High-temperature reaction calorimetry of solid and liquid phases in part of the quasi-binary system Cu2 S-Sb2 S3

High-temperature reaction calorimetry has been applied in a thermochemical study of solid and liquid phases in part of the quasi-binary system Cu₂S-Sb₂S₃. The enthalpies of formation at 298 K of the sulfosalts chalcostibite (CuSbS₂) and monoclinic skinnerite (Cu₃SbS₃) from their end-member component sulfides (Cu₂S and Sb₂S₃) were determined to be −20.2 ± 2.1 kJ·mol⁻¹ and −24.8 ± 2.7 kJ·mol⁻¹, respectively.

Mixtures of solid Cu₂S and liquid Sb₂S₃ at 895 K were studied by solid-liquid reaction calorimetry, and by dilution calorimetry, with pure liquid Sb₂S₃. Measurements of the solid-liquid enthalpies of mixing (in kJ·mol⁻¹) yielded the linear expression

based on experiments with values of X_Cu2S ranging from 0.1 to 0.4. This equation is consistent with a symmetrical, regular-solution model and implies that the heat of fusion of Cu₂S at 895 K (for X_Cu2S = 1.00) is 9.5 kJ·mol⁻¹. Our data yield an average value for ΔC_P,S-L,Cu2S of 6.6 J·K⁻¹ · mol⁻¹.