The inhibitive effect of 6-amino-m-cresol and its Schiff base on the corrosion of mild steel in 0.5 M HCl medium

Abstract

6-Amino-m-cresol (ACr) and newly synthesized Schiff base 2-(3-hydroxybenzylideneamino)-5-methylphenol (ACr-S) using ACr and salicylaldehyde have been investigated as inhibitors for corrosion of mild steel (MS) in 0.5 M hydrochloric acid. For this purpose; polarization curves measurements, electrochemical impedance spectroscopy (EIS) and linear polarization resistance (LP) techniques were utilized. Polarization curves reveal that both compounds are mixed type inhibitors and inhibition efficiency (%IE) increases with increasing concentration of compounds. CPE and polarization resistance (R-p) are derived from Nyquist plots obtained from AC impedance studies. The results of the electrochemical studies have illustrated that the inhibition efficiency of ACr-S is higher than ACr. Both ACr and ACr-S obeyed the Langmuir isotherm, and thermodynamic calculations revealed that ACr-S had larger adsorption constant and more negative free energy of adsorption with respect to ACr. The effect of exposure time on the corrosion behaviour of mild steel in the absence and presence of inhibitor over 168 h was also studied. Possible inhibition mechanism also discussed by establishing potential of zero charge (PZC) of ACr and ACr-S on mild steel surface. The greater inhibitive power of ACr-S may be due to presence of more pi-electrons of an extra substituted phenyl group in the ACr-S molecule. (C) 2008 Elsevier B.V. All rights reserved.