Anion-exchange inhibition of filiform corrosion on organic coated AA2024-T3 aluminum alloy by hydrotalcite-like pigments

Novel anion-exchange anticorrosion pigments consisting of nitrate, carbonate, and chromate exchanged hydrotalcite (HT) are shown to effectively inhibit the propagation of filiform corrosion (FFC) on organic coated AA2024-T3 aluminum alloy. The HT-pigments are dispersed in polyvinyl butyral (PVB) coatings applied to the AA2024-T3 surface. Following FFC initiation by application of aqueous HCl to a penetrative coating defect, the time-dependent extent of coating delamination is determined both optically and by means of repeated in situ scanning using a scanning Kelvin probe apparatus. All HT-pigments are shown to profoundly reduce rates of coating delamination by comparison to unpigmented samples. However, inhibitor efficiency is dependent upon the exchangeable anion and increases in the order carbonate<nitrate<chromate. (C) 2003 The Electrochemical Society.