Crystals

The high-value recovery of valuable components from spent LiFePO₄ (LFP) batteries is of considerable significance for both resource recycling and environmental conservation. This study systematically investigates the simultaneous sulfuric acid leaching of Li, Fe, and P from spent LFP cathode materials, integrating process optimization with kinetic analysis. The effects of acid concentration, temperature, and stirring speed on the leaching behavior of Li, Fe, and P were evaluated to elucidate the underlying kinetic mechanisms. The results demonstrated that under optimal conditions—namely, a sulfuric acid concentration of 2.0 mol/L, a leaching temperature of 60 °C, and a stirring speed of 300 r/min—the leaching rates of Li, Fe, and P all exceeded 99.5%. Kinetic analysis revealed a diffusion-controlled leaching mechanism well described by the Avrami model, with a selective dissolution sequence of Li > Fe > P. The leaching of Li, Fe, and P exhibited apparent activation energies of 9.56 kJ/mol, 14.83 kJ/mol, and 12.82 kJ/mol, respectively. These findings provide theoretical support for the leaching and resource recovery of Li, Fe, and P from spent LFP cathode materials.

HVOF coatings based on tungsten and chromium carbides are widely used in aerospace, energy, and oil and gas industries. However, the selection between the wear resistance of WC–Co and the corrosion resistance of Cr₃C₂–NiCr is often hindered by a lack of systematic data on the effect of powder particle size. In this study, WC–12Co and Cr₃C₂–NiCr coatings were deposited onto 12Kh18N10T stainless steel substrates by HVOF spraying using three particle size fractions: <20, 20–32, and 32–40 μm. Individual spray parameters were selected for each material to ensure high-quality deposition (standoff distance 350 mm, one pass for WC–12Co; 250 mm, two passes for Cr₃C₂–NiCr). The influence of powder particle size distribution on coating properties was investigated using a comprehensive set of methods, including scanning electron microscopy, X-ray diffraction with Rietveld quantitative phase analysis, microhardness testing, tribological testing, electrochemical measurements, and numerical modeling of particle in-flight motion. It was found that the 20–32 μm fraction is optimal for both materials. Different degradation mechanisms were identified: for WC–Co, decarburization of WC with the formation of W₂C and η-phases dominates (maximum for the <20 μm fraction); for Cr₃C₂–NiCr, oxidation and carbide dissociation prevail (in the <20 μm fraction—13.7% Cr₂O₃ and 38.6% Cr₇C₃), leading to low coating thickness (~16 μm) due to loss of ductility and wettability. Numerical modeling confirmed that the high velocity of fine Cr₃C₂–NiCr particles (~680–720 m/s) does not compensate for their overheating, whereas for WC–12Co all fractions have velocities above the critical threshold, but coarse particles (32–40 μm) give porosity up to 3.15% due to insufficient deformation. Corrosion tests showed that under spraying conditions optimized for each material, the Cr₃C₂–NiCr coatings (corrosion rate 0.066–0.102 mm/year) are an order of magnitude superior in corrosion resistance to WC–12Co coatings (corrosion rate 0.353–0.651 mm/year), owing to the passivation of the γ-Ni(Cr) matrix; for WC–Co, the main protective barrier is provided by the structural density.

Improving the energetic performance of established explosives through rational structural modification provides an alternative strategy for the development of entirely new energetic molecules. In this work, bromine substitution was employed to regulate the solid-state properties of TNT derivatives, and two compounds, 3-bromo-2,4,6-trinitrotoluene (3-BrTNT) and 3,5-dibromo-2,4,6-trinitrotoluene (3,5-BrTNT), were synthesized and characterized. Single-crystal X-ray diffraction revealed that different bromination patterns lead to distinct crystal structures and packing characteristics. Electrostatic potential analysis and Hirshfeld surface analysis further revealed that bromine substitution modifies molecular surface characteristics and intermolecular contact distributions within the crystals. Compared with 3-BrTNT, 3,5-BrTNT exhibits a higher crystal density of 2.312 g cm⁻³ and improved calculated detonation performance, with a detonation velocity of 7915 m s⁻¹ and a detonation pressure of 31.86 GPa. Meanwhile, both brominated derivatives exhibit reduced impact sensitivity compared with TNT. These results demonstrate that the bromination pattern, rather than bromine incorporation alone, plays an important role in regulating crystal structures and energetic properties. This study provides insight into substitution-pattern-controlled crystal engineering as a strategy for optimizing TNT-based energetic materials.