Silicon nitride has potential uses in automobile engines, as turbine blades and any other parts needed for very high temperature service. Silicon nitride has high: strength, thermal shock resistance, and oxidation resistance at elevated temperatures. Silicon nitride powder is now produced by a batch process which is very expensive. The PIs plan to explore developing a continuous fluidized bed process which would more economically produce high purity silicon nitride powder in large quantities. The project will proceed in three stages: (1) study of the kinetics of silicon nitride formation (2) elucidation of the reaction mechanisms, and (3) development of a fluidized bed reactor system for producing the material. Specific work done in each of these stages will include: (1) study of the kinetics that may be expected in a fluidized bed reactor by investigation of the reaction mechanisms in detail in terms of the correlations between reaction conditions and product crystal structure using TGA and X-ray diffractometry methods; (2) development of a mathematical model to describe the progress of the reaction on the basis of the data obtained from the above experiments and (3) building and testing a fluidized bed reactor to handle this very complex process. Because particles in the one micron diameter range will be involved, three techniques will be tried to generate the fluidized bed: (1) partly sintering this very fine silicon powder to form aggregates 200 - 300 microns in size which fludize satisfactorily, (2) mixing the fine silicon powder with larger (greater than 100 microns) inert carrier solids which fluidize well, and (3) trying fast fluidized beds and/or pneumatic transport reactors.
