Synergistic effect of sodium dodecyl sulfate and cetyltrimethyl ammonium bromide on the corrosion inhibition behavior of l-methionine on mild steel in acidic medium

Abstract

The corrosion inhibition behavior of amino acid l-methionine (LMT) separately and in combination with very low concentration of surfactants sodium dodecyl sulfate (SDS) and cetyltrimethyl ammonium bromide (CTAB) on mild steel in 0.1M H2SO4 solution was studied, using weight loss and potentiodynamic polarization measurement techniques. The studies were carried out in the temperature range of 30–60°C. The surface morphology of the corroded steel samples was studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM).The results show that LMT is an effective inhibitor for mild steel corrosion in 0.1M H2SO4 which is synergistically improved in the presence of SDS and CTAB. The mixed LMT and CTAB is more effective as an inhibitor than mixture of LMT and SDS. The SEM and AFM photographs show a clearly different surface morphology in the presence of additives. LMT alone and in combination with surfactants obeys Langmuir adsorption isotherm from the fit of the experimental data of all concentrations and temperatures studied. Phenomenon of physical adsorption is proposed from the trend of the IE with temperature and also the values of activation energy (Ea), standard enthalpy of adsorption (ΔHads), and standard free energy of adsorption (ΔGads) obtained. The results obtained by potentiodynamic polarization measurements are consistent with the results of the weight loss measurements. LMT acts as a mixed type inhibitor.