Electrochemical reduction of Tm on Mg electrodes and co-reduction of Mg, Li and Tm on W electrodes

Abstract

The reduction process of Tm(III) ions was investigated in LiCl–KCl–MgCl2 melt on a W electrode and in LiCl–KCl melt on a Mg electrode at 753K, respectively. On the W electrode, in LiCl–KCl–MgCl2 melt the reduction of Tm(III) ions was a two-step process: Tm(III)+e−1 → Tm(II) and yTm(II)+2ye−1+xMg → MgxTmy. The reduction process of Tm(III)/Tm(II) was not observed on the Mg electrode, and only two signals, related to Mg–Tm intermetallic compounds were observed, in the cyclic voltammogram and chronopotentiogram. Galvanostatic electrolysis was employed to prepare Mg–Li–Tm alloys on both W and Mg electrodes. The deposits were characterized by X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM). Mg24Tm5 and Mg2Tm phases were detected in the deposits. The effect of Tm addition on Mg–Li alloy was investigated via potentiodynamic polarization and OM at room temperature. The grain size of Mg–Li alloy becomes much smaller after addition of Tm element. The corrosion potentials of Mg–Li–Tm alloys shift toward a more positive direction than that of Mg–Li alloy.