Electrochemical behaviour of dysprosium in the eutectic LiCl-KCl at W and Al electrodes

The electrochemical behaviour of DyCl3 was studied in the eutectic LiCl-KCl at different temperatures. The cathodic reaction can be written: Dy(III) + 3e <----> Dy(0) which can be divided in two very close cathodic steps: Dy(III) + 1e <----> Dy(II) and Dy(II) + 2e <----> Dy(0) Transient electrochemical techniques, such as cyclic voltammetry, chronopotentiometry, and chronoamperometry were used in order to study the reaction mechanism and the transport parameters of electroactive species at a tungsten electrode. The results showed that in the eutectic LiCl-KCl, electrocrystallization of dysprosium seems to be the controlling electrochemical step. Chronoamperometric studies indicated instantaneous nucleation of dysprosium with three dimensional growth of the nuclei whatever the applied overpotential. Mass transport towards the electrode is a simple diffusion process, and the diffusion coefficient of the electroactive species, i.e. Dy(III), has been calculated. The validity of the Arrhenius law was also verified by plotting the variation of the logarithm of the diffusion coefficient versus 1/T. In addition, the electrode reactions of the LiCl-KCl-DyCl3 solutions at an Al wire were also investigated by cyclic voltammetry and open circuit chronopotentiometry. The redox potential of the Dy(III)/Dy couple at the Al electrode was observed at more positive potentials values than those at the inert electrode. This potential shift was thermodynamically analyzed by a lowering of activity of Dy in the metal phase due to the formation of intermetallic compounds. (C) 2004 Elsevier Ltd. All rights reserved.