Electrodeposition of Tantalum in NaCl ‐ KCl ‐ K 2TaF7 Melts

Electroreduction of dissolved in at 720°C was investigated by transient electrochemical techniques. The primary reaction involves a single reversible five electron step . In addition to the metal deposition, other insoluble compounds were generated during the reduction step; their influence increases as the potential becomes more negative. The formation of these compounds was progressively inhibited by addition of sodium fluoride; simultaneously, a shift of the deposition potential towards more negative values was observed. This result was interpreted as a consequence of the formation of an increasing amount of fluoride rich complexes such as or . When oxide ions were present in the bath, perturbations appeared, which indicates that the reduction of electroactive species containing oxygen occurs at a potential more negative than for oxygen free complexes. The diffusion coefficient of the complex ion containing Ta(V), measured by chronopotentiometry and cyclic voltammetry, is about . The characterization of the tantalum deposits obtained at different overpotentials was determined by x‐ray diffraction and by scanning electron micrography.