For this reason, an attempt was made to investigate the corrosion mechanism of these coatings in a solution containing chloride ions, using the following techniques: infrared spectroscopy (FT-IR), the aforementioned XPS technique, and X-ray diffraction (XRD).įurther, own research led to the replacement of cobalt(II) compounds in electroplating baths with less harmful iron(II) compounds. X-ray photoelectron spectroscopy (XPS) study revealed that the beneficial effect on the corrosion resistance of Zn–Co–Mo coatings has a passive layer which, initially, is composed of Zn(OH) 2, ZnO, Mo(IV) oxide, and hydroxide and small amounts of Co 3O 4. It has been demonstrated that the coatings with a content of about 2.7 wt.% Mo and 3.8 wt.% Co possess significantly better corrosion resistance than that of pure zinc coatings. Recent work has been dedicated to determining the corrosion resistance of bright and homogeneous ternary Zn–Co–Mo alloy coatings in NaCl solution. In the more actual research, the optimal conditions of the deposition of Zn–Co–Mo coatings have been defined.
The addition of molybdenum to zinc alloy coatings with the iron group metal seems to be interesting, and even in the 80s of twentieth century was undertaken research about the addition of Mo to binary zinc alloy coatings to form ternary Zn–Co–Mo alloys. Zinc-based alloys which contain molybdenum can be the potential substitute for toxic cadmium coatings or additional Cr(VI)-based conversion coatings, due to the low harmfulness of Mo(VI) compounds present in the plating baths and the ability of molybdenum to form stable passive layer preventing chloride attack. Finally, comparison of surface composition may be crucial to evaluation of the unknown experimental spectra of corrosion products formed on the surface of zinc alloy coatings exposed in NaCl solution. X-ray photoelectron spectroscopy (XPS) allowed to calculate the modified Auger parameters ( α ′) thereof to 2010.2, 2009.3, 2009.4, 2009.7, and 2009.8 eV, respectively for ZnO, Zn(OH) 2, Zn 5(OH) 8Cl 2
Characteristic infrared absorbance bands were estimated by means of FT-IR ATR spectroscopy. Their crystalline phase structure, thermal behavior, and morphology were examined.