Aminomethylpyridazine isomers as corrosion inhibitors for mild steel in 1 M HCl: Electrochemical, DFT and Monte Carlo simulation studies

Abstract

Three isomers of aminomethylpyridazine, namely 4-pyridazinemethanamine (Pz1), 3-aminomethyl-pyridazine (Pz2) and 3-amino-6-methylpyridazine (Pz3) were studied for their corrosion prevention abilities on mild steel in 1 M HCl with the aid of potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS) and computational methods. Other procedures such as Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible (UV-vis) spectrometer and scanning electron microscopy (SEM) were employed to support the results obtained from the PDP, EIS and computational techniques. The effect of different mode of substitution of aminomethyl group on the pyridazine molecule on corrosion inhibition potentials was investigated. The compounds showed increasing corrosion inhibition efficiency with increase in concentration, with Pz2 showing up to 91% inhibition efficiency at 500 ppm. The order of inhibition efficiency of the compounds is Pz2 ˃ Pz1 ˃ Pz3. The shift in corrosion potential ranged from 17 mV to 44 mV with respect to the blank result, suggesting that the compounds exhibited mixed-type inhibitive effects, though with Pzl and Pz2 being predominantly anodic and Pz3 being mainly cathodic in character. The dissolution of steel in the corrosive electrolytes followed a single-charge-transfer mechanism and the inhibitors formed pseudo-capacitive protective film over the steel surface in 1 M HCl. FTIR and UV-vis spectra revealed the interactions between mild steel and the inhibitor molecules, while the SEM plates revealed the morphology of steel surface in the corrosive electrolytes at varying degree of inhibitor concentration, confirming the protection efficiency of the pyridazines on mild steel. DFT calculations showed that Pz2 has the lowest lying unoccupied frontier molecular orbital. Monte Carlo simulations also confirmed highest magnitude of adsorption energy for Pz2 adsorbed on Fe(110) compared to Pz1 and Pz3.