Electrochemical Formation of Dy–Ni Alloys in Molten CaCl2–DyCl3

Abstract

The electrochemical formation of Dy–Ni alloys was investigated in molten CaCl2–DyCl3 (1.0 mol%) at 1123 K. Cyclic voltammetry indicated the formation of Dy–Ni alloys at more negative than 1.0 V vs. Ca2+/Ca. Higher cathodic currents were observed from approximately 0.6 V, which indicated the formation of Dy–Ni alloys having higher Dy concentration. An open-circuit potentiometry was carried out with Mo and Ni electrodes before and after the addition of DyCl3. After the potentiostatic electrolysis of Mo electrode at −0.50 V for 30 s in molten CaCl2–DyCl3, only one potential plateau appeared at 0.33 V, which was interpreted as the equilibrium potential of Dy3+/Dy. In contrast, four potential plateaus were observed at 0.49, 0.62, 0.87, and 1.04 V for Ni electrode after the potentiostatic electrolysis at 0.25 V for 15 min. According to energy-dispersive X-ray spectroscopy and X-ray diffraction of the electrolyzed samples, the four potential plateaus correspond to the two-phase coexisting states of (DyNi + DyNi2), (DyNi2 + DyNi3), (DyNi3 + DyNi5), and (DyNi5 + Ni). Standard Gibbs energies of formation were calculated for Dy–Ni alloys.