Evaluation of the effectiveness of a mixed green corrosion inhibitor based on Caesalpinia sappan L. and red cabbage extract against carbon steel corrosion in a 3.5% NaCl solution

• Y. Pratesa, I. Baskoro and W.S. Johny

Department of Metallurgical and Materials Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia

Abstract: Caesalpinia sappan L. (secang wood, SW) extract – an abundant and indigenous plant from Indonesia – was evaluated as a corrosion inhibitor for API 5L X-52 steel in 3.5 wt.% NaCl solution. On the other hand, red cabbage (RC) extract is another promising green inhibitor due to anthocyanin concentration inside it. While SW contains tannins as its active substance. So, this study tried to explore the possibility of tannin-anthocyanin combination as a strong corrosion inhibitor. Potentiodynamic polarization revealed a corrosion rate reduction from 0.172 to 0.04 mm·yr^–1 at an optimal SW concentration of 0.75 mL. The EIS data corroborates enhanced surface protection, showing an increased charge-transfer resistance. The adsorption of both SW and SW-RC mixtures followed the Langmuir isotherm, with Gibbs free energies (ΔG_ads) of –20.79 and –7.08 kJ·mol^–1, respectively, indicating physisorption via electrostatic bonding. Fourier-transform infrared spectroscopy (FTIR) identified hydroxyl (–OH) and carbonyl (C=O) groups as key active sites facilitating adsorption. A synergistic parameter (S) of <1 confirmed antagonistic behavior in the SW-RC mixture, demonstrating no synergistic enhancement. These findings establish SW extract as a promising green inhibitor but highlight its incompatibility with RC extract in saline environments.

Keywords: green inhibitor, corrosion, red cabbage, secang wood

Int. J. Corros. Scale Inhib., 2026, 15, no. 2, 507-524
doi: 10.17675/2305-6894-2026-15-2-27

Download PDF (Total downloads: 18)

Back to this issue content: 2026, Vol. 15, Issue 2 (pp. 1-583)