Research On Electrochemical Reduction Of Ce(Ⅲ) In Chloride Molten Salt And Alloy Preparation Mechanism

Tin alloy and magnesium alloy are widely used in aviation,electronic communication and electroplating.Rare earth added to metal alloy can improve its overall properties,such as enhancing hardness,high temperature resistance and corrosion resistance.If rare earth metal alloys are prepared by blending method,metal thermal reduction method and mechanical alloying method,it has the disadvantages of high purity of raw materials,uneven alloy composition and high energy consumption.However,the molten salt electrolysis method has the characteristics of large scale,good continuity,low cost and uniform alloy composition.In this paper,the electrochemical behavior of Ce（Ⅲ）on tungsten electrode in CaCl₂-NaCl molten salt was studied by using transient electrochemical measurement techniques,such as CV,SWV,CP and CA at 903 K,and the electron transfer number and diffusion coefficient of Ce（Ⅲ）were calculated.At the same time,the co-deposition behavior of Ce（Ⅲ）and Mg（II）in CaCl₂-NaCl molten salt tungsten electrode,the co-deposition behavior of Ce（Ⅲ）and Sn（II）in CaCl₂-NaCl molten salt tungsten electrode,and the electrochemical mechanism of preparing Ce-Mg alloy and Ce-Sn alloy were studied,it can provide theoretical reference data for the preparation of rare earth and alloys by molten salt electrolysis.First,the electrochemical behavior of 2%CeCl₃in CaCl₂-NaCl molten salt on tungsten electrode was studied by cyclic voltammetry,square wave voltammetry,chronoamperometry and chronopotentiometry.The results showed that the reduction potential of Ce（Ⅲ）in CaCl₂-NaCl molten salt on tungsten electrode was-2.06 V,a one-step quasi reversible reduction process occurs,and the reduction reaction was controlled by diffusion.The diffusion coefficient of cerium ion was 8.1956×10^-6cm²/s。According to the SWV test results and the calculation of the number of transferred electrons,three electrons were transferred in the one-step reduction reaction of Ce（Ⅲ）,Ce（Ⅲ）→Ce（0）.According to the test results of chronoamperometry,it was concluded that the nucleation mode of cerium was instantaneous nucleation.Then,several electrochemical methods,such as CV,SWV and CP,were used to study the co-deposition behavior of Ce（Ⅲ）and Mg（II）,Ce（Ⅲ）and Sn（II）on tungsten electrode in CeCl₃-MgCl₂-CaCl₂-NaCl and CeCl₃-SnCl₂-CaCl₂-NaCl molten salt,respectively.The results showed that the reduction potentials of Mg（II）and Sn（II）on the melt tungsten electrode were-1.58 V and-0.05 V respectively,and the potentials of Ce-Mg intermetallic compound and Ce-Sn intermetallic compound on the melt tungsten electrode were-1.90 V and-1.08 V respectively.Finally,CeO₂（2wt%）was added to MgCl₂（2wt%）-CaCl₂-NaCl and SnCl₂（2wt%）-CaCl₂-NaCl molten salt,respectively.The electrochemical mechanism of preparing Ce-Mg alloy and Ce-Sn alloy was study.According to the electrochemical reduction process of cerium and magnesium ion on tungsten electrode,the co-deposition potential of cerium ion and magnesium ion on tungsten electrode was-1.91 V.Therefore,the Ce-Mg alloy was prepared as Mg₄₁Ce₅by electrolysis with a constant voltage of-1.95 V for 3h.At the same time,according to the electrochemical behavior of cerium ion and stannous ion on tungsten electrode,the deposition potential of cerium ion and stannous ion on tungsten electrode was-1.02 V.Therefore,the existing form of Ce-Sn alloy in the product was Ce₅Sn₃by electrolysis with a constant voltage of-1.10 V for 3h.