Modification of Passive Film Formed on Environmental Materials by Photo Irradiation

本文报道了在酸溶液中紫外线照射Fe-Cr合金和SUS304不锈钢钝化膜，增强了钝化膜中Cr的富集，从而提高了其在氯化物溶液中的耐点蚀性。在本工作中，在中性溶液中，SUS304不锈钢也观察到类似的Cr富集增强，从而提高了耐点蚀性。电化学阻抗谱分析表明，该钝化膜具有n型半导体性质，且光能增强了供体密度。另一方面，没有观察到由光跃迁产生的分离电子和空穴对引起的电子结构变化。通过电子和空穴对的复合释放能量，在钝化膜内产生点缺陷，促进了钝化膜内离子的运动。促进运动，特别是铁离子优先溶解，导致Cr在钝化膜中富集。用石英晶体微天平研究了紫外光照射对纯铜大气腐蚀的影响。在没有紫外线照射的情况下，腐蚀速率受温度、氧分压和湿度的影响。当紫外线照射时，腐蚀速率不一定取决于氧分压。认为紫外光控制吸附水层中氧的活度是恒定的。

The Authors have reported that Cr enrichment in the passive film on Fe-Cr alloys and SUS304 stainless steel formed was enhanced by ultra-violet light irradiation in acid solution during passivation, resulting in an improvement of pitting corrosion resistance in chloride solutions. In the present work, similarly enhanced Cr enrichment was observed for SUS304 stainless steel in neutral solution, resulting in the improved pitting corrosion resistance. Electrochemical impedance spectroscopy revealed that the passive film has n-type semiconductor property and donor density was increased by photo irradiation. On the other hand, change in the electronic structure induced by separated electron and hole pair generated by photo transition was not observed. It is concluded that the modification was derived by recombination of electron and hole pair to release energy which generate point defects inside the passive film, which promote motion of ionic species inside passive film. Promoted motion, especially for Fe ions to be dissolved preferentially results in Cr enrichment in the passive film.The effect of uv light irradiation on the atmospheric corrosion of pure Cu was also studied using quarts crystal micro-balance. The corrosion rate is influenced by temperature, oxygen partial pressure and humidity without uv light. When uv light is irradiated, the corrosion rate not necessarily depends on oxygen partial pressure. It is considered that activity of oxygen in the adsorption water layer is controlled by uv light to be constant.