| Corrosion is an inevitable catastrophic destruction of metallic structures and has major impacts on economics of industrial nations,Coating is an important way of protection against metal corrosion.Among various type of coating,epoxy coating is widely used to protect metals against corrosion due to its excellent stability,wear resistance and low price,etc.Therefore,researchers have been paying attention to enhance the corrosive protection properties of the epoxy coating by improving its properties.Recently,due to the excellent properties exhibited by nanomaterials,the addition of nano-sized materials as fillers to epoxy coatings has been considered a good way to enhance corrosion protection and barrier performance.As a new type of two-dimensional nano-carbon material,graphene is a good material for enhancing corrosion resistance and barrier properties.However,due to van der Waals forces and the n-n interaction between graphene sheets,the graphene tends to agglomerate,leading to low surface area and poor dispersibility.As the derivative of graphene,graphene oxide has abundant functional groups on the surface and is easy to disperse in polymer matrix than graphene,so the modification of graphene oxide is currently a hot topic.In this thesis,to solve the problems of poor dispersibility and agglomeration of graphene oxide in epoxy coating,the graphene oxide was modified with 2-aminobenzimidazole and 3-mercaptopropyltriethoxysilane,respectively,to increase the physical compatibility between the fillers(e.g.functionalized graphene oxide)and polymer matrix(e.g.epoxy coating).And,the structure of functionalized graphene oxide was characterized by modern spectroscopic methods and high resolution microscopic techniques such as infrared spectroscopy(IR),X-ray diffraction(XRD)and scanning electron microscopy(SEM),etc.Afterward,the corrosion electrochemistry behaviors of mild steel covered by the functionalized graphene oxide-epoxy coating in 3.5%NaCl solution were investigated by means of the traditional electrochemical methods like potentiodynamic polarization curve and electrochemical impedance spectroscopy(EIS),etc.The inhibition mechanisms of the functionalized graphene oxide-epoxy coating to corrosion of mild steel were explored further.The main work is as follows:(1)Study on the preparation of graphene oxide-epoxy coating and its corrosion protection properties for mild steelIn order to explore the effect of content of graphene oxide on the dispersibility in the epoxy coating matrix,the addition of graphene oxide with different contents of 0.05%,0.1%and 0.2%,respectively,to epoxy coating matrix was done to prepare a series of composite epoxy coating.The results of polarization curves and EIS showed that the mild steel covered with epoxy coating with addition of 0.1%graphene oxide exhibited higher impedance modulus and lower corrosion current density in 3.5%NaCl solution,which is probably due to the fact that the addition of an appropriate amount of graphene oxide would prolongate the permeation pathway of aggressive ions and consequently enhance the anti-corrision resistane of the mild steel.If the content of the graphene oxide exceeds 0.1%in epoxy coating,the graphene oxide will agglomerate,which will decrease the physical barrier properties of the coating and lower its corrosion protection capabilities.(2)Study on the preparation of 2-aminobenzimidazole modified graphene oxide-epoxy coating and its corrosion protective properties for mild steelFunctionalized graphene oxide was prepared by covalent reaction between 2-aminobenzimidazole and graphene oxide.IR and EDS results indicated that amide bonds were formed in the functionalized graphene oxide,leading to a steric effect,which will reduce the van der Waals forces between graphene sheets,inhibit the agglomerating tendency of the graphene sheets,improve the stability of dispersion and finally increase the physical barrier properties.A graphene oxide-epoxy resin coating and a functionalized graphene oxide-epoxy resin coating were coated on the mild steel surface,respectively,and the corrosion resistance was investigated.The results of electrochemical studies showed the addition of 0.1%functionalized graphene oxide to the epoxy coating had excellent protection performance and obviously enhanced the corrosion resistance of mild steel.(3)Study on the preparation of 3-mercaptopropyltriethoxysilane modified graphene oxide-epoxy coating and its corrosion protective properties for mild steelA new type of functionalized graphene oxide was prepared by dehydration condensation reaction between 3-mercaptopropyltriethoxysilane and graphene oxide.The results of IR,SEM and XRD indicated that the graphene oxide is combined with 3-mercaptopropyltriethoxysilane by the formation of C-O-Si bonds.Then,different weight fractions of functionalized graphene oxide were added to the epoxy coating to study the effect of 3-mercaptopropyltriethoxysilane functionalized graphene oxide on the properties and protection mechanisms of the composite coatings.It was found that,by adding 0.1%functionalized graphene oxide to the epoxy coating,the corrosion resistance of mild steel coated with functionalized graphene oxide-epoxy resin coating was improved greatly.The key reason is that the covalent bond was formed beween the groups of graphene oxide and epoxy resin molecules,which strengthened the crosslinking density of the composite coating,formed effective physical barried network,extended the diffusion pathway of aggressive ions and reduced the permeation efficiency.Therefore,corrosive media were effectively inhibited to arrive in the interface between coating and metallic substrate to enhance the corrosion protection capabilities of the coating. |
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