Influence of 6-phenyl-3(2H)-pyridazinone and 3-chloro-6-phenylpyrazine on mild steel corrosion in 0.5 M HCl medium: experimental and theoretical studies

Abstract

Two pyridazine derivatives, namely, 6-phenyl-3(2H)-pyridazinone (P1) and 3-chloro-6-phenylpyrazine (P2) were investigated for their influence on mild steel corrosion in 0.5 M HCl, using Tafel polarization, electrochemical impedance spectroscopy (EIS), surface morphology, FTIR and UV-vis techniques. Quantum chemical calculations were also conducted to corroborate experimental findings. P1 was found to accelerate corrosion at low concentrations but exhibits inhibitive action at higher concentrations, attaining 61% inhibition efficiency at 1.25 mM. The inhibitive action of P2 increases with increasing concentration from 88% at 0.1 mM to 96% at 1.25 mM as deduced from EIS measurements. Both compounds are mixed type inhibitors. P2 seems to display chiefly anodic inhibitive effects. The adsorption of P2 on mild steel surface obeys the Langmuir adsorption isotherm and involved competitive physisorption and chemisorption mechanisms. Scanning electron microscopy analyses of steel surfaces in acid-inhibitor solutions showed that both compounds protect mild steel surface effectively at 1.25 mM. FTIR and UV-vis spectroscopic analyses revealed that NH, CO, and CN functional groups of the pyridazine derivatives are actively involved in adsorption of the molecules onto steel surface. Quantum chemical parameters showed that the higher inhibition efficiency of P2 compared to P1 might be related to better electron acceptance ability of P2.