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Larger Pore Size (larger + pore_size)

Distribution by Scientific Domains

Polymers and Materials Science	60%

Selected Abstracts

Development, Analysis, and Application of a Glass,Alumina-Based Self-Constrained Sintering Low-Temperature Cofired Ceramic

INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 5 2007
Takahiro Takada
The effects of an inner constraint layer and alumina particles on the microstructure, strength, and shrinkage of the laminated low-temperature cofired ceramic (LTCC) green sheet were investigated. Alumina particles of several sizes were used in the inner-constraint layer in order to strengthen the LTCC substrate. Smaller alumina particles in the inner-constraint layer produced a substrate with a high bending strength. Sintering shrinkage in the x,y direction of the LTCC is related to the bending strength of the debinded alumina particle layer used for an inner-constraint layer. A larger pore size in the inner-constraint layer was found to increase the distance of the glass penetration from the glass,alumina layer into the inner-constraint layer. The total thickness of the constraint layer changes the shrinkage in the x,y direction and the bending strength. [source]

Paste extrusion control and its influence on pore size properties of PTFE membranes

ADVANCES IN POLYMER TECHNOLOGY, Issue 3 2007
Radium Huang
Abstract Polytetrafluoroethylene (PTFE) is a remarkable membrane material. Owing to its high-melting point, PTFE fine powder cannot be processed using conventional melting processing methods. Instead, techniques such as paste extrusion, rolling, and sintering have to be employed. Each processing step has an important influence on the final pore size quality within the membrane. In this paper, a PID controller (proportional-integral-derivative controller) was used to improve the properties of PTFE paste during the extrusion process and the quality of the PTFE membrane. A range of lubricant content (18, 20, and 22 wt%) was used to monitor the pressure drop at different extrusion speeds (0.5, 1, and 2 mm/s) and reduction ratios (RR = 26.47, 47.06, 80.06). It was found that a higher lubricant content and a higher reduction ratio resulted in a lower pressure drop. It was also found that a higher stretching temperature tends to result in larger pore size and broader pore size distribution at the same stretching rate. At a monitored and controlled constant low-extrusion speed, the porosity of PTFE membrane was increased from 38% to 55% and the mean pore size was decreased from 0.22 to 0.15 ,m because of less migration and more uniform distribution of lubricant during extrusion. Properties and the associated property uniformity of the PTFE extrudate affect the subsequent membrane-forming process and the final pore size and size distribution significantly. © 2008 Wiley Periodicals, Inc. Adv Polym Techn 26:163,172, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20099 [source]

Synthesis of macroporous polymer rods based on an acrylamide derivative monomer

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2006
Ruben Dario Arrua
Abstract New macroporous polymer rods were prepared by free-radical crosslinking copolymerization from N -acryloyl-tris(hydroxymethyl)aminomethane and N,N,-methylenebisacrylamide as a crosslinking agent with different porogenic mixtures and with azobisisobutyronitrile as an initiator. The porous properties of these materials were controlled through changes in the proportions of the porogenic mixture, the polymerization temperature, or the concentration of the crosslinking agent. Pore size distribution profiles that shifted toward a larger pore size were obtained in the following cases: when the percentage of the coporogen was increased, when the copolymerization reactions were carried out at a low temperature (55 °C), and when the crosslinking concentration was reduced. Alternatively, a porogenic mixture formed from dimethyl sulfoxide and a 1:1 combination of tetradecanol and poly(ethylene glycol) 6000 as coporogens yielded a polymer rod with a high porosity and pore size. These hydrophilic materials are promising as base supports for different chromatographic processes and as throughput bioreactors. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6616,6623, 2006 [source]

Activity of samarocene catalysts adsorbed on mesoporous silicates for the polymerization of methyl methacrylate

POLYMER INTERNATIONAL, Issue 11 2004
Dr Hajime Yasuda
Abstract A samarocene complex, (C5Me5)2SmMe(thf), was adsorbed on a series of mesoporous silicates of various pore sizes. Pre-treatment of the latter with AlMe3 before adding the complex was effective in deactivating the surface silanol functionalities. The silicates having relatively larger pore size tended to adsorb a larger amount of the complex. The polymerization of methyl methacrylate (MMA) by the complex adsorbed on the silicates with large pore sizes (>29 Å) quantitatively afforded highly syndiotactic poly(MMA)s with higher molecular weights compared with those obtained by the corresponding homogeneous system. Similar catalyst systems of smaller pore size were much less active. Copyright © 2004 Society of Chemical Industry [source]

Verifying the RTE model: ortho-positronium lifetime measurement on controlled pore glasses

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2007
S. Thraenert
Abstract In porous media, the vacuum lifetime of ortho-positronium (o-Ps) of , = 142 ns can be reduced markedly by pick-off annihilation (interaction with electrons of the host material). So the o-Ps lifetime is determined by the pore size which can be extracted by utilising approved models like the Tao-Eldrup model for pore sizes smaller than 1 nm and the Tokyo model or RTE model for larger pore sizes. The RTE model contains an explicit temperature dependence of the o-Ps lifetime. Experiments on controlled pore glasses (CPG) with different pore sizes (2-70 nm) at different temperatures (50-500 K) were performed to verify the RTE model. A general agreement for T = 300 K could be found. The temperature dependence of the lifetime, especially for low temperatures, could not be approved sufficiently. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]