Satbayev University

Deep reduction of copper smelting slags is a promising route to recover entrained non-ferrous metals and to generate slags suitable for further processing. This work investigates the depletion of fayalite-magnetite slags formed during autogenous smelting of copper concentrates in conditions simulating the oxidation and reduction zones of a two-zone Vanyukov furnace. Laboratory charges of 100 g, containing 14.63-16.82 wt.% Cu, 25.6-27.6 wt.% Fe, 30 wt.% S and 15 wt.%SiO2, were smelted at 1350 degrees C with controlled oxygen injection to produce slags containing 0.93-1.54 wt.% Cu, 30.05-32.30 wt.% SiO2 and 7.8-9.8 wt.% Fe3O4. Subsequent reduction at 1300 degrees C was carried out with activated carbon in a fivefold stoichiometric excess relative to magnetite, at an oxygen-containing blast flow rate of 5 L/h and a 1 h holding time. Chemical analysis shows that Fe3O4 in slag decreases from 7.8-7.95 wt.%to 2.5-2.6 wt.%, while copper content drops from 0.93-1.033 wt.% to 0.43-0.50 wt.% under oxygen partial pressures of 10-12-10-11 atm. X-ray diffraction and electron microscopic studies reveal a transition from fayalite-magnetite slags with dispersed metallic copper and sulfides to fayalite-dominated matrices containing ferruginous sphalerite, copper minerals of the bornite-chalcopyrite type, iron oxides and glassy phases. Simultaneous thermal analysis demonstrates that all major endothermic and exothermic events are completed by 1300 degrees C, supporting this as an optimal temperature for deep slag depletion. The results define an operating window-slag composition, temperature, reductant dosage and pO(2)- under which copper losses to slag can be reduced to about 0.5 wt.% in industrially relevant fayalite slags.

This paper presents the results of experimental and numerical studies of the casting process of 99.85% pure aluminum using investment-casting technologies with patterns produced by additive manufacturing. The influence of pouring temperature, mold-filling time, and gating-system design on porosity formation and casting quality was analyzed. It was established that increasing the pouring temperature within the range of 700-800 degrees C leads to increased porosity due to higher gas solubility and intensified turbulence of the melt flow. It was shown that the separating gating system ensures a minimum number of defects compared to top and bottom metal-feeding systems. In addition, thermal analysis of PLA and a glass-fiber-reinforced PLA composite was carried out. Pure PLA was found to burn out almost completely (residue about 2.4%), whereas the composite was characterized by a high residual content (similar to 43.6%), which may negatively affect mold quality. The simulation results obtained using the AutoCAST software package showed good agreement with the experimental data and confirmed the effectiveness of numerical modeling for optimization of casting processes. It was established that the optimal pouring-temperature range for aluminum is 720-760 degrees C. The obtained results confirm the potential of using PLA in investment casting technology and make it possible to improve the quality of aluminum castings under industrial production conditions.

The article is devoted to the development of a methodology for microstructural and thermal verification of the quality of an industrial Ti-10V-2Fe-3Al triple vacuum arc remelted ingot produced by UK TMP JSC. It was established that all zones of the ingot demonstrate a two-stage thermal evolution characteristic of the beta-metastable Ti-10V-2Fe-3Al alloy: decomposition of the metastable beta phase (approximate to 520-570 degrees C) and an endothermic alpha ->beta phase transformation (approximate to 950-1120 degrees C). It was found that the enthalpy of the exothermic decomposition of the beta matrix increases by approximately 60-80% in the lower zone of the ingot. The width of the phase transition (Delta T) correlates with an increase in microsegregation. It was also determined that the enthalpy of the endothermic alpha ->beta transformation decreases from the bottom part of the ingot toward the steady-state crystallization zone (Middle-1), which correlates with a reduction in the microsegregation parameters obtained from SEM-EDS profiles (Delta C_max, sigma C, L-corr). Thus, thermal analysis confirms the absence of a pronounced vertical gradient of structural stability and can be used as a validating criterion for the integral electrode quality index. For the first time, a quantitative correlation between SEM-EDS profiles and DSC-DTG characteristics has been proposed. Thermal analysis is suggested as an independent validator of microsegregation. An approach to the quantitative evaluation of microsegregation based on SEM-EDS profiles using the parameters Delta C_max, sigma C, L-corr,L- and Delta CO(local) has been developed. Additionally, the use of an integral chemical index I(che)m, and a critical threshold I-chem(crit) is proposed for electrode quality control using thermal analysis results.

The article presents the results of a qualitative analysis of circuits of autonomous current and voltage inverters with cut-off valves. The influence of the charge on the switching capacitor in parallel and series equivalent circuits on the restoration of the switching properties of the thyristors in the inverter power circuit is studied. It is shown that, due to the energy periodically accumulated in the inductive elements of the load, the voltage across the switching capacitor in the cut-off state is higher than in a conventional parallel autonomous current inverter. This ensures increased switching stability of the inverter. Consequently, the circuit of an autonomous current inverter with cut-off valves remains operational in valve converters for variable-frequency electric drives and maintains performance during sudden load surges and short circuits, since the voltage on the switching capacitor does not depend on the load voltage. Thus, the charge on the switching capacitor is preserved even when the load voltage drops sharply between thyristor commutations.

Addressing corrosion and wear in assemblies, components, machine parts, and equipment operating in aggressive environments under severe wear conditions remains a pressing challenge and continues to draw focused scientific attention. This work aimed to investigate how the key magnetron sputtering parameters (working pressure, plasma current, and process-gas flow rates) affect the surface morphology, microstructure, and composition of TiN and CrN films deposited under different conditions. Microstructural analysis revealed that, across the investigated parameter window, the films exhibit a columnar cross-sectional architecture and a smooth surface morphology with no visible defects, showing no pronounced differences between the deposition regimes. After 30 min of deposition, the film thickness ranged from 0.17 to 0.46 mu m for TiN and from 0.59 to 3.46 mu m for CrN, depending on the sputtering conditions. The results demonstrate that plasma current and working pressure have a strong effect on film thickness and chemical composition, whereas variations in the working-gas flow rate exert a coupled influence on thickness, microstructure, and the stoichiometry of TiN and CrN layers. Elemental analysis further indicates that increasing the pressure to 0.65 Pa increases oxygen incorporation in the films. During chromium sputtering, raising the plasma current to 1.5 A leads to film delamination. For TiN, a balanced regime with a moderate N2 flow is preferable, providing a reasonable growth rate and a composition close to stoichiometric. For CrN, the range of stable operating conditions is substantially broader, and the process parameters have a more pronounced impact on its structure and composition. These findings can support the design of TiN/CrN wear-resistant multilayer coatings produced by magnetron sputtering for protecting machine parts and equipment against wear and corrosion.