Novel red-emitting phosphors Sr2MgSi2O7：Eu3＋ were prepared by gel-combustion method assisted by microwave. The phase struc-ture and luminescent properties of as-synthesized phosphors were investigated by XRD and flu...Novel red-emitting phosphors Sr2MgSi2O7：Eu3＋ were prepared by gel-combustion method assisted by microwave. The phase struc-ture and luminescent properties of as-synthesized phosphors were investigated by XRD and fluorescence spectrophotometer, respectively. The results showed that the as-synthesized sample was Sr2MgSi2O7 with tetragonal crystal structure. The excitation spectrum of Sr2MgSi2O7：Eu3＋ was composed of two major parts： one was the broad band between 200 and 350 nm, which belonged to the charge transfer of Eu3＋-O2-; the other consisted of a series of sharp lines between 350 and 450 nm, ascribed to the f-f transition of Eu3＋. The emission spec-trum consisted of two emission peaks at 593 and 616 nm, which was attributed to 5D0→7F1 and 5D0→7F2 of Eu3＋, respectively. The concen-tration of Eu3＋ （x） had great effect on the emission intensity of Sr2-xMgSi2O7：Eu3＋x. When x varied in the range of 0.04-0.18, the intensity of emission peaks at 593 and 616 nm increased gradually with the concentration of Eu3＋ increasing. It was interesting that no concentration quenching occurred. Moreover, the luminescent intensity could be greatly enhanced with incorporation of charge compensator Li＋ ions.展开更多
In the present work,continuous cooling curves were accurately measured by the modified Jominy specimen of 7B50 alloy during water-spray quenching tests.Besides,the time-temperature-properties(TTP) curves of this alloy...In the present work,continuous cooling curves were accurately measured by the modified Jominy specimen of 7B50 alloy during water-spray quenching tests.Besides,the time-temperature-properties(TTP) curves of this alloy were obtained during isothermal treatments.Based on the accurate cooling curves and TTP curves,the hardness distribution along the thickness direction of 7B50 alloy thick plates was predicted by quench factor analysis method.It is found that the quench sensitive temperature range of 7B50 alloy is 240-410℃,the nose temperature is 335℃,and the incubation period at the nose temperature is about 0.87 s.When 7B50 alloy was isothermal treated at 180-400℃ after solid solution treatment(470℃ for 1 h followed by 483℃ for 2 h),the exponent(n) in the Johnson-Mehl-Avrami equation is close to 1 until transformed fraction of new precipitates is up to 60%,indicating that new precipitates first grow into rodlike shape and then coarsen or thicken.When the distance is less than 65 mm from the spray quenching surface of the modified Jominy specimen,the deviation between the predicted and measured hardness is less than 2.7%,confirming the quench factor analysis method as the feasible way to predict the hardness distribution along the thickness direction of 7B50 alloy thick plates.When the distance from the spray quenching surface is 25 mm,the average cooling rate in quench sensitive temperature range is 9.93 ℃·s^-1,while the quench factor(τ) is 9.89 and the corresponding predicted hardness is HV 185.1 equivalent to 97.3% of the maximum measured hardness of 7B50 alloy in T6 temper.展开更多
Gadolinium zirconate（Gd2Zr2O7） nanocrystals were prepared via two different combustion methods： citric acid combustion（CAC） and stearic acid combustion（SAC）. The effects of the different preparation methods on ...Gadolinium zirconate（Gd2Zr2O7） nanocrystals were prepared via two different combustion methods： citric acid combustion（CAC） and stearic acid combustion（SAC）. The effects of the different preparation methods on the phase composition, microtopography, and sintering densification of the resulting Gd2Zr2O7 nanopowders were investigated by thermal-gravimetric and differential thermal analysis（TG-DTA）, Fourier transform infrared spectroscopy（FTIR）, X-ray diffraction（XRD）, and transmission electron microscopy（TEM） techniques. The results indicated that both methods could produce Gd2Zr2O7 nanopowders with an excellent defective fluorite structure. The reaction time was reduced by the SAC method, compared with the CAC method. The nanopowders synthesized by the two methods were different in grain size distribution. The resulting nanoparticle diameter was about 50 nm for CAC and 10 nm for SAC. After vacuum sintering, the sintered bodies also had a different relative density of about 93% and 98%, respectively. Thus the preparation of Gd2Zr2O7 nanopowders by SAC was the first choice to achieve the desired sintering densification.展开更多
La_2Zr_2O_7 ultrafine powders were prepared by sol-gel method.SEM indicated that La_2Zr_2O_7 particles aremosily spherical in shape and average particle sizes are smaller than 0. 5 pe XRD patterns showed that no in-to...La_2Zr_2O_7 ultrafine powders were prepared by sol-gel method.SEM indicated that La_2Zr_2O_7 particles aremosily spherical in shape and average particle sizes are smaller than 0. 5 pe XRD patterns showed that no in-tormediare phase was observed in the course of La_2Zr_2O_7 formation. The crystal structure of La_2Zr_2O_7 wasfound to be of the fluorite type when calcination temperature was 800～900℃ and of the pyrochlore type at1000℃ . The latter is cubic, its space group is Fd3m. Cxlculation of crystallite size indicated that the averagecrystallite size increased with the increasing calculation temperature. The average crystal lattice distortion ratedecreaed with the increase of particle sizes. IR spectra showed that the smaller the particles are , the higher surface activity the particles have.展开更多
(Fe7Co3)0.15(SiO2)0.85 granular alloy solid was prepared successfully using sol-gel method. The samples with different reducing temperatures were investigated by X-ray diffractometer(XRD),transmission electron microgr...(Fe7Co3)0.15(SiO2)0.85 granular alloy solid was prepared successfully using sol-gel method. The samples with different reducing temperatures were investigated by X-ray diffractometer(XRD),transmission electron micrography(TEM) and vibrating sample magnetometer(VSM). The av-erage particIe sizes of the samples were also calculated from Scherrer formula. The magnetic properties of (Fe7Co3 )o. 15 (SiO2)0.85 were studied in detail.展开更多
A method of calculating the safety profile on the HT-7 tokamak has been described in this paper. It is derived from Maxwell's equations, among which we-mainly use .two of them: one is the magnetic field diffusion ...A method of calculating the safety profile on the HT-7 tokamak has been described in this paper. It is derived from Maxwell's equations, among which we-mainly use .two of them: one is the magnetic field diffusion equation, and the other is Ampere's Law. This method can be also used to evaluate the safety factor on other devices with a circular cross sections. It is helpful to the study of the plasma MHD behavior on the HT-7 tokamak.展开更多
Single-phase insulating 12CaO？7Al_2O_3（C12A7） powder was synthesized using an optimized hydrothermal method. Pure phase of C12A7 was got at a comparatively lower temperature（c.a. 300 ℃） than that has been previo...Single-phase insulating 12CaO？7Al_2O_3（C12A7） powder was synthesized using an optimized hydrothermal method. Pure phase of C12A7 was got at a comparatively lower temperature（c.a. 300 ℃） than that has been previously reported. The crystallite size of the synthesized C12A7 powder was 7±2 nm. The surface area values calculated for all the samples at a synthesis temperature range of 250-800 ℃ for 5 h were in the range of about 19-24 m^2/g, with pore sizes of 12-20 nm. This low-temperature-based synthetic strategy along with nano porous structures and a high surface area value can facilitate catalyst application.展开更多
A novel wet-chemical method for the preparation of silver flakes was studied. The well-defined particles were prepared by directly adding FeSO4 solution into AgNO3 solution containing citric acid at an agitation speed...A novel wet-chemical method for the preparation of silver flakes was studied. The well-defined particles were prepared by directly adding FeSO4 solution into AgNO3 solution containing citric acid at an agitation speed of 150 r/min at room temperature. The products were characterized by scanning electron microscopy （SEM） and X-ray diffraction （XRD）. The results show that particles are irregular thin silver flakes. And the sizes of them range from 2 to 10 μm. It is found that citric acid plays an important role in the formation of sliver flakes. There is an optimum amount of citric acid for the preparation of silver flakes by this method. It is also found that high reduction rate is favorable for the formation of silver flakes.展开更多
基金Project supported by the National Natural Science Foundation of China (20675023)
文摘Novel red-emitting phosphors Sr2MgSi2O7：Eu3＋ were prepared by gel-combustion method assisted by microwave. The phase struc-ture and luminescent properties of as-synthesized phosphors were investigated by XRD and fluorescence spectrophotometer, respectively. The results showed that the as-synthesized sample was Sr2MgSi2O7 with tetragonal crystal structure. The excitation spectrum of Sr2MgSi2O7：Eu3＋ was composed of two major parts： one was the broad band between 200 and 350 nm, which belonged to the charge transfer of Eu3＋-O2-; the other consisted of a series of sharp lines between 350 and 450 nm, ascribed to the f-f transition of Eu3＋. The emission spec-trum consisted of two emission peaks at 593 and 616 nm, which was attributed to 5D0→7F1 and 5D0→7F2 of Eu3＋, respectively. The concen-tration of Eu3＋ （x） had great effect on the emission intensity of Sr2-xMgSi2O7：Eu3＋x. When x varied in the range of 0.04-0.18, the intensity of emission peaks at 593 and 616 nm increased gradually with the concentration of Eu3＋ increasing. It was interesting that no concentration quenching occurred. Moreover, the luminescent intensity could be greatly enhanced with incorporation of charge compensator Li＋ ions.
基金financially supported by the National Key Research and Development Program of China(No.2016YFB0300801)the National Natural Science Foundation of China(No.51371045)
文摘In the present work,continuous cooling curves were accurately measured by the modified Jominy specimen of 7B50 alloy during water-spray quenching tests.Besides,the time-temperature-properties(TTP) curves of this alloy were obtained during isothermal treatments.Based on the accurate cooling curves and TTP curves,the hardness distribution along the thickness direction of 7B50 alloy thick plates was predicted by quench factor analysis method.It is found that the quench sensitive temperature range of 7B50 alloy is 240-410℃,the nose temperature is 335℃,and the incubation period at the nose temperature is about 0.87 s.When 7B50 alloy was isothermal treated at 180-400℃ after solid solution treatment(470℃ for 1 h followed by 483℃ for 2 h),the exponent(n) in the Johnson-Mehl-Avrami equation is close to 1 until transformed fraction of new precipitates is up to 60%,indicating that new precipitates first grow into rodlike shape and then coarsen or thicken.When the distance is less than 65 mm from the spray quenching surface of the modified Jominy specimen,the deviation between the predicted and measured hardness is less than 2.7%,confirming the quench factor analysis method as the feasible way to predict the hardness distribution along the thickness direction of 7B50 alloy thick plates.When the distance from the spray quenching surface is 25 mm,the average cooling rate in quench sensitive temperature range is 9.93 ℃·s^-1,while the quench factor(τ) is 9.89 and the corresponding predicted hardness is HV 185.1 equivalent to 97.3% of the maximum measured hardness of 7B50 alloy in T6 temper.
文摘Gadolinium zirconate（Gd2Zr2O7） nanocrystals were prepared via two different combustion methods： citric acid combustion（CAC） and stearic acid combustion（SAC）. The effects of the different preparation methods on the phase composition, microtopography, and sintering densification of the resulting Gd2Zr2O7 nanopowders were investigated by thermal-gravimetric and differential thermal analysis（TG-DTA）, Fourier transform infrared spectroscopy（FTIR）, X-ray diffraction（XRD）, and transmission electron microscopy（TEM） techniques. The results indicated that both methods could produce Gd2Zr2O7 nanopowders with an excellent defective fluorite structure. The reaction time was reduced by the SAC method, compared with the CAC method. The nanopowders synthesized by the two methods were different in grain size distribution. The resulting nanoparticle diameter was about 50 nm for CAC and 10 nm for SAC. After vacuum sintering, the sintered bodies also had a different relative density of about 93% and 98%, respectively. Thus the preparation of Gd2Zr2O7 nanopowders by SAC was the first choice to achieve the desired sintering densification.
文摘La_2Zr_2O_7 ultrafine powders were prepared by sol-gel method.SEM indicated that La_2Zr_2O_7 particles aremosily spherical in shape and average particle sizes are smaller than 0. 5 pe XRD patterns showed that no in-tormediare phase was observed in the course of La_2Zr_2O_7 formation. The crystal structure of La_2Zr_2O_7 wasfound to be of the fluorite type when calcination temperature was 800～900℃ and of the pyrochlore type at1000℃ . The latter is cubic, its space group is Fd3m. Cxlculation of crystallite size indicated that the averagecrystallite size increased with the increasing calculation temperature. The average crystal lattice distortion ratedecreaed with the increase of particle sizes. IR spectra showed that the smaller the particles are , the higher surface activity the particles have.
文摘(Fe7Co3)0.15(SiO2)0.85 granular alloy solid was prepared successfully using sol-gel method. The samples with different reducing temperatures were investigated by X-ray diffractometer(XRD),transmission electron micrography(TEM) and vibrating sample magnetometer(VSM). The av-erage particIe sizes of the samples were also calculated from Scherrer formula. The magnetic properties of (Fe7Co3 )o. 15 (SiO2)0.85 were studied in detail.
文摘A method of calculating the safety profile on the HT-7 tokamak has been described in this paper. It is derived from Maxwell's equations, among which we-mainly use .two of them: one is the magnetic field diffusion equation, and the other is Ampere's Law. This method can be also used to evaluate the safety factor on other devices with a circular cross sections. It is helpful to the study of the plasma MHD behavior on the HT-7 tokamak.
基金Funded by the National Natural Science Foundation of China(No.21377063)the Zhejiang Natural Science Foundation(No.LY15F040004)the Program for Ningbo Key Laboratory of Silicon and Organic Thin Film Optoelectronic Technologies
文摘Single-phase insulating 12CaO？7Al_2O_3（C12A7） powder was synthesized using an optimized hydrothermal method. Pure phase of C12A7 was got at a comparatively lower temperature（c.a. 300 ℃） than that has been previously reported. The crystallite size of the synthesized C12A7 powder was 7±2 nm. The surface area values calculated for all the samples at a synthesis temperature range of 250-800 ℃ for 5 h were in the range of about 19-24 m^2/g, with pore sizes of 12-20 nm. This low-temperature-based synthetic strategy along with nano porous structures and a high surface area value can facilitate catalyst application.
基金Project(B20121806)supported by the Science and Technology Research Program of Education Department of Hubei Province,China
文摘A novel wet-chemical method for the preparation of silver flakes was studied. The well-defined particles were prepared by directly adding FeSO4 solution into AgNO3 solution containing citric acid at an agitation speed of 150 r/min at room temperature. The products were characterized by scanning electron microscopy （SEM） and X-ray diffraction （XRD）. The results show that particles are irregular thin silver flakes. And the sizes of them range from 2 to 10 μm. It is found that citric acid plays an important role in the formation of sliver flakes. There is an optimum amount of citric acid for the preparation of silver flakes by this method. It is also found that high reduction rate is favorable for the formation of silver flakes.
