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The present research work focuses on the synthesis, characterization and properties of novel polyelectrolyte multilayered microcapsules used as smart additives in organic coatings for corrosion protection of steel parts. Urea formaldehyde microcapsules encapsulated with linalyl acetate (UFMCs), sensitive to mechanical stimulus, were synthesized by in situ emulsion polymerization technique. In the next step, dodecylamine, working as a pH stimulus corrosion inhibitor, was loaded into layers of polyelectrolyte molecules, polyethylenimine (PEI) and sulfonated polyether ether ketone (SPEEK). These were applied layer-by-layer over the microcapsules to form inhibitor containing multilayered urea formaldehyde microcapsules (MLUFMCs). In the next step, MLUFMCs (5.0 wt%) and UFMCs (5.0 wt%) were thoroughly dispersed into the epoxy resin and coated on cleaned steel. A comparison of the structural, thermal and anticorrosive properties indicates that coatings modified with multilayered capsules (PMLSCs) demonstrate good thermal stability, improved self-healing characteristics and higher corrosion resistance compared to the coating modified with urea formaldehyde microcapsules. The improved properties of PMLSCs can be attributed to efficient release of the encapsulated self-healing agent and corrosion inhibitor from the MLUFMCs. Therefore, epoxy coatings modified with the novel multilayered capsules may be attractive for corrosion protection of steel parts used in oil and gas and related industries. - 2019, The Author(s). Open Access funding provided by the Qatar National Library. This publication was made possible by NPRP Grant 9–080-2-039 from Qatar National Research Fund (a member of the Qatar Foundation). Statements made herein are solely the responsibility of the authors. R. A. Shakoor would like to acknowledge the financial support of QU internal grant-QUCG-CAM-2018/2019-3 and the Core Labs, QEERI for their SEM and TEM imaging. M.F. Mon-temor thanks Fundac¸ão para a Ciência e a Tecnologia (FCT, Portugal) for financial support under the projects PEst-OE/QUI/UI0100/2013. Scopus

pH-sensitive calcium carbonate microparticles were loaded with polyethyleneimine (PEI), a corrosion inhibitor, and used as anti-corrosion additive in epoxy coatings applied on carbon steel. The presence of PEI in the CaCO3 particles was confirmed by Fourier-Transform Infra-Red Spectroscopy (FTIR) and the loading was quantified by Thermal Gravimetric Analysis (TGA). The protective performance of the modified coatings applied on carbon steel was investigated by Electrochemical Impedance Spectroscopy (EIS) and the results evidenced that the modified coatings provided high corrosion protection and very stable barrier properties over time. The self-healing ability was investigated by Localized Electrochemical Impedance Spectroscopy (LEIS) and by the Scanning Vibrating Electrode Technique (SVET) on coated samples artificially damaged and immersed in NaCl solutions. The results revealed an important corrosion inhibition effect, stable over time, in the coatings modified with the PEI loaded particles. The corrosion inhibition effect involves the dissolution of the calcium carbonate microparticles in the local acid media formed at the anodic sites and subsequent release of the corrosion inhibitor that forms a protective film on the steel surface. - 2019 Elsevier Ltd This publication was made possible by NPRP Grant NPRP-9-080-2-039 from Qatar National Research Fund (a member of the Qatar Foundation). L. M. Calado acknowledges Fundação para a Ciência e Tecnologia ( FCT ) for Ph.D. grant SFRH/BD/127341/2016 . Authors from Portugal acknowledge FCT for the additional funding under the projects UID/QUI/00100/2013 and UID/QUI/00100/2019 ; Sherwin-Williams for providing the coating formulations; Voestalpine AG for providing carbon steel; Dr. Marta Alves (Instituto Superior Técnico) for conducting the XRD tests; Dr. Sónia Eugénio (Universidade Atlântica) and Mário Vale (Instituto Superior Técnico) for performing FTIR and TG/DTG studies; Dr. Nick Laycock and Dr. Abitha Ramesh (Qatar Shell Research and Technology Centre) for the helpful technical guidance. Statements made herein are solely the responsibility of the authors. Scopus

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.

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