Synergistic mixture of Eupatorium Adenophora Spreng stems extract/KI as an efficient inhibitor for the corrosion of steel in H2SO4

The synergistic inhibition effect of Eupatorium Adenophora Spreng stems extract (EASSE) with KI on the corrosion of cold rolled steel (CRS) in 0.50 M H2SO4 medium was examined by gravimetric and electrochemical measurements, as well as various surface characterizations. The results indicate that the maximal inhibition effectiveness of EASSE/KI reaches 93.3% and a coefficient of synergy (s) value larger than 1. Moreover, Langmuir isotherm is suitable for the adsorption of EASSE, KI and their complex on CRS surface. Individual EASSE, KI and their synergistic mixture are all mixed-type inhibitors by "geometric coverage mechanism". Nyquist predominantly demonstrates a dispersive capacitive loop, and EASSE/KI blend synergistically decreases double layer capacitance while increases the charge transfer resistance of steel/solution interface. SEM, AFM and wettability measurements confirm that the combination of EASSE/KI synergistically suppresses the corrosion of CRS surface, and the synergistic inhibited CRS surface appears to have almost no corrosion with a greater contact angle. According to XPS, the active compounds containing polar N and O atoms in EASSE can be incorporated with KI to adsorb on CRS surface. Two kinds of flavonoids and phenylpropanoids in EASSE mainly contribute to the synergistic inhibitory effect with KI.