Electrochemical impedance spectroscopy evaluation on the protective properties of epoxy/DBSAdoped polyaniline-TiO2 nanocomposite coated mild steel under cathodic polarization

The dodecyle benzene sulphonic acid doped polyaniline (DBSA doped PANI) and dodecyle benzene sulphonic acid doped polyaniline-TiO2 (DBSA doped PANI-TiO2) nanocomposite were synthesized via in situ oxidative polymerization and characterized by Fourier transform infrared (FTIR) spectroscopy, ThermoGravimetric/differential ThermoGravimetric analysis (TGA/DTA), scanning electron microscopy (SEM) and energy dispersive Xray spectroscopy (EDX). The protective properties of epoxy/DBSA doped PAM and epoxy/DBSA doped PANI-TiO2 coated mild steel were evaluated by electrochemical impedance spectroscopy (EIS) in NaCl 3.5 wt% at 65 degrees C with and without cathodic protection (CP). Cathodic protection was applied at - 500, - 750, - 1000, - 1250 and -1500 mV vs. Ag/AgCl. The application of cathodic protection at more negative potentials than - 750 mV affected the performance of the both coatings causing the decreasing of coating resistance (R-coat). The coating resistance of epoxy/DBSA doped PANI and epoxy/DBSA doped PANI-TiO2 are in the order of 1 x 10(4) Omega cm(2) and 1 x 10(5) Omega cm(2), respectively. Accordingly, the coating capacitance and water uptake of epoxy/DBSA doped PANI is greater than epoxy/DBSA doped PANI-TiO2 at whole applied potentials. The protective performance of epoxy/DBSA doped PANI coating is improved in the presence of TiO2 nanoparticles under different cathodic potentials.