気相反応法によるTiO2微粉体の生成機構

概要

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Ultra-fine particles of TiO2 were synthesized by the gas-phase oxidation of TiCl4. The formation of TiO2 particles passed through interacting rate steps such as production of monomer TiO2, collision and fusion of particles, and transformation of anatase to rutile. The experiment was carried out in two externally heated tubular reactors connected in series, and the particles were characterized by transmission electron microscope and X-ray diffraction methods. The mean particle sizes calculated from the two methods coincided within 10%. The mean size of particles decreased with increasing initial oxygen concentration. This means that the mixing near the injection nozzle plays an important role in the growth of particles. When the concentration of unreacted TiCl4 was appreciable, fusion of TiO2 particles larger than 50nm occurred at 1000°C. The fusion proceeded above 1200°C without TiCl4, while no fusion in the second reactor was observed below 900°C even though TiCl4 was introduced. The rutile content after aging or the second reaction was dependent on the crystal compositions of initial particles. A model for the explanation of the particle growth and the crystal transformation is proposed.
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