On the thermodynamics of the Ta-Rh system

Abstract

Thermodynamic measurements in the Ta-Rh system were made between 1140 and 1280 K by the e.m.f. method using solid galvanic cells with the arrangements Ta 0.083Rh 0.917, TaRh 3.3, Ta 2O 5¦ThO 2-Y 2O 3¦Fe 0.95O, Fe and Ta 0.083Rh 0.917, TaRh 3.3, Ta 2O 5¦ThO 2-Y 2O 3¦Ta 2O 5, Ta x Rh 1− x ( x ⩽ 0.083). For this purpose, the isothermal section of the Ta-Rh-O system was investigated at a temperature of 1273 K. TaRh 3 and Rh(Ta) are in equilibrium with Ta 2O 5− x . The relative partial molar Gibbs energy of tantalum was determined in the Rh(Ta) solid solution range. The relative partial molar excess Gibbs energy of tantalum in Rh(Ta) at infinite dilution is xsΔ G ̄ Ta ∞ = −250 kJ mol −1 at 1200 K. The Gibbs energies of formation of Ta 0.083Rh 0.917 and TaRh 3.3 are fΔG o = −22 kJ mol −1 and fΔG o = −273 + 0.020 T kJ mol −1 respectively, between 1140 and 1280 K.