The effects of natural Artemisia oil on the corrosion of steel in molar hydrochloric acid were studied by the measurements of weight loss, electrochemical and EIS polarisation. The results obtained revealed that Artemisia oil reduced the rate of corrosion. The corrosion inhibition efficiency increased with the increase of inhibitor concentration. Potentiodynamic polarisation studies clearly revealed that the presence of the natural Artemisia oil did not alter the mechanism of the hydrogen evolution reaction and acted essentially as a cathodic inhibitor. Good agreement between gravimetric and electrochemical polarisation results was noted. The effect of temperature on the corrosion behaviour of steel in 1M HCl, with and without the oil in the temperature range of 308-353 K, indicated that inhibition efficiency increased with temperature. The adsorption of Artemisia oil on the steel is followed by Frumkin adsorption isotherm.
Essential oil from fennel (Foeniculum vulgare) (FM) was tested as corrosion inhibitor of carbon steel in 1 M HCl using electrochemical impedance spectroscopy (EIS), Tafel polarisation methods and weight loss measurements. The results show that the increase of the charge-transfer resistance (R ct ) with the oil concentration supports the molecules of oil adsorption on the metallic surface. The polarization plots reveal that the addition of natural oil shifts the cathodic and anodic branches towards lower currents. Such shifts indicate that FM oil acts as a mixed-type inhibitor. The global rate of corrosion estimated by weight loss measurements confirms the above results. The inhibition efficiency attains a maximum of 76 % at 3 mL/L, but decreases with the rise of temperature. The analysis of FM oil, obtained by hydro-distillation, using Gas Chromatography (GC) and Gas Chromatography/Mass Spectrometry (GC/MS) showed that the major components were limonene (20.8 %) and β-pinene (17.8%). The adsorption of FM on the steel surface has been discussed according to the chemical composition of the oil, giving an explanation to the obtained results.
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