Combustion synthesis of SiC/Si3N4-NW composite powders: The influence of catalysts and gases

Composite powders containing silicon carbide (SiC) particles and silicon nitride nanowires (Si3N4-NWs) were synthesized by combustion synthesis, using elemental Si, carbon black, PTFE and small amount of metal powders as raw materials. The catalyst types and environmental gases and pressures have been altered to study their influence upon the crystal growth and the nature of the products. The products were characterized by X-ray diffraction, scanning and transmission electron microscopy. Results reveal that the metal/silicon liquid (e.g. Ni2Si and Fe3Si) formed during the combustion process is a key factor for the growth of Si3N4-NWs in nitrogen. For the process carried out in non-nitrogen gas (Ar, CO2 or mixed CO2/O2), pure SiC particles were obtained. The rise in nitrogen pressure can promote the growth of Si3N4-NWs as well as large SiC particles. The growth of Si3N4-NWs could be explained by the SLGS mechanism, and the growth of SiC particles was involved in the gas-phase and liquid-phase mechanisms.