Corrosion inhibition potential of Terminalia avicennioides extract on mild steel in 1.0 M HCl: kinetics, thermodynamics and synergestic studies

The corrosion inhibition effect of Terminalia avicennioides (TA) stem extract in 1.0 M HCl solution was investigated using weight loss and electrochemical method. The operation variables considered include temperature (303-333 K) and concentration of the inhibitor (0.2 - 1.0 g/L). Inhibition efficiency increased from 21.88% to 88.71% with concentration but decreased with rise in temperature which is suggestive of physisorption. This was supported by the values of activation energies (Ea) obtained ranging from 22.67 KJ mol−1 to 60.67 KJ mol−1 which was lower than 80 KJ mol−1. The values of Gibb’s free energy of adsorption (∆Gads) indicated that the adsorption of the inhibitor on mild steel surface was a spontaneous process. The Kinetic treatment of the data followed a pseudo-first order reaction while the positive values obtained for enthalpy and entropy of activation is reflective of endothermic reaction nature and associative activation complex respectively. The adsorption mechanism followed the Langmuir adsorption isotherm model. Electrochemical analysis showed that the inhibitor functioned as a mixed type inhibitor. The inhibition efficiency of the inhibitor was found to be enhanced by the presence of KI. Therefore the extract functioned as good corrosion inhibitor for mild steel in 1.0 M HCl.