The study on the corrosion mechanism of protective ternary Zn-Fe-Mo alloy coatings deposited on carbon steel in 0.5 mol dm(-3) NaCl solution

The passive layer on Zn–Fe–Mo coating (7.6 at.% Fe, 1.6 at.% Mo) became damaged in 0.5 M NaCl solution, as shown in ionic current density maps that were observed during 10 h of exposure. The ZnO and Zn(OH) 2 slowly transformed into Zn 5(OH) 6(CO 3) 2 and Zn 5(OH) 8Cl 2·H 2O. At the same time, MoO 2 transformed to MoO 3 and MoO(OH) 2. The barrier properties of the layer of corrosion products deteriorated so the charge transfer resistance decreased from 13 to 7.4 kΩ cm 2 and the double layer capacitance increased from 4.5 to 62 μF cm –2 after 0.5 h and 10 h exposure, respectively.