Corrosion Inhibition by Zinc Corrosion Products on Zinc-coated Steel

The corrosion-inhibition of the iron covered with the corrosion products formed by dissolved zinc in the atmospheric corrosion was investigated by using a multichannel coupling current measurement technique. The coupling current map and coupling charge map of the partially covered iron electrode array in an arrangement of 10 x 10 were traced during the corrosion test. At the initial stage of corrosion test, iron was mainly protected by the sacrificial dissolution of metallic zinc and partially by the corrosion products of zinc precipitated on the iron surface. After complete depletion of metallic zinc, the iron surface covered with hydrozincite acted as cathode, while that covered with zincite layer acted as anode. The discrepancy between these two electrodes can be explained by the higher solubility of hydrozincite than that of zincite.