Corrosion and pitting behaviour of AISI 302 stainless steel in methanol + H2SO4 mixtures

Abstract

Electrochemical and corrosion behaviour of austenitic stainless steel (AISI 302) has been investigated in deaerated methanolic solution containing different concentrations of H2SO4 (0.001 M-1M) using potentiostatic and potentiodynamic techniques. Cathodic polarization studies show that the cathodic process is initially activation controlled and at more negative potentials it tends to be diffusion controlled, particularly in low acid concentrations. Frequent active-passive transitions are observed and the critical current density for the passivity is dependent on the sulphuric acid content in methanol. In anodic polarization studies in 1 M and 0.1 MH2SO4-methanol solutions cathodic loops appear. SEM examination of the electrode surface after the polarization studies showed severe pitting in each concentration of acid-methanol mixtures. Different corrosion parameters and pitting potentials have been evaluated. Repassivation has also been observed. Current vs time transients have been recorded at constant potential. Protection potential is always less nobler than the pitting potential.