The effect of heat-treatment on the grain-size of nanodisperse plasmathermal silicon nitride powder

摘要

Nanodisperse silicon nitride has been synthesized by vapor phase reaction of silicon tetrachloride and ammonia in a thermal plasma reactor and crystallized at temperatures 1250, 1350, 1450 and 1500℃. The average grain-size and the dislocation density of the samples were determined by the recently developed modified Williamson-Hall and Warren-Averbach procedures from X-ray diffraction profiles. A new numerical method provided log-normal grain-size distributions from the size parameters derived from X-ray diffraction profiles. It has been shown that the average grain-size in the amorphous phase is lower than that observed in the crystalline fraction. On the other hand, the average grain-size in the crystalline fraction decreases up to 1450℃ while it increases during heat-treatment at 1500℃. The size distribution and the area-weighted average grain-size obtained by X-rays were in good agreement with those determined by TEM and from the specific surface area, respectively. The dislocation density was found to be of the order of 10~(14) and 10~(15) m~(-2).