Journal of Basic and Applied Research International

Alkaloid, flavonoid and non alkaloid extracts of Medicago sativa stem (AEMSS, NAEMSS and FEMSS) were investigated as corrosion inhibitors of stainless steel metal in 1M H₂SO₄ acid solutions using conventional weight loss, hydrogen evolution and electrochemical impedance spectroscopy studies. The weight loss results showed that the plant extracts are excellent corrosion inhibitors to the metal tested as increase in concentration of the extracts showed a corresponding increase in inhibition efficiency while the temperature rise lead to removal of loosely bounded inhibitor molecules by agitation hence decreasing the inhibition efficiency. The results of electrochemical impedance spectroscopy have shown that the change in the impedance parameters, charge transfer resistance and double layer capacitance, with the change in concentration of the extract is due to the adsorption of active molecules leading to the formation of a protective layer on the surface of the metal. A physical adsorption mechanism was recorded by the inhibitor /metal interface and the Langmuir adsorption isotherm was well obeyed. The inhibitors proved to be stabled one on the metal and a spontaneous reaction process was recorded from the data of the Gibbs free energy.