Research On The Corrosion Inhibition Performance Of Corydalis Extract On N80 Steel In CO₂ Environment

In this paper,the Chinese herbal medicine Astragalus membranaceus rich in alkaloids and various active ingredients was selected as the raw material for extracting corrosion inhibitor.The extract of Astragalus membranaceus was obtained by dipping method and reflux method with methanol as solvent.The corrosion inhibition of Astragalus membranaceus extract in 3.5%NaCl solution saturated CO2 was evaluated by static weight loss method,electrochemical impedance spectroscopy and potentiodynamic polarization curves.The surface morphology and wettability of N80 steel after corrosion in 3.5%NaCl solution saturated CO2 with and without Astragalus membranaceus extract were studied by contact angle test,scanning electron microscope and scanning electrochemical microscopy-EDS.The components of Astragalus membranaceus extract were identified by FT-IR,UV-vis and high performance liquid chromatography-mass spectrometry.Finally,the mechanism of action of extracts was studied by quantum chemical calculation and molecular dynamics simulation.The main results of the above studies are as follows:(1)Astragalus membranaceus extract is a mixed-type corrosion inhibitor with good corrosion inhibition for N80 steel in 3.5%NaCl solution saturated with CO2.Electrochemical impedance spectroscopy and polarization curves showed that the inhibition efficiency could reach 92.36%and 92.30%when the concentration of extract was lg/L at room temperature.The inhibition efficiency was positively correlated with the concentration of extract,and negatively correlated with temperature at the same concentration.(2)The Astragalus membranaceus extract contains N-H,C=O,C-N and other functional groups with lone pairs of electrons,which can supply electrons to the "d" orbital of Fe,then adsorb on the metal surface to form an adsorption film to achieve the purpose of corrosion inhibition.Its adsorption is a thermodynamically spontaneous and exothermic process that obeys Langmuir isotherm adsorption model,both physical and chemical adsorption can occurs.(3)The five main components in the extract of Astragalus membranaceus are berberine(2.2990g/L),palmatine(1.0672g/L),bulbocapnine(0.6193 g/L),protopine(1.4462 g/L)and tetrahydropalatine(3.5066 g/L).Among the five components,tetrahydropalmatine has the best corrosion inhibition effect when the addition is lg/L,the inhibition efficiency can reach up to 90.67%,which is close to the Astragalus membranaceus extract,indicating that tetrahydropalmatine is the extracted species mainly act as a component of corrosion inhibition.(4)The reason for the difference in corrosion inhibition performance of the five components in the extract of Astragalus membranaceus is that each component has different electron-accepting ability.Among them,tetrahydropalmatine has the strongest electron-donating ability and the weakest electron-capacity,so it has the highest reactivity.The active site is mainly distributed on the heterocyclic ring where the N atom is located.(5)The five components in the extract of Astragalus membranaceus can replace the water molecules to adsorb on the Fe(110)surface in parallel adsorption mode.This is the most stable adsorption mode,which is beneficial to the formation of coordination bonds between the extract molecules and metal as well as a high coverage film.