Corrosion Inhibition Mechanisum of Carbon Steel by LiNO3, Li2MoO4 and LiNO3/Li2MoO4 Mixed Inhibitors in Concentrated LiBr Solutions at Elevated Temperature
Katsumi Mabuchi, Tomoko Kikuchi, Heihachiro Midorikawa, Michihiko Aizawa
The corrosion behavior and corrosion inhibition mechanism of carbon steel in concentrated LiBr solution at elevated temperature by LiNO3, Li2MoO4 and LiNO3/Li2MoO4 mixed inhibitors have been investigated. These inhibitors were effective in reducing corrosion, but pitting was likely to occur in the LiBr solution with LiNO3 at some concentrations. With Li2MoO4/LiNO3 initiation of pitting occurred as with LiNO3, but its progression was prevented. The structure and composition of the surface films were analyzed by XRD, AES, SEM-EDX and XPS. A higher OH- concentration in the surface films gave a lower corrosion rate. The surface films formed in the LiBr solutions with Li2MoO4 and LiNO3/Li2MoO4 mixed inhibitors were composed of two layers, consisting of Li-Mo oxide including many OH- ions and oxygen-deficient Fe oxide. On the other hand, with LiNO3 inhibitor, Fe3O4 was formed. The relationships between the amount of corrosion and surface films structures were considered in terms of an interfacial ion-selective diffusion layer.