INHIBITION CAPABILITY OF Dennettia tripetala LEAVES EXTRACT ON CARBON STEEL IN 4 M HCL SOLUTIONS

The inhibitive ability of Dennettia tripetala (DT) leaves extract on the corrosion of carbon steel in 4 M HCl aqueous solution has been investigated by gravimetric and electrochemical techniques. Results obtained reveal that DT leaves extract gave good inhibition efficiency on carbon steel corrosion. Gravimetric results showed that the corrosion inhibition potentials of DT leaves extract decreased with increase in temperature but increased in inhibitor concentration. Tafel polarization studies have shown that DT leaves extract suppresses both the cathodic and anodic processes and thus it acts as mixed-type inhibitor without altering the corrosion mechanism of carbon steel. Electrochemical impedance results gave 87.1% inhibition capacity using 1000mg/L DT leaves extract. The associated activation thermodynamic parameters have been determined, ΔH°ads and ΔS°ads. Values show that the adsorption process is spontaneous and involves electrostatic interactions between the inhibitor molecules and carbon steel surface via physical adsorption. The formation of film layer due to electrostatic interaction essentially blocks cathodic reactions and retards anodic dissolution of the metal. Quantum chemical calculations using DFT were used to calculate some electronic properties of the molecule in order to establish any relationship between the molecular structure of Dennettia tripetala and inhibitive effect. DT leaves extract performed well as inhibitor for carbon steel in 4 M HCl solutions.