Application Of Graphite-like Carbon Nitride In Corrosion Resistant Coatings

Graphite-like carbon nitride（g-C₃N₄）is a two-dimensional semiconductor material,characterized with small particle size,large specific surface area,low density,high physical and chemical stability,stable electronic structure and simple preparation.Based on these advantages,g-C₃N₄ nanosheets can provide barrier effect for penetration of corrosive ions,having broad prospects for development in corrosion-resistant applications.Therefore,this study focuses on the contribution of g-C₃N₄ nanosheets to the enhancement of corrosion protection of epoxy resin（EP）and polypyrrole（PPy）on Q235 steel,as well as the coating forming performance.Firstly,melamine was used as carbon source and nitrogen source to obtain bulk phase g-C₃N₄（bulk g-C₃N₄）by high-temperature polymerization,followed by etching,stripping,and drying to obtain g-C₃N₄nanosheets.The prepared g-C₃N₄ nanosheets were characterized by X-ray powder diffractometer,transmission electron microscope,scanning electron microscope,Fourier transform infrared spectrometer,sedimentation experiment and particle size test.Subsequently,g-C₃N₄/EP composite coatings were prepared on the surface of Q235 steel by the scrape coating.The g-C₃N₄/EP composite coatings were tested in terms to salt corrosion resistance,acid corrosion resistance,adhesion,etc.Finally,g-C₃N₄/PPy composite films were obtained on the surface of Q235 steel by electrochemical co-deposition,and the effects of g-C₃N₄ nanosheets on the film-forming and corrosion resistance of polypyrrole films were then investigated.The main conclusions are as follows:（1）The results of XRD,SEM and TEM analyses showed that prepared g-C₃N₄ was a two-dimensional lamellar material with an average particle size of about 260 nm.The dispersion test showed that g-C₃N₄ had good dispersion.（2）The composite coating thickness of g-C₃N₄/EP prepared on the Q235steel surface was 40±5μm.Electrochemical impedance spectroscopy（EIS）and polarization curves showed that g-C₃N₄/EP composite coating had excellent corrosion resistance in Na Cl and H₂SO₄ corrosive solutions.The results of durability test indicated that the corrosion resistance of the composite coating immersed in Na Cl for 30 d was still better than that of the pure EP coating after 1h immersion.The adhesion of composite EP coating increased from 3B to 5B after2 wt.%of g-C₃N₄ was added to the pure EP coating.（3）The pure PPy film obtained by electrochemical potentiometry under the conditions of 1.5 V potential and 2800 s deposition time had the best corrosion resistance.g-C₃N₄/PPy composite film was obtained by co-deposition of g-C₃N₄and pyrrole monomers on the surface of Q235 steel under the above conditions.Corrosion resistance tests showed that the addition of g-C₃N₄ made the PPy film more corrosion resistant.SEM and EDS tests indicated that the addition of g-C₃N₄improved the film forming performance of PPy film.