Catalytic steam reforming of condensable vapors, i.e. bio-oil, derived from pyrolysis of biomass is an important process for hydrogen production, which is expected to form renewable and clean energy. The generation of...Catalytic steam reforming of condensable vapors, i.e. bio-oil, derived from pyrolysis of biomass is an important process for hydrogen production, which is expected to form renewable and clean energy. The generation of hydrogen from bio-oil was investigated from 250 to 750 ℃ by a MgO mixed C12A7-O^-(C12A7-MgO) catalyst in a fixed-bed micro-reactor. The hydrogen yield on C12A7-MgO was about 44% at 750 ℃. It is found that both the catalytic activity and catalysis life are improved by doping MgO. The XRD results show that the C12A7 structure of the positively charged lattice framework remains in the C12A7-MgO catalyst.展开更多
通过高温固相法制备不同Yb^(3+)+和Eu 3+掺杂浓度的C12A7∶Yb^(3+)/Eu^(3+)多晶粉.利用X射线衍射、上转换荧光光谱和CIE色谱图研究了C12A7∶Yb^(3+)/Eu^(3+)多晶粉的晶体结构和荧光性能,结果表明:在波长980 nm激光激发下,C12A7∶Yb^(3+)...通过高温固相法制备不同Yb^(3+)+和Eu 3+掺杂浓度的C12A7∶Yb^(3+)/Eu^(3+)多晶粉.利用X射线衍射、上转换荧光光谱和CIE色谱图研究了C12A7∶Yb^(3+)/Eu^(3+)多晶粉的晶体结构和荧光性能,结果表明:在波长980 nm激光激发下,C12A7∶Yb^(3+)/Eu^(3+)多晶粉分别于550 nm和663 nm处发射出上转换绿光和红光,它们分别来源于Eu 3+离子的5 D 0→7 F 0和5 D 0→7 F 3跃迁.结合上转换布局机制,分析了不同Yb^(3+)+和Eu 3+掺杂浓度对C12A7∶Yb^(3+)/Eu^(3+)多晶粉光学性能的影响.分析CIE色度光谱,通过改变Yb^(3+)+和Eu 3+离子掺杂浓度可以使C12A7∶Yb^(3+)/Eu^(3+)多晶粉的发光在黄绿光区域到绿色区域间调节.展开更多
Hydrogen production by catalytic steam reforming of the bio-oil, naphtha, and CH4 was investigated over a novel metal-doped catalyst of （Ca24Al28O64）^4＋·4O^-/Mg （C12A7-Mg）. The catalytic steam reforming was ...Hydrogen production by catalytic steam reforming of the bio-oil, naphtha, and CH4 was investigated over a novel metal-doped catalyst of （Ca24Al28O64）^4＋·4O^-/Mg （C12A7-Mg）. The catalytic steam reforming was investigated from 250 to 850℃ in the fixed-bed continuous flow reactor. For the reforming of bio-oil, the yield of hydrogen of 80% was obtained at 750℃, and the maximum carbon conversion is nearly close to 95% under the optimum steam reforming condition. For the reforming of naphtha and CH4, the hydrogen yield and carbon conversion are lower than that of bio-oil at the same temperature. The characteristics of catalyst were also investigated by XPS. The catalyst deactivation was mainly caused by the deposition of carbon in the catalytic steam reforming process.展开更多
Emitter overheating is by far the greatest problem limiting the performance of novel C12A7 hollow cathodes. To explore the failure operating point and degradation mechanism of the C12A7 hollow cathode, microscopic ana...Emitter overheating is by far the greatest problem limiting the performance of novel C12A7 hollow cathodes. To explore the failure operating point and degradation mechanism of the C12A7 hollow cathode, microscopic analyses of a degraded electride emitter after 10 h of thermal electron emission are presented in this paper. The morphology and composition variation of overheated electride emitters by scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction indicate the melting and decomposition of electride of the surface layer. The monitored temperature of the electride emitter during the C12A7 hollow cathode operation shows that to avoid overheating the electride emitter, the average current density allowed should be about 64 m A mm^(-2) for the C12A7 hollow cathode in its current configuration. Experimental results of the heaterless C12A7 hollow cathode demonstrate that xenon(Xe) ion bombardment can remove the insulating layer and restore the thermionic emission capability for less degraded emitters. Based on experimental results and microscopic characterization, the depletion and degradation mechanisms of electride emitters during the hollow cathode operation are discussed.展开更多
To fully realize the superiority of the iodine electric propulsion system in streamlining the size and reducing the operating costs, iodine hollow cathode technology must be developed. Considering the corrosiveness of...To fully realize the superiority of the iodine electric propulsion system in streamlining the size and reducing the operating costs, iodine hollow cathode technology must be developed. Considering the corrosiveness of iodine and the possible impurity of the working propellant, the C12A7 hollow cathode with promising chemical ability was developed and tested. The C12A7 hollow cathode with a nominal current of 1–4 A was successfully ignited with iodine from the reservoir outside the vacuum chamber. It was operated at 1 A of anode current with a 1.2 mg s^(-1) iodine mass flow rate.Despite involuntary extinguishment, the C12A7 hollow cathode could be restarted repeatedly with a single operation time of up to 12 min and a total duration of 30 min. The unexpected fluctuation of iodine flow may be the reason for the short operation time. Experimental results and microscopical observation of the electride emitter show the compatibility of the iodine and electride emitter. For the development and demonstration of future single-iodine electric propulsion of Hall thrusters, the iodine storage and supply system with precise control and regulation may be the critical technology.展开更多
Ca_(12)Al_(14)O_(33)(C12A7)and Y_(0.02)Ca_(11.98)Al_(14)O_(33)(Y-C12A7)single crystals were grown by using the traveling-solvent floating zone(TSFZ)method.The temperature was increased to avoid the bubbles and cracks ...Ca_(12)Al_(14)O_(33)(C12A7)and Y_(0.02)Ca_(11.98)Al_(14)O_(33)(Y-C12A7)single crystals were grown by using the traveling-solvent floating zone(TSFZ)method.The temperature was increased to avoid the bubbles and cracks which may be formed during the preparation of the ingot material.We have started with the flux higher than the normal to avoid the bubbles and make good treatment for the solid-liquid interface.The structures of both Ca_(12)Al_(14)O_(33)(C12A7)and Y_(0.02)Ca_(11.98)Al_(14)O_(33)(Y-C12A7)were studied by using x-ray diffraction(XRD).Optical properties for C12A7 and Y-C12A7 single crystals have been studied in order to determine the optical parameters such as optical energy gap(Eg),refractive index n,oscillating energy(Eo),dispersion energy(Ed),volume energy loss function(VELF),and surface energy loss function(SELF).Finally,a new result for these samples is that the third-order nonlinear optical susceptibility(χ(3))was determined.The results have been discussed with effect of Y-doping on the C12A7 single crystals for optical and industrial applications.展开更多
Rare earth doped 12CaO·7Al_(2)O_(3)(C12A7)glass-ceramics are one of attractive photonic materials due to their high transparency,high luminescent efficiency and eco-friendly nature.A series of C12A7 glasses with ...Rare earth doped 12CaO·7Al_(2)O_(3)(C12A7)glass-ceramics are one of attractive photonic materials due to their high transparency,high luminescent efficiency and eco-friendly nature.A series of C12A7 glasses with different Tb^(3+)doping concentrations was prepared by aerodynamic levitation method.The C12A7:Tb glass-ceramics were obtained via in-situ growth from the glasses with the identical chemical composition at 800℃.The microstructure observation demonstrates that the elemental distributions of Ca and Al are homogeneous in the glass-ceramics and the grain size of C12A7 is 4-70 nm.The in-line transmittance of glass-ceramics reaches as high as 82%at 1500 nm.The emission spectra of the C12A7:Tb glass-ceramics present characteristic Tb^(3+)emission peaks at 486 nm(^(5)D_(4)→^(7)F_6),541 nm(^(5)D_(4)→^(7)F_(5)),585 nm(^(5)D_(4)→^(7)F_(4))and 621 nm(^(5)D_(4)→^(7)F_(3)).The photolumine scence lifetime of C12A7:0.3%Tb glass-ceramic is 1.9 ms.Compared with the emission intensity of the glasses,that of the glass-ceramics increases due to the reducing in concentration of oxygen vacancy associated with network forming(NWF)cations.The highly transparent C12A7:Tb glass-ceramics may be a promising candidate for green light source in solid state lighting.展开更多
文摘Catalytic steam reforming of condensable vapors, i.e. bio-oil, derived from pyrolysis of biomass is an important process for hydrogen production, which is expected to form renewable and clean energy. The generation of hydrogen from bio-oil was investigated from 250 to 750 ℃ by a MgO mixed C12A7-O^-(C12A7-MgO) catalyst in a fixed-bed micro-reactor. The hydrogen yield on C12A7-MgO was about 44% at 750 ℃. It is found that both the catalytic activity and catalysis life are improved by doping MgO. The XRD results show that the C12A7 structure of the positively charged lattice framework remains in the C12A7-MgO catalyst.
基金supported by the National Natural Science Foundation of China (50772107)National Key Basic Research Program of China (973)(2007CB210206)National High-Tech Research and Development Program of China (863) (2009AA05Z435)~~
基金The project was supported by the National Natural Science Foundation of China (50772107)National Key Basic Research Program of China (973)(2007CB210206)National High-Tech Research and Development Program of China (863) (2009AA05Z435)~~
基金supported by the National Natural Science Foundation of China(50772107)National Key Basic Research Program of China(973)(2007CB210206)National High-Tech Research and Development Program of China(863)(2009AA05Z435)~~
文摘通过高温固相法制备不同Yb^(3+)+和Eu 3+掺杂浓度的C12A7∶Yb^(3+)/Eu^(3+)多晶粉.利用X射线衍射、上转换荧光光谱和CIE色谱图研究了C12A7∶Yb^(3+)/Eu^(3+)多晶粉的晶体结构和荧光性能,结果表明:在波长980 nm激光激发下,C12A7∶Yb^(3+)/Eu^(3+)多晶粉分别于550 nm和663 nm处发射出上转换绿光和红光,它们分别来源于Eu 3+离子的5 D 0→7 F 0和5 D 0→7 F 3跃迁.结合上转换布局机制,分析了不同Yb^(3+)+和Eu 3+掺杂浓度对C12A7∶Yb^(3+)/Eu^(3+)多晶粉光学性能的影响.分析CIE色度光谱,通过改变Yb^(3+)+和Eu 3+离子掺杂浓度可以使C12A7∶Yb^(3+)/Eu^(3+)多晶粉的发光在黄绿光区域到绿色区域间调节.
文摘Hydrogen production by catalytic steam reforming of the bio-oil, naphtha, and CH4 was investigated over a novel metal-doped catalyst of （Ca24Al28O64）^4＋·4O^-/Mg （C12A7-Mg）. The catalytic steam reforming was investigated from 250 to 850℃ in the fixed-bed continuous flow reactor. For the reforming of bio-oil, the yield of hydrogen of 80% was obtained at 750℃, and the maximum carbon conversion is nearly close to 95% under the optimum steam reforming condition. For the reforming of naphtha and CH4, the hydrogen yield and carbon conversion are lower than that of bio-oil at the same temperature. The characteristics of catalyst were also investigated by XPS. The catalyst deactivation was mainly caused by the deposition of carbon in the catalytic steam reforming process.
基金supported by the Joint Fund for Equipment Pre-research and Aerospace Science and Technology (No. 6141B061203)。
文摘Emitter overheating is by far the greatest problem limiting the performance of novel C12A7 hollow cathodes. To explore the failure operating point and degradation mechanism of the C12A7 hollow cathode, microscopic analyses of a degraded electride emitter after 10 h of thermal electron emission are presented in this paper. The morphology and composition variation of overheated electride emitters by scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction indicate the melting and decomposition of electride of the surface layer. The monitored temperature of the electride emitter during the C12A7 hollow cathode operation shows that to avoid overheating the electride emitter, the average current density allowed should be about 64 m A mm^(-2) for the C12A7 hollow cathode in its current configuration. Experimental results of the heaterless C12A7 hollow cathode demonstrate that xenon(Xe) ion bombardment can remove the insulating layer and restore the thermionic emission capability for less degraded emitters. Based on experimental results and microscopic characterization, the depletion and degradation mechanisms of electride emitters during the hollow cathode operation are discussed.
基金supported by the Joint Fund for Equipment Preresearch and Aerospace Science and Technology (No. 6141B061203)。
文摘To fully realize the superiority of the iodine electric propulsion system in streamlining the size and reducing the operating costs, iodine hollow cathode technology must be developed. Considering the corrosiveness of iodine and the possible impurity of the working propellant, the C12A7 hollow cathode with promising chemical ability was developed and tested. The C12A7 hollow cathode with a nominal current of 1–4 A was successfully ignited with iodine from the reservoir outside the vacuum chamber. It was operated at 1 A of anode current with a 1.2 mg s^(-1) iodine mass flow rate.Despite involuntary extinguishment, the C12A7 hollow cathode could be restarted repeatedly with a single operation time of up to 12 min and a total duration of 30 min. The unexpected fluctuation of iodine flow may be the reason for the short operation time. Experimental results and microscopical observation of the electride emitter show the compatibility of the iodine and electride emitter. For the development and demonstration of future single-iodine electric propulsion of Hall thrusters, the iodine storage and supply system with precise control and regulation may be the critical technology.
文摘Ca_(12)Al_(14)O_(33)(C12A7)and Y_(0.02)Ca_(11.98)Al_(14)O_(33)(Y-C12A7)single crystals were grown by using the traveling-solvent floating zone(TSFZ)method.The temperature was increased to avoid the bubbles and cracks which may be formed during the preparation of the ingot material.We have started with the flux higher than the normal to avoid the bubbles and make good treatment for the solid-liquid interface.The structures of both Ca_(12)Al_(14)O_(33)(C12A7)and Y_(0.02)Ca_(11.98)Al_(14)O_(33)(Y-C12A7)were studied by using x-ray diffraction(XRD).Optical properties for C12A7 and Y-C12A7 single crystals have been studied in order to determine the optical parameters such as optical energy gap(Eg),refractive index n,oscillating energy(Eo),dispersion energy(Ed),volume energy loss function(VELF),and surface energy loss function(SELF).Finally,a new result for these samples is that the third-order nonlinear optical susceptibility(χ(3))was determined.The results have been discussed with effect of Y-doping on the C12A7 single crystals for optical and industrial applications.
基金Project supported by the National Natural Science Foundation of China (51802186,U1732128)。
文摘Rare earth doped 12CaO·7Al_(2)O_(3)(C12A7)glass-ceramics are one of attractive photonic materials due to their high transparency,high luminescent efficiency and eco-friendly nature.A series of C12A7 glasses with different Tb^(3+)doping concentrations was prepared by aerodynamic levitation method.The C12A7:Tb glass-ceramics were obtained via in-situ growth from the glasses with the identical chemical composition at 800℃.The microstructure observation demonstrates that the elemental distributions of Ca and Al are homogeneous in the glass-ceramics and the grain size of C12A7 is 4-70 nm.The in-line transmittance of glass-ceramics reaches as high as 82%at 1500 nm.The emission spectra of the C12A7:Tb glass-ceramics present characteristic Tb^(3+)emission peaks at 486 nm(^(5)D_(4)→^(7)F_6),541 nm(^(5)D_(4)→^(7)F_(5)),585 nm(^(5)D_(4)→^(7)F_(4))and 621 nm(^(5)D_(4)→^(7)F_(3)).The photolumine scence lifetime of C12A7:0.3%Tb glass-ceramic is 1.9 ms.Compared with the emission intensity of the glasses,that of the glass-ceramics increases due to the reducing in concentration of oxygen vacancy associated with network forming(NWF)cations.The highly transparent C12A7:Tb glass-ceramics may be a promising candidate for green light source in solid state lighting.
