Synthesis of carbon-free Si3N4/SiC nanopowders using silica fume

We have investigated a possible method of synthesizing carbon-free, nano-silicon nitride silicon carbide (Si3N4/SiC) powders from the waste silica fume for the first time, using the integrated mechanical and thermal activation (IMTA) process. This novel process results in the formation of nano-Si3N4/SiC powders at 1465 degrees C with crystallite sizes as small as 45 nm. In order to synthesize carbon-free nano-Si3N4/SiC powders, two different approaches, one using the H-2 gas and the other using air, have been studied for their effectiveness in removing the free carbon present. It is found that the H-2 treatment is not very effective although both Si3N4 and SiC are stable during the H-2 treatment. In contrast, removing the free carbon using air is effective, and the limited oxidation of nano-Si3N4 and SiC can be achieved if the air treatment is terminated soon after the free carbon is eliminated. This study has provided a clear pathway and understanding for effectively synthesizing carbon-free, nano-Si3N4/SiC powders from the silica fume. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.