Evaluation of the inhibition performance of piperazine-based polyurea towards mild steel corrosion: The role of keto-enol tautomerization

The lack of solubility of polyurea materials impedes their application as effective inhibitors against metallic corrosion in aqueous media. Herein, we have synthesized a new piperazine-based polyurea inhibitor (PUCorr) which is readily soluble in water through dispersion in N-methyl-2-pyrrolidone for mild steel corrosion. The inhibitor exhibits a sufficient protection of the surface of mild steel via an intra-molecular keto-enol proton transfer mechanism leading to the formation of the Fe-PUCorr complex. First-principles calculations proposed that the keto-enol tautomerism enhances the adsorption with an increase of adsorption energies of 510, 221, 171 and 211 kJ/mol on {100}, {110}, {111} and {112} surfaces of iron, respectively. The presence of PUCorr at 100 ppm decreases the corrosion current density from 30.3 to 3.05 μA/cm² in 0.5 M NaCl at room temperature, exhibiting a remarkable inhibition efficiency of 94.5%. Electrochemical measurements revealed that PUCorr functions as a mixed-type inhibitor, suppressing both anodic and cathodic processes. The use of synthetic polyurea materials with a low dosage shall provide a promising approach to reduce mild steel corrosion in harsh environments.