SHS-composite materials: multi-authored monograph 9786010425583

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AL-FARABI KAZAKH NATIONAL UNIVERSITY

SHS-COMPOSITE MATERIALS Multi-authored monograph

Edited by Professor Z.A. Mansurov

Almaty «Qazaq university» 2017 1

UDC 541.124; 542.91 S 240 Recommended for publication by the Academic Council (Protocol № 6 dated by 27.02.2017) and the decision of the Editorial-Publishing Council al-Faraby KazNU (Protocol №3 dated by 17.03.2017) Edited by prof. Z.A. Mansurov Editorial team Doctor of Chemistry, Prof. R.G. Abdukarimova Doctor of Chemistry, Prof. G.I. Ksandopulo Reviewers: Doctor of Technical Sciences V.M. Muhin Ph.D. in Chemistry M. Nazhipkyzy I express thanks to Ph.D-student Meiram Atamanov for his assistance in preparation of this multi-authored monograph for publication.

S 240 SHS-composite materials: multi-authored monograph / Z.A. Mansurov, A.G. Merzhanov, G.I. Ksandopulo, A.N. Baideldinova et al.; еd. by prof. Z.A. Mansurov. – Almaty: Qazaq University, 2017. – 340 p. ISBN 978-601-04-2558-3 In this multi-authored monograph "SHS composite materials" there are published scientific reviews of scientists from the Institute of Combustion Problems and foreign partners working in the field of self-propagating hightemperature synthesis (SHS). These articles summarizing some researches and developments as well as current state of the question and prospects of SHS are under discussion. The publication is dedicated to the memory of outstanding Russian scientist of world renown, Doctor of Physical and Mathematical Sciences, professor, academician, a member of Russian Academy of Sciences, director - founder of the Institute of Structural Macrokinetics and Materials Science of the Russian Academy of Sciences A.G. Merzhanov. Who is the founder of new scientific direction «Structural macrokinetics» and selfpropagating high-temperature synthesis method (SHS). This monograph can be useful to a wide range of professionals involved in SHS field as well as bachelors, masters and Ph.D students and doctors.

UDC 541.124; 542.91 ISBN 978-601-04-2558-3

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© Mansurov Z.A. et al., 2017 © Al-Farabi KazNU, 2017

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ONTENTS

Z.A. Mansurov Preface A.G. Merzhanov SHS on the pathway to industrialization

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G.I. Ksandopulo, A.N. Baideldinova The SHS process in the layered systems

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A. Saukhimov, G.A. Almanov, M. Hobosyan, C. Dannangoda, S.E. Kumekov and K.S. Martirosyan The study of the structural and physical properties of yttrium ferrite fabricated by Solution Combustion Synthesis (SCS)

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R.G. Abdulkarimova, Z.A. Mansurov SH-synthesis of carbon containing composition materials in SiO2–Al–C system

120

Zh. Yermekova, Z.A. Mansurov and A.S. Mukasyan Obtaining nanopowder of silicon and silicon carbide by SHS method

155

Z.А.Mansurov, N.N. Моfa Mechanochemical and ultrasonic treatment of mineral raw materials is a method of controlling the process of technological combustion and producing SHS-composites of different purposes

173

S.M. Fomenko, Е.Е. Dilmuhambetov, Z.А. Mansurov Technology of refractory materials based on SHS in metal-oxide systems

212

А.V. Mironenko, G.B. Aldashukurova, Zh.B. Kudyarova, А.B. Kazieva, Z.А. Mansurov The development of nanostructured catalyst systems on the basis of fiberglass for manufacturing processes of light hydrocarbons

258

D.S. Raimkhanova, Z.A. Mansurov, A.S. Rogachev, O. Odavara, R.G. Abdulkarimova The peculiarities of self-propagating high temperature synthesis and structure formation of ceramic materials TiB2-Al2O3 and CrB2- Al2O3.

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PREFACE In memory of academician Alexander Grigoryevich Merzhanov

In this multi-authored monograph «SHS composite materials» there are published scientific reviews of scientists from the Institute of Combustion Problems and foreign partners working in the field of self-propagating high-temperature synthesis (SHS). These articles summarizing some researches and developments as well as current state of the question and prospects of SHS are under discussion. In modern interpretation the SHS – it’s a sub-type of combustion, wherein the valuable solid substances (materials) are formed. The development of work is based on scientific discovery of Soviet scientists such as A.G. Merzhanov, V.M. Shkiro and I.P. Borovinskaya «The Phenomenon of the Wave Localization of Solid-State Autoretarding Reactions» (non-scientific name «The phenomenon of solid flame») made in 1967. The publication is dedicated to the memory outstanding Russian scientist of world renown, Doctor of Physical and Mathematical Sciences, professor, academician, a member of Russian Academy of Sciences, director-founder of the Institute of Structural Macrokinetics and Materials Science of the Russian Academy of Sciences A.G. Merzhanov. Who is the founder of new scientific direction «Structural macrokinetics» and self-propagating high-temperature synthesis method (SHS). 4

During his distinguished career, Alexander Grigoryevich Merzhanov was awarded many major prizes, including State Prizes of Russian Federation, two Orders of Labor Banner, a State diploma for discovery of solid flame, Zeldovich Golden Medal for achievements in combustion theory, and many other governmental and academic honorable distinctions. A.G. Merzhanov – is a prominent scientist in the field of physical chemistry, including general and structural macrokinetics. Under his direct participation and guidance it was created a thermal model of combustion processes and explosion in condensed medium, ingenious research methods of kinetics and nonisothermal processes were developed. The mechanism of chemical and physical and chemical transformations in systems - solid-solid, solid-gas at high temperatures as well as new directions in macroscopic kinetics (gasless and filtration combustion, structural macrokinetics etc.) were developed. In 1967 under the direction of A.G. Merzhanov new phenomenon «solid flame combustion» was opened. Alexander Grigoryevich has estimated the scope and prospects of the discovery as the basis of original highly-economical production technology of inorganic compounds and composite materials is called selfpropagating high-temperature synthesis (SHS). Advantages of new synthetic method based on the use of combustion were apparent as compared to conventional furnace technology. This synthesis process lasts several seconds (instead of hours), the technology is essentially simplified and there is no need for complex and expensive equipment. Using of combustion is particularly preferred for the synthesis of many high-melting compounds and materials such as ceramics, cermets, hard metals, coatings and other. A.G. Merazhnov has formulated the main principles, objectives and approaches of fundamental theory of SHS, he called it structural macrokinetics. As a result of solution of structure formation process of SHS the technological capabilities of SHS were determined and manufacturing base of this technology is established. Special attention should be paid to the work «Development concept of SHS as a field of scientific and technical progress», which was made under the editorship of Academician A.G. Merzhanov, this 5

work includes conceptual articles of Russian and foreign scientists working in the field of SHS. These articles includes the results and developments that performed in particular direction, the current state of the question is discussed, and above all, some authors’ views are sets out concerning what shout be done and what problems remain unsolved today. Academician A.G. Merzhanov call attention to the fact that “the purpose of publication this book was twofold”. First of all, we hope to help the people who are working in the field of SHS to get oriented correctly concerning formation of their interests and current activities in this area, secondly, we are trying to draw the attention of those who are responsible for science and technology development, as well as progressively developing field which was originated in Russia and at large-scale development can be benefited for its economy. A.G. Merzhanov paid special attention to the development of international relations and enhancement of cooperation with the scientists from different countries. The most significant international project was the Spanish-American project «Prometheus». The world's first fully automated factory for the production of certain powders on industrial SHS technology was built in Spain. A.G. Merzhanov is the author and co-author of more than 800 scientific works, inventions and scientific discovery «Spontaneous extension of combustion front in solid phase, without formation of liquid and gaseous products» (solid flame) № 281, 1967. One major result of A.G. Merzhanov during his active creative activity was the establishment of scientific school which has more than 40 doctors and 150 candidates of sciences. Many his students become the leaders and prominent specialists in various fields of chemistry, physics, mechanics, catalysis, chemical kinetics, materials science and other sciences. It is difficult to overestimate the role of A.G. Merzhanov in the development of combustion theory and the development of SHS technology in Kazakhstan, Al-Farabi Kazakh National University. With his support, Professor G.I. Ksandopulo has organized the SHS Centre, which later became the Institute of Combustion Problems (IPG). Since its foundation, the institute has strong ties with different enterprises of Kazakhstan and the former Soviet Union. 6

Alexander Grigoryevich organized the All-Union Symposium on the macroscopic kinetics and chemical gasdynamics (1984) in Almaty city, the First International Symposium on SHS (1991), brought together leading scientists from leading research centers. This had contributed to raise the research at high level in the field of SHS technology in Kazakhstan, at the Institute of Combustion Problems and organize laboratory for SHS-refractories. Within the walls of this laboratory, the effective refractory materials on the basis of ore mining waste from Kazakhstan have been developed, for example, the refractory materials «Furnon» in the form of dry mixes, which harden the aggregates and extend their service life, which gives an economic benefit in tens or hundreds of thousands of dollars. These materials were introduced in 1986-1995. and they are used for today in many industries such as cement industry, metallurgy, oil refining industry of the former USSR, Italy, Germany, England, the United States and Cuba. The refractory production is demanded on steady rising market – the large and financially stable companies in Kazakhstan and the CIS. As a result of these developments the Kazakhstan scientists such as M.B. Ismailov and G.G. Gladun (G.G. Ksandopulo) have defended their doctoral dissertations in Academic Council of Institute of Structural Macrokinetics and Materials Science of the Russian Academy of Sciences is headed by the academician A.G. Merzhanov, in Chernogolovka city. Also, there are defended several Candidate's dissertations.Thus, in Kazakhstan there is created its own new line of SHS technology. The Monograph consists of seven chapters, which are devoted to: In review of A. G. Merzhanov which was presented in the book «Chemistry and chemical technology. Modern problems: «Annual publication of the scientists – chemists» in 2014. «SHS on the way toward industrialization» has a conceptual and scientific nature. Represented concerning SHS research over the past 30 years. The stages of SHS industrialization were considered, investigations of processes and products, as well as process regulations, technological developments, the partners’ contribution to the development of method. The effectiveness of SHS development at different direction is showed. 7

At the celebration of the 80th anniversary of academician of RAS, founder of the Institute of Structural Macrokinetics and Materials Science, A.G. Merzhanov

In article of G.I. Ksandopulo and A.N. Baydeldinov «SHS in layered systems» a review on identification of key factors are influencing on macrokinetics combustion characteristics in layered systems is presented; it was established the nature of this influence, the conditions of layers formation, acceptance limits of initial parameters change of the synthesis process for obtaining of the material with desired composition. In article of K.S. Martirosyan, A.A. Sauhimov, S.E. Kumekova et al., "The study of structural and physical properties of yttrium ferrite is prepared by Solution Combustion Synthesis method (SCS)» there is described the preparation of tertiary oxide of the system YFe-O by SCS method on the basis of yttrium nitrate, ferrous nitrate and different addition of glycine in the form of combustion substance. In review of R.G. Abdulkarimova «SH-synthesis of carbonaceous composite materials in the system SiO2 - Al – C» the possibility for obtaining of multi-component refractory composite materials based on quartziferous raw materials by SHS method is investigated. In review of Zh. S. Ermekova, A.S. Mukasyan, Z.A. Mansurov “Obtaining of of silicon and silicon carbide nanopowders by selfpropagating high-temperature synthesis SHS” there are considered 8

the regularities of solid-phase combustion of chemical systems Mg + SiO2, Mg + SiO2 + C and synthesis processes of silicon and silicon carbide on their basis. In the article of N.N. Mofa «Mechanochemical and ultrasonic traetment of mineral raw materials – control method of technological combustion process and obtaining of SHS composites for different purposes» there are results of pre-activated materials use for production of ceramic systems for various applications, including the SH-synthesis. In review of S.M. Fomenko, E.E. Dilmuhambetova, Z.A. Mansurov “SHS-technology of refractory materials - achievements and prospects” there are presented macrokinetics regularities of aluminothermal combustion in SHS regime of chrome oxide, silicon, iron, constituting the active components of SHS refractories. In article of A.V. Mironenko, G.B. Aldashukurova, Zh.B. Kudyarova, A.B. Kaziyeva, Z.A. Mansurov «The development of nanostructured catalytic systems on the basis of fiberglass for recycling processes of light hydrocarbons» there is considered the construction of nano-dispersed catalysts for carbon dioxide reforming of methane by the forming of low-percentage Co-Ni- и Co-Ni-Mg contacts at supporter from fiberglass. In review of D.S. Raimhanova, Z.A. Mansurov, A.S. Rogachev, O. Odawara, R.G. Abdulkarimova «The peculiarities of selfpropagating high temperature synthesis and structure formation of ceramic materials TiB2-Al2O3 and CrB2-Al2O3» there are observed principal regularities of aluminothermal combustion of boroncontaining systems, features of the phase and structural transformations in combustion wave that determines the properties of synthesized materials We hope the materials that presented in this monograph will be useful for a wide range of the scientific community. Professor of Department of Chemical Physics and Material Science, General Director of the Institute of Combustion Problems Z.A. Mansurov

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SHS ON THE PATHWAY TO INDUSTRIALIZATION A.G. Merzhanov Institute of Structural Macrokinetics and Materials Science, Russian Academy of Sciences, Chernogolovka, Moscow, 142432 Russia ABSTRACT The problem of industrialization of SHS is considered. Prerequisites for SHS commercialization and entering the market are analyzed. Some problems concerning development of SHS-based production as well as special-purpose SHS facilities are discussed. Examples of successful implementation of SHS-based production methods in different countries are given. Key words: SHS, production, implementation, commercialization 1. INTRODUCTION For the time being, SHS represents an individual area of R & D with a developed infrastructure [1, 2]. Research in the field is being carried in various countries over a wide front–from the fundamentals of solid-flame combustion to industrial-scale production of inorganic materials (see reviews [3–7]). The objectives of SHS R&D include:  mechanism of high-temperature chemical reactions (especially in heterogeneous media);  heat release in chemical reactions and heat transfer;  reaction front propagation and structure of the combustion wave;  dynamics of products formation and their structuring;  experimental techniques for investigating rapid high-temperature processes;  mathematical modeling of combustion (mostly non-1D and unsteady);  synthesis of compounds and materials;  processes for production of powders, items, and coatings;  secondary processing of combustion products;  industrial production processes and their effectiveness;  marketing and commercialization. 10

The research arsenal involves the methods of chemical physics, general and structural macrokinetics, inorganic chemistry, materials science, and some other related disciplines. Since the discovery of the solid-flame phenomenon in 1967 [8], SHS research contributed greatly to the science [7]. Chemistry has been enriched with new classes of combustion reactions; combustion theory, with new processes (such as gas-free or infiltration-assisted ones); nonlinear dynamics, with the phenomena and effects of unsteady autowaves; scientific instruments, with apparatuses for time-resolved thermography and XRD; materials science, with new materials (such as nonequilibrium ones); processing technology, with new autothermal processes, etc. Initially, SHS research developed from basic research toward applications. In some cases, the results of fundamental studies were materialized in production processes of that or other scale. This can be illustrated by the following well-known example. Performing synthesis of refractory compounds in the early 1970s (still in FSU), we discovered exceedingly high abrasiveness in SHS-produced TiC [9, 10]. Owing to this finding, we reoriented the direction of research toward practical applications, which resulted in preparation of novel abrasive powders and their industrial-scale production. Having assimilated huge research experience and knowledge, we may now state the use of another strategy – from a practical task objective to purpose-oriented research and then to production processes. In SHS practice, this approach has been used and earlier. When at the Kuibyshev Motor Building Association (in the middle of the 1980s) there appeared an acute need for ceramic heat insulators (for use in direct crystallization furnaces), this task was successfully resolved by SHS technology (choice of materials, development of appropriate SHS process, and setup of workshop). But these are only separate (in some sense, irregular) examples. To date, the problem of industrialization (commercialization) of SHS has become of current importance as can be illustrated by vivid and interesting topical Round Table Discussion at the V SHS Symposium (Moscow, August 1999). Apparently, SHS may and must provide a greater contribution to progress in engineering, production processes, and economy than it does nowadays. 11

In this paper, we will analyze the R & D strategies on the way from a staring technical (or market) idea to specialized SHS production at minimized R & D expenses. A way from a practical task to industrial-scale production is schematically illustrated in Fig. 1. Technical market request

Preliminary analysis. Decision-making

Evaluation of processes and products

Optimization and debugging Development of the necessary equipment Assessment of the effectiveness and a market

possible contribution to the fundamenta l science

possible contribution to the materials science

Installation for laboratory and pilot production

Installation for the industrial production

The solution of technical

The solution of market problems

Fig. 1. Milestones on the pathway to industrialization SHS

Depending on task complexity and the skill of workers, this way may turn out to be short or long. The work gets started with strict formulation of a technical (or market) task objective. Preliminary analysis is then followed by R & D oriented on a given production process. Each step is performed only after successful completion of a 12

previous one. The work is accomplished by creation of the pilot, semi-industrial or industrial production line, depending on the required output volume and demand. Each stage may also be expected to yield the results of academic interest. In this case, the work may provide some contribution to different areas of research, even in case when the major task objective has not been achieved. Let us consider the specificity of individual stages on appropriate examples. 2. FORMULATION OF THE PROBLEM AND PRELIMINARY ANALYSIS We have to distinguish two types of problem: purely technical and market-dictated ones. A technical problem means the creation of a new purpose-oriented (advanced) product with desired properties of limited demand and, accordingly, low production volume. A market-dictated problem aims at setting up a new industrial-scale manufacturing of a cost-effective, high-quality and/or still unavailable product with a strong demand on the market. Preliminary analysis of a given problem must give answers to the following questions: • can the problem be solved by SHS? • if yes, will SHS give better results than other techniques? • if yes, what type of SHS process is most suitable (synthesis from the elements, magnesiothermic SHS, aluminothermic SHS, forced SHS compaction, SHS casting, etc.)? To get the answers, we have to analyze the preparative aspects of the problem (reaction schemes, raw materials), to carry out thermodynamic calculations, the evaluate the economic effect, and to carry out preliminary experiments on combustion. After this, we have to decide whether to go ahead or to refuse from SHS technology. Now let us consider some examples. Back in the 1970s, we had to set up (in FSU) the industrial-scale production of MoSi2 powder (100 tons a year) for use in hightemperature heaters instead of conventionally produced one (by heating Mo–Si powders in an induction furnace). Preliminary analysis showed that, for these powders, SHS technology was 13

suitable and that raw materials were readily accessible and costeffective. The task objective of subsequent studies was optimization of the synthesis conditions for single-phased MoSi2, which was successfully achieved. Another example of opposite sign. Despite a permanent desire to replace the old-fashioned Acheson process for production of abrasive SiC powders by a more advanced and effective one, we finally rejected this idea. Preliminary analysis showed that any raw materials for such an SHS process are too expensive (in the Acheson process, SiC is prepared from inexpensive sand and coke). Moreover, preparation of coarse abrasive crystals requires extra energy consumption (even in case of SHS), which is technically difficult and expensive. At the same time, SHS technology found its practical application in production of SiC ceramics. It follows that competent preliminary analysis may strongly diminish a risk of investments in further R & D. 3. CHARACTERIZATION OF PROCESSES AND PRODUCTS For the time being, the characterization of processes and products makes a major part of papers published in the field of SHS. The most of these studies has been carried out from the academic point of view. Unconventional features of SHS compared to other combustion processes have always been attracting and remain to attract elevated interest in the mechanism of this process. Numerous studies in the field • disclosed the main features in the mechanism of SHS (propagation of the heat wave self-sustained by released chemical energy, formation of combustion products either in the wave or behind the front, important role of heat transfer, influence of various phase transitions and fluid-dynamic phenomena); • shed light on the effect of system parameters (green composition and structure, particle size of reagents, density, size and temperature of starting sample, composition and pressure of ambient gas, etc.); • gave classification of solid-flame combustion processes; 14

•

detected and described some new phenomena and events: combustion and afterburning, laminary (layer-by-layer) and surface combustion, superadiabatic effect, front autooscillations, spinning combustion, heat turbulence, etc.; • formulated the methodology and ideology of structural macrokinetics with the dynamics of product formation (their composition, morphology, and structure); • suggested mathematical models of numerous processes; • developed the procedures for certification of SHS products and described their features. Some data of these studies has been summarized in monograph [11]. The above data are of interest not only from the academic but also from the practical point of view. A designer familiar with the mechanism of SHS is capable of finding out a best solution to a given practical problem, thus minimizing necessary R & D and swiftly obtaining desired resultant information. Below is the list of minimal data (obtained at a laboratory scale) that is required for making a decision about further actions. Process: • character and velocity of wave propagation; • combustion temperature. Product: • chemical composition (main products, unreacted reagents, impurities); • phase composition; • granulometric composition and specific surface (for powders); • microstructure, size of grains and pores (for materials); • configuration and size (for items); • physicochemical and mechanical properties (in view of product destination). In this case, of great importance is appropriate choice of experimental conditions. Normally these experiments aim at measuring most important parameters. After preliminary experiments, one has to come to one of the following decisions: • to carry out optimization; • to carry out developmental work; 15

•

to reject the project (in case of some important unpredictable circumstances). Optimization and Tuning It is often erroneously believed that SHS technology can be readily used to obtain a product that is ready to practical use: for this to achieve, one has to properly choose appropriate reagents, to mix them, and then to ignite. In some rare cases, this happens to be really so (especially if there are no specific requirements to product). But most often requirements to product are strict, so that preparation of desired product requires that a given process be optimized. This means fine adjusting of the composition and structure of product and choice of optimal process conditions. This work requires deep knowledge and high skill. The existing means of optimization and tuning [7] may be subdivided into two groups: simplest (trivial) and special ones. The simplest methods involve variation in the parameters that affect the SHS process (particle size of reagents, density and size of charge, pressure and composition of ambient gas, etc.). These measures allow us to vary (within some limits) the burning velocity, combustion temperature, extent of conversion, and structure/composition of products. The special means are numerous, some of them are listed below. (1) Dilution of charge with inert (including resultant product) compounds aiming at decreasing the combustion temperature (accordingly, the size of product particles) and at adjusting the phase composition of product. (2) Preheating (in furnaces, with electric current, in induction furnaces) in order to elevate the combustion temperature, to stimulate combustion, to increase the extent of conversion, and to adjust the structure of resultant material. (3) Introduction of functional additives in order to affect the reaction route and material structure (this is a most widespread and subtle technique that contains numerous know-how details). (4) External force influence that aims at densification of product and its shaping. To date, the examples of successful application of the above means are numerous. 16

Generally, we have to keep in mind the following three task objectives of optimization: (1) synthesis of compounds with a desired chemical and phase composition; (2) direct synthesis of materials with specific structure and properties; (3) direct synthesis of items (coatings) with specific requirements to their size, configuration, and properties. Some typical and concrete examples are given below: (1) synthesis of single-phase compounds with a minimal impurity content (including unreacted reagents); (2) synthesis of high-purity powders with a desired shape and size of grains; (3) direct synthesis of hard alloys with a desired hardness and strength; (4) fabrication of porous materials with a required porosity; (5) deposition of coatings with a required thickness, wear resistance and/or heat resistance; (6) joining (welding) of refractory materials with a requested strength of junction. Two most interesting (in our opinion) examples are given below. As is known, for Si3N4 powders most important is their phase composition. Normally, the SHS product is two-phased (α- and β-phases). In the processes of sintering and hot pressing, it is the α-phase that is easier to consolidate. For this reason, it is desirable that the product be enriched with the α-phase. The α-phase content of SHS product as a function of the combustion temperature (Fig. 2) was investigated in [12]. It follows that the SHS product contains only the α-phase when Tc ~ 1450°C. The process has found its practical implementation. Control of the structure and electrical properties of the TiN2–BN ceramic was performed by Borovinskaya and coworkers [13–15]. Upon variation in green composition and reaction route, the end product (of identical chemical and phase composition) was found (see Fig. 3) to appear in two different modifications (quasihomogeneous and skeleton-like). 17

Fig. 2. Graph of α-phase content as a function of Tcombustion in system of Si-N2

Microstructure of TiB2+BN SHS reaction: В + Ti2 ≥TiR2+RN

SHS reaction: Ti + 2В + BN > TiB2+BN

Quasi-homogeneous structure

р > 8-10 13 Q at BN р = 1014 Q sm

The skeleton type structure

Resistance: p>8-10 13 Q at TiB2 р = 10'5 Q sm

Fig. 3. The study of the electrical properties of SHS ceramic TiB2+BN

Performing synthesis at this temperature, the workers obtained a high-quality product of the following composition: 18

Nitrogen content of product Impurity oxygen α-Phase

38.9 wt % 0.79 wt % > 95 wt %

Specific surface These 'limiting' structures exhibited strongly different electric conductivity: the qusi-homogeneous one close to that of BN while the skeleton-like one, to that of TiB2. This result has led to fabrication of material with a required resistance (for use in evaporators). Without optimization and tuning of SHS process, any developmental work is hard to imagine. Developmental Work At this stage, a selected process should be scaled up. Moreover, one has to perform the following work: • Fabrication of specialized equipment • Selection of appropriate standard auxiliary equipment • Selection of suitable raw materials • Taking the measures for fire and explosion safety • Evaluating the process effectiveness Analysis of assimilated experience [2] leads to the following processing chart (Fig. 4). It involves the following three stages: preliminary processing of reagents, SHS process, and final processing of combustion products. The second stage is original, while two others are conventional in the technology of inorganic materials. Technological potentialities of SHS are closely associated with its specialized equipment. There exist a few kinds of SHS facilities but all of them are original and have already found their practical application. These are • universal SHS reactors (up to 30 liter in volume) for production of powders; • high-pressure reactors (up to 300 MPa) for direct synthesis of nitride ceramics; • vacuum SHS reactors (heating up to 1000°C) for synthesis of porous materials; 19

•

various molds for forced SHS compaction, including production of large hard-alloy items; centrifugal apparatuses for SHS casting, including production of pipes.

•

Control of quality

Preparation of the blank (drying, weighing, mixing, slugging,

in-situ measurement

Control of quality

SHS (on the air in a reactor, under pressure in vacuum, a press form, in an extruder, in a centrifuge, in surfacing chamber etc.)

Product Processing Surface treatment, milling, grinding, classification, crushing, grinding, cutting and machining

Fig. 4. Scheme of SHS technology [2]

Some kinds of SHS facilities are illustrated in Fig. 5 Progress in the field puts forward a question about in-line SHS production (some schemes are discussed in [16]). Some progress was attained in the continuous SHS production of oxides. A highproductivity SHS reactor (in the configuration of rotating inclined pipe) for continuos production of ferrites was mentioned in [2, 6]. Recently, a shaft furnace for continuous production of pigments was suggested [17]. The work on improvement of SHS processes and facilities is in progress. Production There exist three types of SHS production: pilot-scale, semiindustrial, and industrial-scale ones. Pilot-scale facility produces small batches of products by request. It is closely associated with developmental workers and often is located at their sites. 20

This production normally uses manual labor at a low output volume. Here the major task objective is checking out new technical solutions and their potentialities under the conditions of unsupported R & D.

а)

b)

c)

Fig. 5. Some types of special equipment. a) universal reactor; b) the high-pressure reactor; c) the centrifugal SHS reactor

Semi-industrial production yields serial products for needs of a given (permanent) customer. This production is located at some remote site (often large factory) as its individual division. Normally, such a production is completely or partially automated. Major objectives: industrial-level checking of a new process with the elements of business. Industrial-scale production gives serial products at a large output volume for realization on the market (through dealers and distributors). As a rule, this is a set of automated production lines that forms an individual plant (company). The pilot-scale production at ISMAN has been set up back in 1972 (at that time, Institute of Chemical Physics). The first product was abrasive TiC powder. Recently fabricated products have been high - YBa2Cu3O7-x superconductor (by request of US companies), ceramic (BN) heat insulators, cutting inserts (STIM), functionally graded plates (AlN), thermocouple casings (for Al melts), nozzles for sand blasting machines (Fig. 6). 21

Fig. 6. The one-step process nozzle made for sandblasting machine (according to V.L. Kvanina and H.T. Balikhina)

Fig. 7. Experimental production in ISMAN: filtering elements and devices

The latest product – TiC filters for purification of water from metal ions (including Fe), organic contaminants, and suspended particles has a good demand. These filters take advantage of their following properties: simple regeneration procedure, satisfactory resistance to a flow, bactericidal property, and applicability to various liquids and gases. Fig. 7 shows the filter structure. The experience assimilated at ISMAN was used as a basis for setting up semi-industrial production in other areas of the former Soviet Union (Fig. 8). In 1992, the total output of SHS products attained a value above 2000 tons. Among other countries, Japan was the first to set up SHS production (see ref. [18] and Table 1).

22

Production of Furnon refractories is being developed in Kazakhstan (see ref. [19] and Table 2).

Fig. 8. Industrial applications of SHS in the Soviet Union

Table 1 – SHS production in Japan Manufacturer Kyoritsu Ceramic Co. Ltd.

Product TiNi - powder with good stoichiometry TiAl - powder of high purity

Purpose Orthodontics wire for teeth, braces frames, etc. Sputtering material for turbine blades

Toyo Aluminum Co. Ltd. Grained AIN powder

Filling material in poliimernyh bags

Sumitimo Light Metal Industries Ltd.

In vehicles

TiAl

Sumitimo Osaka Cement SiC/C composites Co. Ltd.

Details for the aerospace industry, the wear-resistant electrodes, parts of machines 23

Table 2 – Pilot production of refractories such as "Furnon" in Kazakhstan Manufacturer

Branch the Institute of Combustion Problems, Almaty

Product Performance

SHS mixture to harden the refractory bricks (in-situ) 120-150 tons / year

Economy

10-20 tons of high quality bricks 1 ton SHS-refractory

Energy savings

1.2-1.5 times

Technical characteristic

High bond strength (10-15 MPa at 1300-1700 ° C)

Increased service life G.I. Ksandopulo

Information about production (in UK) of FeTiC, FeNbC, FeWTiC, FeNbTiC powders for thermal deposition of coatings (London & Scandinavian Metallurgical Co. Ltd.) and submicron TiB2 and TiB2–Al2O3 powders in the USA (Advanced Engineering Materials, LLC) can be found in Internet. A small pilot-scale production line for fabricating high-quality composite TiB2/Al2O3 powders was organized at the American company Tiberian Technology (Kathryn Logan, inventor, and Alan Gravitt) [20]. This production is based on aluminum-thermal SHS process using titanium and boron oxides as reagents and aluminum as a reducing agent. Advantages of the SHS-produced powders over conventionally produced (by carbothermic method) ones are as follows: the SHS composite powder is less expensive, it densifies more easily, and the densified product demonstrates higher performance characteristics. The result of economical estimations is also of significant interest. On a one million pound per year production level, the manufacturing costs are in the range of $3 – $5 per pound of powder. Especially impressive is the fast advance from basic research to industrial implementation that has been made by Chinese workers. Some information about semi-industrial SHS production in China [21, 22] is given in Tables 3 and 4. 24

Table 3 – Pilot production of TiB2 powder Manufacturer Product

Wuhan Minsheng Conducting Ceramics Co. Ltd. TiB2 powder Electro conductive evaporators

Performance

10-30 tons / year

100000-200000 pcs. / year

Process SHS technology Sintering of SHS powders The advantages low cost at the same purity that traditional product of SHS Product Previously in cChina did’t have the production of commercial TiB2 powders Application Crucibles, electrodes, wear-resistant parts, hard alloys, cutting tools, etc.

Great advance has been made by Chinese workers in production of large pipes with inner wear-resistant Al2O3 coating. The idea suggested in [23] and then realized for large pipes [24] was then implemented by Sheng Yin et al. and Shu Ge Zhang et al. in largescale industrial production. The work of Sheng Yin et al. [22] is illustrated in Table 5. Shu Ge Zhang [25] reports the following information about these pipes. SHS-produced pipes are suitable for the transport of abrasive materials. They have a wide variety of application and have already been used in mining, power plants as well as in metallurgical and building industries. In China, about 30 plants are producing ceramic-lined composite steel pipes with a total output about 10 000 tons a year. Shanghai Meishau (Group) Mine Co. Ltd. set up a 25-km tailing line. 2-year operation shows that the transport pressure is much lower that the designed one (designed value is the same as for steel pipes). The wear resistance of SHS pipes is markedly higher than that of steel pipes: at the elbows, it is higher by a factor of 70. In order to promote the production of pipes in China, a new company – Nanjing Jintao Wear Resistant Pipes Co. Ltd. with Shu Ge Zhang as president has been founded. Some relevant photos are given in Figs. 9–11. In the future, we may expect for further achievements of Chinese workers in the field of SHS production

25

Table 4 – SHS production of pipes lined with ceramics in China pipes: at the elbows, it is higher by a factor of 70 Manufacturer Product

Northwest Institute of Nonferrous Metal Research, Xian 7100016 (pilot-scale production) AIV Powder Powder Powder

Manufacturer, of, tons / year

35

Process

3V2О3+16AI 6AIV+5V2О3

Appointment alloying

Ti-6AI-4V alloy

1

0.5

hydrogen storage

The economic effect 5 million. of the yuan / year

1 million.

The advantages of the SHS product

lower oxygen content, the best dispersion

a higher density and purity, homogeneity and phase structure of the chemical composition

0.5

Sheng Yin

One of the latest achievements is setting up [26] a new company (SHS Ceramicas, Rodrigo, Spain) by ENUSA (Madrid) and ISMAN (Chernogolovka, Russia) for production of α-Si3N4, BN, and MgSO4⋅7H2O powders (the latter is obtained upon processing a product of combustion in the BN–MgO system). The quality of these powders correspond to wold standards. Contribution of the partners: ISMAN – developmental work, ENUSA – automated production line. The external and internal overall views of this production site are given in Figs. 12 and 13. The company is currently producing the above powders. In the future, the range of products will be extended. Note in conclusion that the potentialities of SHS technology have found their practical implementation only in the past years, so that much in this respect is still ahead. 26

Table 5 – SHS production of pipes lined with ceramics in China Manufacturer

Jianhu Corundum-Metal Composite Materials Co. Ltd., Jiangsu

University of Science and Technology, Beijing

Product

Steel pipes with ceramic lining (d = 20-800 mm)

Steel pipe (d = 2-600 mm) and knee (d = 20-325 mm) lined with ceramic

Productivity, tons / year Process Lifetime SHS pipe / steel pipe

4000

200-300

Centrifugal SHS 5/20

SHS centrifugal, gravity SHS 5/20

application

Transportation of coal, coke, ash, fertilizers, cement mixture, the molten aluminum, the oil-water mixture The prime cost / price 7/10

Transporting coal, coal dust, coke, fertilizers, cement mixture, the molten aluminum, the oil-water mixture 7-10/10-15

Fig. 9. Manufactory building

27

Fig. 10. SHS pipe ready for shipment

Fig. 11. The tribe, for the first time made of composite pipe

Fig. 12. The Company SHS ceramics in Spain. General form 28

Fig. 13. The plant of SHS Ceramicas Co. in Spain (production line SHS powders)

Effectiveness In deciding on whether or not a new SHS process is to be set up, the effectiveness is a very important factor: ineffective production has no future. Still at the dawn of SHS, primary (physical) analysis showed that SHS was a potentially effective process. The simple diagram taken from [2] and shown in Fig. 14 provides a guide line for the problem. Interesting analysis of the effectiveness for synthesis of ceramic materials was carried out by Pampuch (see ref. [27]. SHS method for production of ceramic materials was demonstrated to be significantly more efficient and easy with respect to many parameters in comparison with conventional production methods. Analysis of technical effectiveness is based on the measured service parameters and represents no special problem. Meanwhile, analysis of economic efficiency admits two approaches: theoretical and practical ones. In the former case, the processing and economic parameters of a new SHS process are compared to those of existing prototype to estimate the real effectiveness of new product for both the customer and manufacturer. This a correct approach, although it is difficult to apply because of confidential character of performance parameters. One of a few examples is given in [28]: for AlN powders, three 29

different semi-industrial technologies – SHS, furnace, and plasmochemical – have been compared. The practical approach is based on calculating the production cost its comparison with the price on the market (selling cost). Information about the production and selling cost of pipes (according to Sheng Yin) is given in Table 5. General analysis for some SHS powders shows [29] that SHS production is profitable.

Fig. 14. Physical basis of the effectiveness of SHS

In creating SHS production, we have to take into account and other factors, such as demand, accessibility of raw materials, shipping expenses, availability of special equipment, extent of automation, fire/explosion safety regulations, etc. Note that the problem of 'breaking through' to the market and finding there a niche is exceedingly complicate. 4. CONCLUSIONS In the 35-year history of SHS, the aspects of industrialization and commercialization still remain to be lagging. There are some 30

achievements in the field but these are still behind the achievements in the field of basic research. And the volume of work is different: much more people (and for a longer period) have been being involved in basic research. But SHS confidently goes along the pathway to industrialization, so that we can expect for increasingly growing interest in SHS production. Acknowledgments I am grateful to Dr. Yu. B. Scheck for translating the text into English, to Dr. M. Yu. Rusanova and Mrs. I. S. Zakieva for preparing the manuscript, to Prof. K. Logan, Prof. Sheng Yin, Prof. Shu Ge Zhang, and Prof. Zheng Yi Fu who kindly presented the information about their results. References 1. Merzhanov A.G. Ceram. Trans.: Adv. Synth. and Process. of Compos. and Adv. Ceram. (Special Issue). – Vol. 56. – Р. 3–25. – 1995. 2. Merzhanov A.G. Russ. Chem. Bull. – Vol.46, no. 1– Рp. 7–31. – 1997. 3. Merzhanov A.G. “Twenty Years of Search and Findings. Combustion and Plasma Synthesis of High-Temperature Materials”, in: Self-Propagating High-Temperature Synthesis, Munir Z.A., Holt J. B., Eds. – New York: VCH. – Рp. 1–53. – 1990. 4. Munir Z.A., Anselmi-Tamburini U. Mater. Sci. Reports, vol. 3, no. 7–8, pр. 277–365, 1989. 5. Varma A., Rogachev A.S., Mukasyan A.S., Hwang S., Adv. Chem. Eng., vol. 24, pp. 79–226, 1998. 6. Merzhanov A.G., Ceram. Int., vol. 5, no. 21, pp. 371–379, 1997. 7. Merzhanov A.G., Int. J. SHS, vol. 6, no. 2, рp. 119–163, 1997. 8. Merzhanov A.G., Shkiro V.M., Borovinskaya I.P. Fr. Pat. 2 088 668, 1972; USPat. 3 726 643; UKPat. 1 321 084, 1974; Jpn.Pat. 1 098 839, 1982; Byul. Izobret., no. 32, 1984. 9. Merzhanov A.G., Karyuk G.G., Borovinskaya I.P., Sharivker S.Yu., Moshkovskii E.I., Prokudina V.K., Dyad'ko E.G. Poroshk. Metall., no. 10, pp. 50–59, 1981. 10. Merzhanov A.G. Chemistry of Advance Materials/ Eds. C. N. R. Rao, Blackwell Sci. Publ., рp. 19–39, 1992. 11. Merzhanov A.G. Tverdoplamennoe gorenie (Solid-Flame Combustion), Chernogolovka, ISMAN Press, 2001. 12. Zakorzhevskii V.V., Borovinskaya I.P. Int. J. SHS, vol. 9, no. 2, pp. 171 – 191, 2000. 13. Borovinskaya I.P. Abstr. III Int. Symp. on SHS, Wuhan, 1995. 14. Borovinskaya I.P., Bunin V.A., Vishnyakova G.A., Karpov A.V. Int. J. SHS, vol. 8, no. 4, pp. 451–457, 1999. 31

15. Karpov A.V., Morozov Yu.G., Bunin V.A., Borovinskaya I.P. Russ. Chem. Bull. (in press). 16. Merzhanov A.G. Int. J. SHS, vol. 4, no. 4, pp. 323–350, 1995. 17. Vadchenko S.G., Merzhanov A.G., Borovinskaya I.P., Ibarreta F. Lopez, I. Caro Calzada, M. Gutierrez Stampa, Spnsh.Pat. 00500126.8-2111, 2000. 18. Miyamoto Y., Int. J. SHS, vol. 8, no. 3, pp. 375–384, 1999. 19. Ksandopulo G.I. Рrivate communication, 2001. 20. Logan K. Рrivate communication, 2001. 21. Zheng Yi Fu Рrivate communication, 2001. 22. Sheng Yin Рrivate communication, 2001. 23. Merzhanov A.G., Kachin A.R., Yukvid V.I., Borovinskaya I.P., and Vishnyakova G.A., USSR Inventor's Certificate 684 849, 1977; USPat. 2 511 747, 1977, 4 217 948, 1980; FRGPat. 2 837 688, 1978. Fr.Pat. 2 401 771, 1978; Ital.Pat. 1 104 078, 1985. 24. Odawara O. USPat. 4 363 832, 1982. 25. Shu Ge Zhang, private communication, 2001. 26. SHS Ceramicas. Poligono Industrial, 2001, Suidad Rodrigo, Spain (leaflet). 27. Pampuch R., Eur J. Ceram. Soc., vol. 19, no. 13–14, pp. 2395–2404, 1999. 28. Merzhanov A.G. in Particulate Materials and Processes. Advances in Powder Metallurgy, Princeton: Metal Powder Ind. Fed. Publ., pp. 341– 368, 1992. 29. Merzhanov A.G., Borovinskaya I.P., Prokudina V.K., Nikulina N.A. Int. J. SHS, vol. 3., no. 4, pp. 353–370, 1994.

32

THE SHS PROCESS IN THE LAYERED SYSTEMS G.I. Ksandopulo, A.N. Baideldinova ABSTRACT In the course of the study the main factors effecting the macrokinetic characteristics of combustion in a layer are determined, the nature of this effect, the conditions of layer formation, admissible limits of changing of the initial parameters of the synthesis process for the obtaining of material with the pre-set composition are established. As a result, the principles of building of new layered compositions and organization therein of directed controlled processes are developed. The variants of vertical and horizontal layer arrangement are considered, since they differ by an extent of influence of gravitation forces on the final product composition. A number of examples are provided with the purpose of revealing of potential possibilities of this promising study direction. Some aspects of conduction of materials self-propagating high-temperature synthesis (SHS) under rotation are considered. INTRODUCTION In the earlier combustion theories flame propagation was represented as the ignition by a burning layer of the adjacent cold layers heated up to self-ignition due to thermal conductivity. N.N. Semyonov [1] pointed to their internal contradiction consisting in an attempt to ignore a chemical part of the process. At present the combustion theory is based upon consideration of the three main cases of the process course, namely: а) Heat release rate is considerably less than heat removal rate. A trivial reaction course. Produced heat is diffused due to high thermal conductivity of the medium. b) Heat release rate is higher or equal to heat removal rate. A wave-like reaction course. In the area where heat release rate is comparable with heat removal rate an initial impulse is rather important as the ignition energy. A minor insulation of the system results in violation of the equilibrium between heat release and heat removal. There appear local overheated zones further increasing the 33

predominance of heat release over heat removal. A heat wave is formed. Thus, a combustion wave is the result of interaction of the two processes. Heat removal to the cold reaction mixture in quantity sufficient for the predominance of heat release over heat removal is the prime cause of the combustion wave propagation. с) Heat release rate is much higher than heat removal rate. Thermal explosion more frequently these are quasiadiabatic or superadiabatic processes. Modern technologies based on combustion in the condensed media are targeted at expansion of the produced materials assortment with various combinations of their physical and chemical properties. Pure metals and multi-component alloys, semiconductors and ferroelectrics are the basis or necessary components of the majority of the structures and mechanisms that are currently operated or being developed. Quality and properties of the materials are determined by their background, and production method and conditions. Each new technology used under conditions of reduction of the natural resources and rapidly changing consumer demand should be of high reconstruction mobility and sufficient universality with unconditionally high quality of the output products. A method based on the solid-phase combustion processes and called by its discoverer A.G. Merzhanov as “Self-Propagating High–Temperature Synthesis” (SHS) [2, 3] complies with the high technical requirements. 1. Peculiarities of Combustion inside a Layer Combustion in a layer proceeds under conditions of intensive heat removal from the hot zone. Similar to the case of bulk samples, the heat energy consumers are primarily heat penetration and afterburning zones, i.e. areas adjacent to the wave front. At other equal conditions (composition, density, initial temperature of the reagent mixture, etc.) the quantity of “useful” heat contributing to the process propagation depends on the surface area of the reaction zone, and therefore, on the layer thickness [3]. Herewith, this dependence may not be considered as directly proportional: increase of the layer thickness may result in front deformation, growth of mass burning rate connected with its surface area, heat redistribution between the 34

zones, and finally, in the change of the process development mechanism. If the system is not closed a diffusion of heat released in the reaction center proceeds also through the surface of the contact between the material layer and medium. The quantity of heat losses depends considerably on the surface area through which heat goes out. In thin layers phase formation connected with the active mixture heating, chemical reactions and cooling of the synthesis products is caused by dislocation of the combustion wave front in the layer plane. Herewith, heat removal produces a decisive effect upon the combustion mode character, and hence, upon the composition and structure of the synthesis products. A combustion wave attenuation, self-oscillatory and spin-based modes of its propagation result in irregularity of the quality and quantity characteristics of distribution of the synthesized materials in the direction of the front dislocation [4]. In case of a stationary process development a determining factor of the final product structure formation is a high rate of cooling, stipulated by intensive heat removal from the layer surface. According to the state diagrams of oxide and metal substances in the majority of known systems mutual solubility of the components significantly changes as the temperature grows and chemical interactions and eutectic and peritectic reactions proceed [5]. Besides, crystalline lattices of some metals (Fe, Ti, etc.) and oxides (TiO2, SiO2 etc.) undergo structural changes in the course of heating. As a result of rapid cooling of all thin layer mass from the synthesis temperature down to the furnace or room temperature characteristic quenching phenomena may be observed: martensite structure in alloys, macro- and micro-defects of the crystalline lattices. Being in such metastable state the materials may display special physical and mechanical properties. Thus, the synthesis peculiarities of the materials in a layer mainly depend on the conditions of heat removal. A phase composition and properties of the reaction products are determined by the temperature conditions and process rate. Therefore study of the SHS in the layer include control over the temperature in the combustion wave, front dislocation rate, and also cooling conditions of the synthesized material and its X-ray phase characteristics. 35

2. Directions of the Combustion Wave Propagation in the Layered Systems The temperature of the metal-oxide systems combustion wave front under the quasiadiabatic conditions may reach (3-4) 103 К. To carry out a high temperature synthesis such conditions may be obtained using such heating scheme when a mixture of the reacting components is formed as a layer that gets heat energy from the parallel energy-carrying layers [6].

а – general view of the layered system, b – system with a repeating combination of three layers, where 1, 3 are auxiliary layers, and 2 is a synthesis layer. Fig. 1. Diagram of the horizontal layers stack

36

In the horizontal variant, when the layers are arranged perpendicular to the horizontal axis as it is shown in Fig. 1а, the combustion products of the oxide systems, in particular reduced metals do not penetrate into the adjacent layers. Such process arrangement will lead only to conductive heat transfer, since the horizontal stack consists of chemically independent layers. To provide a quasiadiabatic course of the process in the layered system a simultaneous combustion is carried out in the adjacent layers. In this case synthesis layers may be repeatedly alternated with heat-carrying layers, attaining herewith the maximum heating. A stack of layers, selected accounting for a set task, is arranged horizontally or vertically (perpendicularly to the horizontal or vertical axis, respectively). In certain cases it may be located in the conditions of the centrifugal force, electric or magnetic field action. Macrokinetics of combustion in a layer is affected not only by the concentration of reagents, temperature and pressure, but also by the external forces, e.g. those caused by a centrifugal acceleration upon rotation around the axis. The characteristic time of the stack combustion τ is composed of the corresponding burn-through times τk of all k layers of the stack: i i nM (1) τ = ∑ τk = ∑ W k k =1 k =1 where n is a number of moles, M is an average value of the initial substances molecular weights, Wk is mass rate of the overall reaction in k layer. Normal combustion rate Uk in the layer is equal to the ratio of each layer thickness (аk) to its combustion time τk. Therefore, an average linear combustion rate of the entire stack

U upon consecutive ignition of the layers is i

U = 1 ∑ ak . τ

(2)

k =1

Let us assume that an optimum synthesis result is determined by an average mass combustion rate of the stack with the k layer substance density ρk 37

i Um = S ∑ a k ρk τ k =1

(3)

The Um value differs from additive Uam equal to an average combustion rate of a separate layer of this stack at the average temperature Тav k a ρ U am =S ∑ ak k k =1 τ ak Let us call the ratio φ = Um U am

(4)

a layer conjugation coefficient upon combustion in the stack characterizing growth of the overall reaction rate in the stack, stipulated by change in the heat transfer conditions, quantity and distribution of ignition points as well as mutual arrangement of layers in the stack. φ = f (λ, ρ, S, Рn),

(5)

where λ in heat conductivity, S is the stack cross section, Рn is the n-th rearrangement, the total number of which in the k-layers Рn stack considering repetitions of the 1st, 2nd, 3d ... kth-layers, respectively, α, β, γ ... times, is Рn = k! / α! β! γ!...

(6)

Noteworthy that the introduced φ value also characterizes the synthesis layers. The Uam value in this case is equivalent to the product accumulation rate at Тav, Um is equivalent to the product

accumulation rate in a layer under the stack conditions.

Thus, for each stack composition the φ value depends on the arguments specified in (5), the change of which produces a

38

predominant effect upon Um . If the parameters λ, ρ and S are constant within the variation limits, the sole cause of the φ coefficient change is a transition from one layers arrangement to the other. The best synthesis effect is attained at a certain average mass rate value; the maximum φ value corresponds thereto. Let us consider a three layer system repeating in the stack k times (Fig.1, b). Layer No.2 requiring creation of the maximum heating conditions is in contact with layer No.1 to the left and layer No.3 to the right. In case of a simple, non-chain reaction in layer No.2 the reaction mixture conversion depth in each point of this layer along the stack axis is determined by the temperature distribution to the right and to the left, established by the moment τk. For this case the φ value in layer No.2 is determined by the heat wave Um rate on the part of the adjacent layers. The resulting φ value within the three layers combination range is as follows: φ = ϕ1 – ϕ

2

+

ϕ3

(7)

The maximum effect (φ' = 0, φ2' = 0) corresponds to the numerical parity of combustion rates of the counter-directed waves in layers 1 and 3: U = Um . m1

3

Temperature distribution within layer 2 is set up by heat wave dislocation to the left and right. Let us assume that enthalpy ΔН in layers 1 and 3 is much higher than the heat absorbed by the reaction in layer 2, than the reaction rate profile in the synthesis layer is determined by the established temperature K distribution. If, herewith, the characteristic reaction time in the synthesis layer is of the same order as heat wave distribution time (the reaction starting in its front), the temperature profile is approximately described by the known Michelson distribution: Т(х) ≈Т0 + (Тг – Т0) expU·X·Cт·ρ/ λ

(8) 39

In point x, where the temperature increases approximately е times (Tx/T0≈2.718 or Т0≈300 К), but the reaction rate may be neglected as before, we get. Tx −T0 ≈e Tг −T0

x≈

λ UC p ρ

(9) (10)

For the graphite diluted reaction mixture TiO2 – Al we have Ср=710 J g-1 degrees-1, λ = 0.05 J cm-1 degrees-1 s-1, ρ = 2.3 g cm-3, U = 0.02 cm s-1, the temperature increase Tx/T0≈2.718 proceeds at a distance of х ≈ 1.5 · 10 –3 cm from the plane dividing the reaction and heating layers. In various mixtures of metal oxides with heating capacity Ср ~ 80 – 130 J g-1 degrees-1 with other different similar parameters the value of x ≈ (1÷2) ∙ 10-2 cm is attained within the limits of 1 second, and with U = 1 cm s-1 – for 10-3s. Extrapolating one may suppose that a 10 cm layer is heated during one second. Since heating is possible both to the left and to the right from the synthesis layer, the yield of the reaction product turns to be maximal closer to the heat source boundary, and the least one in the center of the layer. The ratio of mass rates (4) rather effectively characterizes the connection of thermal and physical properties of the layers in the three layer stack, where the yield of the reaction product in the middle layer is determined by the temperature. Let us assume that at the temperature of furnace Т1 the reaction in the synthesis layer is infinitely small. The combustion wave rate in an auxiliary layer is U1. The composition of two auxiliary layers and synthesis layer, situated between them, represents a system, in which several variants of process proceeding are possible, depending on heat exchange conditions. If the synthesis layer (SL) by its mass significantly exceeds the auxiliary layers, and the contact area is herewith small, then the middle layer plays the role of a heat insulator, a relative yield of the reaction product in it is close to zero, and ϕ value approaches 1. As the SL mass decreases and the contact area increases the conditions 40

may be reached when the reactions in all layers proceed to the end, and in the insulated auxiliary layers the combustion wave rate is equal to zero. This is an ideal case, difficult to attain in practice, when ϕ value tends to infinity. The actual layered systems include auxiliary layers, in which the solid-phase combustion process in the insulated condition proceeds in the stationary mode without changing of the form and violation of the surface integrity, heat losses through the side surface are minimum, and the quantity of the released heat energy is sufficient for excitation and maintenance of reactions in the synthesis layer. 3. Syntheses of the Alkaline-Earth Titanates in the Horizontal Stack An interaction of titan and barium oxides proceeds within the temperature rage of 1350-1450 °С. The composition and parameters of an auxiliary layer (AL) have been chosen accounting for the value of endothermic effect of the reagents interaction in the main layer and its geometric dimensions [7]. The initial mixtures have been thoroughly mixed. On a hydraulic press, equipped with a pressure gauge for molding force registration the samples have been prepared from the mixtures in the form of cylinders of different diameters or rectangular prisms, depending on the experiment goal. From them the layered systems have been formed and placed in furnaces, heated up to the temperature of selfignition of exothermic mixtures. After termination of combustion in the auxiliary layers the sample has been removed for cooling in the air or left in the furnace until temperature equalization. In case of synthesis of materials with the pre-set composition for electronics the requirements to the product purity are high, both a chemical interaction between the layers and a mechanical penetration of the AL combustion products into the synthesis layer are inadmissible. In this connection the layers have been arranged vertically along the common horizontal axis. A cylindrical form of the multi-layer composition has been chosen for decreasing of the contact area with the substrate, and, respectively, reduction of the heat waste. Under such conditions, ensuring a rather high ratio of the summary mass of reagents to the total surface area of the sample, 41

through which a heat consumption proceeds, as well as the maximum contact area of the layers, a stationary AL combustion wave has been obtained and the most complete energy transfer from layer to layer has been attained. The temperature in the furnace has been maintained at the level of 850 ºС. Table 1 – Change of the heating temperature of the synthesis layer substance Тcom in dependence of the composition of the auxiliary layer sludge СAl, mas %

Molding density ρ, (g·cm –3)

Tcom, °С

12.0 15.0 18.0 20.0 23.0 26.5 32.0

2.726 2.828 2.830 2.726 2.725 2.718 2.692

1250 1382 1510 1648 1650 1618 1600

Table 2 – Heating temperature of the synthesis layer substance Тcom in dependence of the change of the auxiliary layer mass m with the aluminum concentration therein equal to 18% Auxiliary layer mass, m, g

Cylinder height, h, mm

Heating temperature of the synthesis layer, Tcom, °С

1.84 3.80 5.74 7.64 9.81

2.55 4.46 6.84 8.98 11.0

1406 1470 1538 1550 1580

In the course of experiments the Al compositions of Al-Cr2O3 with a variable content of a reducer have been studied. With the constant layer diameter of 20 mm and ratio of masses of AL:SL = 2 a change of heating temperature of the mixture of reagents in the synthesis layer has been observed in dependence of the composition and mass of the auxiliary layer. The results are provided in Tables 1 and 2, respectively. 42

The limiting ratio of masses in the synthesis layer (SL) of the composition TiO2-BaCO3 and auxiliary layer (AL) – Al-Cr2O3 has made up 1:2 with aluminum content of 15% in the initial AL composition and 1:1 with 23 %. X-ray phase analysis shows that the ready product in SL is barium titanate in tetragonal modification. Similarly, with the minimum energy losses calcium and magnesium titanates have been synthesized. In this case, in accordance with the calculation and experimental selection of the composition and mass of the layers, at the temperature of furnace equal to 850-900 ºС the temperature in SL has attained 1650-1700 ºС. Synthesis of pure strontium titanate is hindered by the process lag. To bring its rate in compliance with the reaction rate in the auxiliary layers a mechanic and chemical activation of the main layer charge has been applied, the efficiency of which has been shown in the preliminary experiments in the example of Al - Cr2О3 mixture [8]. Thus, on the basis of the developed approach to the synthesis of materials in the layered system a number of compounds have been obtained, the traditional methods of synthesis of which are connected with complex preparation of the initial reagents and long processes of thermal treatment at high temperatures. The combination of the layer method with such methodological techniques as, for example, pressure molding or mechanic and chemical activation of the initial mixtures, allows one to improve the regulation of chemical and technological processes of synthesis. 4. Aluminum Borides Synthesis in the Layers Stack with Protective Interlayers As distinguished from the synthesis of titanates of alkaline-earth elements, when it is practically important to only maintain a lower temperature limit, the synthesis of aluminum boride of particular composition, AlB2, AlB10, AlB12 is complicated by a considerably narrow temperature range: AlB2 α- AlB12

1000 - 1100 ºС 1100 - 1550 ºС 43

β - AlB12 AlB10

1550 - 1660 ºС 1660 - 1850 ºС

Furthermore, aluminum borides are usually formed in the presence of carbon, which accepts uncompensated complex free bonds of borides molecules, and contamination of the finished product with other impurities inflowing as a result of diffusion from auxiliary layers leads to a significant change in electrical properties of borides. Low temperature boride AlB2 is synthesized in a furnace heated to 870ºC in layer Al - B2O3 with additional heating by the auxiliary layer composed on the basis of a stoichiometric mixture (Al + V2O5): Al2O3 (20-25%) - (Al + V2O5) (80 -75%) and V2O5 (20 -25%) - (Al + V2O5) (80-75%). To obtain AlB12 a three-layer system is used with two auxiliary layers arranged on both sides of the core layer, where mixture Al B2O3 is also used as a synthesis layer, and system Al - TiO2 as an auxiliary layer, with a ratio close to stoichiometric composition. The furnace temperature was 950 ºC, with 1500-1600 ºC in the combustion wave. Further increase in temperature leads to an increased rate of interaction between the diffusion layers. Titanium from the auxiliary layer penetrates to the core layer and reacts with boron to form titanium boride. To prevent this phenomenon insulating interlayers of activated carbon were used in AlB10 synthesis. The use of inert refractory layers provides an opportunity to select the spatial arrangement of the layer composition - horizontal or vertical stack. An increase in temperature in the reaction zone was achieved by increasing the number of alternating layers ordered 1-23-2-1-2-3- etc. (Figure 1b). Horizontal arrangement of the layers along a common vertical axis was applied to increase the mechanical strength of the system. Placement of the multilayer system within a cylindrical graphite reactor ensures high adiabatic combustion process.

44

5. Redistribution of Phases. Impurities Rejection The study of SHS-processes leads most researchers to an issue of the crystallization phase following the wave of combustion [9 -11]. As a rule, macro- and micro-heterogeneity of formed patterns is observed, the emergence of which is attributable to the liquid or gas phase resulting from chemical reactions in the hot zone. Anisotropy of the properties of the products was also observed following the front of the combustion wave [12]. Generally, this phenomenon is associated with processes of melting, solidification and recrystallization of phases in the combustion zone. In the synthesis of refractory compounds, such as alkaline-earth metal titanates, run in the core layer of multilayer compositions, solid-phase reactions are observed. The maximum temperature in the hot zone does not exceed the melting temperature of the starting materials and reactions products (Table 3). Table 3 – Correlation of synthesis temperature and phases melting temperature Smelting temperature, ºС Reaction BaO + TiO2 = BaTiO3 CaO + TiO2 = CaTiO3 MgO + TiO2 = MgTiO3

Synthesis temperature, ºС 1350 – 1450 1170 - 1360 1250-1500

Starting oxide AEE 1740 2570 2825

Synthesis product 1915 1630

The results of experiments conducted on cylindrical samples where self-ignition occurs at the geometric center of the object and extends uniformly to the periphery indicate single-phase structure formation in a broad range of optimum synthesis conditions. However, combustion of long cuboids has its own characteristics as compared to the combustion of cylindrical samples having a form of a tablet. At a low temperature gradient in the furnace emergence of combustion wave in active auxiliary layers of the compositions (15% Al-85% Cr2O3), (23% Al-77% Cr2O3) and (32,5% Al - 67,5% TiO2) takes place with both ends simultaneously or with a slight delay. Artificial stimulation of inflammation via termite or direct contact with solid metal bar heated to the furnace temperature allows a directed movement of the combustion front along the major axis of 45

the cuboid. In this cases changing of the phase composition of the core layer was observed.

1 – CaTiO3, 2 – MgTiO3, 3 – TiO2 Fig. 2. Changes in components concentration along the length of the synthesis layer relative to their calculated values with the auxiliary layer composition being 15% Al-85% Cr2O3

A 10 g auxiliary layer (20% Al-80% Cr2O3) was prepared for the experiment sized 50x10x9 mm. Outside the furnace under normal conditions combustion of such plate takes place in a self-oscillating regime. Layer (71% VaSO3 + 29% TiO2) was selected as a starting material of the core layer in which 3% of copper powder was injected. The core layer weighing 5 g sized 50x10x4 mm was placed on the sub-layer in which combustion was initiated by means of thermite mixture. The process took place at room temperature. The combustion wave propagated along the AL with a mean velocity V = 2 mm/s. A temperature of 1300 ºС was reached in the layer. Upon completion of the synthesis the core layer was exposed to X-ray analysis. The analysis results are shown in Table 2 and microstructure prints (Figure 3). Data presented in Table 4 indicate a fairly uniform distribution of barium, titanium and oxygen along the length of the sample, while point-to-point copper concentration varies greatly. The results of 46

analysis of the microstructure of the sample contribute to the explanation of this fact (Figure 3). Table 4 – Changes in the chemical composition of BaTiO3 sample along the direction of the combustion wave of the auxiliary layer

In the microstructure of the sample plots with a more crystallized, partially submelting pattern can be singled out. They are characterized by enlarged grains and banded texture. Signs of such structure are most evident on the far edges, suggesting the material solidifying due to crystallization to form capillary channels and circular cavities. The presence of the metal phase is not observed.

Fig. 3. Microstructure of BaTiO3 sample with copper impurity

Thus, it can be assumed that upon heating up to 1300 ºC copper inclusions melting occurred and barium titanate formation resulted in solid-phase reactions which was more intense in the heated portions of the material. This was accompanied by dissolution of copper in 47

the perovskite structure limited by temperature conditions. Excess liquid phase was forced into the less-heated and, therefore, less crystallized areas where heterogeneous structure was formed with a distorted crystal lattice able to absorb a greater amount of impurity atoms and copper oxide. 6. Combustion in a Confined Sspace as a Kind of Layer Combustion. Immobilization of Contaminated Soils In the laboratory of IPG combustion by SHS an important part of the environmental problem of radioactive contamination was also solved, namely, to prevent the migration of radioactive substances in the soil and spread of contamination over large areas, air and water [13, 14]. Due to the great danger posed by soil contaminated by high activity nuclides, such soils are considered to be similar to radioactive waste and subject to the same methods of disposal. In European countries, particularly in France, the UK, Germany, the processes of solid waste management and curing of liquid waste have been developed for more than 35 years. Studies have made it possible to mix harmful substances with a range of glass materials followed by pouring of the molten mass into solid stainless steel tanks which are then sealed by bonding. Glass-borosilicate extracted from liquid-phase melting waste is packed into special blocks that contain the material which is chemically identical to the high-activity waste intended for recycling. Tanks with glass liquid phase are stored under water in closed reservoirs specially equipped for that purpose. The final location of buried objects requires their isolation from the environment for a long period. An improved method for the immobilization of various forms of high-level radioactive waste was developed in Australia under the scientific guidance of Professor Ted Ringwood of the Australian National University [15]. Named SYNROC, this technology provides for the creation of ceramic matrices from several natural minerals which are characterized by joint capability to accept in their crystal structures almost all currently known elements of high-level radioactive waste rock. Initially, about 57% of titanium dioxide TiO2 was used as a material for Synroc. 48

The most effective modern methods solve the problem of radioactive waste disposal by introducing such waste to the ceramic matrix where a radionuclide is chemically bound ensuring its low leaching rate. It can be used in the nuclear power industry and for fixing radioactive elements in the stable solid phase suitable for further secure disposal. Other forms of fixing may be artificial minerals, similar to natural minerals in terms of composition and properties because they are able to exist in natural conditions without alteration and destruction. The main feature of the problem of immobilization of radioactive components spread in the soil was high volumes of material to be processed. Since contaminated soil is not only unsuitable for processing but also is a source of contamination of the entire local ecosystem, the development of secure technologies for immobilization of hazardous components of contaminated soils has been considered as technological problem requiring special attention. In addressing environmental problems the task of application of SHS for processing large amounts of soil was posed for the first time, and this method indeed has a practical perspective due to the fact that the process does not require massive energy-intensive equipment and can be arranged in close proximity to contaminated terrain. Scientific novelty of the method lies in the use of SHS features to protect the ecosystem combined with the agglomeration of infected material. SHS based on the combustion processes, yields refractory minerals, similar to those natural in terms of structure and phase composition, having high mechanical strength and chemical resistance. Agglomeration allows processing and disposal of large volumes of contaminated materials. Moreover, as compared with known methods of neutralization of hazardous components, this method may be applied to the soil of any composition. Developed method of agglomeration and SHS is as follows. Moulded mechanically stable agglomerates (particles of soil-ground immobilized by a binder in the form of balls or parallelepipeds) are stacked in natural reactors (pits, trenches), the free space between the agglomerates and the charge is filled with bonding composition (a gas mixture consisting of metal oxides, for example, iron oxide) and 49

a reducing agent, such as aluminum powder), followed by initiation of combustion in a wave mode. As a result of this process regarded as SHS cermet material is formed bonding separate agglomerates into a single block. High temperatures result in changes in the structure of agglomerates characterized by sintering, a process similar to ceramics burning. The idea of using soil sintering instead of mixing it with the bonding structure is based on the reduction of thermal energy consumption by reducing the bonding composition costs per unit volume of soil to be treated, since power-consuming sintering process can be performed only in the surface layers of the agglomerates. Presently known portable units for the manufacture of building blocks from any soil allow, thanks to their capacity, to solve the problem of agglomeration. Varying the geometric dimensions and the shape of the ground agglomerates made it possible to investigate the influence of the degree of filling of reactors (filling rate k) on the depth of heating and on the phase composition of the synthesized composite material matrix. In the course of burning metal oxides with a reducing agent under redox reactions temperature conditions were established for agglomerates burning promoting recrystallization phase and soil sintering, and also for bonding of the entire system as a single block by forming a flowable melt of intermediate and end products of the process. Reactions of aluminum with Fe2O3 (red scale), Fe3O4 (black scale) are characterized by the highest adiabatic temperature (Tad), and therefore, high specific heat. Consequently, exothermic mixtures based thereon are chosen as bonding compositions. Reactions of aluminum with FeO and Cr2O3 which are the main components of chromite ore and chromium concentrates are characterized by lower adiabatic temperatures. However, preliminary studies showed [16] that case of combustion of iron and chromium oxides at high heating rate, for example, for heating the bonded agglomerates, the reaction is not complete (metal and Al2O3 formation), and ends at an intermediate stage of the formation of spinel type MeMe2O4, where Me111 - Al, Fe, Cr, Mn, Co; Me11 Mg, Fe, characterized by high mechanical strength and chemical 50

resistance, they can be the basis for processes of SHS-synthesis conducted to immobilize the contaminated soil. The analysis of the experimental data shows that the bonded compositions based on black scale as well as mixtures of black and red scale with chromite ore yield consistently good results – combustion in the stationary mode and full integration of agglomerates in a block. When using red scale combustion wave velocity is substantially higher than the optimal values. As a result, despite the very high temperature of the combustion wave front (3200 – 3500 ºC) no sintering of soil occurs due to insufficient duration of effect of temperature on the agglomerates. The temperature of the combustion and front propagation velocity are amenable to regulation to a certain extent. The most effective method of chemical control of the combustion process is to change the composition and ratio of the components. In case it is necessary to use exactly red scale as a component of the bonding composition methods of lowering the combustion rate can be used by diluting reagent mixtures with various ballasting additives. The infected soil itself can be the simplest additive, if its dispersion is high enough so as not to disturb the macrostructure of the produced block. The study shows that it is effective to use metallurgical slags as ballast. It solves the environmental problem of industrial waste disposal along the way. Studies of high-temperature synthesis carried out by us using extremely active mixtures of metal oxides with aluminum powder [17] have shown that the active inhibitor of explosive combustion thereof is boric anhydride. Although B2O3 transition to the liquid phase commences below the melting point of the main components, its inhibitory effect on the oxidation of the aluminum increases the autoignition temperature and has a retarding effect on the entire process. Boric acid features similar properties among flammable mixtures which upon heating in the temperature range from 277 to 540 ºC gives the crystalline water transforming into anhydride. Although the introduction of boroncontaining additives significantly increases the cost of the results, it increases the efficiency of immobilization of radioactive components in the soil. 51

Another negative property of red scale is its low bulk density as compared with black scale and chromite concentrate. The combustion process results in the production of insufficient amount of flowable melt. The density of the bonded block is small due to the large pores and cavities. In this regard, in the selection of combustion process inhibitor it is necessary to consider not only its chemical properties but physical properties also, as these factors affect the mechanical strength and strong resistance to any natural impacts. Long water resistance of blocks with various bonding compositions is given below (Table 5). Table 5 – Effect of the bonding composition on block water resistance Exposure duration, days 0 1 2 3 4 5 10 20

Bonding composition based on black scale, g 19.5 20.5 21.5 22.0 22.0 21.5 21.5 21.5

Bonding composition based on chrome concentrate, black and red scale Sample mass, g 23.0 24.7 26.0 27.0 26.5 26.5 26.5 26.5

Bonding composition based on red scale

37.5 30.0 25.0 13.5 11.0 11.0 10.7 9.0

The analysis of table data shows that bonded agglomerates with a composition based on red scale are not resistant to water. Due to poor sintering of soil because of the high combustion rate, soil material is washed from the frame formed by the bonding composition. Changes in the mass of samples with bonding compositions based on black scale and based on a mixture of chromite concentrate with black and red oxide scale were observed during the first 3-4 days followed by weight stabilization. Thus, it was found that the mechanical strength and chemical resistance of the blocks mainly depend on the bonding mixture composition and macrokinetic characteristics of its combustion process. In this regard it is necessary to determine optimum 52

conditions for SH-synthesis in a block and to study the mechanism of influence of the combustion process on agglomerates macrostructure. Experimental laboratory determination of the quantitative ratios of the masses of SHS charge and soil agglomerate depending on the placement thereof in the reactor at a filling rate k = 0.5 ÷ 0.7 showed that the spinel formation as an intermediate product of the combustion process taking place in bonding compositions, and favorable for the formation of a chemically stable block matrix occurs at filling rate k = 0.6. At k = 0.5 the process depth increases, with the increase in corundum content in the synthesis of the product, featuring, similar to spinel, high acid resistance, and the metal phase being a solid solution of chromium in iron, a chemically resistant alloy like stainless steel. Table 6 - Dependence of the combustion process duration on the reactor charge and basis of the bonding composition

The only drawback is the overconsumption of the bonding composition. At k = 0.7 a lack of thermal energy released during 53

combustion of the bonding composition is observed, resulting in lower depths of soil agglomerates heating, on the one hand, and a partial shift of combustion to a self-oscillating regime on the other hand. The analysis of the data shows that the optimum condition for the formation of spinel, acid- and alkali-resistant mineral, is filling of the reactor at a filling rate k = 0.6. Table 6 shows the parameters of the combustion process with various combinations of geometric dimensions of soil agglomerates in the reactor. The combustion rate determines the duration of the effect of temperature on the surface layer of agglomerates, and hence the depth of phase recrystallization and the strength of bonding with the block matrix forming in the layer. Bonding mixtures charge was prepared according to the ratio of components previously developed and tested in practice. Bonding compositions were prepared based on red and black scale, with aluminum powder used as a reducing agent. The process took place in accordance with the following reactions. 2Al + Fe2O3 2Fe + Al2O3 8Al +3Fe3O4 → 9Fe + 4Al2O3 Photographs of the microstructure are given in Figure 4.

a b a – sintered soil agglomerate with a transition zone, b – block matrix, x 200 Fig. 4. Microstructure of a spherical two-layer sample

According to the experimental data, the duration of combustion of compositions based on red scale Fe2O3 (samples Nos 1-3) is, on average, 2 - 3 times less than the duration of combustion of the 54

systems based on black scale Fe3O4. That is, despite a sharp increase in the area of heat removal from the hot zone, the linear rate of the process running in accordance with reaction (2) is as high as in the case of balls of the same diameter. The analysis of the microstructure of soil agglomerates exposed to high temperatures from the combustion wave propagating in the substance of the block matrix shows that the surface layer underwent phase recrystallization processes. The presence of pores in the core layer suggests intense sintering of the substance resulting in a significant shrinkage. Spinel is the predominant phase in the block matrix. Location of larger crystals in the zone of transition is indicative of the reduction in the cooling rate in the contact area of the agglomerate material and the bonding composition. Obviously, despite significant changes in the conditions of high temperature block synthesis associated with the change in the proportion of masses of bonded soil and bonding composition, in the system such processes take place as block matrix forming, agglomerates surface layer sintering and melting, as well as formation of the transition layer. The phase composition of the surface layer of soil agglomerates demonstrate high strength properties of soil agglomerates and good chemical resistance of the material. The main phase is quartz, a trigonal variety of silicon oxide, which is known as chemically resistant mineral. Illit, a mineral similar in composition to the muscovite, according to the literature, is chemically stable - does not dissolve in acids, while water removes a certain amount of potassium. When melted and solidified it becomes amorphous and forms quartz glass, stable even in boiling sulfuric acid. Albite NaAlSi3O8 as a hydrothermal plagioclase is stable even in hot water. Thus, the SHS process yields samples of blocks representing a composite material comprising a crystalline matrix and sintered soil agglomerates. The surface of the block is formed by crystals of synthetic minerals, primarily corundum and spinel (gertsenit), characterized by high mechanical strength and chemical resistance to aggressive environments, including rain. Quartz, albite and fayalite are part of the transition layer between the matrix and the surface of the sintered agglomerate. Deep layers of the agglomerates, due to the 55

low thermal conductivity of the material, undergo minimal transformation that in this case is a positive effect - during SHS radioactive components in soil do not spread outside the block. 7. SHS in Aluminothermic Mixtures. Ferroalloy Smelting Extraction of rare and scattered elements from low-grade ores has always been a complicated chemical and metallurgical issue. The depletion of mineral resources raises the relevance of this issue. We can see a growth in the range of metals the production of which in pure form or in alloys involves great technological difficulties. This range includes many commonly used materials such as molybdenum, tungsten, niobium, tantalum, rare earth elements, as well as nickel, cobalt, etc. Reduction in their production threatens a substantial rise in the value of the products of metallurgical production most valuable from a technical point of view, and a slowdown in the technological progress. The study of the possibility of use as a starting reagent of waste from mining and processing industry, used batteries and catalysts for various chemical processes in which the content of valuable metals is limited to percent units and fractions led to the consideration of the process of self-propagating high-temperature synthesis (SHS) as a basis for the technology of metal extraction from poor raw materials. SHS is based on exothermic oxidation-reduction reactions. High temperatures in the combustion wave front characteristic of SHS, allow to melt most of oxide systems which include the most refractory metals, such as aluminum oxide, molybdenum, and tungsten. Flowable state of the system under the influence of gravitational forces provides an active separation of synthesis products to the metal and slag components in accordance with their specific density. The reducing agents in many cases may include carbon, silicon, but to produce high quality alloys from their simple or complex oxides aluminum powder is generally used, the physicochemical properties of which depend on the temperature, the kinetic parameters of the process and, ultimately, the composition of the synthesis products. Thus, aluminothermal reduction of metal, a modern metallurgical process, is given top priority in the production 56

of carbon-free ferroalloys. Its advantages are most evident in the case of alloys with tungsten, molybdenum, vanadium, nickel, titanium. Kazakhstan has significant reserves of these metals in the total volume of proven reserves, and smelting of ferroalloys for the steel industry of the Republic as well as for export to the CIS and other countries is a natural economic perspective. Currently, while we see a tendency to restoration of the industry and extension of the production of high alloyed steels the Republic, the consumption of ferroalloys with the rare metals such as tungsten, molybdenum, vanadium etc. is gradually increasing. Effective addressing the technical and economic challenge of combining a wide range of products with low-tonnage production of these alloys can be achieved by means of the so-called minor metallurgy industry. In Kazakhstan “Minor metallurgy industry and applied chemistry” are developed as a new direction in scientific and applied research designed to process ore concentrates, ores, scrap, industrial waste and other substandard raw materials for the production of metals and alloys, the production of which is not traditional in the Republic of Kazakhstan. Due to the peculiarities of the SHS-based technological processes consisting in the complete independence from powerful sources of electricity, water and other natural resources, the characteristic features of this production are negligible capital investment, simplicity of equipment and technological process, high mobility in responding to capabilities of suppliers of raw materials and consumption market demands. Difficulties arising in smelting of ingots with a weigh of up to 100 kg are connected with the scale factor. The increase in the ratio of heat dissipation to heat release conditioned by the increased specific heat loss in case of reducing the reactor volume leads to an increase in melt viscosity, acceleration of the solidification process, and, consequently, incomplete recovery of metals, especially lightweight metals and metals hard to recover, such as titanium. It was shown that the problem is solved by introducing special additives into the initial charge. The additives can be of two types and different mechanism of action on the process. Strong oxidants react with the aluminum to provide additional heat and hydrocarbon 57

additives increase the temperature of the process due to more complete redox reactions by binding the air oxygen. In the case of metals easy to recover from oxides and having high specific density, another problem may arise being the increase in the rate of exothermic reactions, a significant predominance of heat release rate over heat removal rate accompanied by a sharp rise in temperature in the combustion wave front, sublimation or vaporization with the release of unreacted powdered source components and spraying of liquid synthesis products. A typical example of such reactions may be the recovery of molybdenum from ammonium molybdate. Dilution of the initial charge with inert additives solves the problem of reducing the combustion wave velocity, bringing together the rate of heat release and heat removal from the reaction zone. The system is maintained in the molten state for a longer time, with the increase in the yield of metal, but the quality of the slag as a refractory and abrasive material deteriorates due to the presence of impurities in it. Carrying out the process in sealed crucibles the design of which is specifically designed in LLP Floga for minor steel plants, reduces heat and metal loss by creating additional pressure naturally rising during the exothermic reaction of the metal oxide recovery. The slag in this case has the composition and structure of corundum, whose use as an abrasive material of high hardness and high chemical resistant refractory material increases the economic efficiency of the production cycle. Excessive pressure also renders positive effect on the process of smelting metals from poor raw materials. For example, in these days, of industrial importance is the recovery of molybdenum, cobalt and nickel from spent catalysts for oil hydrotreating, insufficiently enriched ores and so-called tailings accumulating in the mining and processing factories. In connection with the growth of oil production the scope of consumption of raw materials is increasing every year, but for large metallurgical enterprises they are not big enough and homogeneous in composition. Valuable metals content in such raw materials is not more than 10 - 15%. The main phase, aluminum oxide in the amorphous state, is ballast in the combustion process. For this case a method was developed designed to improve energetic efficiency of the process and ferroalloy yield with the extraction of 58

the main alloying element to 95% by conducting the process under pressure generated during the chemical interaction of the components of the initial feedstock. Special additives are introduced into the charge, the combustion of which raises the temperature of the system and is accompanied by considerable gas evolution. Typically an increase in system pressure to 15 atm. increases metal output up to 85-95%. In the context of small-scale manufacturing a more subtle process of synthesis of materials can be used than at large enterprises. In particular, of certain applicability is the layered method developed by the authors involving phased extraction of valuable metal from secondary raw materials and producing multicomponent metallic alloys, specific types of ligatures imparting a complex of valuable properties to the metal. The layered system is comprised of an active exothermic layer the combustion of which is accompanied by the formation of the alloy base, and the thermal effect is used for high temperature reactions in the parallel and less active layer, where small amounts of reduced metal dissolve in the alloy base and settle to the bottom of the reactor in the form of large droplets to form an ingot. The main parameters in this case are the composition of the layers, their location in the reactor, dispersion of the components, the conditions initiating the combustion wave and the direction of its propagation. The study of combustion processes in a variety of layered systems resulted in the development and patenting of a simplified and energy-efficient method of producing ferro-boron-chrome [18] with a high content of boron. It was shown that in this method can be used for recycling manmade waste containing molybdenum and nickel scrap. One of the prominent features that characterize the capacity of minor metallurgical industry is a method of increasing the degree of purity of the material obtained in the course of reduction of metals from oxides. In contrast to the known use of centrifuges, centrifugal acceleration of about 20g used to a limited extent for refining of metals in liquid form at large enterprises is applied to the process of aluminothermic mixture combustion. In static conditions at aluminothermic process it is not possible to achieve full recovery of metal from ore. In this case metal loss can reach 25%, the slag is 59

contaminated with small alloy globules and is not very suitable for use as refractory material at high temperatures. One advantage of ferroalloy smelting by SHS method, as compared to other techniques, is the use as feedstock of oxide materials with a minimum content of useful elements without prior enrichment. This is conditioned by a feature of SHS consisting in the increase in temperatures to a higher level in the combustion wave, obtaining a low viscosity melt and intensive phase separation, which can be exacerbated by the influence of gravitational forces in accordance with the density of the formed products. Under the conditions of centrifugal acceleration an increase in the velocity of movement of heavy metal drops through the molten slag is observed, which creates additional ignition centers in the charge, increasing the heat release rate and temperature of the system, with the melt viscosity decreasing. This effect allows you exclude from the charge composition reagents promoting melt liquefaction and negatively affecting the quality of the slag. Corundum is produced by such process can be used for the production of abrasive powders, refractory materials, and in particular for the lining of reactors in which SHS processes are carried out. Features of the metal melting process are based not only on its physical and chemical properties, but also the production economy. The most costly component of the basic initial charge in the SHS process is generally aluminum powder. Aluminum prices are constantly increasing. Profitability drops, if manufactured metal price growth rates are lower. Thus, the current limit cost of ferrotitanium is 3 - 4 thousand dollars per ton depending on the grade. In the production of ferrotitanium the consumption of aluminum is very high. To produce a ton of FTi-35 600 kg of aluminum are consumed. If the price of aluminum is 2800 - 3000 dollars per ton the sales price limit should be at least 5 thousand dollars. Therefore, although smelting of lowgrade FTi20 from substandard raw materials can be carried out without difficulty, presently the issue of obtaining 70% Aktubinsk ilmenite alloy containing 52-56% TiO2 is being solved, without adding to the charge or melt of titanium metal. For this purpose, SHS 60

process is carried out in 100 - 120 liter hermetically sealed crucibles at a pressure generated by intermediate gaseous products in the course of the combustion reaction. If the price of the metal drops, the profitability of production may be kept by reducing waste and the use of the waste slag. At small metallurgical enterprises the introduction of new developments and experimental practice is facilitated by у range of procedures. In this case, the applied research should be directed at reducing the calcium content in the slag and iron, for example, using a centrifugal process, which may be arranged as a continuous process. If prices for corundum are 1.5 - 2.0 USD per kilogram such measures are justified and the slag use is feasible and appropriate. Unlike titanium, molybdenum is an expensive metal. Currently the price of one kilogram of molybdenum in poor feedstock amounts to 20 - 25 dollars, and rising in the case of the concentrate up to 30 40 dollars on conversion to pure molybdenum and up 70 dollars in the case of alloys. However, molybdenum concentrate contains up to 38% of sulfur. Currently, the problem is solved by burning with waste sulfur in the form of CaSO3. The problem can be solved by a search for ways of using this product on a large scale. Thus, the active development of minor metallurgy industry as a promising sector of the economy is based on the achievements of applied chemistry and stimulates scientific exploration in this field of research. Production mobility ensures fast solution of scientific and technical tasks, and obtaining practical results of theoretical developments. 8. Ferro-Boron-Chrome At present, specific types of ligatures are widely used imparting a complex of valuable properties to metals. Thus, the addition to steel of boron microadditives increases electric resistivity and melting point, with nuclear magnetic moment decreased, and microhardness and modulus of elasticity increased. Increasing the boron content results in the formation of borides which, in its turn, results in an increase in hardness, abrasion resistance, heat resistance and corrosion resistance of the metal [19]. Concurrent addition of chromium, aluminum and boron improves the efficiency of 61

introducing boron into steel. Alloys with boron content of about 20% are used for bonding. In the iron and steel industry producing of high-quality ferroboron-chrome system alloys with varying compositions is an actual scientific problem, which is associated with the identification of features of the combustion process that takes place in complex oxide systems, and rational use of its features, as well as the technological problem of reducing valuable material losses in the slag and increasing its content in the melted metal. In the course of the researches aimed at obtaining a fundamental solution of the problem, the oxide components, Cr2O3 and FeO were introduced into the charge in the form of technically pure chemicals. The content of impurities did not exceed 1%. The use of ПА4 grade aluminum powder brand ensured good reproducibility of experimental results. As the boron-containing raw material boric acid was used as well as boric anhydride in an amorphous state produced by burning of H3BO3 at a temperature of 450ºC. Reactions of recovery of ferro-boron-chrome alloy components are described by the following equations: 3FeO + 2Al → Al2O3 + 3Fe Cr2O3 + 2Al → Al2O3 + 2Cr B2O3 + 2Al → Al2O3 + 2B A series of detailed studies were held to analyze the reduction of iron and chromium from their oxides [20-21], the results of which suggest that, due to significant heat generation during reduction reactions it may be possible to implement the process with high efficacy in terms of metal yield and slag removal. When recovering boric anhydride with aluminum the amount of generated heat is only 33 kJ/g-atom of the charge materials [19], and it significantly changes the overall heat balance in the direction of increasing the relative amount of the loss. In this regard, particular attention was paid to the SHS processes involving boron components. The studies of high-temperature synthesis carried out by us using extremely active mixtures of vanadium oxide with aluminum powder [22; 23] have shown that boric anhydride is a potent inhibitor of the 62

explosive combustion. Although B2O3 transition to the liquid phase begins below the melting point of the main components, its inhibitory effect on the oxidation of the aluminum increases the autoignition temperature and has an inhibition effect on the entire process. Boric acid has similar properties which upon heating in the temperature range from 277 to 540 ºC gives the crystalline water, transforming into an anhydride. Thus, both reagents when used in the industry for out-of-furnace smelting reduce the useful output of iron and chromium. To eliminate the adverse influence exerted on the molten boric anhydride on the reactions (11) and (12) as well as for the better use of the thermal energy generated by them a spatial separation of two reagent mixtures was performed, i.e. two parallel layers were formed, differing in composition, intensity of heat and functional load (Figure 5a). The upper layer was a stoichiometric mixture of aluminum with iron and chromium oxides. Initiation of the combustion process therein had two objectives: smelting of the final product basis - iron-chromium alloy, and generation of thermal energy for the excitation reactions in the lower layer. The weight proportion of each component was calculated based on the final composition of the alloy melted by assuming that the reaction runs until complete recovery of metals. The amount of heat released at the same time also lends itself to a fairly accurate assessment. The lower layer was formed from aluminum and boric acid in a stoichiometric ratio. In laboratory experiments the two-layer system was placed in a green porcelain bowl and was put into the laboratory muffle furnace heated to 920-950 ºС, self-ignition temperature of the compound, forming a high active layer. The bowl was covered with a ceramic tile for preventing of the premature beginning of furnace charge surface layer combustion due to radiant energy of the silicon carbide heater. Considering that the total quantity of substance is equal to 300g, duration of porcelain bowl and furnace-charge heating up to the given temperature made 20 minutes. During this time both components of a low layer liquate, but reaction between them begins only after receiving thermal pulse from a more active higher layer. 63

Fig. 5. Charts of layered systems for ferro-boron-chrome and the yield of final product as percentage of the theoretically possible yield rate

In the upper layer ignition occurs at 920 ºС. High dispersibility of components provides fast distribution of a combustion wave across the whole of the high layer. In the course of compound temperature increase chromium oxide enters into a reaction. Reactions (11) and (12) proceed practically simultaneously. Temperature in the wave front reaches 2200 ºС, and all combustion products are in a liquid state here. Regenerated metals interact among themselves resulting in formation of unlimited solutions. Drops of the forming alloy have density of 8,0*103 kg/m3 that exceeds density of corundum 2-fold and density of the initial furnace-charge 4-fold. By gravity they descend along with the combustion front and reach boundary of layer division, where their intensive heat exchange with the liquid phase consisting of the melted boron oxide and aluminum occurs. Behind combustion wave the front temperature gradually decreases owing to alloy interaction with the environment. Aluminum oxide along with the initial components and intermediate products of reactions dissolved in it in insignificant quantities solidifies and forms a slag crust, which along with the air interlayer located under it hinders heat and mass 64

exchange of the materials located in a reaction zone with the atmosphere in the furnace. At a temperature over 2200 ºС solubility of boron in iron and chromium isn't restricted [19]. Restoration of boron proceeds along with its dilution in an iron-chromium alloy. It decelerates reverse reactions and provides cleaning of the final product from the intermediate connections. The drops of iron- chromium alloy enriched with boron subside on a bottom of porcelain bowl and stiffen, forming an ingot. However, during the liquid-alloy cooling process the solubility of boron in iron-chromium solution sharply decreases to the 100-th shares of percent at 900 ºС and to thousandths at 700 ºС. According to state charts in the researched area of concentration (to 20% of boron) chemical compounds of different composition are formed: Fe2B, FeB, Cr2B, Cr5B3, CrB, and also solid solutions on their basis. The X-ray phase analysis of ingots shows presence at tests of a large amount of iron and σ- FeCr, at which, perhaps, about 0,05% of boron, and also a borid of Cr2B chromium are dissolved. Thus, in case of this diagram of carrying out melting theoretically the content of boron in ferroalloy can't exceed 9,5%. In reality it is significantly lower. Process of boron-containing raw materials evaporation that is intensified with growth of temperature is the reason of low extraction of boron. In case of boric acid use the losses increase due to boron capture by water molecules on transition stages of acid to boric anhydride. Vapors of boric anhydride, penetrating into a high layer, interact with its components and will form several different connections, including Al18B4O33. The large amount of aluminum irrevocably excluded from synthesis process is spent on formation of this connection. Besides, due to lack of a regenerate the synthesis process is decelerated, the metal output percentage decreases. For reduction of boron losses and increase in the relative mass of an ingot it is necessary to reduce evaporation of boron oxide during the period from introduction it in the furnace until spontaneous ignition of a high layer. For this purpose the third layer possessing high activity was entered into the system. The layer was created by division of a high layer into two parts and transferring of one of them to a reactor bottom, taking into account the minimum influence of 65

boron oxide vapors on it (Figure 5b). As a result of such processing method the output of an alloy increased almost twice – from 30 to 58%. Compounds of boron in slag at the same time aren't revealed. It is impossible to refer the evaporation effect to reduction of time of a sample presence in the furnace in case of high temperatures since the average duration of exposure prior to combustion didn't increase, and even increased in some experiments. Thus, the reason of alloy output increase consists in change of the process course in general. After achievement by the center layer of boron oxide and aluminum melting temperature the liquid phase consisting of them penetrates into the free space between particles of a low layer that decelerates evaporation process. However, the same phase inhibits combustion in a low layer, locking the part of the most active component system. In this regard, it is important to determine the minimum mass of a low layer. In case of constant particle size distribution of aluminum that is characterized by its grade, it significantly depends on dispersibility of oxides of iron and chromium. The smaller their particles are the lower bulk density of a compound is and the less the low layer mass can be. In the carried out experiments dispersibility of chromium oxide is extremely high and makes 4-6 um. The minimum dispersibility of oxide of iron varied ranging from 63 to 120 microns. Reduction of the general output of an alloy with increase in a share of large particles in furnace-charge is marked. For the purpose of elimination of their influence on the penetration process of boron oxide and aluminum liquid-alloy to the low layer the stoichiometric mixture of iron oxide and aluminum, making 20% of a low layer mass was moved to the center and uniformly mixed with its principal components (Figure 5 c). The dispersibility of a low layer which increased due to it allowed to reduce its weight and to increase an alloy output by 4%. However, the presence of a small amount of iron in the form of small-sized reguluses is noticed in the slag. Influence of regenerate dispersibility on the process efficiency of a multicomponent alloy synthesis in layered system is analyzed in the conditions of out-of-furnace experiments. Aluminum powders with significantly differing average size of particles are used for this purpose. And the amount of powder for carrying out synthesis in the 66

considered three-layer compositions was calculated taking into account experimentally certain chemical activity of aluminum which is connected to the value of specific surface of its particles. Essential positive changes in the course of process are caused by changeover of boric acid by B2O3 boron oxide. In case of complete maintaining of proportions of the three-layer diagram, filling of the reactor, external experimental conditions and observance of stoichiometry as a part of layers use of boric anhydride raised an alloy output to 86% (Figure 27 g). At the same time the most successful components ratio is reached in this series of experiences: 30,5% of boron, chromium - 46,8%. Advantage of using boric anhydride in comparison with boric acid, is defined, apparently, by absence of release of water that reduces boron losses on average layer and unproductive oxidation of aluminum in the upper layer due to its interaction with water vapors. Received data analysis allows to provide a rather broad picture of the given composition synthesis of materials process in a three-layer system. Due to radiant energy of the heaters located in the upper part of the furnace, the most intensive heating happens on a reactor cover surface. During system heating the top layer consisting of active oxidizers and a regenerator has higher temperature, than the ones located under it. Besides, melting of boric anhydride detains the beginning of oxides metal restoration, which come in direct contact with it and also making the lower layer. Due to this the center of selfignition arises in the top layer, and the combustion wave extends from top to bottom. The stoichiometric structure of components provides high temperature of the reacting mixture, good division of metal and oxidic fractions, merge of the restored metal in large drops. By gravity drops of metal descend with a velocity close to the velocity of the combustion wave moving in the same direction. With increase in the intensity process the velocity of combustion wave rises, temperature in the secondary combustion zone increases at the same time, viscosity of slag decreases, and advance of liquid metal through it is facilitated. On the border with melted boron-containing layer because of lowered viscosity of the environment, apparently, there is an acceleration of metal drops movement, and they become additional 67

energy sources for initiation of reaction (13). The restored boron is dissolved in liquid-alloy of iron and chromium. Temperature necessary for completion of this process is supported by exothermic processes proceeding in the lower layer. When cooling boron reacts with metals, and, according to state charts, forms a chemical compounds with them. The bowl-shaped form of reactor promotes formation of an ingot at the bottom of the bowl. In case of successful course of the process the ingot separates easily from the slag. The main crystal phase of a slag crust is aluminum oxide in a corundum form. Thus, the practical problem of receiving ferrochrome-boron can be combined with synthesis of valuable fire-resistant and abrasive material. In laboratory experiments when the mass of substance quantity was a variable parameter, considering the ratio of the top layer to the heat dispersion surface area of m/Sp Ni_Cu, Co and Fe. As indicated above, the mixtures of hydrogen and carbon monoxide (synthesis gas) are widely used in large chemical processes, such as methanol synthesis, high alcohols and aldehydes, Fischer-Tropsch process and others. For each of these processes the synthesis gas with specific concentration ratio of hydrogen and carbon monoxide (H2 / CO) is necessary. For obtaining of hydrogen and carbon monoxide mixtures with ratio of H2/CO the different reactions of catalytic transformation of paraffins are used. 1.2 Catalysts of carbon-dioxide conversion of methane Carbon dioxide conversion of methane (CCM) occurs at higher temperatures than ПМК and ПОМ, but as a result of CCM the synthesis gas with composition of CO:H2 = 1:1 is formed. This composition is necessary for the synthesis of dimethyl ether, which in turn has a number of advantages in comparison with diesel fuel [3] and can be used as an automotive fuel. In review [5], the authors describe a number of works on investigation of carbon dioxide conversion of methane by different scientists all over the world, beginning from 1998 to 2004. In CCM most often the applied nickel catalysts were used [17-32]. In [17] on 263

the catalyst 13.5Ni-2K/10CeO2-Al2O3 the maximum conversion of methane and carbon dioxide was obtained at the temperature of 1073K and with ratio of initial gases of СН4:СО2:N2 = 1:1:1. Conversion of methane in this case is 90%. The contact time is varied by catalyst mass, at that the methane yield is remain constant at 30 ml / min. With increasing of contact time the conversion of initial gases and yield of reaction products is increased. So at 0.09 kgcatalisth/kgmethane the conversion of СН4 and СО2 is 29.5 and 29.0%, respectively, and the yield of Н2 and СО – 27.0 и 28.0 %, respectively. At contact time of 3.50 (kgcatalisth/kumethane) the conversion of СН4 and СО2 is increased to 80.3 and 79.0% respectively, but the concentration of reaction products at reactor outlet was: Н2 and СО – 80.2 и 78.0 % respectively. In [18, 19] the intermetallics of transition metals (systems Ni-Al, Co-Al) as the contact mass of carbon dioxide conversion of methane were investigated. For synthesis catalyst of this process, the method of SHS is applied, because it’s connected with low energy consumption and high efficiency. The studies have shown that the system on the basis of Ni3Al exhibits a high activity at the temperatures above 1010 K. Intermetallics that having in composition the phase NiAl and Ni2Al3 – are inactive. After catalytic investigations, except indicated phases there are phases of nickel carbide, cobalt and graphite-like carbon are detected. The formation of carbon in reaction of dry reforming of methane is described in more detail in [33]. On hexaaluminate LaNiAl11O19 with the help of physico-chemical methods of analysis (TGA, ТПВ-СО2, ТPО) the formations of carbon during reaction of CCM and decomposition of methane at high temperatures were investigated. There is a formation of carbon on catalysts in two forms is found – the first is graphite which is occurred in CCM in greater degree (48.8-61.4%), and the carbide at decomposition of methane (59.1-66.3%) at the temperatures from 500 to 800 ° C. For decrease of carbon formation in [23] the doping of nickel catalyst Pb, Sb, Bi and Te is occurred. According to experimental findings, the greatest resistance to the formation of carbon on the catalyst showed Pb - Ni / SiO2. At carbon-dioxide conversion of methane (CCM) there is carbonization of catalysts surface is happened. Super activity of 264

catalysts, which are synthesized by SHS method [19], during carbon dioxide reforming of methane process, is associated with the formation of multiphase systems, the presence of interfaces, as well as stabilization of the nickel clusters with desired size. The comparison of industrial nickel catalyst with catalysts such as Ni / SiO2, Ni-Cu / SiO2 in reaction of CCM is shown in [22]. The activity of industrial catalyst in carbon dioxide conversion of methane at 550 °C was higher (the conversion СН4 and СО2 = 57 and 36 %), than catalyst Ni / SiO2 (the conversion СН4 and СО2 = 42 and 34 %). At that the yield of H2 and CO was 53%, and 4 on industrial catalyst, and 40 and 4.7% on Ni / SiO2 catalyst. The addition of Ni / SiO2 to catalyst copper lead to decreased activity. High values of conversions СН4 and СО2 and yields Н2 and СО (95-98%) were obtained on nickel catalysts are synthesized by MgAl-NiY [25]. An optimal catalyst was investigated at 800 ° C during 150 hours and was reused after regeneration. At the surface of catalyst there is 5-10% of carbon is formed, but the catalyst activity and selectivity of reaction products does not reduced. In [28], the nickel catalyst Ni / Mg-Al was prepared by «solid phase crystallization» method (spc-method), which is based on using of precursors ([Mg6Al2(OH)16CO2−3]·H2O), containing in its structure the homogeneously distributed metal, which is after heat treatment forms the high dispersed and stable metal particles at the substrate of substrate. The obtained spc-Ni / Mg-Al catalyst was investigated in reaction of CCM on following conditions: CH4/CO2/N2 = 1/1/1.4, GHSV = 54000 ml h−1g-cat−1. It was shown [28] that on this catalyst with maximum conversion (94%) the methane reach 1073 K, the catalyst was operated at such temperature during 6 hours. In carbon dioxide conversion of methane, besides nickel catalysts there are also cobalt catalysts on the basis of MgO/C, Al2O3, TiO2 [34], MgO [35], and rhodium catalysts on the basis of MgO, TiO2, ZrO2/SiO2 [34,36]. An influence on catalytic activity in the reaction of CCM of cesium additives (3.6 - 12 wt. %) to the basis of nickel catalyst is shown in [30]. The most active catalyst was with content of Ce 6 wt. %. The highest conversion of methane, for this catalyst reaches 89% at a temperature of 750 ° C and conversion of CO2 - 73%. 265

1.3 Overview of recent research of catalysts on fabric carriers, their application in chical technology and catalysis During production of a broad class of chemical products and chemical industry, the heterogeneous catalysts of different geometric shape, physical and -chemical properties of active component, carrier nature and others are used. The basic requirements for such common commercial catalysts are its high activity and selectivity to desired product. The porous materials which used in various fields are varied in chemical composition, physical and hydraulic properties, geometric form. Among them a special place takes the materials on the basis of fiberglass, which have been used recently in chemical technology as the carriers of heterogeneous catalysts, filters and sorbents [37]. The advantages of these materials in comparison with granular or block catalysts are related with physical and chemical properties of the glass, and with peculiarities of their geometry. Catalysts on the basis of fiberglass have unique mechanical properties such as (flexibility, ability to be shaped), and good hydraulic performances. Despite seeming simplicity of geometric structure, the fiberglasses have a complex morphological structure, which is determined by the degree of twisting fibers, are represented an assembly of microfibers, way of their weaving, represents a capillary-porous systems, are created on the basis of elementary microfibers with diameter of 5-13 microns. Thus, woven systems have the dauble porosity: the fibre porosity and fabric porosity, which is determined the filtration properties of woven material as a whole. Usability of fiberglass matrix as catalysts in catalytic systems is considered in patents [38-39]. In these works, the fiberglass basis is used as a substrate for the metal active phase, which is applied to it by traditional co-precipitation methods. Currently the catalysts on the basis of silica fiberglass woven fabrics are widely used, that are activated by implanting of metal ions into fiberglass amorphous matrix of carrier. Such type of catalyst systems was created during solution of concrete technological problem, namely, in the process of suppressing of migration surface mobility and sublimate fly-ash of the platinum 266

catalyst in the reactions of catalytic combustion (in particular, in stage of ammonia conversion during production of azotic acid). The laboratory researchers and industrial tests [40-42] have shown that the silica fiberglass woven catalysts can be very effective in many other technological processes and perhaps even eventually able to oust the traditional bulk granular catalyst materials. The Chinese scientists [43] have developed the fibrous catalyst Cu / Zn / Al / Zr for synthesis of methanol, form hydrogenation reaction CO2. Synthesis methodology consists in mixing of an active ingredient in nitrate solution (Cu, Zn, Al) and ZrOCl2 с Na2CO3 at 353К, with following filtering, washing, drying at 120 0C during 12 hours and calcination at 350 ºС during 4 hours. SiO2 is the basis for obtained sample. With the help of transmission electron microscopy it was revealed that the fiber consists of the agglomerates which are uniformly oriented in the form of fibers with a diameter of 2 nm ~ In [44-51] the description of catalysts is presented, are woven from silicate, amorphous fiberglasses (containing SiO2 55-98% wt.) in the form of webs or nettings, are activated by catalytic components from a wide range of metals (Pt, Pd, Ag, Cr, Ni, Mn, Co et al.). The composition and content of an active component on the surface of fiberglass substrate is determined by the requirements of each particular catalytic process. In the course of search techniques for catalytic activation of silica basis, a number of methods of ions metal implantation in amorphous fiberglass matrix is developed [40-49]. During the preparation process of fiberglass catalysts in [47], the coating of titanium to the surface of fiberglass is carried out by traditional method of impregnation ((dilute titanium alkoxide solution) (DTS)) 10% of DTS with subsequent drying and calcination at 500 ° C. Reduction of temperature was held at 1 ° C per minute over 4 hours. This type of catalyst was called as DTS / GF catalysts. Catalysts which were called (P25 / GF) were synthesized from anatasetype titania powder (Degussa P25). Images of obtained catalysts are shown in Figure 1. In [54] the catalysts Сu/SiO2 were prepared by adsorption of copper (in glass thermostate shaked reactor at 30-70 ºС during 10120 min) from solutions of cationic ammonium complexes of Cu (II) 267

on fiberglass carrier. The concentration of copper in the samples is ranged from 0.05 to 0.08 wt.%.

Fig. 1. TEM images of fiberglass catalysts DTS/GF and P25/GF

The method is based on reactions of ion exchange is most promising, proceeding directly in microporous solid amorphous matrix of SFGC-fiber (silica fiber glass woven catalysts) is placed to special liquid medium from metal ions. Today the main factors can be identified, that determining the fundamental scientific and technological novelty of SFGC-systems that give these systems essential catalytic and operational advantages in comparison with traditional bulk granular catalysts [42, 46-52]: 1) Phase nonequilibrium of SFGC-systems is a fundamental feature, and this factor determines the possibility of extreme catalytic properties of SFGC. 2) Catalytic Activation of these catalysts is carried out with the help of implanting to the amorphous silica matrix of metal ions [42]. This preparation method of catalysts differs from traditional methods of application of catalytically active phases comprising a metal on the surface of the carrier. 3) Fiberglass catalysts have high catalytic activity with low concentration of active component in matrix [52]. This advantage 268

allows using the platinum group metals as an active phase. Thus, in [46-49], the platinum and palladium catalysts on the basis of fiberglass in various reactions are investigated, at that, a low content of active ingredient does not affect to the activity and stability of catalysts. 4) SFGC is characterized by high chemical and thermal stability, mechanical strength, resistance to abrasion and dusting. These qualities of SFGC-systems in conjunction with stability introduced to its matrix of metal component provide to these systems good performances for the duration of the operational path [49-52]. 5) SFGC realizing in reactor an effective cassette design of layered formed catalyst package with significant decrease of total mass of load in comparison with conventional granular bulk catalysts. Such cassette design of catalyst package- cartridge provides an operational simplicity and efficiency of extraction of spent catalyst from reactor [52]. 6) The production process of SFGC-materials is characterized by continuous of technological scheme, its easy tunability on new product, as well as profitability. Thus, in the field of catalytic chemistry, the SFGC- systems can be designated as new, practically unexplored objects. Currently the silica fiberglass woven catalysts are used in industrial sections as: 1. Catalytic purification of gas industrial exhausts from organic impurities, CO and nitrogen oxides. 2. Production of nitric acid and fertilizings. 3. Production of sulfuric acid 4. Various processes of hydrogenation of hydrocarbons. 4.1. Hydrogenation of nitro-aromatic hydrocarbons, in particular with a view to disposal of explosives. 4.2. Selective hydrogenation of acetylene impurities in synthesis gases for production of olefins and monomers of synthetic rubber. 4.3. Hydrogenation of natural oils and fats in production of hydrogenated fats (margarine industry and the production of industrial solid fats). 5. Purification of water from nitrate-nitrite contaminations by hydrogenation method. 269

6. Catalytic surface nitration of details from steels and alloys in mechanical engineering. Creation of catalyst factories for the production of SFGC - materials do not requires the substantial capital investments, because they can be expanded by introducing of some additional steps in existing productions of fiberglass materials of heat-protective, dielectric and constructional assignment. 1.4 Liquid-phase self-propagating high-temperature synthesis or «solution combustion» method (SC) During the past decade, the investigations on synthesis of materials by SHS method have attracted significant attention. However, the high temperatures are necessary for initiation of SHS process, as well as the passage of SHS difficult the applications of this method for obtaining of complex heterogeneous systems. In comparison with this, an application of wet methods in consequence of mixing of initial components on molecular level, allowing to synthesize the systems at relatively low temperatures. This method was proposed by J.J. Kingsleem and K.S. Patil in 1988 [53-55]. In combustion process there is exothermic reaction between oxidant (mostly nitrates) and an organic fuel, such as urea, glycine or carbohydrazides. In this method the premixing of oxidant and a reductant in aqueous medium is occurred, after dehydration at relatively high temperature (300-500 ºС), the passing of reaction with heating of system with the progress by heating to temperatures of 1000-2000 ºС begins almost instantaneously. In [56], the parallel synthesis of nanocomposite materials Y3Al5O12/Tbx with using of this technique is considered. Structure and physico-chemical properties of synthesized materials were investigated by XRD and UV spectroscopy. It was shown that this method of synthesis is applicable to the synthesis of hightemperature compounds. For example, in [57], a liquid-phase SHS synthesis of nickel powder with using of urea as a reducing agent in a microwave oven. Synthesized nickel powder was investigated by a number of physical and chemical methods: XRF, EA, force atomic microscopy (FAM), derivatographic thermal analysis (DTA), thermal gravimetric 270

analysis (TGA), as well as magnetic measurements were made. It was found that in relationship of fuel to nitrate 5:1 and 6:1 the product is different in composition is formed. In another ratio the nickel oxide is in the form of impurity together with metallic nickel. In article the formation mechanism of nickel and its oxide is presented here, which was discussed on the basis of IR spectroscopy, TGA and DTA methods. In [56], an influence of hexamethylenetetramine, as new reducing agent in liquid-phase self-propagating high temperature synthesis of complex metal oxides (double, triple, quadruple) is considered, in particular zirconium, oxide, cerium, as well as perovskites on the basis of lanthanum, manganese and scandium. It was indicated that hydrazine is used in liquid-phase self-propagating high temperature synthesis processes as a reducing agent is highly carcinogenic, but the urea is used for synthesis of oxide systems on the basis of aluminum, because it requires the high temperatures (about 1500 ºС), therefore, according to authors, the search of alternative reducing agents is necessary. In this paper, the advantages of using of hexamethylenetetramine, which is also known as hexamine or methenamine are shown. In article there is also presented the proposed mechanism of liquid-phase self-propagating high temperature synthesis. The combustion temperature of the reaction in depending on initial composition of the components was in the range of 600-1300 ºС. In [58-60] the liquid-phase SHS (LSHS) is considered, as a synthesis method of oxide materials has received recent development in comparison with SHS methods and solid-phase combustion. Figure 2 shows, how the combustion of dried mixture of ferric nitrate with glycine in a volume of glass, standing on an electric stove is occurred. LSHS occurs at an initial temperature of 396 K. Moreover, the specific surface area of obtained sample after reaction of LSHS (γ-Fe2O3) is reduced from 60 to 2.0 m2/g. A wide range of technologically useful oxides such as (alumina, zirconium dioxide) with interesting magnetic, dielectric, electrical, mechanical, catalytic, fluorescent and optical properties was prepared. With the help of LSHS the synthesis of oxide materials 271

with desired composition and structure (spinel, perovskite, etc.) becomes possible.

Fig. 2. - Liquid-phase SHS: combustion in a volume of glass

In [61] the obtaining of CuO, Cu and CuNi alloy with using as a reducing agent of carbohydrazide and N-tertiarybutoxy, and the oxidants were crystallohydrates of copper nitrate and nickel was investigated. It was found that, depending on the ratio of reducing agent to oxidant in the interval from 0.5-1.5, there is a formation of nanopowders or metal oxide forms, or pure metal in particular the alloying of CuNi is found. The structure and morphology of the materials are investigated by XRD and SEM methods. In [62] the possibility of producing of catalytic afterburner of diesel fuel on the basis of perovskite chromite lanthanum La0.9K0.1Cr0.9О3-δ, is deposited at the surface of cellular block by LSHS method. As the result the homogeneous high- active bed surface of perovskite was obtained. The coating characteristics were investigated by XRD, SEM and HDX methods. It is determined that the catalyst surface can withstand high temperatures (900 ºС) and has a prolonged period of operation. However, at continuous operation certain growth on the surface of the perovskite crystals is observed. It is interesting, that some of used reducing agents are specific for formation of various oxides, for example urea - for aluminum oxide; glycine – for chromium oxide [59], etc. These reducing agents serve two functions: 1. Are the sources of C and H which during combustion forms CO2 and H2O with the release of heat. 2. Forms the complexes of homogeneous mixtures of cations in solution. 272

Exothermica of similar oxidation-reduction reactions is in the interval of 1000-1800 K. Depending on used reducing agent, the nature of "burning" of solution changes from flammeous to flameless Liquid-phase condition of synthesis products after passing of combustion wave helped to solve three classes of practical problems. 1. An obtaining of carbide ingots, borides, silicides and metal oxides, hard and refractory alloys, composite and gradient materials. 2. An obtaining of molded articles, including pipes from listed above materials; 3. An obtaining of wear-resistant coatings to machine components and mechanisms; 4. Implementation of industrial waste recycling (metal chips, scale and metallurgical dust and so on.). In this paper, the methodology of fiberglass surface modification by conducting of liquid-phase SH-synthesis (LSHS) is used. Realization of this reaction leads to the formation on the surface of material the uniformly distributed oxide nanoparticles of corresponding metal [63]. 2 EXPERIMENTAL PART 2.1 Synthesis of fiberglass catalysts For the development of catalysts as the carrier, the fiberglasses such as Na-Si- with brands КС-11-ЛА (88) and КТ-11-ТО-30К are withstand the heating temperature of 1200 ºС without changing its characteristics were used. Concentration of active component at the surface of catalysts was varied within 0.2-1.5 wt. % (Table 1). For preparation of catalysts the sample of fiberglass with the size 5x5 cm considering its moisture capacity was impregnated by calculated amount of aqueous solutions from cobalt nitrates, nickel, and glycine, then the sample was dried for 30 minutes in air at the temperature of 100 ºС. After that, the dried sample was placed to the muffle furnace or drying box and heated to temperature of 400-450 ºС for 1 hour. In this temperature range the SHS process is happened, which in certain cases, namely, at application of an active phase of the order 1-1.5% could be observed visually in the form of a weak bluish glow appeared above the sample. This obtaining method in various 273

publications is called as liquid - phase SHS (LSHS) or Solution combustion (SC). This method between primary components meets the following reaction: Ме(NO3)2*nH2O + 4C2H5NO2+2.5O2 = 8CO+16H2O+3N2+MeO,

(7)

Where: C2H5NO2 - glycine which acts as a reducing agent. The additional missing oxygen enters from the atmosphere. Ме(NO3)2*nH2O + 4C2H5NO2

100 оС

400 оС

Fig. 3. The consequence of synthesis stages of fiberglass samples by LSHS method

Table 1 – Synthesis conditions of fiberglass catalysts fiberglass catalysts

Total content МеО,%

СоO / NiO, % /%

IК1 IК2 IК3 IК4 IК5 IK6 С-1 С-2 С-3

1,0 1,0 1,0 1,0 1,0 1,0 1,2 1,2 1,2

100/0 70/30 60/40 50/50 30/70 0/100 50/50 0/100 100/0

274

MeO / Glycine, mole/mole 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/4

2.1.1

The synthesis of polyoxide catalysts on the basis of fiberglass (MgO, СоO, NiO) The samples were prepared on the basis of high-temperature fiberglass brand КТ-11- ТО, which can be use longtime at 1200 °C. Tissue samples with the size of 6x6 cm were used. Afterwards the sample was settling to aqueous nitrate solution of active metals. Calculation of the concentration of nitrates and reducing agent (glycine) was engaged by the equation (1). Prepared aqueous solution of initial salts is poured into the dish of ultrasonic disperser brand DA-3A (30 kHz), after that the sample was placed to the solution and kept there for 4 minutes. The using of ultrasound allows making the uniform and more complete impregnation of fiberglass by working solution. The impregnated samples were dried in thermostat at 110 0С in air for 30-50 minutes.

500 оС

120 оС

Fig. 4. Scheme of synthesis for fiberglass catalysts by "solution combustion" method

275

Table 2 – Matrix for planning of experiment (Catalyst system: MgО-NiOCoO) №

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

MgО, % 2 0,5 1 4 3 2 0,5 1 4 3 2 0,5 1 4 3 2 0,5 1 4 3 2 0,5 1 4 3

NiO, % 0 0,4 0,8 1,2 1,6 0,4 0,8 1,2 1,6 0,0 0,8 1,2 1,6 0,0 0,4 1,2 1,6 0,0 0,4 0,8 1,6 0,0 0,4 0,8 1,2

CoO, % 0,8 0,0 1,2 0,4 1,6 1,2 0,4 1,6 0,8 0,0 1,6 0,8 0,0 1,2 0,4 0,0 1,2 0,4 1,6 0,8 0,4 1,6 0,8 0,0 1,2

τ(k), c 0,9 0,6 0,75 0,3 0,45 0,3 0,45 0,9 0,6 0,75 0,6 0,75 0,3 0,45 0,9 0,45 0,9 0,6 0,75 0,3 0,75 0,3 0,45 0,9 0,6

T, °C 750 800 700 600 850 850 750 800 700 600 600 850 750 800 700 700 600 850 750 800 800 700 600 850 750

K(CH4), % 1,98 99,54 95,53 9,94 99,51 97,3 77,46 91,43 77,35 1,37 1,15 98,14 64,06 45,65 1,62 49,46 63,39 2,14 1,01 87,25 94,15 1,7 2,5 97,94 94,61

K(CO2), % 3,62 88,57 83,81 36,55 100 97,93 80,7 92,98 81,35 1,99 1,59 97,67 69,11 48,01 1,53 55,52 58,76 1,63 2,63 94 96,14 0 0,76 95,85 95,52

CO, %

H2, %

0,5 36,92 33,42 15,96 55,39 46,5 28,77 39,58 31,04 0 0 50,54 31,87 0,08 0,04 16,65 18,06 0,18 0,16 43,86 37,93 0,14 0,004 50,24 40,31

0,08 33,88 29,72 5,92 52,43 48,002 25,45 35,74 28,82 0 0,004 49,07 20,2 0,04 0,01 8,23 23,21 0,08 0,02 43,23 38,13 0,02 0,01 49,45 40,02

Then they were calcining in a muffle furnace at the temperature of 500 ºС (30 minutes), at that the following reaction of synthesis "solution combustion" is occurred: Mg(NO3)2*6H2O+2CH2NH2COOH+2O2= MgO+4CO2+11H2O+2N2

(8)

The work involving the probabilistic and deterministic scheduling experiment varying of 5 factors at five levels [64]. In capacity of factors are chosen: the content of MgO - 0,5-4%; NiO and CoO - from 0-1,6 %, contact time - 0.3-0.9; the temperature from 600 - 850 °C (Table 2). 276

As a result of experimental data processing due to imposed factors the partial dependences of CO и H2, H2O and conversion CH4 and CO2 were obtained. 2.2 Physical-chemical study of catalyst systems The phase composition of fiberglass catalysts was investigated by X-ray diffraction method on device HZG-4C («FRE / Berger Prazisionmechanik», Germany) using monochromate cobalt radiation in the range of angles 10-85º for 2θ. Phase analysis was performed using X-ray database of International Union of Crystallography (JCPDS). The particles size was evaluated according to Scherrer formula: D = kλ/β cos θ, where: k-is shape parameter; λ-is wave length (1.79021Ǻ); β-is half-width of a line; θ- is a line position. 2.3 Investigation of initial fiberglass and catalyst samples is conducted by scanning electron microscopy method (SEM) The studies were conducted on the microscope JSM 6460LV (JEOL, Japan) with an accelerating voltage of 25 kV. Research sample was fixed on a copper holder using a conductive glue or tape. Pre on the sample surface in a special vacuum system applied in a thin conductive layer thickness of 5-10 nm gold to eliminate the effects of charging. 2.4 Investigation of initial fiberglass and catalyst samples is carried out by scanning electron microscopy (SEM) Investigations were conducted on the microscope JSM 6460LV (JEOL, Japan) with accelerating voltage of 25 kV. For research the samples were fixed on a copper holder using a conductive adhesive or tape. Previously, at the surface of samples in a special vacuum system a thin conducting layer of gold with thickness of 5-10 nm for elimination of charging phenomenon was applied. The catalysts samples were investigated with the help of atomicforce microscope in semi-contact mode. For this, they were grounded 277

to powder condition, placed in distilled water and processed by ultrasound with frequency of 22 kHz. Then, to the fresh chip of mica with area of 25-30 mm2 the drop of resulting suspension was deposited (20 mcl) and for 1 hour at room temperature the adsorption was carried out. Remains of aquae were removed with the help of filter paper, after that the scanning of sample surface is carried out. As a result, a response as potential difference between the surface and probe (needle) was obtained. Morphological features, structure and size of an active component at the surface of fiberglass, were examined by transmission microscopy method (TMM) on electron microscope JEM 2010 (JEOL, Japan) with resolution on lattice of 0.14 nm at an external voltage of 200 kV. For execution of local analysis of chemical composition of sample the microscope is equipped with energy-dispersive X-ray spectrometer EDAX (EDAX Co.), is fitted with Si (Li) detector with an energy resolution of 130 eV. For investigation, the samples were deposited by ultrasonic disperser on standard copper grids with carbonaceous coating which were placed to holder that was inserted into the chamber of an electron microscope for analysis. Thermo-programmatic recovery of the samples was carried out on installation is equipped with flow reactor (quartz) and thermal conductivity detector. For this, 100 mg of the sample (as a fraction 10.5) was charged into the reactor, trained in fixed conditions, and then reduced with mixture H2 (10 vol.%) in argon in temperature range of 40-800 ° C at heating rate of 10 ° / min. The water which is formed during recovery of transition metal oxides was frozen in a trap at a temperature of 70 °C. The hydrogen absorption was calibrated according recovery of copper oxide, under similar conditions, assuming that CuO is fully restored to metallic copper in a single step. For study of pretreatment conditions effect on surface state of catalyst, the training of samples was made under two conditions: 1) in oxygen at 400 ºС for 30 minutes, cooled to room temperature in current of oxygen, then purged with argon for removing of oxygen from the pore space of the catalyst 278

2) In argon at 400 ºС for 30 minutes, cooled to room temperature in current of argon. Electron spectra of diffusion reflectivity (ESDR) of fiberglass samples were recorded respectively to BaSO4 in the range 1100054000 cm-1 on spectrophotometer UV-2501 PC (Shimadzu) with a diffuse reflection attachment ISR-240A. The spectra are shown in coordinates: along ordinate - Kubelki-Munka function, along abscissa – wave number. The spectra were recorded without grinding of samples into powder. 2.5 Investigation of catalyst activity on the basis of fiberglass, are modified by СоO and NiO in the process of carbon dioxide conversion of methane Investigation of synthesized fiberglass catalysts in the process of carbon dioxide conversion of methane was conducted chromatographically on gas-liquid chromatograph “Crystal 2000M” in flowing quartz reactor (Figure 5). Experimental conditions: mixture СН4 – 50% + СО2 – 50%; reactor temperature is 600-900 0C; mixture consumption – is 60 cm3 / min; mixed speed of gas stream – is 1440h-1. ВЗ-1’

Реактор

Рот-1

Др

Сброс

ВЗ-1 РП-1

CH4

ВЗ-2’

ВЗ-3

ВЗ-4

Рот-2 ВЗ-2 ГХ Кристалл-2000M

CO2

РП-2

ОБОЗНАЧЕНИЯ ВЗ РП Рот Др

- Вентиль запорный - Регулятор потока - Ротаметр - Дроссель

Fig. 5. Scheme of laboratory setup for realization of carbon dioxide conversion of methane reaction

Gases (CH4 and CO2) from balloons through reduction box, flow control devices RP-1 and RP-2 and calibrated flow meters were delivered to the input of quartz reactor, is located horizontally. 279

Located ahead reactor and behind closing valves allowing to direct the flow of reactants to atmospheric vent of fume hood, either directly to sampling valve of gas-liquid chromatograph for realization of qualitative and quantitative analysis of reaction products. As a chromatograph the apparatus, brand "Crystal 2000M" is used, with a packed column with a diameter of 3 mm and a length of 2.5 m, is filled with carbon sorbent, carrier gas was argon of high purity. 2.5.1

Investigation of activity of polyoxide catalysts (MgO, СоO, NiO) on the basis of fiberglass in the process of carbon-dioxide conversion of methane The catalytic activity of the prepared samples was studied in the process of CH4 and CO2 utilization on installation is schematically shown in Figure 6. The gases from balloons with methane and carbon dioxide are fed through the gears on the calibrated according initial gases of manometers and then then subsequently on the block IRG-3 (gas flow meter) which is allowing to make a fine adjustment of initial gases in the interval of 0.1-100 cm3 / min. All data concerning gas flow are appearing to computer monitor. Then the gases pass to the mixer directly to the catalytic reactor. Investigation of catalytic activity of the samples was conducted in flow installation which is made of quartz glass, is heated by the tubular furnace. The mixed gas is supplied with the rate of 60 cm3 / min (for CO2 - 30 cm3 / min, for methane - 30 cm3/ min) to the catalytic reactor from the top, and after reactor - on the chromatograph. The reactor temperature is set with the help of the thermostat brand TP-720 (BAPTA) and controlled by HAthermocouple (is shrouded in quartz), located inside the reactor at the same level with the catalyst bed. Initial gases and reaction products are analyzed on the chromatograph mark "ХРОМОС ГХ-1000".

280

5

3

2

4 1

2 1

7 8 9

ИРГ3

CH4

2

СО2

6

+ -

6

10

ХРОМОС

1 Н2

11 12

ВАРТА

1 – Gas balloons; 2 – Gas –pressure regulators; 3 – Gas flow meter IRG-3; 4 – Triple adaptor; 5 – Thermocouple; 6 – Closing valves; 7 – Mixer unit; 8 –Catalytic reactor; 9 – Tubular laboratory furnace; 10 – Gas chromotograph; 11 – Thermostatic regulator; 12 - Computer Fig. 6. Scheme of catalytic installation

For pre-installing of necessary rate of initial gas mixture, consisting of methane and carbon dioxide, the calibrated monometers on these gases are used (1). Fine adjustment of rates is carried out with an instrument IRG-3 (3), which is connected gradually in the lines of initial gases. The mixer (7) is designated for complete mixing of incoming gas streams. Closing valves (6) allowing to fed, if necessary, the catalytic reactor with a mixture of methane and carbon dioxide or hydrogen for recovery of oxide catalyst to the metallic state. 3 RESULTS AND ITS DISCUSSIONS 3.1 Physico-chemical properties of synthesized catalyst The phase composition of synthesized samples of catalysts was studied by XFA method. The catalyst sample was triturated into powder previously. The XRD image of samples (CоO/NiO = 100/0, fig.7), IK2 (CоO/NiO = 70/30, fig.8) and IK5 (CоO/NiO = 30/70, fig.9) shows the presence of amorphous phase from fiberglass and 281

oxide phases CoO-NiO. In case of IК1, the formation of spinel phase Co3O4 with a particle size of 20 nm is observed. 28

*

60 Intensity

26

Intensive

50

* *

40

24

22 72

30

74

76

*

78

2θo

80

*

82

*

20 30

40

50

2θ 0

60

70

80

Fig. 7. X-ray diffraction image of catalyst IК1 (CoO/NiO=100/0): * - phase Co3O4

The study of oxide film without substrate (without matrix of fiberglass) the X-ray phase analysis of the samples is also showed the presence of spinel phase Со3О4 and this fact can serve as a check of the data. An Addition of NiO leads to dilution of NiO in Co3O4 and formation of substituted spinel phases (Ni, Co)Co2O4. The XRD image of catalyst IK2 (CoO / NiO = 70/30) is only phase (Ni, Co) Co2O4 (Figure 8). An increasing of concentration NiO in the sample of catalyst IK5 (CoO / NiO = 30/70) leads to formation of two phases, a spinel (Ni, Co) Co2O4 and NiO (Figure 9) with the same particle size of 20 nm. XRD image IK6 (CoO / NiO = 0/100) shows only phase NiO. By scanning electron microscopy method (SEM) the images of pure fiberglass and catalyst samples were obtained. Figure 10a shows that initial fiberglass represents fibers with diameter of 8.7 microns, it also can be seen that on its surface there is some inclusions (apparently contaminations) but the film formations at the surface are clearly not observed. In figures 10 b-c there are particles of active 282

component in the form of individual particles and aggregates, it also can be seen that the fibers are coated with film (figure 10b). All prepared catalysts have similar morphology regardless of the composition. The grounded sample was deposited on copper grid is coated by graphite and studied with an electron microscope, brand JEOL JED 2300 with an accelerating voltage of 200 kV. Photographing is carried out in regime of secondary electrons (SEI). 40

Intensity

35

*

30 25

* *

20

30

40

50

60

*

70

80

2θo

Fig. 8. X -ray diffraction image of catalyst IК2 (CoO/NiO=70/30): * - phase (Ni,Co)Co2O4 21

* Intensity

60

Intensity

50 40

♦

20

♦

*

30

19 72

*

74

76

78

2 θo

20 30

40

50

60

2 θο

70

80

82

*♦ 80

90

Fig. 9. X- ray diffraction image of catalyst IК5 (CoO/NiO=30/70): * - phase NiO, ♦ - phase (Ni,Co)Co2O4

By scanning electron microscopy method (SEM) the images of pure fiberglass and catalyst samples were obtained. Figure 10a shows that initial fiberglass represents fibers with diameter of 8.7 microns, it also can be seen that on its surface there is some inclusions 283

(apparently contaminations) but the film formations at the surface are clearly not observed. In figures 10 b-c there are particles of active component in the form of individual particles and aggregates, it also can be seen that the fibers are coated with film (figure 10b). All prepared catalysts have similar morphology regardless of the composition. The grounded sample was deposited on copper grid is coated by graphite and studied with an electron microscope, brand JEOL JED 2300 with an accelerating voltage of 200 kV. Photographing is carried out in regime of secondary electrons (SEI). It can be seen that the basic mass of material represents single pieces of fiberglass with clearly visible at their surface aggregates are consisting of magnesium oxide, cobalt and nickel. In this case, the electron stream was directed at the surface of fiberglass which is free from phases of deposited components.

a

c

b

d

Fig. 10. SEM images of pure fiberglass (а), catalysts IК1 (b), IК4 (c), IК3 (d)

Figure 11 shows a photograph of fiberglass, brand КТ-11- ТО. It is evident that the diameters of fibers are intertwining the cloth have the sizes in the order of 0.4 microns. 284

Fig. 11. The photograph of fiberglass catalyst surface № 5

Figure 12 shows the electron micrographs of the sample №5 according to planning matrix.

Fig. 12. Photograsph of fiberglass surface in regime of secondary electrons as well as micro-X-ray pattern of secondary electrons surface

It can be seen that the basic mass of material represents single pieces of fiberglass with clearly visible at their surface aggregates are consisting of magnesium oxide, cobalt and nickel. In this case, the 285

electron stream was directed at the surface of fiberglass which is free from phases of deposited components. Figure 12 shows the photographs of fiberglass fibers surface micro-X-ray pattern of surface for sample №5. On the basis of micro-X-ray pattern it can be seen at the surface there are some aggregates which includes elements such as Mg, Co and Ni. The selected elements such as Si, Al, O forms the basis of fiberglass, but the carbon as graphite is used as current-conducting material, because the fiberglass is an insulator. Due to scale size, it can be seen that grounded pieces of fiberglass has the value which is in the range of 10 - 50 microns. Figure 13 shows the AFM image (three-dimensional picture of the field) of catalyst nanoparticles. In horizontal plane there is an area with the size of 3,5х3,5, microns is showed, which is scanning sample field. The figure shows only the area where the particles are detected, the black spots and roughness at the area are the noise of survey errors. The high of particles is characterizing their size, is determined by the vertical scale, and in this case is 8.7 nm.

Fig. 13. AFM image (three-dimensional picture of the field) of catalyst nanoparticles

The pictures taken by TEM (the sample IK3, Table 2) it can be seen that the active component is dispersed at the surface of fibers, generally, in the form of separate particles with the size of about 10 nm. EDX-analysis (Fig. 14) have showed the presence of NI and Co atoms in them. Interplanar distances in particles are characterizing the metallic state of elements. 286

Fig. 14. EDX spectrum (а), TEM image (b) of catalyst IK3 (COO / NiO 60/40)

Fig. 15. TEM image of separate particles of spinel, consisting of NiCo2O4 (catalyst IK3) and digital diffraction of selected field (black square) and consisting of metallic Ni and Co (catalyst IK3)

Fig. 17. TEM images of polyoxide catalysts № 5 and № 9

287

The pictures taken by TEM (the sample №5 and №9, table 3) is also can be seen that the active component is dispersed at the surface of fibers, generally in the form of separate particles with the size of about 5 - 10 nm (Figure 17). For deposited systems the temperature intervals of these reactions can vary, in particular the recovery temperature of transition metal oxide particles may be reduced due to reduction of oxide particle size or increased due to interaction of an active component with the carrier (up to the formation of new phases). Figures 18-20 shows the typical curves of TVP by hydrogen of cobalt, nickel and bicomponent of Co-Ni catalysts. In table 3 the results of TPV experiments are summarized: the temperature of maximum absorption of hydrogen, total absorption of hydrogen, the ratio of H2/M and assignment of this absorption.

1 – sample С-1 (1.2 mass.% Со+Ni, 50Сo/50Ni), 2 – С-2 (1.2 mass.% Со+Ni, 0Сo/100Ni), 3 – sample С-3 (1.2 mass.% Со+Ni, 100Сo/0Ni) The samples were trained in oxygen 400оС/0.5 h. Fig. 18. Absorption rate of hydrogen in TPV experiments

Table 3 – Results of TPV depending on catalyst composition and processing conditions 288

Absorption Н2 Total mole absorpti on Н2 (Gauss decomposition mole ) о Training in oxygen at 400 С 425 3.5*10-6 3.5*1 0-6

Sample

Content of AK , mole/100mg

Fiberglas s

-

С-1, Со/Ni=5 0/50, 1,2% С-3, Со/Ni=1 00/0, 1,2% С-2, Со/Ni=0/ 100, 1,2%

On 1,00*10-

С-1, Со/Ni=5 0/50, 1,2% С-3, Со/Ni=1 00/0, 1,2% С-2, Со/Ni=0/ 100, 1,2%

On 1,00*10

-

С-3, Со/Ni=1 00/0, 1,2%

2,45*10-5

Without training (right after synthesis) 300 5.0*10-6 3.0*10-5 370 2.5*10-5

H2/Сo=1.2, р.5

С-3, Со/Ni=1 00/0, 1,2%

2,03*10-5

After oxidation reaction СО 300 2.0*10-6 2.8*10-5 370 2.6*10-5

H2/Сo=1.4, р.5

5

each 2,03*10-5

2,03*10-5

Temperatur e, оС

183 236 303 435 280 325 405

9.9*10-6 9.1*10-6 2.9*10-5 6.9*10-6 2.75*10-6 2.2*10-5 1.3*10-6

5.5*1 0-5

295

1.84*10-5

2.6*1 0-5

390

7.8*10-6

2.6*1 0-5

Process

Recovery of impurities (Fe) in fiberglass material H2/(Сo+Ni)=0.5 H2/(Сo+Ni)=0.45 H2/(Сo+Ni)=1.45 Fiberglass, Ni 280-325, H2/Сo=1.3 р.5 Fiberglass H2/Ni=0.9, р.1, Fiberglass, Ni

Training in argon at 400оС 192 312 408

3*10-6 2.1*10-5 2.5*10-6

2.6*10-5

2,03*10-5

230 340 405

2.8*10-6 1.7*10-5 1.3*10-6

2.1*10-5

2,03*10-5

275

1.35*10-5

1.9*10-5

5

each

390

5.7*10

-6

H2/Сo=0.3, р.3 H2/Сo+Ni=1.05, р.4 Fiberglass H2/Сo=0.13, р.3 H2/Сo=0.8, р.4 Fiberglass H2/Ni=0.7, р.1 Fiberglass

289

1 – sample С-1 (1.2 mass.% Со+Ni, 50Сo/50Ni), 2 – С-2 (1.2 mass.% Со+Ni, 0Сo/100Ni), 3 – sample С-3 (1.2 mass.% Со+Ni, 100Сo/0Ni) The samples were treated in argon 400оС/0.5 h. Fig. 19. Absorption rate of hydrogen in TPV experiments

1) After training of C-2 in oxygen the ratio H2/Ni =0.9, which is lower than the stoichiometric value is characteristic for recovery of NiO to metallic Ni, which means that the part NiO, is likely is restored at synthesis or training conditions (in other words, the degree of oxidation of Ni is less than 2). 2) After training of C-2 in argon the ratio of H2/Ni is reduced to 0.7, which is also lower than the stoichiometric value is characteristic for recovery of NiO-Ni. From the ratio of H2/Ni follows that the part of NiO is recovered in training conditions or do not recovered in selected conditions during TPV experiment realization. The latest may be connected with interaction of NiO with carrier until the formation of new phases that leads to recovery displacement in the field of higher temperatures. 3) After synthesis С-3 the ratio of H2/ Co, is characterizing the total absorption of hydrogen in the temperature region of 280-390оС, is 1.4, which is close to the stoichiometric value, is characteristic for recovery of Со3O4 to metallic Co Со3O4 in one stage. Such reduction is usually characteristic for recovery of massive oxide Со3O4 in pure 290

hydrogen, but the temperature of maximum recovery higher and is about 370оС. Such displacement of absorption maximum, is observing for applied system, to high temperature side in comparison with the bulk sample may arise from the strong interaction of spinel particles Со3O4 with carrier or localization of this spinel in small pores of carrier. 4) After training C-3 in oxygen the ratio of H2/Со, is characterizing the complete absorption of hydrogen in temperature range of 280-325оС, is preserved and is about 1.23, which is close to stoichiometric value, is characteristic for recovery of Со3O4 to metallic Co in a single stage. It should be noted that after catalyst training in oxygen there is essential displacement of maxium absorption absorption of hydrogen to the low-temperature region, from 370 to 325оС at that the ratio H2/Со is changed slightly. Such changes in TPV experiments for initial sample and trained in oxygen (oxygenated) may indicate to the decrease in particle size of Со3O4 in the process of additional treatment in oxygen. 5) After training of С-3 in argon the ratio of H2/Со is decreased to 1.0 in comparison with the sample, is trained in oxygen. The ratio H2/Со=1 is characteristic for stoichiometric recovery of CoO to Co. It can be assumed that the part of cations Со3+ is recovered to Co2+ during the training process of catalyst in argon (its formal expression because only the part of oxygen is removed). 6) The character of TPV curve is observed for sample C-3 after oxidation reaction of CO is identical to the curve for initial sample C-3 (without training). The ratio of H2/Со is about 1.4, which is close to the value is characteristic for recovery of Со3O4 to metallic Co in one stage. Thus, it is believed that during oxidation reaction of CO, the composition of Co-containing phase is not changed. 7) After training С-1 in oxygen the ratio of H2/Со, is characterizing the total absorption of hydrogen in the field of temperatures 180-303 ºС, = 2.4, which is considerably higher than is necessary for stoichiometric recovery as for CoO-NiO, and for Со2О3, Со3O4, Со. According to the ratio of H2/Со+Ni, is characterizing the recovery in the field of 300 °C, it can be assumed that there is a one-step recovery of spinel Со3O4 is carried out, which is doped by nickel cations to metallic Co. It is difficult to explain a 291

plenty of absorbed hydrogen is observed at low temperature rigion, perhaps it’s associated with reduction of NiO to Ni. 8) after training of С-1 in argon the ratio of H2/Со is decreased considerably and runs about 1.35, which correspond closely to the two-step recovery of Со3O4 -- СоO – Со (in this case, probably contain in their structure cations Ni2+), at that the quantity of absorbed hydrogen at first stage indicates that with temperature 192 ºС the cations Со3+ to Со2+ are recovered, but at the second stage the recovery of Со2+ (Ni2+) to metals is occurred. Thus, formally, during training in argon from catalyst system an excess of oxygen which presents in the system after synthesis is removed. Electronic spectra of diffusion reflectivity (ESDR) of fiberglass samples were recorded respectively BaSO4 in the range of 1100054000 cm-1 on spectrophotometer UV-2501 PC (Shimadzu) with attachment of diffusion reflectivity ISR-240A.

1 – without training (right after synthesis is loaded in TPV reactor); 2 – training in oxygen at 400оС/0.5 h; 3 – training in argon at 400оС/0.5 h; 4 – after oxidation reaction СО Fig. 20. Absorption rate of hydrogen in TPV experiments for the sample С-3 (1.2 mass.% Со+Ni, 100Сo/0Ni) after training in different conditions 292

It is known that ions Со2+ (d7-ion) have the electronic spin S = 3/2 and fundamental term of high-spin state 4F. In electronic spectra the ions Со2+ in octahedral (Со2+Oh) and tetrahedral (Со2+Td) coordinations are differ significantly by the energy of dd-transitions and its extinction [65]. Ions Со2+Oh in oxide structures are manifested in the form of intense absorption band (pp) in the region of 19000 cm-1, which belongs to the transition of 4Т1g(F)–4Т1g(P), but the ions Со2+Td are observed as multiplet in the region of 15000 cm-1, and corresponding to transition 4A2(F)–4Т1(Р). In some cases the ions Со2+Oh also may be manifested in the form of a multiplet in the region of 19000 cm-1. For example, in the case of tetragonal distortion of octahedral environment of ions CO2+Oh (D4h symmetry) the energy splitting of main state 4T1g (P) is observed, and in spectrum there is a multiplet of bands in the field of 16500, 18600 and 22250 cm-1 can be shown is assigned to transitions such as 4Еg–4В1g, 4Еg–4Eg (4Т1g(P)) и 4Еg– 4A2g(4Т1g(P)), respectively. An example of spectrum of tetragonal distorted octahedral ions Co2+Оh is CoCl2*6H2O, in which in the coordination sphere Co2+Оh are there are 4 ligand of H2O (in the equatorial plane) and 2 ligand of Cl- (an axial remote position). On the other hand, the multiplet of ions Со2+Oh may occur due to admixing of spin-forbidden transitions to the doublet state, is connected mainly with 2G и 2H. The transition for 4A2g is very weak and often appears as a shoulder in the region of 12000-16000 cm-1. For ions Со3+ (d6-ion) in octahedral coordination (Со3+Oh) at most complexes [65] is realizing a low-spin state (spin S = 0, the main term 1А1g) and in case of oxide ligands a broad absorption band in the region of 25000-30000 cm-1 is observed, which is conditioned by transition 1A1g–1T2g, and weak absorption band (pp) in the region of 16500 cm-1, is conditioned by transition 1А1g–1T1g. For ions Ni2+ (d8-ion) the main state is 3F, but the main therm in octahedral field is 3А2g and in tetrahedral field is 3Т1. In regular octahedral coordination for ions Ni2+Oh three spin- transitions such as -3Т2g-3А2g, 3Т1g-3А2g, and 3Т1g(Р)-3А2g are allowed, which usually observed in the range of 7000-13000, 11000-20000 and 1900027000 cm-1, respectively and have extinction of 30 l/(mol * cm) [65]. For ions Ni2+Oh, in most cases there are also two spin-forbidden 293

26300

bands have appeared: the first is (the transition to 1Eg) near transition of 3Т1g-3А2g, and the second is (the transition to1Т2g) between the second and third allowed transitions [65]. In actuality, the condition 1Eg с Dq/B∼1 lie so close to3Т1g that it’s significant mixing is occurred, as the result the doublet of band is observed, however the intensity of spin-forbidden transition is increased due to spin-allowed transition. For ions Ni2+Oh in oxide system NiO/MgO in electronic spectrum the absorption bands such as 8600, 14900, 13500 и 24600 см-1, are appeared which belongs to d-d transitions 3Т2g-3А2g, 1Eg-3А2g, 3Т1g3 А2g, and 3Т1g(Р)-3А2g, respectively [65]. The energies of indicated bands are close to characteristic for hexa-aqua complex Ni2+Oh. In case of ammonia complexes Ni(NH3)62+ the observed absorption bands are shifted to the high-frequency spectral region 10750, 17500 and 28200 см-1 [65], but the transition 1Eg-3А2g in the spectrum is not shown.

0,5

F(R)

d-d, Ni2+Oh

23900

0,4

0,3

0,1

12900 13700

0,2

1 2 10000

15000

20000

25000

30000

35000

-1

Wavenumber, cm

Fig. 21. Electronic spectra of diffusion reflectivity of fiberglass sample (curve 1) and Ni-catalyst (1.5 wt.% Ni), is prepared on its basis (curve 2)

The lack of other absorption band in a wide range for unmodified fiberglass material allows to attribute the absorption band are observed for Ni-, Co- and CoNi- catalysts on its basis, to 294

For ions Ni2+Td the spectra in visible region of an electron spectrum are similar in intensity and energies of absorption bands to the spectra of cobalt Со2+Td. Visible band in the region of 15000 cm1, is corresponding to the transition 3Т1(Р)-3Т1(F), exhibits a multiplet structure with an intensity of about 102-103 l/ mol * cm. Transitions to singlet state (3А2) are commonly observed in infrared region (6500-9500 cm-1) between spin-allowed bands (3T2(F) и 3T1(P). It should be noted that for ions Ni2+ in oxide systems the stabilization is not characterized in tetrahedral crystalline fields [66]. Figures 21-23 shows the spectra of fiberglass samples as well as spectra of Ni-Co- and CoNi-catalysts which were prepared on its basis. For unmodified fiberglass sample there is an intense absorption in the region of 40,000 cm-1 is observed, which can be attributed to the fundamental absorption edge (FAE). FAE of fiberglass is in the UV region, which is typical for oxide structures such as dielectric and large-energy-gap semiconductor. cobalt and / or nickel compounds and characterize the electronic state and coordination environment of cations Ni2 + and Con+. In electronic spectrum of Ni-catalyst (1.5 wt.% Ni, Figure 21), the doublet of absorption band 12900 and 13700 cm-1 is observed as well as arm 23900 cm-1 against the CFP. The energies of observed absorption bands can be attributed, respectively to d-d transitions 3 Т1g-3А2g, 1Eg-3А2g, и 3Т1g(Р)-3А2g ions Ni2+ in octahedral coordination. The essential difference of Ni-catalyst from known oxide system NiO/MgO is the displacement of absorption band to low-frequency region (about 600-1400 cm-1) and the decrease in the splitting of doublet (from 1400 to 800 cm-1), which indicates to strong interaction of cations Ni2+Оh with carrier. In electronic spectra of Co-catalyst (Figure 22), with content of cobalt 0.2-1.5 wt.% there is two intensive absorption bands 14000 и 23200 см-1, the energy of which can be attributed to d-d transition 4 A2(F)–4Т1(Р) ions Co2+Td Td in tetrahedral coordination and to transition 1A1g–1T2g ions Со3+Oh in octahedral coordination, respectively. The observation of these cobalt conditions may indicate to the formation of sample with spinal structures during synthesis, for example Co2+](Co3+)2O4 или [Co2+](Al3+,Co3+)2O4. It should be 295

noted that the intensity of both absorption bands increases proportionally to the content of cobalt in the sample. The essential difference of Co-catalysts from the known oxide systems, that containing Co3O4, is the splitting of band in the region of 14000 cm-1 and its shift to the region of lower energies (to 1000cm-1), as well as modification in proportion of absorption bands intensities of corresponding ions Co2+Td и Со3+Oh. Displacement of the absorption bands to the low-frequency region may be conditioned by strong interaction of cations Со2+Td with the carrier. Considering the extinctions Со2+Td и Со3+Oh,, an observation of higher intensity of absorption band in the region of 23200 cm-1 in comparison with absorption band 14000 cm-1, is indicating to predominance in the system of ions Со3+Oh,, and as the consequence on a high defectiveness of spinel structure. Co3+Oh 23200 2+ Td

Co

F(R)

4

14000

2

1 2 3 4 5 6

0 10000

20000

30000

40000

Wavenumber, cm-1

Fig. 22. Electron spectra of diffusion reflectivity of fiberglass sample (curve 1) and Со-catalysts, is prepared on its basis with content Со: 0.2 mass.% (curve 2), 0.5 mass.% (curve 3), 0.8 mass.% (curve 4), 1.2 mass.% (curve 5), 1.5 mass.% (curve 6)

The electronic spectra of СоNi-catalysts (Figure 23) are essentially differs from spectra of one-component catalysts at close content of active component. In spectra of СоNi- catalysts with total 296

content of cobalt and nickel 0.5-1.5 wt.% there is an absorption in the form of shoulder with maximum in the region of intensity 15100 и 23000 см-1, which is significantly smaller (about 5 times) of Cocatalyst intensity with close content of cobalt.

10000

22900

Ni2+Oh 20000

1 2 3 4 5 6

26300

23900

12900 13700

1

0

Co3+Oh

14000

2

Co2+Td

15100

F(R)

3

23200

4

30000

40000 -1

Wavenumber, cm

Fig. 23. Electron spectra of diffusion reflectivity of fiberglass sample (curve) and СоNi-catalysts, is prepared on its basis with the ratio of Co/Ni=1/1 and with total content Со+Ni: 0,6Со-0,6Ni (curve 2), 0,4Со-0,4Ni (curve 3), 0,25Со-0,25Ni (curve 4), Со-catalyst 0.8Со (curve 5) and Ni-catalyst 1,5Ni (curve 6)

The energy of observed absorption can be attributed to d-d transitions of ions Co2+Td in tetrahedral coordination and ions Со3+Oh in octahedral coordination, respectively. Against the background of cobalt ions is almost impossible to allocate the coordination and electronic state of nickel cations, so it is not impossible that two observed bands are superposition of absorption bands are characteristic for cations Ni2+Oh (dublet 13000-15000 cм-1 and 25000 cm-1) and Со2+Td (14000 cm-1), Ni2+Oh (25000 cm-1) and Со3+Oh (23000 cm-1).

297

In this case, СоNi- catalyst may contain the cations Ni2+Oh in content of particles NiO, and the cations Со2+Td и Со3+Oh in composition of spinel structure Co3O4. On the other hand, it can be assumed the stabilizing of cations Ni2+ in tetrahedral coordination (although it is not typical for nickel cations) in composition of spinel [Co2+,Ni2+](Co3+)2O4, in this case, the absorption band in the region of 15000 cm-1 will be correspond to cations Ni2+Td и Со2+Td simultaneously. It should be noted that the intensity of both absorption bands is practically independent of total content of cobalt and nickel in the sample at the ratio of Со/Ni=1/1. In addition, given the low intensity of the absorption band is corresponding to ions Со2+Td it can be assumed that in catalyst the state Co3+ is dominated but the spinel Co3O4 has defective structure. 3.2 Investigation of catalyst activity, are modified by СоО, NiO during carbon dioxide conversion of methane process The catalytic activity in reaction of carbon dioxide conversion of methane was determined for catalyst samples, are presented in Table 1. Figures 24, 25 show the results of investigation on conversion of initial materials such as methane and carbon dioxide, as well as yields of end products - hydrogen and carbon monoxide from the temperature and catalysis time. The sample IK1 (Figure 24) showed a rather high activity: it can be seen that the yield of synthesis gas reaches 46% Н2 and 52% СО at 750°С (Figure 24a). The conversion of СН4 is 33%, but СО2 is 67% at the same temperature (Figure 24b). Significant changes in yield of synthesis gas during 3 hours are not observed, which indicates that the operation of this catalyst is stable in investigated temperature range. Concentration reduction of cobaltous oxide in samples leads to catalyst deactivation in reaction of carbon dioxide conversion of methane (Figure 25a - IK4, 25b IK5 and 25c - IK6). Industrial nickel catalyst (NiO = 6-8%, Al2O3 = 90%) was investigated for comparison with fiberglass catalyst in reaction of carbon dioxide conversion of methane. The ratio of initial gas was СН4/СО2 = 1,25/0,75. The yield of synthesis gas was 53% Н2 and 24% СО at 630 °С, the conversion of СН4 - 58%, СО2 - 75%. 298

However, the service life of industrial nickel catalyst was short, and after approximately 3 hours of work the yeild of carbon monoxide is decreased to 8% and the conversion of carbon dioxide was 82%, which indicates to coking process.

Fig. 24. Alteration of chemical yield (а) - (■-Н2, ○-СО), of initial components of reaction mixture (b) - (▲- СН4, ∇ - СО2) depending on working time at different temperatures on catalyst IК1

299

Fig. 25. Alteration of chemical yield (■-Н2, СО-○) depending on working time at different temperatures on catalysts: (а) - IK4, (b) - IK5, (с) - IK6 300

3.2.1 Investigation of polyoxide catalyst activity (MgO, СоО, NiO) on the basis of fiberglass during carbon dioxide conversion of methane process Investigation of catalytic activity of samples was carried out in flowing catalytic installation, which is made of quartz glass is heated by tube furnace (Figure 5).

- Н2О/СО F1

2.0

Н2О/СО

1.5 1.0 0.5 0.0

600

650

700 750 Т, оС

800

850

Conditions: MgO – 4 %; NiO – 0,4 %; CoO – 1,6 %; Q - 4800 ч-1, Тcatl. - 850 °С Fig. 26. Temperature effect of catalytic process on dependence way Н2О/СО

Another dependen In paper there are results on gas chromatographic analysis on influence to the yield of hydrogen and carbon monoxide, water, conversion of methane and carbon dioxide from the imposed factors. As indicated in literature [4, 5] at atmospheric pressure only at 900°С the yield of Н2 and СО come up to 100%, but the ratio of Н2О/СО come up to zero. Figure 26 shows the dependence of this ratio, is indicating that with temperature rise the striving of this ration to zero is occurred. Another dependence is characterizing the fullness of carbon dioxide conversion of methane reaction passing [H2+CO]/[CO2+H2O] is presented in figure 27. 301

[H2+CO]/[CO2+H2O]

10

- [H2+CO]/[CO2+H2O]

8 6 4 2 0 600

650

700 750 T, oC

800

850

Conditions: MgO – 4 %; NiO – 0,4 %; CoO – 1,6 %; Q – 4800 ч-1, Тcatl –850 Fig. 27. Temperature influence of catalytic process on dependence [H2+CO]/[CO2+H2O]

It visible that the ratio of desired reaction products to the products of full oxidation is approximately composes the size of order 8.5, which indicate about high selectivity of the process. The dependence is describing the ratio between hydrogen and carbon monoxide (Figure 28) has significant importance. As indicated in the literature [4, 5], the most favorable ratio, which is equal of unity is necessary for realization of hydrocarbon synthesis according to Fischer-Tropsch method and production of dimethyl ether. In our case it was possible to attain the ratio of Н2/СО is close to 0.8. Investigation of temperature effect for carbon dioxide conversion of methane process in time is showed in Figure 29. The figure shows that the stepdown descent of reactor temperature leads to a decrease in the conversion of the initial components from 96 - 98% at 850 ºС to 600 ºС at 30-33%.

302

0.8

Н2/СО

0.7 - Н2/СО

0.6 0.5 600

650

700 750 Т, оС

800

850

Conditions: MgO – 4%; NiO – 0,4%; CoO – 1,6%; Q – 4800 ч-1, Тcatl – 850оС Fig. 28. The temperature effect of catalytic process on dependence process [H2]/[CO]

During experimental data processing the material balance of C, H and O was made. It is found that the balance convergence on hydrogen and oxygen in a percentage, for the entire duration of the experiment is close to zero, the unbalance on carbon fall within the limits of 2.4 to - 7% (Figure 30). At the same time, according to the median value, the growth of carbon deposits within 30 hours was increased from -2.8 to -3.5%. Operation time was carried out within 30 hours. It can be seen that during run the catalytic activity was remained at the same level: the conversion of methane – is 95-98%, and for the conversion of carbon dioxide – is 96-98%. The influence of catalytic activity from time on yield of end products (H2 и CO) is showed on figure 32. The figure shows that the yields are on the average for hydrogen – 40 and for carbon monoxide - 51%, respectively.

303

a

b Conditions: MgO – 4%; NiO – 0,4%; CoO – 1,6%; Q – 4800 ч-1, Тcatl. – 850оС Fig. 29. The temperature effect of catalytic process on conversion of methane, carbon (а) and yields of hydrogen and carbon monoxide (b) from time 304

Fig.30. Data of material balance on С depending on process time

Figure 31 shows the data on sample checking for duration of conservation of catalytic activity.

Fig. 31. The influence of catalytic activity from time on yield of end products (H2 and CO) 305

K (CH4, CO2), %

Fig. 32. The influence of catalytic activity from time on yield of end products (H2 and CO)

- CH4 - CO2

100 90 80 70 60 50 40 30

a 600

306

650

700 750 T, OC

800

850

Выход H2, CO %

50

- H2 - CO

40 30 20

b

10 600

650

700 750 T, oC

800

850

Conditions: MgO – 4 %; NiO – 0,4 %; CoO – 1,6 %; Q - 4800 ч-1, Тcatl- 850 оС Fig. 33. The influence of catalyst temperature on conversion of initial components and yield of end products (H2 и CO)

Figure 33 shows the data on conversion of methane and carbon dioxide (a) as well as the yields of hydrogen and carbon monoxide end products from the temperature of catalyst system. It is seen that with the rise of a temperature the curves that describing the conversion are converge, while the difference in reaction yield remains virtually unchanged. Thus, the conducted work helps to clarify and work out the laboratory technological parameters of nanostructured fiberglass catalysts synthesis and on the basis of obtained gas-chromatographic data to determine the catalytic activity of synthesized contacts during the carbon dioxide conversion of methane process.

307

CONCLUSION Nanodispersed catalysts on the basis of fiberglass, are modified by oxides of cobalt, nickel and magnesium by "Solution combustion" method (Liquid-phase SHS) were developed. Investigation of catalyst samples by XRF method have showed that the catalytic activity depends on the ratio of CoO/NiO/MgO. In composition of catalyst samples there are spinel phases such as Co3O4, (Ni, Co) Co2O4, the mixture of spinel and oxide phases (Ni, Co) Co2O4 and NiO or only NiO. The particle size is 20∼ nm. In composition of polyoxide catalysts there are also such phases as NiCo2O4, 3CoO•5NiO, MgO, and also MgNiO2. It was found that with the help of SEM and TEM methods the active component is formed at the surface of fiberglass, generally as individual particles with a size of about 5-20 nm. The typical curves by hydrogen of cobalt, nickel and bicomponent Co-Ni catalysts have showed the temperature shift of maximum absorption of hydrogen in the region of higher temperatures, which is connected with interaction of active phases NiO, Co3O4 with the carrier up to the formation of new phases. Investigation of catalysts in the reaction of carbon dioxide conversion of methane showed that the increasing of concentration CoO, leads to rice of catalyst activity in reaction of carbon dioxide conversion of methane. It is found that the resistance to coking of Co-Ni-catalysts depends on the ratio of CoO / NiO and decreases with an increase of cobaltous oxide in the composition of catalyst. The sample checking (Conditions: MgO - 4%, NiO - 0,4%, CoO - 1,6%, Q - 4800 h-1, Тcatl 750ºС) for the duration of conservation of the catalytic activity was carried out for 30 hours and showed that during run the catalytic activity remained at the same level: for conversion of methane –is 95-98%, and for the conversion of carbon dioxide – is 96-98%. For catalyst system MgO-NiO-CoO/fiberglass during processing of experimental data was reduced according to the material balance of C, H and O. It is found that the convergence of balance on hydrogen and oxygen in percentage, for the entire project duration is close to zero, the unbalance on carbon is from 2+2,4 up to -7 %. At the same time, 308

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THE PECULIARITIES OF SELF-PROPAGATING HIGH TEMPERATURE SYNTHESIS AND STRUCTURE FORMATION OF CERAMIC MATERIALS TIB2-AL2O3 AND CRB2 - AL2O3. D.S. Raimkhanova, Z.A. Mansurov, A.S. Rogachev., O.Odavara, R.G. Abdulkarimova ABSTRACT Optimum compositions and conditions of SH-synthesis of refractory compositions materials based on titanium and chromium borides were developed. The main regularities of aluminothermy combustion of boron containing systems. The peculiarities of phase and structural transformations in the combustion wave determining finally the properties of synthesized materials were stated. Investigations on the phase composition, morphology of the structure of the obtained materials were carried out. 1. INTRODUCTION Among the variety of refractory and heat resistant composition systems, of special interest are materials from boron carbides and nitrides, metal diorites and mixed ceramics due to their unique properties [1-3]. They can be both the main product and a phase in composition materials. Such materials are able to endure high temperatures and work under the conditions of corrosive media, be good heat insulators with high strength and wear resistance. Transition metal borides possess a unique complex of physicchemical properties (high hardness, heat resistance, high temperature strength, high electric and heat conductivity, resistance to the action of melts in combination with low specific gravity corrosions, radiation resistance, wear resistance and are widely used as the most promising materials in many fields of engineering, machine building, electronics, power industry [2, 3]. However, strong covalent bonds inherent to phases of transition metal diorites lead to low plasticity and low breaking and bending strength, this limiting to a grad extent the field of their application in pure form. In this regard, at present, much attention is paid to the technology of production of 314

composition materials based on transition metal borides in combination with more plastic materials playing the role of a binder. So, for example, aluminum oxide can play the role of a high temperature binder and filler decreasing the content of expensive diorite in composition materials. 1.1 Self – propagating high temperature synthesis of boron containing ceramic materials: the modern state At present, the main methods for producing materials of different functional methods are methods of physical and chemical sedimentation from vapour, self-propagating high temperature synthesis (SHS). In work [4], using two methods of ionic deposition, nanostructural boride and nitride nanofilms based on transition metals on different supports were obtained. As a result of the chosen optimum conditions of spraying on tne support there formed films of boride and nitride phases with the thickness of ~3200 and ~8600 nm, respectively, with the transition layer of ~100nm consisting of boron and nitrogen compounds with atoms of the corresponding supports. The authors of [5] obtained filamentary crystals of titanium, zirconium and hafnium diorites with the length of fibres 0.4-0.8 micrometers. However, the widely spread at present methods for production of refractory ceramic materials are labour-consuming and expensive. Products from these materials are manufactured by conditional methods of powder metallurgy: by sintering or hot compaction of pre-pressed bars. Therefore, it is related to great power consumption. Frequently, production of these materials cannot be realized within conventional notions on equilibrium states and requires new approaches and methods of synthesis of a special class of composition ceramic materials [1, 2]. Synthesis of borides directly from elements is one of the simplest but at the same time the most expensive methods providing the most accurate composition and maximum degree of purity of borides. Synthesis of borides from simple substances by sintering, hot compaction realized at temperatures lower than the melting points of tne initial materials is based on solid phase interaction. The stage determining the process parameters is diffusion of boron into metal 315

through the layer of the product being formed. Duration of boride formation process and temperature of interaction are exponentially dependent: 1/τ=A e-Q/kT, where τ is time necessary for homogenation of the corresponding phase at temperature T; A is constant; Q is diffusion activation energy; k is Boltzmann’s constant. A general disadvantage of sintered alloys based on borides is considered to be their friability and insufficiently high thermal stability related to some specific properties of transition metal borides [1, 3]. Production of transition metal borides by the methods of high temperature synthesis is more and more widely used in many branches of national economy, however, their use in pure form for machine engineering and metal working is impeded due to their friability and cold brittleness. Therefore, recently, great attention is paid to the technology of production of composition materials based on borides, one of the directions being their liquid phase sintering with metal binding [4-6]. At the Institute of structural micro kinetics (Chernogolovka, Moscow region), the workers developed SHS-technology with reduction stage of obtaining boron containing powders such as BN, TiB2, B4C, B13C2, TiB2- Al2O3, B4C- Al2O3 and others using oxides of the corresponding elements of magnesium as initial reagent or aluminium as a metal-reducer. Technical characteristics of boron containing powders are not inferior to the best furnace analogs and by most indexes even exceed them. The cost price of SHS powders is 1.2-3.0 times lower than that of their analogs [7]. The use of powder aluminium as an active reducer allows to reach high temperatures of synthesis (1500-2000K) necessary in SHS-processes. High temperature of combustion reaction provides synthesis of phases possessing high temperature of melting allowing to use the materials produced by SHS method in refractory industry [8,9]. Formation of TiB2- Al2O3 and NbB2 - Al2O3 compounds under natural conditions with a wide range of phase composition was carried out by SHS method including thermite reactions of different types in work [10]. Thermite mixture Al-TiO2 and Al-TiO2-B2O3 were introduced into Ti-B system for formation of TiB2- Al2O3 compound within which the increase in the content of Al2O3 in the thermite mixture decreased the reaction temperature and the rate of 316

combustion front propagation. Thermite reaction of the Al with TiO2 is stated to decrease exothermicity of the whole SHS process. In synthesis of NbB2 - Al2O3 compound, two thermite mixtures AlNb2O5 and Al- Nb2O5 -B2O3 were used in Nb-B system. It was found that these systems increase the combustion temperature and the rate of combustion front propagation. This takes place due to high thermic nature of thermite reaction between Al and Nb2O5. For these kinds of compounds, the authors stated that the use of B2O3 as one of thermite reagents effectively improves formation of the product. The samples where thermite mixture Al-TiO2-B2O3 was used possessed a slightly higher rate of the combustion front propagation than in case of thermite mixture Al-TiO2 and a wider range of the composition as is shown by a better level of reaction stability (Figure 1). The authors suppose that this may be caused by formation of a liquid phase of B2O3 which improved the contact between the reacting particles and contributed to ignition and the increase in the reaction level [11]. According to sequence of TiB2 formation and the results of radiography of the synthesized products in works [12-14] the following reaction mechanism for synthesis of TiB2- Al2O3 was proposed. The subsequent reactions necessary for formation of TiB2Al2O3 compounds in SHS process are presented below [1-4]. Ti + B = TiB 4Al + 3TiO2 = 3Ti + 2Al2O3 Al + B2O3 = 2B+ Al2O3 TiB+ B= TiB2

(1) (2) (3) (4)

Interaction of Ti with B is the first step resulting in formation of TiB and starting substitution reaction between termite reagents according to reactions 3 and 4. Then the intermediate phase of TiB boride transforms into TiB2 via the further reaction with B [11, 14]. In work [15], ceramic powder of TiB2 was synthesized using MgTiO2-B2O3 mixture. The authors studied the effect of TiB2 additive as a dilutor on the process of synthesis under the conditions of combustion. The result of thermodynamic calculations and experiments showed that the increase in the content of the TiB2 from 0 to 20 mass % decreases adiabatic temperature from 3100 K to 2896 317

K and the combustion temperature from 2139 K to 1621 K, respectively. The size of particles and semi width of the curve of particles distribution by sizes grew with the increase in the content of TiB2 , MgO and some intermediate phases. The products obtained after treatment with acid contained mainly TiB2, TiO2 and TiN.

Fig. 1. The change in the flame-front propagation velocity in SHS process including two different thermite mixtures for formation of TiB2- Al2O3 [11]

In work [16], the authors considered the processes of high temperature binding in powder composite titanium diboridealuminium oxide which is of interest as a material of wetting cathode of aluminium electrolyzer. X-ray phase analysis and electron microscopy were used to study the formation of surface and boundary phases. It is stated that a determining role in the processes of binding the grains of powder mixture into a monolitli body is played by boron anhydride-a product of TiB2 oxidation and complex oxides synthesized during thermal treatment-aluminium borates Al4B2O9 and Al18B4O33. Electrical resistance of the obtained material with the relative density of 0.60-0.62 sharply decreases with the increase in burning temperature, but above 1200 K it change slightly having the values within (1-3)*10-3 Ohm*m. compression strength reaches 100-150 MPa. 318

The authors of work [17] carried out investigations on the structure of composition ceramics TiB2-CrB2, TiB2-W2B5 and analyzed binding of the structure with mechanical properties. They stated-that: 1) in qnasi-binary systems TiB2-W2B5 and TiB2-CrB2 during formation of a solid solution the dominant structure is phase TiB2; 2) anisotropic changes in the periods during formation of solid solution (Ti,W)B2 can be caused by the competing effect of dissolved atoms of tungsten in the excess concentration of boron atoms; 3) the increase in the temperature of hot compaction resulting in formation of one phase solid solutions contributes to production of dense ceramic materials and provides improvement their strength characteristics. Powders BN, TiB2, B+Mg3B2 obtained by magnesium thermal SHS technology do not yield in their characteristics to the powders produced by the technologies of conventional powder technologies, and their cost is 1.5-3.0 lower than that of their analogs. Boron containing SHS materials can be used as biological shielding in nuclear engineering, abrasive powders and pastes, ceramic products with high temperature strength, solid lubricants (BN hexagonal) and oil additives [8]. In work [18], the authors proposed a method for synthesizing refractory compounds of rare earth metals MeB2 in two stages. The first stage is high temperature synthesis from elements at high pressures, the second stage is additional annealing in argon medium. As a result, the authors obtained samples of terbium, erbium, thulium and lutecium diborides with the content of outside phases not more than 3 mass %. Composition materials based on chromium and aluminium oxides by SHS method in works [19, 20]. The authors studied the reactions of aluminothermy oxidation of chromium oxide under the conditions of SHS synthesis at different ration of reagents. It is show that chromium-aluminium termite burns by a complex mechanism and the final product forms via several subsequent transformations. Kurbatkina V.V. with her coauthors [8] considered production of ceramic materials based on chromium and titanium borides by the method of SHS-compaction from preliminary mechanical activation of the charge. 319

The use of mechanochemical activation (MA) allow realizing SHS-process in low exothermic systems such as Mo-B, Cr-B. According to the investigation results, samples with large dimensions (125 mm in the diameter) based on chromium borides were synthesized. Addition of titanium into the reaction mixture allowed to decrease the residual porosity from 6% in Cr-Bmixture to 2% in Ti-Cr-B mixture, this resulting in the increase of operational properties [8, 21]. In self-propagating high temperature synthesis as well as powder metallurgy, an important role is played by the sizes of particles of the reagents and final products. In this regard, SHS is closely related to nanotechnology. The decrease of particle sizes is an actual task as the dimensions exert a significant effect on both SHS- process itself and the properties of the materials being obtained [22, 32]. Formation of structures from nanocrystalline grains allows impart new properties: physicochemical, functional, operational and other properties to materials [22, 33]. The structure and, correspondingly, properties of nanomaterials are formed at the stage of their production [22, 32-37]. The use of the process of mechanical activation (MA) as a predecessor of SHS results also in formation of nanostructural materials. Mechanical activation of reagents before carrying out SHS-process is a very important stage. It results in the increase inchemical activety of particles on account of increasing the level of defects and/or in the increase of the reaction surface (on account of decreasing the sizes of particles). Milling is carried out with the aim of obtaining maximum surface of powder with minimum expenses of energy and activation is carried out with the aim of accumulation of energy in the form of defect or other charges in a solid substance which allow to decrease activation energy of its subsequent chemical transformation or improve the steric conditions of the process procedure. As a result of investigations. The authors of work [22] developed a method and technology of (Ti, Cr)B2 production by method of high temperature mechanochemical synthesis (HMS). This technology allows obtaining TiB2 and (Ti, Cr)B2 with the dispersity of 40-100 μm. Also, borides were obtained by the method of mechanical activation in works [23, 24]. 320

Formation of the microstructure of products and materials is of no less interest than formation of the crystalline structure of phases. The microstructure is formed due to destruction of structural components of the initial reaction mixture, nucleation and growth of grains (crystals) of products, recrystallization, sintering and other process. To study micro structural transformations, it is necessary to “harden” the combustion wave so that to register intermediate micro structures in different zones of the wave. The existing methods of SHS-process hardening allow to obtain a sufficiently reliable pattern of micro structural transformations in SHS wave. Its advantages are relative simplicity and cheapness of methods, the possibility to control the level pof heat losses changing the angle of the wedge spread or density of the reaction mixture[21, 25]. 2. EXPERIMENTAL As the main initial components, we used the following reagents^ amorphous boron (black) of the brand B-99A (the content of boron is 99,1 %, the specific surface is 12 m2/g, an average size of particles is 4μm); H3BO3 (boric acid obtained from the ore of Inder deposit, West Kazakhstan)- mineral sass line corresponding to boric acid in composition is a white crystalline powder with the content of H3BO3 not less than 98% (the impurity Fe3B7O13Cl is present in a small amount); B2O3- boron oxide of 99,9% purity. Also, to prepare reaction mixtures, transition metals and their oxides were used: -Ti- titanium powder (purity of 99%, particles of 80 μm). -TiO2-titanium oxide in rutile borm of 99,9% purity. -Cr2O3-chromium oxide, green powder of 99,8% purity. -Al2O3-aluminium oxide of 99% purity. Powder of aluminium and magnesium were used as a reducer: -Al-aluminium, powder of the brand PA-4(99% purity, dispersity is 65 μm), magnesium of the brand ACD-4 (purity 99.1%, particles