SURFACE AND INTERFACE ANALYSIS Surf. Interface Anal. 2006; 38: 277–281 Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/sia.2270 In-depth composition study of zirconia-coated steel sheet by XPS R. L ´ opez, R. Romero, F. Mart ´ ın, J. R. Ramos-Barrado and D. Leinen * Laboratorio de Materiales y Superficie, (Unidad Asociada al CSIC), Dpto, F´ ısica Aplicada I & Dpto, Ingenier´ ıa Qu´ ımica, Universidad de M ´ alaga, E-29071 M´ alaga, Spain Received 6 July 2005; Revised 22 November 2005; Accepted 29 November 2005 Zirconia was deposited by spray pyrolysis on large-area aluminized steel sheets using two different types of heat sources: infrared radiation or white light. XPS in-depth composition study has shown that the carbon concentration is 4 at.% when using white light but 15 at.% when using infrared radiation. This carbon is found as zirconium carbide, formed as a diluted phase in the zirconia coatings. In the case of using infrared radiation, reflectance spectroscopy revealed a partial degradation of the optical properties of the coatings due to an incomplete pyrolysis of the precursor. These findings are of direct interest for unglazed solar fa¸ cade elements made of steel, in which the zirconia coating will act as a barrier layer against the degradation of the steel sheet during long-term outdoor exposure. Copyright  2006 John Wiley & Sons, Ltd. KEYWORDS: ZrO 2 ; steel; spray pyrolysis; XPS; depth profiling INTRODUCTION XPS and other surface analytical techniques have often been applied in situ in order to control the different coating parameters at laboratory level. However, at industrial scale such an in situ process control is mostly impossible and coating parameters have to be optimized via ex situ analysis. Valuable information, although time consuming, can be obtained by XPS depth profiling. In this context, an XPS in-depth composition study on spray-pyrolyzed zirconia coatings on aluminized steel sheet is presented showing the capability of the technique for composition control of the coatings as a function of the processing temperature for pyrolysis. Two different systems for substrate heating, i.e. infrared radiation or white light, have been applied yielding different temperatures for pyrolysis, growth velocity and coating quality. Previous experience with spray-pyrolyzed coatings 1 led to the selection of zirconia as the potential barrier-layer material on steel. The steel sheet will be used as base material for unglazed solar fa¸ cade elements. 2 The barrier layer will prevent the degradation of the element 3 subjected to ambient impact during long-term outdoor exposure, for instance, through pinholes or other defects introduced during fabrication and handling. In this work, we show that it is possible to control the quality of zirconia coatings sprayed onto aluminized steel sheet by XPS depth profiling together with complementary surface analytical techniques L Correspondence to: D. Leinen, F´ ısica Aplicada I, Facultad de Ciencias, Universidad de M´ alaga, E-29071 M´ alaga. Spain. E-mail: dietmar@uma.es Contract/grant sponsor: EU; Contract/grant number: ENK6-CT2002-00679. like SEM and diffuse UV-VIS-IR reflectance spectroscopy. From the latter, solar absorptance and thermal emittance are evaluated serving as optical quality parameters of the coatings for solar energy applications. EXPERIMENTAL In chemical spray pyrolysis, the precursor solution is sprayed onto the heated substrate. Two different heating systems were used: (i) a set of quartz lamps working with filaments open to atmosphere and filament temperature ¾1000 K yielding mainly infrared emission; and (ii) a set of halogen lamps with filament temperature ¾3000 K yielding white light. Both lamp sets were adjusted in position to an aluminized steel sheet of 1 m length and 0.4 m width (0.3 mm thick) in order to obtain an overall homogeneous substrate temperature for pyrolysis of ¾523 K (250 ° C) on the surface of the steel sheet. For this purpose, the steel sheet was kept moving during spraying; in case of quartz lamps (system A), at a velocity of 5 cm/s ten times through the spray zone, and in case of halogen lamps (system B), at a velocity of 4 cm/s six times through the spray zone. Zirconium acetyl acetonate (98% purity) at a concentra- tion 10 2 M was used as precursor for the aqueous spray solutions. Four nozzles across the substrate at distance of 20 cm from the substrate were used, spraying at a pumping flow rate of 4 ð 150 ml/h and an air pressure of 2 bar. The steel sheets were obtained from ThyssenKrupp Steel. They were hot-dip coated, fired, aluminized steel sheets with the commercial denomination FAL. The aluminized layer con- sisted of 10% silicon, 3% iron and the remainder aluminum. 4 The abbreviation AS will be used to denote this layer. The Copyright  2006 John Wiley & Sons, Ltd.