Preparation of Mg-Zr alloys through direct electro-deoxidation of MgO-ZrO2 in CaCl2-NaCl molten salt

Abstract

The electro-deoxidation of MgO does not proceed efficiently due to the electrical insulation properties of MgO and large molar volume of metallic magnesium. In this experiment, an attempt was done to prepare Mg-Zr alloy from their oxides using the method of electro-deoxidation. The electrochemical mechanism of the deoxidation process of MgO, ZrO2 and MgO-ZrO2 composite was studied through cyclic voltammetry using metallic cavity electrode (MCE). There was an intermediate phase (Zr3O) in the reduction process of ZrO2. The electro-deoxidation of MgO occurred for MgO-ZrO2 composite in CaCl2-NaCl molten salt. Moreover, the electro-deoxidation of MgO was promoted by the addition of polyvinyl butyral (PVB). The formation of metal phase Mg was confirmed by XRD, EDS, Raman spectroscopy, and inductively-coupled plasma spectroscopy. The electro-deoxidation products showed significant differences with the concentration of PVB and the ratio between MgO and ZrO2. The electro-deoxidation of MgO and ZrO2 was favorable when the PVB concentration was 5.0% (wt.%). Pure metal phase of Mg-Zr alloys was formed when the molar ratio of MgO and ZrO2 was 1:2. The atomic fraction of Mg in the electrolytic product was ca. 28.0 mol.%. This work shows that MgO could be directly electro-deoxidized to Mg without the formation of intermediate phase oxide.