Effect of surface nanocrystallization on corrosion and corrosion inhibition of low carbon steel: Synergistic effect of methionine and iodide ion

The corrosion properties of a nanocrystalline low carbon steel coating (SNCLCS) fabricated on a low carbon steel substrate by magnetron sputtering and the bulk steel (BLCS) were investigated in aerated 0.5 M H2SO4 solution by EIS and polarization techniques. The corrosion inhibiting effect of methionine and synergistic KI additives was also studied. The results show that both specimens underwent active corrosion with no transition to passivation in the potential range studied. Surface nanocrystallization was observed to increase the corrosion susceptibility of low carbon steel, leading to a decrease in interfacial impedance and an increase in the kinetics of the anodic reaction. Methionine inhibited the corrosion of both specimens with comparable inhibition efficiencies and iodide ions synergistically increased the inhibition efficiency. This synergistic effect was, however, more pronounced for BLCS. This has been discussed vis-à-vis the more positive surface charge on BLCS compared to SNCLCS.