Electrochemical Study on the Effects of Osmanthus Flower Water Extract on the Passivation Behavior and Corrosion Inhibition Performance of Carbon Steel in Alkaline Chloride‐Containing Environments

The effect of Osmanthus flower water extract as a natural corrosion inhibitor on the corrosion behavior of carbon steel was investigated in a saturated Ca(OH) 2 solution containing 3.5 wt% NaCl (pH 13.5). Open‐circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization were employed to systematically evaluate the influence of different inhibitor concentrations on interfacial state, impedance characteristics, and corrosion kinetic parameters, and the inhibition mechanism was interpreted based on the passivation‐film mechanism in alkaline environments. The results indicate that the extract is rich in polyphenols, flavonoids, and glycosides, providing a structural basis for adsorption on the steel surface and regulation of passivation‐film formation and stability. The inhibitor did not exhibit a simple concentration‐dependent improvement; instead, an evident optimum concentration range was observed. EIS results showed that moderate concentrations significantly increased the low‐frequency impedance modulus and Faradaic resistance, promoting the formation of a more stable inhibitor‐passivation composite film. The OCP and polarization results further revealed a dual role of the adsorbed Osmanthus molecules: they hindered interfacial adsorption of OH − and H 2 O and thus retarded inner passivation‐layer formation, while also suppressing film dissolution, Fe 2 + interstitial migration, and defect accumulation, thereby improving film integrity. Overall, 200–300 mg/L was the optimal concentration range.