Mechanistic insight of electrochemical reduction of Ta2O5 to tantalum in a eutectic CaCl2–NaCl molten salt

An investigation into the reaction pathway of the electrochemical reduction of Ta2O5 to tantalum in a eutectic CaCl2–NaCl molten salt has been performed in order to better understand the reaction mechanism of the electro-deoxidation process. Partially reduced samples were obtained by interrupting the reduction process after different reaction times at 1123 K, and examined by XRD, SEM and EDX analysis. The results reveal that the reduction process from Ta2O5 to Ta undergoes several intermediate phases, such as Ta2O5·0.5CaO, Ta2O5·2CaO, and Ta2O5·4CaO. The particle morphology in the cathode changed with the various phase transformations. The CaO concentration in the CaCl2–NaCl melt seems to affect the particle size of nodular-shaped tantalum powder products.