Montmorillonite nanoclay-based self-healing coatings on AA 2024-T4

Cation-exchanged montmorillonite (MMT), which is an aluminum-pillared clay, was dispersed into an organic–inorganic hybrid silica matrix sol. Cationic inhibitors Ce³⁺/Zr⁴⁺ were introduced into montmorillonite by two methods, namely (1) physical mixing of MMT with the inhibitor solutions and (2) physical mixing for short durations and evacuation of the mixture of MMT and inhibitor solutions. Coatings using these sols were deposited on aluminum alloy AA 2024-T4 substrates, by the dip coating technique followed by thermal curing at 130°C for 1 h. TEM, BET, and XRD analyses were carried out for the inhibitor-modified montmorillonite powders. Potentiodynamic polarization and electrochemical impedance spectroscopic analyses were carried out on uncoated and coated substrates to evaluate the corrosion protection property after exposure to 3.5 wt% NaCl for varying time durations, up to 120 h. Self-healing ability was evaluated using SVET analysis by creating an artificial scribe on the surface and exposure to 3.5 wt% NaCl. Elemental mapping was carried out on scribed substrates before and after exposure to 5 wt% salt fog. Sols containing montmorillonite intercalated with cationic inhibitors when deposited on AA 2024-T4 substrates exhibited low corrosion currents after a prolonged duration of exposure to corrosion medium.