Clean and efficient recovery of Ag–Bi and Sn–Ag–Bi lead-free brazing materials by vacuum volatilization and thermodynamic modeling

This study proposes a novel method for the clean and efficient recovery of high-value-added Ag-Bi and Sn-Ag-Bi alloys. Vacuum volatilization experiments were conducted on Ag-Bi binary alloys in the temperature range of 1150-1400 K and a system pressure of 5 Pa., the Ag content in the residue was 93.84 % and Bi content in the volatile was 99.15 %, Ag can be effectively separated. Vacuum volatilization of Sn-Ag-Bi ternary alloys with different compositions was conducted in the temperature range of 1100-1180 K and a system pressure of 5 Pa. The Bi content in the residue exhibited a notable reduction, decreasing from 30.19% to 3.90% while Bi content in the volatile reached 99.92%. The results demonstrated that Bi could be effectively separated from Ag and Sn by vacuum volatilization. The activities and activity coefficients of components of Ag-Bi, Sn-Ag, Sn-Bi, and Sn-Bi-Ag alloys were calculated using MIVM, M-MIVM, Wilson equation, and NRTL, respectively. The results demonstrated that M-MIVM yielded the highest prediction accuracy. The vapor liquid equilibrium (VLE) data of the Ag-Bi, Sn-Ag, Sn-Bi, and Sn-Bi-Ag alloys were predicted based on the M-MIVM and VLE theory, and the corresponding VLE phase diagrams were plotted. The predicted VLE values are in good agreement with the corresponding experimental data determined in this study, indicating that the M-MIVM is a reliable model for studying the VLE of tin-based alloys. Based on the calculated values from the M-MIVM model, a vacuum volatilization experiment was conducted on a Sn–Ag–Bi alloy with a composition of x Sn : x Bi : x Ag = 0.6:0.2:0.2 at 1100–1180 K and a pressure of 5 Pa. The experimental results demonstrate that the bismuth content in the gas phase consistently remained above 99.9%. The findings of this research offer lays the foundation for the development of a new vacuum technology for the clean and efficient recovery of binary and multicomponent tin-based alloys.