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

Author: ZhaoCanFeng
Tutor: HanWei
School: Harbin Engineering University
Course: Applied Chemistry
Keywords: molten salts electrolysis under-potential deposition chlorination solubility Mg-Al-Dy alloys
CLC: O646
Type: Master's thesis
Year: 2013
Downloads: 19
Quote: 0
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Abstract


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.

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