Interactions of some Schiff base compounds with mild steel surface in hydrochloric acid solution

The inhibition effect of the Schiff bases N,N′-bis(salicylidene)-1,2-ethylenediamine (Salen), N,N′-bis(5-methoxysalicylidene)-1,2-ethylenediamine (MeO-Salen) and N,N′-bis(5-nitrosalicylidene)-1,2-ethylenediamine (NO2-Salen) on the corrosion of the mild steel in 1.0 M HCl has been studied by electrochemical impedance spectroscopy (EIS), linear polarisation resistance (LPR) and Tafel polarisation measurements. Maximum inhibition for MeO-Salen was obtained. Results showed that the inhibition efficiency have increased when the concentration of the Schiff bases have increased. Polarisation curves revealed that the Schiff bases acted as anodic inhibitors. The surface adsorption of the Schiff bases has lead to a decrease in the double layer capacitance and to an increase in polarisation resistance. The inhibitor performance depended strongly on the type of functional groups on benzene ring. The adsorption process is spontaneous one and follows Langmuir adsorption isotherm model. Scanning electron microscopy (SEM) has been applied to identify the surface morphology of the mild steel both in the absence and presence of the Schiff base molecules.