The high-temperature strength properties of silicon carbide-based ceramic materials reaction-sintered in air and vacuum are proved by experimental data. The ultimate bending strength of pressed and cast ceramic material samples at temperatures up to 1400°C was measured as a criterion. High-temperature tests demonstrate the guaranteed strength of ceramics above 100 MPa. An example of the manufacture of a complex shaped ceramic product using the hot slip casting processing under pressure into additive water-soluble forms is given. An approval of the combined technology makes it possible to manufacture bladed ceramic elements with a thickness of about 1 mm.

Crystallized alloys in the LaB 6 –W 2 B 5 –NbB 2 system are obtained by melting in an electric arc discharge and rapid cooling in an inert gas (Ar) flow. The characteristic eutectic structures of the lamellar and rod types are investigated using scanning electron microscopy. Using X-ray phase and X-ray structural analysis, it is found that the phase composition of crystallized objects is represented by lanthanum hexaboride, an α-solid solution (W x Nb 1 – x ) 2 B 5 and β-solid solution (Nb x W 1 – x )B 2 . An assumption is made about the existence of a ternary phase in the Nb–W–B system, which is close to the composition of Nb 0.5 W 0.5 B 4 . The concentrations of the components in the eutectic regions are determined by the methods of X-ray spectral microanalysis and statistical analysis of the area of the phase components.

Crystallized alloys in the LaB6–W2B5–NbB2 system are obtained by melting in an electric arc discharge and rapid cooling in an inert gas (Ar) flow. The characteristic eutectic structures of the lamellar and rod types are investigated using scanning electron microscopy. Using X-ray phase and X-ray structural analysis, it is found that the phase composition of crystallized objects is represented by lanthanum hexaboride, an α-solid solution (WxNb1 – x)2B5 and β-solid solution (NbxW1 – x)B2. An assumption is made about the existence of a ternary phase in the Nb–W–B system, which is close to the composition of Nb0.5W0.5B4. The concentrations of the components in the eutectic regions are determined by the methods of X-ray spectral microanalysis and statistical analysis of the area of the phase components.

A powder mixture of eutectic composition in the LaB6–NbB2 system has been prepared by carboborothermic reduction of a La(OH)3 + NbO0.5–2(OH)4–1 hydroxide mixture in vacuum at an isothermal holding temperature of 1650°C. The hydroxide mixture was prepared by reverse coprecipitation in a suspension of amorphous boron and carbon from aqueous solutions of lanthanum nitrate, niobium fluoride, and niobium oxyfluoride. We have examined the effect of the boron-to-carbon ratio on the elemental and phase compositions of the boride mixture. The average particle diameter of the synthesized borides has been determined to be 200–250 nm. The powders have been sintered at 1700°C to a relative density of 87% and arc-remelted. The resultant rodlike eutectic structures had a NbB2 rod diameter near 600 nm. The structure of the solidified materials has been studied using scanning electron microscopy, X-ray microanalysis, and X-ray diffraction, and the eutectic composition has been accurately determined (58 mol % LaB6).

The sintering ability and mechanical characteristics of the materials obtained by sintering in the ZrB2–SiC–MoSi2 system are investigated. The density, linear coefficient of thermal expansion 4.9–6.1 × 10–6 K–1, ultimate strength in the bending of ceramic specimens (σmax = 460 MPa), and elastic modulus (up to 360 MPa) are determined; and the microstructure is investigated. The phase composition of some ceramics, in addition to the initial components, contains new phases: MoB, ZrC, and Mo4.8Si3C0.6.

In this work, we obtained ceramic materials based on MoSi2, hardened by SiC and TiB2 particles, which makes it possible to increase the heat resistance of the composite and increase the level of its physical and mechanical properties (at a relative density of more than 99, 0 %, tensile strength in bending 520 ± 10 MPa). The shrinkage, density, porosity and weight loss of composite materials during sintering were studied. The value of the ultimate strength in bending of materials at the optimum sintering temperature is determined. The maximum values of physical and mechanical properties are achieved for a material composition of 50, 0 vol. % MoSi2 + 15, 0 vol. % SiC + 35, 0 vol. % TiB2: E = 471 ± 10 GPa; σb = 520 ± 10 MPa, K1C = 4, 4 ± 0.1 MPa • m1/2; HV = 22.1 ± 0.1 GPa obtained at a sintering temperature of 1950 ° C.

Microstructural analysis and investigations of mechanical properties via indentation-techniques have been performed on a LaB6 - 15 vol. % TiB2 ceramics, obtained by the hot-pressing at T = 1900 °C and P = 30 MPa in argon gas. The relative density of hot-pressed material was up to 97% of theoretical. XRD, SEM and EDX analysis of ceramics were performed. The Vickers hardness (18.5 GPa) and fracture-toughness (3.9 MPa-m1/2) were compared with the values, measured on a single-crystalline LaB6 (Hv = 21 GPa, KIc = 2.4 MPa-m1/2) and arc-melted eutectic composite LaB6-TiB2 (Hv = 23 GPa, KIc = 6.7 MPa-m1/2).

The eutectic composition powder mixture was synthesized in the LaB 6 -ZrB 2 system by borothermal reduction of a mixture of La(OH) 3 and ZrO(OH) 2 in vacuum at isothermal holding temperatures from 1200 to 1600 °С. A mixture of hydroxides was obtained by co-precipitation from aqueous solutions of lanthanum and zirconyl nitrates in a suspension of amorphous boron. The effect of boron excess on the phase and elemental composition of a mixture of borides was studied. The dependence of the dispersion of the obtained powders on the synthesis temperature was established. Ill. 5. Ref. 45.

Eutectic LaB6–ZrB2 powder was synthesized by borothermal reduction of an La(OH)3–ZrO(OH)2 mixture under vacuum with isothermal curing at 1200 – 1600°C. The mixture of hydroxides was prepared via coprecipitation from aqueous solutions of La and Zr nitrates in a suspension of amorphous boron. The effect of an excess of B on the phase and elemental compositions of the boride mixture was studied. The particle size of the obtained powders depended on the synthesis temperature.

Microstructural and indentation-techniques mechanical investigations have been performed on a LaB6-TiB2 eutectic composite, obtained by the electric arc-melting in argon flow. Structure of solidified eutectics consists of directionally crystallized TiB2 fibers in LaB6 matrix. XRD, SEM and EDX analysis of eutectics were performed. The median diameter of the TiB2 fibers, calculated using statistical analysis of SEM micrographs, was 0.45 mu m. The volume fraction of the TiB2 phase in eutectics was 16% as calculated by area fractions from SEM micrographs. The Vickers hardness (25.5 GPa) and fracture toughness (6.7 MPa.m(1/2)) were measured on arc-melted LaB6-TiB2 alloy. Results were compared with the same ones, measured on floating-zone melted monocrystalline LaB6.

Zinc oxide powders made by mechanical high-energy grinding have been investigated using the methods of scanning electron microscopy, thermal nitrogen desorption, and Raman spectroscopy of infrared Fourier spectroscopy. Their structural evolution, including reduction of the average size of crystallites, increase in specific surface area, as well as changes in the number and ratio of adsorption centers, has been demonstrated. The data on the reconstruction of the surface of zinc oxide powders and multiple bond breaking in near-surface areas resulting from long-term dispersion have been presented.

The surface relief of blanks and silica glass fibers is studied by atomic force microscopy. The temperature change during free cooling is recorded using an infrared pyrometer. The results of the measurements of the roughness of the blank and fiber could indicate the effect of the cooling time of the quartz glass (QG) on the morphology of its surface.

AbstractZinc oxide powders made by mechanical high-energy grinding have been investigated using the methods of scanning electron microscopy, thermal nitrogen desorption, and Raman spectroscopy of infrared Fourier spectroscopy. Their structural evolution, including reduction of the average size of crystallites, increase in specific surface area, as well as changes in the number and ratio of adsorption centers, has been demonstrated. The data on the reconstruction of the surface of zinc oxide powders and multiple bond breaking in near-surface areas resulting from long-term dispersion have been presented.

The technological modes of obtaining ceramics based on MoSi2, hardened by SiC and ZrB2, which have enhanced physicomechanical properties (relative density ≥ 99,1 %, bending strength 480 MPa), were investigated and experimentally substantiated. The developed composite materials can be recommended for the creation on their basis of functional structural ceramics working at elevated temperatures in an oxidizing environment. Ill. 3. Ref. 11. Tab. 3.

To obtain the phases of the B 4 C–SiC–TiB 2 system with the eutectic ratio the simultaneous reduction by the carbon black of the powder mixture of boron acid, silicon dioxide and titanium dioxide was carried out. The synthesis was held in vacuum at 1600 °C. Only the predicted phases were detected in the synthesis products. The synthesized powders are represented both by the boron carbide of the size of less than 1 micron and by the nanoparticles. Ill. 5. Ref. 25. Tab. 1.

Dense B4C-based materials containing up to 4.9 wt % Si have been produced by hot pressing in the temperature range 1600–1700°C. In this process, the silicon melts to form a liquid phase, which improves the sinterability of the material. The boron carbide partially dissolves in the liquid Si to form silicon carbide between the B4C grains. The relative density, bending strength, Vickers hardness, and fracture toughness of the materials obtained in this study are 99.0 ± 0.1%, 584 ± 12 MPa, 39.4 ± 0.1 GPa, and 5.3 ± 0.2 MPa m1/2, respectively. The materials experience predominantly transcrystalline fracture.