Investigation of garlic extract (Allium sativum) as a green corrosion inhibitor for St3 steel in H₂S-containing medium

• R.E. Azizov¹, G.R. Gurbanov² and S.H. Gasimov³

¹ Azerbaijan State Oil and Industry University, Baku, AZ1010, Azerbaijan
² Department of Chemistry, Faculty of Chemical Technologies, Azerbaijan State Oil and Industry University, Baku, AZ1010, Azerbaijan
³ Azerbaijan State Oil and Industry University (ASOIU), Baku, AZ1010, Azerbaijan

Abstract: The corrosion inhibition performance of ethanolic garlic (Allium sativum) extract for St3 carbon steel in a controlled H2S-containing corrosive medium was systematically investigated using gravimetric and electrochemical methods. The extract was chemically characterized by gas chromatography–mass spectrometry (GC–MS) and Fourier-transform infrared spectroscopy (FTIR), while its inhibitory performance was evaluated as a function of extract concentration (0–300 ppm) and temperature (25–50℃). Gravimetric measurements demonstrated a pronounced concentration-dependent inhibition effect, with the inhibition efficiency reaching 98% at 300 ppm and 255. Increasing temperature reduced the protective performance; nevertheless, an inhibition efficiency of 81% was retained at 300 ppm and 50℃. Temperature-dependent corrosion-rate data were analysed using Arrhenius and transition-state relationships, revealing an increase in the apparent activation energy from 47.60±2.38 kJ∙mol^–1 in the uninhibited medium to 115.53±13.25 kJ∙mol^–1 at 300 ppm. Adsorption analysis indicated that the experimental surface-coverage data could be satisfactorily described by the Langmuir, Freundlich, and Temkin models, with the Freundlich relationship providing the highest coefficients of determination within the investigated concentration range. Electrochemical impedance spectroscopy showed an increase in charge-transfer resistance from 45 to 260 Ω∙cm², corresponding to an inhibition efficiency of 82.7% at 300 ppm, whereas potentiodynamic polarization measurements showed a decrease in corrosion current density from 120 to 22 µA∙cm^–2, corresponding to an inhibition efficiency of 81.7%. The modest shift in corrosion potential was consistent with mixed-type inhibition, although the relative effects on the individual anodic and cathodic processes could not be quantified without Tafel-slope analysis. Overall, the results demonstrate that garlic extract provides substantial concentration-dependent protection of St3 steel in the investigated H₂S-containing environment, while its effectiveness decreases with increasing temperature.

Keywords: green corrosion inhibitor, garlic extract, H2S environment, adsorption isotherms, Arrhenius analysis, thermodynamic parameters

Int. J. Corros. Scale Inhib., 2026, 15, no. 3, 654-688
doi: 10.17675/2305-6894-2026-15-3-31

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