Calorimetric and phase equilibria studies of the Ni-Sn-Bi system

The phase equilibria at 1273 K were investigated and an isothermal section of the Ni-Sn-Bi phase diagram was constructed. The phase boundaries are inclined to the Bi-rich region that is agreement with phase equilibria at lower temperatures. The molar enthalpies of formation of liquid ternary Ni-Sn-Bi alloys have been determined at 833, 873 and 933 K by direct reaction calorimetry using pellets of 325 mesh powders of pure Ni, Sn and Bi. Measurements were performed with alloys containing from 0.05 to 0.10 mole fractions of nickel, and at ratios of tin and bismuth mole fractions X_Sn,/X_Bi = 2.8, 1.2 and 0.43. The experimental calorimetric data were used to calculate a regular solutions parameter of the ternary liquid phase by means of two different thermodynamic data files. It was found that the Ni-Sn-Bi ternary liquid phase could be described as temperature independent ternary regular solution. The assessed values of the ternary interaction parameter are -280 J·mol^-1 and 56 000 J·mol^-1, depending on the binary parameters used. Enthalpies of formation of solid binary phases were measured, too.