Corrosion behaviour of zirconia barrier coatings on galvanized steel

Galvanized steel sheets coated with a thin top layer of amorphous zirconia by spray pyrolysis have been studied by electrochemical corrosion tests in acid and saline conditions. Two spray solutions, aqueous and 40% alcoholic, using zirconium acetyl acetonate as precursor, and different spray times, 3 to 5 min, as well as posterior thermal treatment have been studied with regard to a corrosion barrier effect of the zirconia coating on the steel sheet. The coatings have been analysed by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and UV–VIS–NIR spectroscopy and results are discussed in relation to the corrosion behaviour of zirconia coated and uncoated galvanized steel sheet. Cyclic voltammetry and potentiodynamic polarization curves have been recorded in aqueous 0.5 M NaCl and 0.5 M H2SO4 electrolyte solutions, respectively. In acid conditions, the zirconia coatings provide a significant protection against corrosion. In saline conditions, no additional corrosion protection is found although corrosion by pitting is reduced compared to the uncoated galvanized steel substrate.