A silicon dioxide fiber-reinforced silicon nitride matrix （SiOJSi3N4） composite used for radomes was prepared by chemical vapor infiltration （CVI） process using the SiCl4-NH3-H2 system. The effects of the process ...A silicon dioxide fiber-reinforced silicon nitride matrix （SiOJSi3N4） composite used for radomes was prepared by chemical vapor infiltration （CVI） process using the SiCl4-NH3-H2 system. The effects of the process conditions, including infiltration temperature, infiltration time, and gas flux were investigated. The energy dispersion spectra （EDS） result showed that the main elements of this composite contained Si, N, and O. The X-ray diffraction （XRD） results indicated that phases of the composite before and after treatment at 1350℃ were all amorphous. A little fiber pull-out was observed on the cross section of the composite by scan electron microscope （SEM）. As a result, the composite exhibited good thermal stability, but an appropriate interface was necessary between the fiber and the matrix.展开更多
Total dose effects and single event effects on radiation-hardened power vertical double-diffusion metal oxide semiconductor（VDMOS） devices with composite SiO2-Si3N4 film gates are investigated.The relationships amon...Total dose effects and single event effects on radiation-hardened power vertical double-diffusion metal oxide semiconductor（VDMOS） devices with composite SiO2-Si3N4 film gates are investigated.The relationships among the important electrical parameters of the samples with different thickness SiO2-Si3N4 films,such as threshold voltage,breakdown voltage,and on-state resistance in accumulated dose,are discussed.The total dose experiment results show that the breakdown voltage and the on-state resistance barely change with the accumulated dose.However,the relationships between the threshold voltages of the samples and the accumulated dose are more complex,and not only positively drift,but also negatively drift.At the end of the total dose experiment,we select the group of samples which have the smaller threshold voltage shift to carry out the single event effect studies.We find that the samples with appropriate thickness ratio SiO2-Si3N4 films have a good radiation-hardening ability.This method may be useful in solving both the SEGR and the total dose problems with the composite SiO2-Si3N4 films.展开更多
Using low-cost precipitated silica(SiO2) as the carrier,a ternary SiO2-TiO2/g-C3N4 composite photocatalyst was prepared via the sol-gel method associated with a wet-grinding process.The asprepared composite exhibits p...Using low-cost precipitated silica(SiO2) as the carrier,a ternary SiO2-TiO2/g-C3N4 composite photocatalyst was prepared via the sol-gel method associated with a wet-grinding process.The asprepared composite exhibits photocatalytic hydrogen production and pollutant degradation performance under solar-like irradiation.The effect of SiO2 carrier on the properties of the heterostructure between TiO2 and g-C3N4(CN) was systematically studied.It is found that SiO2 has important effects on promoting the interaction between TiO2 and CN.The particle size of TiO2 and CN was obviously reduced during the calcination process due to the effects of SiO2.Especially,the TiO2 particles exhibit monodispersed state with particle size below 10 nm(quantum dots),resulting in the improvement of the contact area and the interaction betweenTiO2 and CN,and leading to the formation of efficient TiO2/CN Zscheme heterostructure in SiO2-TiO2/CN.Besides,the introduction of SiO2 can increase the specific surface area and light absorption of SiO2-TiO2/CN,further promoting the photocatalytic reaction.As expected,the optimum SiO2-TiO2/CN composite exhibits 12.3,3.1 and 2.9 times higher photocatalytic hydrogen production rate than that of SiO2-TiO2,CN and TiO2/CN under solar-like irradiation,while the photocatalytic active component in SiO2-TiO2/CN is only about 60 wt%.Moreover,the rhodamine B degradation rate of SiO2-TiO2/CN is also higher than that of SiO2-TiO2,CN and TiO2/CN.展开更多
Si3N4-Si2N2O composites were fabricated with amorphous nano-sized silicon nitride powders by the liquid phase sintering （ LPS ）. The Si2 N2O phase was generated by an in-situ reaction 2 Si3 N4 （ s ） ＋ 1.5 02 （ g...Si3N4-Si2N2O composites were fabricated with amorphous nano-sized silicon nitride powders by the liquid phase sintering （ LPS ）. The Si2 N2O phase was generated by an in-situ reaction 2 Si3 N4 （ s ） ＋ 1.5 02 （ g ） = 3 Si2 N2O （ s ） ＋ N2 （ g ） . The content of Si2 N2 O phase up to 60% in the volume was obtained at a sintering temperature of 1 650℃ and reduced when the sintering temperature increased or decreased, indicating the reaction is reversible. The mass loss, relative density and average grain size increased with increasing the sintering temperature. The average grain size was less than 500 nm when the sintering temperature was below 1 700 ℃. The sintering procedure contains a complex crystallization and a phase transition ： amorphous silicon nitride→equiaxial α- Si3 N4→ equiaxial β- Si3 N4→ rod- like Si2 N2O→ needle- like β- Si3N4 . Small round-shaped β→ Si3 N4 particles were entrapped in the Si2 N2O grains and a high density of staking faults was situated in the middle of Si2 N2O grains at a sintering temperature of 1 650 ℃. The toughness inereased from 3.5 MPa·m^1/2 at 1 600 ℃ to 7.2 MPa· m^1/2 at 1 800 ℃ . The hardness was as high as 21.5 GPa （Vickers） at 1 600 ℃ .展开更多
Two-dimension （2D） fused-silica fiber reinforced porous silicon nitride matrix composites were fabricated using slurry impregnation and cyclic infiltration with colloidal silica sol. The microstructure and fracture ...Two-dimension （2D） fused-silica fiber reinforced porous silicon nitride matrix composites were fabricated using slurry impregnation and cyclic infiltration with colloidal silica sol. The microstructure and fracture surface were characterized by SEM, the mechanical behavior was investigated by three-point bending test, and the dielectric constant was also measured by impedance analysis. The microstructure showed that the fiber and the matrix had a physical bonding, forming a clearance interface. The mechanical behavior suggested that the porous matrix acted as crack deflection, and the fracture surface had a lot of fiber pull-out. However, the interlaminar shear strength was not so good. The dielectric constant of the composites at room temperature was about 2.8-3.1. The relatively low dielectric constant and non-catastrophic failure indicated the potential application in the radome materials field. 2008 University of Science and Technology Beijing. All rights reserved.展开更多
The Si3N4-based nanocomposites reinforced with micro ZrO2 and nano SiC particles were prepared by polarity dispersant and vacuum-sintering technology. The mechanical properties and microstructures were tested. The res...The Si3N4-based nanocomposites reinforced with micro ZrO2 and nano SiC particles were prepared by polarity dispersant and vacuum-sintering technology. The mechanical properties and microstructures were tested. The results show that appropriate amount of micro ZrO2 and nano SiC particles, not only enhance the microhardness, but also block the excessively growth of β-Si3N4 and β-Si3N4 grains, so they finally all grow up to uniformly pole-shaped grains. This process is similar to the strengthening and toughening mechanism of grain whiskers and makes a remarkable improvement on the toughness. Compared with Si3N4 ceramic, the toughness of Si3N4/SiC/ZrO2 nanocomposites are increased from 6.2 MPa·m1/2 to 11 MPa·m1/2.展开更多
Liquid bonding of Si 3N 4 ceramic composite was carried out with RE 2O 3 Al 2O 3 SiO 2 glass solders. The effect of bonding conditions and interfacial reaction on the joint strength was studied. The joint st...Liquid bonding of Si 3N 4 ceramic composite was carried out with RE 2O 3 Al 2O 3 SiO 2 glass solders. The effect of bonding conditions and interfacial reaction on the joint strength was studied. The joint strength under different bonding conditions was measured by four point bending tests. The interfacial microstructures were observed and analyzed by SEM, EPMA and XRD. It is shown that the liquid glass solders react with Si 3N 4 at interface, forming the Si 3N 4/Si 2N 2O/Y(La) sialon glass/Y(La) sialon glass gradient interface. With the increase of bonding temperature and holding time, the joint strength first increased reaching a peak, and then decreased. According to microanalyses, LaYO 3 precipitated from joint glass improves joint strength at room and high temperature.展开更多
基金This study was financially supported by the Key Foundation of National Science in China (No. 90405015), the National Elitist Youth Foundation of China (No. 50425208the Doctorate Foundation of Northwestern Polytechnical University (CX200505).
文摘A silicon dioxide fiber-reinforced silicon nitride matrix （SiOJSi3N4） composite used for radomes was prepared by chemical vapor infiltration （CVI） process using the SiCl4-NH3-H2 system. The effects of the process conditions, including infiltration temperature, infiltration time, and gas flux were investigated. The energy dispersion spectra （EDS） result showed that the main elements of this composite contained Si, N, and O. The X-ray diffraction （XRD） results indicated that phases of the composite before and after treatment at 1350℃ were all amorphous. A little fiber pull-out was observed on the cross section of the composite by scan electron microscope （SEM）. As a result, the composite exhibited good thermal stability, but an appropriate interface was necessary between the fiber and the matrix.
文摘Total dose effects and single event effects on radiation-hardened power vertical double-diffusion metal oxide semiconductor（VDMOS） devices with composite SiO2-Si3N4 film gates are investigated.The relationships among the important electrical parameters of the samples with different thickness SiO2-Si3N4 films,such as threshold voltage,breakdown voltage,and on-state resistance in accumulated dose,are discussed.The total dose experiment results show that the breakdown voltage and the on-state resistance barely change with the accumulated dose.However,the relationships between the threshold voltages of the samples and the accumulated dose are more complex,and not only positively drift,but also negatively drift.At the end of the total dose experiment,we select the group of samples which have the smaller threshold voltage shift to carry out the single event effect studies.We find that the samples with appropriate thickness ratio SiO2-Si3N4 films have a good radiation-hardening ability.This method may be useful in solving both the SEGR and the total dose problems with the composite SiO2-Si3N4 films.
基金partly supported by the National Natural Science Foundation of China(Nos.21577132,21978276)。
文摘Using low-cost precipitated silica(SiO2) as the carrier,a ternary SiO2-TiO2/g-C3N4 composite photocatalyst was prepared via the sol-gel method associated with a wet-grinding process.The asprepared composite exhibits photocatalytic hydrogen production and pollutant degradation performance under solar-like irradiation.The effect of SiO2 carrier on the properties of the heterostructure between TiO2 and g-C3N4(CN) was systematically studied.It is found that SiO2 has important effects on promoting the interaction between TiO2 and CN.The particle size of TiO2 and CN was obviously reduced during the calcination process due to the effects of SiO2.Especially,the TiO2 particles exhibit monodispersed state with particle size below 10 nm(quantum dots),resulting in the improvement of the contact area and the interaction betweenTiO2 and CN,and leading to the formation of efficient TiO2/CN Zscheme heterostructure in SiO2-TiO2/CN.Besides,the introduction of SiO2 can increase the specific surface area and light absorption of SiO2-TiO2/CN,further promoting the photocatalytic reaction.As expected,the optimum SiO2-TiO2/CN composite exhibits 12.3,3.1 and 2.9 times higher photocatalytic hydrogen production rate than that of SiO2-TiO2,CN and TiO2/CN under solar-like irradiation,while the photocatalytic active component in SiO2-TiO2/CN is only about 60 wt%.Moreover,the rhodamine B degradation rate of SiO2-TiO2/CN is also higher than that of SiO2-TiO2,CN and TiO2/CN.
基金Funded by the National Science Foundation of China ( No.50375037)
文摘Si3N4-Si2N2O composites were fabricated with amorphous nano-sized silicon nitride powders by the liquid phase sintering （ LPS ）. The Si2 N2O phase was generated by an in-situ reaction 2 Si3 N4 （ s ） ＋ 1.5 02 （ g ） = 3 Si2 N2O （ s ） ＋ N2 （ g ） . The content of Si2 N2 O phase up to 60% in the volume was obtained at a sintering temperature of 1 650℃ and reduced when the sintering temperature increased or decreased, indicating the reaction is reversible. The mass loss, relative density and average grain size increased with increasing the sintering temperature. The average grain size was less than 500 nm when the sintering temperature was below 1 700 ℃. The sintering procedure contains a complex crystallization and a phase transition ： amorphous silicon nitride→equiaxial α- Si3 N4→ equiaxial β- Si3 N4→ rod- like Si2 N2O→ needle- like β- Si3N4 . Small round-shaped β→ Si3 N4 particles were entrapped in the Si2 N2O grains and a high density of staking faults was situated in the middle of Si2 N2O grains at a sintering temperature of 1 650 ℃. The toughness inereased from 3.5 MPa·m^1/2 at 1 600 ℃ to 7.2 MPa· m^1/2 at 1 800 ℃ . The hardness was as high as 21.5 GPa （Vickers） at 1 600 ℃ .
基金the National Natural Science Foundation of China(No.90405015)the National Young Elitist Foundation(No.50425208).
文摘Two-dimension （2D） fused-silica fiber reinforced porous silicon nitride matrix composites were fabricated using slurry impregnation and cyclic infiltration with colloidal silica sol. The microstructure and fracture surface were characterized by SEM, the mechanical behavior was investigated by three-point bending test, and the dielectric constant was also measured by impedance analysis. The microstructure showed that the fiber and the matrix had a physical bonding, forming a clearance interface. The mechanical behavior suggested that the porous matrix acted as crack deflection, and the fracture surface had a lot of fiber pull-out. However, the interlaminar shear strength was not so good. The dielectric constant of the composites at room temperature was about 2.8-3.1. The relatively low dielectric constant and non-catastrophic failure indicated the potential application in the radome materials field. 2008 University of Science and Technology Beijing. All rights reserved.
文摘The Si3N4-based nanocomposites reinforced with micro ZrO2 and nano SiC particles were prepared by polarity dispersant and vacuum-sintering technology. The mechanical properties and microstructures were tested. The results show that appropriate amount of micro ZrO2 and nano SiC particles, not only enhance the microhardness, but also block the excessively growth of β-Si3N4 and β-Si3N4 grains, so they finally all grow up to uniformly pole-shaped grains. This process is similar to the strengthening and toughening mechanism of grain whiskers and makes a remarkable improvement on the toughness. Compared with Si3N4 ceramic, the toughness of Si3N4/SiC/ZrO2 nanocomposites are increased from 6.2 MPa·m1/2 to 11 MPa·m1/2.
文摘Liquid bonding of Si 3N 4 ceramic composite was carried out with RE 2O 3 Al 2O 3 SiO 2 glass solders. The effect of bonding conditions and interfacial reaction on the joint strength was studied. The joint strength under different bonding conditions was measured by four point bending tests. The interfacial microstructures were observed and analyzed by SEM, EPMA and XRD. It is shown that the liquid glass solders react with Si 3N 4 at interface, forming the Si 3N 4/Si 2N 2O/Y(La) sialon glass/Y(La) sialon glass gradient interface. With the increase of bonding temperature and holding time, the joint strength first increased reaching a peak, and then decreased. According to microanalyses, LaYO 3 precipitated from joint glass improves joint strength at room and high temperature.
