Photocathodic protection of iron oxide nanotube arrays fabricated on carbon steel

The carbon steel (CS) was anodized to coat with vertical arrays of nanotubes in a mixture of aqueous ammonium fluoride solution and ethylene glycol. As-anodized specimens were annealed at 450°C for 4h in Ar ambient. The fabricated iron oxide nanotube arrays (NTA) depicted a layer of nanotubes over 500nm in length, about 80nm in diameter and about 30nm in wall thickness shown from scanning electron microscope images. X-ray diffraction pattern indicated that iron oxide NTA contained α-Fe₂O₃ as the main phase and Fe₃O₄ as the secondary phase. UV-visible absorption spectra revealed iron oxide NTA significantly absorbed light up to 700nm. Potentiodynamic polarization curves of iron oxide NTA and CS were investigated in 0.5wt.% NaCl solutions in the dark and under illumination supplied by solar simulator. We found that iron oxide NTA shows tremendous photoeffect under alternative illumination and dark. It was seen that potential of iron oxide NTA was more negative under illumination than in the dark and the corrosion rate of CS covered with NTA was obviously less than undecorated CS. In addition, the model of photoelectrochemical anticorrosion of iron oxide NTA was explored.