Corrosion inhibition of carbon steel in acidic media by Annona muricata leaf extract: electrochemical, adsorption and spectroscopic insights

Despite the increasing interest in plant-derived green corrosion inhibitors, the inhibition mechanism of Annona muricata leaf extract for carbon steel in acidic media remains largely unexplored. In this study, the corrosion inhibition performance of an ethanolic extract of An­nona muricata leaves was systematically investigated for SAE 1008 carbon steel in 1 mol L-1 HCl, combining gravimetric measurements and electrochemical techniques, electro­chemical impedance spectroscopy and potentiodynamic polarization curves. Complementary, Raman spectroscopy and scanning electron microscopy were used for surface characterization. Phytochemical screening confirmed the presence of several bioactive metabolites such as alkaloids, tannins, phenolic compounds, flavonoids, and lactones, which may contribute to the adsorption capability of the extract. The extract exhibited concentration-dependent inhibition, reaching approximately 92 % efficiency at 6 vol.%. Adsorption analysis showed that the inhibition process follows the Langmuir isotherm, suggesting the formation of a protective organic monolayer on the steel surface. Electrochemical measurements showed a decrease in corrosion current density and an increase in charge transfer resistance in the presence of the inhibitor. Potentiodynamic polarization results revealed that the extract acts as a mixed-type inhibitor. Surface analyses confirmed the adsorption of organic species and the formation of a protective film that reduces corrosion damage. These findings provide new mechanistic insights into the corrosion inhibition behaviour of Annona muricata leaf extract and demonstrate its potential as a sustainable, environmentally friendly corrosion inhibitor for carbon steel in acidic environments.