Gas Phase Production of Silicon Nitride Using a DC Plasma
Silicon nitride powder has been prepared by the gas phase reaction of the metal chloride with ammonia using a nitrogen DC plasma as the heat source. A wide range of particle sizes from 0.005 – 0.2μm can be prepared by control of the gas recirculation in the reaction zone.
This synthesis method results in a high purity ultra fine white powder with a spheroidal morphology. Either amorphous or crystalline forms of silicon nitride can be produced dependent upon reaction temperature. The product is associated with a surface oxygen layer as shown by XPS surface analysis. However fine tuning of the process to grow the particles can result in bulk oxygen contents of less than 1.5 % 0, whilst retaining a specific surface area greater than 25 m2/g.
Sintering studies using relatively low levels of common additives indicate that high density and high α — β conversion can be achieved at low temperatures. The sintered product has a sub-micron grain size and exhibits high strength.
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