Effect of sulfur-containing amino acids on the corrosion of mild steel in sulfide-polluted sulfuric acid solutions

Abstract

The influence of cysteine (RSH) and cystine (RSSR) on the corrosion behavior of mild steel in sulfide-polluted H2SO4 solutions was studied by potentiodynamic polarization methods and AC impedance technique. The results show that S2− accelerates the corrosion process markedly, especially the anodic dissolution of iron. Tafel polarization curves show that RSH and RSSR act mainly as anodic-type inhibitors without affecting the mechanism of the hydrogen evolution reaction or iron dissolution. Adsorption of RSH and RSSR in most sulfide-polluted H2SO4 solutions obeys Temkin’s isotherm. Impedance studies indicate that in the inhibited and uninhibited solutions, charge transfer controls the corrosion process either at Ecorr or at 30 mV vs Ecorr. Potentiodynamic anodic polarization curves show that RSSR effectively inhibits the steel dissolution both in the active and passive states and greatly reduces the current oscillations observed in the passive region.