Electrochemical formation of Mg–Li–Ca alloys by codeposition of Mg, Li and Ca from LiCl–KCl–MgCl2–CaCl2 melts

Abstract

This work presents electrochemical formation of Mg–Li–Ca alloys via codeposition of Mg, Li and Ca on a molybdenum electrode in KCl–LiCl–MgCl₂–CaCl₂ melts at 943 K. Cyclic voltammograms (CVs) showed that the underpotential deposition (UPD) of calcium on pre-deposited magnesium leads to the formation of a liquid Mg–Ca alloy, and the succeeding underpotential deposition of lithium on pre-deposited Mg–Ca alloy leads to the formation of a liquid Mg–Li–Ca solution. Chronopotentiometric measurements indicated that the codepositon of Mg, Li and Ca occurs at current densities more negative than −0.31 A cm⁻² in LiCl–KCl–MgCl₂ (5 wt%) melts containing 1 wt% CaCl₂. Chronoamperograms demonstrated that the onset potential for the codeposition of Mg, Li and Ca is −2.200 V, and the codeposition of Mg, Li and Ca is formed when the applied potentials are more negative than −2.200 V. X-Ray diffraction (XRD) indicated that Mg–Li–Ca alloys with different phases were formed via galvanostatic electrolysis. The microstructures of typical α and β phases of Mg–Li–Ca alloys were characterized by optical microscope (OM) and scanning electron microscopy (SEM). The analysis of energy dispersive spectrometry (EDS) showed that the element Ca mainly distributes along grain boundary in Mg–Li–Ca alloys. The results of inductively coupled plasma analysis determined that the chemical compositions of Mg–Li–Ca alloys correspond with the phase structures of XRD patterns, and the lithium and calcium contents of Mg–Li–Ca alloys depend on the concentrations of MgCl₂ and CaCl₂.