Effect Of Carbon Nanotubes On Photocathode Protection Of Titania Films For304Stainless Steel

The TiO₂semiconductor materials on the metal photocathode protection has beenwidely concerned since Fujishima and Tsujikawa etc found TiO₂film on the metalsurface has photo-electrochemical anti-corrosion properties. Unlike traditionalsacrifice anode method, TiO₂in the process of cathode protection is not consumedwhich can sustain a long time anti-corrosion protection of metals. Additionally, Dueto working in the solar energy, easy to prepare, environment-friendly and low costing,TiO₂photocathode protection has a broad application prospects in the metalanti-corrosion.In this thesis, we prepared successfully the MWCTN/TiO₂composite films on the304stainless steel in order to reduce the recombination of photo-generated carriersand increase the photocurrent through the introduction of carbon nanotubes due totheir excellent photoelectric properties in collecting and transferring electrondirectionally to the semiconductor. The study results are as follows:At room temperature, MWCNT/TiO₂films on304stainless steels were preparedvia sol-gel spin-coating method and treated under various temperatures. Thesecomposite films were characterized by X-ray diffraction（XRD）, electron microscopes（SEM, TEM）, Energy-dispersive X-ray spectroscopy（EDS）. The results showedthat the particle size distribution of the film was uniform and no large particles ofreunion were observed. The size of TiO₂particles is about20nm. The carbonnanotubes wrapped closely with TiO₂particles intersperse into the TiO₂films andform a conductive network.The effect of the contents and types of carbon nanotubes, the layer thickness, thecomposite mode, heating temperature and illumination mode on thephotoelectrochemical property have been studied by photoelectrochemical testingsystem. The results show that the potentials of the samples are not always increasingin the negative direction with the increase of MWCNT, but a downward trend when the content of MWCNT is over0.3wt%. Therefore, MWCNT can enhance thephotocathode protection property of304SS coated by the composite film as theamount of WMCNT is less than0.3wt%. A trend of the photopotential positively shiftwith increasing thickness was observed clearly in the experiments, which indicatesthat the good photocathode protection property for304SS can be generated by justcoating a very thin MWCNT/TiO₂composite film. The heating temperature has alsoan important effect on the photoelectric property. The open circute potentials cannegatively shift to the maximum value when the calcination temperature is450℃. Inrespect with the diameter of carbon nanotubes, MWCNT2040displays the betterdispersion in the films, leading to the better photoelectric property.The potentiodynamic polarization curve and impedance test of the MWCNT/TiO₂composite films showed that the composite films exhibit an obvious anti-corrosioneffect for304stainless steels. The stable photoelectric properties of samples havebeen obtained under different illumination conditions. Simultaneously,304stainlesssteels can be protected efficiently by MWCNT/TiO₂composite films underillumination because their open circuit potentials can much more negative than thecorrosion potential of304stainless steels. Dipped in3.5%NaCl solution for7days,no obvious corrosion of the sample coated with the composite films can be detected,but the sample of pure304stainless steels had been corroded heavily, which showsthat304stainless steels can be protected for a long time by coated with theMWCNT/TiO₂films under illumination.