Measurement of particle size distribution during flame synthesis using in situ sampling probe

J Aerosol Sci. Vol. 30, Suppl. I, pp. $351-$352, 1999 © 1999 Published by Elsevier Science Ltd. All fights reserved Printed in Great Britain 0021-8502/99/$. see front matter

Pergamon

MEASUREMENT OF PARTICLE SIZE DISTRIBUTION DURING FLAME SYNTHESIS USING INSITU SAMPLING PROBE C. H. Jung', B. Han", K. H. Ahn'*, M. Choi', and J. S. Lee" * National CRI Center for Nano Particle Control, School of Mechanical and Aerospace Engineering, Seoul National University, Seoul 151-742, Korea ** School of Mechanical and Aerospace Engineering, Seoul National University, Seoul 151-742, Korea *t National CRI Center for Nano Particle Control, Department of Mechanical Engineering, Hanyang University, Ansan Kyungki Do 425-791, Korea t corresponding author : E-mail) [email protected] KEYWORDS Diffusion Flame, Flame Synthesis, Sampling Probe, TEOS, SiO2 INTRODUCTION Particle generation by flame synthesis is very efficient process for manufacturing highly pure materials. Properties of these materials depend on characteristics of particles, especially size and morphology. So the control of particle size and morphology during flame synthesis is very important in obtaining fine quality materials (Pratsinis, 1998). The morphology of particles can be changed by controlling the characteristic collision time and the coalescence time (Windeler et al., 1997). Coupled with morphology and size of particles depends on many process parameters. In principle, two methods (optical method and micro probe sampling method) are applicable for in situ particle investigations (Kasper et al., 1997). EXPERIMENT In this experiment, particle size distributions during flame synthesis are measured using in situ sampling probe. The experimental set-up is shown in Fig. 1 which consists of four main units, i.e., the gas and precursor feeder, the co-flow hydrogen-oxygen diffusion flame burner, the sampling and analysis unit for particle size distribution measurement. The SiO2 particles are formed using precursors of TEOS in the co-flow hydrogen-oxygen diffusion flame burner. The extraction of samples is done by the probe that enables both quenching and dilutions. Particle Aorol~l

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Abstractsof the 1999EuropeanAerosolConference

size distribution in the diluted gas is measured using SMPS. TEM image analysis using local sampling system is also adopted to investigate the morphology of sampled particles. RESULTS The most important parameters of particle generation during flame systhesis are known to be temperature and precursor concentration. The reaction mechanism of SiO2 particle formation from TEOS is not well defined. However, Okuyama et a1.(1997) reported that the intermediate species plays important role in the formation of particles. This intermediate species form liquidlike particles by the homogeneous nucleation during the reaction. This similar process has been observed in this experiment. Fig. 2 shows the liquid-like particles in Fig. 2 (a) and the

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(a) z = 30mm

(b) z = 75mm

Figure 2 TEM photographs at different hight aggregates in Fig. 2 (b), which are sampled at different distance from the burner exit plane. Particles sampled at 75mm from the burner exit plane show the complete shape of SiO 2 particles rather than the liquid-like particles sampled at 30ram. To verify the particle growth and characteristics in the co-flow diffusion flame synthesis using TEOS precursors, the in situ sampling and measurement method has been employed at various flame conditions. It is found that some of the sampled particles show liquid like particles and some are aggregates depending on the sampling locations. The effect of temperature and precursor concentration on particle size distribution and morphology is investigated. REFERENCES Pratsinis, S. E. (1998) Prog. Energy Combust. Sci. , 24, 197 Windeler, R. S., Friedlander, S. K., and Lehtinen, K. E. (1997)Aerosol Sci. Technol., 27, 174 Kasper, M., Siegmann, K., and Sattler, K. (1997)J. Aerosol Sci., 28(8), 1569 Okuyama, K., Fujimoto, T., Hayashi. T, and Adachi, M. (1997) AIChE J., 43(11A), 2688