Fabrication Of Silane Hybrid Films On Metallic Substrates And Research On Anti-corrosion Properties In Seawater

Metal material corrosion phenomenon is everywhere, not only brings hugeeconomic losses to the society, but also obstacles the development of science andtechnology. The beginning of metal corrosion is mainly located in the interfacebetween metal and sea, and the corrosion goes deep into interior form metal suface stepby step. Consequently, metal surface treatment could prevent or delay the metalcorrosion. Traditional metal surface treatment technology （chrome treatment） is toxicand cost much. So it is an important topic to develop a environment friendly, low cost,easy-operate metal anticorrosion technology.Previous studies showed that silane film is easy to form on metal surface afterhydrolysis, but the coatings cannot offer an adequate long-term protection due to thepresence of micropores, cracks and areas with low-link density. Combining silane withother inorganic corrosion protection system such as nanoparticles or metallic salts insilane solution to form organic-inorganic silane composite film improved the defect ofsilane films effectively. In this paper, bis-[triethoxysilylpropyl] tetrasulfide（BTESPT）/TiO₂/multi-walled carbon nanotube （MWCNT） silane composite film hasbeen obtained on304stainless steel substrates （304SS） by dip-coating method. Thedurabilities of the BTESPT/TiO₂and the BTESPT/TiO₂/MWCNT composite filmswere further evaluated by electrochemical measurement technology. Potentiodynamicpolarization results suggest that BTESPT/TiO₂/MWCNT composite films exhibited abetter electrochemical stability to BTESPT/TiO₂composite films. Besides,electrochemical impedance spectroscopy （EIS） results indicate that theBTESPT/TiO₂/MWCNT composite films display long-term protection propertity to304SS. In seawater environment, TiO₂will be corroded preferentially due to Cl-. ButTiO₂could be fixed on the composite films with the addition of MWCNT. In addition,MWCNT increases the density and intensity of the films, as the result, the compositefilms can prevent the intrusion of the corrosive medium effectively. The BTESPT/TiO₂silane composite films anticorrosive system is introduced inthe2024aluminum alloy substrate, but the adhesion between film and substrate isweak which would have impact on the corrosion resistance in seawater. To overcomethese problems, BTESPT silane film, BTESPT/TiO₂and BTESPT/TiO₂/MWCNTsilane composite films were successfully prepared on AA2024substrates by cathodicelectro-deposition method. Scanning electron microscope （SEM） results showed thatthe thickness, compactness and uniformity of BTESPT film prepared by cathodicelectro-deposition method are superior to dip-coating method. Potentiodynamicpolarization results suggest that BTESPT/TiO₂silane composite films prepared byelectro-deposition method could prevent the intrusion of the corrosive medium moreeffectively. And the long-term impedance characteristics of BTESPT/TiO₂/MWCNTcomposite film and BTESPT/TiO₂silane film were also investigated in aerated3.5wt.%NaCl solution by EIS. The results show the BTESPT/TiO₂/MWCNT compositefilm offer much better durability than BTESPT/TiO₂silane film. On the one hand, thefacilitation in film formation at cathodic potentials was believed being caused by theOH-condensation of silanols （Si-OH） by oxygen reduction or water electrolysisreaction near the electrode surface, which will increase the Si-O-Me andTi-O-Mecovalent bond between films and substrates. On the other hand, the carboxyl group ofthe MWCNT could form chemical bonds with BTESPT and TiO₂which will increasethe compactness and prevent the fall off of the films.