Electrochemical behaviour 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. Electrochemical impedance spectroscopy and polarisation techniques have been used to investigate the open-circuit growth of the passive film. The stability 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-Nb 2 O 5 -1M HNO 3 does not behave as a perfect dielectric. The flat band potential and donor concentration of the semiconducting anodic oxide film have been calculated from the Mott-Schottky plots.