Cascabela Thevetia Plant Extract as Corrosion Inhibitor for Carbon Steel in Polluted Sodium Chloride Solution

Abstract

The inhibiting effect of Cascabela Thevetia extract (CTE) in polluted sodium chloride (3.5% NaCl+16 ppmNa2S) on the corrosion of carbon steel (CS) was studied by weight loss (WL), potentiodynamic polarization (PP), electrochemical frequency modulation (EFM) and electrochemical impedance spectroscopy (EIS) techniques. The results showed that the inhibition efficiency (IE) increases with increase in extract dose and decreases with raising the temperature. %IE reached to ≈95% at 300 ppm CTE. The obtained results indicated that the investigated extract is physically adsorbed on the CS surface and follows Freundlich adsorption isotherm. The PP data revealed that this extract acts as mixed type inhibitor. Surface morphology was tested using atomic force microscope (AFM) technique. Some quantum chemical calculations were used to support the experimental data. The results obtained from the different techniques are in good agreement;