Aniline electropolymerization on mild steel and zinc in a two-step process

A two-step process for aniline electropolymerization on mild steel and zinc from aqueous electrolytes has been developed. The first step is the electrodeposition of a thin polypyrrole film. It acts as a pretreatment of the surface and completely modifies its electrochemical response to usual acidic solutions suitable for aniline electropolymerization. It is much faster than any chemical pretreatment (less than 3 s) and can be performed with almost no metal dissolution. Pretreated mild steel or zinc substrates can then be used for the electrodeposition of a PAM film of controllable thickness. No or very little metal oxidation occurs in this second step. The films show stable electroactivity in acidic electrolytes, similar to that of PANI deposited on platinum, which indicates that the underlying oxidizable metal is fully protected. The overall system has a bilayer structure, indicating that the electrochemical interface during aniline electrodeposition might be situated at the polypyrrole\solution interface. This suggests a new interpretation for the anticorrosion properties of conductive polymers based on the displacement of the electroactive interface from its usual location (metal\solution) to the polymer\solution interface. (C) 2000 Elsevier Science S.A. All rights reserved.