Corrosion Behavior of Carbon Steel in Concentrated LiBr-LiNO₃-KCl Solution at Elevated Temperature

Abstract

Corrosion of carbon steel has been investigated for 200h in concentrated aqueous solution of mixed LiBr-LiNO₃-KCl-LiOH salts at elevated temperatures as functions of temperature and concentration of LiNO₃ and Li₂MoO₄O. The structure and composition of the surface films were analyzed by XRD, SEM and XPS. At 463K, addition of LiNO₃ (>0.0125mol/kg) decreased the total amount of iron corroded (W_T), amount of iron ions in the oxide (W_F) and amount of Fe²⁺ ions dissolved into the water (W_D) drastically, however pits were observed. At LiNO₃=3.01mol/kg, W_T and W_F increased as temperature rises, whereas W_D decreased as temperature rises. Pit was observed at LiNO₃=3.01mol/kg between 363K and 463K. Below 403K, pit depth was less than 15μm, while above 433K the pit depth was more than 80μm. These corrosion behavior did not depend on the addition of Li₂MoO₄. Outermost parts of oxide films formed at LiNO₃=3.01mol/kg, were composed of γ-Fe₂O₃ and the decrease in the LiNO₃ concentration changed the composition from γ-Fe₂O₃ to Fe₃O₄. The role of surface film in the corrosion behavior was discussed in terms of its ion-selectivity and OH^- ion stabilizing ability.