Thermodynamics of Formation and Vaporization of Tin-Zinc Solutions

The tin vapor pressure, partial and integral thermodynamic functions of mixing and vaporization of Sn-Zn melts are calculated based on the zinc vapor pressure values determined by the boiling point method. The formation of alloys proceeds with heat absorption and an attendant increase in disorder relative to an ideal solution. The peak integral entropy of mixing corresponds to similar to 60 at % Zn and is 3.25 +/- 0.15 kJ/mol. The extreme integral excess entropy of mixing relates to the equimolar composition and is 2.22 +/- 0.38 J/(mol K). The tin-zinc phase diagram is supplemented with liquid-vapor coexistence fields at the atmospheric pressure (101.3 kPa) and at 100 and 1 Pa, which fields imply that, regardless of pressure, the vapor phase is represented virtually by elemental zinc solely. The positions of boundaries of equilibrium vapor-liquid fields indicate the absence of technological difficulties and the possibility of complete distillation separation of the Sn-Zn system into constituent metals. The process limitation consists in the lowest pressure of 30 Pa that prevents the crystallization of the solid zinc solution from the liquid phase. The reason behind the increased tin content in the condensate at the final stage of zinc evaporation is the high intensity of its transfer to the vapor phase and the entrainment of melt microdroplets by the vapor flow.