Vaporization chemistry and thermodynamics of the lead–indium–sulfur system by computer-automated Knudsen and torsion effusion methods

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Abstract
Vaporization of PbIn2S4(s) was studied by computer‐automated simultaneous Knudsen and dynamic torsion effusion. Vapor pressures and the apparent molecular weight of the effusing vapor were displayed in real time. The vaporization reaction was PbIn2S4(s)=In2S3(s)+PbS(g). The vapor pressure was measured 108 times in the temperature range 948–1086 K. For the vaporization reaction, third‐law analyses gave ΔH°(298 K)=253.0±0.1 kJ/mol. The enthalpy of PbIn2S4(s) with respect to its constituents PbS(s) and In2S3(s) was −23±4 kJ/mol. The apparent molecular weight showed stoichiometry changes in indium sulfide during the experiment. Residual indium sulfide, remaining after loss of all PbS, vaporized with some nonstoichiometry by In2S3(s)= In2S(g)+S2(g). The vapor pressure of the residual indium sulfide was measured 57 times in the temperature range 1035–1121 K;third‐law analyses yielded ΔH°(298 K)=613.4±0.4 kJ/mol for the dissociative vaporization reaction. The compound Pb2In6S11(s), found at lower temperatures, had negligible stability at the temperatures of this investigation. The unit cell of PbIn2S4(s) was orthorhombic with a=2.275 nm, b=1.356 nm, and c=1.953 nm.

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