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Mechanochemical preparation of nanocrystalline TiO2 powders and their behavior at high temperatures

Nanocrystalline TiO2 powders were prepared by high-energy ball-milling using a zirconia vial and balls. The phase changes in the samples were monitored by Raman and X-ray powder diffraction (XRD). The milling of the starting TiO2 powder (anatase + rutile traces) induced the phase transitions to a high-presure TiO2 polymorph and rutile, and this mechanochemical process was associated with the crystallite/particle size decrease. Changes in crystallite size were obtained by the Scherrer method, the particle size changes were monitored by transmission electron microscopy (TEM), the morphology of the particles was monitored by scanning electron microscopy (SEM), whereas the crystal phases in these particles were analyzed by selected area electron diffraction (SAED). The kinetics of phase changes, a decrease in crystallite/particle size, as well as zirconia contamination depended on the powder-to-ball weight ratio. Behavior of the starting powder, selected ball-milled samples and the corresponding sinters at high temperatures were investigated by in situ Raman spectroscopy and in situ XRD. A difference in the results obtained by two techniques was explained by different physical backgrounds of these techniques, as well as the chemical and microstructural differences between the surface and the bulk of TiO2 particles at high temperatures.

TiO2; B: mechanochemistry; Raman spectroscopy; XRD; electron microscopy; in situ sintering

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