Solvothermal synthesis of titania-zirconia composite
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Nanocomposite particles of anatase-type titania (TiO2) and cubic/tetragonal zirconia were synthesized from hydrothermal processing of TiCl4 and ZrOCl2·8H2O or ZrCl4 alcohol solutions at 160–200 °C. It was found that the morphologies and composition of the composite particles were mainly controlled by the precursors and the sequence by which the precursors were added. The TiO2–ZrO2 composite particles with nanoscale uniformity can be obtained by solvothermal processing of TiCl4 or a ZrO2 precursor together with preformed ZrO2 or yttria stabilized zirconia (YSZ) nanoparticles in ethanol. A novel one-step and non-template method for preparing ZrO2–TiO2 core–shell structured composite particles with hollow interior was identified, and possible reaction mechanism was suggested.
I. INTRODUCTION
Ceramic composite materials have attracted much research attention in recent decades due to their superior mechanical, electrical, optical, and thermal properties as compared to single component ceramics.1–3 In recent years, with the advances in synthesis techniques, the particle size of ceramic powders went down to the nanometer range for which colloidal processing of ceramic powders is required.4,5 It was found that when nanosized ceramic particles were used in ceramic composite materials, several major advantages such as very homogeneous distribution of components, superplasticity, low processing temperatures, and much improved mechanical performance were obtained.6–8 Titania-zirconia (TiO2– ZrO2) and titania-yttria stabilized zirconia (TiO2–YSZ) composites are widely used in catalysis, solid oxide fuel cells (SOFCs), sensors, and biomaterials, and as structural components.9–16 TiO2–YSZ/ZrO2 is a particulate composite system, in which the performance of the material is affected by defects, the agglomeration of disperoids, and the segregation of particles.3 A promising solution to these problems is to use nano-sized composite particles where nanoscale dispersity can be maintained throughout the processing, defects, agglomeration, and segregation can be suppressed by the nanometer range uniformity, and so a high mechanical strength can be expected. However, few attempts had been made for the preparation of TiO2–ZrO2 and TiO2–YSZ nanocomposite particles.17–19 Coprecipitation, mechanical mixing, and hydrothermal synthesis are most widely used methods to make a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0042 J. Mater. Res., Vol. 21, No. 2, Feb 2006
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titania-YSZ (TiO2–YSZ) or titania-zirconia (TiO2–ZrO2) composite particles. 9,11,12,16,20–24 For ZrO 2 –TiO 2 nanocomposite particles prepared by coprecipitation and calcination, normally an equimolar sample yields a single phase of crystalline TiZrO4 (or ZrTiO4), while other combinations give binary oxides contain TiZrO4 and ZrO2 or TiO2 phases. While after sintering at high temperature, e.g., 1500 °C, the TiO2 phase tends to react with ZrO2 to form TiZrO4; in this case,
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