The composite protective coating is the most widespread technology among various methods used in corrosion protection for the marine industry. Carbon-based materials are the most promising as anticorrosion pigments due to its mechanical strength, chemical inertness, non-cytotoxicity, and very strong absorption of ultraviolet (UV) and visible light. In present study graphene oxide (GO) and multiwalled carbon nanotubes (MWCNT) were investigated as addictive and also, they were modified by nitrogen-doping. The samples of stainless steel (316L) coated by epoxy resin with carbon-based pigments were exposed to UV irradiation (340nm) for 1000h and corrosion behavior in 3.5 wt% sodium chloride (NaCl) solution was investigated before and after UV degradation. Experimental results showed that corrosion current significantly decreased in presence of carbon-based materials, especially nitrogen-doped ones, in the composite coating. The degradation of the epoxy coating after UV exposure was retarded by the presence of the GO, MWCNT and the nitrogen-doped pigments, suggested that carbon-based nanomaterials may enhance the lifetime of composite coating. Finally, a protection mechanism was built to explain the carbon-based nanomaterials improved corrosion resistance and effect of nitrogen-doping on the corrosion behavior.
Protective coatings are widely used in corrosion prevention. The main advantage of it is that they are easy to apply and maintain compared with other methods and they provide long-term protection in different corrosion environment.1 Marine environment is the most aggressive one.2 A number of factors, such as moisture, temperature, winds, airborne contaminants, chloride ion, electrical conductivity, oxygen concentration, pH, pollution, and biofouling contribute to marine corrosion.3 The coating system should meet with the requirements such as corrosion protection, water impermeable, abrasion resistance, smooth, antifouling, weather and UV resistance, impact, and scratch - resistant.4 Red lead, lead silicochromate, zinc chromate, calcium, strontium and zinc molybdate, calcium plumbate, zinc phosphate, zinc dust, micaceous iron oxide are used as anticorrosion pigments.5 But the most of these pigments are very toxic and nowadays do not use in industry. Carbon-based materials are alternative and very promising anticorrosion pigment. There are several forms of nanostructured carbons which might be used: graphene,6-11 carbon nanotubes,12,13 and fullerenes.14 These materials have extremely high mechanical strength, exceptional chemical inertness, non-cytotoxicity, outstanding thermal and electrical conductivity, very strong absorption of UV and visible light to protect the paint from degradation and excellent antibacterial/anticorrosive properties.15,16 The mechanism of protection by graphene is based on the barrier formation which will reduce the permeability of water and oxygen atoms.17 Carbon nanotubes compared with graphene have different mechanisms of protection. Carbon nanotubes can play not only barrier effect but also passivation effect via adsorbing molecular species in three ways: on the end of the nanotube, on the side of the wall and inside the carbon nanotube.18,19