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%.
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 electrochemical behavior of Mg,Li,Al and Er were investigated by electrochemical techniques in LiClKCl-MgCl2-AlCl3-ErCl3 melts at 823 K.The cyclic voltammetry and chronopotentiometry indicated that the co-reduction of Mg,Li,Al and Er occurs at current densities more negative than-0.89 A.cm-2.Er(III) under-potential deposited on pre-reduced Al electrode formed Al-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-Al-Er alloys could be controlled by concentration of AlCl3 and cathodic current density.
Yi SUNMilin ZHANGWei HANMei LIYusheng YANGYongde YANMeng ZHANG
An electrochemical approach for the preparation of Mg-Li-Ce alloys by co-reduction of Mg,Li and Ce on a molybdenum electrode in KCl-LiCl-MgCl2-CeCl3 melts at 873 K was investigated.Cyclic voltammograms (CVs) and square wave voltammograms indicated that the underpotential deposition (UPD) of cerium on pre-deposited magnesium led to the formation of Mg-Ce alloys at electrode potentials around-1.87 V.The order of electrode reactions was as follows:discharge of Mg(Ⅱ) to Mg-metal,UPD of Ce on the surface of pre-deposited Mg with formation of Mg-Ce alloys,discharge of Ce(Ⅲ) to Ce-metal and after that the discharge of Li+ with the deposition of Mg-Li-Ce alloys,which was investigated by CVs,chronoamperometry,chronopotentiometry and open circuit chronopotentiometry.X-ray diffraction (XRD) illuminated that Mg-Li-Ce alloys with different phases were obtained via galvanostatic electrolysis by different current densities.The microstructures of Mg-Li-Ce alloys were characterized by optical microscopy (OM) and scanning electron microscopy (SEM),respectively.The analysis of energy dispersive spectrometry (EDS) showed that Ce existed at grain boundaries to restrain the grain growth.The compositions and the average grain sizes of Mg-Li-Ce alloys could be obtained controllably corresponding with the phase structures of the XRD patterns.
