Abstract:
The inhibitory effect of ethanolic extracts of Ficus capensis and Lecaniodiscus cupanioides on mild steel in hydrochloric acid solution was studied by weight loss and electrochemical methods at room temperature. The experimental results revealed that the extracts have a good inhibiting effect on the metal tested in 2 M HCl solution. The inhibition efficiency increases with inhibitor concentration for both extracts (from 45.03 % at 0.2 g/100mL to 78.17 % at 1 g/100mL in the presence of ethanolic extract of Lecaniodiscus cupanioides (EELC) and from 48 % at 0.2 g/100mL to 82.85 % at 1 g/100mL in the presence of ethanolic extract of Ficus capensis ( EEFC)). However,
inhibition efficiency remarkably decreased when temperature was raised from 303-333K. Positive enthalpy suggests the endothermic nature of the dissolution of mild steel in presence and absence of the extracts while the negative value of free Gibb’s energy confirms the spontaneity. Increase in half life with increasing concentration of the extracts further revealed the effectiveness of the extracts, while the kinetics of the reaction in the presence of the extracts is first order reaction. Inhibition of corrosion was found to be due to adsorption of the extract on metal surface (physisorption) which is in conformity with Langmuir’s adsorption isotherm. Potentiodynamic polarization measurement revealed that the two extracts act as effective mixed-type inhibitors. Fourier Transform Infra-red spectroscopy (FT-IR) revealed that the ethanolic extracts contains C=O, O-H, N-H functional groups. Scanning Electron Microscopy (SEM) and Atomic Absorption
Spectroscopy (AAS) studies confirmed that the inhibition of corrosion on mild steel occurs through adsorption of the inhibitor molecules.
