Degradation of organic coatings on steel: Mathematical models and predictions

• Published in: Progress in organic coatings 1994, Vol.25 (1), p.23-41
• Main Authors: Pommersheim, James M., Nguyen, Tinh, Zhang, Zhuohong, Hubbard, Joseph B.
• Format: Article
• Language: English
• Subjects: Anodic and cathodic sites; Applied sciences; Blisters; Coatings; Coatings. Paints, varnishes and inks; Corrosion; Diffusion; Exact sciences and technology; Film formation and curing, properties, testing; Flux; Interface; Mathematical model; Polymer industry, paints, wood
• ISSN: 0300-9440; 1873-331X
• DOI: 10.1016/0300-9440(94)00501-X

Conceptual and mathematical models are developed for blistering processes induced by the corrosion of defect-containing coatings on steel substrate exposed to electrolytes. Models were developed based on cation transport along the coating/steel interface from the anodic sites at the defect to the cathodic sites under the coatings. The models accounted for both an initial induction period before cations have broken through into the blister and a subsequent propagation period when ions accumulate within the blister. The mathematical models are solved analytically to predict cation fluxes and concentrations along the interface and within the blisters. Solutions of the models are expressed in terms of dimensionless parameters. Model variables include blister size, distance between the blister and defect, ion diffusivity and potential gradients. The conditions under which ion transport is likely to be controlled by either potential or concentration gradients are established. Model results indicate that large blisters are more likely to grow than small ones because higher cation concentrations can build up within them. Implications of this conclusion for maintaining the integrity of organic coatings are discussed.