J. Aemsof Sci. Vol. 29, Suppl. I, pp. S9074908, 1998 0 1998 Published bv Elswier Science Ltd. All rights rwxwd

Printed in &eat Britain 0021-8502/98 $19.00 + 0.00

EFFECTS OF PREPARATION CONDITIONS ON THE CHARACTERISTICS OF TITANIUM DIOXIDE PARTICLES PRODUCED BY A CVD METHOD

K. OKUYAMA, M. SHIMADA, T. FUJIMOTO, T. MAEKAWA, K. NAKASO and T. SETOt

Department of Chemical Engineering, Hiroshima University, l-4- 1, Kagamiyama, Higashi-Hiroshima 739-8527, Japan, ‘Mechanical Engineering Laboratory, AIST-MITI,

1-2, Namiki, Tsukuba 305-8564, Japan

KEYWORDS nanoparticles, titanium dioxide, agglomerate, sintering, discrete sectional model,

gas phase reaction

In the manufacturing of nm-sized material particles by gas-phase chemical reaction, it is important to evaluate gas-phase chemical reaction, nucleation, agglomeration by coagulation and sintering to control the size distribution and morphology of produced particles. In this study, the production of titanium dioxide particles by the thermal decomposition of titanium tertaisopropoxide (TTIP) and oxidation of titanium tetrachloride (TiC14) is investigated both experimentally and theoretically.

The laminar flow aerosol reactor used in the experiment consists of a ceramic tube of 13 mm in inner diameter and 1.50 m in length equipped with a tubular furnace. The source gas, TTIP or Tic& vapor, is fed into the reactor with carrier gas (pure nitrogen for TTIP and a mixture of nitrogen and oxygen for Tic&) at a constant flow rate. Figure 1 shows typical examples of the change in particle size with furnace temperature, Tf, at a constant feeding rate with a constant source gas concentration. The volume mean diameter of gasborne agglomerates was obtained by using a differential mobility analyzer and condensation nucleus counter installed at the exit of the reactor, whereas the diameter of primary particles was determined by collecting the particles on a plate and observing them with TEM. The size of the agglomerates (open symbols) prepared from the two source gases tends to decrease slightly with Tf for Tf < -1000 ‘C but increase with Tf for Tf > -1400 ‘C. The change of primary particle size with Tf exhibits a tendency opposite to that of agglomerate size. These changes indicate that the agglomerate and primary particle size are considerably affected by sintering of particles which rate depends strongly on temperature. Therefore, sintering must be taken into consideration as well as coagulation to predict the morphology of prepared particles.

The symbols in Fig. 2 show the measured distributions of agglomerate (d,) and primary particle (dr) diameters at T, = 1000 ‘C. The lines in the figure are the distributions of d, and d, calculated numerically by considering the particle size change by sintering. In this calculation, the discrete-sectional model (Wu and Flagan, 1988) for computing the particle formation by chemical reaction and growth by coagulation is extended by combining it with a two dimensional representation of particle size (Xiong and Pratsinis, 1993; Seto et al., 1997), to predict the evolution of the distributions of d, and d, in the reactor. The reaction rate of the source gases and the temperature distribution in the reactor were also taken into account in this calculation. Although the agreement between the measured and calculated results is not perfect, the present calculation is considered to provide good prediction for particles prepared from the two source gases.

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Abstracts of the 5th International Aerosol Conference 1998

furnace temperature, q [Cl

Fig. 1. Change in volume mean diameter of agglomerate and primary particles with furnace temperature, T,; Feeding rate and source gas concentration are 2 Umin and 7.64 x IO-’ mol/L.

1o14

lo4 lo-’ loo 10’ lo* lo3 lo4 10-l loo 10’ 102 10s 104

particle diameter,d [nm] particle diameter,d [nm] (a) 03

Fig. 2. Measured and calculated size distribution of agglomerates, d,, and primary particles, d,; Source gas is (a) TTIP and (b) TiCI,; Feeding rate and source gas concentration are the same as Fig. 1.

ACKNOWLEDGEMENTS

Part of this work was supported by Grants-in-Aid for Scientific Research from the Ministry of Education, Science, Sports and Culture of Japan (Nos. 09555231 and 09750829) and “Research for the Future” Project (96POO402) and a Research Fellowship for Young Scientists (No. 3685) of Japan Society of the Promotion of Science.

REFERENCES

Seto, T., A. Hirota, T. Fujimoto, M. Shimada and K. Okuyama, (1997) Sintering of polydisperse nanometer-sized agglomerates, Aerosol Sci. Techn., 27 422-438.

Wu, J. J. and R. C. Flagan, (1988) A discrete-sectional solution to the aerosol dynamic equation, J. Colloid Interface Sci., 123 339-352.

Xiong, Y. and S. E. Pratsinis, (1993) Formation of agglomerate particles by coagulation and sintering - Part I. A two dimensional solution of the population balance equation, J. Aerosol Sci., 24 283-300.