Corrosion inhibition of mild steel by fennel seeds (Foeniculum vulgare mill) essential oil in 1 m hydrochloric acid solution

Abstract

As the importance of environmental protection has become increasingly recognized, the development of new green corrosion inhibitors has received increasing attention. In the present work, the corrosion inhibition ability of essential oil of Fennel seeds (EOFs) on the mild steel (MS) in 1.0 M HCl was evaluated by using different chemical and electrochemical methods such as: weight loss, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) methods at various temperatures. Potentiodynamic polarization curves showed that EOFs acts essentially as a mixed-type inhibitor controlling cathodic and anodic reactions, and the inhibition efficiency of up to 88% at 2 g/L was obtained. The EIS results showed an increase in polarization resistance (Rp) while the double layer capacitance (Cdl) decreases with an increase in EOFS concentrations. Weight loss analysis proved 89% inhibition efficiency for the acid solution containing 2 g/L of EOFs. The obtained results also showed that the inhibition efficiency decreased with an increase in the temperature, and the efficiencies of 89, 86, 80, and 76% were obtained at 303, 313, 323, and 333 K, respectively. The activation energy (Ea) of the corrosion process is 2.60 kJ/mol, the * * enthalpy (ΔHa) is 79.95 kJ/mol and the entropy (ΔSa) is 1.4 J·mol–1·K–1.