Mitigation of the Corrosion of Mild Steel in Acidic Solutions Using An Aqueous Extract of Calopogonium muconoide (cm) as a green corrosion inhibitor

Abstract

Okoche Kelvin Amadi, Stella Mbanyeaku Ufearoh, Innocent Ajah Okoro

The applications of inorganic and some organic corrosion have received several setbacks because of their toxicity. Consequently, current research interests are directed toward the design, synthesis and application of green corrosion inhibitors. This paper reports the use of the ethanol extract of Calopogonium muconoide against the corrosion of mild steel in 0.5 M hydrochloric acid using weight loss measurements at 303 K and 333 K. Results obtained from weight loss measurements indicated that the plant extract retarded the corrosion of mild steel coupons in the acid media at 91.39 % and 56.79 % inhibition efficiency thereby functioning as a good corrosion inhibitor against the dissolution of steel in 0.5 M hydrochloric acid. The inhibition efficiency of plant extract on mild steel in 0.5 M HCl was investigated. The inhibition performance was tested by weight loss technique. The results obtained from the weight loss method showed that inhibition efficiencies increase with an increase in the concentration of the plant extract molecules and with the highest inhibition efficiency observed at the optimum concentration of 1.2 g/L. At 303 K and 333 K, the inhibitor showed inhibition efficiency of 91.39 % and 56.79 % respectively. Inhibition efficiencies were also found to decrease with an increase in temperature. Apparent activation energy values in the inhibited systems (35.62 kJ/mol, 39.23 kJ/mol/44.47 kJ/mol, 49.49 kJ/mol, 56.64 and 58.10) were found to be greater than that of the free acid solution (12.98 kJ/mol) showing the adsorption of the plant extract on the steel surface to be by physical mechanism.  The following adsorption isotherms were implored in the study; Freundlich, El-Awardy et al and Langmuir isotherms with Langmuir showing the best description of the experimental data with correlation coefficient value (R² > 0.99). In the study, values of enthalpy, Δ???? were all negative showing the exothermic nature of the corrosion and inhibition processes while free energy values for the inhibition processes at 303 and 333 K were -16.84 kJ/mol and -15.56 kJ/mol respectively revealing the inhibition of mild steel in the acid media by the plant extracts to be spontaneous except at 1.0 g/L and 1.2 g/L concentrations at both temperatures.