ELECTROCHEMICAL-BEHAVIOR OF NIOBIUM AND NIOBIUM PASSIVE FILMS IN NITRIC-ACID SOLUTIONS

Electrochemical behaviour of bare niobium and-phosphoric acid anodized niobium electrodes is investigated in nitric acid solutions. Electroc hemical impedance spectroscopy and polarisation techniques have been u sed to investigate the open-circuit growth of the passive film. The st ability of the anodic oxide film has been studied as a function of the formation voltage, formation current density and concentration of the ambient electrolyte. The results show that the Nb-Nb2O5-1M HNO3 does not behave as a perfect dielectric. The flat band potential and donor concentration of the semiconducting anodic oxide film have been calcul ated from the Mott-Schottky plots.