In this work we report the synthesis of polyurea microcapsules loaded with corrosion inhibitor 2-mercaptobenzothiazole (MBT) for corrosion protection of 2024 aluminum alloy. The microcapsules were prepared by interfacial polycondensation. The resulting capsules exhibit spherical shape, with diameter ranging between 100 nm and 2 mu m. The loading content of MBT was found to be 5 wt% and release studies showed that MBT is preferentially released under acidic and alkaline conditions and follows a Fickian diffusion model. This pH dependency seems suitable for protection of metallic alloys where corrosion processes are accompanied by local pH changes. Furthermore, the microcapsules were added to a hybrid sol-gel coating and its performance assessed by electrochemical and accelerated standard tests. The results obtained indicate that capsules loaded with MBT do not affect negatively the barrier properties of sol-gel coatings, and contribute for the enhancement of adhesion of coatings to the metallic substrate. More relevant, these additives impart active corrosion protection suppressing corrosion activity at defect sites, which opens prospects for application of polyurea microcapsules as additives for high-performance coatings. (C) 2015 Elsevier B.V. All rights reserved.

The active corrosion protection of metallic substrates can be achieved by the addition of corrosion inhibitors to protective coatings. However, direct mixing of inhibitors with coating formulations can lead to important drawbacks, decreasing barrier properties of the coating and diminishing activity of the inhibitor. Nanocontainers for corrosion inhibitors were developed in this work using layered double hydroxides (LDH) as nanocarriers. The LDH were used as nanosized particles, which are then included in a sol-gel hybrid coating, and as a LDH layer directly formed on the metal surface (conversion film) and covered by a sol-gel hybrid layer. Electrochemical impedance spectroscopy (EIS) has been used for evaluation of corrosion protective properties of the coatings. The results show that the LDH with incorporated vanadate inhibitor provide efficient active corrosion protection in both cases.