Multicriteria optimization of mechanical processing for Pb–C composite charge material

Abstract

This study investigates a two-stage processing approach for a charge of Pb–C composite powder material composed of lead (PS1) and graphite (GISM) powders in a high-energy mill under ambient air conditions. The study aims to determine the influence of graphite content (Cg ) and mechanical activation time (τ) on the particle size distribution of the charge. The results indicate that the particle size distribution can be effectively described using the Rosin–Rammler equation. Furthermore, a correlation between the equation's parameters and the quality of the resulting hot compacted materials, as well as an index derived from the generalized desirability function, has been identified. The study delves into the mechanism behind the formation of the Pb–C powder charge during mechanical activation, which involves the creation of loosely bound agglomerates of composite particles. These agglomerates can be easily disrupted during manual processing of the charge in a mortar. Notably, the research reveals that the extremum of the particle size distribution shifts towards smaller average sizes of the Pb–C composite particles that constitute the agglomerates. The size of these formed agglomerates is shown to depend on both the graphite content in the charge and the duration of mechanical processing. Using multicriteria optimization, the study identifies the optimal values for technological factors (τ = 1.8 ks, Cg = 0.15 wt. %) for charge preparation in the two-stage mechanical processing mode. These optimal values result in an enhanced set of physical and mechanical properties for the Pb–C hot-compacted composite material, including shear strength (σshear = 6.3 MPa), hardness (HRR = 109), and electrical conductivity (L = 1.812 Ω–1) of Pb–C. X-ray diffraction analysis conducted during the study reveals the formation of lead oxides during the mechanical activation of the Pb–C charge. Additionally, it indicates an increase in the half-width of the diffraction profile of lines (111) and (222), which subsequently decreases after the hot-compaction process. Comparative data involving the use of lead-based chip waste and lead powder-based composites are also presented in the study. These data suggest that a lower optimum graphite content is required for lead powder PS1 (Cg = 0.15 wt. %) compared to chip waste (Cg = 0.5 wt. %).