Preparation of nanocrystalline titania powder via aerosol pyrolysis of titanium tetrabutoxide
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Preparation of nanocrystalline titania powder via aerosol pyrolysis of titanium tetrabutoxide P.P. Ahonen and E.I. Kauppinena) Aerosol Technology Group, VTT Chemical Technology, P.O. Box 1401, FIN-02044 VTT, Finland
J.C. Joubert and J.L. Deschanvres Laboratoire des Mate´riaux et du Ge´nie Physique, ENSPG, Rue de la Houille-Blanche, Domaine Universitaire, BP 46, F-38402 Saint-Martin-D’Heres, France
G. Van Tendeloo EMAT-University of Antwerpen, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium (Received 17 July 1998; accepted 21 June 1999)
Nanocrystalline titanium dioxide was prepared via aerosol pyrolysis of titanium alkoxide precursor at 200–580 °C in air and in nitrogen atmospheres. Powders were characterized by x-ray diffraction, thermogravimetric analysis, Brunauer–Emmett– Teller analysis, scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, x-ray fluorescence, Raman and infrared spectroscopy, and Berner-type low-pressure impactor. The anatase phase transition was initiated at 500 °C in nitrogen and at 580 °C in air. Under other conditions amorphous powders were observed and transformed to nanocrystalline TiO2 via thermal postannealing. In air, smooth and spherical particles with 2–4-m diameter were formed with an as-expected tendency to convert to rutile in the thermal postannealings. In nitrogen, a fraction of the titanium tetrabutoxide precursor evaporated and formed ultrafine particles via the gas-to-particle conversion. At 500 °C thermally stable anatase phase was formed in nitrogen. A specific surface area as high as 280 m2 g−1 was observed for an as-prepared powder.
I. INTRODUCTION
Titanium(IV) oxide is a widely used ceramic material. It is found in three natural crystalline structures: rutile (tetragonal, P42/mnm), anatase (tetragonal, I41/amd), and brookite (orthorhombic, Pcab). Thermodynamically rutile is the only stable phase, whereas anatase and brookite are metastable at all temperatures.1,2 Experimental data show that pure anatase (bulk material) is stable up to 600 °C in normal pressure.3 However, anatase to rutile transformation is reported to occur between 400 and 1000 °C4 and is known to depend on crystallite size, impurity content, and reaction atmosphere. Decreased crystallite size (ultrafine) is shown to enhance anatase–rutile transition rate.5 Also, a decreased initial transition temperature with ultrafine crystallite size is presented6,7 compared to bulk titania experimental data. The impurity or dopant dependence is studied.8–10 Additives such as CuO, MnO2, Fe2O3, LiF, and LiCO38 as
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J. Mater. Res., Vol. 14, No. 10, Oct 1999 Downloaded: 03 Feb 2015
well as aluminum9 are known to promote the anatase– rutile transformation. Inhibiting action is observed, e.g., for sulfate, chloride, and fluoride ions as well as silicon, phosphorus, and boron halide.10 An effect of different reaction atmospheres for anatase–rutile t
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