Pitting point defect model

Fig. 33. Cartoon outlining various stages of pit nucleation according to the point defect model. Reproduced from J. Electrochem, Sec. 139, 3434 (1992) by permission of the Electrochemical Society.

Perfluorosulfonic acid (PFSA) 200, 245 Perovskite 63, 67, 68, 81, 83 Phthalocyanine 332 Pitting 128, 180 Point defect model 163 Poisson s equation 132 Polyacetylene 310, 352, 354, 365 Polyacrylonitrile 361, 366 Polyaniline 379... 

Lin, L.R, Chao, C.Y. and Macdonald, D.D. (1981) A point defect model for anodic passive films II. Chemical breakdown and pit initiation. Journal of The Electrochemical Society, 128, 1194-1198. 

On the other hand, pit initiation which is the necessary precursor to propagation, is less well understood but is probably far more dependent on metallurgical structure. A detailed discussion of pit initiation is beyond the scope of this section. The two most widely accepted models are, however, as follows. Heine, etal. suggest that pit initiation on aluminium alloys occurs when chloride ions penetrate the passive oxide film by diffusion via lattice defects. McBee and Kruger indicate that this mechanism may also be applicable to pit initiation on iron. On the other hand, Evans has suggested that a pit initiates at a point on the surface where the rate of metal dissolution is momentarily high, with the result that more aggressive anions... 

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