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多孔氮化硅(Si_3N_4)陶瓷由于具有优异的力学性能、良好的抗热震和低介电常数等特点,在极端力/热环境下具有很大的应用潜力。研究表明:不同的制备工艺对多孔氮化硅陶瓷晶粒尺寸、微结构有很大影响,从而影响材料的力学性能;介电性能受气孔率、相组成影响;渗透率受气孔率、气孔尺寸、弯曲度的影响。综述了多孔Si_3N_4陶瓷的烧结工艺、成型工艺及其相关性能研究,并结合目前的研究热点,指出了未来多孔氮化硅陶瓷研究的发展方向。 相似文献
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通过添加烧结助剂,采用常压烧结工艺制备出不同气孔率(19%~54%)的氮化硅陶瓷.采用Archimedes法、三点弯曲法和Vickers硬度测试法测量了材料的密度、气孔率、抗弯强度及硬度.用X射线衍射及扫描电镜检测了相组成和显微结构.用谐振腔法测试了氮化硅陶瓷在10.2 GHz的介电特性.结果表明:材料具有优良的介电性能.随着烧结助剂的减少,样品中气孔率增加,力学性能有所下降,介电常数和介电损耗降低.添加Lu2O3所制备的氮化硅陶瓷的力学性能和介电性能优于添加Eu2O3或Y2O3制备的氮化硅陶瓷.当气孔率高于50%时,多孔氮化硅陶瓷(添加入5%的Y2O3或Lu2O3,或Eu2O3,质量分数)的抗弯强度可达170 MPa,介电常数为3.0~3.2,介电损耗为0.000 6~0.002. 相似文献
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多孔氮化硅陶瓷材料因其能够充分发挥氮化硅陶瓷和多孔陶瓷两者的优异性能,广泛应用于机械、化工、海洋工程、航空航天等重要领域。制备孔隙率和孔隙结构可控、高强度、低介电常数的氮化硅多孔陶瓷是实现其应用的关键。本文在检索了大量国内专利文献的基础上,对氮化硅多孔陶瓷制备技术信息进行统计和分析,并对其未来技术发展进行了预测。 相似文献
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Hongkun He Wenwen Li Melissa Lamson Mingjiang Zhong Dominik Konkolewicz Chin Ming Hui Karin Yaccato Timothy Rappold Glenn Sugar Nathaniel E. David Krishnan Damodaran Sittichai Natesakhawat Hunaid Nulwala Krzysztof Matyjaszewski 《Polymer》2014
A series of porous polymers with different pore volumes, pore sizes, and crosslinking densities were synthesized by high internal phase emulsion (HIPE) polymerization. The crosslinked polymerized HIPEs (polyHIPEs) were formed by the copolymerization of 4-vinylbenzyl chloride and divinylbenzene using water droplets in conventional or Pickering HIPEs as the templates. These porous materials were further modified by quaternization and ion exchange to introduce quaternary ammonium hydroxide groups. The resulting polyHIPEs were utilized as sorbents for reversible CO2 capture from air using the humidity swing. The effect of pore structure on the CO2 adsorption and desorption processes was studied. The polyHIPEs containing large pores and interconnected porous structures showed improved swing sizes and faster adsorption/desorption kinetics of CO2 compared to a commercial Excellion membrane with similar functional groups. 相似文献
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Porous silica ceramics with tri-modal pores were prepared, based on the generation of foams from silica/starch composite slurry and the subsequent stabilization of the structure by starch consolidation. The rheology of the original slurry and the foamed one were evaluated and compared. After drying, the green bodies were debindered and sintered at 1250 °C for 5 h. The resulting materials consisted of a hierarchical structure with large-sized cells, moderate-sized pores in cell wall and small-sized voids among silica grains. The compressive strength of the sintered samples varied within the range of 4–17 MPa, corresponding to relative densities of 18–30%. 相似文献
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In this paper, we have reported a simple and rapid approach for the large-scale synthesis of β-Co(OH)2 nanoplatelets via the microwave hydrothermal process using potassium hydroxide as mineralizer at 140 °C for 3 h. Calcining the β-Co(OH)2 nanoplatelets at 350 °C for 2 h, porous Co3O4 nanoplatelets with a 3D quasi-single-crystal framework were obtained. The process of converting the β-Co(OH)2 nanoplatelets into the Co3O4 nanoplatelets is a self-supported topotactic transformation, which is easily controlled by varying the calcining temperature. The textural characteristics of Co3O4 products have strong positive effects on their electrochemical properties as electrode materials in lithium-ion batteries. The obtained porous Co3O4 nanoplatelets exhibit a low initial irreversible loss (18.1%), ultrahigh capacity, and excellent cyclability. For example, a reversible capacity of 900 mAh g−1 can be maintained after 100 cycles. 相似文献
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In this work, porous TiO2 hollow spheres with an average diameter of 100 nm and shell thickness of 20 nm were synthesized by a facile hydrothermal
method with NH4HCO3 as the structure-directing agent, and the formation mechanism for this porous hollow structure was proved to be the Ostwald
ripening process by tracking the morphology of the products at different reaction stages. The product was characterized by
SEM, TEM, XRD and BET analyses, and the results show that the as-synthesized products are anatase phase with a high surface
area up to 132.5 m2/g. Gas-sensing investigation reveals that the product possesses sensitive response to methanal gas at 200°C due to its high
surface area. 相似文献
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A fine porous gold catalyst has been fabricated by selective leaching of Cu from an ordered AuCu3 intermetallic compound with 50%HNO3 aqueous solution at 50 °C. This catalyst exhibited comparable areal rate (mol min−1 m−2-cat) with the Au/TiO2 catalyst for CO oxidation. The present study demonstrates that high catalytic activity of gold is originated neither from
the presence of fine dispersed Au particles nor from Au-support perimeter interface. 相似文献
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Young-Wook MoonKwan-Ha Shin Young-Hag Koh Won-Young ChoiHyoun-Ee Kim 《Journal of the European Ceramic Society》2012,32(5):1029-1034
This study reports a novel way of increasing the pore size of highly aligned porous alumina ceramics by heat-treating an extruded alumina/camphene body at a temperature near its solidification point. The pore size obtained increased remarkably from 51 ± 8 to 125 ± 27 μm with increasing heat-treatment time from 1 to 24 h, due to the continuative overgrowth of the camphene dendrites during heat-treatment, while a highly aligned porous structure was preserved. In addition, interestingly, this heat-treatment enabled alumina walls to be densified quite well, whereas porous walls were observed in the sample produced without heat-treatment, which led to a considerable increase in compressive strength. The sample produced with a heat-treatment time of 12 h showed a high compressive strength of 11.6 ± 1.2 MPa at a porosity of approximately 84 vol%, which was much higher than that (0.28 ± 0.1 MPa) of the sample produced without heat-treatment. 相似文献
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S. Vercauteren K. Keizer E.F. Vansant J. Luyten R. Leysen 《Journal of Porous Materials》1998,5(3-4):241-258
The preparation and characterization of porous ceramic membranes is presented. These membranes consist of a macroporous support system, with or without a mesoporous intermediate layer, and a microporous top layer. For the macroporous support membranes two manufacturing routes are described: a conventional and a RBAO (Reaction Bonded Aluminium Oxide) route. The mesoporous -Al2O3 layer is obtained by means of a sol-gel dipcoating technique. Three microporous top layers are considered: SiO2, Al2O3-pillared montmorillonite and Laponite. These top layers have different pore structures which results in different gas transport properties. A SiO2 membrane can be used for H2 removal from a gas mixture. Al2O3-pillared montmorillonite and Laponite membranes do not show specific gas separation properties. Dehydration of water/2-propanol mixtures by means of pervaporation also proved a different behavior for these microporous membranes. 相似文献
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Pascal Williams Claude Lévy-Clément Ana Albu-Yaron Nathalie Brun Christian Colliex 《Journal of Porous Materials》2000,7(1-3):159-163
First results of an Electron Energy Loss Spectroscopy in the Near Field (NFEELS) mode of n+ porous silicon are described here. Sequences of EELS spectra in the low loss energy range (0–30 eV) were recorded, using a scanning transmission electron microscope, as the e-beam was scanned across a nano-hole surrounded by Si platelets. This technique is shown to be very sensitive to spectral and spatial changes in the electromagnetic field distribution outside the surface of nanoparticles, governed by their local nature and shape. 相似文献
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R. Mendoza-Serna J. Méndez-Vivar E. Loyo-Arnaud J.A. Moreno-Rodríguez P. Bosch V.H. Lara 《Journal of Porous Materials》2003,10(1):31-39
An experimental strategy was developed to obtain Si—Al—Zr transparent sols via the sol-gel process. The sol was prepared from Al(OBus)3 (OBus: C2H5CH(CH3)O), Zr(OPrn)4 (OPrn: OCH2CH2CH3) and Si(OEt)4. The chelating agents acetylacetone (2, 4 pentanedione, acacH), and itaconic anhydride (2-methylenesuccinic anhydride, anhH) were employed separately to stabilize Al and Zr precursors in order to control their chemical reactivity, avoiding precipitation. In all cases a prehydrolyzed tetraethyl orthosilicate (TEOS) sol was the Si source. We use the Partial Charge Model as a theoretical indication of the stabilization of the Al and Zr species derived from the reaction with anhH and acacH. The sols were polymerized at room temperature (293 K) to obtain gels and these were dried and calcined at 673, 773 and 873 K in air. The characterization techniques were Small Angle X-ray Scattering (SAXS), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Thermal Gravimetric (TGA) and Differential Thermal Analyses (DTA). The porosity and surface area of solids calcined at 673, 773 and 873 K were determined by N2 adsorption/desorption isotherms. The corresponding average pore diameter was evaluated using the methods BJH, HK and DA. These models were used because all together cover the full range of the pore size. 相似文献
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以长江沿岸低品位石英砂为主要原料,采用真空烧结制备了石英质多孔材料。通过实验分析发现:随烧结温度的升高、水料比的增大或发泡剂含量的增加,多孔材料的气孔率增大,抗压强度降低;而随着保温时间的延长,多孔材料的气孔率降低,抗压强度升高。通过优化得出最佳配比为:石英砂60 wt%、高岭土30 wt%、助烧剂9.6 wt%、发泡剂0.4 wt%。按这一最佳配比配料,在水料比为0.9的条件下球磨2 h制浆发泡,而后在1175°C烧结1 h,可以制备得到性能较佳的石英质多孔材料。 相似文献