Wüest M. 51 Wykes M. 82 Yamaguchi M. 17 Ybarra G. 129 Yubero F ...

JUNE 26 MONDAY AFTERNOON
RIVA-TF-MoA-OR.15 OXIDE THIN FILM COATINGS BY SPRAY PYROLYSIS
ONTO STEEL COILS. R. López Ibáñez. Departamento de Física Aplicada I, Facultad de Ciencias,
Universidad de Málaga, E-29071 Málaga, Spain. F. Martín. Departamento de Igeniería Química,
Facultad de Ciencias, Universidad de Málaga, E-29071 Málaga, Spain. J.R. Ramos-Barrado. Departamento
de Física Aplicada I, Facultad de Ciencias, Universidad de Málaga, E-29071 Málaga,
Spain. D. Leinen. Departamento de Física Aplicada I, Facultad de Ciencias, Universidad de Málaga,
E-29071 Málaga, Spain.
A large scale spray pyrolysis coater has been designed and constructed for industrial pilot trials in
the aim of depositing different functional metallic oxide thin films onto metallic substrates, such as
antireflective layers, self-cleaning films, barrier layers, selective thin films, photocatalytic coatings,
etc. Within the field of solar thermal energy, a zirconia film has been produced onto an aluminized
steel coil of 0.4 m width which has been previously coated with a selective layer elsewhere. The zirconia
film as a top-coat has the function of anticorrosion and protection against ambient impact in
outdoor conditions.
Technical details: Zirconium acetyl-acetonate in a 0.02 molar aqueous solution was used as precursor
for spraying onto the 200º C heated substrate, growing in these conditions aproximately a 10 nm
thick zirconia thin film. After several coating repetitions an 80 nm ZrO 2 thin film was produced.
Characterization: UV-Vis-NIR-MIR hemispherical reflectance spectroscopy showed that the zirconia
coating is highly transparent and acts as an antireflection layer, increasing the solar absorptance in
about 10 %, but not degrading the thermal emittance at 373K, thus improving optical properties for a
solar thermal device. SEM revealed a dense film which covers well the substrate sealing existing
pores. No cracks could be seen on the surface of the coating even after repeating the coating process
for several times, rolling up and unrolling the steel belt from its cylindrical storage. XPS depth profile
analysis showed that the material was well pyrolysed to zirconium oxide. Only 3% of carbon remaining
from the precursor was found inside the film, stabilized in a ZrC phase homogeneously diluted
across the zirconia film thickness. No crystalline structure was detected by XRD. Linear polarization
measurements were carried out in 0.5 molar sodium chloride aqueous electrolyte solutions.
A reduction in the registered current densities showed a decrease in corrosion attack by approximately
one order of magnitude when comparing to the corrosion behaviour of the substrate itself.
Conclusions: Compact, homogeneous and well synthesized zirconia thin films have been deposited
onto a continuously moving steel belt with an industrial scale spray pyrolysis pilot station. The zirconia
film improves corrosion resistance and the optical properties of the layer stack, zirconia topcoat,
selective layer, aluminized steel substrate, with regard to solar thermal applications.
Acknowledgements: Funds from the EU (project SOLABS: ENK6-CT2002-00679) are gratefully
acknowledged.
EU Project SOLABS: Development of unglazed solar absorbers (resorting to coloured selective coatings on steel material)
for building facades, and integration into heating systems. www.solabs.net
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