Thermodynamic properties of the Au-Zn system

Abstract

A series of alloys from the α, β′ and γ-phase fields were used in an investigation of the thermodynamic properties of the Au-Zn system. Enthalpy of mixing values at 717°K were obtained using liquid-tin solution calorimetry and partial free energies of mixing at 850°K from vapour pressures determined by the dew-point method. Assessment of these and other available enthalpy and free energy data led to a selection of values which were combined to obtain excess entropies of mixing for α- and β′-phase alloys. The values obtained suggest the α-alloys to be substantially disordered above 717°K but with minimum entropy around 18 a/o zinc, which suggests that the Au 4Zn-phase may have a more exothermic enthalpy of formation than the A 3Zn-phase, which forms at a higher temperature. The β′-phase alloys, on the other hand, are substantially ordered with minimum entropy at the stoichiometric composition of AuZn.