The specimens were prepared by molding the mixture of silica fume （ w（ SiO2 ） =94. 5% ; average particle size ： 0. 08 μm ） and silicon nitride （ ≤ 0. 074 mm ） with a mass ratio of 1 ： 1, carbon embedded firi...The specimens were prepared by molding the mixture of silica fume （ w（ SiO2 ） =94. 5% ; average particle size ： 0. 08 μm ） and silicon nitride （ ≤ 0. 074 mm ） with a mass ratio of 1 ： 1, carbon embedded firing at 1 300 ℃, 1 450℃, 1 500℃, 1 550 ℃ and 1 600 ℃ for 3 h in air, and then water-cooling, respectively. The microstructure and phase composition of the specimens were analyzed. The results show that： （1） silica fume reacts obviously with Si3N4 forming Si2N2O above 1 550 ℃. The edges and corners of Si3N4 grains become smooth and the Si3 N4 grains distribute in the continuous cementation phase of Si2N2O forming the dense structure of Si2N2o packed Si3N4 ; （2） below 1 500 ℃ , the edges and corners of Si3N4 grains are clear, Si2N2O doesn＇t form, and only SiO2 crystallizes from silica fume which happens obviously at 1 300 ℃.展开更多
文摘The specimens were prepared by molding the mixture of silica fume （ w（ SiO2 ） =94. 5% ; average particle size ： 0. 08 μm ） and silicon nitride （ ≤ 0. 074 mm ） with a mass ratio of 1 ： 1, carbon embedded firing at 1 300 ℃, 1 450℃, 1 500℃, 1 550 ℃ and 1 600 ℃ for 3 h in air, and then water-cooling, respectively. The microstructure and phase composition of the specimens were analyzed. The results show that： （1） silica fume reacts obviously with Si3N4 forming Si2N2O above 1 550 ℃. The edges and corners of Si3N4 grains become smooth and the Si3 N4 grains distribute in the continuous cementation phase of Si2N2O forming the dense structure of Si2N2o packed Si3N4 ; （2） below 1 500 ℃ , the edges and corners of Si3N4 grains are clear, Si2N2O doesn＇t form, and only SiO2 crystallizes from silica fume which happens obviously at 1 300 ℃.
