Localised SKP studies of Cathodic Disbondment on Chromium/Chromium Oxide Coated Steel; The Influence of Coating Oxide

Organically coated thin (submicron) chromium PVD coatings have been studied as a means of protecting low carbon sheet steel from localised corrosive attack in the presence of aqueous chloride electrolyte. Novel coating wedges have been utilised to characterise the influence of coating and oxide thickness of chromium coated steel on cathodic disbondment of an applied organic coatings. SKP was used to characterise the delamination kinetics over the wedge and thus identifying optimum coating thicknesses to reduce or even prevent disbondment. It has been demonstrated that the thickness of the metallic coating offered limited influence in altering the disbondment rate with disbondment being limited by cation diffusion. However, through increasing the amount of oxide on the surface it is possible to not only change the limiting mechanism from cation diffusion to electron transfer but also stop the disbondment occurring altogether. Through these experiments it has been demonstrated that the use of wedge coatings and SKP it is possible to quantify optimum coating thicknesses in one single experiment.