Silicon carbide (SiC) ceramic with YAG (Y3Al5O12) additive added by sol-gel method was liquid-phase sintered at different sintering temperatures, and the sintering mechanism and microstructural characteristics of resu...Silicon carbide (SiC) ceramic with YAG (Y3Al5O12) additive added by sol-gel method was liquid-phase sintered at different sintering temperatures, and the sintering mechanism and microstructural characteristics of resulting silicon carbide ceramics were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and elemental distribution of surface (EDS). YAG (yttrium aluminum garnet) phase formed before the sintering and its uniform distribution in the SiC/YAG composite powder decreased the sintering temperature and improved the densification of SiC ceramic. The suitable sintering temperature was 1860 °C with the specimen sintered at this temperature having superior sintering and mechanical properties, smaller crystal size and fewer microstructure defects. Three characteristics of improved toughness of SiC ceramic with YAG added by sol-gel method were microstructural densification, main-crack deflection and crystal ‘bridging’.展开更多
Lu3Al5O12 single crystals grown in pure N2 atmosphere by Czochralski method were annealed in oxidizing atmosphere （air）and reducing atmosphere （H2 ＋ N2）, respectively. Effects of annealing treatments on luminesce...Lu3Al5O12 single crystals grown in pure N2 atmosphere by Czochralski method were annealed in oxidizing atmosphere （air）and reducing atmosphere （H2 ＋ N2）, respectively. Effects of annealing treatments on luminescence and scintillation properties of the crystals were investigated. The crystal annealed in air showed the highest luminescence intensity under blue light or vacuum ultraviolet excitation in comparison with that annealed in reducing flux or the as-grown crystal. Under X-ray excitation, crystal annealed in reducing atmosphere had the lowest light yield, and crystal annealed in air had the fastest decay time under ^137Cs 662 keV γ-ray excitation. Different annealing treatments resulted in different luminescence and scintillation properties, which might related with oxygen vacancies or defect existing in the crystals.展开更多
Lutetium aluminum garnet （LuAG） precursors doped with different Pr^3＋ concentration （0.25at.%, 0.5at.%, 1.0at.%, 3.0at.%, 5.0at.%） were synthesized via a co-precipitation method using ammonium hydrogen carbonate ...Lutetium aluminum garnet （LuAG） precursors doped with different Pr^3＋ concentration （0.25at.%, 0.5at.%, 1.0at.%, 3.0at.%, 5.0at.%） were synthesized via a co-precipitation method using ammonium hydrogen carbonate as precipitant. The phase evolution and morphology of the precursor were characterized with X-ray diffractometer （XRD） and transmission electron microscopy （TEM）. The resultant LuAG：Pr^3＋ powder was sintered into translucent ceramic without any additives in vacuum at 1150 ℃ and then in nitrogen atmosphere at 1700 ℃. spectra of LuAG：Pr^3＋ powder and ceramic were measured at room temperature in vacuum ultraviolet （VUV） and ultraviolet （VU） region. For the 5d-4f transition of Pr^3＋ ions, dominant emission of ceramic samples peaking round 311 um had higher luminescence intensity. And the host absorption in ceramic samples was not as intensive as that in powder samples. The luminescent intensity of LuAG：Pr^3＋ varied with the Pr^3＋ contents and the quenching concentration was about 1.0at.% for ceramic and 3.0at.% for powder, which was much higher than 0.24at.% for LuAG：Pr^3＋ single crystals. This phenomenon showed that the ceramic had some superiority over single crystals.展开更多
用高温固相法制备了YAG:5%Dy^3+以及(Ce 0.01 Dy y Y 0.99-y)3A15O12(y=0%,1%,3%,5%,7%,9%)荧光粉。XRD结果表明,NH 4Cl、LiCl、H3BO3三种助熔剂比较,添加H3BO3可有效降低YAG晶体的结晶温度,有效阻止中间相YAlO 3的形成。H3BO3做助熔剂...用高温固相法制备了YAG:5%Dy^3+以及(Ce 0.01 Dy y Y 0.99-y)3A15O12(y=0%,1%,3%,5%,7%,9%)荧光粉。XRD结果表明,NH 4Cl、LiCl、H3BO3三种助熔剂比较,添加H3BO3可有效降低YAG晶体的结晶温度,有效阻止中间相YAlO 3的形成。H3BO3做助熔剂在1450℃煅烧6 h制备的Dy^3+和Ce^3+掺杂Y 3Al 5O 12荧光粉具有单一YAG立方相结构,且随Dy^3+掺杂浓度增加,(420)衍射峰逐渐向小角度偏移。在583 nm监测下;与单掺1%Ce^3+样品比较,Ce^3+与Dy^3+共掺样品在342 nm处的吸收均减弱;与单掺5%Dy^3+样品比较,Ce^3+与Dy^3+共掺样品在351 nm处的吸收明显增强。351 nm激发下,随Dy^3+掺杂浓度增加,Ce^3+与Dy^3+共掺样品中Ce^3+在526 nm处的发射强度逐渐减小,而在583 nm处的发射强度先增加后减弱,这说明351 nm激发下,Ce^3+与Dy^3+共掺样品中存在Ce^3+向Dy^3+的部分能量传递。465 nm激发下,Ce^3+与Dy^3+共掺杂样品中只出现Ce^3+的发射峰,且随Dy^3+浓度增加,Ce^3+发光减弱。当Dy^3+离子浓度为3%时,Ce^3+与Dy^3+共掺样品中Dy^3+相对光强达到最大,此时Ce^3+→Dy^3+能量传递效率为15.7%。405 nm激发下,随Dy^3+掺杂浓度增加,合成粉体中Ce^3+的寿命逐渐减小。经计算,Ce^3+→Dy^3+能量传递临界距离为3.464 nm,为电四极-电四极相互作用的共振能量传递。展开更多
Laser remelting and rapid solidification were performed in preparing the high-performance Al2O3/Y3Al5O12(YAG) eutectic in situ composite. The microstructure characteristic and solidification behavior were studied usin...Laser remelting and rapid solidification were performed in preparing the high-performance Al2O3/Y3Al5O12(YAG) eutectic in situ composite. The microstructure characteristic and solidification behavior were studied using scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), X-ray diffractometry(XRD) and simultaneous thermal analysis(STA). The hardness and fracture toughness were obtained using an indentation technique. The results show that the laser remelted Al2O3/YAG composite has a homogeneous eutectic microstructure without microcrack and pore. The component phases of Al2O3 and YAG are three-dimensionally and continuously reticular connected, and finely coupled without grain boundaries, colonies and amorphous phases between interfaces. The eutectic interspacing is greatly refined with increasing the scanning rate and average is only 1 μm. The synthetically thermal analysis indicates that the eutectic temperature of Al2O3-YAG is 1 824 ℃, well matching the phase diagram of Al2O3-Y2O3 system. The maximum hardness reaches 19.5 GPa and the room fracture toughness is 3.6 MPa·m1/2.展开更多
基金Project (No. 2004C31044) supported by the Science & TechniqueProject of Zhejiang Province, China
文摘Silicon carbide (SiC) ceramic with YAG (Y3Al5O12) additive added by sol-gel method was liquid-phase sintered at different sintering temperatures, and the sintering mechanism and microstructural characteristics of resulting silicon carbide ceramics were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and elemental distribution of surface (EDS). YAG (yttrium aluminum garnet) phase formed before the sintering and its uniform distribution in the SiC/YAG composite powder decreased the sintering temperature and improved the densification of SiC ceramic. The suitable sintering temperature was 1860 °C with the specimen sintered at this temperature having superior sintering and mechanical properties, smaller crystal size and fewer microstructure defects. Three characteristics of improved toughness of SiC ceramic with YAG added by sol-gel method were microstructural densification, main-crack deflection and crystal ‘bridging’.
基金Project supported by the National Natural Science Foundation of China (20571088)the Science and Technology Project of Guangdong Province (2005B10301016, 2006B14801001)
文摘Lu3Al5O12 single crystals grown in pure N2 atmosphere by Czochralski method were annealed in oxidizing atmosphere （air）and reducing atmosphere （H2 ＋ N2）, respectively. Effects of annealing treatments on luminescence and scintillation properties of the crystals were investigated. The crystal annealed in air showed the highest luminescence intensity under blue light or vacuum ultraviolet excitation in comparison with that annealed in reducing flux or the as-grown crystal. Under X-ray excitation, crystal annealed in reducing atmosphere had the lowest light yield, and crystal annealed in air had the fastest decay time under ^137Cs 662 keV γ-ray excitation. Different annealing treatments resulted in different luminescence and scintillation properties, which might related with oxygen vacancies or defect existing in the crystals.
基金supported by the National Natural Science Foundation of China (10774140)Funds for International Cooperation and Exchange of the National Nature Science Foundation of China (50711120504)+1 种基金Specialized Research Fund for the Doctoral Program of Higher Education (20060358054)Special Foundation for Talents of Anhui Province, China (2007Z021)
文摘Lutetium aluminum garnet （LuAG） precursors doped with different Pr^3＋ concentration （0.25at.%, 0.5at.%, 1.0at.%, 3.0at.%, 5.0at.%） were synthesized via a co-precipitation method using ammonium hydrogen carbonate as precipitant. The phase evolution and morphology of the precursor were characterized with X-ray diffractometer （XRD） and transmission electron microscopy （TEM）. The resultant LuAG：Pr^3＋ powder was sintered into translucent ceramic without any additives in vacuum at 1150 ℃ and then in nitrogen atmosphere at 1700 ℃. spectra of LuAG：Pr^3＋ powder and ceramic were measured at room temperature in vacuum ultraviolet （VUV） and ultraviolet （VU） region. For the 5d-4f transition of Pr^3＋ ions, dominant emission of ceramic samples peaking round 311 um had higher luminescence intensity. And the host absorption in ceramic samples was not as intensive as that in powder samples. The luminescent intensity of LuAG：Pr^3＋ varied with the Pr^3＋ contents and the quenching concentration was about 1.0at.% for ceramic and 3.0at.% for powder, which was much higher than 0.24at.% for LuAG：Pr^3＋ single crystals. This phenomenon showed that the ceramic had some superiority over single crystals.
基金Project(50102004) supported by the National Natural Science Foundation of ChinaProject(04G53048) supported by the Aeronautical Science Foundation of China+2 种基金Project(20040699035) supported by the Specialized Research Fund for the Doctoral Program of Higher Education of ChinaProject(W018101) supported by the Research Fund of Northwestern Polytechnical University, ChinaProject supported by the Developing Program for Outstanding Persons in Northwestern Polytechnical University, China
文摘Laser remelting and rapid solidification were performed in preparing the high-performance Al2O3/Y3Al5O12(YAG) eutectic in situ composite. The microstructure characteristic and solidification behavior were studied using scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), X-ray diffractometry(XRD) and simultaneous thermal analysis(STA). The hardness and fracture toughness were obtained using an indentation technique. The results show that the laser remelted Al2O3/YAG composite has a homogeneous eutectic microstructure without microcrack and pore. The component phases of Al2O3 and YAG are three-dimensionally and continuously reticular connected, and finely coupled without grain boundaries, colonies and amorphous phases between interfaces. The eutectic interspacing is greatly refined with increasing the scanning rate and average is only 1 μm. The synthetically thermal analysis indicates that the eutectic temperature of Al2O3-YAG is 1 824 ℃, well matching the phase diagram of Al2O3-Y2O3 system. The maximum hardness reaches 19.5 GPa and the room fracture toughness is 3.6 MPa·m1/2.
