Measurement of Mixing Enthalpies for Sn-Bi-Sb Lead-Free Solder System

Predictions of the thermodynamic behavior of higher-order multicomponent alloys from thermodynamic data of binary and ternary systems have been proven to be very crucial, as it is extremely challenging to investigate the thermodynamic properties of higher-order systems. Therefore, it is necessary to assess the thermodynamic data of various binary and ternary systems that are important to lead-free solder applications. The literature lacks thermodynamic information for some lead-free systems. Tin-bismuth-antimony (Sn-Bi-Sb) is a good option as a solder ternary system free of lead. The integral and partial mixing enthalpies of a Sn-Bi-Sb system were determined using a drop-solution calorimeter. At 923 K, 973 K, and 1023 K, calorimetric measurements of the Sn-Bi-Sb system were made along five of the cross-sections. Pieces of pure tin were dropped into molten Sb0.25Bi0.75, Sb0.50Bi0.50, Sb0.75Bi0.25 alloys, bismuth into Sb0.50Sn0.50 , and antimony into Bi0.50Sn0.50. Using the calorimetric data, partial and integral thermodynamic properties were determined. The integral mixing enthalpy was used to plot iso-enthalpy curves. It was found that the mixing enthalpies were temperature-independent. The substitutional solution Redlich-Kister-Muggianu model was used to derive the interaction parameter based on ternary enthalpy values and, to obtain these parameters, a least square fitting model was used. When the estimated and measured values were compared, it was found that there was a good agreement between them.

Automated summary

Predicting the thermodynamic behavior of higher-order multicomponent alloys is crucial but challenging. In this study, the thermodynamic data of the Sn-Bi-Sb system, which is a lead-free solder ternary system, was assessed. The integral and partial mixing enthalpies were determined using a drop-solution calorimeter. The mixing enthalpies were found to be temperature-independent, and the interaction parameter was derived based on the ternary enthalpy values using the Redlich-Kister-Muggianu model.