Study On The Electrochemical Behaviors And Preparation Of Rare Earth Cobalt Alloy By Molten Salt Electrolysis

Cobalt alloys are widely used in many fields due to their excellent performance such as national defense industry,aerospace,automobile industry,watchmaking industry,etc.In this paper,rare earth cobalt alloys were prepared by molten salt electrolysis,and the electrochemical behaviors of the co-deposition of cobalt ion and rare earth ions were studied,providing theoretical basis for industrial electrolysis production.The electrochemical behaviors of in rare earth ions(RE,including Ce,Pr,Sm,Gd,Dy,Er,Yb)and cobalt ion(Co(Ⅱ))were investigated at 923K on Mo electrode in KCl-LiCl system.The diffusion coefficient of Co(Ⅱ)and RE in molten salt system were discussed.The redox mechanism of cobalt and RE were studied by cyclic voltammetry,square wave voltammetry and open circuit chronopotentiometry in LiCl-KCl-CoCl2-RECl3(RE=Ce,Pr,Sm,Gd,Dy,Er,Yb)molten salt system.As the results shown that Co-RE intermetallic compounds were obtained by co-deposition of Co(Ⅱ)and RE(Ⅲ)in KCl-LiCl system.The reduction of Co(Ⅱ),Ce(Ⅲ),Pr(Ⅲ),Gd(Ⅲ),Dy(Ⅲ),Er(Ⅲ)on Mo electrode is one-step electron transfer reduction to metal at 923K in KCl-LiCl system,and the results confirm that the reduction reaction of these rare earth ions(except Gd)are diffusion-controlled quasi-reversible reaction by different scan rate measurements.The reduction of Gd(Ⅲ)is a reversible reaction controlled by diffusion.The diffusion coefficients of Co(II),Ce(Ⅲ),Pr(Ⅲ),Gd(Ⅲ),Dy(Ⅲ),Er(Ⅲ)are 1.7×10-5 Cm2 s-1、3.15×10-5 cm2 s-1,3.26×10-5 cm2 S-1,1.27×10-5cm2 s-1,4.88×10-4 cm2 s-1,7.37×10-5 cm2 s-1,respectively.In addition,the deposition potentials of different Co-RE(including Ce,Pr,Sm,Gd,Dy,Er,Yb)intermetallic compounds were obtained.Since Sm(Ⅲ)and Yb(Ⅲ)are valence elements,they cannot be reduced to metal samarium and ytterbium on an inert electrode.The corresponding rare earth cobalt alloys were prepared by potentiostatic electrolysis for 3 h.XRD qualitative analysis showed that the phase composition of the alloy were CesCo19(obtained at-1.9 V);Co2Pr(obtained at-1.91 V);Co2Sm(obtained at-2.20 V);Co2Gd(obtained at-2.11 V);Co5Dy,Co2Dy(obtained at-1.82V);Co17Er2(obtained at-1.88 V);Co2Yb(obtained at-1.88 V);SEM observation of Co-Pr,Co-Gd alloy microscopically under lamellar,while other alloys are blocky;EDS further confirms the type and content of elements in the alloys.It was found that the equilibrium potential is more positive with ttie increasing of the atomic radius.According to this rule,the mathematical relationship between the equilibrium potential of the cobalt-rich phase alloy and the atomic radius is established:1/E×r23=8.781(x1lnx1+x2lnx2)+5.629...