Enhancing the corrosion inhibition performance of Mannich base on mild steel in lactic acid solution through synergistic effect of allicin: Experimental and theoretical study

Abstract

Protonated Mannich base N,N′-bis(3-oxo-3-phenylpropyl)ethane-1,2-diamine dihydrochloride (EDAM) was synthesized and its chemical structure was characterized by means of 1H NMR, 13C NMR, Fourier-transform infrared spectroscopy (FTIR) and elemental analysis. The synergistic inhibitive effect of EDAM with allicin on N80 steel in 15 % lactic acid solution at 363 K was investigated using weight loss experiments, electrochemical tests, and surface analysis techniques (including scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray Photoelectron Spectroscopy (XPS), and contact angle measurement), quantum chemical calculation and molecular dynamics (MD) simulation methods. The results show that the inhibition performance was significantly improved by combining EDAM and allicin. The inhibition efficacy (IE) reached 99.60 % at the mass ratio of 10:1 (EDAM/allicin) with total inhibitor dosage of 0.1 %. Electrochemical impedance test (EIS) proves that the charge transfer-controlled corrosion process is greatly hindered with the addition of allicin. The small changes in the corrosion potential of Tafel curves indicate that the complex system is a hybrid corrosion inhibition mechanism. SEM, AFM, XPS and contact angle surface analyses suggest that EDAM in cooperation with allicin forms a dense and strongly adsorbed protective film on the metal surface. The density functional theory (DFT) and molecular dynamics simulation (MD) calculations further elucidate the mechanism of the synergistic corrosion inhibition effect.