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Synthesis of titania particles by vapour-phase decomposition of titanium tetraisopropoxide
J Aerosol Sci. Vul. 3 I, Suppl. 1, pp. $927-$928,2000
Pergamon www.elsevier.com/locate/jaerosci
Poster session II. Nanoparticles and nanomaterials SYNTHESIS OF TITANIA PARTICLES BY VAPOUR-PHASE DECOMPOSITION OF TITANIUM TETRAISOPROPOXIDE
P. MORAVEC l, J. SMOLiK l and V.V. LEVDANSKY 2 qnstitute of Chemical Process Fundamentals, Academy of Sciences of the Czech republic, Prague, Czech Republic. 2A. V. Luikov Heat and Mass Transfer Institute, National Academy of Seienees of Belarus, Minsk, Belarus.
Keywords: titania, nanopartieles, CVD, synthesis techniques. INTRODUCTION We investigate preparation of fine particles by decomposition of various aikoxide vapours in a tube flow reactor. In previous studies we prepared fine particles of silica by oxidation oftetraethylorthosilicate (Smolik and Moravec, 1995) and alumina by decomposition of ahminum tri-sec-butoxide (Moravec et al., 1997). In this work we report the results of titania fine particle synthesis by decomposition of titanium tetraisopropoxide (TTIP). METHODS The particles were prepared in an externally heated tube flow reactor of i.d. 27 ram. The dry deoxidized and particle free nitrogen, used as a carrier gas, was saturated by TTIP vapour in an externally heated saturator. Then it was fed into the center of the reactor through a nozzle surrounded by coaxial stream of either nitrogen or air. Particle-laden gas leaving the reactor was cooled in a diluter by mixing it with another stream of nitrogen. Particle size distribution was monitored by an aerosol sizing system DMPS/C (TSI model 3932) or SMPS (TSI model 3934C). Samples of particles were also collected for SEM/TEM (JEOL-2000FX) and/or EDAX (Philips JXA 50A) analysis on Cu grids by point-to plate electrostatic precipitator and/or Millipore filters. The particle production was investigated in dependence on the reactor temperature (TR), TTIP concentration (Crne) and residence time of the reaction mixture in the reactor (RTR). The influence of the presence of oxygen in the reaction mixture was also tested. The prepared particles were white and spherical in shape or consisted of agglomerates of primary particles. In dependence on experimental conditions synthesized particles varied from almost monodisperse particles with Geometric Mean Diameter (GMD) < 30 nm and Geometric Standard Deviation (GSD) less than 1.45 (Fig. 1) to very polydisperse particles (Fig. 2). EDAX analyses revealed that they consist of titanium and oxygen. Selected area electron diffraction showed us that they are predominantly amorphous. Only very large particles contained crystalline nuclei. An interchange of nitrogen and air as a carrier gas had no observable effect either on morphology or composition of generated particles. The particle synthesis was investigated within the temperature range from 100 to 500°C for TTIP concentrations ranging from 8.8. I0 8 to 7.1.10 -7 mol]l. It was found that the particle production occurred already at temperature 100°C and up to 325°C nearly monodisperse particles were prepared (Fig. 1). In this temperature range Cvrw had practically no effect on GSD and Nt, (Nt ~ 8' 10 6 c m -3, GSD ~ 1.48) but GMD increased from 28 nm at c~rw 8.8" 108 mol/l to 70 nm at C-crrp7.1-10 -7 mol/l. At the reactor temperature 400°C and Crr~ < 5.3-10 -7 mol/! the particle production practically diminished and occurred again after increasing the precursor concentration. With further increase of temperature the dispersity of the product increased (Fig. 2), whereas number concentration of particles decreased.
; $927
$928
Abstracts of the 2000 EuropcanAerosolCon['c['encc
Also the influence of the residence time in the reactor was different at temperatures below and above 350°C. At 300°C Nt, GMD and GSD of generated particles increased with increasing RTR, whereas at 400°C GMD decreased with RTR and Nt and GSD had a maximum, respective minimum at RTR - 20 s. The observed variation of particle production with reactor temperature is probably caused by changes in mechanism of precursor decomposition. The possible explanation might be the hydrolysis of precursor by traces of water vapour remaining in the carrier gas even after drying that occurs already at lower temperatures and pyrolysis of precursor vapours prevailing at higher temperatures. The pyrolysis at higher temperatures catalyzed by TiO2 particles deposited on the reactor wall was observed by Kirkbir and Komiyama (1988). It resulted in further deposition of the TiO2 on the reactor wall followed by reentrainment of particles that increased the dispersity of the product.
1
ID ~11_
-,
Fig. 1 SEM photo of TiO2 particles prepared at 300°C. Magnificeation 52000.
Fig. 2 SEM photo of TiO2 particles prepared at 500°C. Magnification 44000. o
CONCLUSIONS Ultrafine titania particles were prepared in a tube flow reactor at temperatures below 350°C probably by hydrolysis of TTIP. Above 350°C particles were produced only at higher precursor concentration and they were highly polydisperse. ACKNOWLEDGEMENTS This work was supported by the GA AS CR grant A4072807. SEM/TEM images were taken by Dr. Bohumil Smola from the Faculty of Mathematics and Physics of the Charles University. EDAX analyses were performed by Dr. Anna Langrov~i from the Geological Institute, AS CR. REFERENCES Smol~, J. and P. Moravec (1995). Gas phase synthesis of free silica particles by oxidation of tetraethylorthosilicate vapour, J. Material Science Letters 14, 387. Moravec, P., J. Smoh'k and V.V. Levdansky (1997). Fine particle synthesis by decomposition of aluminum tri-sec-butoxide vapour, 3. Aerosol Science 28, $481. Kirkbir, F. and H. Komiyama (1988). Low temperature synthesis of TiO2 by vapor-phase synthesis of titanium isopropoxide, Chemistry Letters of the Chemical Society of Japan 791.
Pergamon www.elsevier.com/locate/jaerosci
Poster session II. Nanoparticles and nanomaterials SYNTHESIS OF TITANIA PARTICLES BY VAPOUR-PHASE DECOMPOSITION OF TITANIUM TETRAISOPROPOXIDE
P. MORAVEC l, J. SMOLiK l and V.V. LEVDANSKY 2 qnstitute of Chemical Process Fundamentals, Academy of Sciences of the Czech republic, Prague, Czech Republic. 2A. V. Luikov Heat and Mass Transfer Institute, National Academy of Seienees of Belarus, Minsk, Belarus.
Keywords: titania, nanopartieles, CVD, synthesis techniques. INTRODUCTION We investigate preparation of fine particles by decomposition of various aikoxide vapours in a tube flow reactor. In previous studies we prepared fine particles of silica by oxidation oftetraethylorthosilicate (Smolik and Moravec, 1995) and alumina by decomposition of ahminum tri-sec-butoxide (Moravec et al., 1997). In this work we report the results of titania fine particle synthesis by decomposition of titanium tetraisopropoxide (TTIP). METHODS The particles were prepared in an externally heated tube flow reactor of i.d. 27 ram. The dry deoxidized and particle free nitrogen, used as a carrier gas, was saturated by TTIP vapour in an externally heated saturator. Then it was fed into the center of the reactor through a nozzle surrounded by coaxial stream of either nitrogen or air. Particle-laden gas leaving the reactor was cooled in a diluter by mixing it with another stream of nitrogen. Particle size distribution was monitored by an aerosol sizing system DMPS/C (TSI model 3932) or SMPS (TSI model 3934C). Samples of particles were also collected for SEM/TEM (JEOL-2000FX) and/or EDAX (Philips JXA 50A) analysis on Cu grids by point-to plate electrostatic precipitator and/or Millipore filters. The particle production was investigated in dependence on the reactor temperature (TR), TTIP concentration (Crne) and residence time of the reaction mixture in the reactor (RTR). The influence of the presence of oxygen in the reaction mixture was also tested. The prepared particles were white and spherical in shape or consisted of agglomerates of primary particles. In dependence on experimental conditions synthesized particles varied from almost monodisperse particles with Geometric Mean Diameter (GMD) < 30 nm and Geometric Standard Deviation (GSD) less than 1.45 (Fig. 1) to very polydisperse particles (Fig. 2). EDAX analyses revealed that they consist of titanium and oxygen. Selected area electron diffraction showed us that they are predominantly amorphous. Only very large particles contained crystalline nuclei. An interchange of nitrogen and air as a carrier gas had no observable effect either on morphology or composition of generated particles. The particle synthesis was investigated within the temperature range from 100 to 500°C for TTIP concentrations ranging from 8.8. I0 8 to 7.1.10 -7 mol]l. It was found that the particle production occurred already at temperature 100°C and up to 325°C nearly monodisperse particles were prepared (Fig. 1). In this temperature range Cvrw had practically no effect on GSD and Nt, (Nt ~ 8' 10 6 c m -3, GSD ~ 1.48) but GMD increased from 28 nm at c~rw 8.8" 108 mol/l to 70 nm at C-crrp7.1-10 -7 mol/l. At the reactor temperature 400°C and Crr~ < 5.3-10 -7 mol/! the particle production practically diminished and occurred again after increasing the precursor concentration. With further increase of temperature the dispersity of the product increased (Fig. 2), whereas number concentration of particles decreased.
; $927
$928
Abstracts of the 2000 EuropcanAerosolCon['c['encc
Also the influence of the residence time in the reactor was different at temperatures below and above 350°C. At 300°C Nt, GMD and GSD of generated particles increased with increasing RTR, whereas at 400°C GMD decreased with RTR and Nt and GSD had a maximum, respective minimum at RTR - 20 s. The observed variation of particle production with reactor temperature is probably caused by changes in mechanism of precursor decomposition. The possible explanation might be the hydrolysis of precursor by traces of water vapour remaining in the carrier gas even after drying that occurs already at lower temperatures and pyrolysis of precursor vapours prevailing at higher temperatures. The pyrolysis at higher temperatures catalyzed by TiO2 particles deposited on the reactor wall was observed by Kirkbir and Komiyama (1988). It resulted in further deposition of the TiO2 on the reactor wall followed by reentrainment of particles that increased the dispersity of the product.
1
ID ~11_
-,
Fig. 1 SEM photo of TiO2 particles prepared at 300°C. Magnificeation 52000.
Fig. 2 SEM photo of TiO2 particles prepared at 500°C. Magnification 44000. o
CONCLUSIONS Ultrafine titania particles were prepared in a tube flow reactor at temperatures below 350°C probably by hydrolysis of TTIP. Above 350°C particles were produced only at higher precursor concentration and they were highly polydisperse. ACKNOWLEDGEMENTS This work was supported by the GA AS CR grant A4072807. SEM/TEM images were taken by Dr. Bohumil Smola from the Faculty of Mathematics and Physics of the Charles University. EDAX analyses were performed by Dr. Anna Langrov~i from the Geological Institute, AS CR. REFERENCES Smol~, J. and P. Moravec (1995). Gas phase synthesis of free silica particles by oxidation of tetraethylorthosilicate vapour, J. Material Science Letters 14, 387. Moravec, P., J. Smoh'k and V.V. Levdansky (1997). Fine particle synthesis by decomposition of aluminum tri-sec-butoxide vapour, 3. Aerosol Science 28, $481. Kirkbir, F. and H. Komiyama (1988). Low temperature synthesis of TiO2 by vapor-phase synthesis of titanium isopropoxide, Chemistry Letters of the Chemical Society of Japan 791.