Chemical Composition and Inhibitory Effect of Mentha Spicata Essential Oil on the Corrosion of Steel in Molar Hydrochloric Acid

The essential oil from aerial parts of Mentha spicata L. an aromatic member of the Lamiaceae family, collected from "Tazouka" (Errachidia-Morocco), was obtained by hydrodistillation using Clevenger apparatus and analyzed by GC and GC/MS. The constituents were identified by their Mass spectra and Retention indices. Forty one compounds consisting 91.90% of the total components were identified from the oil obtained. Among those, Carvone (29.00%) and Trans carveol (14.00%) were the major oil components. The inhibitory effect of this oil was estimated on the corrosion of steel in 1M hydrochloric acid using electrochemical polarisation and weight loss measurements. The corrosion rate of steel is decreased in the presence of natural oil. The inhibition efficiency was found to increase with oil content to attain 97% at 2.00 g/l. Polarisation curves revealed that this natural oil act as mixed type inhibitor. The temperature effect on the corrosion behaviour of steel in 1M HCl without and with the inhibitor at 2.00 g/l was studied in the temperature range from 303 and 333 K, the associated activation energy have been determined. The adsorption of oil on the steel surface was found to obey Langmuir's adsorption isotherm. EIS measurements show that the increase of the transfer resistance with the inhibitor concentration.