Phase equilibria and thermodynamic modeling of the Sn–S, Ag–S, and Sb–S systems

Critical evaluations and thermodynamic optimizations of the tin-sulfur (Sn–S), silver-sulfur (Ag–S), and antimony-sulfur (Sb–S) binary systems were carried out over the whole composition range. The Modified Quasichemical Model (MQM) in the pair approximation was applied for the liquid phase to consider the short-range-ordering (SRO) in the phase. The binary compounds SnS, Sn2S3, SnS2, Ag2S, and Sb2S3 were treated as stoichiometric compounds. The allotropic transformations were taken into account in the formulation of the Gibbs energy equations. In the Ag–S system, the face-centered cubic (fcc) Ag solid solution was modeled by the Bragg-Williams (BW) model to improve the calculations for the solubility of S as a function of temperature. In the present study, particular focus was placed on the accurate prediction of the measured activities and enthalpies of the liquid phase. Using the MQM, these thermodynamic quantities could be calculated with high accuracy. Published measurements of the phase diagrams, invariant temperatures, and compounds could be reproduced within typical experimental errors.