Crystallization Behavior of Amorphous Silicon Nitride Powder

Abstract

Amorphous silicon nitride powder (particle size: 0.04μm) obtained by the vapor phase reaction of Si(CH3)4-NH3 system was compacted into pellet and heat-treated in N2 to investigate the crystallization behavior. The amorphous powder crystallized to 100% α-Si3N4 by the heat treatment for 1h at 1550°C. The equiaxed crystalline particles having the size of 1-2μm were obtained when powder was compacted, whereas acicular particles were produced when powder was not compacted. When Si3N4 powder was used as powder bed which covered pellet, the crystalline particles grew extensively and the crystallinity increased with a decrease in the packing fraction of particles in pellet. The heat-treated powder with a low crystallinity consisted of fine amorphous particles and coarse crystalline particles. The crystallization seemed to proceed by a vapor phase growth mechanism, in which SiO vapor takes part as silicon carrier between amorphous particles and crystalline ones. When BN powder was used as powder bed, the crystallization and grain growth were retarded, and the crystal phase contained a small amount of β-Si3N4. Crystallization inhibitor, e. g. boron oxide, may have penetrated into pellet from BN powder.