Thermodynamic Properties of Ni–Dy Intermetallic Compounds Measured Electrochemically in Molten CaCl₂–DyCl₃

Abstract

The temperature dependence of the coexisting phase potentials of various Nickel–Dysprosium (Ni–Dy) intermetallic compounds in a molten CaCl₂–DyCl₃ (1.0 mol% added) system was determined between 1073 K and 1173 K at 25 K intervals. The coexisting phase potentials of (NiDy + Ni₂Dy), (Ni₂Dy + Ni₃Dy), (Ni₃Dy + Ni₅Dy), and (Ni₅Dy + Ni) were measured via open-circuit potentiometry using a Ni flag electrode. The Dy activities and the Dy relative partial molar Gibbs energies in Ni–Dy intermetallic compounds were calculated from these potentials. Then, the Ni activities and the Ni relative partial molar Gibbs energies were calculated using the Gibbs-Duhem equation. Thereafter, the relative partial molar enthalpies and entropies of Dy and Ni were obtained by comparing the temperature dependence equations of the relative partial molar Gibbs energies. Finally, the relative partial molar Gibbs energies of Dy and Ni were used to calculate the standard Gibbs energies of formation for various Ni–Dy intermetallic compounds and compared with reported values.