The corrosion inhibition effects of alkaloids and non- alkaloids extracts of andrographis paniculata (King Bitters) leaves on mild steel.- B.U. Ugi and I. E.Uwah
The corrosion inhibition performance of the alkaloid and non -alkaloid extracts of andrographis paniculata (AEAP and NAEAP)leaves on the corrosion of mild steel in 0.5 M HCl solution at 3030K and elevated temperatures of 313, 323 and 333oK was investigated and compared using weight loss method (gravimetric) and hydrogen evolution (gasometric) technique respectively. The results indicate that both extracts inhibit the corrosion of mild steel in the medium. However, AEAP exhibits higher maximum inhibition efficiency (97.87%) than NAEAP (54.6%) at 2.0g/L. Generally inhibition efficiency was found to increase with increase in concentration of both leaf extracts but decreased with rise in temperature. The result further revealed the highest inhibition efficiency of 97.8% and 54.6% for the AEAP and NAEAP respectively. However, 2.0g/L concentration showed a better performance in the inhibition of 0.5M HCl for both samples. Inhibition mechanism was deduced from the temperature dependence of the inhibition efficiency as well as from activation parameters that govern the process. Adsorption of both extracts on the mild steel coupon was found to obey the Langmuir adsorption isotherm. The mechanism of physical adsorption is proposed from the obtained thermodynamic parameters as equilibrium constant (Kad) showed a decrease with increased temperature, free energy of adsorption (-∆Goad) values were more negative than 40KJ/mol, standard enthalpy of activation (∆H)
values were low (i.e < 100KJ/mol) and activation energy (Ea) values obtained were less than 80KJ/mol.