The approach of utilizing combustion synthesis to make fine particles of SiO2, A1203 and TiO 2 is a quite modern technology. Through the chemical reaction in post-flame region, fine SiO 2 particles can be formed with high purity on plate surface. Therefore, the combustion synthesis of SiO2 powders is an important area for further research and development, especially for the application of SiO 2 in the semiconductor industry. This investigation proposes an experimental approach (i.e., a gas-phase combustion synthesis) using two different kinds of organic compounds, Hexamethyldisilazane (HMDSA) and Hexamethyldisioxane (HMDSO), as the silicon precursors. A premixed gas bumer is chosen with C3H 8 as fuel, air as oxidant and part of the air was used as the carrying gas to entrain HMDSA/HMDSO vapor into the combustible mixture. Observations show that the C3Hs/air flame changed color from a pale-blue flame to light yellow and then orange when different amounts of precursors were introduced. Through the chemical reaction in the post-flame region, fine SiO 2 particles were formed in the gas phase and then quenched and collected on an aluminum flat plate. The objective of this paper is to study the effects of HMDSO and HMDSA concentrations and flame temperatures on the synthesis of SiO 2 particles.

This study is using HMDSA (C6H19NSi2) or HMDSO (C6HIROSi2) vapor into C3Hs/air premixed flames to form SiO2 thin film on the surface of an aluminum plate. With the addition of HMDSO or HMDSA to premixed flames, an orange secondary flame or a flame brush appeared and was contributed to the formation of SiO2 particles. Based upon the EDS, XPS and FTIR analysis, it is believed that the synthesized products consist of mainly SiO2 and a small amount of SiO. The pure SiO2 crystal structure, was proved by XRD analysis, which may form from the SiO2 amorphous structure after high temperature (1300°C) thermal treatment. The nano-size SiO2 particles, which ranged from 2.5-25 nm, are proved by analysis of the BET and TEM. A 2-D CFD-RC code with 12 reduced chemical reaction mechanism, based upon the SIMPLER procedure, was successfully employed to predict the flame temperature and both of the SiO2 and SiO concentration profiles. Compared with the experimental results, the calculated temperature profiles in the post-flame region are in good agreement with the measured data and observation phenomena.

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