Influence of substrate topography on cathodic delamination of anticorrosive coatings

The cathodic delamination of a commercial magnesium silicate and titanium dioxide pigmented epoxy coating on abrasive cleaned cold rolled steel has been investigated. The rate of delamination was found to depend on interfacial transport from the artificial defect to the delamination front and thereby the substrate topography, whereas the coating thickness had little influence.

The presence of a significant potential gradient between the anode and the cathode and the dependency of the delamination rate on the tortuosity of the steel surface suggests that cathodic delamination is controlled by migration of cations from the defect to the delamination front. This means that abrasive blasting, to some extent, can be applied to control and minimize the observed rate of cathodic delamination.

The lifetime of the species causing disbondment suggested that sodium hydroxide or potassium hydroxide and not peroxide species or radicals are the causative agents at free corrosion potential (i.e. without impressed current).