Fennel seed extract as green corrosion inhibitor for 304 stainless steel in hydrochloric acid solutions

The inhibitive and adsorptive characteristics of ethanol extract of fennel seeds for the corrosion of 304 stainless steel (SS) in 1 M HCl solutions have been studied using weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy, and electrochemical frequency modulation methods for monitoring corrosion. Ethanol extract of fennel is a good adsorption inhibitor for the corrosion of 304 SS in HCl. The inhibitive property of the extract is attributed to the presence of anethol and fenchone as major constituents in the extract. Inhibition efficiency increased with increasing concentration of the extract but decreased by increasing the temperature. Adsorption studies revealed that Langmuir adsorption isotherm is the best adsorption model applicable to the adsorption of fennel extract on 304 SS surface. Activation and adsorption parameters were evaluated and discussed. Potentiodynamic polarization measurements indicated that the inhibitor is of mixed type. The results obtained from these techniques were in good agreement to prove the validity of these tools in the measurements of the tested inhibitor.