Corrosion behavior and thermal stability of electrodeposited PANI/epoxy coating system on mild steel in sodium chloride solution

The corrosion behavior, sorption characteristics and thermal stability of epoxy coatings electrodeposited on mild steel (MS) and mild steel with electrochemically deposited polyaniline (PANI) film were investigated in 3% NaCl solution using electrochemical impedance spectroscopy (EIS) and thermogravimetric analysis (TGA). Electrochemical deposition of PANI film on mild steel was performed from aqueous solution of 0.5 M sodium benzoate and 0.1 M aniline at constant current density of 1.5 mA cm−2. Epoxy coatings on mild steel and mild steel with PANI film were deposited at constant voltage. It was shown that during initial time of exposure to 3% NaCl, PANI/epoxy coating system on mild steel has lower values of pore resistance (obtained from EIS), greater amount of absorbed water and lower thermal stability (obtained from TGA) which indicate more porous structure comparing to epoxy coating on mild steel. During prolonged exposure to 3% NaCl, PANI/epoxy coating system exhibited increased corrosion protection of mild steel comparing to epoxy coating due to the barrier effect of PANI film and the influence of the dissolved molecular oxygen on cathodic and anodic reaction. Differences between corrosion behavior of epoxy coated and PANI/epoxy coated mild steel in acid and neutral solutions has been discussed.