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.
Highlights
Generation a large variety of structural defects under highenergy ball mechanical milling (MM) [1,2,3,4,5] is known as an alternative technological resolution allowing approaching high-entropy amorphous state of parent crystalline substances, even those possessing extremely low glass-forming ability [6]
In the first heating run, two endothermic thermally induced melting effects are revealed in both samples, near * 305 °C and * 315 °C, testifying in a favor of incongruent melting. The first of these effects is well detectable in Cp0 due to strong peak Tm1 at 304.1 °C observed in reference REHE-0, and more reduced peak at 303.2 °C detected in MM REHE-500 sample, i.e., at the liquidus of this alloy near arsenic monosulfide line [23]
Continuous generation of amorphous phase in addition to parent crystalline b-As4S4 one was probed in directly synthesized high-temperature polymorph of tetra-arsenic tetra-sulfide under high-energy mechanical milling with 100–600 min-1 rotational speeds
Summary
Generation a large variety of structural defects under highenergy ball mechanical milling (MM) [1,2,3,4,5] is known as an alternative technological resolution allowing approaching high-entropy amorphous state of parent crystalline substances, even those possessing extremely low glass-forming ability [6]. We shall parameterize the amorphization effect in b-As4S4 arsenical, driven by high-energy MM under different rotational speeds, exploring heat capacity measurements with temperature-modulated DSC TOPEMÒ. Commercial arsenic sulfide b-As4S4 prepared by direct synthesis from elemental constituents (98% in purity, purchased in Sigma-Aldrich, USA) was used as a precursor for high-energy MM Small pieces of this arsenical were coarse-grained powdered and sieved under 200 lm. The calorimetric heat capacity measurements were taken with multifrequency DSC TOPEMÒ using DSC-1 calorimeter (Mettler-Toledo, Switzerland) In this method, the stochastic temperature modulations are superimposed on underlying rate of conventional DSC scans, resulting in distinguished frequency-dependent and frequency-independent phenomena [20, 21]. It worth mentioning that evident growing tendency was observed with rotational speed n in amorphous halos in the experimental XRPD profiles of milled arsenicals starting from REHE-200 sample
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