Carbon steel corrosion inhibition in acid medium by imidazole-based molecules: Experimental and molecular modelling approaches

This paper deals with application of imidazole (IMI) and four imidazole derivative molecules: 4-(imidazole-1-il)-phenol (PHEN), [4-(1H-imidazole-1-yl)-phenyl]methanol (METH), 2-(1H-imidazol-1-yl)-1-phenylethan-1-one (ETHAN) and 4-(1H-imidazole-1-yl)benzaldehyde (BENZ), towards corrosion inhibition of 1020 carbon steel in acidic medium. From IMI to ETHAN, the corrosion inhibition efficiency more than doubled in gravimetric experiments and increased 85% and 68% in the potentiodynamic polarization and electrochemical impedance assays, respectively. Both gravimetric and electrochemical tests gave the following decreasing order for the corrosion inhibition efficiency: BENZ > ETHAN > METH > PHEN > IMI. Quantum chemical calculations based on density functional theory (DFT) method showed that global hardness of the inhibitor molecules and inhibition efficiency were inversely proportional, which means that a softer molecule (or lower charge/radius ratio considering HSAB theory) leads to higher anticorrosion efficiency. Monte Carlo method (MC) was used to calculate the adsorption energies in a simulated water environment, and Compass force field was selected towards obtaining the solvation energy between inhibitor and metallic surface. The calculated solvation energy showed an inverse correlation between solvation energy and corrosion inhibition, having BENZ molecule lower solvation energy and lower global hardness which explains better anticorrosion efficiency among other IMI-based molecules, which shows the importance of molecule polarity over the corrosion inhibition of carbon steel.