Photoeffect on Corrosion Behavior of SrTiO_3-Coated Galvanized Steel

摘要

The n-type semiconductor SrTiO_3 was coated on the hot-dip zinc coated steel (Z18). Different from the sacrificial zinc coating, the coating acted as a stable photo-anode to offer non-sacrificial cathodic protection to substrate steel. With ZnO formed on the galvanized steel by anodizing in 0.1 M NaOH aqueous solution, a good photoeffect was found. With the sol-gel derived SrTiO_3 additionally coated on ZnO, the photoeffect was further improved. The open-circuit potential was maintained less noble even after stopping illumination for the coating with intermediate Fe-doped SrTiO_3 layer, SrTiO_3/Fe- SrTiO_3/ZnO/Z18. Moreover, photo-decomposition that appeared for ZnO-coated galvanized steel could be prevented by the SrTiO_3 coating. The couples of SrTiO_3//Fe (Fe coupled with SrTiO_3/Fe- SrTiO_3/ZnO/Z18) and Zn//Fe (Fe coupled with Z18) were developed as ACM (atmospheric corrosion monitor) sensors to evaluate the corrosion behavior of galvanized steel with and without SrTiO_3 coating in atmosphere. For the SrTiO_3//Fe sensor, an anodic output was detected in the dark to show dissolution of Fe electrode, while it changed to cathodic one upon illumination. The cathodic value was larger than that of Zn//Fe sensor under certain conditions of lower amount of deposited sea salt and lower relative humidities, where substrate steel could be protected from rusting with the non-sacrificial coating.