A New Approach to Study the Synergistic Inhibition Effect of Cationic and Anionic Surfactants on the Corrosion of Mild Steel in HCl Solution

The corrosion inhibition characteristics of cation-rich and anion-rich catanionic mixtures of cetyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) as corrosion inhibitor for mild steel (MS) in aqueous solution of 2 M HCl were investigated. The interaction between the two surfactants in the solid–liquid interface was analyzed on the basis of regular solution theory for the first time. Mixed surfactants showed good inhibition properties due to strong adsorption on the surface and formation of a protective film. Adsorption of the inhibitors obeyed the Flory–Huggins isotherm. Potentiodynamic polarization investigations indicated that the inhibitors studied were mixed-type inhibitors.