Study of the inhibition of the corrosion of iron steel in neutral solution by electrochemical techniques and theoritical calculations

The effect of triazole organic molecules (triazole thiol and amino triazole) containing heteroatoms such as nitrogen or sulfur on the corrosion behavior of iron was investigated. Electrochemical studies of the iron samples were performed in an aerated solution of NaCl (3%) by means of electrochemical impedance spectroscopy (EIS) as well as polarisation curves. These results are completed with theoretical calculations, which allow determining the possible anchoring site suitable for bonding.The recorded electrochemical data showed that the corrosion resistance was greatly enhanced in presence of aminotriazole which acts on the anodic electrochemical processes. The inhibition effect depends on molecule concentration. The maximal protection efficiency reached 67%. These results were confirmed by impedance measurements where it was observed that the inhibitor increases the polarisation resistance. For triazole thiol, the protection is about only 17%. These molecules show three different possible sites suitable for protonation. Theoretical calculations indicate that protonation is favoured on the site N = C of the molecule. The corrosion protection could be explained by adsorption of the inhibitor through the N-atom and the consequent growth of an organo metallic layer attached to the metal surface which prevents the formation of porous corrosion products in chloride medium.