Adsorption and electrochemical studies on the synergistic interaction of alkyl benzimadazoles and ethylene thiourea pair on mild steel in hydrochloric acid

Corrosion protection properties of alkyl benzimidazoles (MBI, EBI & PBI) and ethylene thiourea (ETU) on mild steel in hydrochloric acid at different temperatures have been studied by polarization, electrochemical impedance study (EIS), adsorption, surface morphological studies and computational calculations. Synergistic and hydrogen bonded interaction takes place on metal surface and the extent of synergistic interaction increases with temperature. Computational quantum chemical approach is used to derive electronic properties of the inhibitor molecules for ascertaining the extent synergistic interaction, inhibitive effect and molecular structures. The corrosion inhibition efficiencies and the global chemical reactivity relate to parameters such as total energy, EHOMO, ELUMO and gap energy (ΔE). Ethylene thiourea interacts with alkyl benzimidazoles up to a bond length of approximately 1.99 Å. This interaction and bond length represents the formation of a hydrogen bond between the ETU and alkyl benzimidazoles. This synergistic interaction offer extended inhibition efficiency toward mild steel in hydrochloric acid especially at elevated temperatures.