Formation and characterization of α-Si3N4 whiskers from laser synthesized nano amorphous SiNC powders

alpha-Si3N4 whiskers have been prepared from the laser-synthesized nanometric amorphous Si-N-C powders at 1873 K under 1 atm N-2. The as-formed whiskers were characterized by TEM, STEM, FTIR and XRD techniques and the process conditions were studied. The whiskers exhibit four types of morphologies: the long, thick, straight, the prismatic, the ribbon-like, and knuckled whiskers. The gas phase reaction among N-2, SiO, and CO gases leads to the formation of Si3N4, nucleated on the pre-crystallized alpha-Si3N4 grains, which ensures an in situ formation, and grows rapidly by a VS mechanism along specific crystal planes such as {1101}. Thermochemical analysis indicates that the higher Si3N4 whisker formation temperature of 1873 K for the gas phase reaction results from the lower P-CO/P-SiO ratio in the Si-N-C system.