Iron contained in coal fly ash of the Ekibastuz power station is distributed between magnetite and hematite. XRD data showed that ~80 wt % of iron is contained in magnetite and ~20 wt % in hematite. The leaching of iron from CFA by HCl was studied. It was determined that leaching efficiency increased with the increase in hydrochloric acid concentration and temperature. The maximum iron extraction efficiency was 52%. Aluminum is contained in the mullite and was practically not leached. The maximum aluminum extraction efficiency was 3.7%. The kinetics investigation showed that the process of iron leaching was controlled by chemical reaction and diffusion process steps, with an activation energy of 33.25 kJ·mol⁻¹. The aluminum leaching process is controlled by a diffusion process step with an activation energy of 19.89 kJ·mol⁻¹. The reaction order of hydrochloric acid is determined to be 0.9 and 0.23 for iron and aluminum, respectively.

Sandy grade alumina is a valuable intermediate material that is mainly produced by the Bayer process and used for manufacturing primary metallic aluminum. Coal fly ash is generated in coal-fired power plants as a by-product of coal combustion that consists of submicron ash particles and is considered to be a potentially hazardous technogenic waste. The present paper demonstrates that the Al-chloride solution obtained by leaching coal fly ash can be further processed to obtain sandy grade alumina, which is essentially suitable for metallic aluminum production. The novel process developed in the present study involves the production of amorphous alumina via the calcination of aluminium chloride hexahydrate obtained by salting-out from acid Al-Cl liquor. Following this, alkaline treatment with further Al₂O₃ dissolution and recrystallization as Al(OH)₃ particles is applied, and a final calcination step is employed to obtain sandy grade alumina with minimum impurities. The process does not require high-pressure equipment and reutilizes the alkaline liquor and gibbsite particles from the Bayer process, which allows the sandy grade alumina production costs to be to significantly reduced. The present article also discusses the main technological parameters of the acid treatment and the amounts of major impurities in the sandy grade alumina obtained by the different (acid and acid-alkali) methods.

Composite materials "base–transition layer–surface metal layer (Ta/Ti)" were produced using a complex vacuum technology including magnetron sputtering. The structure (by scanning electron microscopy, Auger electron spectroscopy, X-ray diffractometry) and mechanical properties were studied. An almost linear increase in the thickness of both the surface and transition layers was observed with increasing deposition time and power; however, the growth of the surface layer slowed down with increasing power above some critical value. The transition zone with the growth of time stopped growing upon reaching about 300 nm and was formed approximately 2 times slower than the surface one (and about 3.5 times slower with power). It was noted that with equal sputtering–deposition parameters, the layer growth rates for tantalum and titanium were the same. In the sample with a Ta surface layer deposited on titanium, a strongly textured complex structure with alpha and beta Ta was observed, which is slightly related to the initial substrate structure and the underlying layer. However, even at small thicknesses of the surface layer, the co-deposition of tantalum and titanium contributes to the formation of a single tantalum phase, alpha.

The analysis of modern approaches in choosing compositions of cermets based on TiC carbide and Ni matrix doped with additional Mo, W, Cr, Nb, and Ta carbides is carried out. The hardness and transverse strength of the cermets based on TiC carbide and Ni matrix increases with the use of additional Mo, W, Cr carbides owing to the formation of an annular zone around TiC. The calculated microhardness of carbides in the cermet increases with an increase in their volume fraction and with the use of Mo, W, and Cr carbides. On the basis of an analysis of the literature, TiC–Cr₃C₂–WC–TiB₂–SiC–Mo–B–Si–Ni cermets with additional carbon content for plasma coatings are proposed and studied. Mechanical alloying and liquid phase sintering at temperatures of 950, 1250, and 1450°C are used to evenly distribute the carbides in the base phase and to establish strong bonds between them with high values of microhardness, up to 2438 kgf/mm² at a load on the indenter of 20 G and 2030 kgf/mm² at a load on the indenter of 200 G. The maximum values of microhardness are obtained at higher sintering temperatures at which the minimum content of oxygen is fixed. The positive effect of carbides based on W, Mo, and Cr on the organization of a strong titanium carbide compound with a base phase is confirmed experimentally, which is proved by the calculated value of the contribution of microhardness of TiC carbide to the cermet microhardness. At a volume fraction of the carbides of 77% and a load on the indenter of 20 G, the contribution of microhardness of the carbide is equal to 2906 kgf/mm², which is close to the TiC hardness of 3200 kgf/mm². This contribution of microhardness is equal to 2145.5 kgf/mm² at a load on the indenter of 200 G.

To determine the possibility of maintaining the maximum possible carbon content in TiC carbide, a powder additionally doped with chromium carbide, molybdenum, and carbon was produced by...

The structure, phase composition, and C, O, and N content in two cermet coatings sprayed from powders of the initial composition of 30SiC–NiCr and 30SiC–TiNi are studied. The change in the...