Characterization of the passive inorganic interphase and polypyrrole coatings formed on steel by the aqueous electrochemical process

Polypyrrole coatings have been successfully formed on steel from aqueous ox alic acid-pyrrole solutions by electrochemical polymerization. Formation of the coatings was found to be dependent on the pH of the reaction solution and the applied current. In acidic medium, the formation of polypyrrole was characterized by an induction (passivation) period before electropolymeriz ation of pyrrole. At the end of the induction period, a crystalline passive interphase was formed. The morphology and composition of the electrodeposi ted passive interphase and the resultant polypyrrole coatings were investig ated by scanning electron microscopy, reflection-absorption infrared spectr oscopy, and X-ray photoelectron spectroscopy. Our results reveal that the c hemical composition of the passive interphase was similar to that of iron(I I) oxalate dihydrate, FeC2O4 . 2H(2)O, crystals. Size and orientation of th e crystalline passive interphase varied with electrochemical process variab les. (C) 1999 John Wiley & Sons, Inc.