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 condition...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
Porous Ti3SiC2with high purity was synthesized using TiH2,Si and C powders with mole ratio of Ti to Si to C being3:1.2:2by reactive synthesis method.The corrosion behaviors of porous Ti3SiC2in nitric acid and aqua reg...Porous Ti3SiC2with high purity was synthesized using TiH2,Si and C powders with mole ratio of Ti to Si to C being3:1.2:2by reactive synthesis method.The corrosion behaviors of porous Ti3SiC2in nitric acid and aqua regia were investigated byimmersing test.Scanning electron microscope(SEM),X-ray diffractometer(XRD),energy dispersive spectrometer(EDS)and X-rayphotoelectron spectroscopy(XPS)were used to analyze the morphology,compositions and element contents of the samples beforeand after corrosion to determine the corrosion product and corrosion mechanism.The mass loss values of porous Ti3SiC2are26.9and132.5μg/cm2,respectively after immersing in nitric acid and aqua regia for600h.The results indicate that Ti3SiC2transforms toTi5Si3which has better corrosion resistance in nitric acid and aqua regia with mass loss values of9.34and7.06μg/cm2under thesame immersing time,respectively.The dramatic dissolution of porous Ti3SiC2in the acids is due to its special microstructure.展开更多
We investigate the properties of light emission from amorphous-Si:H/SiO2 and nc-Si/SiO2 multilayers (MLs). The size dependence of light emission is well exhibited when the a-Si:H sublayer thickness is thinner than...We investigate the properties of light emission from amorphous-Si:H/SiO2 and nc-Si/SiO2 multilayers (MLs). The size dependence of light emission is well exhibited when the a-Si:H sublayer thickness is thinner than 4 nm and the interface states are well passlvated by hydrogen. For the nc-Si/Si02 MLs, the oxygen modified interface states and nanocrystalline silicon play a predominant role in the properties of light emission. It is found that the light emission from nc-Si/SiO2 is in agreement with the model of interface state combining with quantum confinement when the size of nc-Si is smaller than 4 nm. The role of hydrogen and oxygen is discussed in detail.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).
摘要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.
基金Projects(51604305,51504296) supported by the National Natural Science Foundation of ChinaProject(2016M592445) supported by the China Postdoctoral Science FoundationProject(169715) supported by the Postdoctoral Science Foundation of Central South University,China
摘要Porous Ti3SiC2with high purity was synthesized using TiH2,Si and C powders with mole ratio of Ti to Si to C being3:1.2:2by reactive synthesis method.The corrosion behaviors of porous Ti3SiC2in nitric acid and aqua regia were investigated byimmersing test.Scanning electron microscope(SEM),X-ray diffractometer(XRD),energy dispersive spectrometer(EDS)and X-rayphotoelectron spectroscopy(XPS)were used to analyze the morphology,compositions and element contents of the samples beforeand after corrosion to determine the corrosion product and corrosion mechanism.The mass loss values of porous Ti3SiC2are26.9and132.5μg/cm2,respectively after immersing in nitric acid and aqua regia for600h.The results indicate that Ti3SiC2transforms toTi5Si3which has better corrosion resistance in nitric acid and aqua regia with mass loss values of9.34and7.06μg/cm2under thesame immersing time,respectively.The dramatic dissolution of porous Ti3SiC2in the acids is due to its special microstructure.
基金Supported by the National Natural Science Foundation of China under Grant Nos 60508009, 90301009, 60471021, 50472066, and 10574069, and the State Key Basic Research Programme of China under Grant No 2006CB932202.
摘要We investigate the properties of light emission from amorphous-Si:H/SiO2 and nc-Si/SiO2 multilayers (MLs). The size dependence of light emission is well exhibited when the a-Si:H sublayer thickness is thinner than 4 nm and the interface states are well passlvated by hydrogen. For the nc-Si/Si02 MLs, the oxygen modified interface states and nanocrystalline silicon play a predominant role in the properties of light emission. It is found that the light emission from nc-Si/SiO2 is in agreement with the model of interface state combining with quantum confinement when the size of nc-Si is smaller than 4 nm. The role of hydrogen and oxygen is discussed in detail.