The corrosion behaviour of nitrogen-containing austenitic stainless steel in methanol containing different concentrations
of H
2SO
4, HCl, LiCl and H
2SO
4 + HCl has been investigated using a potentiostatic polarization method. The cathodic reaction in the H
2SO
4, HCl and H
2SO
4 + HCl solutions was proton reduction whereas in the neutral LiCl solution, oxygen reduction was the predominant cathodic
reaction. Active, passive and transpassive behaviours were observed only for higher concentrations of H
2SO
4 (0.01–2.0 M) due to the inherent water content. A cathodic loop, characterized by measured negative current in the anodic
region, was also observed in solutions, in which the concentration of H
2SO
4 was 1.0 M or higher. The relative stability of the passive films decreased as the H
2SO
4 concentration increased, and thus the steel suffered from mild pitting corrosion. In the chloride environment, the rate of
corrosion increased as the Cl
− ion concentration increased. The presence of acid along with Cl
− ions enhanced corrosion, and the corrosion rate increased significantly. The steel suffered from mild intergranular corrosion
in acidic chloride solutions of methanol. In the H
2SO
4 + HCl solutions, passive films were only formed when the H
2SO
4 to HCl concentration ratio was greater than ∼10:1.
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