Probabilistic cellular automata model of generalised corrosion, transition to localised corrosion

Numerical modelling is an effective tool for predicting corrosion. We make use of a stochastic Cellular Automata (CA)-based modelling for corrosion studies at a mesoscopic scale. Physico-chemical phenomena that cannot be satisfactorily described by standard deterministic and macroscopic methods are here taken into account. In this CA modelling, materials and their environments are described by a 3D lattice, where each cell has a state. The physico-chemical phenomena are represented as simple rules that define the temporal evolution of the states of the cells. These rules can be combined to model complex systems. Our model is stochastic in the sense that the transition rules are given probabilities and diffusion in the electrolyte is modelled as a random walk. Simultaneous anodic and cathodic reactions describe the corrosion mechanisms. Special emphasis is given to the electric connection between the anodic and cathodic cells. The anodic and cathodic reactions occur simultaneously, maintaining the electric balance. In this work, we study the evolution of the generalised corrosion of a metallic surface. Two regimes are found that are determined by local acidity of the electrolyte. Uniform corrosion is predominant in the first regime, where anodic and cathodic half-reactions occur homogeneously over the surface. In the second regime, a local increase in acidity appears that induces the predominance of localised corrosion. The competition between these two regimes determines the global corrosion kinetics. [GRAPHICS] .