An optical transmission method was used in-situ to measure the rate of pyrolytic deposition from Mn_2(CO)_(10) induced by a CW CO_2 laser. The effect of the laser intensity, Mn_2(CO)_(10) vapor pressure and added gase...An optical transmission method was used in-situ to measure the rate of pyrolytic deposition from Mn_2(CO)_(10) induced by a CW CO_2 laser. The effect of the laser intensity, Mn_2(CO)_(10) vapor pressure and added gases (CO, O_2 and Ar) on the deposition rate has been examined.展开更多
Silicon-alloyed isotropic pyrolytic carbon(Si-IPyC)was prepared by steady-state fluidized bed chemical vapor deposition(SFBCVD).The effects of deposition temperature and propane concentration on the microstructure and...Silicon-alloyed isotropic pyrolytic carbon(Si-IPyC)was prepared by steady-state fluidized bed chemical vapor deposition(SFBCVD).The effects of deposition temperature and propane concentration on the microstructure and deposition process of Si-IPyC were investigated using X-ray diffraction(XRD),X-ray energy dispersive spectrometer(EDS)and scanning electron microscope(SEM).The results show that the Si-IPyC with different silicon content is composed of both spherical granular and laminar structures,and silicon element is uniformly dispersed in pyrolytic carbon in the form of β-SiC.The deposition temperature and propane concentration have a great influence on the microstructure of Si-IPyC,with the increase of deposition temperature or propane concentration,the laminar structure in Si-IPy C decreases gradually,spherical granular morphology becomes increasingly obvious and the density decreases with the deposition model changing from surficial growth mechanism to gaseous nucleation mechanism.For getting a faster average coating rate,deposition temperature and propane concentration should not be too high.展开更多
Pyrolytic carbon(PyC) coatings are deposited on the Nextel-440 fiber fabrics by chemical vapor deposition(CVD).The dielectric properties of the Nextel-440 fiber fabrics with PyC coatings(Nextel-440/PyC) are investigat...Pyrolytic carbon(PyC) coatings are deposited on the Nextel-440 fiber fabrics by chemical vapor deposition(CVD).The dielectric properties of the Nextel-440 fiber fabrics with PyC coatings(Nextel-440/PyC) are investigated in a temperature range from room temperature to 700℃ in X-band. Compared with the permittivity of the original Nextel-440 received,the complex permittivity of the Nextel-440/PyC(the real part εand the imaginary part ε), is significantly improved: εof the Nextel-440/PyC has a positive temperature coefficient, in contrast, εof the Nextel-440/PyC exhibits a negative temperature coefficient. Moreover, the reflection loss in units of d B is calculated. The results indicate that the microwave absorbing properties of the Nextel-440/PyC coatings is enhanced at 700℃ compared with that at lower temperatures.展开更多
A new method of fabricating C/C composite materials, namely electric heating CVD method, was used, which electrified the carbon fiber directly by using the conductivity of itself. Acetylene was used as the carbon sour...A new method of fabricating C/C composite materials, namely electric heating CVD method, was used, which electrified the carbon fiber directly by using the conductivity of itself. Acetylene was used as the carbon source with nitrogen as dilution gas, and the pyrolytic carbon started to deposit on the carbon fiber surface when the deposition temperature was reached. The morphology of pyrolytic carbon was characterized by SEM, and the surface properties of carbon fibers before and after CVD were characterized by Raman spectroscopy. The experimental results show that the electric heating method is a novel method to fabricate C/C composite materials, which can form a dense C/C composite material in a short time. The order degree and the average crystallite size of the carbon fiber surface were decreased after the experiment.展开更多
Carbon filaments with diameter from several to hundreds deposition of methane without catalyst. The morphology micrometers were synthesized by chemical vapor microstructure and mechanical properties of the carbon fila...Carbon filaments with diameter from several to hundreds deposition of methane without catalyst. The morphology micrometers were synthesized by chemical vapor microstructure and mechanical properties of the carbon filament were investigated by scanning electronic microscopy, optical microscopy, X-ray diffraction and mechanical testing. The results show that the carbon filament is inverted cone shape and grows up along the gas flow direction. The stem of it is formed of annular carbon layers arranged in a tree ring structure while the head is made up of concentrical layers. The tensile strength of the carbon filament is increased after graphitization for the restructuring and growing large of graphene. The growth mechanism of carbon filament was proposed according to the results of two series of experiments with different deposition time and intermittent deposition cycles.展开更多
文摘An optical transmission method was used in-situ to measure the rate of pyrolytic deposition from Mn_2(CO)_(10) induced by a CW CO_2 laser. The effect of the laser intensity, Mn_2(CO)_(10) vapor pressure and added gases (CO, O_2 and Ar) on the deposition rate has been examined.
文摘Silicon-alloyed isotropic pyrolytic carbon(Si-IPyC)was prepared by steady-state fluidized bed chemical vapor deposition(SFBCVD).The effects of deposition temperature and propane concentration on the microstructure and deposition process of Si-IPyC were investigated using X-ray diffraction(XRD),X-ray energy dispersive spectrometer(EDS)and scanning electron microscope(SEM).The results show that the Si-IPyC with different silicon content is composed of both spherical granular and laminar structures,and silicon element is uniformly dispersed in pyrolytic carbon in the form of β-SiC.The deposition temperature and propane concentration have a great influence on the microstructure of Si-IPyC,with the increase of deposition temperature or propane concentration,the laminar structure in Si-IPy C decreases gradually,spherical granular morphology becomes increasingly obvious and the density decreases with the deposition model changing from surficial growth mechanism to gaseous nucleation mechanism.For getting a faster average coating rate,deposition temperature and propane concentration should not be too high.
基金supported by the National Natural Science Foundation of China(Grant No.51072165)the Fund of the State Key Laboratory of Solidification Processing in Northwestern Polytechnical University,China(Grant Nos.KP201307 and SKLSP201313)
文摘Pyrolytic carbon(PyC) coatings are deposited on the Nextel-440 fiber fabrics by chemical vapor deposition(CVD).The dielectric properties of the Nextel-440 fiber fabrics with PyC coatings(Nextel-440/PyC) are investigated in a temperature range from room temperature to 700℃ in X-band. Compared with the permittivity of the original Nextel-440 received,the complex permittivity of the Nextel-440/PyC(the real part εand the imaginary part ε), is significantly improved: εof the Nextel-440/PyC has a positive temperature coefficient, in contrast, εof the Nextel-440/PyC exhibits a negative temperature coefficient. Moreover, the reflection loss in units of d B is calculated. The results indicate that the microwave absorbing properties of the Nextel-440/PyC coatings is enhanced at 700℃ compared with that at lower temperatures.
基金Funded by the National Natural Science Foundation of China(51165006)
文摘A new method of fabricating C/C composite materials, namely electric heating CVD method, was used, which electrified the carbon fiber directly by using the conductivity of itself. Acetylene was used as the carbon source with nitrogen as dilution gas, and the pyrolytic carbon started to deposit on the carbon fiber surface when the deposition temperature was reached. The morphology of pyrolytic carbon was characterized by SEM, and the surface properties of carbon fibers before and after CVD were characterized by Raman spectroscopy. The experimental results show that the electric heating method is a novel method to fabricate C/C composite materials, which can form a dense C/C composite material in a short time. The order degree and the average crystallite size of the carbon fiber surface were decreased after the experiment.
文摘Carbon filaments with diameter from several to hundreds deposition of methane without catalyst. The morphology micrometers were synthesized by chemical vapor microstructure and mechanical properties of the carbon filament were investigated by scanning electronic microscopy, optical microscopy, X-ray diffraction and mechanical testing. The results show that the carbon filament is inverted cone shape and grows up along the gas flow direction. The stem of it is formed of annular carbon layers arranged in a tree ring structure while the head is made up of concentrical layers. The tensile strength of the carbon filament is increased after graphitization for the restructuring and growing large of graphene. The growth mechanism of carbon filament was proposed according to the results of two series of experiments with different deposition time and intermittent deposition cycles.
