Reduction of cathodic delamination rates of anticorrosive coatings using free radical scavengers |
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Authors: | P A Sørensen C E Weinell K Dam-Johansen S Kiil |
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Affiliation: | (1) Department of Chemical and Biochemical Engineering, Technical University of Denmark, Building 229, 2800 Kgs. Lyngby, Denmark;(2) Hempel A/S, Lundtoftevej 150, 2800 Kgs. Lyngby, Denmark; |
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Abstract: | Cathodic delamination is one of the major modes of failure for anticorrosive coatings subjected to a physical damage and immersed
in seawater. The cause of cathodic delamination has been reported to be the result of a chemical attack at the coating–steel
interface by free radicals and peroxides formed as intermediates in the cathodic reaction during the corrosion process. In
this study, antioxidants (i.e., free radical scavengers and peroxide decomposers) have been incorporated into various generic
types of coatings to investigate the effect of antioxidants on the rate of cathodic delamination of epoxy coatings on cold
rolled steel. The addition of <5 wt% free radical scavengers to epoxy coatings improved the resistance toward cathodic delamination
by up to 50% during seawater immersion, while peroxide decomposers had a limited effect. Testing using substrates prepared
from stainless steel, copper, aluminum, galvanized steel, and brass also showed a reduction in the rate of cathodic delamination
when the coating was modified with a free radical scavenger. The protective mechanism of free radical scavengers investigated
for the primers are similar to that of antioxidants used for protection against photochemical degradation by UV-radiation
of top coatings. Both substrate corrosion and degradation of a coating exposed to UV-radiation lead to the formation of free
radicals as reactive intermediates. |
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