Superhydrophobic oligoaniline-containing electroactive silica coating as pre-process coating for corrosion protection of carbon steel

This paper provided a novel coating system for Q235 steel using electrodeposited oligoaniline modified silica coating (E-M-SiO₂) as a pre-process coating, which was prepared by one step coelectrodeposition of a mixture of tetraethyl orthosilicate (TEOS) and N,N′-Bis(4′-(3-triethoxysilylpropylureido)-phenyl)-1,4-quinonenediimine (TSUPQD). Microstructure, contact angle, electroactivity and anticorrosion performance were investigated by FTIR, UV–vis, AFM, SEM, OCA20 contact angle analyzer, CV and CHI-660E electrochemical workstation. The CA test indicated, in comparison with pure silica and sol–gel modified silica hybrid coatings, the electrodeposited modified silica coating exhibited a super hydrophobic performance. The CV test illustrated that the special redox property of aniline trimer was maintained in these modified silica hybrid coatings. More importantly, the anticorrosion effectiveness for Q235 steel in 3.5% NaCl solution was improved by the addition of oligoaniline modified silica as the pre-process coating. By comparison, it turned out that the epoxy/E-M-SiO₂ coating system presented the lowest i_corr value and the highest |Z|_0.01Hz value. The corrosion protection mechanism was the synergistic effect of super hydrophobic nature of E-M-SiO₂ pre-process coating and special catalytic capability of aniline trimer unit, which effectively restrained the permeation of corrosion medium and induced the formation of passive films consisted of α-Fe₂O₃ and Fe₃O₄ on the Q235 surface.