Preparation and corrosion resistance of phosphorus-nitrogen graphene-sulfonic acid-doped polyaniline/epoxy emulsion composite coatings

To further enhance the dispersion of graphene-polyaniline （GO-PANI） composites in aqueous epoxy emulsion （EPE） and improve the long-term corrosion resistance of the composite coating, phosphorus-nitrogen graphene （PNGO） was prepared by modified graphene oxide （GO） with phytic acid （PA） and ammonia （NH₃·H₂O）, and PNGO-PANI（SA） composites were prepared by in situ chemical polymerization of sulfonic acid-doped polyaniline （PANI（SA）） on the surface of PNGO lamellae. The PNGO-PANI（SA）/EPE composite anticorrosion coatings were prepared on the surface of Q235 steel using EPE as the film-former. The structures of PNGO-PANI（SA） were characterized by XPS, SEM and TEM, etc. The anticorrosion ability of the composite coating was tested by electrochemical impedance and polarization curves, etc. The PNGO-PANI（PSSA）/EPE composite coatings showed the best corrosion resistance when molar ratio of polystyrene sulfonic acid to aniline （n（PSSA）׃n（Ani）） is 1׃1, the impedance value reaches 5.24×10⁹ Ω·cm², the corrosion current density is merely 1.49×10⁻¹⁰ A/cm². The impedance value still reaches 10⁸ Ω·cm² or more even after 960 h immersion, and no obvious corrosion marks appear after 480 h of salt spray test. This study provides a new process route for the preparation and application of water-based composite anticorrosive coatings.