A periclase?hercynite brick was prepared via reaction sintering at 1600℃for 6 h in air using magnesia and reaction-sintered hercynite as raw materials. The microstructure development of the periclase-hercynite brick...A periclase?hercynite brick was prepared via reaction sintering at 1600℃for 6 h in air using magnesia and reaction-sintered hercynite as raw materials. The microstructure development of the periclase-hercynite brick during sintering was investigated using X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy in combination with energy-dispersive X-ray spectroscopy. The results show that during sintering, Fe^2+, Fe^3+ and Al^3+ ions in hercynite crystals migrate and react with periclase to form(Mg1-xFex)(Fe2-yAly)O4 spinel with a high Fe/Al ratio. Meanwhile, Mg^2+ in periclase crystals migrates into hercynite crystals and occupies the oxygen tetrahedron vacancies. This Mg^2+ migration leads to the formation of(Mg1-uFeu)(Fe2-vAlv)O4 spinel with a lower Fe/Al ratio and results in Al3+ remaining in hercynite crystals. Cation diffusion between periclase and hercynite crystals promotes the sintering process and results in the formation of a microporous structure.展开更多
The state and formation mechanism of α-Si3N4 in Fe-Si3N4 prepared by flash combustion were investigated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results indicate t...The state and formation mechanism of α-Si3N4 in Fe-Si3N4 prepared by flash combustion were investigated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results indicate that α-SiaN4 crystals exist only in the Fe-Si3N4 dense areas. When FeSi75 particles react with N2, which generates substantial heat, a large number of Si solid particles evaporate. The product between Si gas and N2 is a mixture of α-Si3N4 and β-Si3N4. At the later stage of the flash combustion process, α-Si3N4 crystals dissolve and reprecipitate as α-Si3N4 and the β-Si3N4 crystals grow outward from the dense areas in the product pool. As the temperature decreases, the α-SiaN4 crystals cool before transforming into β-SiaN4 crystals in the dense areas of Fe-Si3N4. The phase composition of flash-combustion-synthesized Fe-SiaN4 is controllable through manipulation of the gas-phase reaction in the early stage and the α→β transformation in the later stage.展开更多
基金the National Nature Science Foundation of China (No. 51172021)the National Science-Technology Support Plan Projects of China (No. 2013BAF09B01)the Fundamental Research Funds for the Central Universities (No. FRF-SD-13-006A)
文摘A periclase?hercynite brick was prepared via reaction sintering at 1600℃for 6 h in air using magnesia and reaction-sintered hercynite as raw materials. The microstructure development of the periclase-hercynite brick during sintering was investigated using X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy in combination with energy-dispersive X-ray spectroscopy. The results show that during sintering, Fe^2+, Fe^3+ and Al^3+ ions in hercynite crystals migrate and react with periclase to form(Mg1-xFex)(Fe2-yAly)O4 spinel with a high Fe/Al ratio. Meanwhile, Mg^2+ in periclase crystals migrates into hercynite crystals and occupies the oxygen tetrahedron vacancies. This Mg^2+ migration leads to the formation of(Mg1-uFeu)(Fe2-vAlv)O4 spinel with a lower Fe/Al ratio and results in Al3+ remaining in hercynite crystals. Cation diffusion between periclase and hercynite crystals promotes the sintering process and results in the formation of a microporous structure.
基金financially supported by the National Natural Science Foundation of China (No. 51572019)the National Science-Technology Support Plan Projects of China (No. 2013BAF09B01)
文摘The state and formation mechanism of α-Si3N4 in Fe-Si3N4 prepared by flash combustion were investigated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results indicate that α-SiaN4 crystals exist only in the Fe-Si3N4 dense areas. When FeSi75 particles react with N2, which generates substantial heat, a large number of Si solid particles evaporate. The product between Si gas and N2 is a mixture of α-Si3N4 and β-Si3N4. At the later stage of the flash combustion process, α-Si3N4 crystals dissolve and reprecipitate as α-Si3N4 and the β-Si3N4 crystals grow outward from the dense areas in the product pool. As the temperature decreases, the α-SiaN4 crystals cool before transforming into β-SiaN4 crystals in the dense areas of Fe-Si3N4. The phase composition of flash-combustion-synthesized Fe-SiaN4 is controllable through manipulation of the gas-phase reaction in the early stage and the α→β transformation in the later stage.