Preparation And Self-healing Properties Of Epoxy Composite Coating Containing Silane/Hollow Mesoporous Silica

Organic coatings are one of the most effective ways to improve the corrosion resistance of Mg alloy,but pure organic coatings can only provide it with passive protection.When the coating is influenced by the external factors such as stress and high temperature,or the internal factors containing hydrogen evolution,it is easy to produce micro-defects,accelerate the degradation of the coating,and cause serious corrosion of Mg alloy.It is very important to confer active protection properties on the organic coating in order to achieve long-term protection of Mg alloy.The coating can be offered self-healing ability by adding nanocontainers loaded with corrosion inhibitors,which can effectively extend service life of the coating.In this paper,silanes with different functional groups serve as corrosion inhibitors to achieve bidirectional self-healing of organic coating and metal substrate.The hollow mesoporous silica(HMS)with high thermal stability and adjustable micro-nano structure acts as the nano-container.A smart protective organic coating on the surface of the Mg alloy is constructed by HMS,silane and epoxy.This paper mainly includes the following aspects:1H,1H,2H,2H-perflfluorooctyltriethoxysilane(FTES)was used as a corrosion inhibitor and loaded into HMS(FHMS).Morphology,structure and silane loading of FHMS nanocontainers were characterized through scanning electron microscope(SEM),transmission electron microscope(TEM),energy dispersive spectroscopy(EDS),thermogravimetry(TG)and N₂ adsorption/desorption test(BET).FHMS epoxy resin coating was prepared the coating method on the surface of Mg alloy,and the corrosion resistance of FHMS epoxy coating was also investigated.The results show that the prepared HMS and FHMS particles have a hollow structure with a diameter between 350-400 nm.FHMS can enhance the corrosion resistance of epoxy coating.Especially for the FHMS-0.5%epoxy coating,its low-frequency impedance modulus can still reach 6.29×10⁸?·cm²after 2688 hours of immersion in 3.5 wt%Na Cl solution,and there is no obvious corrosion on its surface.The self-healing performance of FHMS epoxy coating was studied by artificial micro-defect test.The results show that FHMS-0.5%epoxy coating has good self-healing properties.The micro-defects of the coating are self-healed after 7 hours,which makes the service life of the coating effectively extend.HMS loaded with bis-(3-(triethoxysilane)propyl)-tetrasulfide(KH-69)was prepared(HMS-69)under vacuum and added into the epoxy resin in three proportions(0.2%,0.5%and 1%).Electrochemical impedance spectroscopy(EIS)was used to evaluate the corrosion resistance and self-healing properties of the coating on Mg alloy surface.The results show that the corrosion resistance of HMS-69-0.2%and HMS-69-0.5%coatings is significantly improved compared with EP coating.It is found that the coating resistance(R_c)and charge transfer resistance(R_ct)values of the HMS-69-0.5%coating by fitting the EIS data increase wavelike during the immersion period,suggesting that the coating has good self-healing performance.HMS(HMS-560)loaded with 3-glycidoxypropyltrimethoxysilane(KH-560)was added to the epoxy coating on the surface of the Mg alloy.The corrosion resistance of epoxy coatings with different contents of HMS-560 is investigated.The results show that HMS-560 can effectively enhance the barrier performance of epoxy coating.The artificial micro-defects were measured by SEM,EDS and XPS.Silane can release from HMS to produce Si-OH by hydrolysis when it encounters the electrolyte solution.This hydroxyl group can interact between epoxy resin and Mg alloy matrix by chemical bond.Meanwhile,it can also form by itself a hydrophobic crosslinked silane network.These hinder the penetration of the electrolyte solution to the matrix and coating,and inhibit the corrosion electrochemical behavior.Finally,the micro-defects of the coating are healed.