The effect of an artificially synthesized simonkolleite layer on the corrosion of electrogalvanized steel

Electrochemical behavior of low alloy steel covered by a synthetic layer of simonkolleite was studied alone and in galvanic couple with zinc. Simonkolleite on steel inhibits cathodic oxygen reduction in 5 wt.% NaCl at pH = 7 and 9 but it is unstable at pH = 11. In NaCl solution the galvanic current density between Zn and steel is reduced by more than twice if the synthetic simonkolleite layer is deposited on steel. The polarity between Zn and steel is inverted after several hours in NaHCO3 solutions. X-ray diffraction confirmed the instability of simonkolleite in this conditions and its transformation into carbonate containing salts.

► Simonkolleite (ZHC) formed by dissolution of Zn layer from galvanized steel.
► Cathodic inhibition of steel by synthetic simonkolleite at pH = 7 and 9.
► Inhibition due to oxygen diffusion blocking.
► Cathodic current decrease but active galvanic protection for Fe/ZHC//5%NaCl//Zn.
► Loss of galvanic protection for Fe/ZHC//NaHCO3//Zn due to transformations of ZHC.