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Sol-Gel Derived Ti-Fe Oxide Coating for Photoelectrochemical Cathodic Protection of Carbon Steel

1998; Volume: 47; Issue: 3 Linguagem: Inglês

10.3323/jcorr1991.47.193

1881-9664

Jianshun Huang, Tomoyoshi Konishi, Tadashi Shinohara, Shigeo Tsujikawa,

Lubricants and Their Additives

On the novel approach of corrosion protection of carbon steel by TiO2 coating under illumination, photoeffect of TiO2/C-steel system is affected by the structural and electronic properties of the interfacial Ti-Fe oxide. In the present work, Ti-Fe oxide with a wide range of composition, from TiO2 to α-Fe2O3, was prepared by sol-gel method. By studying the characteristics of the Ti-Fe oxides and their influences on the photoeffect of TiO2/C-steel system, a multi-layer coating, expressed as from outer coating layer to substrate: TiO2 (amorphous)/TiO2 (anatase)/Ti-Fe oxide/α-Fe2O3/C-steel, was proposed for more effective photoelectrochemical cathodic protection of carbon steel. TiO2 (anatase) layer without Fe contamination exhibits a good photoeffect and behaves like the source of photo-excited electrons. The inner α-Fe2O3 layer acts as both a barrier to retard the diffusion of Fe into TiO2 and a way for the transfer of photo-excited electrons from the TiO2 (anatase) coating to the substrate. The outer layer of amorphous TiO2 inhibits the oxygen reduction and reduces the photopotential to a more less noble value. The intermediate layer of amorphous Ti-Fe oxide provides deep levels for Fe2+/Fe3+ redox couple, for which Fe3+ is reduced to Fe2+ by the photo-excited electrons under illumination. The state of Fe2+ left after stopping illumination contributes to phenomenon that the electrode potential is maintained at considerably less noble value until all the Fe2+ is re-oxidized by oxygen reduction.