Diffusion of Cations Beneath Organic Coatings on Steel Substrate

摘要

Theoretical and experimental studies were carried out for the transport of cations in the channel between a polymer coating and a metal substrate from a defect in the absence of an electrical applied potential. The model consists of two stages: an initial period during which ions diffuse in the coating/metal interfacial 'channel' and adsorb on the coating surface and a propagation period during which ions also diffuse into the coating. The mathematical models were solved to predict the cation concentration and flux under the coating and the relative rate of diffusion between initial and propagation periods. Model parameter values were derived from the results of an experiment conducted in a specially designed diffusion cell. The results also indicated that during the propagation period, the rate limiting step was the lateral diffusion along the coating/metal interface rather than diffusion through the coating.