Correlation between bulk and surface properties of ternary Ag–Sn–Zn liquid alloys and concerned binaries

Abstract

A correlative study of the bulk and surface properties of the ternary Ag–Sn–Zn liquid alloys has been undertaken by extending the descriptions of concerned binaries (Ag–Sn, Sn–Zn, and Ag–Zn), obtained from statistical mechanical theory in the frame-work of quassi-lattice approximations. An improved model, in which the selection of binary compositions involves the correlation of one particular component with other components of the ternary system, has been used to compute the free energy of mixing of Ag–Sn–Zn system. The concentration dependence of the surface tension and surface composition has been explained by obtaining expression for the activity coefficients and extending the surface description of binary systems. It is worth mentioning that same set of interaction energies as those used for the bulk and surface calculations of the concerned binaries has been used to investigate the concentration dependence of free energy of mixing, surface tension (σ) and surface composition of the ternary system. The theoretical investigation of binary systems suggest the presence of short range order in Ag–Sn and Ag–Zn systems leading to the formation of intermetallic compounds (Ag3Sn in Ag–Sn and AgZn in Ag–Zn) in the melt. Sn–Zn system is characterized by the existence of diatomic tin in the melt. The concentration dependence of the free energy of mixing of Ag–Sn–Zn system for three cross section (Ag : Sn = 1 : 1, 1 : 3 and 3 : 1) has been clearly explained by our theoretical model. There is slight decrease in σ for Ag : Sn = 1 : 1 up to x Zn ≈ 0.4 whereas sharp decrease up to 50% Zn is observed in case of Ag : Sn = 3 : 1. The σ for Ag : Sn = 1 : 3 remains almost constant up to x Zn ≈ 0.25. The surfaces of Ag–Sn–Zn system for all three cross section (Ag : Sn = 1 : 1, 1 : 3 and 3 : 1) are quite enriched with Sn-atoms. The degree of segregation is lowest in Ag : Sn = 3 : 1.