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Unified Model for the Degradation of Organic Coatings on Steel in a Neutral Electrolyte.


pdf icon Unified Model for the Degradation of Organic Coatings on Steel in a Neutral Electrolyte. (1341 K)
Nguyen, T.; Hubbard, J. B.; Pommersheim, J. M.

Annual Meeting, 73rd. Federation of Societies for Coatings Technology (FSCT). Proceedings. October 10, 1995, St. Louis, MO, 1995.

Journal of Coatings Technology, Vol. 68, No. 855, 45-56, April 1996.

Keywords:

coatings; corrosion; degradation; electrolyte; quantitative

Abstract:

A unified model is presented for the degradation of an organic protective coating on a steel substrate exposed to a neutral electrolytic environment. This model is based on theoretical and experimental studies from our laboratory and on current understanding of the degradation process. The assumptions of the model are based on the concept that degradation of a coating/steel system occurs following the transport of ions through conductive pathways, which are presumably formed by an attack by water in the "hydrophylic", low-molecular-weight/low-cross-linked regions, followed by the connections of these regions. Models for the blistering and delamination resulting from corrosion processes are based on the diffusion of cations along the coating/steel interface from the detects to cathodic sites under the coatings. The resulting equations are solved to predict ion fluxes and concentration profiels along the interface and within blisters. Model variables include blister size, distance between blister and defect, ion diffusivity, and potential gradients. Experimental results agree well with theoretical predictions.