Abstract
The formation of SiC-Si3N4 composite particles by the vapor phase reaction of Si(CH3)4-NH3-H2 system at 1200°C was investigated with emphasis on the effect of mixing temperature of Si(CH3)4 and NH3 streams. Powders produced were amorphous. When Si(CH3)4 was mixed with NH3 in a low temperature zone below 900°C, the particle size was 0.05 to 0.07μm and decreased with an increase in NH3 concentration. When the mixing temperature was 1100°C, the particle size was nearly 0.02μm regardless of NH3 concentration. The amorphous powders crystallized into β-SiC and α-Si3N4 (partially including β-Si3N4) by the heat treatment at 1550°C in Ar-N2 atmosphere. The crystallized phase from amorphous powder produced in low temperature mixing was SiC phase, SiC-Si3N4 composite and Si3N4 phase depending on the NH3 concentration used, among which the composite particles had hybrid structure consisting of Si3N4 core and SiC shell. On the other hand, SiC-Si3N4 composite particles were obtained even at a high NH3 concentration in high temperature mixing, and they consisted of SiC core and Si3N4 shell. The following formation processes of composite particles in the vapor phase reaction were proposed: in low temperature mixing (Tm=700°-900°C), nitride particles were produced at first by the reaction between Si(CH3)4 and NH3 immediately after the mixing and then carbide layer deposited on their surfaces from the unreacted Si(CH3)4, while in high temperature mixing (Tm=1100°C), Si(CH3)4 polymerized and decomposed into SiC particles in a low temperature zone and then the SiC particles were nitrided with NH3 in a high temperature zone.
