Crystallization and phase changing of amorphous silicon nitride nanopowders by liquid phase sintering

The amorphous silicon nitride nanopowders were sintered by liquid phase sintering (LPS) with A1₂O₃ and Y₂O₃ nanopowders as additives. The crystallization and phase changing of sintered body were investigated. The sintered body consists of amorphous and crystalline phases (β-Si₃N₄ and Si₂N₂O) when the sintering temperature is 1500°C. The sintered body crystallizes completely at the sintering temperature of 1600°C. The volume percentage of Si₂N₂O is in maximum value when sintering temperature is 1650°C, which indicates the reaction of O₂ and Si₃N₄is completed. When the temperature is greater than 1700°C the volume percentage of Si₂N₂O reduces gradually and there is no SiO₂, which confirms the reaction, 2Si₃N₄ (s) + 1.5O₂ (g) = 3Si₂N₂O (s) + N₂ (g), is reversible. The crystallized microstructure at 1600°C indicates that grain size is in the range of 150-250 nm and only a few of them are less than 100 nm. The aspect ratios of some grains reach 1.5.