| Corrosion is one of the main failure forms of materials,which causes numerous accidents and economic losses every year.Among the many protection methods,coating protection is the most widely used protection method due to its convenience and economy.Graphene has excellent properties and can be used as a nanofiller to improve the performance of coatings.The importance of coating is far greater than the coating itself.Coatings can play their role in decoration,protection and the special functions only after coating and forming a film.In previous studies,the research on organic coatings focused on the influence of coating composition on the microstructure and properties of coatings,while ignoring the influence of coating methods on coatings.Many studies have shown that spraying and dipping are beneficial to form a microscopic rough structure with a hydrophobic surface and improve the anticorrosion performance of the coating.Therefore,based on the rare earth modified graphene and water-based epoxy resin coatings in the previous research,this paper uses air spraying,roller coating and brush coating to prepare coatings on the surface of Q235 steel and 6061 aluminum alloy substrates to study the effect of different coating methods on the structure and properties of coatings.The main results are as follows:(1)Rare earth modified graphene waterborne epoxy resin composite coating is mainly composed of water-borne epoxy resin emulsion,curing agent and 0.5 wt%rare earth cerium modified graphene.Macroscopically,the composite coating is a uniform grey-black,while microscopically,graphene is distributed evenly on the epoxy resin in small layers.After curing,the cross-section fracture of coating has a typical river-like "silver streak".In addition,there is a physical bond between graphene and epoxy resin.(2)Modified graphene water-borne epoxy composite coating was coated on steel substrate and aluminum substrate by spraying,rolling and brushing respectively.After curing at room temperature,the surface of the coating was uniform grey black with no obvious pores.Microscopically,the coating has a stacked structure of lamellar graphene.The bonding force and hardness of composite coating are improved by the introduction of graphene,the adhesion level of the coating is 0～1 and the hardness is 2H.The surface roughness of the coating is～2μm,showing a certain hydrophilicity.(3)The thickness of the modified graphene waterborne epoxy composite coating prepared by spraying,rolling and brushing on steel and aluminum substrates ranged from 30 μm to 90μm.The thickness increases in turn due to the obvious difference in the force of coating molecules under different coating methods.Spraying method uses the pressure of the external high-pressure gas to make the coating molecules impact the surface of the substrate.Rolling and brushing apply pressure with the help of wire rod coater and soft brush,and the pressure is gradually reduced.(4)On the steel substrate,the corrosion current density(Icorr)of the composite coating by spraying,rolling and brushing is 0.013 μA·cm-2,0.492 μA·cm-2,0.198 μA·cm-2.Compared with epoxy coating,the corrosion rate decreased by～420 times,～2 times and～4 times.On the aluminum substrate,the Icorr of the composite coating by spraying,rolling and brushing is 9.937×10-4 μA·cm-2,2.127×10-4 μA·cm-2,1.225×10-4 μA·cm-2,respectively.Relative to pure epoxy coating,its corrosion rate decreases by～1350 times,～1070 times and～300 times.Among them,spraying method has the highest improvement on coating performance.(5)Spraying method is the best coating way for preparing rare earth modified graphene waterborne epoxy resin coating.The process is spraying on the pretreated substrate surface with a pressure 0.2～0.3 MPa,and then cured at room temperature.Its protective mechanism is that the coating molecules with a certain viscosity are driven by the high-speed moving gas to impact the surface of the substrate and quickly accumulate and spread to form a film,which is tightly bonded with the substrate while purifying the surface.The coating is further thickened and densified under several subsequent small-energy impact,resulting in an ideal protection performance. |
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