Calculation of evaporation rates of all components in Ag-Pb-Sn ternary alloy in vacuum distillation using modified molecular interaction volume model

Abstract

In this study, the activities of each component in Ag-Pb, Ag-Sn, Pb-Sn binary and Ag-Pb-Sn ternary alloy systems were predicted using molecular interaction volume model (MIVM), modified molecular interaction volume model (M-MIVM), Wilson equation and nonrandom two-liquid (NRTL) model, respectively. The average standard deviation and average relative deviation of these four models are also calculated. The results show that the prediction deviations of M-MIVM are smallest among four models, which indicates that M-MIVM is reliable for prediction of activity of these alloy systems. The volatilization coefficients ( α ) of Ag-Pb, Ag-Sn and Pb-Sn binary alloy systems were calculated based on M-MIVM. The results show that α _Ag-Pb ≫ 1 and α _Pb-Sn ≪ 1, which indicates that Pb will be enriched in the vapor phase while Ag (or Sn) in the liquid phase in vacuum distillation of Ag-Pb alloy (or Pb-Sn alloy). The values of α _Ag-Sn were in the range from 0.1 to 10 which indicates that Ag-Sn alloy is difficult to be separated by vacuum distillation. The evaporation rates of each component in Ag-Pb, Ag-Sn, Pb-Sn and Ag-Pb-Sn alloy systems at 1173 K, 1273 K and 1373 K were calculated based on M-MIVM. The results indicate that the evaporation rate of Pb is in the order of magnitude 10 ^−1 ∼ 10 ^1 in Ag-Pb, Pb-Sn and Ag-Pb-Sn alloy systems and it is 10 ^4 ∼ 10 ^6 times larger than that of Sn (or Ag). The evaporation rate of Pb in Pb-Sn alloy decreases with the addition of the third component Ag. This work provides a new method for the development of kinetics research and a theoretical guidance for industrial production in vacuum distillation.

Keywords

• alloys
• volatilization coefficient
• evaporation rate
• M-MIVM
• vacuum distillation