Corrosion behaviour of mild steel in weak acidic solutions containing nitrite ions and hypericum perforatum

In this study, inhibitive corrosion efficiency of nitrite based inorganic inhibitor, commercially named Teknophos (TP), total extract of plant Hypericum perforatum (HP) and their mixtures (TP+ HP) on mild steel have been investigated at different temperatures and different inhibitor concentrations in fully de-aerated weak acidic solutions. Tafel extrapolation technique was used to evaluate the corrosion parameters of TP, HP and TP+ HP. Kinetic and thermodynamic properties such as corrosion activation energy, Arrhenius pre-exponential coefficient, corrosion enthalpy and corrosion entropy, respectively, were calculated and discussed. Inhibitors? inhibitive action was satisfactorily explained by using both thermodynamic and kinetic models. Adsorption isotherms are used to determine the surface coverage and performance of the inhibitors. Therefore in order to clarify the adsorption mechanisms of TP, HP and TP+ HP on mild steel surface, adsorption isotherms were tested. After the Tafel extrapolation experiments, optical microscope was used to examine the surface morphology of the samples to provide the confirmatory evidence for corrosion prevention caused by inhibitors.