(i) Presented that when the electrostatic field across the film/solution interface reaches a critical value corresponding to the critical breakdown potential, the anions adsorbed on the oxide film enter and penetrate the film.
(i) Favored sites for ion migration are suggested to be high-energy regions like grain boundaries and impurities where thinner passive films are produced. (ii) If the aggressive ions meet a metal cation, contaminated film is produced that encourages further ions to penetrate the film. Then, this process continues as an autocatalytic reaction.
(i) Did not explain the observation that pits often form from mechanical breaks in the oxide film or from scratches.
(i) Presented a theoretical model to explain the chemical breakdown of passive film.
(i) Proposed that metal vacancies may accumulate as a result of the diffusion of metal cations from the metal/film to the film/solution interface, forming voids at the metal/film interface. When the voids grow to a critical size the passive film will collapse leading to pit growth.
(i) Surface discontinuities such as grain boundaries and so forth were not considered in developing the model. (ii) No direct observation of void formation was made. (iii) As the measured induction times usually show a large scatter, definite quantitative agreement is difficult to obtain.
