Simple model for demixing binary liquid alloys

A simple model has been proposed for demixing liquid alloys, where the existence of polyatomic self associates (clusters of like atoms) has been considered to investigate the large positive deviations of the thermodynamic functions. The concentration fluctuations [S_cc (o)] in the long wavelength limit and the chemical diffusions (D) are found to be most sensitive, both as a function of concentration and temperature, above the miscibility gap. The role of the size of the self associates and its energetics with respect to large positive deviations in activity, excess free energy, entropy of mixing, heat of mixing, S_cc (o) and D have been critically examined. The critical concentration and temperature are provided for different hypothetical demixing liquid alloys; application is made to Bi - Zn liquid alloys. The results of the model correspond to an optimized set of thermodynamic functions obtained by a least-squares method.