Abstract: Eupatorium Adenophorum Spreng leaves extract (EASLE) was prepared by heating reflux extraction method. The inhibition performance of EASLE on CRS in 0.10 M Cl₂CHCOOH solution was fully studied by weight-loss, electrochemical techniques and surface characterizations. The main chemical components in EASLE were analyzed by liquid chromatography-mass spectrometry (LC-MS). The adsorption mechanism of these active components was theoretically studied by quantum chemical calculations and molecular dynamic (MD) simulations. The results show that EASLE can efficiently retard the corrosion of CRS in Cl₂CHCOOH media, and the maximum inhibition efficiency of 400 mg L^-1 EASLE reaches as high as 91.4% at 40 °C. The adsorption of EASLE on CRS surface conforms to Langmuir isotherm. From potentiodynamic polarization curves, EASLE is a mixed inhibitor through “geometric blocking effect”. Nyquist appears a capactive loop with one time constant, and the charge transfer resistance increases significantly after adding EASLE. The inhibition performance is inversely proportional to the surface tension, but proportional to the conductivity of the inhibited solutions. The microanalysis of CRS surface verifies that EASLE can efficiently adsorb onto CRS surface to form a protective film. EASLE exerts inhibition through its various components, in which the main corrosion inhibiting components are flavonoids and purines. The active adsorption sites of these compounds are concentrated on the benzene ring, C=O as well as N-heterocyclic ring. MD simulations indicate that quercetin, guanine, and their protonated molecules adsorb on Fe (001) surface in a nearly flat orientation.

Key words: Corrosion, Inhibitor, steel, Eupatorium Adenophora Spreng, Cl₂ CHCOOH