ELECTROSYNTHESIS OF STRONGLY ADHERENT POLYPYRROLE COATINGS ON IRON AND MILD-STEEL IN AQUEOUS-MEDIA

Strongly adherent polypyrrole (PPy) films have been obtained by electr opolymerization of pyrrole on pretreated iron and mild steel. Several chemical pretreatments of the metal surfaces have been compared. The r esults show that a treatment by 10% aqueous nitric acid inhibits iron dissolution without preventing the pyrrole oxidation. Very adherent th ickness-controlled PPy films were obtained at constant-current in vari ous aqueous media containing Na2SO4, K2C2O4 or KNO3. A maximum coulomb ic efficiency of 95% was obtained in the presence of KNO3 for a curren t density lower than 10mA/cm(2), but dropped to 70% and 50%, in the pr esence of Na2SO4 and K2C2O4, respectively, and for a current density b etween 2 and 4mA/cm(2). Copyright (C) 1996 Elsevier Science Ltd