共查询到20条相似文献,搜索用时 15 毫秒
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Amikam Birnboim Tayo Olorunyolemi Yuval Carmel 《Journal of the American Ceramic Society》2001,84(6):1315-1320
This work is devoted to the theoretical understanding of the microstructure and thermal conductivity relationships of compacted ceramic powders in the initial, nondensifying stage of sintering. A model based on surface diffusion of vacancies for the growth of the neck between particles is combined with numerical fully three-dimensional code calculations, which solve for the effective heat conductivity coefficient of lightly sintered particles. The predictions of the model are in agreement with experimental observations. The approach presented can be applied to solve a series of related problems, like dielectric properties, with arbitrary microstructure and multicomponent composite of the powders. 相似文献
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Binder evolution information generated using thermal analysis techniques is used along with microstructural information to define a thermal cycle for debinderizing injection-molded articles. In addition, the roles of binder chemistry, powder morphology, binder loading, article size, heating rate, and environmental conditions in determining a satisfactory thermal cycle are investigated. Major binder evolution events and types of defects generated are identified. An improved binder removal cycle is developed from this evaluation for organics elimination of a honeycomb structure. 相似文献
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Fumed silica is a synthetic amorphous silicon dioxide produced by burning silicon tetrachloride in an oxygen-hydrogen flame. Surface areas range from 50–400 m2/g. Using particle sizing techniques, fumed silica shows micron sized particles leading to surface areas markedly lower than expected. Fumed silica appears as a fluffy solid with bulk densities down to 0.03 g/cm3, being invariant over the wide range of surface areas. Attempts to relate the variation of the surface area directly to the performance of fumed silica in technical applications, such as its thickening efficiency in fluids, mainly fail and remain ambiguous. 相似文献
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Raja Wusirika 《Journal of the American Ceramic Society》1990,73(10):2926-2929
The reaction between fumed silica and ammonia has been studied between 600° and 1200°C. Up to 24 wt% nitrogen can be introduced into vitreous silica by adjusting the partial pressure of ammonia, temperature, and reaction time. The experiments show that the amount of nitrogen incorporated into silica has a linear dependence on the partial pressure of ammonia and a square root dependence on the reaction time. The activation energy for the reaction was found to be 76.0 kJ/mol. The nitrided powders as well as several hotpressed samples were crystallized at 1550° to 1650°C. Silica glasses containing 0 to 1 wt% nitrogen crystallize to cristobalite. Glasses containing 2 to 10 wt% nitrogen are stable against devitrification in nitrogen, even at 1650°C. Glasses with 12 to 28 wt% nitrogen crystallize to fine-grained Si2 N2 O with residual glass. 相似文献
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外墙外保温材料的阻燃设计已成为建筑安全发展的重要趋势,本文采用溶胶-凝胶法,以硅灰为原料,对比研究了NaOH(2 mol/L,3 mol/L,4 mol/L和5 mol/L),KOH(2 moL/L,3 mol/L,4 mol/L和5 moL/L)和Na2SiO3(1 mol/L,1.5 mol/L,2 mol/L和2.5 mol/L)以及它们二者混合所制备硅灰基涂料的阻燃性能.结果表明,以KOH(2 mol/L)和Na2SiO3(1 mol/L)为化学活化剂时阻燃效果最佳,其可使EPS的极限氧指数可达38.6%,燃烧性能达到UL-94 V0级别;并提出了KOH和Na2SiO3对硅灰的协同反应原理,SEM结果证实其有助于硅灰发展成结构更加致密的无定型硅质层,热重-差式量热结果表明该硅灰基涂料具有良好的热稳定性;XRD和FT-IR结果表明在碱性环境下硅灰结构发生了“解聚-重组”,所制备涂料在燃烧过程中可将EPS中有毒的Cl元素固化为NaCl. 相似文献
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Fracture Toughness of Spray-Dried Powder Compacts 总被引:1,自引:0,他引:1
The strengths and fracture toughness values were measured for alumina powder compacts containing two different binder systems. Diametral compression was used to measure both the tensile strength and the fracture toughness (through-thickness notch). This methodology was very useful in linking processing parameters, such as binder choice and compaction stress, to the quality of the green bodies. Observations of the compact structure before and after fracture showed that the binders segregated to the region between the spray-dried granules. The presence of the excess binder in this region was linked to both the failure mode and the creation of secondary cracks. 相似文献
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利用流变仪对SiO2微粉悬浮液进行稳态剪切和动态剪切实验,通过同轴旋转剪切、小振幅振荡剪切、大振幅振荡剪切3种方式对悬浮液的剪切流变行为进行表征,得到悬浮液结构稳定性的动力学条件及结构破坏条件。结果表明:同轴旋转法可对悬浮液结构稳定性的强弱进行定性判断,非牛顿系数n能够表征悬浮液结构稳定性的强弱;小振幅振荡法可对其强弱进行定量分析,确定了悬浮液的线性黏弾区,获得了悬浮液结构开始破坏、开始流动时的应变和剪切应力;大振幅振荡法实验下,Cox-Merz经验公式适用于SiO2微粉悬浮液,能够确定存储模量为零的状态,进而得到悬浮液结构完全被破坏时所需的剪切应力和剪切速率。 相似文献