Potentiodynamic evaluation of sol–gel coatings with inorganic inhibitors

Sol–gel coatings were investigated as potential replacements for chromate-based surface treatments on aircraft aluminum alloys. Unlike chromate based treatments current sol–gel coatings do not have the ability to leach corrosion inhibitors upon coating damage and minimize corrosion of the unprotected area. As an alternative, environmentally compliant non-chromate inhibitors of Ce(NO3)3, NaVO3 and Na2MoO4 were incorporated into a Zr-epoxy sol–gel. Results are reported on the coatings chemical analysis and their corrosion protection performance based on electrochemical studies. Aluminum alloy 2024-T3 test coupons coated with protective sol–gel films were found to provide considerable corrosion protection. The improved performance characteristics were derived from the sol–gel ability to form a uniform, low defect, barrier coating. Coatings doped with Ce(NO3)3 had barrier properties at least as good as the standard sol–gel coatings. Coatings with Na2MoO4 and NaVO3 did not provide adequate corrosion protection. The use of corrosion inhibitors within organically modified sol–gel coatings is discussed.