Investigation of Pourbaix Diagrams of 316L Stainless Steel in Air-Saturated Aqueous Solutions Containing Chloride by Cyclic Polarization Technique

摘要

The Pourbaix diagrams of AISI 316L stainless steel in air-saturated aqueous solutions containing chloride 5, 50, 500 ppm at 25°C were investigated by polarization technique. The corrosion potentials, primary passivation potentials, protection potentials and transpassive potentials were determined from the polarization curves and plotted with respect to the solution pH. Increasing chloride concentration has no effects on the corrosion and primary passivation potentials, but transpassive and protection potentials were decreased. The results has reflected on the Pourbaix diagrams which defined that the passivity areas including perfect and imperfect passivities decrease when the chloride concentration increase, however, the immunity and general corrosion areas were insignificant changed. In acid solution, chloride has more influence on the change of passivity area than in basic solution. Possible dissolved ions in general corrosion and pitting corrosion conditions were chemically analyzed. There was no ion detected in general corrosion condition. In the pitting corrosion, ferrous ion (Fe~(+2)), ferric ion (Fe~(+3)), chromic ion (Cr~(3+)), nikelous ion (Ni~(2+)) and molybdate ion (MoO_4~(2-)) were detected.