Etude de l’inhibition de la corrosion d’acier doux par des composés organiques en milieu acide.

Abstract

The corrosion inhibitions of mild steel in 0.5M H2SO4 solution by synthetized 5-(Phenyl)-4H- 1,2,4-triazole-3-thiol (5-PTT) and 5-(2-hydroxyphenyl)-1,3,4-oxadiazole-2-thiol (5-HOT) inhibitors have been investigated by different methods (weight loss, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques…) at various concentrations and temperatures. The results obtained revealed that these compounds performed excellently as corrosion inhibitors for mild steel in 0.5M H2SO4 solution. It was found that the inhibition efficiencies increased with inhibitor's concentration to reach efficiencies up to 91 % at 0.5 mM. The addition of potassium iodide to PTT in solution increased the inhibition efficiencies of these latter. A synergistic effect was observed between KI and inhibitor with optimum of concentration of 0.5 mM / inhibitor + 0.2% potassium iodide. Potentiodynamic polarization studies have shown these inhibitors act as mixed-type inhibitors retarding the anodic and cathodic corrosion reactions with predominant effect on the cathodic reaction. The effect of temperature on the inhibition efficiency was also determinate in the range from 25°C to 50°C; some thermodynamic parameters such as apparent activation energy and adsorption free energy have been calculated and discussed. Adsorption of inhibitors alone or in combination with potassium iodide on the metal surface obeyed the Langmuir adsorption isotherm. The values of free energy of adsorption (∆G°ads) indicated that adsorption of inhibitors derivatives is a spontaneous process and they are adsorbed chemically as well as physically in the absence and presence of KI and inhibited the corrosion of mild steel by blocking the active site of the metal. Scanning electron microscopy (SEM) study confirmed that the inhibition of corrosion of mild steel by these inhibitors is through adsorption of the extract molecules on surface of metal. Quantum chemical parameters were also calculated to characterize adsorption mechanisms. Acceptable correlations were obtained between experimental (inhibition efficiencies, ΔG°ads, Ea) and quantum calculation parameters (dipole moment, EHOMO, ELUMO). Results obtained with different methods are in good agreement. Originality/value – Electrochemical techniques have been used for the first time to study synergistic effect of studied inhibitors and potassium iodide KI on the inhibition corrosion of mild steel in 0.5M H2SO4 solution. The results suggest that the mixture (inhibitor + KI) could find practical application in corrosion control in aqueous acidic environment.