ゾル-ゲル法TiO₂被覆による304ステンレス鋼の光カソード防食

抄録

In order to study the cathodic protection of type 304 stainless steel (type 304 SS) by sol-gel derived TiO₂ coating under illumination of light, the photoelectrochemical behavior of TiO₂/type 304 SS system was investigated. During both the dipping and subsequent heat treatment procedures, the compositional elements of type 304 SS were found to be included into the TiO₂ coating, especially Fe involvement being much more intense than the other elements, which greatly decreased the photoeffect of TiO₂ coating. To avoid Fe involvement, a passivation treatment with HNO₃ solution was performed before TiO₂ coating, resulting in the formation of a Cr enriched passive film on the type 304 SS. This Cr enrichment in the passive film retarded the Fe involvement during the TiO₂ coating process, and enabled the TiO₂/type 304 SS specimens to exhibit remarkably less noble photopotentials when the heating temperature was 400°C. Under the optimum conditions for the HNO₃-treatment and TiO₂ coating, the feasibility of cathodic protection for type 304 SS by TiO₂ coating under illumination was clearly demonstrated, as the photopotentials of TiO₂/type 304 SS in neutral chloride solutions were much less noble than the critical repassivation potential for crevice corrosion of type 304 SS.