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 electrore?ning 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-?uorides,all-chlorides and mixed chloride-?uoride 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 work concerned the electrochemical behaviors of Y(Ⅲ) on W and Ni electrodes in molten LiCl-KCl salts by a series of electrochemical techniques. The electrochemical reaction of Y(Ⅲ) to Y(0) proceeded in a one-step reduction process with the exchange of three electrons, Y(Ⅲ)+3e~–→Y(0). Compared with the cyclic voltammogram and square wave voltammogram obtained on W electrode, the reduction potential of Y(Ⅲ) on Ni electrode was observed at less negative potential than the one of Y(Ⅲ) to give pure Y metal on W electrode, which revealed the occurrence of underpotential deposition of Y(Ⅲ) on Ni electrode. Electromotive force(emf) measurements were performed to calculate the relative partial molar Gibbs energies and activities of Y in Y-Ni alloys. The standard Gibbs energies of formation for different Y-Ni intermetallic compounds were also estimated. The different Y-Ni alloys were formed by potentiostatic electrolysis at different potentials and characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), and energy dispersive spectrometry(EDS). It was found that four intermetallic compounds, YNi_5, Y_2Ni_7, YNi_3 and YNi_2, were selectively produced by controlling applied potential.
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.
This work presents an electrochemical extraction of cerium and synthesization of Al–Ce alloy in LiCl–KCl melts on Mo and Al electrodes by chlorination of CeO2 using AlCl3 at 873 K. The cyclic voltammogram on Mo electrodes in LiCl–KCl–CeO2 melt showed no obvious reduction wave other than the reduction of Li(I). After the addition of AlCl3, the signals of the reaction of Ce(ⅡI)/Ce(0) and the synthesization of Al–Ce and Al–Li alloys were investigated by cyclic voltammetry, square-wave voltammetry, open-circuit chronopotentiometry and chronopotentiometry. These results indicated that AlCl3 can chloridize CeO2 and that it is possible to extract cerium and form Al–Ce and Al–Li–Ce alloys in LiCl–KCl–CeO2–AlCl3 melts. According to potentiostatic electrolysis, only the Al4 Ce layer coated the Al electrodes. According to galvanostatic electrolysis, Al–Ce(Al4Ce, Al3 Ce, and Al92Ce8), Al2Li3, and Al phases were formed on Mo electrodes, and the content of cerium in the Al–Li–Ce alloys was more than 17 wt%.
This work presents a new method for preparation of samarium alloy. Using Al rod as anode, electrochemical formation of Sm-Al alloy on Mo electrode from Sm2O3 in LiCl-KCl-MgCl2-KF molten salts was investigated. Samarium mainly exists in the form of Al2 Sm in Li-Mg matrix, and the concentration of Sm in this alloy runs up to be as high as 34.7%. The reaction of samarium preparation appears like a replacement reaction. The new preparation method makes possible a high samarium content in electrochemical deposition of Sm-Al alloy. Using Al rod as anode consumedly decreased the electrolytic cell voltage, and facilitated Sm deposition from Sm2O3 . This preparation method uses Sm2O3 as raw materials to gain samarium alloy directly, which could revolutionize the industrial production of samarium alloys.
