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    Effect of pressure on TiO2 crystallization kinetics using in-situ high-temperature synchrotron radiation diffraction

    Access Status
    Fulltext not available
    Authors
    Albetran, H.
    O'Connor, Brian
    Low, It Meng
    Date
    2017
    Type
    Journal Article
    
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    Citation
    Albetran, H. and O'Connor, B. and Low, I.M. 2017. Effect of pressure on TiO2 crystallization kinetics using in-situ high-temperature synchrotron radiation diffraction. Journal of the American Ceramic Society. 100 (7): pp. 3199-3207.
    Source Title
    Journal of the American Ceramic Society
    DOI
    10.1111/jace.14798
    ISSN
    0002-7820
    School
    Department of Physics and Astronomy
    URI
    http://hdl.handle.net/20.500.11937/55424
    Collection
    • Curtin Research Publications
    Abstract

    The phase transformation behavior of TiO 2 sol-gel synthesized nanopowder heated in a sealed quartz capillary from room temperature to 800°C was studied using in-situ synchrotron radiation diffraction (SRD). Sealing of the capillary resulted in an increase in capillary gas pressure with temperature. The pressures inside the sealed capillary were calculated using Gay-Lussac's Law, and they reached 0.36 MPa at 800°C. The as-synthesized material was entirely amorphous at room temperature, with crystalline anatase first appearing by 200°C (24 wt% absolute), then increasing rapidly in concentration to 89 wt% by 300°C and then increasing more slowly to 97 wt% by 800°C, with there being no indication of the anatase-to-rutile transformation up to 800°C. The best estimate of activation energy for the amorphous-to-anatase transformation from the SRD data was 10(2) kJ/mol, which is much lower than that observed when heating the material under atmospheric pressure in a laboratory XRD experiment, 38(5) kJ/mol. For the experiment under atmospheric pressure, the anatase crystallization temperature was delayed by ~200°C, first appearing after heating the sample to 400°C, after which crystalline rutile was first observed after heating to 600°C. The estimated activation energy for the anatase-to-rutile transformation was 120(18) kJ/mol, which agrees with estimates for titania nanofibers heated under atmospheric pressure. Thus, heating the nanopowders material under pressure promoted the amorphous-to-anatase transformation, but retarded the anatase-to-rutile transformation. This behavior is believed to occur in an oxygen-rich environment and interstitial titanium is also expected to form when the material is heated under high gas pressure. This suggests that atmospheric oxygen appears to accelerate the amorphous-to-anatase transformation, whereas interstitial titanium inhibits TiO 2 structure relaxation, which is required for the anatase-to-rutile transformation.

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