FTIR spectroscopic characterization of NafionA®-polyaniline composite films employed for the corrosion control of stainless steel

NafionA (R)-polyaniline (PAn) composite films deposited by a two-step process on a stainless steel (SS) substrate were characterized in this study using Fourier transform infrared (FTIR) spectroscopy under various conditions employed to evaluate their anticorrosion properties. The SS|NafionA (R) electrode was first prepared by placing a certain amount of NafionA (R) on the SS substrate, and then polymerization of aniline was carried out potentiodynamically on the SS|NafionA (R) electrode. The SS|NafionA (R)-PAn electrodes subjected to both potentiodynamic polarization and open-circuit conditions in sulfuric acid solutions without and with chlorides appeared to have distinct differences in their FTIR spectra. It is proposed that under the electrochemical conditions used in this study, the PAn is mostly formed inside the NafionA (R) membrane with a high proportion of oligomers influencing the ionic transport through the membrane. The inhibition of pitting corrosion arises primarily from the enhanced permselectivity of the composite film due to the NafionA (R) membrane that prevents chloride transport. An essential beneficial effect comes also from the PAn redox properties on the growth of the passive oxide film. Even under severe corrosion conditions, NafionA (R)-PAn films retain their redox activity and chemical stability, whereas the membrane crystallinity seems to be enhanced.