Corrosion Inhibition Efficiency of Cysteine-Metal ions Blends on Low Carbon Steel in Chloride-Containing Acidic Media

This paper addresses the effect of some metal ions (e.g., Cu2+, Ni2+ and Fe2+) in their blends with cysteine (an environmentally friendly organic compound) on the inhibition efficiency (IE) of the corrosion of low carbon steel (LCS) in three different media, i.e., 0.5 M H2SO4 in the absence and the presence of 3.5 wt% NaCl or 0.5 M Na2SO4. The results obtained from both electrochemical impedance spectroscopy (EIS) and electrochemical polarization measurements indicated a significant increase in IE of cysteine in the presence of a few micro molar amounts of Cu2+ ions instead of cysteine alone. On the other hand, blending cysteine with Ni2+ or Fe2+ decreased IE. That is IE reached ca. 90, 91 and 92% in the presence of 8 mM cysteine and 25 mu M Cu2+ ions in the first, second and third medium, respectively, compared to ca. 70%, 66% and 58% in the presence of cysteine alone (i.e., in absence of Cu2+ ions). Moreover, polarization experiments indicated that cysteine and Cu2+ ions blend acts as a mixed-type inhibitor for the corrosion of LCS. The formation of Cu(I)-cysteinate complex and/or cysteine SAM at Cu atop the LCS surface (as evident from EDX and SEM results) protects the metal surface from exposure to the aggressive chloride ions. IE of cysteine-Cu2+ blend remains effectively high with time indicating its high stability in the applied chloride-containing acidic media.