KINETIC-STUDY OF CURRENTLESS DISSOLUTION OF BISMUTH OXIDE FILM IN AQUEOUS-SOLUTION CONTAINING ELECTROACTIVE SPECIES

The results of open-circuit potential and impedance measurements show that the dissolution rate of the anodic oxide film on bismuth is dependent on the nature of the dissolving medium. The dissolution rate of the oxide film is found to increase with increasing chromate concentration, particularly the outer layer of the oxide film. The outer layer is more defective than the inner layer because of its contamination by SO42- anions during anodization in H2SO4 solution. The increase in the dissolution rate with increasing chromate concentration may be attributed to the oxidative type of dissolution of bismuth oxide in chromate solution. Dissolution of bismuth oxide film in solutions containing other electroactive species such as Fe2+, HCOOH and I- is also studied. It is found that the dissolution rate of the oxide film decreases in the order CrO42- (high) > Fe2+ > HCOOH > I- (low). The dissolution mechanism of the duplex-nature bismuth oxide film follows a zero-order mechanism in all the test solutions.