Study of different inorganic oxide thin films as barrier coatings against the corrosion of galvanized steel

The chemical spray pyrolysis technique has been used to deposit thin films of MgO, NiO and ZrO2 on galvanized steel substrate. These films have been studied as barrier coatings against the degradation of the galvanized steel sheet during long term outdoor exposure. The corrosion protective effect of the coatings is discussed taking into account results from scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and UV–VIS–NIR–MIR spectroscopy. By means of SEM, it has been observed that the coatings are dense and compact but the MgO coatings revealed film cracking. XPS and FTIR analysis have shown that the NiO coating has no residuals from the precursor solution, as inclusions of water or carbon. The MgO coating reveal traces of hydration. With respect to specific applications, the solar absorption and thermal emittance have been determined. The corrosion behaviour of the coatings has been estimated with electrochemical methods as potentiodynamic polarization and amperometry curves. Polarization resistances and corrosion rates were calculated and indicate a decreased pitting of the aluminized steel when coated with nickel oxide or zirconia.