Modification of Passive Film Formed on Environmental Materials by Photo Irradiation

作者报道了在酸性溶液中紫外光照射能促进Fe-Cr合金和SUS 304不锈钢钝化膜中Cr的富集，从而提高其在氯化物溶液中的耐点蚀性能。在目前的工作中，类似的增强Cr富集观察到的SUS 304不锈钢在中性溶液中，导致提高耐点蚀。电化学阻抗谱表明，钝化膜具有n型半导体特性，光照射后，钝化膜中施主密度增加。另一方面，没有观察到由光跃迁产生的分离的电子和空穴对引起的电子结构的变化。结果表明，钝化膜的改性是通过电子和空穴对的复合释放能量，在钝化膜内部产生点缺陷，促进钝化膜内部离子物种的运动而实现的。促进运动，特别是Fe离子的优先溶解，导致Cr在钝化膜中富集。采用石英晶体微天平研究了紫外光辐照对纯铜大气腐蚀的影响。在无紫外光照射的条件下，腐蚀速率受温度、氧分压和湿度的影响。当紫外光照射时，腐蚀速率不一定取决于氧分压。据认为，吸附水层中的氧的活性由紫外光控制为恒定。

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.