Homogeneous Modification Of Silane Solution By Metal Alkoxides And The Barrier Performance Of Obtained Films

Silane films have been widely used in electroanalysis, biosensors, optical devices, as well as surface pretreatment for corrosion protection. Compared with pretreatments of metals by chromate or phosphate systems, silanization is more environmentally compatible without toxicity and becoming an efficient replacement of traditional methods. However, silane film prepared by simple methods is too thin (usually from tens to hundreds nanometers) and not hard enough to protect metal substrate against corrosion for a long period. These shortages limit its further application and many efforts have been done to solve these problems to improve the anticorrosive property of silane film in recent years. The common feature of previous works is that they are all heteropical modified methods. Their preparing processes are often complex and cost more time and money. In this thesis, a novel homogenous modified method was firstly provided just by adding tiny amount of metal alkoxide in silane precursor at the initial stage. The results showed that during the co-hydrolytic process, the hydrolysis reaction of silane monomers and condensation reaction of the produced silanols are promoted, which further facilitates the formation of silane films on substrates. The main contents are listed as follows:(1) Homogenous modification of methyltrimethoxysilane (MTMS) solution by tiny amount of tetrabutyl orthotitanate (TBOT) and the barrier performance of obtained films were investigated. It was observed that the hydrolysis reaction of silane monomers and condensation reaction of the produced silanols in TBOT modified MTMS solution are quicker than blank MTMS contrast. Films prepared by dip-coating method is thicker, compacter and more hydrophobic, leading to the high improvement of anticorrosive performance. Electrochemical impedance spectroscopy (EIS) study showed that the anticorrosive property of silane films raised gradually with the increase of TBOT concentration, then stayed at a platform. After immersing in a strong corrosive medium (3.5 wt% NaCl) for about 5 days, the obtained films still exhibited high corrosion resistance. As for galvanized steel substrates, the modified film also provided good barrier property.(2) Tetrabutyl orthozirconate (TBOZ) modified MTMS solution and films were also investigated. The results of solution chemistry showed that the catalytic capability of TBOZ for MTMS hydrolytic process is weaker than that of TBOT. Compared with TBOT modification, films prepared from the same amount of TBOZ modified MTMS solution, which endured identical hydrolysis time, exhibited lower anticorrosive property. It needed longer hydrolysis time to reach an optimal status and obtain film with similar corrosion resistance. Both the blank MTMS solution and metal alkoxide modified MTMS solution were stable in the whole procedure. EIS study showed that the anticorrosive property of pure MTMS film and TBOZ modified MTMS film increased when prolonged the hydrolysis time of their precursor. Based on the analysis of solution chemistry and film property, a possible film formation scheme in metal alkoxide modified MTMS solution was proposed and verified initially through MTMS pre-polymer mimic experiment.