Adsorptive studies of the inhibitive properties of ethanolic extracts of Parinari polyandra on Mild steel in acidic media

Communication in Physical Sciences 2019, 4(1): 39-47 Authors: F E Awe, M Abdulwahab & H A Otaru  Corrosion inhibition effectiveness of ethanol extracts of Parinari polyandra for mild steel was investigated using gravimetric and polarization methods. The influence of extract concentrations (0.1g/l to 0.5g/l) and temperatures (303K to 323K) on corrosion and corrosion inhibition were assessed. The results obtained showed that the plant extracts decreased the corrosion rate of mild steel in the acid medium. The corrosion rate decreased with increasing extract concentration for mild steel at 303 K. Inhibition efficiency in all the systems decreased with a rise in temperature, suggesting physical adsorption of the extract constituents on the metal surfaces. Linear polarization studies showed that the plant extract suppressed both the anodic and cathodic half reactions of the corrosion processes, thereby acting as mixed-type inhibitors. Langmuir isotherm was found to be the best isotherm that described the adsorption behaviour of the extract on the surfaces of mild steel at room temperature, whereas the adsorption property at elevated temperature was best described by the Freundlich and Temkin adsorption isotherms. Calculated values of free energy of adsorption, ∆????????????????????, on mild steel in the presence of the inhibitor was found to be within the range expected forphysical adsorption mechanism. Corrosion activation energy (Ea) values for mild steel in the acid solutions increased in the presence of the inhibitor and were found to be less than 80 kJmol-1