Abstract
The synthesis of 15R-SiAlON in FexSiy-Si3N4-Al2O3 composites was carried out at 1800 °C in flowing nitrogen. The role of the vapour phases from ferrosilicon nitride (FexSiy-Si3N4) and Al2O3 was studied by phase evolution, microstructure, and thermodynamic analyses. The results show that the formation of 15R-SiAlON is highly related to SiO(g), Si(g), Al2O(g) and Al(g) from FexSiy-Si3N4-Al2O3 composites. At 1800 °C in flowing nitrogen, SiO(g) and Si(g) are generated from ferrosilicon nitride. Al2O(g) and Al(g) are released from Al2O3, and their pressures depend on that of oxygen. The increase of ferrosilicon nitride promotes the generation of vapour phases. The diffusion of Al2O(g) and Al(g) into Si3N4, and of SiO(g) and Si(g) into Al2O3 particles enable the growth of 15R-SiAlON flakes based on both the Si3N4 and Al2O3 substrates by solid-gas reaction. In the presence of the Fe-Si liquid, 15R-SiAlON whiskers with Fe-Si sphere on the top are generated by the liquid-solid-gas mechanism. The reactions between Al2O(g)/Al(g) and SiO(g)/Si(g) in nitrogen generate large amounts of 15R-SiAlON whiskers by the gas-gas mechanism.
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