Corrosion Behavior of Metals in Supercritical Water Solutions in the Presence of Salts Available to Purchase

The corrosion behavior of constituent metals (Fe, Cr, Mo) of iron-base and nickel-base alloys has been examined in 5 mass% NaCl at temperatures of 300-450 °C and at a constant pressure of 30 MPa. The mass changes of pure Cr are very small in the range of 300 to 450 °C and their magnitude is close to the limit of detection, whereas pure Fe and Mo show significant mass losses at temperatures of 300 to 450 °C. The mass loss of pure Fe is higher than that of pure Mo at 300-350 °C, but is lower at 400-450 °C. The oxide films on pure Fe, Cr, and Mo consist of Fe₃O₄ and γ-Fe₂O₃, Cr₂O₃, and MoO₂ and MoO₃, respectively. The surfaces of pure Cr were homogenous and blue in color, but no trace of corrosion. The surfaces of pure Fe were covered with a thick oxide film by the treatment at temperatures of 300 to 450 °C. Pure Mo grew up to be uniform oxide layer with a needle-like shape with increasing temperature.