Effects of Cl , NO3 and SO4 2 anions on the anodic behavior of carbon steel in deaerated 0.50 M NaHCO3 solutions

The effects of Cl , NO3 and SO4 2 aggressive anions on the corrosion and passivation behavior of carbon steel electrode in deaerated 0.50 M NaHCO3 solutions were studied using potentiodynamic anodic polarization and SEM techniques. It was found that the presence of Cl , NO3 and SO4 2 anions stimulates the anodic dissolution rate in both the active and the pre-passive potential regions. Moreover, significantly great effects were observed in both the passive and the trans-passive potential regions. Pitting corrosion was observed only in the presence of Cl anions, while the presence of NO3 and SO4 2 anions facilitate only passivation by oxygen of water without themselves participating in the cathodic process. Also, it was observed that the effect of NO3 anion,which is a strong oxidizing agent acting ‘‘primarily’’ as stimulator of the cathodic process and then its reaction product acts ‘‘indirectly’’ retarding the anodic process. On the other hand, the effect of SO4 2 anion, which is a non-oxidizing agent, exerts an ‘‘indirect’’ effect on the cathodic reaction increasing its rate and then ‘‘directly’’ influence on the anodic reaction, retarding it.