Effects of Interfacial Iron Oxides on Corrosion Protection of Carbon Steel by TiO₂ Coating under Illumination

Abstract

On the approach of corrosion protection of metal by TiO₂ coating under illumination, the effects of iron oxides on the photoelectrochemical response of TiO₂/carbon steel were studied. The iron oxides, magnetite (Fe₃O₄), maghemite (γ-Fe₂O₃) and hematite (α-Fe₂O₃), were prepared on the carbon steel by using both the chemical conversion method (blackening treatment) and the heat treatments. From the examinations for the structures and the photoelectrochemical behavior of sol-gel derived TiO₂ coating, it is found that the interfacial α-Fe₂O₃ demonstrates a significant photoelectrochemical response while the interfacial Fe₃O₄ and γ-Fe₂O₃ show poor performance. Although a vivid photoeffect for the TiO₂/α-Fe₂O₃/steel system was observed, the Fe was still found to diffuse into TiO₂ during the heat treatment of TiO₂. Consequently, by changing the TiO₂ coating procedure, particularly the heat treatment of TiO₂ to suppress the diffusion of Fe ions, the photoeffect of TiO₂/α-Fe₂O₃/steel could be improved. For TiO₂/α-Fe₂O₃/steel under illumination, the stability of iron oxides was also studied. It was found that α-Fe₂O₃ was stable in aerated solution, while in a thoroughly deaerated solution α-Fe₂O₃ was reduced slightly by the photo-excited electrons.