Demixing tendencies in some Sn-based liquid alloys

We study the demixing tendencies observed in some Sn-based liquid alloys, specifically, Ga-Sn, AI-Sn and Fe-Sn liquid alloys using a phenomenological model. With the aid of the model, we investigate the concentration dependence of thermodynamic properties viz: activity, free energy of mixing, enthalpy of mixing, entropy of mixing and the chemical diffusion. The parameters that characterize the model, enable us to describe the energetics of the system in terms of the concentration-concentration fluctuations in the long wavelength Limit. We deduce from our study that of the three liquid alloys, the thermodynamic properties of Fe-Sn are most asymmetric as a function of concentration, the observed asymmetry is explained on the basis of the size effect. From the results for Ga-Sn and Al-Sn, we infer that with increase in the atomic number of the element in group III that is added to liquid Sn, there is a reduced tendency for segregation. We deduce within the present framework that In-Sn would be a hetero-coordinated system. This deduction is in agreement with available experimental data. (C) 1999 Elsevier Science S.A. All rights reserved.