DSC TOPEM® study of high-energy mechanical milling-driven amorphization in β-As4S4-based arsenicals

Abstract

Temperature-modulated DSC TOPEM® method was applied to study amorphization in directly synthesized high-temperature polymorph of tetra-arsenic tetra-sulfide β-As4S4 affected to high-energy mechanical milling in a dry mode with 100–600 min−1 rotational speeds. The appeared amorphous phase is shown to possess dual nature, being related to As-rich glassy-like substances with low- and high-temperature glass transition midpoints. In respect of DSC TOPEM® studies, the crystalline–amorphous heterogeneity of chemical environment around β-As4S4 crystallites results in incongruent double-peak melting revealed through two endothermic effects at~ 305 °C and ~ 315 °C. Amorphous phase continuously generated under ball milling with increased rotational speed is identified as compositionally authentic to arsenic monosulfide, but different in medium-range order from stoichiometric As2S3. The overall amorphization in commercial arsenic sulfide prepared by direct synthesis from elemental constituents under high-energy ball milling occurs from two sources, these being high-to-low-Tg amorphous phase transformation and direct vitrification of β-As4S4 phase. These data testifies in favor of “shell” model treated solid-state amorphization in terms of defect generation in parent β-As4S4 phase, the amorphous substance being nucleated heterogeneously from grain boundaries followed by stretching into crystalline grain interior.