Comprehensive examination of the electrochemistry of indium in the molten LiCl±KCl eutectic M. Mohamedi *, S. Martinet, J. Bouteillon, J.C. Poignet Laboratoire d'Electrochimie et de Physicochimie des Mate Âriaux et des Interfaces, UMR 5631 associe Âe a Á l'U.J.F., I.N.P.G., E.N.S. d'Electrochimie et d'Electrome Âtallurgie, BP 75, 38402 Saint-Martin d'He Âres, France Received 4 March 1998; received in revised form 8 June 1998 Abstract The reduction processes on glassy carbon electrode in molten LiCl±KCl eutectic containing InCl 3 was studied by cyclic voltammetry, chronopotentiometry, convolution voltammetry and numerical simulation of the experimental voltammograms. The cathodic discharge of indium ions to form metallic indium was shown to take place by a consecutive two-step electrochemical reaction. This process is identi®ed as: In 3+ + 2e \ In + (reversible) and In + +e \ In 0 (quasi-reversible). The diusion coecients of both In 3+ and In + were found equal to 4  10  5 cm 2 s  1 at 4408C, the exchange current density for the In 3+ /In + couple equal to 0.01 A cm  2 , the rate constant for the In + /In 0 was found to be in the order of 0.001 cm s  1 and the amount of indium metal needed to cover the electrode surface was found to be 5  10  7 mol cm  2 . # 1998 Elsevier Science Ltd. All rights reserved. Keywords: Indium; LiCl±KCl; Voltammetry; Chronopotentiometry; Modelling 1. Introduction Indium, generally associated with zinc blend, becomes superconductor at nearby zero absolute. Its exceptional plasticity, relative inalterability and low toxicity are the main qualities that were exploited at diverse degrees. The growth of the application in the photoconductor ®eld augmented the requirement for high grade purity of indium and inspired the study of new indium electrore®ning processes in fused salt media. In the AlCl 3 ±NaCl±KCl-melt at 1358C, Anders et al. [1] reported that indium metal reacts completely with the solvent to give aluminum metal and mono- valent indium according to Al 3+ + 3In 0 cAl + 3In + . The indium monovalent could be further electrochemi- cally reoxidized into indium trivalent. Using a glassy carbon working electrode, De Guibert et al. [2] claimed that In 3+ is reduced to In + through a single step in molten 0.77PbCl 2 + 0.23KCl. In LiCl±KCl±ZnCl 2 con- taining InCl 3 at 4508C, Jafarian [3] observed by cyclic voltammetry that indium trivalent was reduced into indium monovalent onto a tungsten electrode. No further reduction of In + into metallic indium was noticed. In NaCl±KCl±ZnCl 2 only one wave ascribed to In 3+ /In + couple was observed onto a gold electrode [4]. More recently, Castrillejo et al. [5] stu- died the electrochemical behavior of the In 3+ and In + ions in the ZnCl 2 ±2NaCl melt at 4508C onto a tung- sten electrode. Their work reveals that In 3+ /In + exchange is quasi-reversible and found that metallic indium in contact with the melt reacts quantitatively to give zinc metal and indium monovalent. It seems that metallic indium reacts with Zn(II) ions to give metallic zinc and indium monovalent as it was earlier stated by Omel'chuck et al. [6] in pure ZnCl 2 . In LiCl±KCl, Laitinen and Liu [7] concluded that indium trichloride was reduced directly to metallic indium in a single step. The same result was obtained by Popov et al. [8] Electrochimica Acta 44 (1998) 797±803 0013-4686/98/$ - see front matter # 1998 Elsevier Science Ltd. All rights reserved. PII: S0013-4686(98)00239-4 PERGAMON * Corresponding author. Present address: Department of Metallurgy, Faculty of Engineering, Tohoku University, Sendai 980-77, Japan. Fax: +81-22-217-7310; E-mail: moha- med@stu.material.tohoku.ac.jp