Investigations on growth mechanism of poly(o-anisidine) coatings on low carbon steel by electrochemical synthesis method

The growth mechanism of poly(o-anisidine) (POA) coating on low carbon steel (LCS) substrates has been investigated. In this work, the POA coatings on LCS substrates have been synthesized by electrochemical polymerization (ECP) of o-anisidine (OA) under galvanostatic conditions from aqueous solution of oxalic acid at room temperature (27 °C) and 40 °C. At room temperature, uniform and strongly adherent dark green POA coatings were obtained on LCS substrates. These coatings were characterized by potential–time (E–t) curves, X-ray diffraction (XRD) measurements, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and UV-visible absorption spectroscopy. The E–t curves in conjunction with FTIR, XRD and SEM studies clearly reveal that the growth of POA coatings on the LCS occurs in three distinct stages: (i) an induction time for ECP, (ii) passivation of LCS electrode surface via the formation of polycrystalline iron oxalate (FeC2O4, 2H2O) interphase and (iii) decomposition of the interphase followed by ECP of OA. However, at 40 °C with an applied current density ∼0.66 mA cm−2, the E–t curve shows the undesirable behavior, which is attributed to non-decomposition of the interphase during the third growth stage. As a consequence, at 40 °C the ECP of OA has not occurred on the LCS electrode surface. Thus, the formation of the interphase and its subsequent decomposition is necessary for the ECP of OA to occur on the LCS electrode surface.