The kinetics of anodic oxidation of niobium have been studied in 0.1M L-ascorbic acid without and with addition of a millimole of sodium phosphate at a constant current density of 8 mA.cm-2 and at room temperature (300 K). The addition of phosphate ions found to improve the kinetics of film formation. This trend and mechanism of anodic oxide film growth is confirmed from radio-tracer studies using labeled phosphate ions. The conclusion of the results obtained is migration of anion impurity and accumulation of active phosphate in the inner layers of the oxide film formed.
