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The hot press method obtained the SiC composite from different morphology and partial size powder. The starting SiC powder was: 1) fragmentation particle shape industrial charge of silicon carbide obtained by the Acheson method with sintering additive (9 wt.% Y2O3 − Al2O3) by Saint Gobain, 2) spherical particles SiC obtained by SHS in a laboratory. Bending strength, critical stress intensity factor, density, the friction coefficient of samples of the obtained ceramics were determined. It has been established that the properties of ceramics obtained from SHS silicon carbide powder (spherical particles with sizes of 100–400 nm), due to better compaction, were at least 10% higher than samples from Saint Gobain powder: bending strength 400 ± 22 MPa, density 3.23 ± 0.01 g/cm3, critical stress intensity factor К1С = 4.8 ± 0.3 MPa∙m1/2, friction coefficient 0.1126 ± 0.0031.

The oxidation resistance of ultra-high-temperature ceramic material (HfB2-30 vol%SiC)-2 vol%rGO (rGO: reduced graphene oxide) under long-term exposure (2000s) to a supersonic air flow has been studied. The ceramics were obtained by reactive hot pressing of HfB2-(SiO2-C)-rGO composite powder at a temperature of 1800°C (pressure 30 MPa, holding time 15 min, Ar). The surface temperature of graphene-modified ceramics under the influence of heating by high-enthalpy air flow (heat flow q reached 779 W·cm–2) did not exceed 1700°C, which is 650–700°C less than for the HfB2-30 vol%SiC baseline ceramics. This may be related to an increase in the efficiency of heat transfer from the sample to the water-cooled module, due to the higher thermal conductivity of the rGO-containing material. Thereby, a decrease in the material degradation degree has been noted, i.e. decrease in the recession rate and decrease in the total thickness of the oxidised ceramic layer by tenth. The peculiarities of the oxidised surface and near-surface region microstructure upon aerodynamic heating of the graphene-modified ceramic material, have been shown.

Fully dense high-entropy carbide (HEC) ceramic has been prepared from a mixture of the group IV and V transition metal oxides by a two-step technique, which involved the vacuum carbosilicothermic reduction (VCSTR) synthesis of a composite powder containing 75 vol.% HEC, 20 vol.% (Nb1-xMex)Si2 (where Me = Ti, Zr, Hf, Ta), and 5 vol.% SiC followed by hot pressing of the as-synthesized product. It was found that the reaction between (Nb1-xMex)Si2 and HEC took place during hot pressing, thereby allowing effective sintering to occur. The mechanical properties of the obtained nearly single-phase HEC ceramic were comparable to or even slightly better than those of HEC ceramics prepared by other methods. The use of VCSTR synthesis as a key step in the preparation of fully dense HEC ceramic was concluded to be effective both in lowering the sintering temperature and in improving the mechanical properties.

The method of fabricating dense ultra-high temperature ceramic materials ZrB

Oxidation under exposure to a supersonic dissociated air jet (with heat fluxes in the range 363–779 W/cm2, total exposure time: 2000 s) was studied for HfB2–30 vol % SiC ultra-high-temperature ceramics (UHTC) doped with a lowered amount (1 vol %) of reduced graphene oxide (GO). Doping the ceramics with a relatively low amount of reduced GO (1 vol %) did not prevent a dramatic increase in the average surface temperature to 2300–2400°С. However, the existence time of surface temperatures below 1800–1850°С increased considerably, probably due to an increase in the thermal conductivity of the ceramics. The ablation rate of the material was determined as 6.5 × 10–4 g/(cm2 min), which is intermediate between the respective values for HfB2–SiC ceramics and the ceramics doped by 2 vol % graphene. The microstructure features and elemental composition of the oxidized surface and chips of the material were studied. The structure and thickness of the oxidized near-surface region were determined.

Using hot uniaxial pressing in an argon atmosphere with a stress of 35 MPa and with holding at 800°C for 1 h, ceramic composites of Bi3Ru3O11–50 wt % Bi1.6Er0.4O3 and Bi3Ru3O11–65 wt % Bi1.6Er0.4O3 were obtained. It was found that phase composition of the composites does not change during gas chromatographic testing at 800°C and corresponds well to the specified one. The microstructure of the obtained composites was tested, and the formation of dense composites with a total porosity of less than 1% and with a uniform distribution of the Bi3Ru3O11 and Bi1.6Er0.4O3 components in the bulk of material was demonstrated. Transport properties (total conductivity, oxygen fluxes, and selectivity of separating oxygen over nitrogen) of the obtained composites at 600–800°C was investigated. Thus, at 800°C, the electrical conductivity of Bi3Ru3O11–50 wt % Bi1.6Er0.4O3 and Bi3Ru3O11–65 wt % Bi1.6Er0.4O3 was about 200 and 50 Ω–1 cm–1, respectively, while the metallic nature of their temperature dependence of conductivity is correlated to that for Bi3Ru3O11. The value of oxygen permeability for the obtained ceramic composites of about 7 × 10–9 mol cm–1 s–1 at 800°C, which is comparable to other membrane materials based on bismuth oxide, demonstrated the potential of their further use in the tasks for obtaining of pure oxygen from the air.

Novel C/SiC core-shell fibers have been synthesized through incomplete conversion of carbon fibers by their siliconization with SiO gas. The synthesis was performed in the laboratory-made semi-closed batch-type reactor at 1380 °C for 3 h using a 9:1 M ratio mixture of Si and SiO2 powders as a solid source of SiO gas. The conversion rate of carbon into SiC was 34.0%. All synthesized fibers had a distinct C/SiC core-shell composite structure. The fiber product was of fairly good uniformity in respect of the shell thickness which varied approximately from 0.6 μm to 0.8 μm depending on the location of fibers inside the reactor. It was revealed that the formation of the shell was the result of inward growth of the SiC product layer. The effectiveness of the proposed semi-closed reactor for the synthesis of C/SiC core-shell fibers has been demonstrated.

Ti3SiC2 was synthesized by hot pressing at 1400°С for 15 and 30 min at a pressure of 30 MPa from powder mixtures, mainly from Ti/Si/TiC and Ti/TiSi2/TiC. The amount of the Ti3SiC2 phase synthesized from these mixtures was 94.0 and 95.9 vol %, respectively (1400°С, 30 min). The Ti3SiC2 phase crystallized as elongated grains. The effect of the hot pressing time on the formation of the Ti3SiC2 phase from the starting Ti/Si/TiC powders was determined. The final products contained titanium carbide and a small amount of silicon carbide as intermediate phases (for composites containing the starting silicon carbide powders). An excess of silicon leads to the formation of the largest amount of the Ti3SiC2 phase.

The conditions for β-SiAlON to be prepared by reacting highly dispersed mixed silicon and aluminum alkoxide xerogels with molecular nitrogen at 1600–1700°С are determined. The nitrogenation of mixed xerogels is shown to be due to the catalytic pyrolytic decomposition of hydrolysis products of silicon and aluminum alkoxides in a nitrogen atmosphere, namely, a mixture of alcohols that are adsorbed or chemisorbed on aluminosilicate xerogel particles. The pyrolysis of alcohols in a nitrogen atmosphere catalyzed by highly dispersed alumina yields hydrogen and carbon monoxide, which activate nitrogenation and affect the phase composition of the samples and change the sialon stoichiometry from β-Si3Al3O3N5 to the 15R polytype.

The preceramic oligomer organomagnesiumoxanealumoxane was synthesized by the co-condensation of organoaluminoxane and magnesium acetylacetonate. Powders of magnesium aluminate spinel (MAS) were obtained by the pyrolysis of the oligomer at 700 and 1250°C. The effect of the pyrolysis temperature on the physicochemical and rheological properties of the powder was studied. With increasing pyrolysis temperature, the particle shape becomes closer to isometric, which leads to a decrease in the limiting length of the linear portion of the compaction curves. A MAS powder containing 3 wt % Sm2O3 was produced to study the effect of the sintering additive. The sintering kinetics was investigated by dilatometry, and the effect of the sintering additive Sm2O3 on the process and the mass-transfer mechanism during the sintering of spinel was estimated. According to the quantitative analysis data, the activation energies for the pure MAS and the MAS doped with Sm2O3 are Q1250 = 481 kJ/mol and QSm2O3 = 775 kJ/mol, respectively. The sintering additive does not affect the mass-transfer mechanism; however, it increases the activation energy by 60%, doubles the shrinkage, and decreases the temperature of the beginning of sintering from 1546 to 1494°C.

Powders of cerium-containing hydroxyapatites (Ce–HA) with an estimated cerium concentration of up to 0.5 mol % have been synthesized. The phase formation and luminescent properties of the compounds after heat treatment in oxidizing and reducing atmospheres have been investigated. It has been shown that a high HA luminescence intensity can be achieved by preventing the cerium(III) → cerium(IV) transition in a reducing atmosphere at 900–1200°C, as well as by cosubstitution of Ce3+ and Li+ ions for Ca2+ ions to compensate for the excess charge of the additive. The dependence of the luminescence intensity of materials on the heat treatment temperature and cerium concentration is shown.

A new approach to the fabrication of C/SiC core–shell composite fibers through the high-temperature siliconization of carbon fibers with SiO gas in a laboratory-made semi-batch reactor using a granulated 9Si + SiO2 mixture as a solid-phase source of SiO reactive gas has been proposed. The flowsheet of the process provides a uniform siliconization of the material throughout the entire volume of the reactor. It has been shown that C/SiC composite fibers can thus be prepared. Carbon fiber conversion can vary over a wide range depending on the reactor load parameters. The core–shell composite structure is a result of the growth of the SiC layer inward the fiber, which can give rise to deep longitudinal–radial cracks when the SiC shell thickness exceeds 0.7–0.8 µm. At lower conversions, no cracking of the SiC shell occurs, and the produced C/SiC core–shell composite fibers retain their integrity.

Experimental data on the effect of the ambient atmosphere (a vacuum or argon) on the phase composition of silicon carbide fibers formed upon the siliconization of carbon felt are presented. The major phases produced in the siliconization of carbon felt are β-SiC (3C) in vacuo and α-SiC (6H) in the argon atmosphere. When carbon felt is siliconized in vacuo, residual silicon is present on the surface of the silicon carbide felt fibers. The ambient atmosphere determines the nature of the siliconization process at 1650°C: in vacuo, SiC is formed due to the reaction of carbon fibers with the silicon melt wetting them, while in argon, it is formed due mainly to the reaction with vaporous silicon.

The compaction of initial powders, the bending strength, and the microhardness of 21R sialon ceramics obtained by hot pressing have been studied experimentally. It is found that the Sm2O3 sintering additive substantially reduces the annealing temperature and enhances the properties of the ceramics. The samples of 21R sialon ceramics without additives, which are prepared by annealing at 1950°C, have a density of 3.01 g/cm3, a bending strength of 240 ± 15 MPa, and a Vickers microhardness of 16.2 ± 0.4 GPa; the samples of 21R sialon ceramics with 2.5 wt % Sm2O3, which are annealed at 1750°C, are characterized by a density of 3.39 g/cm3, a bending strength of 315 ± 16 MPa, and a Vickers microhardness of 21.9 ± 0.2 GPa. It is shown that Sm2O3 reacts with 21R sialon in the temperature range of 1600–1700°C to form the 27R sialon and SmAlO3 impurity phases. In the samples annealed at 1750°C, the 27R sialon and Sm–sialon (Sm3Si2.5Al3.5O12.5N1.5) impurity phases are detected.

The oxidation of an ultra-high-temperature ceramic material (HfB2-30 vol%SiC)-10 vol%Ta4HfC5 produced by reactive hot pressing at a temperature of 1800°C (pressure 30 MPa, holding time 30 min, Ar) under long-term exposure (2000s) to a supersonic flow of dissociated air was studied. It was found that the sample surface temperature, set during heating and oxidation on a high-frequency induction plasmotron, was significantly lower than for samples unmodified with super-refractory tantalum-hafnium carbide Ta4HfC5. It was also found that under similar exposure conditions there was no sharp temperature rise to 2500−2700°C – the temperature did not exceed 1850°C. Features of the oxidised material surface microstructure were noted, in particular, the existing gradient in the elemental composition and morphology of the oxide particles forming the surface. It was found that the main crystalline oxidation product was a complex hafnium-tantalum oxide Hf6Ta2O17, which had a phase stability up to temperatures of ∼2250°C, which set it apart from individual hafnium oxide.

Specific features of the synthesis of sialons (SiAlON) in the Si–Al–O–N system by firing at 1600–1700°C in a nitrogen atmosphere of mixtures of different initial compositions corresponding to the same composition of the final product Si3Al3O3N5 have been studied. β-Sialon was synthesized from reaction mixtures based on crystalline silicon and aluminum nitrides and amorphous highly dispersed hydrated oxides—(1) AlN + SiO2(sol), (2) Si3N4 + Al2O3(sol), and (3) AlN + Si3N4 + Al2O3(sol)—obtained by applying sols based on silicon or aluminum alkoxides (based on the β-sialon stoichiometry) to the surface of nitride powders by the sol-gel method. It has been demonstrated that β-Si3Al3O3N5 can form in the reaction at 1600°C of highly dispersed mixed xerogels made of silicon and aluminum alkoxides—(4) (SiO2 + Al2O3) (mixed sol)—with molecular nitrogen without the participation of the initial nitrides. The influence of the starting composition of xerogel mixtures and synthesis conditions on the phase composition and morphological features of sialons obtained in one stage of calcination in a nitrogen atmosphere has been studied by thermogravimetry, X-ray powder diffraction analysis, and electron microscopy. It has been shown that the proposed reactions of the formation of sialons involving crystalline nitrides, xerogels, and molecular nitrogen are related to reduction–nitridation reactions, in which the reducing agents are organic products of hydrolysis of silicon and aluminum alkoxides and their pyrolytic decomposition in a nitrogen atmosphere.

Ultra-high-temperature ceramic (UHTC) materials with a density of 94.5 ± 1.3% have been manufactured by hot pressing a (HfB2–30 vol % SiC)–5 vol % Y3Al5O12 composite powder, which has been prepared sol–gel method, at a moderate temperature of 1850°C (holding time, 30 min; pressure, 30 MPa). The oxidation resistance of this ceramic has been studied at elevated temperatures under the effect of a supersonic dissociated air flow (on a high-frequency induction plasmatron). The maximum surface temperature has been ~2550°C. An analysis of the kinetics of temperature changes depending on the heat load indicate that, when five percent of Y3Al5O12 by volume of HfB2–30 vol % SiC is introduced into the ceramics, the thermal conductivity of the material decreases. This is not critical from the point of view of the stability of the obtained sample to single temperature drops of ~700–1400°C in a few seconds with sharp heating and cooling of the sample. A decrease of ~35–40% in weight loss of the (HfB2–30 vol % SiC)–5 vol % Y3Al5O12) sample has been noted as the result of exposure as compared with unmodified analogs. Due to the presence of Y3Al5O12 in the initial ceramics, there is also a certain amount of the stabilized phase of cubic HfO2 in the oxidized layer in addition to the monoclinic.

Dense silicon carbide-based ceramic composites reinforced with SiCf fiber have been produced by hot pressing at a temperature of 1850°C. The reinforcing agent used was silicon carbide fiber produced by siliciding carbon cloth with SiO vapor. It has been shown that raising fiber content from 1 to 7 wt % increases the density, bending strength, and fracture toughness of the material, which reach ρ = 3.20 ± 0.01 g/cm3, δb = 450 ± 26 MPa, KIс = 5.6 ± 0.1 MPa m1/2 at 7 wt % SiC fiber.

Samples of a solid solution aluminum oxonitride (γ-AlON) of spinel structure with different ratios of components (Al2O3 and AlN) were prepared by the sol–gel technique combined with high-temperature solid-state synthesis at 1750°C in a nitrogen atmosphere. The X-ray diffraction study of polycrystalline samples was performed by the Rietveld method. It was shown that the crystal structure of γ-AlON can be described by the model of permanent anions. The occupancies of tetrahedral and octahedral positions by aluminum atoms in the cationic sublattice of spinel are less than one, and the vacancies are predominantly located in octahedral positions. The lattice constant of the spinel phase (7.9499 A) in the sample with 67 mol % of Al2O3 and the near-stoichiometric composition Al23O27N5, almost coincides with early published data. The spinel parameter u slightly depends on the concentration and is equal to ∼0.3810.

The method of siliconizing carbon fabric with SiO vapours yields a textile SiC material that preserves the structure and integrity of the fibers of the original fabric, as well as the average diameter of the monofilament. According to X-ray phase analysis, it was found that SiC fibres obtained by siliconizing silicon fabric with SiO vapor consist of a mixture of two modifications of 3C–SiC and 6H–SiC. According to infrared absorption, the oxygen content in the composition of silicon carbide fibers does not exceed 2.1 wt%. The mechanical properties of the obtained fibers were investigations: the mechanical tensile strength of silicon carbide fibers is σp = 1350 ± 120 MPa, the nanoscale hardness is 10 ± 0.5 GPa, and the elastic modulus is 100 ± 10 GPa.

By hot pressing (1900 °C, 30 MPa, holding time 15 min) of HfB2-(SiO2-C) composite powder, an ultra-high-temperature ceramic material of HfB2-30 vol% SiC composition with nanocrystalline silicon carbide has been obtained. The effects of subsonic and supersonic dissociated air flow on the surface of produced materials have been studied on a high-frequency induction plasmatron in the geometry of a cylindrical sample with a flat face, fixed in a copper water-cooled holder with a 1 mm protrusion. It has been shown that a sudden rise in the average surface temperature of the samples to ∼2600 °C is characteristic for both modes, which is associated with the occurrence of local sites with a temperature >2000 °C and a subsequent increase in their area. It is a matter of evaporation of the borosilicate glass layer from the surface of the oxidized sample and formation of the ceramic layer of a highly catalytic and low thermal conductive porous HfO2 layer, which is confirmed by the emission spectroscopy data, XRD and elemental analysis of the material surface after the experiments. The features of heating the oxidized surface of the samples under the impact of subsonic and supersonic dissociated air flow have been noted: there are differences in the location of overheated sites, initiating a sharp temperature rise and the rate of growth of their area.

Porous HfB2–65 vol % SiC samples (porosity 34.5%) were produced by reactive hot pressing of HfB2–(SiO2–C) composite powder at 1800°C (heating rate 10 deg/min, holding duration 15 min) and 30 MPa. Using a high-temperature induction plasmatron, their resistance to oxidation by a supersonic dissociated air flow was studied (the heat fluxes in the course of the experiment were varied from 363 to 779 W/cm2). The observation of the temperature distribution over the surface of the sample during the experiment showed that a sharp increase in temperature from ~1770–1850 to ∼2600°C in the samples under investigation occurred at lower heat fluxes and shorter treatment times than that in denser HfB2–30 vol % SiC samples (porosity 9–11%). This indicated that increasing the density of the HfB2–SiC material and also increasing the silicon carbide content reduced the oxidation resistance. However, the fact that the studied sample withstood 37-min exposure to a high-enthalpy dissociated air flow (including 27 min at a surface temperature of 2560–2620°C) without destruction or complete oxidation makes it possible to assign it to ultra-high-temperature materials.

Si3N4–TiN ceramic composites have been produced by hot-pressing mixtures of silicon nitride and metallic titanium powders at temperatures from 1600 to 1800°C in a nitrogen atmosphere. We have examined the influence of the concentration and morphology of metallic Ti particles in the starting mixture and synthesis conditions on the microstructure, phase composition, and mechanical strength of the Si3N4–TiN ceramic composites. The results demonstrate that the sintering process ensures complete titanium nitridation, leading to the formation of a nonstoichiometric titanium nitride with the composition TiN0.9. The Si3N4–TiN composites prepared from the mixtures containing 5–30 wt % Ti have densities in the range 3.02–3.41 g/cm3, water absorption from 0.01 to 0.14%, open porosity from 0.03 to 0.44%, and bending strength from 250 to 584 MPa. The Si3N4–TiN ceramics prepared using calcium aluminates as sintering aids consist of dense intergrowths of silicon nitride crystallites, which ensures increased strength of the materials. Moreover, the samples containing 25–30 wt % TiN offer high electrical conductivity.

Highly disperse and reactive (HfB2–SiC)@(Ta2O5–HfO2–C) composite powders were manufactured by sol–gel technology where Ta2O5–HfO2–C amorphous components were nanostructured and distributed in each other as uniformly as possible. The reactive sintering of the prepared composite powders at a relatively low temperature (1800°С) with an exposure time of 30 min and the pressure 30 MPa yielded (HfB2–30 vol % SiC)–xTa4HfC5 ultra-high temperature ceramics (UHTCs), where x = 5, 10, and 15 vol %, with a relative density of 75–78%. X-ray powder diffraction proved the complete conversion of tantalum and hafnium oxides to complex carbide Ta4HfC5. The average grain size as determined by scanning electron microscopy did not exceed 2–3 µm in HfB2 and 30–60 nm for the Ta4HfC5 phase. Thermal analysis in flowing air showed that, in the temperature range 20–1400°С, the increasing percentage of tantalum–hafnium carbide (the least oxidation resistant phase) leads to a systematic increase in oxidation-induced weight gain; however, a tendency to saturation is observed. The microstructural specifics of the oxidized surface are noticed depending on the composition of HfB2–SiC–Ta4HfC5 ceramics.

The technique was developed, the installation was done, and the conditions for the production of Si3N4 and Si2N2O by the method of gas-phase pyrolysis of hexamethyldisilazane (CH3)3-Si-NH-Si-(CH3)3 (HMDS) were experimentally studied. In the experiments, two different methods of inputting the raw material were used—the input of a vapor–gas mixture (bubbling feeder with heating to supply the HMDS vapor in a stream of carrier gases) and input as a gas-droplet stream (pneumatic nozzle). The effect of gas-dynamic synthesis conditions at temperatures up to 1100°C on the properties of silicon oxonitride and silicon nitride nanopowders was studied. The influence of the conditions of mixing the reactants, the volume ratio of nitrogen/ammonia, and the content of HMDS in the vapor–gas mixture on the yield of products was shown. The dependences of the degree of conversion of the feedstock on the gas flow rate and the concentration of ammonia in the gas phase were obtained. The optimal conditions for the pyrolysis process were found: temperature, the ratio of the components of the gas mixture, the conditions of mixing, and the contact times of the phases. X-ray amorphous Si3N4 and Si2N2O powders with particle sizes of 50–200 nm and a specific surface area of up to 15 m2/g and powders of alpha modification of silicon nitride Si3N4 in the form of threadlike crystals with a particle diameter of 50–200 nm were obtained.

We report an experimental study concerned with the synthesis and luminescence properties of Al5O6N aluminum oxynitride doped with Tb3+ in the concentration range 0.025–0.5 at %. All of the samples, prepared by firing appropriate mixtures in a nitrogen atmosphere at 1600°C, consisted predominantly of phase-pure γ-ALON (Al5O6N), with small amounts of impurity phases: Al7O3N5 aluminum oxynitride and Tb3Al5O12 terbium aluminate. Their pulsed cathodoluminescence and photoluminescence spectra contain emission bands typical of Tb3+ ions. The concentration threshold for luminescence quenching corresponds to a Tb3+ concentration at a level of 0.4 at %. A Tb3+ cross relaxation effect found in Al5O6N:Tb3+ is discussed and photoluminescence spectra are shown to be inhomogeneous at low Tb3+ concentrations in Al5O6N.

Samples of an ultra-high-temperature HfB2–30 vol % SiC ceramic material with an SiC crystallite size of ~50 nm have been fabricated by hot pressing of an HfB2–(SiO2–C) composite powder synthesized through a sol–gel route. It has been found that the selected hot-pressing conditions (1800°C, 15 min, 30 MPa) ensure complete conversion of silica to silicon carbide and afford a material with a relative density of 96.9%. The effect of a relief applied to the sample surface in the form of ring grooves with a depth of

—The main factors affecting the transparency of ceramics are analyzed: the presence of pores, the character of structure, and multiphasicity. The requirements on powder precursors, synthesis methods, and conditions of their grinding, as well as solid-phase technologies for the production of transparent ceramics, are considered.

Methods of obtaining metal nitrides are examined. The main advantages and disadvantages are highlighted for each method. The possibilities of using these materials in different industries are briefly discussed.

Silicon-carbide materials with 5 – 10 wt.% additions of oxides were prepared by liquid-phase sintering at 1860 – 2100 °C. The highest physicomechanical properties were achieved in SiC material containing 20 wt.% of a three-component eutectic composition in the MgO–Y2O3–Al2O3 system. The mechanical characteristics of liquid phase-sintered materials containing 15 wt.% of the three-component oxides additive exceed those of both the reactive-sintered and the solid-phase sintered materials and approach those of hot-pressed materials. Ill. 5. Ref. 30. Tab. 2.

The heterogeneous CaB6–TiB2 powder mixtures were synthesized by reducing the mixture of TiO2 and CaCO3 with boron carbide in vacuum at 1400 – 1650°C. Reaction hot pressing was conducted according to the following regime: 1500°C (synthesis in vacuum) – 1900°C (pressing in Ar). As a result of synthesizing CaB6–TiB2 at mass ratio of 1:1 and 1600°C followed by isothermal soaking for 1 hour, a heterogeneous mixture was obtained containing crystalline phases of CaB6 and TiB2 with the residual B4C impurity (0.5 wt. %). The powder particles represent grains measuring 1 – 3 μm in diameter and containing two phases CaB6 and TiB2 in the form of crystallites measuring 0.1 – 1.0 μm in diameter uniformly distributed throughout the particle volume.

The literature on preparation methods and signature features of composites based on transition-metal carbides, nitrides, and borides; covalent compounds (SiC, Si3N4); and Al2O3 reinforced with fibers and whisker crystals is reviewed. The main properties of the fibers and whisker crystals are studied.

Dense materials based on silicon carbide were obtained by liquid-phase sintering. The oxides MgO, Y2O3 , and Al2O3 , corresponding to the composition of yttrium-aluminum garnet and the triple eutectic point on the line of binary sections garnet-spinel, were used as the sintering additive. The oxides were deposited on the surface of powder by the SiC method of coprecipitation from a solution of salts. The maximum density (ρrel = 99.5%) was attained on SiC materials which include 20% (by weight) sintering additives consisting of a three-component oxide mixture at temperature 1800°C.

High-density (with a relative density of up to 98.8%) ultra-high-temperature ceramic materials (UHTCs) based on the ZrB2–TaC–SiC system were obtained by hot pressing for 15 min at 2000°C 30 MPa of pressure in an argon atmosphere. Phase composition, lattice parameters, microstructure, flexural strength, Vickers hardness and crack resistance were studied. The maximum values of strength, hardness and crack resistance were 440 MPa, 20.3 GPa and 5.3 MPa·m1/2, respectively. The effect of the ZrB2/TaC ratio on the lattice constants and the mechanical properties of the material is established.

The main results of scientific sessions at the Sixth Interdisciplinary Scientific Forum with international participation “New Materials and Advanced Technologies” were presented; the sections included: “Nanomaterials and nanotechnology”; “Inorganic functional materials”; “Construction materials”; “Biomaterials and technologies”; “Materials and technologies for green chemistry”; “New materials and technologies in oil and gas industry (gas, oil, energetics).” More than 700 scientists from Russia, Azerbaijan, Belarus, Kazakhstan, Moldova, Tajikistan, Uzbekistan, France, and Czech Republic took part online in the forum, which gave rise to both national and international contacts. Two hundred and twenty six oral reports were presented at the forum, and lectures by famous scientists were organized. Scientific sessions and round tables with participation of representatives of foundations, industries, and scientific journals were held; the foresight sections were devoted to problems of the development of new materials and their commercialization and coverage. The topics included in the program of the forum gathered members of various interdisciplinary research groups concerned with the creation of materials and their use in various sectors of economy, and also the representatives of industrial enterprises interested in the latest developments. The high level of scientific training demonstrated by Russian and foreign scientists at the forum and wide discussion of their original and significant results is an important basis for further development of materials sciences, introduction of advanced technologies, and successful implementation of important priority programs for the development of science and technology.

The heterogeneous CaB6‒TiB2powder blends were synthesized by means of the TiO2and CaCO3mixture boron carbide reduction under vacuum at 1400‒1650 °C, and reactive hot pressing was used according to the condition: 1500 °C (synthesis in vacuum) ‒ 1900 °C (Argon pressing). As a result of the CaB6‒TiB2synthesis with the mass ratio 1:1 at 1600 °C and isothermal time 1 hour the heterogeneous mixture was prepared which contained the CaB6and TiB2crystal phases as well as the residual B4C admixture (0,5 mass percent). The powder particles were the grains 1‒3 micrometers in diameter containing two phases CaB6and TiB2as the micro crystals 0,1‒1,0 micrometers in diameter uniformly spaced over the particle volume.Ill. 6. Ref. 37. Tab. 1.