Construction of stable passivation sites in coatings by functionalized surface modified fly ash and its unique anti-corrosion properties

In this study, nitrogen-doped carbon quantum dots with non-covalently functionalized imidazole groups on their surface were chemically grafted onto fly ash filler via hydrothermal synthesis and equivalent-volume impregnation. An epoxy composite coating was then prepared by spraying. The I-CFA filler uses citric acid as carbon source and imidazole as nitrogen source, and a large number of nitrogen-doped carbon quantum dots are grown in-situ in the fly ash surface and inside, thereby improving the compatibility of the filler and epoxy resin. In addition, when the coating is damaged, nitrogen-doped carbon quantum dots will be released, and the imidazole groups on their surface can act as corrosion inhibitors to chemically adsorb Fe atoms on the surface of the substrate, and a continuous complexation reaction can be formed to form a passivation protective film grown in situ, which is adsorbed on the surface of carbon steel, thus playing a good barrier effect and slowing down the erosion of corrosive media. Compared with pure epoxy coating, the impedance modulus of I-CFA composite epoxy coating after double modification is 1000 times higher at common temperature condition, and 10⁵–10⁶ times higher at harsh CO₂-rich high temperature and high pressure conditions. This study is expected to provide new insights into the preparation of fly ash coatings with unique functions.