A comparative study of the inhibitory performance of Ammi visnaga and Smyrnium olusatrum extracts on mild steel: Electrochemical, thermodynamic, and surface analysis approaches

Abstract

The corrosion of mild steel in acidic industrial environments poses major technical and economic challenges. In this study, two methanolic seed extracts, Ammi visnaga (AVME) and Smyrnium olusatrum (SOME), were evaluated as sustainable corrosion inhibitors for mild steel in 0.5 M H 2 SO 4 . The inhibition performance was investigated using electrochemical methods (potentiodynamic polarization, electrochemical impedance spectroscopy) supported by surface analyses (SEM-EDX, UV–Vis, FTIR, XRD) and phytochemical characterization (HPLC-MS). Both extracts acted as efficient mixed-type inhibitors with anodic predominance, reaching maximum inhibition efficiencies of 91.5 % (AVME) and 94.1 % (SOME) at 0.4 g/l. The efficiency decreased with rising temperature, consistent with an increase in activation energy and adsorption governed by the Langmuir isotherm. Calculated Gibbs free energy values ( Δ G ads o ) indicated a mixed physisorption-chemisorption mechanism. Morphological analyses confirmed the formation of a protective film on the steel surface, while phytochemical studies revealed the presence of aromatic and heteroatom-rich compounds responsible for the inhibition. Overall, this work highlights the promising potential of Apiaceae seed extracts as green and effective corrosion inhibitors, with SOME showing slightly superior performance to AVME.