Investigation of the Inhibitive Properties of Alchornea laxiflora leaves on the Corrosion of Mild Steel in HCl: Thermodynamics and Kinetic Study

Abstract

The use of naturally occurring compounds as corrosion inhibitors is of potential interest because of their cost effectiveness, abundant availability and environmental acceptability. Therefore, the study investigates the inhibition efficacy of acid extract of Alchornea laxiflora leaves on mild steel in acidic medium using gravimetric method. Experiments were performed by varying the immersion time, concentration of extract and the temperature. The results showed that acid extract of Alchornea laxiflora leaves is a potential inhibitor for the corrosion of mild steel in acidic medium. The corrosion rate of mild steel in 1M HCl decreases with increase in the concentration of the extract. The inhibition efficiency increases progressively as the concentration of the extract increases but decreases with rise in temperature and the exposure time. The highest inhibition efficiency observed in the presence of the extract was 96 %. Activation energy was found to be 21.81 kJ mol-1 for the blank and increases to 82.57 kJ mol-1 in the presence of the extract. Thermodynamic parameters such as enthalpy change, entropy change and Gibb’s free energy were evaluated. Kinetics of the reaction in the presence of the extracts revealed that it follows a first order reaction and the half-lives increase as the concentration of the extract increases. Adsorption studies revealed that Langmuir adsorption isotherm is the best adsorption model applicable to the adsorption of the extract on mild steel surface. Preliminary investigation of the phytochemical cons