Comparison of the synergistic effects of inhibitor mixtures tailored for enhanced corrosion protection of bare and coated AA2024-T3

Abstract

The replacement of chromate-based corrosion inhibitors is a requirement for the aerospace sector. New developments demand additional studies to find synergistic combinations of inhibiting species. This paper discusses the synergistic effect resulting from various corrosion inhibitor mixtures proposed for the corrosion protection of aluminum alloy 2024-T3. The corrosion inhibition efficiency and the synergistic factors were determined for AA2024-T3 coupons immersed in 0.05 M NaCl solutions, containing either a single inhibitor or binary combinations of inhibitors. The following inhibitors were tested: Ce 3 +, 8-hydroxyquinoline (8HQ), salicylaldoxime (SAL), and 2,5-dimercapto-1,3,4-thiadiazolate (DMTD). Electrochemical impedance spectroscopy (EIS) and ATR-FTIR in Kretschmann geometry were used to evaluate the chemical and electrochemical variations during the exposure of bare coupons to inhibitor-containing NaCl solutions. The results allowed calculating the synergistic effect for binary mixtures and the most effective mixtures were those containing 8HQ-SAL and DMTD-8HQ. The synergistic effect was also determined for coated coupons. A water-based epoxy coating was modified with calcium carbonate microparticles, loaded beforehand with single inhibitors or with binary mixtures. EIS measurements were performed in 0.5 M NaCl and the results revealed that the epoxy coatings modified with CaCO3 microparticles, loaded with inhibitor mixtures, provided enhanced corrosion protection. The most effective corrosion protection was observed for two mixtures: CaCO3(8HQ + SAL) and CaCO3(Ce + SAL). Interestingly, the results revealed that the synergistic effect on bare AA2024-T3 can be different from the situation where the same inhibitor mixtures are used in smart, anti-corrosive coatings.