Galvanostatic polymerisation of aniline on steel: Improving the coating performance in chloride-containing environment

In this study, polyaniline (PANI) was coated on a steel using galvanostatic polymerisation technique. The coating was performed under two different electrolyte bath conditions, i.e. unstirred and stirred. The unstirred-condition coating (UC) showed large defects, whereas the stirred-condition coating (SC) exhibited only a few fine defects. The performance of the coatings was tested using electrochemical techniques in chloride-containing solution. Electrochemical impedance spectroscopy (EIS) results showed that the SC sample exhibited almost two orders of magnitude higher polarisation resistance (Rp) than that of the UC sample. Long-term EIS results revealed that the Rp for UC sample dropped gradually with exposure time (Rp = 1200 Ω cm2, after 78 h exposure), while the SC sample showed an initial increase in Rp value (Rp = 4300 kΩ cm2, after 78 h exposure) and then gradually decreased to Rp = 700 kΩ cm2, after 168 h exposure. However, it should be noted that the Rp value of the SC sample even after 168 h exposure was close to three orders of magnitude higher than the UC sample after 78 h exposure. Potentiodynamic polarisation results confirmed the higher corrosion resistance of the SC sample as compared to the UC sample. The study clearly suggests that stirring the electrolyte bath during polymerisation of aniline on steel produces high performance coating.