Application of MIVM for Pb-Sn System in Vacuum Distillation

Abstract

The activity coefficients of components of the Pb-Sn binary alloy system were calculated based on the molecular interaction volume model (MIVM). A significant advantage of this model lies in its ability to predict the thermodynamic properties of liquid alloys using only two binary infinite activity coefficients. Based on the MIVM, the vapor-liquid phase equilibrium of the Pb-Sn alloy system in vacuum distillation has been predicted using the activity coefficients of Pb and Sn. The results showed that the content of tin in the vapor phase was 0.008 wt pct, while in the liquid phase, it was 83 wt pct at 1173 K (900 °C); it reached 0.022 wt pct in the vapor phase, while in the liquid phase, it was 92 wt pct at 1223 K (950 °C); and it was 0.052 wt pct in the vapor phase, while in the liquid phase, it was 97.88 wt pct at 1273 K (1000 °C). The content of tin in the vapor phase increased with the distillation temperature increasing. Experimental investigations into the separation of Pb and Sn from the Pb-Sn alloy by vacuum distillation were carried out for the proper interpretation of the results of the model. The influence of the distillation time (20 to 80 minutes) and the distillation temperatures of 1173 K, 1223 K, and 1273 K (900 °C, 950 °C, and 1000 °C) on the separating effect was also studied. The experimental results showed that the content of tin in the vapor phase was 0.085 wt pct, while in liquid phase, it was 83 wt pct under the operational conditions of distillation temperature of 1173 K (900 °C), evaporation time of 20 minutes, and chamber pressure of 20 Pa; it reached 0.18 wt pct in the vapor phase, while in the liquid phase, it was 92 wt pct at 1223 K (950 °C), 20 minutes, and 20 Pa; and it was 0.35 wt pct in the vapor phase, while in the liquid phase, it was 97.88 wt pct at 1273 K (1000 °C), 20 minutes, and 20 Pa. In all these experiments, it was observed that the content of tin in the vapor phase increased as the distillation time and temperatures were increased. The experimental results are in good agreement with the predicted values of the MIVM for the Pb-Sn binary system.