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1 Polish Journal of Chemistry

1 2004

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Simulations of Corrosion Processes with Spontaneous Separation of Cathodic and Anodic Reaction Zones

Vautrin-Ul C., Chausse A., Stafiej J., Badiali J.

Polish Journal of Chemistry

2004

Vol. 78 / nr 9

1795-1810

We present a simple cellular automata model for mimicking corrosion processes of corrodable materials covered by an ideal insulating and protective layer.Asmall defect in this layer brings the corrodable material into the contact with the outer environment and initiates the formation of a cavity. We study the evolution of the cavity in terms of time dependence of its size, morphology and chemical composition as determined by the corrosion- passivation phenomena at the corrosion front and diffusion within the cavity.We mimic the diffusion of reaction products as a random walk and we can control the diffusion rate with respect to that of corrosion. If the diffusion is very fast the cavity can be assimilated to a half-circle filled up by a neutral solution. When the diffusion rate decreases the cavity shape becomes more and more irregular and the solution contains large domains essentially acidic or basic comparable to cavity size. A quantitative analysis of simulations also reveals the existence of an incubation time during which the corrosion is not clearly visible. If the diffusion rate is low, the stochastic processes that we have considered lead to an unpredictable shape for the cavity and to a large dispersion of the incubation times. Then we clearly observe spontaneous formation of the cathodic and anodic reaction zones at the corrosion front. We discuss these results in a simple case.