Tailoring the Relative Si ₃ N ₄ and SiC Contents in Si ₃ N ₄ / SiC Nanopowders through Carbothermic Reduction and Nitridation of Silica Fume

This study demonstrates the synthesis of nanostructured Si ₃ N ₄ /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 Si ₃ N ₄ / SiC powders have crystallite sizes as small as 17 nm for SiC and 42 nm for Si ₃ N ₄ . It has been shown that the carbothermic reduction and nitridation temperature, as well as the graphite concentration in the starting SiO ₂ + C mixture are the important parameters to obtain Si ₃ N ₄ and SiC nanopowders and control their crystal sizes. The synthesis conditions to tailor the relative contents of α‐ Si ₃ N ₄ and α‐ SiC (changing from as high as 49 vol.% to as low as 21 vol.% α‐ 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.