Coarse-grained β-Si3N4 powders prepared by combustion synthesis

Coarse-grained beta-Si3 N4 powders were prepared by combustion synthesis under N-2 pressure of 6 MPa, with a low diluent content of not more than 10 wt.% and high reaction temperature of >1900 degrees C. beta-Si3 N4 was obtained as the major phase in the products, except for a small amount of residual Si. The addition of carbon black was effective to reduce the residual Si, but resulted in the formation of beta-SiC when too much carbon black was used. The coarse-grained beta-Si3 N4 powders consisted of beta-Si3 N4 crystals with an average thickness of more than 10 mu m, and some crystals were thicker than 20 mu m. The growth mechanism of the coarse beta-Si3 N4 crystals was discussed, associated with the particular reaction conditions in combustion synthesis.