Effect of Sulfuric Acid on Corrosion and Passivation of 316 SS in Organic Solution

Abstract

Organic solvents like methanol have potential application in fuel cells, chemical and surface treatment processes. The corrosion investigation of austenitic stainless steels in methanol containing reducing acids (HCl, H2SO4 etc.) is very limited, in particular the passivation and pitting kinetics. In this work, the corrosion, passivation and pitting kinetics of 316 stainless steel (SS) have been investigated in methanolic solutions containing LiCl, HCl and mixture of HCl and H2SO4 by polarization, EIS, SEM and XPS. The rate of corrosion was higher in HCl solutions as compared to LiCl solutions. Passivation was promoted in methanol–HCl + H2SO4 solutions with molar ratio of H2SO4 to HCl ≥ 10: 1. The presence of anions, water content and solution acidity were the key factors determining the stability of passive film. Pit nucleation was inhibited with increasing H2SO4 concentration. Primary components of the passive film were iron/chromium oxyhydroxides with incorporated and ions.