Processing and Application of Ceramics 2016 Volume 10, Issue 4, Pages: 235-241
https://doi.org/10.2298/PAC1604235G
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Heating rate dependence of anatase to rutile transformation
Galizia Pietro (CNR-ISTEC National Research Council of Italy, Institute of Science and Technology for Ceramics, Faenza, Italy + Polytechnic of Turin, Department of Applied Science and Technology, Torino, Italy)
Maizza Giovanni (Polytechnic of Turin, Department of Applied Science and Technology, Torino, Italy)
Galassi Carmen (CNR-ISTEC National Research Council of Italy, Institute of Science and Technology for Ceramics, Faenza, Italy)
Commercial titania powders were calcined in order to investigate the
influence of the heating history on the thermally stable phase (rutile).
Temperatures from 620 to 700°C and heating rates from 50 to 300°C/h were used
in order to evaluate their influence on the kinetics of transformation and
microstructure evolution. The quantitative analysis of anatase-rutile
mixtures based on X-ray diffraction intensities was performed. The results
were plotted as cumulative transformation rate vs. cumulative coarsening rate
in order to address the heating history of the anatase to rutile
transformation. As the main result it was found that the amount of anatase
transformed into rutile increases with increasing heating rate at fixed
soaking time and temperature of calcination. Through linear extrapolation of
experimental data obtained from the calcined commercial titania Degussa P25,
it was found that 83 nm for the rutile crystallite size is the lowest limit
needed for getting 100% of rutile powders. A substantial improvement in the
anatase to rutile kinetic transformation was achieved after pressing the
starting powders in order to exploit the interface nucleation.
Keywords: titania, calcination, X-ray diffraction, polymorphic phase transformation kinetic