ELECTROCHEMICAL STUDY OF THE REDUCTION OF SOLUTIONS OBTAINED SEVERAL HOURS AFTER DISSOLVING K2NBF7 IN MOLTEN NACL-KCL AT 750-DEGREES-C

Solutions of K2Nb7, in molten NaCl-KCl were maintained at 750 degrees C over days in a vitreous carbon crucible under argon atmosphere, and the mechanism of niobium electrodeposition was studied using chronopotentiometry and cyclic voltammetry with convolution at tungsten, vitreous carbon, and silver electrodes. Nb(IV) the stable species found in the melt, was reduced to Nb via a slow four-electron exchange step. The rate constant was k degrees = 9 . 10(-7) cm s(-1). The peak intensity decreased with time. Anodic oxidation of Nb(IV) species occurred, according to the fluoride ion content of the melt, via two steps corresponding, respectively, to an F-rich and a Cl-rich complex entity.