Electrochemical Behavior of Dy(III) and Formation of Dy-Zn Alloy by Co-Reduction with Zn(II) in Eutectic NaCl-KCl Melts

The electrochemical behavior of Dy(III) and its co-reduction process with Zn(II) on a tungsten electrode were studied in eutectic NaCl-KCl melts at 700 °C by using a series of electrochemical techniques. The results indicate that the reduction of Dy(III) to Dy(0) is a diffusion controlled quasi-reversible process through a one-step reaction of exchanging three electrons. The diffusion coefficient of Dy(III) was calculated to be 1.7 × 10-5 cm2 s-1. Furthermore, the co-reduction of Dy(III) and Zn(II) on the tungsten electrode makes Dy(III) be reduced at more positive potentials due to the formation of various Dy-Zn intermetallic compounds. The electromotive force measurements were performed to determine the thermodynamic properties of the Dy-Zn intermetallic compounds, including the activities and relative partial molar Gibbs free energies of dysprosium in the two-phase coexisting state, as well as the standard formation Gibbs energies of Dy-Zn intermetallic compounds. Finally, potentiostatic electrolysis at -2.0 V was carried out in molten NaCl-KCl-DyCl3(1.0 mol%)-ZnCl2(1.0 mol%) at 700 °C for 11 h to prepare Dy-Zn alloy. X-ray diffraction and scan electron micrograph - energy dispersive spectrometry analyses showed that the obtained Dy-Zn alloy mainly comprised of DyZn2, as well as the minor phases of Dy2Zn17, DyZn3 and DyZn.