Study On The Protective Effect And Mechanism Of Silane Epoxy Coating On Steel Bars In Different Corrosive Environment

Reinforced concrete is widely used in marine engineering because of its abundant raw materials,convenient construction and low cost.However,the harsh marine corrosive environment seriously threatened the durability of reinforced concrete.In particularly,the corrosion of steel bars caused by the penetration and diffusion of high-concentration chloride ions is the primary factor leading to the destruction of concrete structures.Therefore,the corrosion and protection of steel bars has become an extremely important topic.Applying organic coatings on the surface of steel bars is considered to be a reliable technique for preventing corrosion,and the most commonly used coating is epoxy anti-corrosion coating.However,the high brittleness and porosity of epoxy coating as well as the weak interface bonding features between epoxy and steel bar greatly limited the protective performance of epoxy coating.In addition,the corrosion media inside concrete are complex and variable,such as p H and corrosion ions,which have a significant impact on the protective performance of epoxy coatings.In this paper,ethyl orthosilicate（TEOS）and isobutyltriethoxy-silane（IBTS）were used as raw materials to prepare silane coating by electrodeposition to enhance the protection performance of epoxy coating on steel bars.At the same time,the influence of p H and different erosion ions on the corrosion resistance of silan-epoxy coating was studied.The anticorrosive effect and mechanism of the coating were studied by means of microscopic characterization and electrochemical experiments,which was committed to providing theoretical guidance for the development of green and long-lasting epoxy anticorrosive coating.The research content of this paper includes three parts:The main research results are as follows:（1）Using silane to improve the interfacial interaction between epoxy and reinforcement matrix,and revealing the mechanism of silane improving the corrosion resistance of epoxy coatings.Electrodeposited silane can form reliable covalent bonds with carbon steel and epoxy.Due to the hydrophobicity of the silane coating,the time of electrolyte penetrate into the carbon steel surface is effectively delayed in the early exposure period.In the medium term,the passivation product of steel can fill the pores in the silane film and make the film denser.In the later stage of exposure,the development of corrosion products from the carbon steel surface is limited by the tight connection between the silane coating and the carbon steel,which reduces the expansion stress of the corrosion products on the entire coating and reduces the cracking of the coating.（2）Aiming at the characteristics of the variable p H inside concrete,the regularity of the protective performance of silane epoxy coatings varying with p H was studied.During the whole process from alkaline to neutral inside the concrete,the silane-epoxy coating will not lose its protective effect.After the corrosive solution is penetrated into the silane coating,the silane coating can also undergo recondensation reaction to further enhance the corrosion resistance of the silane-epoxy coating.At the same time,with the increase of p H the recondensation reaction is enhanced.The p H of corrosive solution can also affect the corrosion products of carbon steel under silane coating.The type of corrosion products also affects the corrosion resistance of the coating to a certain extent.（3）Silane coating can significantly reduce the corrosion of carbon steel in KCl solution.The critical concentration of chloride ion of bare steel is 0.5%in the three chloride salt corrosive solutions.The critical chloride ion concentration of carbon steel can be increased to 1.5%by silane coating in Ca Cl₂corrosive solutions with p H of 12.5and 9,and to 2.0%and 1.0%in KCl and Na Cl corrosive solutions with p H of 12.5.