On the constitution and thermodynamics of Ni–Tb alloys

Abstract

The thermodynamic properties of the Ni–Tb system were determined between 873 and 1073 K from electromotive force measurements using CaF 2 single crystals as solid electrolytes. The results yield a complete set of thermodynamic functions for the intermetallic phases (Ni), Ni 17Tb 2, Ni 5Tb, Ni 7Tb 2, Ni 3Tb, Ni 2Tb, NiTb, Ni 2Tb 3, and NiTb 3 as well as information on the phase relations. The system is characterized by pronounced negative deviations from ideality. The relative partial excess Gibbs energy of Tb at infinite dilution was determined to be −(99±2) kJ/mol. This value is interpreted by taking electronic and elastic effects into account. The liquidus line was fixed over the entire range of composition by differential thermal analysis. The present results were used as basis for a thermodynamic optimization of the Ni–Tb system using a computer program based on the least squares method. The optimized thermodynamic functions which turned out to be in excellent accordance with the experimental results were subsequently used to calculate the phase diagram.