Abstract
The effect of metal species such as Cr (VI), Ce (IV), V (V) and Ru (III) on corrosion of 25 Cr-20 Ni-Nb stainless steel was evaluated through electrochemical and chemical measurements in boiling nitric acid solutions. As the addition of 0.005 M-Ru (III) accelerated the corrosion remarkably, its acceleration mechanism was studied. Ruthenium (III) was oxidized to ruthenium tetraoxide in nitric acid, and it was proposed that corrosion of stainless steel was promoted first through the reduction process of ruthenium tetraoxide to ruthenium dioxide, and then by the catalyzed reduction of nitric acid with the deposited ruthenium dioxide. While the anodic polarization was not affected by the presence of metal species, the corrosion was dependent on the cathodic polarization. Further, the corrosion mechanism in the transition state from passive to transpassive regions was investigated by analysis of the impedance.
