Kinetics of the mild steel corrosion protection by polypyrrole-oxalate coating in sulfuric acid solution

Abstract

Kinetics of the mild steel corrosion protection in 0.1 mol dm(-3) H2SO4 by polypyrrole coatings have been investigated by the means of electrochemical impedance spectroscopy (EIS), cyclic voltammetry, polarization measurements and linear polarization. It has been concluded that during the initial time of immersion the coating resistance parameters increase which was connected with diffusion controlled dedoping of oxalate anions, simultaneously with hydrogen evolution reaction on polymer and dissolution of iron through polymer pores. Dedoping of oxalate anions from the bulk of the polymer decreases the polymer conductivity which provokes decrease of overall corrosion rate. After similar to 40 h, the completely dedoped PPy coating acts as a classical polymer.