Naslov
Characterization of nanostructured TiO2 prepared by mechanochemical treatment

Autori
Gajović, Andreja ; Tomašić, Nenad ; Furić, Krešimir ; Musić, Svetozar

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
13th Slovenian-Croatian Crystallographic Meeting : Book of abstracts / Leban, Ivan ; Popović, Stanko - Ljubljana : The Slovenian Crystallographic Society, 2004, 36-36

Skup
13th Slovenian-Croatian Crystallographic Meeting

Mjesto i datum
Bovec, Slovenija, 16.06.2004. - 20.06.2004

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
TiO2; ball-milling; Raman spectroscopy; XRD

Sažetak
The high-energy ball-milling of TiO2 induces changes in the crystal structure and decreases particle sizes to nano dimensions. In this work the conditions of changing TiO2 microstructure during the mechanochemical process were studied. The milling of TiO2 was performed in air using the Fritsch Pulverisette 6 planetary ball mill with vial and balls made of zirconia ceramic. The speed of mill rotation was 500 rpm. Two different powder-to-ball weight ratios (R) were used: R1=1:50 and R2=1:10. The milling time varied from 1 min to 10 hours. The particle dimensions and crystal structure of the milled powder were studied by Raman spectroscopy (RS), X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). In both series, different milling times induced the sequence of phase transitions: anatase (tetragonal, I41/amd)  high-pressure TiO2-II (orthorhombic, Pbcn)  rutile (tetragonal, P42/mnm). In the first series of experiments with R1=1:50 the phase transition from anatase to TiO2-II was completed after 20 min as observed both by RS and XRD. A small amount of rutile was observed by XRD already after 5 min of milling (R1=1:50). After 20 minutes the intensity of rutile XRD lines increased considerably, despite the fact that rutile bands were not resolved in the Raman spectrum until 40 min of milling time reached. The domination of rutile structure in a sample milled for 1 h with R1=1:50 was observed by both methods. Two XRD lines in surplus, and attributed to cubic ZrO2 as contamination appeared in the sample due to milling assembly wear. On the other hand, in the second series of experiments with R2 = 1:10, TiO2-II was evidenced by RS and XRD in a 20 min milled sample. Five hours of milling (R2=1:10) were necessary to complete the phase transition from anatase to TiO2-II. The weak XRD lines of rutile were evident in the 20 min milled sample (R2 = 1:10). The intensity of rutile XRD lines considerably increased in the 5 h milled sample, even though the rutile band had not been observed by RS yet. After 10 hours, the rutile along with the TiO2-II were detected by RS and XRD. No lines belonging to contamination were observed using R2 = 1:10 even after 10 h of milling. Although both RS and XRD indicate a transition from anatase through TiO2-II to rutile induced by progressive milling, XRD detected the rutile presence earlier than RS. This discrepancy could be interpreted by the scope of each method. XRD detects the interior of the studied sample, whereas RS spectroscopy predominantly brings into focus structural features in the surface area. Bearing this in mind, it could be inferred that the anatase  rutile phase transition initiated in the particle center due to local heating, whereas the anatase  TiO2-II phase transition commenced on the particle surface. Since high pressure conditions were more prominent at the particle surface due to collisions with balls, they favored the TiO2-II high pressure phase formation. The decrease in crystallite sizes during the TiO2 milling was estimated from XRD broadening using the Scherrer equation after a correction for instrumental broadening. The decrease of the crystallites was faster using R1=1:50. The mean crystallite size of the 1 h milled sample (R1=1:50) was (12  2) nm. During milling with R2=1:10 a decrease in the crystallite size to (14  0.5) nm after 10 h was also observed. As a consequence of nanosized crystallites, SAED produced a pattern with continuous rings, whose positions indicated the crystal structures observed by RS and XRD. A diminution of particle dimension was observed by TEM. Both milling experiments proved a decrease in particle and crystallite sizes with an increase in the milling time. Although in both milling experiments final crystallite sizes were similar, in the milling experiment with R1=1:50 the crystallite size did not match the mean particle size. The second milling experiment (R2=1:10) produced a more homogeneous material, which could be important in possible material application in nanotechnology. The ball-milling was shown to be a simple method for the preparation of nanostructured TiO2. The rate of phase transition and a decrease in particle size, along with the purity of TiO2 nanosized particles, depended on powder-to-ball weight ratios. The phase transition and diminution of particles were faster using R1=1:50, but contamination was greater.

Izvorni jezik
Engleski

Znanstvena područja
Fizika, Geologija, Kemija

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