Alternanthera philoxeroides extract as a corrosion inhibitor for steel in Cl3CCOOH solution

The corrosion inhibition of Alternanthera philoxeroides extract (APE) for cold rolled steel (CRS) in Cl3CCOOH solution was examined by weight loss and electrochemical measurements. AFM, SEM, CLSM and XPS techniques were executed to determine the inhibition mechanism. The results show that APE acts as an excellent inhibitor for CRS in 0.10 M Cl3CCOOH solution with the inhibition efficiency (eta w) of 94% at 200 mg L-1. The adsorption of APE on CRS surface follows Langmuir model at 20 and 30 oC, while Freundlich isotherm at 40 and 50 oC. APE is a mixed type inhibitor that mainly retards the anodic reaction. Nyquist diagram presents a depression capacitive loop at high frequency region followed by a small inductive section at low frequency region. With the addition of APE, the charge transfer resistance is significantly increased, but the double layer capacitance is dropped to some extent. Electrical conductivity further confirms that the presence of APE greatly hinders the corrosion of the metal by the acid medium. The efficient inhibition of APE is clearly confirmed from SEM and AFM micrographs. CLSM observation confirms the adsorption heterogeneous of APE. Meanwhile, XPS demonstrates that the polar groups of organic molecules in APE are bound to the iron matrix.