VOL 95, No. 1 (2022)

Specific mechanisms of grain structure effect on the thermoelectric properties (specific electrical resistivity and total
thermal conductivity) of the Bi1.9Gd0.1Te3 compound have been analyzed. These mechanisms are as follows: 1) forming the surface Te vacancies at grain boundaries acting as donor centres; 2) changing the elemental composition of the grains
at high-temperature Te evaporation under thermal treatment of material to prepare the samples with desired average grain size.

By means of the method of the spark plasma sintering (SPS) on the basis of nanodimensional powder of nickel oxide (with an average particle size of about 100 nm), the fine-grained (of 250 – 500 nanometers approximately), dense (5.93 g/cm3), strong ceramics with the high microhardness Hv = 8.2 GPa, ultimate compressive strength ?B = 0.4 GPa and Young?s modulus of elasticity E = 140 GPa is created. The obtained ceramic sample was nickel oxide NiO (73-1519) with cubic structure, space group Fm3m (No. 225) and lattice size a = 4.168 ?.

The paper presents the results of a study on the durability of cutting ceramics: a replaceable polyhedral plate developed
at NSTU and cutting ceramics WOK-60 when processing hardened steel blanks made of 40X (45HRC) steel. As a result
of the tests carried out, it was found that with the use of cutting modes developed at KNAU, the durability of SMP from cutting ceramics created at NSTU is more than 1.7 times higher than the performance of plates based on the WOK-60
material. At the same time, the roughness of the treated surface of the work piece was Ra = 0.35 ? 0.05 microns when using SMP from the developed ceramics Ra = 0.55 ? 0.05 microns when using WOK-60 plates. The stages of destruction
of cutting ceramic plates are revealed, taking into account the hierarchy of structural scales.

In this work we studied the effect of mechanochemical activation on the formation of the cobalt ferrite phase from iron and cobalt oxalates. X-ray phase, X-ray diffraction and synchronous thermal analysis, scanning electron microscopy,
low-temperature nitrogen adsorption-desorption method were used to study the composition and properties of the resulting product. It has been established that cobalt ferrite is formed at a temperature of 1100 °C during solid-phase interaction
of the initial components, and the use of mechanochemical activation of the initial components in a roller-ring vibration mill makes it possible to reduce the synthesis temperature to 400 °C. It is shown that CoFe2O4 obtained using the method
of mechanochemical synthesis has a more developed specific surface area and porous structure in comparison with cobalt ferrite obtained by the ceramic method.

In this work, the effect of the annealing temperature and the chemical history of the precipitate on the morphology and phase composition of the Nb2O5 powder was studied. Nb2O5?nH2O precipitate and gel-like niobium citrate were obtained by solution methods. The synthesis of niobium oxide was carried out at temperatures of 600, 1000, and 1200 °C, the synthesis products were analyzed using X-ray diffraction, scanning electron microscopy, X-ray microscopy, and differential thermal and thermogravimetric analysis. Annealing of niobium citrate at a temperature of 600 °C makes it possible
to obtain niobium oxide particles with an average size of about 70 nm, which is 4 – 6 times smaller than Nb2O5 obtained from the Nb2O5?nH2O precipitate.

The article provides an overview of mineral oxide fibers of various chemical composition: aluminosilicate, alumina, silica, bio-soluble, zirconium oxide fibers and others. Methods for producing discrete and continuous fibers, such as spinning
fibers from melts, sol-gel technology, spinning from solutions of metal salts, etc., are described. filtration for alumino-silicate and bio-soluble fibers; thermal insulation up to 1600 or 2000 C and reinforcement of composites used in the
aerospace and defense industries for alumina fibers and fibers based on zirconium dioxide, etc. Producers of mineral
oxide-containing fibers and products based on them abroad and in Russia are represented.

The article discusses the mechanochemical synthesis of a catalyst for the synthesis of methanol. Comparative mechanical activation of both individual components of the catalyst (copper oxide, zinc oxide, and aluminum oxide) and their various mixtures under different conditions has been carried out. The article discusses the structural characteristics of the catalyst for the synthesis of methanol, obtained using X-ray phase analysis, scanning microscopy and low-temperature adsorption of nitrogen.

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