Effect of 2-amino-3-mercaptopropanoic acid (cysteine) on the corrosion behaviour of low carbon steel in sulphuric acid

The effect of cysteine (cys) on the corrosion of low carbon steel (LCS) in sulphuric acid solution was investigated using electrochemical and scanning electron microscopy (SEM) techniques. Electrochemical impedance spectroscopy (EIS) results reveal that the presence of cys at low concentrations (0.1–0.5 mmol L−1) promoted the LCS corrosion process, whereas an inhibiting effect was observed at higher concentrations (1.0–5.0 mmol L−1), which was enhanced on deaeration of the test solution. Polarization results revealed that cys actually inhibited the cathodic process at all concentration but exerted a stimulating effect on the anodic metal dissolution reaction. Despite the cathodic inhibiting effect, the polarization resistances at low cys concentrations were less than that in the blank acid. This suggests that the anodic reaction was the predominant influence determining the corrosion rates in the presence of cys. This has been discussed vis-à-vis the catalytic effect of the Fe–cys complex, which turns the Fe surface more electrochemically active.