Green corrosion inhibition of carbon steel in hydrochloric acid medium by three polarity-graded plant extract fractions of Lepidium draba and Artemisia herba-alba: A comparative gravimetric and thermodynamic study

• H. Bounab¹, A. Boultif², M. Belferragui^3,4, A. Benyamina¹, S. Remache⁵, W. Azabi¹, A. Kalla⁶, M. Benahmed¹, I. Ferhoune⁴, A. Zellagui⁷ and N. Gherraf¹

¹ Laboratory of Natural Resources and Management of Sensitive Environments, Oum El Bouaghi University, 04000 Oum El Bouaghi, Algeria
² Laboratory of Applied Chemistry and Materials Technology, Oum El Bouaghi University, 04000 Oum El Bouaghi, Algeria
³ Laboratory of Physical Chemistry, University 08 May 1945, BP 401, 24000 Guelma, Algeria
⁴ Department of Process Engineering, Faculty of Sciences and Applied Sciences, Larbi Ben M'hidi University, 04000 Oum El Bouaghi, Algeria
⁵ Scientific and technical research center in physico-chemical analysis (CRAPC) BP 384, Zone Industrielle Bou-Ismail RP 42004 Bou-Ismail, Tipaza, Algeria
⁶ Laboratory of Bioactive Molecules and Applications (LBMA), Echahid Cheikh Larbi Tebessi University, 12002 Tebessa, Algeria
⁷ Laboratory of Biomolecules and Plant Breeding, Larbi Ben M'hidi University, 04000 Oum El Bouaghi, Algeria

Abstract: The replacement of toxic, non-biodegradable synthetic corrosion inhibitors with low-cost, renewable plant-based alternatives is a growing priority for industries operating in acidic environments. This study compares three polarity-graded plant extract fractions − dichloromethane (DM), ethyl acetate (AE) and n-Butanol (n-Bu) − obtained from Lepidium draba and Artemisia herba-alba collected in the Oum El Bouaghi region of north-eastern Algeria. The two plant systems were investigated separately on API X60 and API X48 carbon steels, respectively, in 1 M hydrochloric acid using the weight-loss method according to ASTM G31-72. Extract concentrations of 100–500 ppm and temperatures of 30–50°C were evaluated after 1 h immersion; an additional 20°C point was available for the A. herba-alba system. Inhibition efficiency increased with concentration and generally decreased with temperature. The AE fraction gave the highest efficiency within each plant system, reaching 98.6% for L. draba/X60 at 500 ppm and 30°C and 60.0% for A. herba-alba/X48 under the same nominal conditions. However, because each plant was tested on a different steel grade, the difference between the two systems cannot be attributed to extract composition alone. Langmuir adsorption generally provided the strongest fit, although the Freundlich model was superior for L. draba/DM at 50°C. Calculated ΔG⁰_ads values were negative (about −20 to −31 kJ·mol⁻¹), while adsorption enthalpies were exothermic. The thermodynamic data therefore support predominantly physical adsorption under the tested conditions, while a specific chemisorption contribution cannot be established without complementary surface and electrochemical measurements. The results demonstrate concentration- and temperature-dependent inhibition by the investigated plant fractions and identify AE as the best-performing fraction within each separately tested plant/steel system.

Keywords: green corrosion inhibitor, plant extract, carbon steel, weight-loss method, adsorption isotherm, Lepidium draba, Artemisia herba-alba, ethyl acetate fraction

Int. J. Corros. Scale Inhib., 2026, 15, no. 4, 423-437
doi: 10.17675/2305-6894-2026-15-4-18

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