THE INFLUENCE OF OXIDE ON THE ELECTROCHEMICAL PROCESSES IN K2NBF7-NACL-KCL MELTS

Transient electrochemical techniques showed that in NaCl-KCl melts the reduction of K2NbF7 occurs through a two-step reaction Nb(V) --> Nb(I V) --> Nb. When oxide ions were introduced, cyclic voltammetry indicat ed that the waves corresponding to reduction of the complex NbF72- pro gressively disappeared. Oxo complexes, such as NbOFn(n-3-) are reduced at a potential close to that of the Nb(IV) fluoro complexes. Niobium metal deposition was perturbed by; the formation of niobium suboxides like NbO or Nb4O5. For molar ratios of oxide to Nb greater than one, a black layer of niobium oxide, NbO2, appeared at the electrode surface . The present study confirms the high oxygen affinity of niobium and s hows that a careful purification of the electrolyte and feeding materi als is required for producing niobium with a low oxygen content.