ELECTROCHEMICAL REDUCING OF TERBIUM AND HOLMIUM IONS IN THE SODIUM AND POTASSIUM CHLORIDES MELT WITH EQUIMOLAR COMPOSITION

Vadym Kovalenko, Olga Chernova, Valerii Kotok, Sergey Zhykovin, Ihor Kovalenko, Denis Kondratyev, Viktor Ved, Volodymyr Verbitskiy

Abstract


Interest to rare-earth metals (REM) and their alloys is due to the possibility of using them for the creation of new materials need for modern technology. For instance, REM as alloying components allows for preparation of material with special magnetic properties. A promising method for forming such coating is the surface treatment of metals. This process has an electrochemical character as such for the organization of technology the knowledge of kinetics and mechanism of these processes is important. Despite significant interest in rare-earth metals, these issues are not well described in the literature. In order to choose an adequate mathematical model for calculation of kinetic primers, preliminary experiments that allow evaluating the reversibility of the electrode process have been conducted. Based on that, it was concluded that cathodic reduction of terbium and holmium ions in equimolar NaCl-KCl melt is irreversible. By means of voltammetric analysis, kinetic parameters (transfer coefficients, heterogeneous constants of charge transfer rate) of terbium and holmium electroreduction in equimolar NaCl-KCl melt were determined. The experiment was conducted in a three-electrode cell under a purified argon atmosphere. A dependency of kinetic parameters on the concentration of terbium and holmium chlorides wt (%): 1, 3, 5, 7, 10, was determined. The experiment was conducted in 1073–1173K temperature range. Values of kinetic parameters increase with temperature but decrease with the increase of REM chloride. Based on obtained data, it was found that electroreduction of chloride complexes LnCl63– (Ln–Tb, Ho) in equimolar NaCl-KCl melt is irreversible in the studied range of temperatures and REM concentrations. In summary of experimental data, in range of temperature and rare-earth chloride concentration, and assumption was made that reduction of terbium and holmium ions occurs in two stages. The process includes the preceding stage of complex dissociation. A mechanism of LnCl63– complex reduction in the mentioned melt is proposed. The obtained results are in agreement with literate data for analogues systems.


Keywords


chloride melts; terbium; holmium; kinetic parameters; voltammetry

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DOI: http://dx.doi.org/10.21303/2461-4262.2019.00980

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Copyright (c) 2019 Vadym Kovalenko, Olga Chernova, Valerii Kotok, Sergey Zhykovin, Ihor Kovalenko, Denis Kondratyev, Viktor Ved, Volodymyr Verbitskiy

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