Corrosion behaviour of zirconia barrier coatings on galvanized steel R. Romero Pareja, R. López Ibáñez, F. Martín, J.R. Ramos-Barrado, D. Leinen ⁎ Laboratorio de Materiales y Superficies (Unidad Asociada al CSIC), Dpto. Física Aplicada I and Dpto. Ingeniería Química, Facultad de Ciencias, Universidad de Málaga, Málaga E-29071, Spain Available online 20 December 2005 Abstract 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 H 2 SO 4 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. © 2005 Elsevier B.V. All rights reserved. Keywords: Spray pyrolysis; Zirconium oxide thin film; Galvanized steel; Corrosion 1. Introduction Galvanized steel sheet has corrosion protection through a sacrifice top layer, normally made of zinc or aluminium. Depending on the corrosion atmosphere conditions, material is homogeneously dissolved at the surface or localized dissolved by pitting. In order to enhance the lifetime of galvanized steel sheet under certain circumstances of exposure, it would be interesting to cover the exposed surface by a ceramic barrier layer but not altering its optical appearance. Such compact, dense and transparent ceramic top coatings could find their applications in, for instance, steel facade elements and unglazed solar collectors made of steel. 1 They should increase the weatherability for such type of construction elements which have to comply with their outdoor function over decades exposed to very different types of climate. In a previous work [1], different oxide materials (ZnO, TiO 2 , ZrO 2 ) were deposited by spray pyrolysis on various types of galvanized steel sheet, studying their morphological, optical and chemical properties. Best results with respect to homogeneous coverage and film growth velocity were found for the zirconia (ZrO 2 ) coatings on aluminized steel sheet. Zirconia is an interesting material since it offers high mechanical strength, temperature resistance and chemical stability. Therefore, thick and thin zirconia coatings have been applied to a broad range of devices, for instance, turbine blades exposed to extremely high temperatures [2], optical coatings with high transparency and refractive index [3], oxygen-conductive membranes for fuel cells and oxygen sensors [4], catalyst support and also as anticorrosion barrier coatings [5–10]. The aim of this work is centred in the applications of a zirconia coating as a barrier layer for steel protection in outdoor conditions at moderate tempera- tures. Such a barrier layer should be compact, transparent and homogeneously cover the steel sheet for protection against environment corrosion. It should also comply with optical properties like transparency, solar absorptance and thermal emittance, when applied to unglazed solar collectors and facade elements made of steel. So we look for an optimization of anticorrosion behaviour and optical properties of zirconia coat- ings deposited by spray pyrolysis onto aluminized steel sheet. Sol–gel techniques [8,9,11], chemical vapor deposition [5,12] and electrophoretic deposition [13] can be quoted as Surface & Coatings Technology 200 (2006) 6606 – 6610 www.elsevier.com/locate/surfcoat ⁎ Corresponding author. Dpto. Física Aplicada I. Facultad de Ciencias. Universidad de Málaga. E-29071-Málaga (Spain). Tel.: +34 952131928; fax: +34 952132382. E-mail address: dietmar@uma.es (D. Leinen). 1 www.solabs.net. 0257-8972/$ - see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2005.11.098