Inhibitive effect of Thymus satureioides essential oil as a green corrosion inhibitor for mild steel in an acidic medium

Abstract

The efficiency of Thymus satureioides essential oil (EO) as inhibitor of mild steel corrosion in hydrochloric acid 1.0 M has been studied using polarization curves, electrochemical impedance spectroscopy (EIS) and weight loss measurements. The chemical composition of essential oil was characterized by 29 components, which accounted for 99.24% of the total oil. The major constituents were carvacrol (29.65%), followed by borneol (19.04%), linalool (11.79%), p-cymene (8.53%), camphene (7.01%), γ-terpinene (6.10%), α-pinene (4.55%) and caryophyllene (2.39%). The maximum inhibition efficiency (IE) (90%) was observed at the optimum concentration of 1.5 g/L. The electrochemical impedance spectroscopy data have shown that the formation of a protective film decrease the double layer capacitance and increases in the charge transfer resistance of mild steel. Increasing temperature reduces surface covered by the inhibitor, which results in a decrease of percentage inhibition efficiency from 89% to 76%. Polarization curves indicated that this EO can be classified as a mixed inhibitor in acidic medium with a predominant anodic inhibition. The value of enthalpy change is positive, which indicated endothermic adsorption process. The inhibition efficiencies calculated by weight loss exhibit a trend parallel to that of polarization and electrochemical impedance spectra measurements. We can conclude that essential oil extracted from T. Satureioides may be suggested as a green inhibitor against corrosion under acidic environment.