Electrodeposition of poly(N-methylpyrrole) coatings on steel from aqueous medium

Poly(N-methylpyrrole) coatings were formed on low carbon steel by an electrochemical method from aqueous oxalate solutions. The electrochemical reactions were performed in a wide range of pH of the reaction medium and applied current density. The formation of poly(N-methylpyrrole) on steel occurred in three stages: (i) dissolution of the steel, followed by (ii) passivation of the steel, and, finally, (iii) electropolymerization of N-methylpyrrole on the passivated steel. The time taken to form the passive interphase (induction time) is decreased by an increased applied current. Passivation occurred instantaneously at pH 8.4. Below pH 7, the shortest passivation time occurred at pH 2.6. The quantity of the charge consumed during passivation (passivation charge) remained independent of the applied current at pH approximate to 2.6 and decreased with the applied current at pH 4.1 and 5.7. The polymerization potential increased with the pH and the applied current. Polymerization potentials greater than 2.0 V resulted in film degradation. By controlling the electrochemical process parameters, good quality poly(N-methylpyrrole) was formed at a controlled induction time. (C) 1999 John Wiley & Sons, Inc.