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

The effect of chromate ( ) and molybdate ( ) 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 and have inhibition effect on carbon steel corrosion, and the inhibition efficiency increases with increase in concentrations of and ; at the same concentration, the inhibition efficiency of is higher than that of . The increase in concentrations of and 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 is higher than that of . Electrochemical impedance spectroscopy (EIS) tests reveal that the charge transfer resistance and passive film resistance increase with increase in concentrations of or ; at the same concentrations, as for the charge transfer resistance and passive film resistance were bigger than those of . AFM imaging technique shows that local corrosion was inhibited obviously after the addtion of or , and passive film of was much more compact than that of . AFM force–distance curves indicate that the passive film of is much stiffer than that of .