Limitations of a regular associated solution approximation in describing the thermodynamic behaviour of complex liquid alloys

The validity of the regular associated solution (RAS) model for describing the thermodynamic properties of complex liquid alloys has been analysed by applying it to the Cu-In system. The presence of Cu,In as the associated sp ecies in equilibrium with the free atoms in the liquid state was assumed. L iquid copper-indium alloys exhibit a very complex thermodynamic behaviour w here the deviations from ideality of activities and integral enthalpy of mi xing vary from positive to strongly negative and the properties are strongl y temperature dependent. It is seen that a regular solution type interactio n among species is insufficient to model the thermodynamic properties of li quid Cu-In alloys and the temperature dependence of interaction energies am ong the species has to be taken into account. A modified associated solutio n model incorporating volume effects and temperature dependence of interact ion energies could successfully describe the thermodynamic properties of li quid Cu-ln alloys.