Investigation of the effect of CrO and MoO on carbon steel corrosion using AFM and electrochemical techniques

✍ Scribed by Z. Chen; X. Guo; X. Zhang; L. Huang

• Publisher: John Wiley and Sons
• Year: 2009
• Tongue: German
• Weight: 166 KB
• Volume: 60
• Category: Article
• ISSN: 0947-5117
• DOI: 10.1002/maco.200905095

✦ Synopsis

Abstract

The effect of chromate (${\rm CrO}_4^{2 - }$) and molybdate (${\rm MoO}_4^{2 - }$) ions on the corrosion of carbon steel in 0.5 M NaCl solution has been studied using electrochemical measurements and atomic force microscopy (AFM) technique. Potentiodynamic polarization data suggest that both ${\rm CrO}_4^{2 - }$ and ${\rm MoO}_4^{2 - }$ have inhibition effect on carbon steel corrosion, and the inhibition efficiency increases with increase in concentrations of ${\rm CrO}_4^{2 - }$ and ${\rm MoO}_4^{2 - }$; at the same concentration, the inhibition efficiency of ${\rm CrO}_4^{2 - }$ is higher than that of ${\rm MoO}_4^{2 - }$. The increase in concentrations of ${\rm CrO}_4^{2 - }$ and ${\rm MoO}_4^{2 - }$ anions causes a shift of the breakdown potential (E~b~) in the positive direction, indicating the inhibitive effect of the added anions on the pitting attack. At the same concentrations, the breakdown potential of ${\rm CrO}_4^{2 - }$ is higher than that of ${\rm MoO}_4^{2 - }$. Electrochemical impedance spectroscopy (EIS) tests reveal that the charge transfer resistance and passive film resistance increase with increase in concentrations of ${\rm CrO}_4^{2 - }$ or ${\rm MoO}_4^{2 - }$; at the same concentrations, as for ${\rm CrO}_4^{2 - }$ the charge transfer resistance and passive film resistance were bigger than those of ${\rm MoO}_4^{2 - }$. AFM imaging technique shows that local corrosion was inhibited obviously after the addtion of ${\rm CrO}_4^{2 - }$ or ${\rm MoO}_4^{2 - }$, and passive film of ${\rm CrO}_4^{2 - }$ was much more compact than that of ${\rm MoO}_4^{2 - }$. AFM force–distance curves indicate that the passive film of ${\rm CrO}_4^{2 - }$ is much stiffer than that of ${\rm MoO}_4^{2 - }$.