Kinetics and thermodynamic study of corrosion inhibition of mild steel in 1.5m HCl medium using cocoa leaf extract as inhibitor

Abstract

This study examined the corrosion inhibition of mild steel in 1.5M HCl solution using cocoa leaf extract as an inhibitor. The effect of inhibitor concentrations, kinetics, and time of immersion were undertaken at 30^oC while the thermodynamic parameters were determined with temperature range of 35^oC – 55^oC. FTIR result indicated that the actual adsorption of the inhibitor is as a result of donation of single pair of electrons on oxygen to the vacant d – orbitals of the metal (mild steel) that leads to the formation of complexes on the mild steel surface. The corrosion rate decreased from 1.64 g/cm²hr to 0.09gm/cm²hr in the presence of inhibitor used. However, increased in temperature showed a decreased in inhibition efficiency this resulted to an increase in rate of corrosion. Half – life of the corrosion kinetics ranges from 49.71 – 53. 15hr which is directly proportional to the inhibitor concentrations. Activation energy Ea, enthalpy (ΔH^o), and entropy (ΔS^o) calculated showed good interactions. The enthalpy of activation ranges from 63.28kJ/mol to 97.55kJ/mol. Rise in activation energy with inhibitor concentration confirmed the physical (physisorption) adsorption mechanism for the corrosion of mild steel surface. Endothermic nature of the corrosion process is ascertained with the positive value of ΔH^o obtained.

Keywords: Gravimetric, thermodynamic, adsorption, activation energy