Stochastic Models of Pitting Corrosion of Stainless Steels: II . Measurement and Interpretation of Data at Constant Potential

The experimental evaluation of the parameters of a general stochastic model for the initiation of pitting corrosion on stainless steels is described. The variation of these parameters with experimental conditions is used in the development of a microscopic model. A microscopic model which accords with the observed behavior attributes the initiation of pitting corrosion to the production and persistence of gradients of acidity and electrode potential on the scale of the surface roughness of the metal. The observed fluctuations are related to fluctuations in the hydrodynamic boundary layer thickness. A pit becomes stable when it exceeds a critical depth related to the surface roughness.