Electrodeposition of a highly adherent and thermally stable polypyrrole coating on steel from aqueous polyphosphate solution

Abstract

Electrochemical deposition of polypyrrole (PPy) on steel surface has been carried out from an aqueous polyphosphate medium using constant potential coulometry (CPC) and cyclic voltammeter (CV), and the adherence, anticorrosion property and thermal stability of the coated material have been studied. Open circuit potential (OCP) measurements were carried out in a 3.5% NaCl solution. The high OCPs maintained for a period of 40 days suggest that polyphosphate-doped PPy (PPy/PP) retains its oxidative state and provide good corrosion protection for SS-304. It seems that, the large polyphosphate counter-ion prevents the ingress of chloride ions much better than other dopants reported elsewhere. The amount of polypyrrole formed on the steel surface increased with electrodeposition time, monomer concentration and applied potential. However, the effect of potential was higher than the effects of either monomer concentration or deposition time. Also, the effect of electrolyte concentration on the polymer formation was insignificant. Scanning electron microscopy (SEM), however, showed that PPy surface morphology was affected by polyphosphate concentration. Very smooth, compact and adherent PPy films with significantly smaller globules were obtained from solutions with high concentration of polyphosphate. Thermogravimetric analysis of the coated material indicated that PPy/PP has excellent thermal stability at temperatures up to 700 °C, much higher than other conductive polymer coatings cited.