In Situ X-ray Diffraction and Crystal Orientation Analysis for Dy–Ni Electrochemical Alloying and De-alloying in Molten LiCl–KCl–DyCl3

Abstract

In situ white X-ray diffraction was used to investigate the electrochemical alloying and de-alloying processes of Dy–Ni alloys in molten LiCl–KCl–DyCl3 at 723 K. X-ray diffraction peaks of Ni and DyNi2 and fluorescence peaks of Dy were obtained. DyNi2 was the only identified Dy–Ni alloy, although previous ex situ studies have reported the formation of several Dy–Ni alloys. During the de-alloying process, the apparent lattice constant of DyNi2 decreased to a small value. Also, the area of Dy fluorescence peaks increased, which can be attributed to the formation of a Dy compound layer on the electrode surface. Electron backscatter diffraction was performed to clarify the relationship between the crystal orientations of Ni and DyNi2 after electrochemical alloying or sequential alloying and de-alloying. The results confirmed that Dy–Ni alloying was faster at the Ni grain boundaries. In addition, DyNi2 or porous Ni grains in reacted regions had similar crystal orientations as adjacent Ni grains in unreacted regions. These results help clarify the rapid electrochemical formation mechanism of Dy–Ni alloys in molten LiCl–KCl, which can help facilitate the separation and recovery of rare-earth elements, such as Dy, from spent magnets.

Keywords

• molten salt electrolysis
• rare-earth
• in situ x-ray diffraction
• crystal orientation