The study on the corrosion mechanism of protective ternary Zn[sbnd]Fe[sbnd]Mo alloy coatings deposited on carbon steel in 0.5 mol dm–3 NaCl solution

Abstract

The passive layer on ZnFeMo 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 Zn5(OH)6(CO3)2 and Zn5(OH)8Cl2·H2O. At the same time, MoO2 transformed to MoO3 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 cm2 and the double layer capacitance increased from 4.5 to 62 μF cm–2 after 0.5 h and 10 h exposure, respectively.