Surface tension and viscosity of Sn‐based binary liquid alloys

Abstract The concentration‐dependent variation of the surface tension and viscosity of Sn–X (X = Ag, Bi, In and Zn) liquid alloys has been theoretically investigated. The grand partition function for the surface has been solved in the framework of quasi‐lattice approximations to obtain analytical expressions for the surface tension and surface composition of the different types of binary liquid alloys. For the computation of viscosity, an expression has been used that involves not only thermodynamic properties but also hard sphere diameter, masses and some microscopic functions. The hard sphere diameter of the constituent atoms in the binary systems has been calculated by minimizing the pair potential obtained from pseudopotential formalism. The theoretical investigation not only reproduces the experimental results but also predicts similar variations in surface tension and viscosity of these alloys with the increase of the Sn component. The viscosities and surface tension of Ag–Sn and Sn–Zn systems decrease with the addition of Sn atoms, showing a negative deviation from the additive rule of mixing. The extent of the deviation is large in Ag‐rich and Zn‐rich alloys. The Sn–In system exhibits a decrease in viscosity up to 20% Sn followed by linear values, while no appreciable change is observed in surface tension values. The surfaces of Ag–Sn and Sn–Zn are quite enriched with Sn atoms whereas the Sn–In system exhibits much less of a segregation of Sn. In contrast, both surface tension and viscosity of the Sn–Bi system increase with the increase of the Sn component. The surface composition of Sn–Bi is quite different from that of the other systems because of the segregation of Bi atoms. The difference of hard sphere diameters affects viscosity considerably. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)