Emerging action of corrosion prevention based on sustained self-healing coatings

The present study reports the mechanism of a silica-based novel self-healing/defect inhibiting coating for the efficient renewal of defects and corrosion on metal substrates, effective from sub-micron to mm dimensions. The coating predominantly employs silica nanoparticles that act as tiny containers evidencing a homogeneous mesoporous surface morphology. The containers were preloaded with the dopant of oxalic acid. After loading the container, aniline monomers were introduced to be preferentially adsorbed on the surface of the silica containers. The aniline on being doped by oxalic acid with electrons joins to form long chains of polyaniline (PANI), covering the entire surface of the silica containers, forming a protective sheet thereby forming sphere-like PANI-SiO2 reservoirs (PSR). The oxalic acid-PANI acts as a charge transfer complex where acid acts as a donor due to the oxalate and an inhibitor at the onset of corrosion, serving the original purpose. Also, Polyaniline (PANI) detects simultaneously and frequently to release the doping ion, and these ions passivate the metal, plus PANI back to the original position getting doping ions from the silica reservoir. The superior corrosion protection of this developed active system compared to traditional epoxy coating was confirmed by electrochemical impedance spectroscopy (EIS) and an imitated corrosion process by the scanning vibrating electrode technique (SVET) in 3% NaCl solution. The observations affirm that the sustained release behavior of the acid dopant is triggered by surface corrosion, revealing self-healing phenomena.