Mixing enthalpy of Ag–Sn system at 1150 °C

Abstract

This paper presents thermodynamic results of Ag–Sn alloys mixing at 1150 °C. The need for binary data on mixing enthalpy ΔH mix appeared obvious in the process of calorimetric study of the ternary system Ag–Cu–Sn known as the promising lead-free solder. The mixing enthalpies of Ag–Sn system were measured by drop calorimetry method using SETARAM MHTC thermal analyzer. All the tests were conducted in the dynamic protective atmosphere of argon. The calorimeter’s sensitivity calibration was performed with the use of pure metals (Ag, Sn) and standard leucosapphire samples and consisted of two stages. The use of two-stage calibration procedure improves significantly the convergence of two branches of ΔH mix isotherm plotted from the pure component toward each other. The experimental results were approximated with analytical function using quasi-chemical modification of subregular solutions model (quasi-chemical model of Sharkey et al.) postulating the presence of both pair and triple interactions in solution. The resultant equation is ΔH mix = N Ag·N Sn·(− 27.7075·N Ag − 0.9977·N Sn + 27.7079·N Ag·N Sn), kJ mol−1, where N is the component mole fraction. The measured compositional dependence of ΔH mix is substantially asymmetric like the previous results of the other authors, but, in contrast to those results, it does not change the sign and is entirely negative in the whole range of concentrations.