Silane Post-treatment Of Electrodeposited Silica Films And Their Application In Organic Coating System

As a kind of new green pretreatment method, silane pretreatment technology is receiving more and more extensive and in-depth research, due to its good performance, environmentally friendly and energy saving preparation process, and its potential as an alternative of traditional phosphorization and chromation metal pretreatment process. Because of its flexible regulation and the good performance of so produced membrane layer, electrochemical assisted deposition (EAD) method in silane sol-gel film preparation has become a new research hotspot in recent years. In the previous work, our group proposed to use electric-assisted deposited E-SiO2film as the organic coating pretreatment layer. With the M-O-Si bond and the roughness of E-SiO2film, there could establish great adhesion between metal substrate and organic coating. Based on this work, we used E-SiO2film as a skeleton template, modified a layer of organosilane with the method of dip coating, and build a new type of metal protective coating system with the so produced complex pretreatment layer. FT-IR, TG and other test results suggest that some organosilane adheres in E-SiO2film in the form of physical adsorption, while a small amount of organosilane is evenly distributed on the surface of SiO2microspheres in the form of chemical bonding. Study shows that organosilane modification enhances the hydrophobicity of E-S1O2film so as to endow the E-SiO2pretreatment layer with some degree of short-term protective property, while it keeps the surface roughness of E-SiO2film in general so that the adhesion with subsequent organic coating is retained. How well the short-term protective performance is is associated with the hydrophobicity of organosilane. On one hand, the strong hydrophobicity of organosilane provides the pretreatment layer with the ability of blocking the invasion of external corrosive medium (H2O et al), thus establishes better protection property. While on the other hand, if the organosilane is too hydrophobic, it would be too difficult to be dissolved out when the pretreatment layer is damaged, thus losses the self-healing function. From the SEM image of [E-SiO2/organosilane/epoxy coating] cross section structure, we can observe that epoxy coating permeates well into the porous structure of E-SiO2skeleton. But the too much organosilane or too hydrophobic organosilane may form gel microspheres and blocking part of the channel of the E-SiO2film, reducing the permeability of the coating, and thus the coating adhesion would be certain effected. The introduced organosilane modification layer not only enhances the blocking performance of corrosive medium (H2O et al) of the Metal/E-SiO2/epoxy coating protective system, bus also plays as a role of self-healing component, since organosilane can be dissolved out and gather to form condensation gel on the broken spot when the coating gets damaged. Electrochemical impedance spectroscopy (EIS), Machu test, salt spray test, Fe2+dissolution quantity test and other researches show that the epoxy coating system with organosilane modified E-SiO2film as pretreatment lay has very good adhesion and anticorrosion performance, and vast application prospect.