Surface protection activities of some 6-substituted 3-chloropyridazine derivatives for mild steel in 1 M hydrochloric acid: Experimental and theoretical studies

Three 6-substituted 3-chloropyridazine derivatives were tested for their potentials to protect mild steel surface and inhibit mild steel corrosion in 1 M HCl solution. The compounds are 3-chloro-6-(1H-pyrazol-1-yl)pyridazine (Pz1), 1-(6-chloropyridazin-3-yl)piperidin-4-ol (Pz2), and 3-chloro-6-(3,5-dimethyl-1H-pyrazol-1-yl)pyridazine (Pz3). Corrosion tests were conducted using potentiodynamic polarization and electrochemical impedance spectroscopy techniques. The interactions of the pyridazine molecules with mild steel were investigated using FTIR spectroscopic technique. Further insights into the molecular behaviour of the studied pyridazines as corrosion inhibitors were derived from theoretical density functional theory and Monte Carlo simulations studies. The results showed increasing corrosion inhibition efficiency with increasing concentrations of pyridazine derivatives. Polarization measurements suggested that the studied pyridazines are mixed-type inhibitors, inhibiting both oxidative and reductive reactions involved in the corrosion process. The impedance spectroscopy results revealed single-charge-transfer moderated dissolution of mild steel in 1 M HCl and formation of pseudo-capacitive protective film of the studied compounds on the steel surface. Protective action of the new pyridazines for mild steel was reaffirmed by scanning electron microscopy surface analyses. Density functional theory and Monte Carlo simulations calculations substantiated experimental results. The trend of surface protection efficiency of the compounds is Pz3 > Pz2 > Pz1 as observed from both experimental and theoretical studies.