Detailed assessment of partial thermodynamic quantities of tin in molten Bi-Sn alloys from electromotive force measurements

Abstract

All the partial thermodynamic quantities, including the activity and activity coefficient of tin,a Sn and γSn, in the liquid Bi-Sn alloys between 300 °C and 500 °C are assessed in detail from electromotive force (emf) data. The emf values were obtained from a modified molten salt electrolyte concentration cell that had extraordinary stability within +0.005 mV. The composition dependence of γSn did not follow Darken’s quadratic formalism, nor did the alloy behave as a regular solution. The excess partial quantities, Δ¯H Sn ,Δ¯S Sn xs , and Δ¯G Sn xs , are oscillating across the composition, and the activity curve exhibits double, positive and negative, deviations from Raoult’s law. The aSn, γSn, and Δ¯G Sn xs change from positive to negative departure from ideality in the tin-rich region beyond about xSn = 0.82. All those partial quantities and γ Sn o , including the β° (the α function of tin) at infinite dilution, are determined accurately by means of Chiotti’s method.