摘要:
The state and formation mechanism of α-Si
3N
4 in Fe–Si
3N
4 prepared by flash combustion were investigated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results indicate that α-Si
3N
4 crystals exist only in the Fe–Si
3N
4 dense areas. When FeSi75 particles react with N
2, which generates substantial heat, a large number of Si solid particles evaporate. The product between Si gas and N
2 is a mixture of α-Si
3N
4 and β-Si
3N
4. At the later stage of the flash combustion process, α-Si
3N
4 crystals dissolve and reprecipitate as β-Si
3N
4 and the β-Si
3N
4 crystals grow outward from the dense areas in the product pool. As the temperature decreases, the α-Si
3N
4 crystals cool before transforming into β-Si
3N
4 crystals in the dense areas of Fe–Si
3N
4. The phase composition of flash-combustion-synthesized Fe–Si
3N
4 is controllable through manipulation of the gas-phase reaction in the early stage and the α→β transformation in the later stage.