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In this study, effect of Fumaria officinalis extract, as a natural inhibitor, on the corrosion of carbon steel in hydrochloric acid solution has been studied by using electrochemical polarization and electrochemical impedance spectroscopy methods. The results show that the Fumaria officinalis extract have 94.97% mean efficiency at 2.0 g/L concentrations which shows that this extract is a fairly good inhibitor. Polarization curves indicated that this inhibitor is a mixed (cathodic/ anodic) one. According to the obtained results, inhibition efficiency increases by increasing the inhibitor concentration. Investigation of the effect of temperature on the efficiency of the extract was done by electrochemical polarization method in the range of 35- 65°C which shows that efficiency of the extract decrease by increasing the temperature. Adsorption of inhibitor follows the Langmuir adsorption isotherm in this range of temperature. Thermodynamic adsorption parameters (Kads, ΔGads) of inhibitor were calculated by using the Langmuir adsorption isotherm. The values of ΔGads for all temperatures were close to -16 kJ mol-1, which indicates the electrostatic adsorption (physical adsorption) of the extracts molecules on the surface of the metal. Activation parameters of the corrosion process such as activation energies, Ea, activation enthalpies, ΔH* and activation entropies, ΔS*, were calculated by the obtained corrosion rates at different temperatures. The amount of activation energy of the acid solution with the extract is larger than it without the extract which confirm that the adsorption is physical.

Keywords: Natural inhibitor, Carbon steel, Hydrochloric acid, Fumaria officinalis extract, Electrochemical polarization method, Electrochemical impedance spectroscopy

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