Abstract
The cathodic reduction of Dy(III) ions at inert molybdenum and active gallium electrodes in molten NaCl–2CsCl eutectic and a temperature range of 843–973 K in an inert atmosphere is studied by stationary and nonstationary electrochemical methods. Anhydrous dysprosium trichloride (Aldrich) is used as received, and sodium and cesium chlorides are additionally purified from oxygen-containing impurities by directional crystallization. In addition, a zirconium getter is placed in an experimental cell to absorb the oxygen and moisture traces adsorbed on the inner walls of the quartz tube. One cathodic current peak corresponding to the reduction of Dy(III) ions to metallic dysprosium and one anodic peak associated with dysprosium dissolution are recorded on a cyclic voltammetric curve on the molybdenum electrode for NaCl–2CsCl–DyCl3 melt in the “electrochemical window” under study. Therefore, the reduction of Dy(III) ions to the metal proceeds in one step. Using diagnostic criteria, the reduction is found to be irreversible and controlled by the charge transfer rate. The diffusion coefficients of [DyCl6]3– ions are calculated. Their temperature dependence is described by the equation log D = –2.81 – 1920/T ± 0.02 and obeys the Arrhenius law. The temperature dependence of the apparent standard potential of the Dy(III)/Dy couple is determined using open-circuit potentiometry and described by the linear equation \(E_{{{\text{Dy}}\left( {{\text{III}}} \right)/{\text{Dy}}}}^{{\text{*}}}\) = –(3.827 ± 0.005) + (6.6 ± 0.1) × 10–4T ± 0.003 V. The changes in the apparent standard Gibbs energy, enthalpy, and entropy of dysprosium trichloride formation from elements in molten NaCl–2CsCl eutectic are determined. The alloy formation preceding the formation of metallic dysprosium at the cathode is observed on the cyclic voltammetric curve recorded at the gallium electrode for the NaCl–2CsCl–DyCl3 melt. The temperature dependence of the apparent standard potential of a Dy–Ga alloy is established using open-circuit potentiometry. This dependence is described by the linear equation \(E_{{{\text{Dy-Ga}}}}^{{{\text{**}}}}\) = –(3.092 × 0.006) + (3.6 ± 0.2) × 10–4T ± 0.005 V. The activity coefficients of solid dysprosium in liquid gallium are calculated as a function of temperature.
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This work was supported by the Russian Foundation for Basic Research, project no. 20-03-00743.
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Translated by E. Yablonskaya
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Novoselova, A.V., Smolenski, V.V. Electrochemical and Thermodynamic Properties of Dysprosium Trichloride in Molten NaCl–2CsCl Eutectic on Inert and Active Electrodes. Russ. Metall. 2022, 142–147 (2022). https://doi.org/10.1134/S0036029522020124
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DOI: https://doi.org/10.1134/S0036029522020124