On the approach of corrosion protection of metal by TiO
2 coating under illumination, the effects of iron oxides on the photoelectrochemical response of TiO
2/carbon steel were studied. The iron oxides, magnetite (Fe
3O
4), maghemite (γ-Fe
2O
3) and hematite (α-Fe
2O
3), 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 TiO
2 coating, it is found that the interfacial α-Fe
2O
3 demonstrates a significant photoelectrochemical response while the interfacial Fe
3O
4 and γ-Fe
2O
3 show poor performance. Although a vivid photoeffect for the TiO
2/α-Fe
2O
3/steel system was observed, the Fe was still found to diffuse into TiO
2 during the heat treatment of TiO
2. Consequently, by changing the TiO
2 coating procedure, particularly the heat treatment of TiO
2 to suppress the diffusion of Fe ions, the photoeffect of TiO
2/α-Fe
2O
3/steel could be improved. For TiO
2/α-Fe
2O
3/steel under illumination, the stability of iron oxides was also studied. It was found that α-Fe
2O
3 was stable in aerated solution, while in a thoroughly deaerated solution α-Fe
2O
3 was reduced slightly by the photo-excited electrons.
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