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Average Pore Size (average + pore_size)
Selected AbstractsMicrostructure and Mechanical Properties of Lu2O3 -Doped Porous Silicon Nitride Ceramics Using Phenolic Resin as Pore-Forming AgentINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 3 2010Xiaowei Yin The joint process consisting of pressureless sintering and chemical vapor infiltration (CVI) was developed to prepare porous Si3N4 ceramics with controlled microstructure. Lu2O3 and phenolic resin acted as sintering aid and pore-forming agent, respectively. The 5 wt% Lu2O3 -doped ceramics using 12,57 vol% phenolic resin attained a porosity ranging from 46% to 53%. With increasing the resin content, the average pore size increased from 1 to 2 ,m. The porous ceramic infiltrated with CVI Si3N4 had an improved microstructure. The decreased pore size and porosity led to an increase in flexural strength, and the densified surface led to an improved surface hardness. [source] Preparation and properties of ,-chitin-whisker-reinforced hyaluronan,gelatin nanocomposite scaffoldsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010Parintorn Hariraksapitak Abstract Tissue scaffolds made of naturally derived polymers present poor mechanical properties, which may limit their actual utilization in certain areas where high strength is a key criterion. This study was aimed at developing tissue scaffolds from a 50 : 50 w/w blend of hyaluronan (HA) and gelatin (Gel) that contained different amounts of acid-hydrolyzed ,-chitin whiskers (CWs) by a freeze-drying method. The weight ratios of the CWs to the blend were 0,30%. These scaffolds were characterized for their physical, physicochemical, mechanical, and biological properties. Regardless of the CW content, the average pore size of the scaffolds ranged between 139 and 166 ,m. The incorporation of 2% CWs in the HA,Gel scaffolds increased their tensile strength by about two times compared to those of the other groups of the scaffolds. Although the addition of 20,30% CWs in the scaffolds improved their thermal stability and resistance to biodegradation, the scaffolds with 10% CWs were the best for supporting the proliferation of cultured human osteosarcoma cells (SaOS-2). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Hindered diffusion of residue narrow cuts through polycarbonate membranesAICHE JOURNAL, Issue 8 2010Zhentao Chen Abstract Hindered diffusion plays an important role in catalytic processing of residue and heavy oil because of large size molecules in these feedstocks. Vacuum residue of Athabasca oil sand bitumen was fractionated into 13 narrow fractions and an end-cut by supercritical fluid extraction and fractionation (SFEF). Diffusion transport of five SFEF cuts through four polycarbonate membranes was investigated using a diaphragm cell at 308 K. The results showed that diffusion coefficients of the five SFEF cuts decreased as the experiment proceeded, which illustrates that these cuts are polydisperse in size. The effective diffusion coefficients varied with molecular size and pore size. Hindered diffusion of the five SFEF cuts is significant in the membranes with nominal pore diameter of 15 nm, which is around the average pore size of typical hydrotreating catalyst. Comparisons between experimental data and theoretical prediction revealed that the actual hindered degree for diffusion of the five SFEF cuts is higher than that calculated by the Renkin equation. There were slight differences in diffusivity among saturate, aromatic, and resin constituents. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Characteristics of ammonia permeation through porous silica membranesAICHE JOURNAL, Issue 5 2010Masakoto Kanezashi Abstract A sol,gel method was applied for the preparation of silica membranes with different average pore sizes. Ammonia (NH3) permeation/separation characteristics of the silica membranes were examined in a wide temperature range (50,400°C) by measurement of both single and binary component separation. The order of gas permeance through the silica membranes, which was independent of membrane average pore size, was as follows: He > H2 > NH3 > N2. These results suggest that, for permeation through silica membranes, the molecular size of NH3 is larger than that of H2, despite previous reports that the kinetic diameter of NH3 is smaller than that of H2. At high temperatures, there was no effect of NH3 adsorption on H2 permeation characteristics, and silica membranes were highly stable in NH3 at 400°C (i.e., gas permeance remained unchanged). On the other hand, at 50°C NH3 molecules adsorbed on the silica improved NH3 -permselectivity by blocking permeation of H2 molecules without decreasing NH3 permeance. The maximal NH3/H2 permeance ratio obtained during binary component separation was ,30 with an NH3 permeance of ,10,7 mol m,2 s,1 Pa,1 at an H2 permeation activation energy of ,6 kJ mol,1. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Two-scale continuum model for simulation of wormholes in carbonate acidizationAICHE JOURNAL, Issue 12 2005Mohan K. R. Panga Abstract A two-scale continuum model is developed to describe transport and reaction mechanisms in reactive dissolution of a porous medium, and used to study wormhole formation during acid stimulation of carbonate cores. The model accounts for pore level physics by coupling local pore-scale phenomena to macroscopic variables (Darcy velocity, pressure and reactant cup-mixing concentration) through structure-property relationships (permeability-porosity, average pore size-porosity, and so on), and the dependence of mass transfer and dispersion coefficients on evolving pore scale variables (average pore size and local Reynolds and Schmidt numbers). The gradients in concentration at the pore level caused by flow, species diffusion and chemical reaction are described using two concentration variables and a local mass-transfer coefficient. Numerical simulations of the model on a two-dimensional (2-D) domain show that the model captures the different types of dissolution patterns observed in the experiments. A qualitative criterion for wormhole formation is developed and it is given by , , O(1), where , = . Here, keff is the effective volumetric dissolution rate constant, DeT is the transverse dispersion coefficient, and uo is the injection velocity. The model is used to examine the influence of the level of dispersion, the heterogeneities present in the core, reaction kinetics and mass transfer on wormhole formation. The model predictions are favorably compared to laboratory data. © 2005 American Institute of Chemical Engineers AIChE J, 2005 [source] Porous anodic alumina microreactors for production of hydrogen from ammoniaAICHE JOURNAL, Issue 4 2004Jason C. Ganley Abstract The synthesis and properties are described of a ruthenium-impregnated anodic aluminum catalyst for use in microreactors for the production of hydrogen from an ammonia feed. The catalyst structure was synthesized using microelectric discharge machining to create a series of 300 × 300-,m posts on an aluminum substrate. The posts were anodized to yield a 60-,m covering of anodic alumina, with an average surface area of 16 m2/gm and an average pore size of 50 nm. Ruthenium metal was dispersed on the alumina using conventional wet impregnation. A 0.9 × 0.9-cm reactor containing 250 posts decomposed 95% of anhydrous ammonia at 650°C to yield 15 sccm of hydrogen. A possible application of these microreactor fabrication methods is hydrogen generation for fuel cells in mobile power production. 2004 American Institute of Chemical Engineers AIChE J, 50:829,834, 2004 [source] Nanostructure and Micromechanical Properties of Silica/Silicon Oxycarbide Porous CompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2004Araceli Flores The microhardness,nanostructure correlation of a series of silica/silicon oxycarbide porous composites has been investigated, as a function of pyrolysis temperature, Tp. The pyrolyzed products have been studied by means of scanning electron microscopy, mercury porosimetry, chemical analysis, solid-state 29Si-NMR, X-ray diffraction, Raman spectroscopy, and microindentation hardness. Two distinct regimes are found for the microhardness behavior with Tp. In the low-temperature regime (1000°C ,Tp < 1300°C), the material response to indentation seems to be dominated by the large amount of pores present in the samples. In this Tp range, low microhardness values, H, are found (<110 MPa). Above Tp= 1300°C, a conspicuous H increase is observed. In this high-temperature regime (Tp= 1300,1500°C), microhardness values are shown to notably increase with increasing pyrolysis temperature. The H behavior at Tp= 1300,1500°C is discussed in terms of (i) the volume fraction of pores and the average pore size, (ii) the bond density of the oxycarbide network, and (iii) the occurrence of a nanocrystalline SiC phase. [source] Influence of the OMCs pore structures on the capacitive performances of supercapacitorASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2009Gu-Zhen Nong Abstract In the present study, two mesoporous carbons OMC-KIT-6 and OMC-SBA-16 were nanocasted using mesoporous silica of KIT-6 and SBA-16 as templates and furfuryl alcohol as carbon precursor. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) characterizations confirmed that the resultant samples are mesoporous carbons, and the as-prepared OMC-KIT-6 has an Ia3d ordered structure, whereas OMC-SBA-16 belongs to Im3m space group. The surface area and the average pore size are (1658 m2 g,1 and 3.4 nm) for OMC-KIT-6 and (1638 m2 g,1 and 2.9 nm) for OMC-SBA-16, respectively. The results of cyclic voltammograms and galvanostatic charge-discharge tests show that these two mesoporous carbons have excellent capacitive performances. But the difference of capacitive behavior between OMC-KIT-6 and OMC-SBA-16 may be a result of the difference of pore geometries of these two carbons. In order to find out the function of mesopore in a supercapacitor, we compared the capacitive properties of mesoporous and microporous carbons; the experiment results indicated that these two kinds of carbon exhibit nearly ideal capacitive behavior at low scan rate. When the scan rate is enhanced up to 50 mV s,1 the performance of mesoporous carbon is more stable than microporous carbon. This outcome demonstrated that mesopore plays an important role in forming double layers in the electrode materials. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Effects of TiO2 Film on the Performance of Dye-sensitized Solar Cells Based on Ionic Liquid ElectrolyteCHINESE JOURNAL OF CHEMISTRY, Issue 12 2005Xu Pan Abstract Photo correlation spectroscopy was used to measure the particle size distribution of TiO2 films. Other parameters, such as porosity, BET surface area, average pore size, crystallite size D101, distribution of pore size etc. were also measured. The effects of these parameters on the ionic liquid based dye-sensitized solar cells (DSC) were studied. It was concluded that the particle size distribution of nanocrystalline TiO2 played an important role on the performance of DSC. The narrow particle size distribution of nanocrystalline TiO2 increased the efficiency of DSC, while the wide distribution decreased the efficiency of DSC. From the result above, it was also concluded that the photo correlation spectroscopy was a good method to identify the performance of TiO2 films. Based on electrochemical impedance spectroscopy, we found that the particle size distribution could affect the electronic contact between the TiO2 layers as well. The narrow particle size distribution made the electronic contact between TiO2 layers better than the wide particle size distribution of the TiO2 films, and then better the electronic contact, higher the efficiency of the DSC. [source] Characteristics of ammonia permeation through porous silica membranesAICHE JOURNAL, Issue 5 2010Masakoto Kanezashi Abstract A sol,gel method was applied for the preparation of silica membranes with different average pore sizes. Ammonia (NH3) permeation/separation characteristics of the silica membranes were examined in a wide temperature range (50,400°C) by measurement of both single and binary component separation. The order of gas permeance through the silica membranes, which was independent of membrane average pore size, was as follows: He > H2 > NH3 > N2. These results suggest that, for permeation through silica membranes, the molecular size of NH3 is larger than that of H2, despite previous reports that the kinetic diameter of NH3 is smaller than that of H2. At high temperatures, there was no effect of NH3 adsorption on H2 permeation characteristics, and silica membranes were highly stable in NH3 at 400°C (i.e., gas permeance remained unchanged). On the other hand, at 50°C NH3 molecules adsorbed on the silica improved NH3 -permselectivity by blocking permeation of H2 molecules without decreasing NH3 permeance. The maximal NH3/H2 permeance ratio obtained during binary component separation was ,30 with an NH3 permeance of ,10,7 mol m,2 s,1 Pa,1 at an H2 permeation activation energy of ,6 kJ mol,1. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] | |||||||||||||