共查询到19条相似文献,搜索用时 93 毫秒
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超临界流体干燥理论,技术及应用 总被引:10,自引:0,他引:10
超临界流体干燥法是制备具有很高比表面和孔体积及较低堆密度、折光指数和热导率的块状气凝胶或粉体的重要途径之一。本文详细评述了超临界流体干燥理论和技术的历史背景与研究现状,简要介绍了气凝胶在催化剂、热绝缘材料、高能物理粒子探测器、超细材料、玻璃和陶瓷等诸方面的应用和发展前景。 相似文献
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超临界石油醚干燥和超临界二氧化碳干燥在制备有机和炭气凝胶中的比较研究 总被引:2,自引:5,他引:2
热固性酚醛树脂—羟甲基三聚氰胺经历聚合反应、溶胶—凝胶、超临界干燥和裂解过程生成了有机和炭气凝胶。比较了超临界石油醚干燥(240℃、6.0MPa下1h)和超临界二氧化碳干燥(60℃、10.0MPa下7d)在制备有机和炭气凝胶过程中的作用。结果发现:超临界石油醚干燥时间比超临界二氧化碳的显著短,虽然前者制备的有机气凝胶的BET比表面和中孔孔容比后者小,但前者制备的有机气凝胶在热裂解过程中的热稳定性比后者好,因此,超临界石油醚干燥制备的炭气凝胶的BET比表面和中孔孔容均比超临界二氧化碳的大。超临界石油醚干燥可以替代超临界二氧化碳干燥来制备炭气凝胶。 相似文献
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超临界CO2流体干燥合成ZrO2气凝胶及其表征 总被引:4,自引:0,他引:4
以无机盐为原料,采用沉淀法结合超临界CO2流体干燥技术成功地制备了ZrO2气凝胶.借助TG/DSC、XRD、TEM、DLS以及N2物理吸附等手段对其性能进行表征.结果显示,超临界CO2流体干燥可以有效地防止干燥过程中胶体粒子之间的硬团聚作用,在基本保持湿凝胶网络结构的情况下实现液相的脱除,从而使合成的ZrO2具有高比表面积和大孔体积等特点.此外,样品的TEM和DLS分析显示,纳米ZrO2颗粒首先形成具有空间网络结构的簇团,尺寸为数百个纳米的簇团堆积形成ZrO2气凝胶;气凝胶的空间网络结构特征在中等温度的热处理过程中不会遭到完全破坏. 相似文献
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以碳酸铈、氧化镧和硝酸锰为主要原料,采用"溶胶-凝胶"法结合"超临界流体干燥"技术获取Ce-La-Mn气凝胶,在850℃热处理制备Ce-La-Mn混合氧化物,并采用TG-DTA、XRD、FT-IR和TEM进行表征,用"2CO+2NO=2CO2+N2"特征反应测试超细粒子的催化活性,考察超临界流体干燥技术与铈掺杂对超细Ce-La-Mn混合氧化物的结构、形貌和催化活性的影响。结果显示:经260℃超临界流体干燥得到的Ce-La-Mn气凝胶为分散性好的棕色絮状粉末,由大量直径小于10nm的球型颗粒组成,晶相为CeO2、MnO、La5O7NO3和La(OH)2NO3;经850℃热处理得到的Ce-La-Mn混合氧化物的粒径约为20nm,晶相为LaMnO3+λ、La2O3和CeO2;铈掺杂增加了LaMnO3+λ晶格中氧空缺数量,改善了催化的气氛条件,提高了Ce-La-Mn混合氧化物的催化活性。 相似文献
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利用溶胶-凝胶技术和超临界干燥技术,制备了PMMA/SiO2复合气凝胶,并对气凝胶样品进行了表征。 相似文献
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Al2O3气凝胶的制备技术研究 总被引:3,自引:0,他引:3
Al2O3气凝胶是一种新型、轻质的纳米多孔材料,具有许多独特的物理、化学性质和潜在的应用价值.综述了Al2O3气凝胶的超临界干燥及非超临界干燥制备方法以及各种制备参数(醇铝盐与水的比例、醇盐的类型、溶剂的类型、温度、乙醇的用量、由催化剂所决定的溶液的pH值、老化时间以及干燥过程)对Al2O3气凝胶性质的影响,并探讨了Al2O3气凝胶进一步研究的方向. 相似文献
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超临界流体干燥法制备纳米级TiO2的研究 总被引:10,自引:0,他引:10
本文以廉价无机盐为原料,采用溶胶-凝胶法(Sol-Gel)结合超临界流体干燥(SupercriticalFluidDrying简称SCFD)制备了纳米级TiO2,并采用XRD、DTA-TG、TEM技术研究了Sol-Gel过程中溶液的pH值、浓度、陈化时间及SCFD技术等条件对TiO2粒径大小的影响,实现了干燥晶化一步完成.用该方法制得的TiO2超细粉体,粒径大都在3~6um之间,呈球形微粒,粉体晶型为锐钛矿型,并具有纯度高、热稳定性好、失重小和粒度分布均匀等特性. 相似文献
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高效隔热材料掺TiO2及玻璃纤维硅石气凝胶的研制 总被引:11,自引:0,他引:11
研究了掺TiO2粉末物玻璃纤维的硅石气凝胶的热导率与气压,温度的关系,结果表明,这种掺杂的硅石气凝胶在高温下具有比普通隔热材料低得多的导热系数,因此用来作为高效高温隔热材料将颇具前景。 相似文献
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《Journal of Experimental Nanoscience》2013,8(3):233-242
Using cerium carbonate, lanthanum oxide and manganese nitrate as raw materials, ultrafine particles of Ce–La–Mn mixed oxides were prepared by the sol–gel method combined with supercritical drying technology. The prepared materials were characterised by thermo-gravimetric and differential thermal analysis, X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscope. The catalytic properties of ultrafine Ce–La–Mn mixed oxides were tested by the reaction ‘2CO?+?2NO?=?2CO2?+?N2’. The key aim was to examine the effect of supercritical fluid drying technology and Ce-doping on the crystal structure, morphology and catalytic activity of ultrafine Ce–La–Mn mixed oxides. The results show that at 260°C, Ce–La–Mn mixed oxides are brown loose flocculent powders with good dispersibility. The particles are spherical about 10?nm in size. The main crystal components are CeO2, MnO, La5O7NO3 and La(OH)2NO3. After thermal treating at 850°C, Ce–La–Mn mixed oxides were made up of plenty of quasi-global grains smaller than 20?nm; the main crystal components of the Ce–La–Mn mixed oxides are LaMnO3+ λ , La2O3 and CeO2; heat treatment can enhance the crystallinity of the materials. Cerium-doped mixtures just exist as crystal CeO2, which contributes to the crystallisation of Ce–La–Mn mixed oxides in the process of supercritical fluid drying at 260°C, enhancing the catalytic activity of ultrafine Ce–La–Mn mixed oxides which are thermal treated at 850°C. 相似文献
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Liping LIANG Shu''''e DANG Dong WU YuhanState Key Laboratory of Coal Conversion Institute of Coal Chemistry Chinese Academy of Sciences Taiyuan ChinaDepartment of Materials Science Engineering Taiyuan Heavy Machinery Institute Taiyuan ChinaGraduate School of the Chinese Academy of Sciences Beijing China 《材料科学技术学报》2004,20(4):435-438
Coprecipitation supercritical fluid drying technology has been employed to synthesize calcia-stabilized zirconia ultrafine powder with low-cost inorganic salts as the starting materials. The sintering behaviors of these powders were also investigated. The results showed that supercritical fluid drying could effectively alleviate the hard agglomeration of grains during the gel drying process, and the morphology of the powder retained the network texture of the original gel. The resulting particles were characterized by small particle size (5-20 nm), better monodispersity and high surface area, which gave rise to high activity and sinterability. Consequently, these powders could readily be compacted into the desired shape and their densification could be carried out in shorter time and at lower temperatures. For instance, nanometer-sized powder calcined at 600癈 for 2 h could be cold-pressed into a green body and sintered at 1100?for 0.5 h to attain a dense body with bulk density of 5.9718 g/cm3 and speci 相似文献
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Effect of the drying conditions on the microstructure of silica based xerogels and aerogels 总被引:1,自引:0,他引:1
Durães L Ochoa M Rocha N Patrício R Duarte N Redondo V Portugal A 《Journal of nanoscience and nanotechnology》2012,12(8):6828-6834
Nanostructured silica based xerogels and aerogels are prepared by sol-gel technology, using methyltrimethoxysilane as precursor. The influence of the drying method and conditions on the microstructure of the obtained materials is investigated, since the drying stage has a critical influence on their porosity. Two types of drying methods were used: atmospheric pressure drying (evaporative), to produce xerogels, and supercritical fluids drying, to obtain aerogels. Although the supercritical fluids drying technique is more expensive and hazardous than the atmospheric pressure drying, it is well known that aerogels are less dense than the xerogels due to less pore shrinkage. However, the ideal situation would be to use atmospheric pressure drying in conditions that minimize the pore collapse. Therefore, in this work, different temperature cycles for atmospheric pressure drying and two heating rates for the supercritical fluids drying are tested to study the gels' shrinkage by analyzing the density and porosity properties of the final materials. The best materials obtained are aerogels dried with the lower heating rate (approximately 80 degrees C/h), since they exhibit very low bulk density (approximately 50 kg/m3), high porosity (95%)-mainly micro and mesopores, high surface area (approximately 500 m2/g), moderate flexibility and a remarkable hydrophobic character (>140 degrees). It was proved that the temperature cycles of atmospheric pressure drying can be tuned to obtain xerogels with properties comparable to those of aerogels, having a bulk density only approximately15 kg/m3 higher. All the synthesized materials fulfill the requirements for application as insulators in Space environments. 相似文献
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T. Tachiwaki Y. Takase J. Sugimoto M. Oda S. Kawanaka 《Particulate Science and Technology》1998,16(2):109-124
In order to prepare fine Y-Ba-Cu oxides, a suspension of oxide was synthesized by simultaneous hydrolization of 2-propanol solution of yttrium triisopropoxide - barium diisopropoxide - copper diisopropoxide. The suspension could not be dried by the freeze-drying method because the freezing point of aqueous alcohol solvent in the suspension was so low: therefore, supercritical fluid drying was used. Although the diameters of dried powders were larger than expected, the powders containing no BaCO3 were obtained.
The results from this experiment suggest that the supercritical fluid drying method is useful for drying a suspension prepared by the alkoxide method. 相似文献
The results from this experiment suggest that the supercritical fluid drying method is useful for drying a suspension prepared by the alkoxide method. 相似文献