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Porosity Values (porosity + value)
Selected AbstractsAerogel and Xerogel Catalysts Based on ,-Alumina Doped with Silicon for High Temperature ReactionsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 3 2005Aurelien Florin Popa Abstract Numerous materials (supports and catalysts) based on alumina have been prepared using the sol-gel process and carbon dioxide supercritical drying. In this work two types of solids, i.e. xerogels and aerogels, were systematically compared and a way of introducing platinum metal with a content of 5% percent by weight was examined. The structural data, the surface area, Pt dispersion and catalytic activity for the decomposition of the propellant were measured for the various samples. The (Al2O3)0.88(SiO2)0.12 samples prepared show very interesting porosity values, especially for the aerogel. For this reason, they were chosen as supports for the synthesis of 5 wt% platinum on alumina catalysts. The results presented in this work allowed us to obtain an overall view of the influence of the preparation mode on the properties of platinum on alumina supported catalysts. The dispersion of the metal phase is directly dependent on the specific surface of the support. A significant value for the surface area implies a large amount of centers for interaction with the metal precursor and, consequently, the appearance of more centres of simultaneous germination. Although aerogels obtained by carbon dioxide supercritical drying always show superior properties compared with xerogels, for catalytic decompositions the xerogels still remain superior. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Shrinkage of initially very wet soil blocks, cores and clods from a range of European Andosol horizonsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2007F. Bartoli Summary In advanced stages of volcanic ash soil formation, when more clay is formed, soil porosity values and soil water retention capacities are large and the soils show pronounced shrinkage on drying. Soil shrinkage is a key issue in volcanic soil environments because it often occurs irreversibly when topsoils dry out after changes from permanent grassland or forest to agriculture. European Andosols have developed in a wide range of climatic conditions, leading to a wide range in intensity of both weathering and organo-mineral interactions. The question arises as to whether these differences affect their shrinkage properties. We aimed to identify common physically based shrinkage laws which could be derived from soil structure, the analysis of soil constituents, the selected sampling size and the drying procedure. We found that the final volumetric shrinkage of the initially field-wet (56,86% of total porosity) or capillary-wet (87,100% of total porosity) undisturbed soil samples was negatively related to initial bulk density and positively related to initial capillary porosity (volumetric soil water content of soil cores after capillary rise). These relationships were linear for the soil clods of 3,8 cm3, with final shrinkage ranging from 21.2 to 52.2%. For soil blocks of 240 cm3 and soil cores of 28.6 cm3 we found polynomial and exponential relationships, respectively, with thresholds separating shrinkage and nearly non-shrinkage domains, and larger shrinkage values for the soil cores than for the soil blocks. For a given sample size, shrinkage was more pronounced in the most weathered and most porous Andosol horizons, rich in Al-humus, than in the less weathered and less porous Andosol horizons, poor in Al-humus. The Bw horizons, being more weathered and more porous, shrank more than the Ah horizons. We showed that the structural approach combining drying kinetics under vacuum, soil water analysis and mercury porosimetry is useful for relating water loss and shrinkage to soil structure and its dynamics. We also found that the more shrinkage that occurred in the Andosol horizon, the more pronounced was its irreversible mechanical change. [source] Random porosity fields and their influence on the stability of granular mediaINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 10 2008José E. Andrade Abstract It is well established that the mechanical behavior of granular media is strongly influenced by the media's microstructure. In this work, the influence of the microstructure is studied by integrating advances in the areas of geostatistics and computational plasticity, by spatially varying the porosity on samples of sand. In particular, geostatistical tools are used to characterize and simulate random porosity fields that are then fed into a nonlinear finite element model. The underlying effective mechanical response of the granular medium is governed by a newly developed elastoplastic model for sands, which readily incorporates spatial variability in the porosity field at the meso-scale. The objective of this study is to assess the influence of heterogeneities in the porosity field on the stability of sand samples. One hundred and fifty isotropic and anisotropic samples of dense sand are failed under plane-strain compression tests using Monte Carlo techniques. Results from parametric studies indicate that the axial strength of a specimen is affected by both the degree and orientation of anisotropy in heterogeneous porosity values with anisotropy orientation having a dominant effect, especially when the bands of high porosity are aligned with the natural orientation of shear banding in the specimen. Copyright © 2007 John Wiley & Sons, Ltd. [source] DETERMINATION OF COOLNESS AND DAMPNESS SENSATIONS CREATED BY FABRICS BY FOREARM TEST AND FABRIC MEASUREMENTSJOURNAL OF SENSORY STUDIES, Issue 4 2009SIBEL KAPLAN ABSTRACT Clothing is continuously in an interaction with the body both thermally and mechanically. Different sensations constituting the comfort status of a person arise as a result of this interaction. Coolness sensation perceived during skin-fabric contact is one of these sensations arising from the transient heat flow from skin to the fabric as skin is usually warmer than clothing. In this study, coolness to touch and dampness sensations created by knitted fabrics having different compositions and physical surface characteristics were investigated by forearm test conducted on seven males. Besides physical properties (weight, yarn count, thickness, density), surface roughness and friction properties of the inner surfaces of the fabrics touching the skin were also determined. Microscopic photographs were taken to have an idea about hairiness properties of the inner surfaces and optical porosity values were calculated by analysis of the microscopic images by using MATLAB software. It was found out that coolness and dampness sensations arise during skin,fabric contact are mostly related to the permeability and surface roughness characteristics of fabrics, and the effect of fabric material is more on dampness sensation than coolness sensation. PRACTICAL APPLICATIONS In the recent years, consumers pay attention more to the mechanical, thermal and visual sensations stimulated by the dynamic body,clothing interactions besides the aesthetic properties of their clothing. They take into consideration feelings they have during first touch with the clothing into their purchase decisions. Coolness to touch sensation perceived during first contact with the fabric and dampness sensation , which is very important during wear conditions including sweating , are two of them and they are related to the thermophysiological aspect of clothing comfort. For producing garments giving desirable feelings, it is very important to determine fabric properties influencing these sensations. A subjective evaluation method , the forearm test , was used to find out the relationships between coolness and dampness sensations and fabric properties. Results of this study are thought to be beneficial data for fabric manufacturers aiming to produce clothing for specific end users. [source] Phonon polariton modes in porous III,V semiconductorsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2005K. S. Joseph Wilson Abstract The phonon polariton modes in the bulk porous III,V semiconductor materials like GaP and GaAs are investigated for different porosity values. Their behavior under an external hydrostatic pressure is also studied. The frequencies of the various modes shift to higher values. The model has been extended to the case of self assembled GaP quantum dots (QDOTs) in GaAs matrix. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||