Eupatorium adenophorum Spreng root extract as an efficient inhibitor for the corrosion of steel in sulfamic acid solution

Abstract

Eupatorium adenophorum Spreng root extract (EASRE) was prepared using a reflux extraction method with 40 % ethanol (C₂H₅OH) as the extractant solvent. The corrosion inhibitory impact of EASRE on cold rolled steel (CRS) in 0.10 M sulfamic acid (NH₂SO₃H) solution was explored through gravimetric tests, potentiodynamic polarization curves, and electrochemical impedance spectroscopy (EIS) methods. Metallographic microscopy (MM), scanning electron microscopy (SEM), atomic force microscopy (AFM), and confocal laser scanning microscopy (CLSM) were employed to examine the micrographs of CRS specimens. The adsorbed chemical substances on the inhibited CRS surface were examined via X-ray photoemission spectroscopy (XPS). And the main chemical constituents of EASRE were analysed by high performance liquid chromatography-mass spectrometry (HPLC-MS). The results of the study showed that EASRE at a concentration of 500 mg L⁻¹ in 0.10 M NH₂SO₃H at 30 °C for 12 h had a significant inhibitory effect on CRS, with a maximum inhibitory efficiency of 89.7 %. At all set temperatures, the adsorption of EASRE onto CRS surface adheres to Langmuir isotherm. EASRE functions as a mixed-type inhibitor through a “geometric covering effect”. EIS show that the addition of EASRE significantly improves the charge transfer resistance at the steel/sulfamic acid interface, and the charge transfer resistance increases with increasing inhibitor concentration. XPS analysis confirm the presence of a “protective film” generated by EASRE on the CRS surface, and it consists of O-H, N-H, C-O, C-H, CC, CN, CO. Microscopic graphs of MM, SEM, AFM and CLSM reveal that EASRE efficiently alleviates the corrosion on the CRS surface. The HPLC-MS suggest that the main components of EASRE are flavonoids and phenylpropanoid compounds.