| Metal corrosion spread widely in various fields of national economic development,resource consumption and economic losses caused by the corrosion phenomenon severely limit the development of the national economy,therefore,delaying or curbing metal corrosion has become a hot issue for many researchers.Coating protection method is the most commonly used and effective metal protection measure.The traditional solvent-based coating system contains a certain amount of volatile organic compounds(VOCs),which seriously pollutes and harms the environment.At present,it has gradually transformed from the use of traditional solvent-based coating into the development of environment-friendly waterborne coating.Waterborne coating system usually contain hydrophilic groups and surfactants,which will limit the barrier effect on corrosion media,and the corrosion protection performance still needs to be improved.Graphene possess one-atom-thick structure and impermeability,which shows a broad application prospect in the field of corrosion protection.Adding graphene as filler into waterborne coatings can significantly improve the corrosion protection performance of the coatings.However,due to the large specific surface area,high surface energy and strong interlayer force of graphene,it is easy to agglomerate in the coating matrix,resulting in defects in the internal structure of the coating and the comprehensive performance of the coating.Therefore,in this paper,the surface modification of graphene oxide by vinyl triethoxysilane and poly(3,4-vinyldioxythiophene)are carried out to realize the good dispersion of graphene in waterborne coatings,respectively.The basic physical properties and corrosion resistance of graphene composite coating are characterized by adhesion strength,hardness,EIS,Tafel curve,salt spray test and water absorption test.The main research contents and results are as follows:(1)Hydrophobic condensation reaction of vinyl triethoxysilane is used to prepare hydrophobic silane-functional graphene composite which contact angle is 95.8°.Due to the presence of vinyl sesquioxane on the surface of graphene sheet,the interfacial compatibility between graphene and waterborne polyurethane matrix is improved,and SEM image of the cross-sectional and surface morphology confirm that 0.5wt.%PVSQ-GO/WPU composite coating exhibits fewer defects in the internal structure;Compared with pure polyurethane coating,the basic physical properties of graphene composite coating have been improved to a certain extent.The hardness of 0.5wt.%PVSQ-GO/WPU composite coating is 11.9HV,the adhesion strength is 2.97MPa,and the friction mark is shallow.EIS measurement results show that the impedance modulus|Z|f=0.01Hz value of 0.5wt.%PVSQ-GO/WPU composite coating is still maintained at a high level after immersion time for 30 days in 3.5wt.%NaCl solution,,the corrosion potential is-0.325V,the corrosion current density is 7.079×10-9A·cm-2,which decreases by two orders of magnitude compared with the pure polyurethane coating.The picture of the salt spray test after 200h exposure time exhibits less corrosion area of 0.5wt.%PVSQ-GO/WPU composite coating,which shows that it has excellent corrosion resistance.When the amount of PVSQ-GO composite is added up to1.0wt.%,the excess graphene cannot be dispersed uniformly,which resulting in the formation of defects inside the coating,and the performance of the coating will decline.(2)Graphene oxide is prepared by Hummers method,and conducting polymer graphene composite are prepared by self-polymerization of 3,4-ethylene dioxothiophene monomer.FT-IR,UV-vis and Raman spectra confirm the presence of?-?bond interaction between the poly(3,4-ethylenedioxythiophene)molecules and graphene oxide after the polymerization reaction,and AFM results show that the thickness of graphene oxide is exfoliated to 1.6?2.3nm.The results of cross-sectional morphology and Raman spectrum surface scanning show that the PEDOT-GO composite exhibit good dispersion in the waterborne epoxy matrix.The hardness of PEDOT-GO/WEP composite coating is 0.25GPa,and the adhesion strength was 4.21MPa.Compared with the pure WEP coating,the thermal stability of PEDOT-GO/WEP composite coating is improved due to the good physical barrier effect of graphene,and at the same time,the penetration of corrosive medium is also delayed,|Z|f=0.01Hz value is still maintained at about 108ohm·cm2 after immersed in a 3.5wt.%NaCl solution for 40days,and the water absorption rate is decreased to 9.90wt.%,which shows better protection performance.On the one hand,it is due to the blocking effect to corrosive medium of graphene,on the other hand,it is due to the electrochemical activity of poly3,4-ethylenedioxythiophene,which induces the formation of passivation layer on the surface of metal matrix so as to further protect the metal substrate. |
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