Production of Pure, Intimately Mixed Silicon Nitride/SiliconCarbide Powders by a Novel Gas Phase Combustion Synthesis Process

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Fine, ultrapure, uniform, loosely agglomerated particles are desirable starting materials for advanced ceramics. Mixtures of silicon nitride and silicon carbide are particularly valuable. In this program, the use of silane/acetylene/ammonia flames to produce silicon nitride/silicon carbide powders will be studied. Specific tasks include: (1) Experimental determination of flame stability limits on a flat-flame burner for selected mixtures of silane, ammonia, and acetylene as a function of unburned gas velocity; (2) Thermodynamic determination of expected flame temperatures and product yields as functions of input compositions, pressure, and initial temperature; (3) Determination of the effects of operating conditions on the properties of the powder produced, specifically what operating conditions devermine whether the individual particles are a mixture of the carbide and nitride or whether the nitride and carbide are in separate particles; (4) Determination of the product properties (chemical composition, purity, particle size distribution, morphology); and (5) Interpretation of the results in terms of mechanisms and commercialization potential. High quality ultrafine silicon nitride/silicon carbide powders have a large potential market in the preparation of advanced ceramic materials via sintering or hot pressing. Progress in production of advanced ceramics is currently limited by the unavailability of a US-made high quality powder. In addition, an understanding of the mechanisms involved in this process will have broad implications for combustion synthesis (especially of mixed materials) in general.