Preparation and properties of high-α-phase Si3N4 powder by low-temperature combustion synthesis

To overcome the poor compositional homogeneity of mechanically mixed precursors in the conventional carbothermal reduction nitridation (CRN) process, a two-step synthesis route combining low-temperature combustion synthesis (LCS) with carbothermal reduction nitridation (CRN) was proposed. An amorphous porous SiO 2 /C composite precursor with nanoscale homogeneous mixing was first prepared by LCS, followed by CRN to synthesize high-purity α-Si 3 N 4 powder. The effects of the precursor C/SiO 2 weight ratio, nitridation temperature, and holding time on the phase composition and α/β phase selectivity of the products were systematically investigated. The results showed that a Si 3 N 4 yield of 96.76 wt% with an α-phase content of 99.07 wt% was achieved under the optimized conditions of a C/SiO 2 weight ratio of 2.5:1, a nitridation temperature of 1450 °C, a holding time of 6 h, and a nitrogen flow rate of 350 mL/min. The amorphous porous precursor provides abundant reactive sites and facilitates nitrogen diffusion, thereby enhancing the efficiency of the carbothermal reduction nitridation reaction and enabling the synthesis of high-purity α-Si 3 N 4 at relatively low temperature within a short reaction time, resulting in reduced energy consumption. Furthermore, low-cost silicic acid was employed as the silicon source, allowing the efficient and cost-effective preparation of high-purity α-Si 3 N 4 powder. This work provides a promising strategy for the low-cost synthesis of high-performance silicon nitride powders and is of significance for promoting the application of advanced structural ceramics.