Abstract:

The corrosion inhibition by 5-(Phenyl)-4H-1,2,4-triazole-3-thiol (PTT) on mild steel in 0.5M H2SO4 solution has been investigated by weight loss, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques at various concentrations and temperatures. The results obtained revealed that this compound performed excellently as corrosion inhibitor for mild steel in 0.5M H2SO4 solution. It was found that the inhibition efficiency increased with inhibitor concentration reached a maximum of 91.6 % at 0.5 mM. The addition of potassium iodide to PTT in solution increased the inhibition efficiency of this latter. A synergistic effect was observed between KI and inhibitor with optimum of concentration of 0.5 mM/PTT + 0.2% potassium iodide. Potentiodynamic polarization studies have shown that PTT inhibitor acts as a mixed-type inhibitor retarding the anodic and cathodic corrosion reactions with predominant effect on the cathodic reaction. Adsorption of inhibitor alone or in combination with potassium iodide on the metal surface obeyed the Langmuir adsorption isotherm. The effect of temperature on the inhibition efficiency was also determinated, some thermodynamic parameters such as apparent activation energy and adsorption free energy have been calculated and discussed. Results obtained with different methods are in good agreement. Scanning electron microscopy (SEM) study confirmed that the inhibition of corrosion of mild steel is through adsorption of the extract molecules on surface of metal. Quantum chemical parameters were also calculated to characterize adsorption mechanism. Acceptable correlations were obtained between experimental (inhibition efficiencies, ΔGads, Ea) and quantum calculation parameters (dipole moment, EHOMO, ELUMO). The high inhibition efficiency was declined in terms of strongly adsorption of protonated inhibitor molecules on the metal surface and forming a protective film. Originality/value–Electrochemical techniques have been used for the first time to study synergistic effect of PTT inhibitor and potassium iodide on inhibition of corrosion of mild steel in 0.5M H2SO4 solution. The results suggest that the mixture (PTT + KI) could find practical application in corrosion control in aqueous acidic environment. The effect of molecular structure on the inhibition efficiency has been investigated by quantum chemical calculations. The electronic properties of inhibitor were calculated and are discussed. The theoretical results were found to be consistent with the experimental data reported.

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