Data acquisition in thermodynamic and electrochemical reduction in a Gd(III)/Gd system in LiF–CaF2 media

The electrochemical reduction of GdF3 was studied in the LiF–CaF2 eutectic (77/23 mol%) on a tantalum electrode for various GdF3 concentrations in the 800–900 °C temperature range. A previous thermodynamic study showed that gadolinium trifluoride is reduced into metal in a one-step process:Gd(III)+3e−=GdGd(III)+3e−=GdCyclic voltammetry and square wave voltammetry were used to confirm this mechanism, and the results show that the electrochemical reduction process is limited by the diffusion of Gd(III) in the solution.The Gd(III) diffusion coefficient was calculated at different temperatures and the results obey the Arrhenius law with an activation energy of 83 ± 4 kJ mol−1.The activity coefficient of Gd(III) and the Gd(III)/Gd standard potential E° were determined in the melt at various temperatures and concentrations. The values obtained for the activity coefficients were close to 1 at the highest temperatures and between 1.3 and 1.6 at lower temperatures.