The Oxide Film on Steel and Cathodic Disbondment of a Protective Organic Coating
- 1 May 1985
- journal article
- Published by The Electrochemical Society in Journal of the Electrochemical Society
- Vol. 132 (5) , 1005-1009
- https://doi.org/10.1149/1.2114004
Abstract
Cathodic disbondment of an oleoresinous organic coating on steel with an air‐formed oxide film has been investigated in 0.1N sodium borate solution (pH 9.2) and in pH 7.6 borate buffer solution. This is compared with oxygen reduction and with oxide film reduction for uncoated steel surfaces. The rate of oxygen reduction on the steel surface is found to increase as Fe+3 in the oxide film is reduced. The rate of cathodic delamination of the organic coating is a function of the oxygen reduction rate as determined by the oxide film properties. Reduction of Fe+3 in the oxide film may result in either soluble Fe+2 or in intermediate film compositions from to , dependent upon pH and potential. At sufficiently negative potentials, once a portion of the Fe+3 in the oxide film is reduced, the steel substrate becomes active, yielding soluble or insoluble oxidation product, dependent upon pH and potential. This explains observed surface roughening and oxide film thickening beneath disbonded organic coatings.Keywords
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