Simulations of diffusion limited corrosion at the metal|environment interface

Using a simple cellular automaton model we describe the role of diffusion and reaction processes in a corrosion phenomenon in which there is formation of an unsoluble film on a surface. Working on a mesoscopic scale, we focus on three main processes: the corrosion of the substrate, the diffusion of species across the layer already formed and the precipitation of these species on the layer. Since the concentration of chemical species involved in these processes can be important, we introduce an interaction between them. Due to these interactions, there is a feedback effect on the evolution and the structure of the corrosion front. We show that the initial corrosion rate is progressively replaced by a corrosion rate determined by a diffusion process. In parallel, we observe a flattening of the corrosion front, which loses the fractal character predicted by traditional models of growth. We also investigate the distribution of diffusing particles across the layer in formation. Although simple, the mechanisms involved in the model lead to a highly nonlinear behavior due to complicated couplings between processes. A first mapping between our simulations and real systems is attempted, which shows that the mechanisms considered here might appear at real metal|environment interfaces.