Coating of Fine Particles with Ultrafine Silicon Powder by Gas-Phase Monosilane Pyrolysis

Silicon nitride particles with a diameter of 5~20μm were coated with ultrafine, submicron silicon powder. The product is expected to show extreme properties in a reactive sintering process. A uniform and dilute suspension of core particles of silicon nitride in monosilane diluted with argon were introduced into a CVD reactor from a bed of core particles. Additional argon gas was also introduced into the reactor, from the annulus at the bottom of the reactor. The flow resistance of the procuct layer was found to be proportional to the amount of silicon fines. From the results of SEM and TEM, it was found that the core particles were uniformly coated with ultrafine silicon powder with primary particle diameter of around 0.01 μm. In the XRD chart, a weak pattern of silicon fines was found to overlap the pattern of silicon nitride. Without the use of additional gas, on the other hand, core particles coated with a thick deposit were manufactured and a broad XRD chart without the silicon pattern was observed. Heterogeneous deposition of silicon on core particles was found to be avoided by the use of additional gas. The additional gas seemed to be heated in the bottom of the reactor and to mix with reactant gas, thereby causing the homogeneous reaction and suppressing heterogenous CVD by reducing the residence time in the reactor.