Organo-modified layered double hydroxide in coating formulation to protect AA2024 from corrosion

• Corrosion inhibitor agent released from LDH nanocontainer.
• Elemental mapping onto metal surface before and after exposure to corrosive media.
• Long-term investigation of coating properties.

Suggested as efficient filler for impact resistance when dispersed into a coating formulation, layered double hydroxide (LDH) materials organo-modified by aniline and benzene derivatives, 3- and 4-aminobenzensulfonic acid (ABSA) and 3,4-dihydroxybenzoic acid (HHBA), are further investigated here to protect from corrosion aluminium alloy 2024. The concomitant release of interleaved organic molecule as well as the uptake of chloride anion was studied by X-ray diffraction to demonstrate the LDH framework efficiency to act as chloride nanotrap. HHBA was found to be immobilised while the two other molecules are released. DC-polarization experiments demonstrate the efficiency of all three hybrid LDH materials in lowering the corrosion current suggesting that the corrosion inhibition mechanism should either proceed by an anion exchange and/or by a complete dissolution of inorganic framework inducing both the anions release but in the latter case by an additional leaching of the LDH sheet cations. Electrochemical impedance spectroscopy experiments indicate two opposite phenomena: an increase in the barrier properties of the coating in the presence of LDH pigments but as well as in the water uptake process that subsequently causes the protective polymer film to blister. Such delamination allows the electrolyte to migrate but also the corrosion inhibitor agents to flow onto the damaged area. Elemental analyses mapping around damaged area using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy confirm the release of interleaved anticorrosive species that is occurring by anion exchange and/or platelets dissolution when LDH fillers are dispersed into the polymer coating formulation.

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