Thermochemical properties and phase transitions of Ba–Sn alloys from thermal characterization and emf measurements

Abstract

Thermodynamic properties of Ba–Sn alloys were determined for Ba mole fractions (xBa = 0.03–0.69) by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and electromotive force (emf) measurements. Six intermetallic compounds (BaSn5, BaSn3, Ba3Sn5, BaSn, Ba5Sn3, and Ba2Sn) were identified by XRD and the phase transition temperatures were determined by DSC up to xBa = 0.50, which were used to delineate phase boundaries for constructing an experimentally-determined phase diagram. In addition, thermochemical solution properties were calculated by measuring emf values of Ba–Sn alloys using the following electrochemical cell: Ba(s) | CaF2–BaF2 | Ba(in Sn) over 713–1063 K, including activity and partial molar quantities of Gibbs energy, entropy, and enthalpy. The activity of Ba in Sn was as low as 1.5 × 10−11 at xBa = 0.03 and 923 K, indicating highly non-ideal solution behavior with a large excess partial molar Gibbs energy (−164 kJ mol−1). By integrating solution properties from emf measurements with the phase behavior by DSC and XRD, a reliable description of the Ba–Sn system was established.