Fine, ultrapure, spherical particles are desirable starting materials for producing high performance afvanced ceramic products. AeroChem has a unique flame synthesis process for preparing such high quality powders, including silicon nitride. This process differs from the usual combustion synthesis in that no oxygen is used: the particle-producing reactants also support the flame. For silicon nitride, silane, ammonia, hydrazine, and nitrogen are burned on a flat flame burner. A high quality powder is produced of which a sample, without additives, was successfully subjected to hot isostatic pressing. However, the use of hydrazine makes the process commercially unacceptable because of the cost, explosive nature, and toxicity of hydrazine. While thermodynamic and other considerations indicate that ammonia should support a flame without hydrazine present, we have not been able to operate without some hydrazine. A computer modeling study is proposed to understand why the ammonia/silane system does not support a flame under the conditions which have been employed, and to define the conditions under which a flame could be supported. Experiments will then be performed to determine the practical feasibility of operating under the defined conditions. Successful completion of this program would make available for advanced ceramic manufacture a higher quality powder than is currently available. The final product of the proposed research would be an economical process for the preparation of a high quality silicon nitride powder for use in advanced ceramics. Present progress in advanced ceramics is limited by the unavailability of a US made high quality powder.
