Electrochemical Behavior Of Heavy Rare Earth(Yb、Ho) And The Preparation Of Associative Alloys

The electrochemical behaviour of Yb （Ⅲ）、Ho（Ⅲ） ions was investigated by transientelectrochemical techniques such as cyclic voltammetry, square wave voltammetry,chronoamperometry， chronopotentiometry and open-circuit chronopotentiometry in theLiCl–KCl molten salt in the temperature range833–893K. A novel preparation method ofAl–Li–Yb alloys by electrochemical codeposition from Yb₂O₃in LiCl–KCl–AlCl₃moltensalts was studied. X–ray diffraction （XRD）, scan electron micrograph （SEM）, energydispersive spectrometry （EDS）, optical microscope （OM） and inductively coupled plasmaatomic emission spectrometer （ICP-AES） were employed to characterize the alloys.1, The electrochemical behaviour of Yb （Ⅲ） was studied in LiCl–KCl molten salts at893K. And the condition of co–electrodeposition of Al、Li、Yb was further investigated inLiCl–KCl–AlCl₃–Yb₂O₃molten salt. CV indicates the potential of ytterbium metal depositionis different, the deposition potential value on Al was more positive than the potential on Mo.The reduction of Yb （Ⅲ） into Yb （0） proceeded according to a two-step mechanism. Only thefirst step, which was diffusion controlled and reversible, could be observed in molten chlorideon the molybdenum electrode. The diffusion coefficient of ytterbium ions in the melts wasalso determined, D=6.15×10^–5cm²·s^–1.2, In this paper, the Al–Li–Yb alloys were directly obtained by electrochemicalcodeposition method from Yb₂O₃in LiCl–KCl–AlCl₃molten salts at Mo at893K. In thismolten system, solid Yb₂O₃was chlorinated by AlCl₃, and formed YbCl3which was thesource of Yb ions in the melts. The mechanism of electrochamical co-deposition of Al、Li、Yb was investigated by cyclic voltammetry, chronopotentiometry etc. inLiCl–KCl–AlCl₃–Yb₂O₃molten salts. Cyclic voltammograms （CVs） showed that theunderpotential deposition （UPD） of ytterbium on pre–deposited aluminum led to theformation of Al–Yb alloy. The codeposition of Al、Li and Yb occurred when appliedpotentials were more negative than–2.40V （vs. Ag/AgCl） or current densities were higherthan–0.931A·cm–2in LiCl–KCl–10%AlCl₃–2%Yb₂O₃molten salts. Al–Li–Yb alloys withdifferent phases were prepared via galvanostatic electrolysis. The lithium and ytterbiumcontents in Al–Li–Yb alloys could be adjusted by changing the addition of AlCl₃into themelts. The microstructure of alloy sample was characterized by scanning electron microscopy （SEM）.3, The electrochemical behaviour of Ho （Ⅲ） ions in the LiCl–KCl molten salt wasinvestigated in the LiCl–KCl molten salt. CV showed that electrochemical reduction of Ho（Ⅲ） ions in LiCl–KCl melts occurred at–1.91V （vs. Ag/AgCl）. The diffusion coefficient ofHo （Ⅲ） ions in the melts was calculated through three methods consists of CV in differentscan rate, chronoamperometry and chronopotentiometry. The mechanism of electrochamicalco-deposition of Mg, Li and Ho was investigated by cyclic voltammetry,open-circuitchronopotentiometry etc. in LiCl–KCl–MgCl₂–HoCl₃molten salts, the codeposition of Al、Liand Ho occurred when current densities were higher than–0.470A·cm^–2. The composition ofMg–Li–Ho alloys could be adjusted by changing the addition of MgCl2and HoCl₃.