. [60], which presents an analysis of Indian patent data and could provide firms with information that could help them with their strategic planning efforts. An analysis of patents accepted by the Indian patent office in the field of electric communication techniques over the last 5 years has been carried out with the intention of assessing whether data available in these

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Nanotechnology in Space Economy

patent applications would enable Indian firms to accurately assess technological advances and innovations occurring in this sector. It is also compared with data on patents granted by the US Patent Office. Public policy measures that could make Indian patent data more useful for Indian firms are also suggested [60]. The analysis of patents trend can also contribute to the evaluation of the evolution of nanotechnology development in different countries, as done in Ref. [61] for the United States and China. This study, in fact, uses patent analysis to identify the differences between nanotechnology topics addressed in the USPTO and CNIPA patents, key players in nanotechnology fields in both domestic and foreign markets, and the player collaboration patterns. The patent analysis is crossed with bibliographic, content, and social network analyses [61]. In this chapter, we limited ourselves to patent analysis, but the next actions include the performance of complementary analyses, such as bibliometric, detailed market trends, and possibly interviews with key players. In the following figures, we summarize the results of the patent analysis obtained for the six space domains identified as the most relevant for applications of nanotechnologies [13], namely: 1. 2. 3. 4. 5. 6.

Engineered materials and structures Sensors, electronics, and devices Energy storage, power generation, and power distribution Life support systems Payload/satellites Space transportation and propulsion systems

In these space technology domains, patent analysis carried out confirmed that nanotechnologies could have a significant impact on all of them, even though with different development periods. The contribution of nanotechnologies to space technologies is potentially disruptive in terms of mass and consequent cost reduction, capability of innovating to be able to realize more challenging robotic and human space missions. Figure 6.40 shows the trend in publication of patents for the period 2010–19. As already noted in the previous paragraphs, 2019 represents a partial picture since patents are still veiled in secrecy for 18 months before been published. Therefore, we can generally identify an increasing trend in all areas.

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Conclusion and Perspectives 247

Nanotechnology in Space Economy

Figure 6.41 aims at providing a general overview of all the space technological domains taken into consideration, on who are the most active players in terms of IPR. Here it is worth noticing that as already pointed out in the study carried out in 2010 [13], the University of California and the California Institute of Technology are among the most active (>30 patents) organizations. 120

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Syngenta Participations

Tego

GM Global Technology Operations

California Institute of Technology

BASF

University of California

Harbin Institute of Technology

Qualcomm

Samsung Electronics

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Semiconductor Energy Laboratory

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Figure 6.41 Top assignees by space domain (>30 patents).

Figure 6.42 shows the other main assignees (