Electrochemical, Spectroscopic and Quantum Chemical Calculation Studies on Some Quinoxaline Derivatives As Corrosion Inhibitors for Mild Steel in Hydrochloric Acid Medium
In this study, the corrosion inhibition and adsorption characteristics of four quinoxaline derivatives (Me-4-PQPB, Mt-3-PQPB, Mt-4-PQPB and Oxo-1,3-PQPB) on mild steel surface in 1 M HCl were investigated. Potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) techniques were used in the study. Fourier transform infrared (FTIR) and ultraviolet-visible (UV-Vis) spectroscopic techniques were used to investigate possible formation of Fe/inhibitor complex and/or adsorption of the inhibitors on steel surface. Quantum chemical calculations were carried out on the molecules to correlate experimental results with quantum molecular parameters. The results showed that the studied molecules inhibit corrosion of mild steel in HCl medium with Me-4-PQPB having the best inhibition property. The inhibitors are mixed-type in their activities. All the inhibitors physisorb and chemisorb spontaneously on mild steel surface and their adsorption behaviour obeyed Langmuir equation. Some quantum chemical parameters support the observed trend of inhibition potencies and suggest that the inhibition effects were attributed to the protonated forms of the quinoxaline derivatives. The graphical surfaces of condensed Fukui indices suggest possible adsorption sites on the inhibitors.
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