大気酸化処理による炭素鋼の高温濃厚LiBr水溶液中での腐食抑制作用

抄録

The corrosion behavior and corrosion mechanism of air-preoxidized carbon steel have been investigated in concentrated LiBr solution at elevated temperature. The structure and composition of the surface films before and after corrosion were analyzed by XRD, AES, SEM and XPS. The air-preoxidized treatments at above 673K are effective in reducing corrosion weight loss about one order of magnitude in LiBr solution with Li₂MoO₄ inhibitor. Mass loss of the carbon steel air-preoxidized at 673K does not depend on the presence of Li₂MoO₄ in the LiBr solution, because the films have no defects. Mass loss of carbon steel air-preoxidized at 573K varies within a range in LiBr solution with Li₂MoO₄ which is due to defects of the preoxidized film. However, the maxium variation is not larger than that of no-preoxidized carbon steels. The oxide films both before and after corrosion are composed of Fe₃O₄ and α-Fe₂O₃. After corrosion, in the case of preoxidation at 573K, concentrated Mo layer which was observed at the oxide films/solution interface above 673K, is not observed in the oxide films. Li₂MoO₄ in the LiBr solution can repair the defects in the air-preoxidized film. The relationships between the corrosion behavior and surface film structures are considered using an interfacial ion-selective diffusion layer.