Underpotential Deposition And Chlorination Of Dy（Ⅲ）in Chloride Molten Salt System And Electrodeposition Of Mg-Al-Dy Alloy

The under-potential deposition of Dy（III）, the Dy₂O₃chloridized to the DyCl₃byMgCl₂and AlCl₃, and the mechanism of electrochamical co-deposition of ternaryMg-Al-Dy alloys were researched by Electrochemical techniques, such as cyclicvoltammetry, square wave voltammetry, chronopotentiometry and open-circuitchronopotentiometry in the molten salts, respectively.The under-potential deposition of Dy（III） in different concentrations was determinedby transient electrochemical techniques （such as cyclic voltammetry, square wavevoltammetry） and steady state electrochemical （open-circuit chronopotentiometry） on analumimum electrode in the temperature range of803K to903K in LiCl-KCl-DyCl₃moltensalt. The results show that the value of under-potential deposition increased with theincreasing of the Dy（III） content, but the value of under-potential deposition decreasedwith the increasing of the temperature.The chlorination of MgCl₂and AlCl₃were studied in LiCl-KCl melts. The solubility ofDy₂O₃in LiCl-KCl-MgCl₂and LiCl-KCl-AlCl₃melts were determined by isothermalsaturation method. The results indicate that the solubility of Dy₂O₃increased with theaddition of MgCl₂and AlCl₃. XRD showed that Dy₂O₃is chloridized by MgCl₂and AlCl₃tothe formation of DyCl₃in the molten salts. The mechanism of codeposition of Mg-Li-Dyand Al-Li-Dy alloys were investigated in LiCl-KCl-Dy₂O₃-MgCl₂andLiCl-KCl-Dy₂O₃-AlCl₃molten salt at803K, respectively. The electrochemical codepositionof Mg（II）, Li（I） and Dy（III） occurred at current densities higher than0.5A cm-2or at anapplied potential more negative than–2.30V; the codeposition of Al（III）, Li（I） and Dy（III）metal occurred at current densities higher than0.4A cm-2or at an applied potential morenegative than–2.30V. XRD showed that the phase of Mg2Dy was formed in Mg–Li–Dyalloys, and the phases of Al3Dy, Al2Dy3and AlDy in Al-Li-Dy alloys.The electrochemical behavior of Dy（III） ions was explored in LiCl-KCl-DyCl₃moltensalt on a molybdenum electrode by different electrochemical methods. The results showedthat the cathodic peak potential value of Dy（III） ions was–2.046V （vs. Ag/AgCl）, and thedeposition reaction is reversible when the sweep rates is lower than500mV/s.Electrochemical codeposition of Mg（II）, Al（III） and Dy（III） on a molybdenum electrode in LiCl-KCl-DyCl₃-MgCl₂-AlCl₃melts to form Mg-Al-Dy alloys was investigated by cyclicvoltammetry and chronopotentiometry. The codeposition of Mg, Al and Dy occurred whenapplied potentials were more negative than–2.05V （vs. Ag/AgCl） or cathodic currentdensities were higher than0.87A/cm2. XRD indicated that the Mg-Al-Dy alloys preparedvia galvanostatic electrolysis consist of Mg2Dy, Al3Dy and AlDy phases.