Fabrication of fine-grained Si₃N₄-Si₂N₂O dual-phase ceramic by in-situ reaction

Fine-grained Si₃N₄-Si₂N₂O dual-phase ceramic was fabricated with amorphous nano-sized silicon nitride powders and nano-sized Al₂O₃ and Y₂O₃ powders as additives by in-situ reaction 2Si₃N₄(s) + 1.5O₂(g) = 3Si₂N₂O(s) + N₂(g). XRD analysis confirms that content of Si₂N₂O phase is 25%. The microstructure sintered at 1600°C for 30 min of holding time indicates that grain size is about 210 nm and the aspect ratio of some grains reaches 1.5. The pore size decreases with increasing holding time, but density is improved and grain size grows up. The pores close up completely, average grain size is 280 nm and relative density reaches 99.1% when the holding time is 60 min.