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Four types of microchannel reactors were built, using a combination of smallest alumina-tubes commercially available, for testing the feasibility of applying high-temperature microchannel reactors to the ammonolysis of SiO for producing nano-sized silicon nitride powder. The innermost tube used for feeding SiO vapor had an inner diameter (ID) of about 500 micrometers, while the outermost tube used for ammonia feed had an ID of 3180 micrometers, and between these two was a 1600 micrometers ID tube for argon flow to separate the two reactant gases: SiO and ammonia. The microchannel reactors were operated at temperature between 1300 degrees C and 1350 degrees C at pressure slightly above atmospheric pressure.
All the microchannel reactors built for this study could be operated without any serious problems, such as clogging of micro-tubes with whiskers or nano-sized powder. The reduction of residence time and quenching of reactant/product mixture decreased the average particle size down to about 10 nm. The smallest size for particles to grow was estimated based on thermodynamic consideration and found to be on the same order of magnitude as those observed in TEM pictures. Based on the successful operation of microchannel reactors, potential structures for a scalable set of multi-microchannel reactors were proposed for future study. |
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