Niobium - Oxygen interaction in halide melts

The oxygen effect on niobium complexation in NaCl-KCl-K₂NbF₇ melts has been studied at 700-720°C by means of linear sweep voltammetry, potentiostatic electrolyses, X-ray diffraction, IR-spectroscopy and optic crystallography analyses. The NaCl-KCl-K₂NbOF₆, NaCl-KCl-K₂Nb0₂F₄ and NaCl-KCl- K₂NbF₇ melts with addition of Na0₂ and Nb₂0₅ as source of oxygen were investigated. It was shown that at a molar ratio O/Nb=l the predominating complexes in the melt is NbOF₅Cl^3-. The reduction of these oxo complexes occurred at potentials more cathodic than those for oxygenless complexes. Increase in the O/Nb molar ratio in excess of one leads to a decrease of niobium concentration in the melt. The mechanism of the solubility of K₃Nb0₂F₄ compound in NaCl-KCl melt was determined.