Poly(o-toluidine) coatings on low carbon steel: synthesis and characterisation

Abstract

Poly(o-toluidine) (POT) coatings have been synthesised on low carbon steel (LCS) substrates by the electrochemical polymerisation (ECP) of o-toluidine in an aqueous solution of oxalic acid under galvanostatic conditions. Uniform and strongly adherent dark green POT coatings were obtained on LCS substrates. These coatings were characterised by potential - time E-t curves, ultraviolet (uv) visible absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). It was found that oxalic acid is a suitable medium for the ECP of o-toluidine on an LCS substrate, and the electrochemical growth process is characterised by three distinct stages: dissolution of the LCS electrode surface and formation of iron oxalate interphase, complete passivation of the LCS electrode surface and decomposition of the interphase, followed by ECP of o-toluidine. The induction time was observed to decrease with an increase in applied current density. An optical absorption spectroscopy study revealed exclusive formation of the insulating pernigraniline base (PB) form of POT at a lower current density, whereas at a higher current density the coating comprised a mixed phase of conducting emeraldine salt (ES) and PB forms. The FTIR spectroscopy indicated the formation of a POT coating. The surface morphology of the POT coating was observed to depend on the applied current density, and it improved with an increase in current density.