Construction Of A Novel Anticorrosion System Based On The Use Of Electrodeposited Silica Films

Coating system has been widely used for corrosion protection of metals. A painting system comprises at least two individual compartments:the pre-treated conversion layer (CL) and top-coat. Most of the effective painting systems use chromate or phosphate films as the CLs. These conventional CLs offer satisfactory adhesion and, in turn, ensure the excellent corrosion protection properties of the final painting system. Unfortunately, chromium (VI) is highly toxic and has carcinogenic effects on humans, while phosphorus can lead to water eutrophication. The application of chromate and phosphate were restricted by these reasons. Searching for a new generation of pretreatment technique, not only providing desired corrosion prevention property but also being environmentally friendly, is urgent for both academic research and industrial applications. Inorganic, organic and inorganic-organic hybrid sol-gel derived films have been used as the alternatives of chromate or phosphate-based pre-treatments. These methods were not been widely used due to thicker oxide films (>1μm) are difficult to achieve without cracks, or the specific selectivity between the sol-gel film and the organic coatings. Many efforts have been done to solve these problems, such as doping rare earth element to silane film. However, there were no effective ways to solve the compatibility between sol-gel film and top-coat. In this thesis, we report for the first time to use highly rough and porous electrodeposited pure silica (E-SiO2) film as the pre-treated layer for a variety of metallic substrates, aiming to develop a new generation of corrosion protection system. The main contents are listed as follows:(1) The E-SiO2film was used as the pretreatment layer of metal/epoxy coating system. It was observed that the E-SiO2film, which was combined with the substrate through M-O-Si chemical bond and has highly porous surface, has good adhesion both to the substrate and to the top-coat. Electrochemical impedance spectroscopy (EIS) and salt spray test (SST) results suggested that the corrosion performance of the newly developed system was even superior to phosphate-and chromate-pretreated technique. In addition, the E-SiO2film was used as receiver for corrosion inhibitor (BTA). EIS and immersion test suggested that metal/coatings system after pretreated with the E-SiO2film+BTA exhibited better corrosion protection property.(2) The E-SiO2film provided a novel approach for the fabrication of super-hydrophobic films. It is well-known that two requirements are desirable for fabrication of super-hydrophobic films, one is the high surface roughness and the other is the low-surface-energy materials. Our research demonstrated that the E-SiO2film surface was highly rough. The surface roughness and thickness were changeable by adjusting the applying potential and time of the electro-deposition process. Super-hydrophobic films were obtained after coated with dodecyltrimethoxysilane (DTMS). Contact angle (CA) test results suggested that the CA was increased with prolonging the deposition time and potential. EIS test results demonstrated that corrosion protection property of super-hydrophobic films were better than general films.