Kinetics of corrosion-driven cathodic disbondment on organic coated trivalent chromium metal-oxide-carbide coatings on steel

Chromium metal-oxide-carbide coatings of varying composition and thickness, cathodically electrodeposited from a Cr (III)-formate electrolyte are compared for their ability to resist the corrosion driven delamination of an adherent polymer overcoat. Cathodic disbondment rates are determined using an in-situ scanning Kelvin probe technique. The rates of cathodic disbondment decreased with increasing thickness and Cr (III) oxide content of the Cr (III) derived coating. Disbondment kinetics are explained in terms of coating porosity, chemical composition and electrocatalytic activity of the various metallic surfaces for the cathodic oxygen reduction reaction (ORR). Diminished electrocatalytic activity for on, as determined from cathodic polarisation measurements with a rotating disk electrode, are found to correlate with diminished delamination kinetics.