Phase relations and equilibrium copolymerization in the SeS system

The phase relations in the SeS system were investigated by the appearance of phase method, differential thermal analysis, and differential scanning calorimetry. High purity selenium melts at 216 ± 2°C. A peritectic exists at 85 at. % Se and 168 ± 2°C; the peritectic isotherm extends from 92 to 73.5 at. % Se. A temperature minimum of 102 ± 1°C exists at a composition of 35 ± 1 at. % Se. High purity sulfur melts at 114 ± 1°C and polymerizes at 160 ± 2°C. Addition of 10 at. % Se lowers the polymerization temperature to 118 ± 3°C. The SeS system shows complete liquid miscibility and in this respect it differs from the majority of selenide type systems that generally show one or more fields of liquid immiscibility. The complete liquid miscibility in the SeS system can best be explained by the equilibrium copolymerization theory. Investigation of the subsolidus relations in the SeS system shows a miscibility gap in the Se-rich part of the system. The eutectoid proposed by W. E. Ringer (Z. Anorg. Chem. 32, 183 (1902)) in the S-rich part of the system was not detected.