Tailoring the Relative Si3N4 and SiC Contents in Si3N4/SiC Nanopowders through Carbothermic Reduction and Nitridation of Silica Fume

This study demonstrates the synthesis of nanostructured Si3N4/SiC composite powders from silica fume, for the first time. The processing approach to convert the waste silica fume to advanced nanocomposites is based on the integrated mechanical and thermal activation (IMTA) process. The synthesized nanostructured Si3N4/SiC powders have crystallite sizes as small as 17 nm for SiC and 42 similar to nm for Si3N4. It has been shown that the carbothermic reduction and nitridation temperature, as well as the graphite concentration in the starting SiO2 similar to C mixture are the important parameters to obtain Si3N4 and SiC nanopowders and control their crystal sizes. The synthesis conditions to tailor the relative contents of a-Si3N4 and a-SiC (changing from as high as 49 vol.% to as low as 21 vol.% a-SiC) in the final powder mixture have been investigated, and the mechanisms responsible for the observed relationship between processing conditions and the characteristics of the final powder have been identified.