Aiming at developing novel microwave-transparent ceramics with low dielectric loss, high thermal conductivity and high strength, Si3Na-AIN （30%, mass fraction） composite ceramics with La203 as sintering additive wer...Aiming at developing novel microwave-transparent ceramics with low dielectric loss, high thermal conductivity and high strength, Si3Na-AIN （30%, mass fraction） composite ceramics with La203 as sintering additive were prepared by hot-pressing at 1 800 ℃ and subsequently annealed at 1 450 ℃ and 1 850 ℃ for 2 h and 4 h, respectively. The materials were characterized by XRD and SEM. The effect of annealing process on the phase composition, sintering performance, microstructure, bending strength, dielectric loss and thermal conductivity of the materials was investigated. The results showed that both annealing at 1 850 ℃ and 1 450 ℃ promoted the phase transformation of α-Si3N4 to β-Si3N4. After annealing at 1 850 ℃, grain growth to a certain extent occurred in the materials. Especially, the elongated β-Si3N4 grains showed a slight increase in diameter from 0.2 μm to 0.6 μm approximately and a decrease in aspect ratio. As a result, as the annealing time increased to 4 h, the bending strength declined from 456 MPa to 390 MPa, whereas the dielectric loss decreased to 2.15× 10^-3 and the thermal conductivity increased to 16.3 W/（m.K） gradually. When annealed at 1 450 ℃, increasing the annealing time to 4 h significantly promoted the crystallization of glassy phase to La2Si6N803 phase in the materials, which led to the increase in bending strength to 619 MPa and thermal conductivity to 15.9 W/（m·K）, respectively, and simultaneously the decrease in dielectric loss to 1.53× 10^-3.展开更多
A new zinc hydrogen phosphite C4H8N2H4·Zn（HPO3）2 was prepared by hydrothermal method in the presence of piperazine as a structure-directing agent and the crystal structure was determined by single-crystal X-ray...A new zinc hydrogen phosphite C4H8N2H4·Zn（HPO3）2 was prepared by hydrothermal method in the presence of piperazine as a structure-directing agent and the crystal structure was determined by single-crystal X-ray diffraction analysis and further characterized by X-ray powder diffraction, IR, ICP, elemental analysis and TG analysis. This compound has one-dimensional anionic chains containing four-membered rings built from corner-sharing linked alternating ZnO4 tetrahedra and HPO3 pseudo pyramids. The zinc hydrogen phosphite chains are interacted with the templates of diprotonated piperazine by N—H…O hydrogen bond. Crystal data for C4H8N2H4·Zn（HPO3）2∶monoclinic, space group C2/c. a=1.774 8（2） nm, b=0.724 28（9） nm, c=0.880 87（11） nm, β= 105.345（3）°, V=1.091 9（2） nm 3, Z=4, Dc=1^907 Mg/m 3, R1=0.022 9, wR2=0.058 8.展开更多
The novel polyoxometalate, 32[Mo8ⅣMo4ⅤV2ⅣO38(PO4)], was synthesized and characterized by elementary analysis, EPR, IR spectra and X ray diffraction. The compoundcrystallizes in triclinic system, space group with a=...The novel polyoxometalate, 32[Mo8ⅣMo4ⅤV2ⅣO38(PO4)], was synthesized and characterized by elementary analysis, EPR, IR spectra and X ray diffraction. The compoundcrystallizes in triclinic system, space group with a= 1.41999(2)nm, b=1.43467(2)nm, c=1.694610(10)nm, α=95.7250(10)°, β=92.2110(10)°, γ=92.6060(10)°, V=3.42829(7)nm3, Z=2, Dc=2.388g·cm-3, Mr=2465.10g·mol-1, μ=2.489mm-1, F(000)=2388, R1=0.0584, wR2=0.1461, S=1.164. The heteropolyanion is a bi capped pseudo Keggin complex. CCDC: 186645.展开更多
基金Project(50872052) supported by the National Natural Science Foundation of ChinaProject(2009AA05Z313) supported by the National High Technology Research and Development Program of ChinaProject supported by the Commission of Science,Technology and Industry for National Defence,China
文摘Aiming at developing novel microwave-transparent ceramics with low dielectric loss, high thermal conductivity and high strength, Si3Na-AIN （30%, mass fraction） composite ceramics with La203 as sintering additive were prepared by hot-pressing at 1 800 ℃ and subsequently annealed at 1 450 ℃ and 1 850 ℃ for 2 h and 4 h, respectively. The materials were characterized by XRD and SEM. The effect of annealing process on the phase composition, sintering performance, microstructure, bending strength, dielectric loss and thermal conductivity of the materials was investigated. The results showed that both annealing at 1 850 ℃ and 1 450 ℃ promoted the phase transformation of α-Si3N4 to β-Si3N4. After annealing at 1 850 ℃, grain growth to a certain extent occurred in the materials. Especially, the elongated β-Si3N4 grains showed a slight increase in diameter from 0.2 μm to 0.6 μm approximately and a decrease in aspect ratio. As a result, as the annealing time increased to 4 h, the bending strength declined from 456 MPa to 390 MPa, whereas the dielectric loss decreased to 2.15× 10^-3 and the thermal conductivity increased to 16.3 W/（m.K） gradually. When annealed at 1 450 ℃, increasing the annealing time to 4 h significantly promoted the crystallization of glassy phase to La2Si6N803 phase in the materials, which led to the increase in bending strength to 619 MPa and thermal conductivity to 15.9 W/（m·K）, respectively, and simultaneously the decrease in dielectric loss to 1.53× 10^-3.
文摘A new zinc hydrogen phosphite C4H8N2H4·Zn（HPO3）2 was prepared by hydrothermal method in the presence of piperazine as a structure-directing agent and the crystal structure was determined by single-crystal X-ray diffraction analysis and further characterized by X-ray powder diffraction, IR, ICP, elemental analysis and TG analysis. This compound has one-dimensional anionic chains containing four-membered rings built from corner-sharing linked alternating ZnO4 tetrahedra and HPO3 pseudo pyramids. The zinc hydrogen phosphite chains are interacted with the templates of diprotonated piperazine by N—H…O hydrogen bond. Crystal data for C4H8N2H4·Zn（HPO3）2∶monoclinic, space group C2/c. a=1.774 8（2） nm, b=0.724 28（9） nm, c=0.880 87（11） nm, β= 105.345（3）°, V=1.091 9（2） nm 3, Z=4, Dc=1^907 Mg/m 3, R1=0.022 9, wR2=0.058 8.
文摘The novel polyoxometalate, 32[Mo8ⅣMo4ⅤV2ⅣO38(PO4)], was synthesized and characterized by elementary analysis, EPR, IR spectra and X ray diffraction. The compoundcrystallizes in triclinic system, space group with a= 1.41999(2)nm, b=1.43467(2)nm, c=1.694610(10)nm, α=95.7250(10)°, β=92.2110(10)°, γ=92.6060(10)°, V=3.42829(7)nm3, Z=2, Dc=2.388g·cm-3, Mr=2465.10g·mol-1, μ=2.489mm-1, F(000)=2388, R1=0.0584, wR2=0.1461, S=1.164. The heteropolyanion is a bi capped pseudo Keggin complex. CCDC: 186645.
