ELECTRODEPOSITION OF TANTALUM FROM A NOVEL LOW TEMPERATURE MOLTEN SALT

摘要

The eleptrochemical reductions of Ta(V) in a novel TaCl_5-EMIC (1-ethyl-3- methylimidazolium chloride) low temperature molten salt were investigated by using various voltammetric techniques. The compositions of the melts used were 55 mol% TaCl_5 (i.e., Lewis acidic) and 66.7 mol% of EMIC (i.e., Lewis basic), and the experiments were carried out at 373-423 K. Cyclic voltammograms were measured with tungsten or platinum electrodes in both compositions of melts, and wave shape analyses for two reduction waves observed at potentials positive than that of the reduction of EMI cations were done. Normal pulse voltammetry and differential pulse voltammetry were also performed to examine the stoichiometry and the number of electrons involved in the reactions for those two waves. From the results, a possible reaction sequence for the reduction of Ta(V) in TaCl_5-EMIC melts was deduced, and its dependence on the melt acidity was discussed. Voltammetric measurements and galvanostatic electrolyses were further executed using a basic TaCl_5-EMIC melt containing LiF to study the effect of LiF addition on the reduction process of Ta(V). The possibility of tantalum electrodeposition from the LiF-added TaCl_5-EMIC melt was accessed.