| Summary: | 碩士 === 國立高雄應用科技大學 === 化學工程與材料工程系博碩士班 === 105 === Modified silica-based sealing layers are prepared to improve the corrosion resistance of galvanized steel in this study, as well as compared with phosphate-based passivation layers. The silica-based sealing layers were formed through dip-coating the surface a sol solution prepared by the sol-gel process using tetraethoxysilane (TEOS; T) or/and mixing with 3-glycidylpropyloxy-trimethoxysilane (GPTMS; G) as the sol precursor, and then drying the coating on the surface of galvanized steel to form a cured layer. The phosphate-based passivation layers were formed by soaking the galvanized steel in phosphate passivation solution of nickel nitrate added, or manganese nitrate added, respectively, and then rinse and drying. Fourier Transform Infrared Spectrometer (FT-IR), Scanning Electron Microscope (SEM), Potentiostat, Ink-Penetration Combined Cross-Patch Tape Adhesion test, Acid-Bath Immersion test were applied to evaluate the proceeding of sol synthesis and film formation, the morphology, the polarization current, the film adhesion, and the acid-resistance of the formed layers, respectively.
The FT-IR spectrum reveals that the silica sol has successfully hydrolyzed and then condensed by high temperature drying. The results of the analysis of SEM and SEM-EDS show that sealing layer and passivation layer are respectively successfully formed on the galvanized steel surface to a dense protective layer. At the same time, the sealing layer is superior to the passivation layer in reducing the surface pores of galvanized steel surface. In addition, the Potentiostat test results that the galvanized steel pretreatment (i.e., water-rinse after chemical surface cleaning) temperature and sol aging time will affect the corrosion resistance of sealing layers. The TG series sealing layer has better corrosion resistance and acid-etching resistance among all passivation and sealing layers. Finally, the cross-patch adhesion test found that these passivation and sealing layers behave good adhesion on the surface of galvanized steel, except that film cracks into pieces seriously. These results show that the modified silica-based TG-H2SO4-4H-Zn(Fe)-30 is the most suitable protective layer for improving the anti-corrosion of galvanized steel sheet in this study.
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