The Study On Preparation Of The Intermediate Alloys Of Aluminum Terbium And Aluminum Magnesium Terbium And Underpotential Deposition Of Terbium On Aluminum Electrode By Electrolysis In Molten Salts

The electrochemical mechanism and technological parameters of the Al-Tb andAl-Mg-Tb alloys and depolarization of Tb（Ⅲ） on aluminum electrode were investigated.Formation mechanism and codeposition conditions of Al-Tb alloys were studied on amolybdenum electrode in NaCl-KCl-AlF₃-Tb₄O₇melt at800℃by electrochemical methods,such as cyclic voltammetry, open ciruit chronoptentimetry, chronoamperometry andchronopotentiometry. The cyclic voltammetry curves indicated that as the potential negativescanning, Al （Ⅲ） ions deposited on the electrode at the potential of-0.6V. However, thesample obtained at more cathodic potential,–1.24V, is found to be the Al-Tb alloy. Theresults are consistent with the results obtained from the open ciruit chronoptentimetry,chronoamperometry and chronopotentiometry curves. The Al-Tb alloys were obtained byconstant current electrolysis in different electrolytic conditions. The current efficiency wascalculated by results of ICP. The effect of the content of MgCl₂, electrolyte temperature,current density and electrolysis time on current efficiency and alloys composition were alsostudied. The Al-Tb alloys obtained were analyzed by XRD, SEM with EDS.The formation mechanism and codeposition conditions of Al-Mg-Tb alloys wereinvestigated by cyclic voltammetry, chronoamperometry and chronopotentiometry in theNaCl-KCl-AlF₃-MgCl₂-Tb₄O₇melts at800℃. The redox signal of metal Al, Al_xMg, Al_xTband metal Mg were observed on cycle volt-ampere curve. When the cathode current is higherthan-29mA, the Al-Mg-Tb alloys can be prepared by co-electrodeposition process. Indifferent electrolytic conditions, the Al-Mg-Tb alloys were prepared and analyzed by ICP,and then the current efficiency were calculated. The effect of electrolytic temperature, currentdensity and electrolytic time on the composition of the alloys and current efficiency were alsoexplored. The results analyzed by XRD confirms there are four phase: Al, Mg, Al₃Mg₂andAl₃Tb in the sample. The microstructure and the distribution of Mg and Tb in the Al-Mg-Tballoys were analyzed by SEM with EDS.The electrochemical behavior of Tb（Ⅲ） ion on molybdenum and aluminum electrodeswere investigated by using cyclic voltammetry, square wave voltammetry and open circuitchronopotentiometry on techniques in LiCl-KCl-TbCl₃molten salts （TbCl₃=3wt%）,respectively. The resuts on molybdenum electrode show that the Tb（Ⅲ） ion is reduced in a one-step process exchanging three electrons, i.e.（Tb（Ⅲ）+3e-→Tb）. And the depositionpotential value of Tb（Ⅲ） shift to more positive with temperature increasing. The results onaluminum electrode indicate that the deposition potential value of Tb（Ⅲ） on aluminumelectrode is more positive than the one on inter electrode, which is underpotentialdeposition（UDP）. The underpotential values of Tb（Ⅲ） onto Al descend with temperatureincreasing at different temperature of500℃,550℃and600℃by analysis of cyclicvoltammetry and chronoptentimetry.