The role of adsorption in passivation phenomena modelled by discrete lattice gas automata

Abstract

Simulation results are presented for a simple modification of recent lattice gas cellular automata model of passivation. In the previous model, the passive layer sites produced at the corroding surface, neither adhere to nor are repelled from the surface. As a result, no net adsorption or desorption, at equilibrium, is possible for this model. Nonetheless, the crucial features of passivation appear due to the kinetic crowding of the passive layer sites. This crowding effect is further enhanced by the aggregation of the passive layer sites introduced via asymmetric exclusion rules. The results of this model challenge a common view that adsorption is crucial for passivation. This analysis calls for the evaluation of the role of adsorption. Therefore, in this paper, the model takes into account the attraction of the passive layer sites with the metallic substrate. The present model is compared with the model examined in the previous paper. It demonstrates that although adsorption does not modify essentially the overall image of passivation, as seen in the polarization curves, there are important quantitative and qualitative new features in the passivation phenomenology introduced by adsorption. These new features result from the appearance of two regimes of passivation: a thin layer regime at the passivation transition followed by a thick layer regime at more anodic potentials.