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Relevance. Currently, there is an active search for photocatalytic materials suitable for water decomposition and hydrogen production that exhibit activity when exposed to visible light, and are also accessible, chemically stable and safe. In this regard, a number of materials with the general formula TinO2n-1 (n=2–10) are distinguished, they are called Magnéli phases. Despite the fact that Magnéli phases exhibit significantly higher photocatalytic activity compared to traditional titanium oxides (rutile, anatase, brookite), their practical application is currently extremely difficult due to the complexity of their synthesis. Promising approaches are those that provide well-controlled conditions with the possibility of rapid stabilization of the system, among which plasma synthesis methods stand out. Aim. To develop a method for synthesizing a product containing Magnéli phases in a high-speed jet of electric discharge plasma. Objects. Dispersed materials obtained in the Ti-O system. Methods. Plasma dynamic synthesis, X-ray diffractometry (X-ray phase analysis), scanning electron microscopy, transmission electron microscopy. Results. Using a high-speed jet of electric discharge plasma generated by a coaxial magnetoplasma accelerator, experimental studies were performed on the synthesis of non-stoichiometric titanium oxides in a carbon dioxide environment. The composition and microstructure of the obtained dispersed products were studied. It was revealed that the materials contain Magnéli phases TinO2n−1, as well as traditional stoichiometric rutile and anatase. From the point of view of the efficiency of obtaining Magnéli phases, the single-pulse mode of operation is more attractive (content over 50%), while the efficiency of CO2 conversion is higher in the multi-pulse mode (up to 10% of CO2 is converted into CO). A distinctive feature of the synthesized materials at both the micro- and nanolevels is the tendency to form particles with a high degree of sphericity. The nanofraction of the products mainly consists of rounded particles with sizes up to hundreds of nanometers, of which the Magnéli phases primarily include nanoparticles with a characteristic highly defective crystalline structure with dislocation shifts.

Relevance. The search for suitable materials for creating a new generation of anodes in lithium-ion batteries that have not only high capacity, but also high electrical conductivity. For this purpose, the attempts have been made to use silicon Si, which has a high specific capacitance, instead of graphite C, but this material does not have high electrical conductivity. Copper silicides, in addition to high specific capacity, have high electrical conductivity values, since they do not react with lithium during operation, and therefore can be used to solve problems in the development of the above-mentioned lithium-ion anodes. Aim. To obtain dispersed materials in a high-speed jet of electric discharge plasma in the Cu-Si-C system. Objects. Dispersed materials obtained in the Cu-Si-C system. Methods. Plasma dynamic synthesis, X-ray diffractometry (X-ray phase analysis), scanning electron microscopy, transmission electron microscopy. Results. The authors have carried out the experimental studies to obtain dispersed materials of the Cu-Si-C system in a high-speed electric-discharge plasma jet and studied the microstructure and composition of the synthesized materials. It was revealed that the product consists of nanodispersed particles, which is confirmed by the results of scanning and electron microscopy. According to the results of X-ray diffractometry, crystalline phases of copper of the cubic system and copper silicides Cu3Si and Cu7Si of the hexagonal system are identified in the composition of the synthesized material.

Relevance. The search for a useful application of carbonaceous residues of rice husks thermal processing. These residues due to high silicon content in the inorganic part can potentially be used to produce silicon carbide – an important functional material for various fields of science and technology. Useful utilization of this waste will allow not only solving the environmental problem associated with their inefficient application and formal disposal, but also obtaining value-added products in the form of SiC-based ceramics. Aim. To obtain SiC-based bulk products from carbonaceous residues of rice husk thermal processing by spark plasma sintering with a minimum number of additional stages of feedstock processing. Objects. SiC-based bulk products obtained using carbonaceous residues of rice husk thermal processing. The samples were obtained by spark plasma sintering at 1800 °C, pressure of 60 MPa and holding time of 10 minutes. Methods. Spark plasma sintering; X-ray diffractometry (X-ray phase analysis); scanning electron microscopy; vacuumless arc discharge synthesis method. Results. The authors have carried out the experimental studies to assess the possibility of applying carbonaceous residue of rice husk thermal processing as a precursor for the synthesis of silicon carbide in bulk (ceramics) and dispersed (powder) forms. A series of experiments on spark plasma sintering of carbonaceous residue from rice husk thermal processing in the initial and milled form, with SiO2 silica sand additives, as well as with the use of silicon carbide powders synthesized from carbonaceous residue by vacuumless arc discharge method were implemented. The latter is performed within a one-stage fast-flowing process in an air environment and does not require the use of a vacuum system. Preliminary results demonstrated the possibility of obtaining bulk products and dispersed powders based on silicon carbide with a content of at least 50 and 60 wt %, respectively, and indicate the prospects of further increasing phase purity by optimizing spark plasma sintering and vacuumless arc discharge synthesis.

Relevance. The fact that composites with a metal matrix and structural products based on them are in great demand in various industries, including the automotive industry, aerospace industry, and shipbuilding. Aluminum matrix composites are the most popular since they combine the excellent ductility, low density, good corrosion resistance of aluminum and the high strength, hardness and wear resistance of a ceramic reinforcing component. Aim. To obtain bulk Al-WC metal matrix composites with different contents of the reinforcing phase and with increased physical and mechanical characteristics using spark plasma sintering. Objects. Sintered bulk products made of pure aluminum and obtained at 400, 450, 500, 550, 600°C and bulk metal matrix composites Al-1%WC, Al-5%WC, Al-10%WC, Al-15%WC obtained at 600°C. Methods. Spark plasma sintering; X-ray diffractometry (XRD phase analysis); scanning electron microscopy; indentation (microhardness measurement). Results. The authors have obtained bulk composite metal matrix products with an aluminum matrix and tungsten carbide as a reinforcing component. Compacting mixtures of nanosized initial powders of aluminum and tungsten carbide using spark plasma sintering made it possible to obtain products with a WC content of 1 to 15 wt %. Taking into account the results of a preliminary series of experiments, when pure aluminum samples were sintered to determine the optimal sintering temperature, bulk composite materials were obtained. A distinctive feature of the obtained samples is their high degree of compaction, which is due to the simultaneous application of a heating current and external pressure, coupled with the relative preservation of the fine-grained structure of the material due to the short process time. The analysis of various sintering modes revealed the need to carry out sintering of composites at 600°C. The research has shown that, although adding a reinforcing phase to a metal matrix significantly reduces the degree of compaction of the material from 97.45% in the absence of an additive to 62.32% with the addition of 15%WC, an increase in the microhardness of products is observed when the concentration of the reinforcing component increases from 3.95 to 5.75 HV. This proves the possibility of reinforcing a metal material using ceramic WC particles. The results can be used in a variety of structural applications, including automotive and aerospace.

Relevance. Caused by the problem of developing methods for obtaining tungsten carbide, especially from tungsten-containing waste. As a solution, a non-vacuum electric arc method is proposed. It is easy to operate and cheap compared to a direct analogue (arc discharge method in inert gas atmosphere). The resulting product can be used as a catalyst carrier in hydrogen production reactions. Aim. To determine the current and the energy entered in the system, necessary to obtain a product with a largest proportion of the hexagonal phase of tungsten carbide WC from tungsten ore concentrate by a non-vacuum electric arc method and investigate a sample with the largest proportion of tungsten carbide phase. Object. Electric arc synthesis in open air from tungsten ore concentrate. Methods. Grinding in a SAMPLE SPEX 8000M ball mill, magnetic separation, non-vacuum electric arc method of synthesis, X-ray phase analysis on a Shimadzu XRD 7000s X-ray diffractometer (λ=1.54060 Å), scanning electron microscopy combined with X-ray fluorescence energy-dispersive analysis based on a TESCAN VEGA 3 microscope SBU with OXFORD X-Max prefix, transmission electron microscopy combined with energy dispersive spectroscopy and selected area electron diffraction based on the JEM-2100F microscope, scanning electron-ion microscopy based on the QUANTA 200 3D microscope. Results. The authors have built the dependence of the phase composition of the product of non-vacuum electric arc synthesis at current strengths from 50 to 220 A. Mass fraction of each of the identified phases in the synthesis product was determined using the reference intensity ratio. The current and the energy entered in the system, which provide the largest proportion of tungsten carbide WC in the synthesis product, are determined. The authors studied the product containing the largest proportion of tungsten carbide WC using scanning and transmission electron microscopy methods.

Link for citation: Tsimmerman A.I., Shanenkov I.I., Nassyrbayev A.R., Nikitin D.S., Sivkov A.A. Influence of configuration of the electrode system of a coaxial magneto plasma accelerator on arc discharge formation and development. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 8, рр. 39-50. In Rus. The relevance of the research is explained by a wide range of practical areas, where various plasma generators can be used, including analytical devices, technological installations, tokamaks, ion and plasma engines, satellites, laser technology, as well as by the possibility of applying them for both producing coatings on various surfaces and synthesizing fine and nanopowders. The main aim of the research is to determine the best way to initiate an arc discharge in the acceleration channel of the coaxial magnetoplasma accelerator, to estimate the effect of the plasma formation zone configuration on the electrodynamic loads of the accelerator, and to calculate the efficiency of conversion of stored energy to supplied one. Objects: coaxial magnetoplasma accelerator, arc discharge initiation, central electrode, electrode-barrel, plasma formation zone. Methods: experiment, plasma dynamic synthesis, measurement and registration of pulsed currents and voltages, electrical erosion measurement by means of weighing the eroding electrode-bore, high-speed photoregistration of the plasma jet. Results. Two methods of arc discharge initiation using metal wires and graphitization were considered. It is established that they do not affect the energy parameters of the plasma dynamic synthesis, but the graphitization looks preferable due to the greater processability of the procedure that provides easy accelerator preparation and reliability of its operation. The possibility of reducing the arc discharge current amplitude by 29 % with increasing the plasma formation zone length from 5,5 to 11,5 mm was established that results in reducing electrodynamic loads on all system nodes. The optimal plasma formation zone length of 9,5 mm was determined to provide obtaining a high efficiency of conversion of stored energy into supplied energy and reliability of the system operation.

Dispersion and aggregation of nanoparticles in aqueous solutions are important factors for safe and effective application of nanoparticles, for instance, in the oil industry. As conventional oil reserves are depleted, it is necessary to advance chemical enhanced oil recovery (cEOR) techniques to develop unconventional oil reservoirs. Nanoparticles modified by surfactants can be a promising reagent in cEOR. These nanomaterials can reduce interfacial tension and change the wettability of reservoir rock, which leads to an increase in oil recovery. However, the application of nanoparticles is limited by their substantial aggregation in aqueous solutions. The purpose of this work is to select nanoparticles for obtaining stable sols in water in the presence of an anionic surfactant and to optimize the conditions (pH) for further modifying the nanoparticles with the anionic surfactant. Sodium dodecyl sulfate (SDS) is used as an anionic surfactant. The aggregation of oxide and carbon nanoparticles in water and anionic surfactant solutions was studied by laser diffraction, dynamic and electrophoretic light scattering methods. Most of the studied nanoparticles in water form aggregates with bi-, three- and polymodal particle size distributions. TiO2 nanoparticles obtained by plasma dynamic synthesis form the most stable sols in anionic surfactant solutions. The range of 5–7 pH is defined as optimal for their modification with surfactants. The stability of carbon nanoparticles in aqueous solutions increases significantly in the presence of a surfactant. The obtained results form the basis for further research on the modification of marked nanoparticles in surfactant solutions.

Link for citation: Nikitin D.S., Shanenkov I.I., Nassyrbayev A., Vympina Yu. N., Orlova E.G., Ivashutenko A.S., Sivkov A.A. Obtaining bulk products from Cu-SiC metal-matrix composite for energy-efficient heat-conducting systems. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 7, рр. 93-101. In Rus. The relevance of the research is associated with the rapid development of modern high-performance computing systems, superneurocomputers and artificial intelligence devices. Today such development is held back largely due to the lack of an effective cooling system for high-power elements of their structures. Composite materials Cu-SiC with improved physical, mechanical and thermophysical characteristics can be used to solve problems of heat removal intensification. The main aim of the research is to obtain bulk products from metal-matrix composite Cu-10% SiC with improved physical, mechanical and thermal characteristics by spark plasma sintering. Objects of the research are bulk products from metal-matrix composite Cu-10%SiC. The samples were obtained by spark plasma sintering at temperatures of 700, 750, 800, 850 °C and a pressure of 60 MPa. Methods: spark plasma sintering, X-ray diffractometry (X-ray phase analysis), scanning electron microscopy, indentation, laser flash method. Results. Experimental studies have been carried out to obtain bulk metal-matrix composites with a copper matrix and the addition of reinforcing superhard particles of silicon carbide Cu-10%SiC. The compaction of dispersed composite materials was carried out by spark plasma sintering at various temperatures of 700, 750, 800, and 850 °C. The microstructure and composition of initial dispersed materials and final bulk products have been studied. It is shown that the spark plasma sintering method has advantages for obtaining relatively dense materials with high physical, mechanical and thermal properties. Analysis of the obtained samples showed the formation of a dense (up to ~88 %) homogeneous fine-grained composite structure. The greatest densification of the material is achieved at the highest sintering temperature of 850 °C, which causes this sample to demonstrate the maximum hardness (H=3,63 GPa) and Young's modulus (E=159,63 GPa), as well as the thermal conductivity at room temperature (λ=223 W/m K). The obtained composite materials can be used as structural and functional materials for energy-efficient heat-conducting systems.

The relevance of the research is caused by the interest in ensuring the thermal costs of oil refining technologies at the expense of by-products (oil sludge), as well as the need to reduce harmful emissions of technological processes. The main aim is research of the possibility of burning the carbon residue obtained during steam gasification of oil sludge as part of a fuel composition with the addition of peat. Objects of the research are carbon residue of oil sludge obtained after steam gasification of oil sludge at 600 °C, and a fuel composition based on it with the addition of peat (25 wt. %). Methods. Thermotechnical characteristics of the studied samples are determined according to SS R 55661-2013, 33503-2015 and 55660-2013. Net calorific values of the peats were determined in the ABK-1 calorimeter (Russia), the elemental composition of the organic matter was determined using the analyzer Vario Micro Cube (Elementar, Germany). Particle size (СROS) was determined using a scanning electron microscope JSM-6000C (JEOL, Japan). The study of the combustion of the samples under consideration was carried out using the differential thermal analyzer STA 449 F3 Jupiter (Netzsch, Germany) and an experimental stand equipped with a high-speed video camera FASTCAM CA4 5 (Photron, USA). The characteristic melting temperatures of ash and its composition are determined according to the SS 2057-94 and the SS 10538-87, respectively. Results. The carbon residue has a calorific value exceeding peat and comparable to brown coals and a rather low ignition temperature (220 °C), which is due to a rather high content of volatile substances (Vdaf =64,3 %). However, high values of ash content (Ad=60 %) and sulfur content (Sdaf=4,3 %) indicate the need to dispose of a large amount of ash and capture sulfur oxides SOx. It is shown that the joint combustion of carbonaceous residue and peat (25 wt. %) allowed reducing the amount of ash residue formed. In addition, when adding 25 wt. % of sukhovskoу peat it was possible to reduce the amount of generated SO2 emissions by more than 3 times. This effect is due to the gas phase interaction with peat mineral part, namely, with calcium and magnesium carbonates.

High-performance magnetite-based hollow spheres with the advantages of low density and low loading content are promising as an ideal lightweight electromagnetic (EM) wave absorption candidate. However, the effective preparation methods for these hollow spheres are still limited, and as a result, materials design and practical applications based on their size-dependent EM microwave attenuation properties are poorly accessible. In this study, high quality magnetite hollow spheres were successfully prepared by a simple, fast, one-step, and scalable plasma dynamic method with sole use of inexpensive precursors (oxygen and mild steel). The experimental results reveal that the as-prepared products are hollowed multiple-component magnetite spheres and have a very wide size distribution with a diameter of several tens of nanometers to hundreds of micrometers, which can be further separated into three fractions with different particle size distributions (0-30 μm, 30-100 μm, and >100 μm) by a simple magnetic separation method. The EM wave absorption results demonstrate that the hollow microspheres can exhibit excellent absorption ability with an effective absorption bandwidth (reflection loss ≤-10 dB) of 11.9 GHz from 3.7 to 15.6 GHz for an only 2 mm thick test absorber (50 wt% filler) and a maximum RL value of -36 dB at ∼8.2 GHz. Moreover, the positions of these resonant absorption peaks strongly depend on the sphere sizes and can be regulated at the L + C band, X band, and Ku band. Strikingly, differing from the nearly negligible microwave absorption for the ground powders, the dominating absorption mechanism for the hollow microspheres could be ascribed to the enhanced magnetic loss and multiple scattering due to the novel hollow magnetic structures, which are beneficial for the attenuation ability and improvements to their permeability and impedance matching.