Preparation And Anticorrosion Properties Of Mercapto Functional Silica Sol-gel Coatings

Copper has already been applied to various fields of national economy due to its excellent thermal conductivity, electrical conductivity, ductility and corrosion resistance. In general, Copper doesn't appear an obvious corrosion tendency due to its relatively higher potential. However, when long-timely exposed to solution with Cl-?NH4+, sea water or marine-atmosphere environment, copper could be corroded seriously. Generally speaking,copper corrosion can be divided into three types: physical corrosion, chemical corrosion and electrochemical corrosion. These three types often simultaneously exist and promote mutually.In order to prolong the service life of copper products and save copper resource, it is necessary to protect the copper surface.In this paper, various mercapto functional silica sol-gel coatings were prepared. The corrosion resistance of the coatings was investigated.Firstly, a detailed comparative study of anticorrosion properties between alkylthiol self-assembled monolayers(SAMs) and mercapto functional silica sol-gel coating prepared by 1-octanethiol(OT), n-dodecanethiol(DT) and(3-mercaptopropyl)trimethoxysilane(MPTMS) was carried out. Results demonstrated that compared to other alkylthiol SAMs, the mercapto functional silica sol-gel coating showed the best anti-corrosion performance in sodium chloride solution because it owned a multiple hierarchic Si–O–Si network structure,thus to achieve a higher range of thickness, lengthen the diffusion path way of corrosive medium.Secondly, mercapto functional silica sol-gel coatings with high solid content were prepared on copper surface by means of hydrolysis-condensation reaction.3-Mercaptopropyltrimethoxysilane(MPTMS), tetraethylorthosilicate(TEOS) andhydrochloric acid were used as organic precursor, inorganic precursor and catalysts respectively. The influence of TEOS content on the anti-corrosion property of Sol-gel coating was studied. The results showed that the thermostability of the coatings was significantly improved due to the addition of TEOS. However, the average size of sol particles increased with the increase of TEOS content. Excessive addition of TEOS can induce holes and cracks at the surface of coatings or within the coatings. The coatings owned the best corrosion resistance performance when the molar ratio of TEOS to MPTMS was 0.6 due to their larger crosslinking density and fewer defects.Finally, surface with certain roughness of copper alloy was constructed by chemical etching. Then, hydrophobic mercapto functional silica sol-gel coating with excellent anticorrosion performance was obtained after further modification with mercapto functional silica sol. The influence of chemical etching time on the wettability and anticorrosion behaviors of Sol-gel coating were investigated. The results showed that the morphology,wettability and anticorrosion property of mercapto functional silica sol-gel coating was changed with the change of etching time. The coating owned the best corrosion resistance performance when etching time reached 120 min due to the appropriate micro/nano-structure and the synergy of mercapto functional silica sol-gel coating with low surface energy. The coating can effectively prevent the corrosion liquid from contacting with the copper substrate.