Thermodynamic Properties of Ni–Nd Intermetallic Compounds Measured Electrochemically in Molten CaCl2–NdCl3

Abstract

The electrochemical formation of Ni–Nd intermetallic compounds has been investigated in a molten CaCl2–NdCl3 system. For further understanding the thermodynamic properties of different Ni–Nd intermetallic compounds, an electrochemical investigating method was used. The temperature dependences of the Nd3+/Nd potential and two-phase coexisting potentials of the Ni–Nd intermetallic compounds were determined via open-circuit potentiometry using Mo and Ni flag electrodes, respectively. Expressing the two-phase coexisting potentials with respect to the Nd3+/Nd potential, the relative partial molar Gibbs energies of Nd were calculated. The Nernst and Gibbs-Duhem equations were used to determine the activities of Ni and Nd, respectively. The relative partial molar Gibbs energies of Ni were calculated using its activities. Thereafter, the relative partial molar enthalpies and entropies of Ni and Nd were obtained using the temperature dependences of the relative partial molar Gibbs energies. Finally, the standard Gibbs energies, enthalpies, and entropies of formation of the various Ni–Nd intermetallic compounds were calculated using the relative partial molar Gibbs energies of Nd and Ni. The obtained thermodynamic parameters were compared with previously reported values obtained by the CALPHAD method and modeling calculations.