Polypyrrole Coating on Zinc for Corrosion Prevention of Zinc-coated Steels

The polypyrrole (PPy) coating was prepared by constant current oxidation on zinc from aqueous solution of sodium tartrate containing sodium molybdate and pyrrole monomer to make new coating for corrosion prevention of zinc-coated steels.The coating is started with an initial formation of salt layer of zinc tartrate and/nor zinc molybdate during the oxidation. Nucleation and growth of PPy take place on the salt layer in the second stage. The PPy layer thus formed is doped by tartrate ions and/nor molybdate ions, which was confirmed by a depth profile measurement of glow discharge optical emission spectroscopy (GD-OES). The conductance of the coatings was as small as 1×10−3 S cm−2 for the 5 μm-thick layer probably due to the formation of the salt layer underneath the PPy layer. Corrosion test of the PPy-coated zinc electrode in 3.5 wt% NaCl solution showed that the zinc electrode was passivated and protected over 48 h by action of the oxidative PPy coating doped by tartrate and molybdate ions.