This paper presents the results of studies on silicon carbide production by self-propagating high-temperature synthesis. To provide the necessary energy for the process, the synthesis was performed using magnesium-thermal reduction of silicon dioxide in an argon atmosphere. This study was characterized by the use of carbon fibers as a carbon source. It was determined that during magnesium-thermal synthesis, hexagonal particles with a size of 1 – 2 μm and a thickness of approximately 0.2 – 0.3 μm were mainly formed. X-ray phase analysis showed the predominant formation of a cubic syngony of silicon carbide.

The results of studies on the synthesis of aluminum nitride and AlN‒Al 2 O 3 ‒Y 2 O 3 compositions with a low oxygen impurity content by the SHS method are presented. The dependence of the lattice parameter c of aluminum nitride on the oxygen impurity content is shown. The conditions for the synthesis of AlN‒Y 2 O 3 compositions with a low oxygen content in the structure of aluminum nitride are determined. The dependence of the composition of oxide phases in compositions on the content of yttrium oxide in the reaction mixture is shown. The optimal content of yttrium oxide in the compositions has been determined. The results of sintering AlN‒Al 2 O 3 ‒Y 2 O 3 composite powders with different oxygen content in the aluminum nitride structure are shown.

Studies on the production of silicon carbide by self-propagating high-temperature synthesis (SHS) have been carried out. To provide the necessary energy for the process, the synthesis was carried out by magnesium-thermal reduction of silicon dioxide in an argon atmosphere. A special feature of this study is the use of carbon fibers as a carbon source. It has been determined that during magnesium-thermal synthesis, hexagonal particles with a size of 1‒2 µm and a thickness of about 0,2‒0,3 µm are mainly formed. X-ray phase analysis showed the predominant formation of silicon carbide cubic syngony.

We have studied the influence of the combustion temperature of Al + AlN mixtures in nitrogen and the cooling time of the synthesis products on the content of oxygen impurities dissolved in the aluminum nitride lattice. The results demonstrate that, in the temperature range 1460–2000°C, surface oxygen is incorporated into the structure of AlN. It has been shown that, with increasing synthesis temperature, the content of oxygen dissolved in aluminum nitride rises. The concentration of dissolved oxygen is higher in the case of a finer particle diluent (AlN). Raising the synthesis temperature leads to aluminum nitride grain growth and coalescence, characteristic of secondary recrystallization. We demonstrate that, to reduce the concentration of oxygen impurities dissolved in aluminum nitride, the starting mixture should contain additives facilitating the reduction of aluminum oxide or surface oxygen vaporization.

Results are given for synthesis of AlN–Al 2 O 3 –Y 2 O 3 composites in a combustion regime in an industrial reactor. The effect of synthesis temperature on formation of the microstructure, phase composition, and impurity oxygen content dissolved in the crystal lattice of aluminum nitride is studied. The optimum synthesis temperature is determined. Experimental batches of composite powders are produced for the manufacture of dielectric ceramics with high thermal conductivity.

The article presents the results of studies into the gas-phase synthesis of silicon carbide fibers using silicon powder, polytetrafluoroethylene (PTFE) energy additive and polyethylene (PE) powder by self-propagating high-temperature synthesis (SHS). Stoichiometric mixtures were used for experiments. Green mixture components were mixed in a 3 liter drum with tungsten carbide balls for 30 min. The green mixture weight was 500 g. Experiments were conducted in the SHS-30 industrial reactor. Silicon + PTFE mixture combustion was accompanied by a rapid increase in pressure from 0.5 to 4.0 MPa in less than 1 s, and a relatively rapid pressure drop to 1.5 MPa in 1.5 min. The combustion rate was more than 50 cm/s. It was established that there was a spread of the mixture components during the combustion due to the high combustion rate and intense gas emission. A cottonlike material of light blue color was obtained; it consisted of 100-500 nm thick silicon carbide fibers. The maximum pressure in the reactor reached 3.1 MPa in 1 s during the silicon + PTFE + PE combustion and then decreased to 1.5 MPa in 3 min. The combustion rate was about 40 cm/s. The entire volume of the reactor was filled with blue-grey cotton-like silicon carbide and SiC powder with equiaxed 0.5-3,0 μ m particles merged into conglomerates. Needle-like silicon crystals were formed in the transition layer between the powder and silicon carbide fibers. The results of experiments proved the possibility of obtaining silicon carbide nanofibers in relatively large quantities during the combustion of exothermic mixtures.

Рассматриваются технологические приемы, применяемые в СВС-процессах для создания оптимальных условий при получении порошков, спечённых материалов и керамических изделий. Эти приемы основываются на предварительном изучении закономерностей горения в каждой индивидуальной системе «твёрдое-твёрдое», «твёрдое-газ» и др. и направлены на управление условиями и параметрами горения, а именно: скоростью и температурой горения, фильтрацией газообразного компонента и полнотой превращения. Приводится сравнение СВС-продуктов с аналогами, полученными другими способами, показано, что СВС-продукты отличаются более высокой химической и фазовой чистотой и меньшим содержанием примесей, что объясняется значительным тепловыделением в процессе горения, способствующим самоочистке от летучих примесей.

We have studied the effect of low-melting-point salt additives on the morphology and phase composition of silicon nitride prepared by combustion synthesis. The additives have been shown to influence the structure formation mechanism. Based on equilibrium compositions calculated for particular synthesis conditions, we have proposed mechanisms underlying the influence of the additives on the structure formation process. The synthesis temperature and additives have been shown to influence the phase composition of the synthesis products. Conditions have been found for the preparation of alpha-silicon nitride powders consisting of equiaxed particles.

It has been shown that raising the oxygen impurity concentration in starting mixture components reduces the temperature of the α–β phase transition of silicon nitride. At oxygen contents above 2 wt %, the phase transition involves silicon oxynitride formation and decomposition. With decreasing oxygen impurity concentration in silicon nitride, the temperature of the α–β phase transition rises, approaching the dissociation temperature.

The investigating results are shown on the V‒Al alloy nitriding while burning in the large-scale reactor. The nitriding optimal condition were defned. The phaseforming behavior was investigated while the V‒All alloy nitriding under the burning condition. The processing method was developed for the self-propagating hightemperature nitriding. The test batch of the nitrided V‒ Al‒N alloy was manufactured.Ill.5. Ref. 5.

Nitriding of a V–Al–N alloy during combustion in an industrial reactor was investigated. The optimum nitriding conditions were determined. Phases formed by nitriding of VnAl-65 alloy during combustion were characterized. Self-propagating high-temperature nitriding technology was developed. Test batches of nitrided V–Al–N alloy were prepared.

The investigating results are shown on the V‒Al alloy nitriding while burning in the large-scale reactor. The nitriding optimal condition were defned. The phaseforming behavior was investigated while the V‒All alloy nitriding under the burning condition. The processing method was developed for the self-propagating hightemperature nitriding. The test batch of the nitrided V‒ Al‒N alloy was manufactured.Ill.5. Ref. 5.

The paper considers preparation of a strong and dense ceramics based on silicon nitride by sintering in a SHS reactor. As a sintering agent, an additive was used in the Al2O3-CaO system. The content of the additive varied from 5 to 15 wt. %. It is established that an increase in the amount of silicon introduced into the initial charge increases the strength characteristics of the material due to the formation of secondary silicon nitride during sintering.

We have studied the combustion of titanium in nitrogen in the presence of ammonium chloride. It has been shown that the use of NH4Cl in the self-propagating high-temperature synthesis of TiN considerably reduces the combustion temperature, prevents sintering of the synthesized titanium nitride particles, and increases their specific surface area. The synthesis products have the form of nanostructured titanium nitride particles which reproduce the shape of the starting titanium particles but consist of equiaxed titanium nitride grains ranging in size from 50 to 500 nm. We have obtained nanostructured titanium nitride powders ranging in specific surface area up to 80 m2/g.