Study On The Application Of Nano TiO₂ In Metal Protective Coatings

In this essay, non-ionic surfactant was used to modify the nano TiO2. The results showed that using surface active agent with HLB value smaller than 10 to modify nano TiO2 can improve the compatibility of nano TiO2 with organic slurry. The modified nano TiO2 dispersed well in organic slurry and there's no aggregate, so the modified nano TiO2 can be used in oily system. UV-visible absorption spectra testing showed that the modified nano TiO2 can not only absorb the UV light, but also can absorb visible light and near-infrared light to some degree. Under the excitation light source of 325nm,493nm,700nm and 800nm for fluorescence spectrum, the modified nano TiO2 was able to generate emission peak.After being modified, the surface of nano TiO2 was changed from hydrophylic to oleophylic, and the nano TiO2 showed good compatibility with polyurethane coatings, epoxy zinc-rich coatings and fluorocarbon coatings. Coated the polyurethane coatings on the surface of copper, stainless steel and A3 steel electrodes, coated the epoxy zinc-rich coatings on the surface of weathering resistant steel electrodes and coated the fluorocarbon coatings on the surface of aluminum electrodes. From the polarization curves in the 3.5% NaCl electrolyte solution, it can be concluded that nano TiO2 modified coatings can enhance the protective effect to the metal matrix.This was because that the nano TiO2 in the coatings can generate the photo-induced carriers under the light, that is the electrons (e-) in the donor level was excited to conduction band, or valence band electron was excited to the acceptor level, in the meantime there were cavities (h+) left in the valence band. Due to the existing of photo-induced carriers, the conductivity of metal surface coating was changed from insulate to conductive. The metals can accept e- and (or) h+. If the e-moved from the conduction band of nano TiO2 to the micro cathode region, the potential in the micro cathode region of the metal (E micro cathode) would change to negative potential; If the h+ moved from the valance band of nano TiO2 to the micro anode region, the potential in the micro anode region of the metal (E micro anode) would change to passive potential. Due to the negative potential of E micro cathode and passive potential of E micro anode, the AE of the metal corrosion microcells was decreased. According to relationship ic= (E micro cathode-E micro anode)/(Pa+Pk), assuming the average polarization P was constant, the ic will be entirely dependent onΔE. The smaller theΔE, the correspondingly smaller of metal corrosion current ic.Purification effect tests of formaldehyde and toluene by nano TiO2 modified polyurethane coating and fluorocarbon coating showed the purification effect of formaldehyde was 83.1% and 80.4% respectively, the purification effect of toluene was 38.7% and 40.9% respectively. They both reached the standards of I type of material. The other tests showed that the mechanical properties of the nano TiO2 modified coatings can meet the requirements of other basic performance.