Enhanced corrosion resistance and adhesion of epoxy coating by two-dimensional graphite-like g-CN nanosheets.

Graphene is usually used to enhance the corrosion protection of epoxy (EP) coating. Graphite-like CN (g-CN) nanosheets can be a substitute for graphene to perform good barriers for the penetration of corrosive ions. Herein, g-CN nanosheets were obtained via calcining melamine at 520 °C for 3 h (bulk g-CN) and exfoliating bulk g-CN by supersonic stirring for 10 h. The EP coatings with different levels of g-CN nanosheets performed better corrosion protection for Q235 steel. Compared with pure EP coating, the maximum enhancement of corrosion resistance was achieved by the addition of 2 wt% g-CN in EP coating, with an increase of electrochemical impedance by two orders of magnitude in 3.5 wt% NaCl solution and an order of magnitude in 0.1 M HSO solution, as well as a decrease of corrosion current by nearly two orders of magnitude and an order of magnitude in above-mentioned electrolyte solutions, respectively. The immersion test demonstrates the good durability of 2 wt% g-CN/EP coating against corrosion. Also, it is interesting to note that the addition of g-CN nanosheets enhanced the adhesion of EP coating from 3B to 5B rating thanks to the formation of hydrogen bonds between CN nanosheets and EP as well as steel surface.