Two-dimensional pitting corrosion of aluminium thin layers

The influence of Cl− and Fe3+ ions on the morphology of pits grown in aluminium thin films was investigated. Under open circuit conditions various morphologies ranging from percolation-cluster-like patterns to dense holes with smooth perimeters were observed. Temporal fluctuations in the free corrosion potential did not reflect significant differences in pit shapes. The growth of two-dimensional pits is likely to be influenced by two main factors: (a) local fluctuation in the electrolyte aggressiveness due to copious hydrogen bubbling at dissolution sites; (b) global restriction of pit growth imposed by the cathodic reactions occurring on the oxidised surface. A spreading percolation model with feed-back is able to reproduce all the morphologies observed and provides a possible explanation to the 1/f2 character of the potential noise.