engleski

Structural changes in TiO2 induced by ball milling or high temperature

In this work, the Raman spectroscopy and transmission electron microscopy (TEM) were used to explain kinetics and mechanism of phase transition, and diminution to nano-particle TiO2. On the other hand, the Raman spectroscopy and light microscopy were used to elucidate the structural changes after the heating of anatase TiO2 and anatase TiO2 with 5 mol% ZrO2. After milling time as short as 3 min using WC set the bands of high-pressure TiO2 II phase (a-PbO2 structure) were detected in the Raman spectra. However, 14 minutes were necessary for appearance of the same new bands when milling was performed by agate set. Nearly five times longer milling time necessary for beginning of structural changes by agate set was correlated to five times greater ball-to-powder weight ratio for the WC milling set. The prolonged milling times was needed for transformation to rutil (180 min using WC set and 600 min using agate set). The low-frequency Raman band of samples milled for long time was broad, that suggests the wide dispersion in nano-particle dimensions and shapes. The position of low- frequency band (10 to 30 cm-1) in longer milled samples indicated the dimensions from 7 to 21 nm (the diameter of the particle is inverse proportional to the low-frequency mode of spherical particles). We showed by experiments on ball-milled samples that the kinetic of phase transformations from anatase through TiO2 II to rutil were dependent on milling media and that the particle dimensions were decreased to nanometric size. The high temperature experiments indicated that solid solution of ZrO2 in TiO2 was stabile only if it was prepared on temperature high enough to achieve the sintering between ZrO2 and TiO2 grains.

Raman ; electron microscopy ; TiO2 ; ball-milling ; high temperature sintering ; phase transitions

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