Corrosion protection provided by homo- and copolymer films synthesised in various oxalic and sulphamic acid electrolyte mixtures

Aqueous mixtures of oxalic acid (OX) and sulphamic acid (SA) solutions at different concentrations were used to synthesise polyaniline (PANI), poly(N-methylaniline) (PNMA) and poly(aniline-co-N-methylaniline) (PANI-co-PNMA) films on stainless steel (SS) surface (AISI 316). Variation in the OX/SA ratio affected the PANI, PNMA and PANI-co-PNMA growth rates, leading to film formation with different redox and structural properties, which contributed to their protection efficiency against the SS corrosion. Study of homo- and copolymer coatings proved that equal volume of 0.30M OX and 0.50M SA solution mixture was a suitable medium for the deposition of uniform, compact and strongly adherent coatings on SS electrode. It was observed that addition of SA to OX solution also provided an increase in electropolymerisation rate. Evaluation of the anticorrosion performance of homo- and copolymer coatings in 3.5%NaCl solution was investigated by using ac impedance spectroscopy technique and anodic polarisation curves. Polyaniline coatings exhibited a significant physical barrier property against the attack of corrosive products on SS, over longer periods.