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Gas Permeability (gas + permeability)
Selected AbstractsScaling Analysis of the Effect of Binder Content and Binder Distribution on the Gas Permeability of Porous Green CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2008Jeong Woo Yun Two models have been developed to describe how variations in binder content and binder distribution influence the specific surface and the gas permeability of porous media. In the Core-Shell model, a shell of binder surrounds each ceramic particle, and the specific surface increases with decreasing volume fraction of binder. In the Multi-Sphere model, binder particles occupy the interstices between the ceramic particles, and the specific surface generally decreases with decreasing volume fraction of binder. The variation in the permeability with binder content predicted by each model is different as compared with the case of a constant specific surface. [source] Barrier properties of blends based on liquid crystalline polymers and polyethylenePOLYMER ENGINEERING & SCIENCE, Issue 9 2000G. Flodberg Blends of an extrusion-grade polyethylene and two different liquid crystalline polymers of Vectra type were prepared by melt mixing using poly(ethylene-comethacrylic acid) as compatibilizer. Oxygen and water vapor permeability, transparency and welding strength of compression molded and film blown specimens were studied. The compression molded blends showed gas permeabilities conforming to the Maxwell equation assuming low permeability liquid crystalline polymer spheres in a high permeability polyethylene matrix. One of the liquid crystalline polymers with suitable rheological properties formed a more continuous phase in the film blown blends and a substantial decrease in oxygen and water vapor permeability was observed in these blends. The compression molded blends with 50% liquid crystalline polymer and some of blow molded blends showed very high gas permeabilities. It is believed that voids forming continuous paths through the structure were present in these samples. The blends showed significantly higher opacity than pure polyethylene. [source] Novel Polymer Electrolyte Membranes for Automotive Applications , Requirements and Benefits,FUEL CELLS, Issue 4 2004C. Wieser Abstract During the past few years, the feasibility of using polymer electrolyte fuel cells in automotive power trains at an impressive performance level has been proven repeatedly. However, current fuel cell stacks are still largely based on decade-old polymer electrolyte membrane technology thus limiting performance, durability, reliability, and cost of the fuel cell systems. The major challenge for membrane R&D constitutes the demand for polymer electrolytes that allow for system operation at higher temperatures and lower water management requirements without increased conduction losses. None the less, demanding automotive requirements will not compromise on other properties such as mechanical and chemical stability and gas permeability. [source] A Case Study of Soil-Gas Sampling in Silt and Clay-Rich (Low-Permeability) SoilsGROUND WATER MONITORING & REMEDIATION, Issue 1 2009Todd A. McAlary Soil-gas sampling and analysis is a common tool used in vapor intrusion assessments; however, sample collection becomes more difficult in fine-grained, low-permeability soils because of limitations on the flow rate that can be sustained during purging and sampling. This affects the time required to extract sufficient volume to satisfy purging and sampling requirements. The soil-gas probe tubing or pipe and sandpack around the probe screen should generally be purged prior to sampling. After purging, additional soil gas must be extracted for chemical analysis, which may include field screening, laboratory analysis, occasional duplicate samples, or analysis for more than one analytical method (e.g., volatile organic compounds and semivolatile organic compounds). At present, most regulatory guidance documents do not distinguish between soil-gas sampling methods that are appropriate for high- or low-permeability soils. This paper discusses permeability influences on soil-gas sample collection and reports data from a case study involving soil-gas sampling from silt and clay-rich soils with moderate to extremely low gas permeability to identify a sampling approach that yields reproducible samples with data quality appropriate for vapor intrusion investigations for a wide range of gas-permeability conditions. [source] Experimental study and constitutive modelling of elasto-plastic damage in heat-treated mortarINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 4 2010Xiao-Ting Chen Abstract This study investigates the effect of a heat-treatment upon the thermo-mechanical behaviour of a model cement-based material, i.e. a normalized mortar, with a (w/c) ratio of 0.5. First, a whole set of varied experimental results is provided, in order to either identify or validate a thermo-mechanical constitutive model, presented in the second paper part. Experimental responses of both hydraulic and mechanical behaviour are given after different heating/cooling cycling levels (105, 200, 300, 400,C). The reference state, used for comparison purposes, is taken after mass stabilization at 60,C. Typical uniaxial compression tests are provided, and original triaxial deviatoric compressive test responses are also given. Hydraulic behaviour is identified simultaneously to triaxial deviatoric compressive loading through gas permeability Kgas assessment. Kgas is well correlated with volumetric strain evolution: gas permeability increases hugely when ,v testifies of a dilatant material behaviour, instead of contractile from the test start. Finally, the thermo-mechanical model, based on a thermodynamics approach, is identified using the experimental results on uniaxial and triaxial deviatoric compression. It is also positively validated at residual state for triaxial deviatoric compression, but also by using a different stress path in lateral extension, which is at the origin of noticeable plasticity. Copyright © 2009 John Wiley & Sons, Ltd. [source] Rheology behavior of high-density polyethylene/diluent blends and fabrication of hollow-fiber membranes via thermally induced phase separationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2010Jianli Wang Abstract The phase-separation behavior of high-density polyethylene (HDPE)/diluent blends was monitored with a torque variation method (TVM). The torque variation of the molten blends was recorded with a rheometer. It was verified that TVM is an efficient way to detect the thermal phase behavior of a polymer,diluent system. Subsequently, polyethylene hollow-fiber membranes were fabricated from HDPE/dodecanol/soybean oil blends via thermally induced phase separation. Hollow-fiber membranes with a dense outer surface of spherulites were observed. Furthermore, the effects of the spinning temperature, air-gap distance, cold drawing, and HDPE content on the morphology and gas permeability of the resultant membranes were examined. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Relationship between gas transport properties and fractional free volume determined from dielectric constant in polyimide films containing the hexafluoroisopropylidene groupJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Sou Miyata Abstract The dielectric constant and gas transport properties (i.e., permeability, diffusivity, and solubility) in 2,2,-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA)-based polyimides were systematically investigated in terms of their polymer fractional free volumes (FFVs) at 30°C. The permeability and diffusion coefficients of the 6FDA-based polyimide films to hydrogen, oxygen, nitrogen, methane, and carbon dioxide were correlated with their FFVs estimated using van Krevelen's group contribution method. There appeared, however, small linear correlation coefficients. Linear correlations were also observed between the gas transport properties and dielectric constant of these polyimides. This study described FFVas a function of the dielectric constant based on the Clausius-Mossotti equation. It was found that the gas permeability and diffusion coefficients of these 6FDA-based polyimide films increased as their dielectric constant-based FFV increased. A better linear relationship was observed between the gas transport properties and the FFV determined from the polymer dielectric constant in comparison to that estimated using the group contribution method. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008 [source] Poly[1-(trimethylgermyl)-1-propyne] and poly[1-(trimethylsilyl)-1-propyne] with various geometries: Their synthesis and propertiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2003V. S. Khotimsky Abstract The polymerization of 1,2-disubstituted acetylenes [1-(trimethylgermyl)-1-propyne and 1-(trimethylsilyl)-1-propyne] initiated by Nb- and Ta-based catalytic systems was studied within a wide temperature range (,10 to +80 °C) with solvents (cyclohexane, CCl4, toluene, anisol, and n -chlorobutane) with variable dielectric constants (2.023,7.390). Conditions ensuring the synthesis of poly[1-(trimethylsilyl)-1-propyne] (PTMSP) containing 20,80% cis units and poly[1-(trimethylgermyl)-1-propyne] (PTMGP) containing 3,65% cis units were determined. The PTMSP and PTMGP samples were amorphous, exhibited a two-phase structure characterized by the presence of less ordered regions and regions with an enhanced level of ordering, and differed in solubility. A correlation was found between the cis/trans ratio and the morphology, the geometrical density of PTMSP and PTMGP films, and the gas permeability of the polymers. The gas permeability and solubility behavior of PTMSP and PTMGP were examined in terms of the molecular characteristics of the polymer samples (the thermodynamic Kuhn segment and the Kerr electrooptic effect). It was demonstrated that the gas permeability, as well as the solubility of the polymers, was defined by their supramolecular ordering, which depended on the lengths of continuous sequences composed of units of analogous microstructures and on the flexibility of macrochains. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2133,2155, 2003 [source] Scaling Analysis of the Effect of Binder Content and Binder Distribution on the Gas Permeability of Porous Green CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2008Jeong Woo Yun Two models have been developed to describe how variations in binder content and binder distribution influence the specific surface and the gas permeability of porous media. In the Core-Shell model, a shell of binder surrounds each ceramic particle, and the specific surface increases with decreasing volume fraction of binder. In the Multi-Sphere model, binder particles occupy the interstices between the ceramic particles, and the specific surface generally decreases with decreasing volume fraction of binder. The variation in the permeability with binder content predicted by each model is different as compared with the case of a constant specific surface. [source] Biodegradable Polylactide and Its Nanocomposites: Opening a New Dimension for Plastics and CompositesMACROMOLECULAR RAPID COMMUNICATIONS, Issue 14 2003Suprakas Sinha Ray Abstract The academic and industrial aspects of the preparation, characterization, mechanical and materials properties, crystallization behavior, melt rheology, and foam processing of pure polylactide (PLA) and PLA/layered silicate nanocomposites are described in this feature article. Recently, these materials have attracted considerable interest in polymer science research. PLA is linear aliphatic thermoplastic polyester and is made from agricultural products. Hectorite and montmorillonite are among the most commonly used smectite-type layered silicates for the preparation of nanocomposites. Smectites are a valuable mineral class for industrial applications because of their high cation exchange capacities, surface area, surface reactivity, adsorptive properties, and, in the case of hectorite, high viscosity, and transparency in solution. In their pristine form, they are hydrophilic in nature, and this property makes them very difficult to disperse into a polymer matrix. The most common way to overcome this difficulty is to replace interlayer cations with quaternized ammonium or phosphonium cations, preferably with long alkyl chains. In general, polymer/layered silicate nanocomposites are of three different types: (1) intercalated nanocomposites, in which insertion of polymer chains into the layered silicate structure occurs in a crystallographically regular fashion, regardless of polymer to layered silicate ratio, with a repeat distance of few nanometer; (2) flocculated nanocomposites, in which intercalated and stacked silicate layers are sometimes flocculated due to the hydroxylated edge,edge interactions between the silicate layers; (3) exfoliated nanocomposites, in which individual silicate layers are uniformly distributed in the polymer matrix by average distances that totally depend on the layered silicate loading. This new family of composite materials frequently exhibits remarkable improvements in its material properties when compared with those of virgin PLA. Improved properties can include a high storage modulus both in the solid and melt states, increased flexural properties, a decrease in gas permeability, increased heat distortion temperature, an increase in the rate of biodegradability of pure PLA, and so forth. Illustration of the biodegradability of PLA and various nanocomposites. [source] Modified atmosphere packaging of fresh produce using microporous earthenware materialPACKAGING TECHNOLOGY AND SCIENCE, Issue 5 2006Jung Hyun Yun Abstract Microporous earthenware sheets of 5.5,5.6mm thickness were fabricated with or without a glazing treatment by passing through a sequential firing procedure in a furnace. Their microstructure and gas permeability against oxygen and carbon dioxide were measured and examined for their usability in modified atmosphere packaging of fresh produce. Compared with plastic packaging materials, earthenware sheets with a high proportion of micropores had very high gas permeability and gave CO2:O2 permeability ratios close to 1. Glazing treatment smoothed the surface by clogging the pores on the surface and significantly decreased gas permeability, without affecting the internal microstructure of the earthenware. When the earthenware sheet was combined with a plastic box and used in packaging for strawberries and enoki mushrooms at 5°C, its unique permeability properties developed a modified atmosphere that was beneficial for preserving the quality of the produce. Changes in the earthenware's permeability characteristics due to moisture adsorption and condensation need to be resolved so that the dynamic changes occurring in package atmosphere over time can be better understood. Copyright © 2006 John Wiley & Sons, Ltd. [source] Steady-state field-scale gas permeability estimation and pore-gas velocity calculation in a domain open to the atmosphereREMEDIATION, Issue 4 2000Dominic C. Digiulio Field-scale estimation of gas permeability and subsequent computation of pore-gas velocity profiles are critical elements of sound soil venting design. It has been our experience, however, in U.S. Environmental Protection Agency's (EPA's) technical assistance program, provided by the Office of Research and Development in support EPA regional offices, that many venting practitioners are unaware of equations and data interpretation methods appropriate for gas permeability estimation and pore-gas velocity computation. To ameliorate this situation, we use data collected at a U.S. Coast Guard Station in Traverse City, Michigan, to demonstrate gets permeability estimation and pore-gas velocity calculation for steady-state, axisymmetric, two-dimensional gas flow in a domain open to the atmosphere. For gas permeability estimation, we use random guesses constrained with decreasing intervals of radial and vertical permeabilityand analysis of root mean square errors to ensure attainment of a global versus local minimum. We demonstrate confidence in permeability estimation by providing plots of observed versus simulated pressure response. Finally, we illustrate how plots of pore-gas velocity as a function of distance and flow rate can be helpful in venting design. [source] | |||||||||||||