PHENOL ELECTROPOLYMERIZATION ON PHOSPHATED MILD-STEEL VIA ZINC ELECTRODEPOSITION

Phenol electropolymerization to polyoxyphenylene coatings on phosphate d steel and phosphated galvanized steel, normally impossible under the conditions allowing effective coating formation on either steel or zi nc, is activated by cathodic deposition of zinc. A critical zinc amoun t has been found to be necessary to suppress electrochemical processes competitive with electropolymerization and induce coating formation w ith nearly 100% efficiency. SEM analysis showed -that this critical am ount of zinc corresponded to the formation of a low number of zinc nuc lei emerging at the surface of the phosphate layer, on which, however, polyoxyphenylene was formed as a continuous coating. A.c. impedance t ests showed that initial barrier properties are worse for coatings gro wn on zinc-plated phosphated samples than for those grown on steel fro m the same solutions. However, the long term corrosion resistance is m uch better in the former case, the improvement being largely associate d with zinc cathodic protection.