Corrosion Resistance of Ni Base Alloys in Supercritical Water Containing Sulfuric Acid : Dependencies on Alloying Elements

摘要

Supercritical water is recognized as a promising medium for various chemical processes. However, one of the major problems to industrial application of the processes is thought to be corrosion of structural materials. In this paper, dependencies of corrosion resistance on alloying elements were investigated on twelve kinds of nickel base alloys in 400oC30MPa and 400oC60MPa supercritical water containing 0.01mol/kg sulfuric acid. The investigations reveals that Cr controls the corrosion resistance of the alloys in the test conditions and thresholds of changes in improvement rate in corrosion resistance with increasing Cr content are observed for the testing pressures. Properties of oxide on the specimens are examined by X-ray diffraction technique (XRD) to investigate correlation between the corrosion resistance of the Ni base alloys and crystallinity of the oxides on the Ni base alloys. The investigation suggests that corrosion resistance of the alloys improve with higher oxide crystallinity. The reasons for the effect of crystallinity on corrosion resistance are discussed.