Electrochemical Behaviour Of Tb(?)and The Preparation Of Ni-Tb Intermetallic Compounds And Mg-Li-Tb Alloys In Molten Salts

The electrochemical behaviour of Tb(?) ions was researched on inert W and reactive Ni electrodes in LiCl-KCl-TbCl3 molten salts. The electrochemical preparation of Ni-Tb intermetallic alloys and Mg-Li-Tb ternary alloys were obtained by cathodic alloying and co-reduction method, respectively. The microstructure and composition of alloys obtained by potentiostatic and constant current electrolysis were characterized by XRD, SEM-EDS and ICP-AES.The electrochemical behaviour of Tb(?) ions in LiCl-KCl-TbCl3 melt on an inert W electrode were investigated in the temperature range from 450 to 550 ? by electrochemical techniques, such as cyclic voltammetry, square wave voltammetry,chronopotentiometry and open ciruit chronoptentimetry. The results from cyclic voltammogram and square wave voltammogram show that the electrochemical reduction of Tb (?) ions process was determined to exchange three electrons reversible process and be controlled by mass transfer. And the diffusion coefficient of Tb (?) was calculated to be 0.49�10 5 cm-2�s-1.According to the equation of diffusion coefficient changing with temperature(450-525?) logDTb(?)=-1.1917-3184/T,the activation energy of Tb (?) ions ( EaTb(?))) was calculated to be 26.48 kJ�mol-1.The electrochemical behaviour of Tb(?) ions on a reactive Ni electrode in LiCl-KCl-TbCl3 melt were researched by cyclic voltammetry, square wave voltammetry and open ciruit chronoptentimetry at 500? . The under-potential deposition of Tb (?) occurs on the reactive Ni electrode. And square wave voltammogram and open circuit chronopotentiometry put into evidence the formation of Ni-Tb intermetallic compounds at around -1.27 V, -1.63 V and -1.88 V, respectively.Three alloy samples were obtained by potentiostatic electrolysis on a Ni electrode at various potentials and analyzed by XRD, SEM and EDS. The analysis results confirmed the formation of Ni17Tb2, Ni5Tb and Ni2Tb alloy compounds. By open circuit chronopotentiometry, the ?Gf of each Ni-Tb intermetallic compound was calculated: ?fGexp(Ni17Tb9) =-22.263 kJ mol-1,? fGexp(Ni5Tb) =-27.667 kJ mol-1,?fGexp(Ni,Tb)=-33.000kJ mol-1.The electrochemical behaviour of Tb(?) and Mg(?) ions on an inert W electrode in LiCl-KCl-TbCl3-MgCl2 melt were investigated by cyclic voltammetry,square wave voltammetry and chronopotentiometry at 500? . While the cathode potentials were more negative than -2.38 V (vs. Ag/AgCl) or cathode current densities were higher than -0.50 A�cm-2 in LiCl-KCl-MgCl2-TbCl3 molten salts, the codeposition of Mg (?), Tb (?) and Li(?) happend. Mg-Li-Tb alloys under different process conditions were prepared by co-reduction method. The structure and composition Mg-Li-Tb alloy were characterized by ICP, XRD, SEM and EDS. The current efficiency and content of Mg, Li and Tb in Mg-Li-Tb alloys obtained by constant current electrolysis could be controlled by temperature of the electrolysis,cathode current density and the concentration of MgCl2. The XRD results show that a-Mg, Mg2Tb and ?-Li phases coexist in Mg-Li-Tb alloys. The Tb elements presented reticular distribution in Mg-Li-Tb alloys by surface scanning and energy dispersive spectrometer.