The influence of molybdenum on the corrosion resistance of ternary Zn–Co–Mo alloy coatings deposited from citrate–sulphate bath.

Ternary Zn–Co–Mo alloy coatings were deposited from a citrate–sulphate bath. In a pH range of 5.5–5.9 the coatings contained 2.3–3.6 wt.% molybdenum and 3.4–3.7 wt.% cobalt. DC and EIS measurements revealed that in the course of 24 h exposure to NaCl solution the corrosion resistance of Zn–Co–Mo alloy coatings was higher than that of Zn and Zn–Co coatings. On the basis of XRD, ALSV and XPS studies it can be stated that the beneficial effect on the corrosion resistance of Zn–Co–Mo coatings has a passive layer composed of: Zn(OH) 2 , ZnO, Mo(IV) oxide and hydroxide and a small amounts of Co 3 O 4 . [ABSTRACT FROM AUTHOR]