Combustion Synthesis of Na α‐SiAlON Powders

ABSTRACT

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.