Abstract
Apparatus has been developed for conducting electrodeposition experiments from fused electrolytes, under vacuum or an inert atmosphere. Procedures have been developed for the preparation of chloride electrolytes free from oxygen and extraneous impurities. Attempts have been made to prepare niobium chlorides in situ, but these have met with little success. Current - polarisation measurements have been made by means of a standard reference electrode. Coulometric measurements have shown that niobium dissolves anodically to give trivalent ions in solution at low current densities. These form a reversible electrode system with a niobium electrode. At higher current densities the niobium dissolves to give tetravalent ions in solution. These are in the form of complex anions, possibly NbCl[6][--], and can only be reduced by a secondary reaction involving alkali metal dissolved in the electrolyte. Approximate estimations of the free energies of formation of niobium chlorides have been made, and are in good agreement with recently published results.