Mixed rare earth elements were incorporated into alumina ceramic materials. Hot-pressing was used to fabricate alumina matrix composites in nitrogen atmosphere protection. Microstructures and mechanical properties of ...Mixed rare earth elements were incorporated into alumina ceramic materials. Hot-pressing was used to fabricate alumina matrix composites in nitrogen atmosphere protection. Microstructures and mechanical properties of the composites were tested. It was indicated that the bending strength and fracture toughness of alumina matrix ceramic composites sintered at 1550 ℃ and 28 MPa for 30 min were improved evidently. Besides mixed rare earth elements acting as a toughening phase, AlTiC master alloys were also added in as sintering assistants, which could prompt the formation of transient liquid phase, and thus nitrides of rare earth elements were produced. All of the above were beneficial for improving the mechanical properties of alumina matrix ceramic composites.展开更多
Er^(3+)-doped heavy metal oxyfluoride silicate glass was fabricated and characterized, and the absorption spectrum and fluorescence spectrum of the glass were studied. The Judd-Ofelt intensity parameters Ω_t (t =2, ...Er^(3+)-doped heavy metal oxyfluoride silicate glass was fabricated and characterized, and the absorption spectrum and fluorescence spectrum of the glass were studied. The Judd-Ofelt intensity parameters Ω_t (t =2, 4, 6), spontaneous transition probability, fluorescence branching ratio and radiative lifetime of each energy levels for Er^(3+) were calculated by Judd-Ofelt theory, and stimulated emission cross-section of (()~4I_(13/2))→(()~4I_(15/2)) transition was calculated by McCumber theory. The results show that fluorescence full width at half maximum and stimulated emission cross-section of Er^(3+)-doped heavy metal oxyfluoride silicate glass are broad and large, respectively. Compared with other host glasses, the gain bandwidth property of Er^(3+)-doped heavy metal oxyfluoride silicate glass is close to those of tellurite and bismuth glasses, and has advantage over those of silicate, phosphate and germante glasses.展开更多
Cordierite-based glass-ceramics with non-stoichiometric composition doped with rare earth oxide (REO_2) and heavy metal oxide (M_2O_3) respectively were fabricated from glass powders. After sintering and crystallizati...Cordierite-based glass-ceramics with non-stoichiometric composition doped with rare earth oxide (REO_2) and heavy metal oxide (M_2O_3) respectively were fabricated from glass powders. After sintering and crystallization heat treatment, various physical properties, including compact density and apparent porosity, were examined to evaluate the sintering behavior of cordierite-based glass-ceramics. Results show that the additives both heavy metal oxide and rare earth oxide promote the sintering and lower the phase temperature from μ- to α-cordierite as well as affect the dielectric properties of sintered glass-ceramics. The complete-densification temperature for samples is as low as 900 ℃. The materials have a low dielectric constant (≈5), a low thermal expansion coefficient ((2.80～3.52)×10^(-6) ℃^(-1)) and a low dissipation factor (≤0.2%) and can be co-fired with high conductivity metals such as Au, Cu, Ag/Pd paste at low temperature (below 950 ℃), which makes it to be a promising material for low-temperature co-fired ceramic substrates.展开更多
The oxide ZrW_2O_8 displays unusual property of isotropic negative thermalexpansion in a large wide temperature range, which makes it have a number of important potentialapplications. The cubic Zr_(1-x)Hf_xW_2O_8 (x v...The oxide ZrW_2O_8 displays unusual property of isotropic negative thermalexpansion in a large wide temperature range, which makes it have a number of important potentialapplications. The cubic Zr_(1-x)Hf_xW_2O_8 (x velence 0,0.3, 0.5, 0.7, and 1.0) were synthesized bystandard solid state reaction technique. The high and low temperature X-ray diffraction analysisindicate that the substitution of the Hf^(4+) for Zr^(4+) only leads to reducing the latticeconstants, and the changes of negative thermal expansion coefficients are not obvious. The linearexpansion coefficients of Zr_(1-x)Hf_xW_2O_8 (x velence 0,0.3, 0.5, 0.7, and 1.0) are about -6 X 10^(-6) K^(-1) in the temperature range of 298 to 973 K, while that of Zr_(0.5)Hf_(0.5)W_2O_8 is -9.6X 10^(-6) K_(-1) from 83 to 298 K. The phase transition temperatures from alpha-ZrW_2O_8 tobeta-ZrW_2O_8 structure were also determined by X-ray diffraction method. Thermogravimetric analysis(TGA) exhibits that Zr_(1-x)Hf_xW_2O_8 is not hygroscopic in air.展开更多
基金the Outstanding Young Scientist Rewards of Shandong Province (05BS04008)the Natural Science Fund of Shandong Province (Y2007F29)
文摘Mixed rare earth elements were incorporated into alumina ceramic materials. Hot-pressing was used to fabricate alumina matrix composites in nitrogen atmosphere protection. Microstructures and mechanical properties of the composites were tested. It was indicated that the bending strength and fracture toughness of alumina matrix ceramic composites sintered at 1550 ℃ and 28 MPa for 30 min were improved evidently. Besides mixed rare earth elements acting as a toughening phase, AlTiC master alloys were also added in as sintering assistants, which could prompt the formation of transient liquid phase, and thus nitrides of rare earth elements were produced. All of the above were beneficial for improving the mechanical properties of alumina matrix ceramic composites.
文摘Er^(3+)-doped heavy metal oxyfluoride silicate glass was fabricated and characterized, and the absorption spectrum and fluorescence spectrum of the glass were studied. The Judd-Ofelt intensity parameters Ω_t (t =2, 4, 6), spontaneous transition probability, fluorescence branching ratio and radiative lifetime of each energy levels for Er^(3+) were calculated by Judd-Ofelt theory, and stimulated emission cross-section of (()~4I_(13/2))→(()~4I_(15/2)) transition was calculated by McCumber theory. The results show that fluorescence full width at half maximum and stimulated emission cross-section of Er^(3+)-doped heavy metal oxyfluoride silicate glass are broad and large, respectively. Compared with other host glasses, the gain bandwidth property of Er^(3+)-doped heavy metal oxyfluoride silicate glass is close to those of tellurite and bismuth glasses, and has advantage over those of silicate, phosphate and germante glasses.
文摘Cordierite-based glass-ceramics with non-stoichiometric composition doped with rare earth oxide (REO_2) and heavy metal oxide (M_2O_3) respectively were fabricated from glass powders. After sintering and crystallization heat treatment, various physical properties, including compact density and apparent porosity, were examined to evaluate the sintering behavior of cordierite-based glass-ceramics. Results show that the additives both heavy metal oxide and rare earth oxide promote the sintering and lower the phase temperature from μ- to α-cordierite as well as affect the dielectric properties of sintered glass-ceramics. The complete-densification temperature for samples is as low as 900 ℃. The materials have a low dielectric constant (≈5), a low thermal expansion coefficient ((2.80～3.52)×10^(-6) ℃^(-1)) and a low dissipation factor (≤0.2%) and can be co-fired with high conductivity metals such as Au, Cu, Ag/Pd paste at low temperature (below 950 ℃), which makes it to be a promising material for low-temperature co-fired ceramic substrates.
基金This project is financially supported by the National Natural Science Foundation of China (No. 50002001) the Natural Science Foundation of Yunnan Province (No. 2000E0006Q)
文摘The oxide ZrW_2O_8 displays unusual property of isotropic negative thermalexpansion in a large wide temperature range, which makes it have a number of important potentialapplications. The cubic Zr_(1-x)Hf_xW_2O_8 (x velence 0,0.3, 0.5, 0.7, and 1.0) were synthesized bystandard solid state reaction technique. The high and low temperature X-ray diffraction analysisindicate that the substitution of the Hf^(4+) for Zr^(4+) only leads to reducing the latticeconstants, and the changes of negative thermal expansion coefficients are not obvious. The linearexpansion coefficients of Zr_(1-x)Hf_xW_2O_8 (x velence 0,0.3, 0.5, 0.7, and 1.0) are about -6 X 10^(-6) K^(-1) in the temperature range of 298 to 973 K, while that of Zr_(0.5)Hf_(0.5)W_2O_8 is -9.6X 10^(-6) K_(-1) from 83 to 298 K. The phase transition temperatures from alpha-ZrW_2O_8 tobeta-ZrW_2O_8 structure were also determined by X-ray diffraction method. Thermogravimetric analysis(TGA) exhibits that Zr_(1-x)Hf_xW_2O_8 is not hygroscopic in air.
