Combustion Synthesis of Na α-SiAlON Powders

α-SiAlON, as a solid solution of α-Si 3 N 4 , exhibits excellent mechanical properties, making it attractive for structural applications at both room and elevated temperatures. α-SiAlON ceramics stabilized by Li, Mg, Ca, Y, Mn, and rare-earth cations have been extensively investigated. In contrast, Na-stabilized α-SiAlON has received little attention, and the synthesis of single-phase Na α-SiAlON has not yet been reported. In this work, nearly single-phase Na α-SiAlON powders were prepared by combustion synthesis for the first time. The effects of starting composition and α-Si 3 N 4 diluent content on the phase composition and microstructure of the synthesized products were systematically investigated. Increasing the m and n values promoted the formation of α-SiAlON and suppressed the formation of β-SiAlON. The α-Si 3 N 4 diluent content strongly influenced the phase evolution and microstructure of the products. Nearly single-phase Na α-SiAlON powders were obtained at an appropriate α-Si 3 N 4 diluent content. The Na α-SiAlON powders mainly consisted of rod-like and equiaxed grains. Based on the experimental results, a dual-pathway formation mechanism was proposed, involving the direct precipitation of α-SiAlON crystal from a supersaturated Na–Si–Al–O–N liquid phase and heterogeneous nucleation on undissolved α-Si 3 N 4 particles. This work establishes combustion synthesis as an effective route for the preparation of high-purity Na α-SiAlON powders and advances the understanding of their formation mechanisms.