Electrochemical formation process and phase control of Mg-Li-Ce alloys in molten chlorides

Abstract

An electrochemical approach for the preparation of Mg-Li-Ce alloys by co-reduction of Mg, Li and Ce on a molybdenum electrode in KCl-LiCl-MgCl2-CeCl3 melts at 873 K was investigated. Cyclic voltammograms (CVs) and square wave voltammograms indicated that the underpotential deposition (UPD) of cerium on pre-deposited magnesium led to the formation of Mg-Ce alloys at electrode potentials around −1.87 V. The order of electrode reactions was as follows: discharge of Mg(II) to Mg-metal, UPD of Ce on the surface of pre-deposited Mg with formation of Mg-Ce alloys, discharge of Ce(III) to Ce-metal and after that the discharge of Li+ with the deposition of Mg-Li-Ce alloys, which was investigated by CVs, chronoamperometry, chronopotentiometry and open circuit chronopotentiometry. X-ray diffraction (XRD) illuminated that Mg-Li-Ce alloys with different phases were obtained via galvanostatic electrolysis by different current densities. The microstructures of Mg-Li-Ce alloys were characterized by optical microscopy (OM) and scanning electron microscopy (SEM), respectively. The analysis of energy dispersive spectrometry (EDS) showed that Ce existed at grain boundaries to restrain the grain growth. The compositions and the average grain sizes of Mg-Li-Ce alloys could be obtained controllably corresponding with the phase structures of the XRD patterns.