ABSTRACT
In this study, extracts from Ocimumgratissimum(O.G) and Hyptissuaveolens(H.S) leaves were subjected to the following analyses: physicochemical and phytochemical analyses. The medium carbon steel samples were subjected to corrosion inhibition test using gravimetric method, mechanical tests (hardness, tensile, and impact) and surface morphology evaluation using scanning electron microscopy (SEM). The corrosion inhibition effects of the leaves extracts on medium carbon steel surface in 0.5M of HCl, H2SO4 andNaCl solutions were investigated at different temperatures (30, 40, 50 and 60oC). The results obtained show that the inhibition efficiency (IE) increased (with at least 1.8% in HCl, 1.6% in H2SO4 and 2.6% in NaCl)with increase in the inhibitors concentration (0-8% v/v) but decreases with increase in temperature from 30-600C for both inhibitors. The results showed that O.G has highest IE of 82.9% in HCl, 73.4% in H2SO4 and 82.7% in NaCl. Also H.S has IE of 81.5% in HCl, 69.7% in H2SO4 and 88% in NaCl. As the concentration of the inhibitors increases, higher values of the positive activation energy (Ea) (from 32.80-53.1kJ/mol, 22.5-33.2kJ/mol and 20.3-37.7 kJ/molin HCl, H2SO4 and NaCl respectively) and positive enthalpy of adsorption (�”H)were obtained, indicating the physical adsorption and endothermic nature of the inhibitors on carbon steel. Also the negative values of free energy of adsorption (�”Gads) (between 18kJ/mol-24kJ/mol) indicating a physisorption of the inhibitors and the adsorption of both O.G and H.S leaves extracts on the steel surface in the three media was found to obey the Langmuir adsorption isotherm. The results obtained from the mechanical properties of the steel showed higher values (97.5HRB, 637.5N/mm2 and 52.2J) for the inhibited samples than uninhibited ones (96.5HRB, 559.3N/mm2 and 46.0J). Finally the results obtained from SEM confirmed the high performance of the inhibitor by minimizing the pits and severe damage on the carbon steel samples