Design of a new bilayer polypyrrole-xerogel hybrid coating for corrosion protection

In order to improve the anticorrosion protection properties of polypyrrole (PPy) films deposited on iron or mild steel, the organic conductive polymer was covered by a thermally and mechanically resistant xerogel layer. The anticorrosion protective effect of such a bilayered coating was evaluated by electrochemical measurements (i=f(E); E=f(t); polarization resistance (Rp)) in NaCl (30 g L-1) and in HCl (1 M) aqueous solutions and by analysis of NaCl and HCl aqueous solutions in which samples coated by PPy and the xerogel were immersed for one and seven days. The results were compared with those obtained, in the same conditions, for naked mild steel plates, PPy or xerogel coated mild steel plates. The bilayer coating ensures a very efficient protection of mild steel against corrosion. A synergy between PPy and the xerogel was revealed. Moreover, the weak adherence of the xerogel on PPy was improved by the incorporation in the organic polymer of carboxylic acid-functionalized pyrrole units, and the corrosion protection of these modified layers was still increased.