Cationic Gemini Surfactants as Novel Corrosion Inhibitor for Mild Steel in 1M HCl

The corrosion inhibition characteristics of synthesized cationic gemini surfactants of the series, 14-n-14 (n=4,6) namely, 1,4-bis(N-tetradecyl-N,N dimethyl ammonium) butane dibromide (14-4-14) and 1,6-bis(N-tetradecyl-N,N dimethyl ammonium) hexane dibromide (14-6-14), on the mild steel in 1 M HCl solution as a function of inhibitor concentration (2.5 × 10-5 - 2.5 × 10-7 M) and the solution temperature (30-60 °C) was studied. The synthesized surfactants were characterized by Nuclear Magnetic Resonance (NMR) spectroscopy. The inhibition efficiency (IE) of the inhibitors was investigated by weight loss measurements, solvent analysis of iron ions, potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS). The surface analysis of the corroded steel samples in absence and presence of surfactants was also evaluated by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The %IE of the inhibitors increased with increase in surfactant concentration and temperature; the %IE being in the range 70-98%. The adsorption of gemini surfactants on the steel surface obey Langmuir adsorption isotherm from the fit of the experimental data of all concentration and temperature studied. The associated activation energy of corrosion (Ea) and other thermodynamic parameters such as enthalpy of adsorption (ΔH), entropy of adsorption (ΔS), adsorption equilibrium constant (Kads) and standard free energy of adsorption (ΔGads) were calculated to elaborate the mechanism of corrosion inhibition.