By using metal nitrates as starting materials and citric acid as a complexing agent, Y2Si207：Re3＋ （Re=Eu, Tb） phosphors were prepared by a sol-gel method. X-ray diffraction was employed to characterize the resulti...By using metal nitrates as starting materials and citric acid as a complexing agent, Y2Si207：Re3＋ （Re=Eu, Tb） phosphors were prepared by a sol-gel method. X-ray diffraction was employed to characterize the resulting samples. The results of XRD indicate that the α-Y2Si2O7 nanocrystal with size of 27 nm is obtained at 1000 ℃ and the doping ion content does not influence the structure. The excitation spectra in the UV and VUV ranges and the emission spectra of Re^3＋ doped samples were measured. The excitation spectra in the VUV range is due to absorption of host, that in the UV range is ascribed to absorption transitions from 4f to 5d state of the Tb^3＋ and the charge transfer in the En^3＋-O^2- bond. The spectral energy distribution of the Tb^3＋ emission depends strongly on the Tb3＋ concentration. The dependence of photolumineseenee intensity on Re^3＋ concentration is also discussed in detail. The fluorescent decay curves at room temperature were measured and analyzed.展开更多
A process was proposed based on the combination of chemical and physical activation for the production of activated carbons used as the electrode material for electric double layer capacitor (EDLC). By material charac...A process was proposed based on the combination of chemical and physical activation for the production of activated carbons used as the electrode material for electric double layer capacitor (EDLC). By material characterization and electrochemical methods, the influences of the activitation process on the specific surface area, pore structure and electrochemical properties of the activated carbons were investigated. The results show that specific surface area, the mesopore volume, and the specific capacitance increase with the increase of the mass ratio of KOH to char (m(KOH)/m(char)) and the activation time, respectively. When m(KOH)/m(char) is 4.0, the specific surface area and the mesopore volume reach the maximum values, i.e. 1 960 m2/g and 0.308 4 cm3/g, and the specific capacitance is 120.7 F/g synchronously. Compared with the chemical activation, the activated carbons prepared by chemical-physical activation show a larger mesopore volume, a higher ratio of mesopore and a larger specific capacitance.展开更多
The on-orhit transient temperature of reflector laminate film was analyzed by using finite element method （FEM）. Numerical simulation was used by FEM software ANSYS. Results reveal that the temperature levels of the...The on-orhit transient temperature of reflector laminate film was analyzed by using finite element method （FEM）. Numerical simulation was used by FEM software ANSYS. Results reveal that the temperature levels of the laminate composite membrane alternate greatly in the orbital period, which is about±80℃. This range exceeds the material ＇ s operating temperature level. So it is necessary to put effective thermal control into effect to the laminate composite membrane. There is temperature gradient in the thickness direction of the laminate composite membrane; there is a light change in Kevlar/Epoxy layer. The temperature of the laminate composite membrane is obviously lower than the seam＇ s temperature. Results provide reference to the thermal control of the inflatable reflector with high precision requirement.展开更多
In this study, phosphorus(P) sorption of thirteen light-weight aggregates(LWAs) from USA was compared during batch equilibrium experiments in order to identify those materials which had the highest P sorption capacity...In this study, phosphorus(P) sorption of thirteen light-weight aggregates(LWAs) from USA was compared during batch equilibrium experiments in order to identify those materials which had the highest P sorption capacity for further study. Seven different levels of sorption activity were observed, which were broadly grouped into three categories—high performing, middle performing, and low performing aggregates. Chemical analysis of Ca, Al, Fe, and Mg was used to describe the differences between LWAs. There was a significant correlation between cation(especially Al, Ca, Fe, and Mg) content and P sorbed. Langmuir isotherms were used to describe P sorption maximum and binding affinity for four of the top five performing LWAs, Universal, Stalite "D", Stalite "Mix", and TXI.The fifth aggregate, Lehigh, exhibited more complex sorption, and was better described by the Freundlich isotherm. Universal had a mean P sorption at the highest concentration of 824 mg kg-1, well above its calculated sorption maximum(702 mg kg-1), and also had the highest binding affinity(1.1 L mg-1). This experiment suggests that the top performing LWA(Universal) may perform poorly in column and field studies due to observed precipitates, which could degrade constructed wetland performance. Other LWAs may exhibit superior field performance due to their high calculated sorption maxima. In general, these results highlight the importance of batch experiments as a first step in identifying materials suitable for column and field experiments.展开更多
文摘By using metal nitrates as starting materials and citric acid as a complexing agent, Y2Si207：Re3＋ （Re=Eu, Tb） phosphors were prepared by a sol-gel method. X-ray diffraction was employed to characterize the resulting samples. The results of XRD indicate that the α-Y2Si2O7 nanocrystal with size of 27 nm is obtained at 1000 ℃ and the doping ion content does not influence the structure. The excitation spectra in the UV and VUV ranges and the emission spectra of Re^3＋ doped samples were measured. The excitation spectra in the VUV range is due to absorption of host, that in the UV range is ascribed to absorption transitions from 4f to 5d state of the Tb^3＋ and the charge transfer in the En^3＋-O^2- bond. The spectral energy distribution of the Tb^3＋ emission depends strongly on the Tb3＋ concentration. The dependence of photolumineseenee intensity on Re^3＋ concentration is also discussed in detail. The fluorescent decay curves at room temperature were measured and analyzed.
基金Project(2007BAE12B01) supported by the National Key Technology Research and Development Program of China
文摘A process was proposed based on the combination of chemical and physical activation for the production of activated carbons used as the electrode material for electric double layer capacitor (EDLC). By material characterization and electrochemical methods, the influences of the activitation process on the specific surface area, pore structure and electrochemical properties of the activated carbons were investigated. The results show that specific surface area, the mesopore volume, and the specific capacitance increase with the increase of the mass ratio of KOH to char (m(KOH)/m(char)) and the activation time, respectively. When m(KOH)/m(char) is 4.0, the specific surface area and the mesopore volume reach the maximum values, i.e. 1 960 m2/g and 0.308 4 cm3/g, and the specific capacitance is 120.7 F/g synchronously. Compared with the chemical activation, the activated carbons prepared by chemical-physical activation show a larger mesopore volume, a higher ratio of mesopore and a larger specific capacitance.
文摘The on-orhit transient temperature of reflector laminate film was analyzed by using finite element method （FEM）. Numerical simulation was used by FEM software ANSYS. Results reveal that the temperature levels of the laminate composite membrane alternate greatly in the orbital period, which is about±80℃. This range exceeds the material ＇ s operating temperature level. So it is necessary to put effective thermal control into effect to the laminate composite membrane. There is temperature gradient in the thickness direction of the laminate composite membrane; there is a light change in Kevlar/Epoxy layer. The temperature of the laminate composite membrane is obviously lower than the seam＇ s temperature. Results provide reference to the thermal control of the inflatable reflector with high precision requirement.
基金Supported by the Soil Characterization Laboratory,University of Masachusetts,Amherst,MA,USA
文摘In this study, phosphorus(P) sorption of thirteen light-weight aggregates(LWAs) from USA was compared during batch equilibrium experiments in order to identify those materials which had the highest P sorption capacity for further study. Seven different levels of sorption activity were observed, which were broadly grouped into three categories—high performing, middle performing, and low performing aggregates. Chemical analysis of Ca, Al, Fe, and Mg was used to describe the differences between LWAs. There was a significant correlation between cation(especially Al, Ca, Fe, and Mg) content and P sorbed. Langmuir isotherms were used to describe P sorption maximum and binding affinity for four of the top five performing LWAs, Universal, Stalite "D", Stalite "Mix", and TXI.The fifth aggregate, Lehigh, exhibited more complex sorption, and was better described by the Freundlich isotherm. Universal had a mean P sorption at the highest concentration of 824 mg kg-1, well above its calculated sorption maximum(702 mg kg-1), and also had the highest binding affinity(1.1 L mg-1). This experiment suggests that the top performing LWA(Universal) may perform poorly in column and field studies due to observed precipitates, which could degrade constructed wetland performance. Other LWAs may exhibit superior field performance due to their high calculated sorption maxima. In general, these results highlight the importance of batch experiments as a first step in identifying materials suitable for column and field experiments.
