Electrochemical Behavior Of Y(?) On Cu And Liquid Bi Electrodes And Preparation Of Y-M(M=Cu,Bi)Alloys

With the rapid development of global science and technology,rare earth metals and their alloys have been a major breakthrough in permanent magnetic and hydrogen storage materials.In addition,rare earth metal materials play an important role in the field of aerospace,navigation,weapons and equipment,etc.Molten salt electrolysis is an important method for the preparation of rare earth alloys.Thus,in this paper,the electrochemical behavior of rare earth Y(?)ions was studied on W,Cu,liquid Bi and Bi film electrodes in LiCl-KCl molten salts.Meanwhile,Cu-Y and Bi-Y alloys were prepared by electrolysis under different conditions.The details were as follows:(1)The square wave voltammetry was performed on W electrode at different frequencies in LiCl-KCl-YCl3 molten salt.The average electron transfer value of Y(?)ions was found to be 3.191.The result indicated that the reduction of Y(?)ions on W electrode is one step with three electrons exchanged process.The diffusion coefficients of Y(?)ions were calculated at different temperatures by cyclic voltammetry and chronopotentiometry.According to the Arrhenius formula,the activation energy for diffusion was 34.01 kJ mol-1 and 24.54 kJ mol-1 respectively.(2)At 773 K,the electrochemical behavior of Cu(?)ion on Mo electrode was studied in LiCl-KCl molten salts.The reduction of Cu(?)ion on Mo electrode was found to be two step electron transfer process:Cu(?)+e-?Cu(?);Cu(?)+e'?Cu(0).The electrochemical behavior of Y(?)was investigated on Cu electrode by different electrochemical techniques.The value of underpotential deposition of Y(?)ions was obtained on Cu electrode.Meanwhile,the Gibbs free energy of five Cu-Y intermetallic compounds at 773 K was estimated by open circuit chronopotentiometry.Moreover,the samples of Cu-Y alloys were prepared by potentiostatic and galvanostatic electrolysis,respectively.According to the results of XRD and SEM-EDS,Cu4Y and Cu2Y were obtained by potentiostatic electrolysis at-1.80 V and-1.90 V for 5 h,respectively.(3)Cyclic voltammetry was performed on liquid Bi electrode in LiCl-KCl-YC3 molten salts at 773 K.The result exhibited that the deposition potential of Y(?)ions on liquid Bi electrode is about 0.93 V more positive than the inert electrode,which indicated the under potential deposition of Y(?)occur on liquid Bi electrode.Then,the electrochemical behavior of Bi(?)ions on W electrode was studied in LiCl-KCl-BiCl3 molten salts.The diffusion coefficient of Bi(?)ions in molten salts was calculated to be 5.68 ×10-6 cm2 s-1 at 773 K by cyclic voltammetry.Meanwhile,the electrochemical behavior of Y(?)ions on Bi film electrode was explored in LiCl-KCl-YCl3 molten salts.Compared with the cyclic voltammogram and square wave voltammogram,two new reduction peaks were observed due to the formation of two Bi-Y intermetallic compounds.The formation Gibbs free energies of BiY and Bi3Y5 was calculated by open circuit chronopotentiometry and found to be-208.99 kJ mol-1 and-929.15 kJ mol-1,respectively.What's more,Bi-Y alloy was formed on liquid Bi electrode by galvanostatic electrolysis at-500 mA and-100mA,respectively.The alloy samples were characterized by the SEM-EDS and XRD.The results showed that the alloys were composed of Bi and BiY phases.