Phenol electropolymerization on phosphated mild steel via zinc electrodeposition

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