Fabrication of poly(N-methylaniline)/SiC-ZnO bilayer coatings onto the carbon steel substrate and studies on its anticorrosion properties

Abstract In this investigation, a comparative study on the anticorrosion properties of poly(N-methylaniline) (PNMA) coating, as well as PNMA-ZnO and PNMA/SiC-ZnO bilayer coatings, was carried out. The polymeric materials (PNMA and PNMA/SiC composite) were synthesized by emulsion polymerization method. The structures of the obtained polymeric materials were determined by different optic techniques, and the electrochemical activity and stability were examined by cyclic voltammetry. Subsequently, PNMA was spread on the surfaces of carbon steel and ZnO coating by chemical deposition method, and PNMA/SiC was spread on the surface of ZnO coating, which led to obtaining PNMA coating, PNMA-ZnO and PNMA/SiC-ZnO bilayer coatings. The structures of ZnO coating were characterized by X-ray diffraction and energy dispersive spectrometer, and the surface morphologies of all the coatings were also studied by field emission scanning electron microscopy. The anticorrosion properties of all the coatings were evaluated by electrochemical corrosion and accelerated immersion in the presence of a 3.5% NaCl solution. The results demonstrated that the polymeric materials-ZnO bilayer coatings had excellent corrosion protection ability, and in specific, for the carbon steel protected by PNMA/SiC-ZnO bilayer coatings it was higher than PNMA-ZnO bilayer coatings, with a corrosion rate of 0.004 mm/year and the protection efficiency was up to 97.43%. Overall, this study proves that the rough ZnO coating is beneficial to the embedding and pinning of polymeric materials, and the formed PNMA/SiC-ZnO bilayer coatings possess a strong adsorption ability and wide coverage area to the carbon steel substrate, which facilitates the external PNMA/SiC film to develop its unique barrier and passivation effects to prevent carbon steel from being corroded. The protection mechanism conferred by polymeric materials-ZnO bilayer coatings has also been discussed.