共查询到20条相似文献,搜索用时 15 毫秒
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《Carbon》1985,23(2):215-222
The applicability of the flash technique for measuring thermal diffusivity of fiber-reinforced composites has been examined. While the usefulness of this technique has been demonstrated previously for randomly dispersed composites and for layered structures, problems arise from preferential heat paths in fibrous-reinforced composites. For these materials the concept of diffusivity must be expanded to include dependencies upon sample thickness to unit cell ratios and transient times in addition to the usual constituent property ratios and temperature dependencies of properties. Nevertheless, the flash technique has been shown to be a powerful tool for examining heat flow in these materials. It is possible to obtain diffusivity data which are equivalent to steady-state properties. In addition, it is possible to determine in situ properties for the fiber and matrix and to examine defect structures. 相似文献
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Electrochemical supercapacitive (ES) properties of liquid-phase synthesized mesoporous (pore size distribution centered ∼12 nm) and of 120 m2/g surface area nickel hydroxide film electrodes onto tin-doped indium oxide substrate are discussed. The amounts of inner and outer charges are calculated to investigate the contribution of mesoporous structure on charge storage where relatively higher contribution of inner charge infers good ion diffusion into matrix of nickel hydroxide. Effect of different electrolytes, electrolyte concentrations, deposit mass and scan rates on the current-voltage profile in terms of the shape and enclosed area is investigated. Specific capacitance of ∼85 F/g at a constant current density of 0.03 A/g is obtained from the discharge curve. 相似文献
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Biljana Babić Maja Kokunešoski Miroslav Miljković Branko Matović Jelena Gulicovski Marija Stojmenović Dušan Bučevac 《Ceramics International》2013,39(4):4035-4043
The new porous carbon materials were obtained by templating procedure using mesoporous silica (SBA-15) as template. The ordered mesoporous silica materials were synthesized by using Pluronic P123 (non-ionic triblock copolymer, EO20PO70O20). SBA-15/cryogel carbon composites were obtained by sol–gel polycondenzation of resorcinol and formaldehyde in the presence of different amount of SBA-15. The polycondenzation was followed by freeze drying and subsequent pyrolysis. One set of SBA-15/sucrose carbon composites was prepared by using sucrose as carbon source. The silica template was eliminated by dissolving in hydrofluoric acid (HF) to recover the carbon material. The obtained carbon replicas were characterized by nitrogen adsorption–desorption measurements, X-ray diffraction and scanning electron microscopy (SEM). It was revealed that the samples have high specific surface (533–771 m2 g?1), developed meso- and micro-porosity and amorphous structure. Porous structure of carbon replicas was found to be a function of the carbon source, properties of SBA-15 and silica/carbon ratio. Room temperature adsorption of nitrogen and adsorption of phenol from aqueous solutions were investigated. 相似文献
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《Catalysis communications》2005,6(10):679-683
Transition metal substituted polyoxometalate (TMSP) compounds were used as catalysts for the liquid-phase oxidation of benzene to phenol by molecular oxygen with ascorbic acid as a reducing agent in an acetone/sulfolane/water mixed solvent. [(C4H9)4N]5[PW11CuO39(H2O)] is the best catalyst tested in this study. It showed 9.2% benzene conversion (TON = 25.8) and 91.8% selectivity to phenol for the oxidation of benzene at 323 K for 12 h. The effect of the substituted transition metal in the TMSP compounds on the benzene conversion is in the order: Cu > V > Fe ≫ Mn > Ti > Cr > Co > Ni > Zn. The effect of the central atom in the TMSP compounds on the benzene conversion is in the order: P ≈ Si > Ge > B. [SiW11O39]8− is a good polyoxometalate ligand for transition metal ions as [PW11O39]7− for the oxidation of benzene. The selectivity to phenol was dramatically improved by adding the sulfolane solvent, but the benzene conversion decreased when a large amount of sulfolane was used in the mixed solvent. Ascorbic acid is indispensable for forming phenol from benzene oxidation by O2 over TMSP compounds. Higher O2 pressure in the catalytic system ensured more oxygen molecules solving in the solvent, and promoted the benzene conversion. 相似文献
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疏水微/介孔材料的合成及其对苯及其同系物的吸附 总被引:1,自引:1,他引:1
以含氢聚甲基硅氧烷(PMHS)、正硅酸乙酯(TEOS)为硅源,在室温、无模板剂条件下合成了一种疏水微孔/介孔材料,通过调节PMHS/TEOS的比例,获得了3种具有不同微孔,介孔比例的多孔材料.并通过N2吸附,脱附、HRTEM、热重等手段对上述3种材料的结构特征及热稳定性进行了表征.结果发现,所得材料均具有微孔和介孔两种孔隙结构,且具有良好的热稳定性和疏水性,在500℃以下不会发生热分解.进一步利用脉冲色谱技术研究了上述3种材料对苯及其同系物的热力学吸附行为.结果表明,上述3种材料均能够实现苯及其同系物的完全分离,相应的亨利常数、吸附热、分离因子的大小顺序为:正丁基苯>正丙基苯>乙苯>甲苯>苯,且随着PMHS/TEOS比例的增加,亨利常数、吸附热以及分离因子都增加. 相似文献
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Huimin Zheng Liang Zhao Jingjing Ji Qing Yang Haokai Huang Jinsen Gao 《American Institute of Chemical Engineers》2016,62(8):2778-2785
On the basis of our recently proposed “ideal” and “insertion” adsorption mechanisms of aromatics in HY zeolites, changes in energetic and dynamic properties with loading were investigated through Monte Carlo and molecular dynamic (MD) calculations. Loading‐dependent isosteric heat could be divided into three linear ranges. The two inflection points were attributed to adsorbate interactions and inherent adsorption mechanism changes. With regard to the loading dependence of diffusivity, diffusivity decreased faster at high loadings than at low and medium loadings, separated by an inflection point. This result confirmed a two‐stage diffusion mechanism based on the distribution of adsorbate from MD simulations which was able to qualitatively predict the further restriction of the mobility. This study provided insights into the modeling of mobility at high loadings on the basis of site‐hopping mechanism. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2778–2785, 2016 相似文献
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Maria de Fátima V. Marques Ordovaldo F. C. da Silva Ana C. S. L. S. Coutinho Antonio S. de Araujo 《Polymer Bulletin》2008,61(4):415-423
Summary In this work, different mesoporous materials were employed for the preparation of supported metallocene
catalysts to be evaluated in ethylene polymerization and their performance was related to the chemistry
of the materials surface used as support. The supports employed were MCM-41, SBA-15 and mesoporous TiO2.
The performance of the prepared catalysts was compared with the homogeneous catalyst precursor system.
Those mesoporous materials, as well as the prepared metallocene catalysts, were analyzed by infrared
absorption spectrometry (FTIR). Polymers were also characterized by FTIR, for the determination of the
number-average molecular weight, and by differential scanning calorimetry (DSC) to determine thermal
characteristics of the produced polyethylene. Among the studied metallocene supported catalysts, the
one based on the mesoporous support SBA-15 achieved the highest activities, almost as high as that observed
for the homogeneous system. 相似文献
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A. Vinu Dhanashri P. Sawant K. Ariga M. Hartmann S.B. Halligudi 《Microporous and mesoporous materials》2005,80(1-3):195-203
Aluminum-containing mesoporous molecular sieves AlSBA-15 with different nSi/nAl ratios and AlMCM-41 have been synthesized hydrothermally and characterized in detail by physicochemical methods, viz. XRD, N2 adsorption and 27Al NMR spectroscopy. The low angle XRD and N2 adsorption measurements reveal that the structural order of SBA-15 was retained after the incorporation of Al. The increase of the unit cell parameter with increasing aluminum content and 27Al MAS NMR spectroscopy confirm the incorporation of aluminum in the framework. Benzylation of benzene and substituted benzenes reaction employing benzyl chloride as the alkylating agent over AlSBA-15 and AlMCM-41 have been investigated. The influence of various reaction parameters such as reaction temperature, reactant feed ratio and catalyst amount affecting the activity and selectivity of AlSBA-15, have been studied. Among the mesoporous catalysts studied, AlSBA-15(45), where the number in parentheses indicates the molar nSi/nAl ratio, shows both high conversion and high selectivity for the benzylation of benzene. The activity of this catalyst for the benzylation of different aromatic compounds is in the following order: benzene > toluene > p-xylene > mesitylene > anisole. Kinetics of the benzene benzylation over different catalysts have also been investigated. 相似文献
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Effective diffusivity is the most important key parameter needed in the analysis, design, and optimization of heat and mass transfer during food drying process. In general, two types of effective diffusivities are used to develop the mathematical modeling of food drying, namely, moisture-dependent effective diffusivity (MDED) and temperature-dependent effective diffusivity (TDED). However, no study has extensively investigated which effective diffusivity is more accurate in predicting drying kinetics. The main goal of this study is to determine the appropriate effective diffusivity for predicting the drying kinetics. Drying models were developed for different fruits and vegetables based on moisture-dependent and temperature-dependent effective diffusivities. COMSOL Multiphysics, a finite element-based engineering simulation software is used to solve the coupled heat and mass transfer equations. 3D moisture profiles were developed to investigate the spatial moisture distribution during drying. Extensive experimental investigation on five types of fruits and vegetables was conducted and results were compared with the simulated results. The experiments were repeated thrice, and the average of the moisture content at each value was used for constructing the drying curves. Close agreement between experimental and simulated results validates the models developed. It was observed that the moisture profile and temperature profile in case of MDED were more closely fitted with the experimental results. For all fruits and vegetables, the moisture ratio with MDED was significantly lower than moisture ratio with TDED. This finding confirms that the MDED is more accurate for predicting kinetics in food drying. Moreover, the moisture ratio of apple was lowest whereas pear showed the highest moisture ratio. On the other hand, carrot showed a considerably lower moisture ratio compared to potato. 相似文献