Rare earth（RE） metals and their alloys have attracted considerable practical interests due to their functional properties. Because of their negative deposition potentials, RE metals cannot be electrochemically deposited from aqueous media. Using molten salt as medium provides a unique opportunity for the electrowinning and electrorefining of high-purity RE metals, as well as for the electrochemical formation of their alloys and intermetallic compounds. Certainly, the electrochemical behaviors of RE metals and their alloys have been investigated in a number of different molten salts comprising all-fiuorides,all-chlorides and mixed chloride-fiuoride media. Based on the results, RE and their alloys were produced by molten salt electrolysis. In this paper, the developments of preparation of RE metals and their alloys by electrolysis in molten salts in recent years were systematically summarized on both the local and international levels. Attention was paid mainly to the electrodeposition of RE metals and their alloys, including RE-Mg, RE-Al, RE-Ni, RE-Co,RE-Cu, RE-Fe and RE-Zn alloys.
The electrochemical behavior of Mg, Li, AI and Er were investigated by electrochemical techniques in LiCI- KCI-MgCI2-AICI3-ErCI3 melts at 823 K. The cyclic voltammetry and chronopotentiometry indicated that the co-reduction of Mg, Li, AI and Er occurs at current densities more negative than -0.89 A.cm-2. Er（lll） under-potential deposited on pre-reduced AI electrode formed AI-RE alloys. X-ray diffraction （XRD） results indicated that Mg17Al12, Al2Er, Al2Er3 and Al4Li9 phases were prepared by galvanostatic electrolysis. ICP analyses of samples showed that lithium and aluminum contents of Mg-Li-AI-Er alloys could be controlled by concentration of AICI3 and cathodic current density.
Yi SUNMilin ZHANGWei HANMei LIYusheng YANGYongde YANMeng ZHANG
The reduction of Tm(Ⅲ) on a liquid Zn electrode was investigated in a Li Cl-KCl melt via cyclic voltammetry,square wave voltammetry, and open circuit chronopotentiometry. On a liquid Zn electrode, the reduction mechanism of Tm(Ⅲ) ions is through one step with the exchange of three electrons via the formation of a Zn-Tm alloy. This differs from that on an inert electrode, as the reduction is Tm(Ⅲ) ions were though two consecutive steps. Galvanostatic electrolysis was carried out at a liquid Zn electrode at different current densities in a LiClKCl-TmCl3 melt. The Tm2Zn17 intermetallic compound was identified in the deposit, except in the Zn phase,by X-ray Diffraction(XRD).
The chlorination of rare earth oxides by MgCl2 was investigated in the molten chlorides. To reduce the solvent salt volatility, the LiCl-NaCl mixture was selected as a solvent by comparing the mass loss of the Li ClNaCl with LiCl-KCl melts after the addition of MgCl2 in the temperature range of 873 K to 1073 K. The dissolution behavior of La2O3 was investigated in the LiCl-NaCl-MgCl2 melts by XRD measurements and ICP-AES analysis of the melts, which indicated that La2O3 was chlorinated by Mg Cl2 to produce La Cl3. The reduction peak of La(Ⅲ) in the LiCl-Na Cl-MgCl2-La2O3 melts was observed from cyclic voltammogram and square wave voltammogram. The Mg-La alloy obtained by galvanostatic electrolysis in the LiCl-NaCl-MgCl2-La2O3 melts was characterized by XRD and SEM-EDS, indicating that the Mg-La alloy consisted of Mg and La2Mg17 phases.
Direct electrodeposition of quarternary Mg-Zn-Li-Ca alloys on a molybdenum electrode from LiCl-KCl-MgCl2-ZnCl2-CaCl2 melts at 943 K was investigated.Cyclic voltammograms（CVs） show that the deposition potential of Li shifts in a positive direction after adding MgCl2,ZnCl2 and CaCl2.Chronopotentiometric measurements indicate that the codepositon of Mg,Li,Zn,and Ca occurs at current densities lower than-1.55 A/cm2.X-ray diffraction（XRD） indicates that Mg-Zn-Li-Ca alloys with different phases were prepared via galvanostatic electrolysis.The microstructures of typical phase of Mg-Zn-Li-Ca alloys were characterized by optical microscopy（OM） and scanning electron microscopy（SEM）.The analysis of energy dispersive spectrometry（EDS） shows that elements of Mg and Ca distribute homogeneously in the Mg-Zn-Li-Ca alloy.However,element Zn mainly locates at the edges of the domain.
