Fabrication Of Silane Composite Films On Stainless Steel Surfaces And Studies Of Corrosion Properties In Seawater

The loss of national economy causing by metal corrosion arouses more and morehuman’s attention. Metal corrosion is a kind of damage proceeding slowly, corrosioncarrys on all the time. As a result, the loss caused by metal corrosion is enormous.Therefore, the corrosion protection of metal is intimately involved with the people’slivelihood and sustainable development of economy. As we all know, the beginning ofstainless steel corrosion is mainly located in the interface between metal andenvironment, corrosion goes deep into interior form metal suface step by step. So wecan prevent stainless steel corrosion at a certain extent by metal surface treatment torealizing anti-corrosion effect.Traditional Cr （Ⅵ）-based pre-treatments are harmful to human and environment,so the possible non-toxic and efficient anti-corrosion alternatives to chromate-basedtreatments are exigent. Pretreatment based on silane has attracted a considerableindustrial interest because silanes are known as good coupleing agents, conferringinaddition, corrosion protection. However, one major drawback with the applicationof silane pretreatment is that the coatings cannot offer an adequate long-termprotection due to the presence of micropores, cracks and areas with low-link density.And, the connatural defect of organic film also restricts the application of silane films.The research results indicate combining silane with other inorganic corrosionprotection system such as nanoparticles or metallic salts in silane solution to formorganic-inorganic silane composite film improved the defect of silane films effectively.In this paper, BTESPT/Ce silane composite film has been obtained on304stainless steel substrates （304SS）. At the same time, the effect of different cerium saltwas evaluated by electrochemical impedance spectroscopy （EIS）, and the resultsindicate that the BTESPT/Ce silane composite film using cerium nitrate as ceriumsource has the best corrosion protection to304SS. The surface microstructuremorphologies and chemical composition of the films were characterized by scanning electron microscopy （SEM）, and energy dispersive X-ray analysis （EDS）. The resultsshow that the addtion of cerium ions increase the surface roughness of silane film.The protective performance of BTESPT film and BTESPT/Ce silane composite filmwas evaluated by potentiodynamic polarization and EIS measurements, and the resultsindicate that the anti-corrosion property of BTESPT/Ce silane composite film is farbetter than BTESPT film. What is more, the stablility of BTESPT/Ce silanecomposite film and BTESPT film was evaluated in3.5wt.%NaCl solution, andBTESPT/Ce silane composite film performs much better durability than BTESPT film.It is generally accepted that the silanes and tetrabutyl titanate, which are hybridmolecules contain hydrolysable alkoxy groups, which after hydrolysis are convertedto silanol groups （SiOH） and TiOH, respectively. SiOH and TiOH adsorb on304SSsurface competitively, which increase the adhesion force of films onto the substratesurface. The BTESPT/TiO₂composite film was absorbed on304SS surface usingtetrabutyl titanate as titanium precursor. The corrosion protection performance ofBTESPT/TiO₂composite film was examined using potentiodynamic polarizationtechnique and electrochemical impedance spectroscopy in aerated3.5wt.%NaClsolution. The polarization technique and corrosion resistance measured by the bodeplots suggested that the BTESPT/TiO₂composite film exhibited superior performanceto that displayed by BTESPT silane film. And the long-term impedancecharacteristics of BTESPT/TiO₂composite film and BTESPT silane film were alsoinvestigated in aerated3.5wt.%NaCl solution by EIS. The results show theBTESPT/TiO₂composite film offer much better durability than BTESPT silane film,After15days immersion in3.5wt.%NaCl solution, the BTESPT/TiO₂composite filmstill had good protection ability. Firstly, the addition of TiO₂increases thecompactness of film, restraining the permeation of corrosion product and aggressivemedium, such as Cl-, H2O and O2. Secondly, TiOH and SiOH will absob on stainlesssteel surface synergeticly, which increasings the adhesion strength of interface. Itprevents the occurence of stripping in immersion. Thirdly, TiO₂will react withhydroxyl ion, forming titanate passive film, which will suppress the electrochemicalreaction of corrosion. Lastly, TiO₂will be corroded preferentially, preventing thesilane film from corrosion. TiO₂plays an athodic protection.One of the mechanisms of corrosion resisitance is TiO₂will be corrodedpreferentially, it plays an athodic protection. However, the protection will disappearwhen TiO₂work out. Multi-wall carbon nanotubes （MWCNT） were doped in BTESPT/TiO₂composite film to postpone the loss of TiO₂. In this part, multi-wallcarbon nanotubes was treated with TiO₂Sol, and then mixed with silane solution.BTESPT/TiO₂/MWCNT composite film was absorbed on304SS surface. Thecorrosion resistance of BTESPT/TiO₂/MWCNT composite film was investigated inaerated3.5wt.%NaCl solution by potentiodynamic polarization technique and EIS.The results show the BTESPT/TiO₂/MWCNT composite film offer much betterdurability than BTESPT/TiO₂composite film.