Preparation Of Water Based Silanization Solution And Its Application

Silanization of metal surface could significantly improve the corrosion resistance of materials and adhesion of paints upon substrates. And it has been studied as environmentally friendly surface treatment technology for replacing the pollutive chromate conversion chromating and phosphating treatments. But the traditional treatment chemicals are methanol or ethanol rich solutions which results in the waste of alcohol. So, the application of silane treatment is limited. In this paper the water based silanization solutions were prepared and the corrosion protection performance of silane treated aluminum and carbone steel were studied.1. Preparation and characterization of water based silanization solutions. According to the polarity change of hydrophobic silane monomers and hydrolysis products, water based silanization solutions were prepared by a multiphase which was conposed of silane/n-heptane oil mixture and deionized water with adjusted pH value. In the meanwhile, bis-[triethoxysilylpropyl] tetrasulfide (BTESPT) silanol concentration was monitored by conductivity and the parameters of vinyltriethoxysilane (VTES) hydrolysis process were optimized by orthogonal experiments. Fourier transform infrared (FT-IR) and electrospray ionization mass spectrometry (ESI-MS) were used to analysis the chemical composition of silanization solutions. The reasons indicate that numerous BTESPT silanol with two or three hydroxyl groups are generated after about 3 hrs reaction in this multiphase. The concentration of silanol will not change much when the hydrolysis time continue to increase. The optimum hydrolysis parameters of VTES are depicted as:temperature is about 35℃, pH value is 7 and hydrolysis time is below 10 hrs. Aluminum samples treated by water based silanization solution synthesized under this condition show the best anticorrosive performance.2. Preparation and characterization of BTESPT layer upon aluminum in water based silanization solution. BTESPT layers upon aluminum were prepared by using of dip-coating and electrodeposition techniques. Scanning electron microscopy with X-ray microanalysis (SEM/EDS) were used to characterize surface topography and chemical composition of aluminum samples. They electrochemical behavior in 0.1 mol/L NaCl solution were measured using electrochemical impedance spectra (EIS) and tafel polarization curves. The results demonstrate that aluminum samples coated with BTESPT layers, which is about 188 nm in thickness, show chromate alternative corrosive resistance after 72 hrs dipping in salty water. SEM and EIS observation of BTESPT layers deposited at different potentials indicate that BTESPT layer deposited at -1.0 VSCE was dense and uniform. Compared with the blank control samples, low frequency impedance (|ZLF|) value of silane layers covered aluminum was increased by two order of magnitude that attained 60000Ω·cm-2. And the potential -1.0 VSCE is a critical value for electrodeposition BTESPT layers upon aluminum in water based silanization solution.3. Silane treatment as alternative to phosphating of carbon steel.Traditional phosphating bath were optimized by orthogonal experiments and zinc-manganese phosphating film with additional corrosion resistance was achieved. EIS and Tafel results indicate that carbon steel show superior corrosion resistance after phosphating for 15 minitures. Its corrosion current density is reduced to about 1/30 in comparison with bare carbon. In order to replace the heavy-polluting phosphating technology and assure the protection performance, silane layers of BTESPT, VTES and y-glycidoxypropyltrimethoxysilane (GPTMS) were prepared upon carbon steel. In the meanwhile, EIS and tafel curves were used to verify their protection efficiency. The results demonstrate that VTES and BTESPT layers with about 0.95% porosity could provide at least 90% corrosion inhibition for carbon steel. The porosity of GPTMS layer is slightly more,7.52%, and its protection efficiency is about 87.5%. SEM images of BTESPT coated sample show 260 nm of organic layer with dense and uniform surface. Overall, current densities of silane treated carbon steel decreased almost 90% and the thin silane layers exhibit phosphatic film alternative corrosion resistance.