Phase equilibria and vapor pressures in the Ga + P system

Abstract

Compositions and vapor pressures have been redetermined along the Ga-rich liquidus of the system Ga + P. A third-law treatment of the pressures gives a standard enthalpy ΔH o(298.15 K) = −(45.3 ± 0.2) kcal th mol −1 and a standard entropy ΔS o(298.15 K) = −(23.7 ± 0.15) cal thK −1mol −1 for the reaction Ga(s) + 1 2 P 2(g) = GaP(s) . The standard enthalpy of formation and entropy of GaP are ΔH f o (GaP,s,298.15 K) = −(24.0 ± 0.5) kcal thmol −1 and S o(GaP,s,298.15 K) = (12.10 ± 0.25) cal thK −1mol −1. The activities of phosphorus are evaluated along the liquidus and indicate that the deviations from ideality in the Ga-rich solutions results primarily from a small positive excess entropy of mixing. A self-consistent analysis of the liquid- and vapor-phase equilibria based on a simple solution treatment of the Ga + P liquid is presented.