Combustion co-synthesis of nano SiC and purified Si₃N₄ powders by coupling strong and weak exothermic reactions

Silicon carbide (SiC) powders and silicon nitride (Si₃N₄) powders are critical raw materials for advanced ceramic technology and industry. There are two challenges in their synthesis and production: (ⅰ) phase formation of nano SiC powders due to harsh reaction temperature and (ⅱ) preparation of high-purity Si₃N₄ powders due to difficulties in removing trace oxygen impurities. Combustion synthesis is a cheap, scalable method for producing SiC and Si₃N₄ powders. However, there are two additional challenges: (ⅲ) combustion synthesis of SiC requires intense external energy input due to the weak exothermic reaction between Si and C and (ⅳ) combustion synthesis of Si₃N₄ requires a diluent to slow down the self-accelerated reaction and fully convert Si to Si₃N₄ due to the strong exothermic reaction between Si and N₂. Here, we reported a new combustion co-synthesis of nano SiC and high-purity Si₃N₄ powders in one chamber, which addressed all four challenges mentioned above: (ⅰ) the production of nano SiC powders resolved by fast synthesis, (ⅱ) purified pink-grade Si₃N₄ powders using carbon as an efficient high-temperature oxygen getter, (ⅲ) ignited Si–C combustion by a strongly exothermic Si–N₂ reaction, and (ⅳ) more controllable Si–N₂ combustion with less diluent usage and less residual Si. We demonstrated nano β-SiC powders with ~30 nm primary particle size and high-purity pink-colored β-Si₃N₄ powders with oxygen impurity content down to 0.46 wt%. This study not only offers practical solutions to the production of high-quality SiC and Si₃N₄ powders but also refreshes the design of combustion synthesis with new possibilities and improved controllability.