No 4 (2025)

The paper presents the results of a study on the reducing-nitrating roasting of perovskite concentrate from the Afrikanda deposit to convert titanium into its nitride, which can then be subjected to low-temperature chlorination (300–500 °C) with the extraction of titanium in the form of TiCl₄. The material composition of the perovskite concentrate has been clarified. A thermodynamic assessment of the equilibrium compositions in the CaTiO₃-SiO₂-C-N₂ system in the temperature range of 1250–1350 °C has been carried out. The phase compositions of the roasting products obtained at the specified temperatures with different amounts of SiO₂ additive used to bind CaO formed during perovskite nitriding have been studied. It has been shown that the maximum conversion of titanium into its nitride is achieved at temperatures above 1300 °C. At the same time, an increase in the amount of SiO₂ additive in the batch also promotes the formation of the oxynitride phase. When SiO₂ is added in the molar ratio CaO:SiO₂ = 3:1, unreacted perovskite remains in the calcination product. In addition, the product contains residual calcium oxide, and the silicate phase consists of CaO·SiO₂ and 2CaO·SiO₂. The maximum transfer of titanium to the nitride phase is achieved at a molar ratio of CaO:SiO₂ = 1:1. Under these conditions, CaO·SiO₂ will predominate in the silicate phase.

The thermodynamic analysis of chlorination of the mineral part of the overburden carbonaceous rock of the Ekibastuz deposit (a natural multicomponent raw material) is of theoretical and practical interest. The nature of the change in the Gibbs energy value under the given conditions makes it possible to establish the fundamental possibility of the reaction. The assessment of the feasibility of each reaction is determined not only by the thermodynamic factor, but also by the rate of reaching equilibrium and the reaction rate. The calculated Gibbs energy and equilibrium constants characterizing the yield of the final reaction products in the temperature range of 400–2000 K show that in the presence of a reducing agent, the equilibrium of reactions is shifted towards the formation of chlorides. The effect of the reducing agent in the process of chlorination of oxide compounds is reduced to the binding of oxygen to form oxygen compounds of carbon. Thermodynamic analysis of systems (I–VII) showed that at a certain ratio of the initial components of the chlorination reaction at temperatures of 1000–1200 K passes through to the end with the formation of compounds in the gas and condensed phases, this is confirmed by the conducted research. Thermodynamic analysis of systems (I–VII) showed that a model based on theoretical calculations of the equilibrium compositions of reactions of chlorine with oxides, which are part of the mineral part of the carbonaceous rock, in the presence of a reducing agent, can be used to approximate the chlorination of aluminum-containing raw materials. Differences in the thermodynamic characteristics of the compounds that make up the carbonaceous rock, from a theoretical point of view, determine the fundamental possibility of selective chlorination of multicomponent raw materials. Ideally, a high degree of chlorination of aluminum oxide should be achieved with a minimum degree of chlorination of the accompanying oxides. The results of laboratory studies have fully confirmed the possibility of thermodynamic modeling of the chlorination process of multicomponent raw materials.

We propose a modified Taylor model for quantitative evaluation of the normal anisotropy coefficient (NAC). The model takes into account the texture and grain shape contribution of the material under study. The model was used to predict the dependence of the NAC on the angle between the rolling and strain directions in the plane of Al-Mg-Si alloy sheets. There is good agreement between the calculated and experimental NAC values  of 6016 aluminum alloy sheets. The good agreement was achieved by taking into account the texture heterogeneity through the sheet thickness and the elongation of grains in the longitudinal and transverse directions.

Ti-TiB₂ coatings were prepared by electric spark treatment with a non-localized electrode (NE) of a titanium substrate. Titanium granules and titanium diboride powder in various ratios were used for application. During the coating process, all samples monotonously gained weight. The average weight gain values for 10 minutes of treatment ranged from 1.6 to 3.8 mg/cm², with a minimum at sample B9 and a maximum at B6. A study of the average thickness of the coatings obtained showed comparability with the cathode gain. There are no clear boundaries and longitudinal cracks between the deposited layer and the substrate. All coatings have an inhomogeneous structure, represented by a metal matrix with dark gray inclusions, which are particles of the initial titanium diboride. The surface roughness of all prepared coatings according to the Ra criterion was very close and ranged from 5.13 to 9.27 microns. The average values of the microhardness of the coatings varied in the range from 13.28 to 13.91 GPa, which is 3.4 to 4.3 times higher than the uncoated titanium alloy. The cyclic heat resistance test was carried out at a temperature of 900 °C for 100 hours and showed that the final weight gain of the samples ranged from 487.0 to 583.8 g/m², which is lower than that of titanium alloy Ti6Al4V without coating (630.6 g/m²)
from 7 to 23%. The average values of the coatings’ wear intensity ranged from 1.26∙10^–6 to 6.3∙10^–6 mm³/Nm at 25 N and from 0.75∙10^–6 to 3.6∙10^–5 mm³/nm at 70 N.

The paper analyzes the production technology of corrosion-resistant 08Kh18N10T steel to determine the causes of overgrowth of steel filling cups and contamination with non-metallic inclusions. In the course of the work, the oxygen content found in various types of nonmetallic oxide inclusions and the total nitrogen and oxygen content in the metal were determined at the stages of bucket processing and casting of steel. The results of the electron microscope study confirmed the results of the FGA, namely, the predominance of unfavorable nonmetallic inclusions for corrosion-resistant steels: titanium oxides and nitrides, aluminates and spinels. It is shown that after the titanium wire was recoated into the metal, titanium oxides were the main type of HB. It is shown that the causes of overgrowth of steel filling equipment are complex non-metallic inclusions based on titanium oxide, which «stick» to the inner surface of the steel filling cup dispenser when casting steel.

A study of the structural state and microhardness of the surface layer of monocrystalline tungsten samples after exposure to pulsed fluxes of He⁺ ions and helium plasma generated in the Plasma Focus facility “Vikhr′” (IMET RAS) has been carried out. Irradiation parameters: plasma power density of 10⁸ W/cm², ions power density 2•10⁹ W/ cm² with a duration of exposure to plasma and ions of 100 and 20 ns, respectively; number of pulses– 15; energy of helium ions ~100 keV, plasma temperature ~1 keV. It is shown that beam-plasma exposure in this mode results in surface melting and the appearance of a crystallographically oriented network of microcracks. In contrast to the intergranular cracking typical for polycrystalline samples, in W single crystals the formation of a network of microcracks occurs against the background of plastic flow along active sliding planes under the influence of thermal stresses arising at the cooling stage after crystallization of the melt. A fine-mesh structure with a cell size of 200 nm is formed in the solidified layer. The formation of unopened blisters and craters has been observed due to the release of helium from the surface layers. Using X-ray diffraction analysis it has been shown that irradiation in the implemented mode, accompanied by evaporation of a thin surface layer, helps to reduce distortions of the crystal lattice and structural defects of a technological nature that have arisen in the surface layer of single crystal samples at the stage of their mechanical processing in preparation for experiments. As a result of radiation-thermal melting and directional solidification of the W surface layer, a crystallization texture is formed in it in the direction determined by the crystallographic orientation of the sample surface exposed to radiation and coinciding with the temperature gradient vector. A slight (up to 15%) decrease in microhardness was found in the remelted surface layer of W single crystals, while a spread of H_μ values over the irradiated surface area has been observed.

Using the method of sessile drop, the interaction of rail steel with the Al₂O₃-based refractory ce-ramics has been studied depending on the holding temperature and time and also on the gas-phase composition. It is shown that wetting angles were changed substantially (from about 145° to 125–130°) only upon isothermal holding at low temperatures. The effect of the roughness of ceramic substrate on a change in the wetting angle is studied. It is stated that its lower values took place on ceramics with the smaller roughness. The surface tension and density of rail steel are studied. An essential difference in the surface tensions upon heating and cooling was shown. It is found that, unlike pure iron, the inversion of the temperature coefficient ∂σ/∂Τ was observed for the rail steel. The adhesion work was calculated. It was shown its sharp increase for the initial 30 minutes of experiment (up to 600 mN/m) and, then, a gradual growth (to about 700 mN/m) independently of regimes of heating and cooling.