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Fabrication of Ag~+ Doping Titania Film on 304 Stainless Steel Substrates and Anti-corrosion Properties Research

Author: HongHaiXia
Tutor: YinYanSheng
School: Ocean University of China
Course: Materials Physics and Chemistry
Keywords: Ag~+ doping TiO2 film marine corrosion SRB
CLC: TG174.4
Type: Master's thesis
Year: 2010
Downloads: 104
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Abstract

As the rapid development of science in the coming ocean epoch, the marine materials and the technic of surface protection are urgent needed in the area of exploitation of marine resources, transportation in ocean and marine engineering. The flaws of the conventional anti-corrosive measures are toxicity, contamination, lossy, short-lived, higher cost etc. It’s urgent to find a new way to protect metals from marine corrosion and microbial corrosion especially. Therefore, research on the fabrication of advanced materials and failure-mechanism as well as new anti-biocorrosive model is significant to marine exploitation strategically.As protecter for cathodic protection, nano-TiO2 coatings are applicable to steel substrates the same as the sacrificial anode protection. TiO2 coatings produce electron-hole pair under illumination, the electrons are injected into steel substrates and decrease the electrode potentials of the steel to cathodic protection zone, protecting the steel from marine corrosion. As photo-induced antibacterial agent, titanium dioxide (TiO2) is promising to remove microorganisms in self-cleaning and self-sterilizing materials with the characterization of non-toxicity, cheapness and chemical stability. Whereas, titania antibacterial agent has the disadvantage of low photocatalytic and bactericidal activity, which requires UV irradiation to activate, so its photocatalytic activity needs to be improved in the practical applications. The silver ion is used as electron acceptor to decrease the e--h+recombination and improve the photocatalytic and bactericidal activity. Thus the silver ions doped TiO2 is bactericidal photocatalytically under strong illumination and anti-microbial in the darkness because of Ag. A brand new idea is provided to the anticorrosion research under the marine environment.In this paper, sulphate-reducing bacterium (SRB) from Qingdao offshore is obtained by isolation and purification method, for SRB is a main bacterium which caused the corrosion of metals. The growth pattern of SRB is confirmed by analyzing its growth curve, and the properities of as-obtained materials are studied in environment in which SRB existed.TiO2 sol and Ag+ doped TiO2 sol are formed by sol-gel method, dense and fine TiO2 thin film and Ag+/TiO2 film are gained through dip-coating and proper heating process. The parameters of fabrication are diacussed, on the basis of which, the optimum fabrication technology is obtained. Researching by TG-DTA、XRD、SEM and EDS etc shows that the constituent is anatase crystal without simple substance silver. It’s assumed that Ag+ is doped into the grain boundary by the complexation between AgNO3 and citric acid, causing teratogenesis of the TiO2 crystal as the increasing doping of Ag+. The spectral response of TiO2 thin film and Ag+/TiO2 film are researched by analyzing the UV-Vis transmittance spectra, a red-shift of absorption edge is observed for both films. It’s noticeable that the doping of Ag+ broadens the photoresponse range of TiO2 film, absorption peaks of Ag+/TiO2 film red-shift markedly and the absorption intensity increases comparing to TiO2 film; Under the illumination of ultraviolet light, photo-electric transform capability of Ag+/TiO2 film is stronger than TiO2 film obviously, the decrease of the open circuit potential (OCP) of Ag+/TiO2 film is more than twice the TiO2 film. The aforesaid test results show that, TiO2 film and Ag+/TiO2 film both exhibit an additional cathodic protective function to 304ss, while the latter is noticeably stronger than the former.Bactericidal ratios of TiO2 and Ag+/TiO2 are obtained by Most Probable Number (MPN) method. The result shows that, the bactericidal ratios of Ag+/TiO2 is up to 97%, 11.7% higher than TiO2. This illuminates that the doping of minim Ag+ improves the bactericidal activity of TiO2 strongly. It’s assumed that Ag+ acts as collaboration bactericide agent.The corrosion rules of 304ss electrode, TiO2/304ss electrode and Ag+/TiO2/304ss electrode are gained through electrochemistry method. The results show that, the existence of TiO2 film and Ag+/TiO2 film decrease the corrosive electric current density and the corrosion rate of 304ss. The charge transfer resistance of electrode reaction increases, explaining that the film prevents the corrosion of seawater and SRB efficiently. The SEM analysis of corrosion appearance also illuminates the same corrosion rule.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metal corrosion protection,metal surface treatment > Corrosion control and protection > Metal surface protection technology
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