The incongruent effusion of ZnGa 8S 13(s)

Abstract

The chemistry and thermodynamics of vaporization in a Knudsen effusion cell of the phase ZnGa 8S 13 was studied in the range 1115–1246 K where the vapor pressure ranged from 0.25 to 10.0 Pa. Samples prepared by sealed-tube methods and characterized by X-ray diffraction were studied by the simultaneous Knudsen and torsion (Volmer) effusion method. ZnGa 8S 13(s) effused incongruently in equilibrium with a saturated solid solution (sss) of ZnS in Ga 2S 3, Ga 2S(g), Zn(g), and S 2(g), always on the ZnSGa 2S 3 join. Ga 2S 3(sss) then effused with net loss of ZnS to the vapor until the composition of Ga 2S 3 was reached. Vapor analysis by combining measured rates of mass loss and momentum loss allowed analysis of the vapor and calculation of equilibrium constants of the effusion equations. Thermodynamic treatment by the third-law method yielded the ΔH° (298 K) of ZnGa 8S 13(s) with respect to those of ZnS(s) and 4Ga 2S 3(s), − 52 ± 22 kJ mol − 1.