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.
Purification of lanthanum chloride from high-load zinc contaminants remains a major challenge in producing grade 5N lanthanum oxides. This study investigates the process of matrix-driven solvent extraction using tertiary amine N235 to treat a 1.41 M rare earth oxides (REO) industrial lanthanum chloride feed containing 3000 mg/L zinc. Thermodynamic modelling with Medusa Hydra and Langmuir isotherms revealed that the high chloride activity (> 4 M) of the matrix induced significant changes in coordination towards the extractable [ZnCl4](2-)complex. This transition has a spontaneous Gibbs free energy of-14.68 kJ/mol. While the two-stage countercurrent flow sheet meets the industry target of less than 50 mg/L zinc, the five-stage configuration achieves a four-log reduction to 0.23 mg/L, effectively achieving 99.999% purity. This reagent's lean approach, using water-induced stripping, offers a sustainable and mathematically validated framework for ultra rare earth finishes.
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.
This study focuses on the solid phase extraction of biogenic amines (BAs) using a sol-gel adsorbent immobilized with a hydrazone ligand, named 2-hydroxy-5-nitrobenzaldehyde-2,4-dinitrophenylhydrazone. The hydrazone compound was synthesized and characterized through Fourier Transform Infrared Spectroscopy (FT-IR) and Nuclear Magnetic Resonance (NMR) spectroscopy. The efficiency of the sorbent material for extracting BAs was evaluated using the solid phase extraction (SPE) method. Key experimental parameters affecting BA extraction, including pH, equilibrium time, ligand concentration, and biogenic amine (BA) concentration, were systematically investigated. The results indicated a strong recovery of BAs from aqueous samples, demonstrating a significant affinity between the sol-gel matrix containing the hydrazone ligand and the target analytes. The findings demonstrate that incorporating the hydrazone ligand resulted in a marked enhancement of extraction efficiency at a concentation of 17 & times; 10(-3) M. Notably, the method exhibited high selectivity for aliphatic biogenic amines such as putrescine (PUT), cadaverine (CAD), and spermidine (SPD). This extraction method was successfully applied to food samples, yielding good recovery rates.
