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 electr odeposition of a thin polypyrrole film. It acts as a pretreatment of the su rface and completely modifies its electrochemical response to usual acidic solutions suitable for aniline electropolymerization. It is much faster tha n any chemical pretreatment (less than 3 s) and can be performed with almos t no metal dissolution. Pretreated mild steel or zinc substrates can then b e used for the electrodeposition of a PAM film of controllable thickness. N o or very little metal oxidation occurs in this second step. The films show stable electroactivity in acidic electrolytes, similar to that of PANI dep osited on platinum, which indicates that the underlying oxidizable metal is fully protected. The overall system has a bilayer structure, indicating th at the electrochemical interface during aniline electrodeposition might be situated at the polypyrrole\solution interface. This suggests a new interpr etation for the anticorrosion properties of conductive polymers based on th e displacement of the electroactive interface from its usual location (meta l\solution) to the polymer\solution interface. (C) 2000 Elsevier Science S. A. All rights reserved.