Corrosion inhibition studies by surfactants in the presence of 2-methyl thiophene on mild steel

Abstract

In this research, three surfactants, namely cetyl trimethyl ammonium bromide (CTAB), sodium lauryl sulfate (SLS) and polysorbate-80 (Tween 80) have been examined as corrosion inhibitors for mild steel in absence and presence of a thiophene derivative (2-methyl thiophene) in 2 M hydrochloric acid (HCl). The inhibition action was investigated through weight loss, potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS). The morphology before and after placing mild steel in the corrosive media was studied by scanning electron microscopy (SEM). The inhibition efficiencies of these inhibitors were found to be depended on surfactant concentration, immersion time and temperature. Adsorption isotherm was tested with Langmuir, Freundlich and Temkin models. It was found that the adsorption of surfactants CTAB/SLS/Tween 80 in absence and presence of 2-methyl thiophene on mild steel surface fitted best to the Langmuir adsorption isotherm. From the polarization curve, the inhibition of surfactants in presence of 2-methyl thiophene was observed to be a mixed type. The interactive effects of inhibitor immersion time, temperature and concentration were optimized for maximum response of inhibition efficiency using Response Surface Methodology (RSM) based on Historical Data. The potential of zero charge (PZC) at the metal-solution interface was determined for surfactants in absence and presence of 2-methyl thiophene to provide the mechanism of inhibition. The positive value of Antropov’s “rational” corrosion potential (Er) for all the surfactants with respect to potential of zero charge (EPZC) suggested that mild steel surface is positively charged at open circuit potential in the presence of these inhibitors. So, the most efficient surfactant in presence of 2-methyl thiophene as corrosion inhibitor follows this sequence: SLS > CTAB > Tween 80.