Electrosynthesis of adherent polyaniline films on iron and mild steel in aqueous oxalic acid medium

Polyaniline (PANi) films can be electrosynthesized by oxidation of aniline on iron and mild steel in a one-step process from an aqueous oxalic acid medium which passivates substrates. Homogeneous and strongly adherent films of controlled thickness can be deposited either in the potentiodynamic or galvanostatic modes. These films are characterized by IR, X-ray photoelectron spectroscopy (XPS), gel permeation chromatography (GPC) and matrix-assisted UV-laser desorption ionization (MALDI) techniques, and have a structure similar to that of PANi deposited on platinum. Iron samples coated with PANi exhibit much better protection against corrosion in an acidic solution (0.4 M NaCl + 0.1 MHCl) than the polypyrrole-coated ones. Attempts to grow PANi films on zinc or zinc—nickel alloy in oxalic acid were unsuccessful because the formation of insulating layers prevents electropolymerization.