Preparation and Characterization of Anatase (Tio 2 ) Nanoceramics
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PREPARATION AND CHARACTERIZATION OF ANATASE (TiO2) NANOCERAMICS A.WEIBEL, R.BOUCHET, P.KNAUTH Laboratory MADIREL, University of Provence-CNRS (UMR 6121) Faculty of Sciences of Marseille St-Jérôme, 13397 Marseille Cedex 20, France.
ABSTRACT We have systematically investigated the influence of various parameters (pressure, temperature, time, sample size) on the hot pressing process of TiO2 nanoceramics. This study is backed by thermodilatometric experiments and microscopic observations of the microstructure. Impedance spectra of TiO2 nanoceramics with different porosity are also presented. INTRODUCTION Nanocrystalline titanium dioxide is important for many applications, including dyesensitized solar cells 1, photocatalytic decomposition of organic pollutants in waste water 2 and solid state gas sensors 3. For all these applications, a well-defined, large surface area and porosity are important. Following many studies on the preparation of nanoporous and nanocrystalline thin layers of TiO2 4, a fundamental study of dense nanocrystalline TiO2 is worthwhile to check the influence of a nanometric grain size on the electrical properties. The usual technique for preparation of conventional ceramics, low temperature forming followed by high temperature sintering 5 is not applicable to nanocrystalline anatase ceramics, because the high temperature treatment leads invariably to large grain growth and phase transition 6. The objective of nanocrystalline oxide ceramics is not attainable by this way. The method of choice for preparation of nanocrystalline ceramics is hot-pressing (HP). Here, compaction of nanocrystalline precursor powders and sintering are performed during the same treatment by application of a high pressure at moderate temperature. HP was previously explored for nanocrystalline ceria 7 and titania 8, but the influence of the experimental parameters was not fully investigated. The objective of this paper is to present a study of density versus the physical parameters temperature, pressure and time for nanocrystalline TiO2 (anatase) ceramics. Furthermore, the influence of the sample dimensions is explored and preliminary impedance spectra are presented. EXPERIMENT Pellets of different relative densities are obtained by HP phase-pure anatase powder (Bayer, Germany) calcined at 300°C for 1 hour. This powder is prepared by the sulfate process and is nominally undoped (only residual impurities from the preparation process are present, essentially Na+). The precursor particles have an average size of 17.5 nm, determined from X-ray diffraction (XRD) and BET adsorption measurements 9. The hot-press is a prototype built in collaboration with Cyberstar S.A.; it permits to work up to 5 tons weight and temperatures up to 1100°C. This apparatus is equipped with a digital comparator Sylvac S229 with ±1µm precision, which allows to follow the dilatation of sample
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and sample holder. The dyes are from pure alumina with internal diameters of 4, 6 and 12.7 mm (SOTIMI S.A.). The dilatometric curves are obtaine
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