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Different Porosities (different + porosity)
Selected AbstractsThe High-Temperature Oxidation Behavior of Reaction-Bonded Porous Silicon Carbide Ceramics in Dry OxygenJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2010Chuanwei Zheng The oxidation behavior of reaction-bonded porous silicon carbide (RPSC) ceramics in dry oxygen between 1100° and 1500°C was investigated based on four specimens with different porosities. RPSC ceramics exhibited a rapid mass increase in the initial stage of oxidation but a slow mass increase in the following oxidation, which was considerably different from the oxidation behavior of dense SiC. The oxidation kinetics for RPSC can be better represented by an asymptotic law rather than the parabolic law for dense SiC. We suppose that, although oxidation occurred in the entire pore channels at the beginning, the pores were rapidly blocked by the oxide as their growth rate near the pore mouth was very fast due to sufficient oxygen. As the result, the oxidation of the pore interior was stopped in the absence of further oxygen supply. [source] Fabrication of Gradient Pore TiO2 Sheets by a Novel Freeze,Tape-Casting ProcessJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2007Linlin Ren Gradient pore structure TiO2 sheets were fabricated by a novel freeze,tape-casting process. Aqueous TiO2 ceramic slurries were prepared by the traditional tape-casting processing and were then cast onto an aluminum foil carrier. The slurries were immediately frozen on the substrate, whose temperature was about ,18°C. After freezing completely, the green sheets were then dried in a lyophilizer. Freeze,tape casting led to formation of a gradient pore microstructure of the TiO2 sheet. The results showed that the solid loading of slurry considerably affected the pore microstructure, pore morphology, and the porosity. Solid loadings of 10, 20, 30, 40, and 50 wt% slurries were used, respectively, and the gradient pore structure TiO2 sheets with different porosities of 75%,88% were obtained. [source] Mesoporous GaAs double layers for layer transfer processesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 12 2009Enrique Garralaga Rojas Abstract Mesoporous GaAs double layers with different porosities and thicknesses up to 7,µm are formed on highly doped p-type 4,inch GaAs substrates by means of electrochemical etching in highly concentrated hydrofluoric acid electrolytes. Small ,111, oriented pyramids form at the interface between porous layer and substrate if etching current densities below 7.5,mA,cm,2 are applied. Porous double layers with different porosities are obtained by varying simultaneously the etching current density and the electrolyte concentration. The porosity of the porous GaAs layers decreases nearly linearly from 69 to 53% with electrolyte concentrations increasing from 30 to 50,wt.%, respectively. The etching process increases the mean roughness of the porous layer surface from 0.15 to 0.24,nm. [source] Preparation and mechanical properties of poly(chitosan- g - DL -lactic acid) fibrous mesh scaffoldsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 2 2008Ying Wan Abstract DL -lactic acid was grafted onto chitosan to produce poly(chitosan- g - DL -lactic acid)(PCLA) without using a catalyst. These PCLAs were then spun into filaments and further fabricated into fibrous mesh scaffolds using an improved wet-spinning technique. The diameter of filaments in different scaffolds could vary from a few micrometers to several tens of micrometers. The scaffolds exhibited various pore sizes ranging from about 20,µm to more than 200,µm and different porosities up to 80%. The several main processing conditions were optimized for obtaining the desired scaffolds with well-controlled structures. The tensile and compressive mechanical properties of the mesh scaffolds in both dry and hydrated states were mainly examined. Significantly improved tensile strength and modulus, enhanced compressive modulus, and stress as well as the dimensional stability for these mesh scaffolds in their hydrated state were observed. Copyright © 2007 John Wiley & Sons, Ltd. [source] Centrifugal seeding of mammalian cells in nonwoven fibrous matricesBIOTECHNOLOGY PROGRESS, Issue 1 2010Robin Ng Abstract Three-dimensional (3D) cell cultures have many advantages over two-dimensional cultures. However, seeding cells in 3D scaffolds such as nonwoven fibrous polyethylene terephthalate (PET) matrices has been a challenge task in tissue engineering and cell culture bioprocessing. In this study, a centrifugal seeding method was investigated to improve the cell seeding efficiency in PET matrices with two different porosities (93% and 88%). Both the centrifugal force and centrifugation time were found to affect the seeding efficiency. With an appropriate centrifugation speed, a high 80,90% cell seeding efficiency was achieved and the time to reach this high seeding efficiency was less than 5 min. The seeding efficiency was similar for matrices with different porosities, although the optimal seeding time was significantly shorter for the low-porosity scaffold. Post seeding cell viability was demonstrated by culturing colon cancer cells seeded in PET matrices for over 5 days. The centrifugal seeding method developed in this work can be used to efficiently and uniformly seed small fibrous scaffolds for applications in 3D cell-based assays for high-throughput screening. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] Analysis of the parameters of the sintered loop heat pipeHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 8 2004K.J. Zan Abstract The purpose of this paper is to establish an experimental formula for sintered dendritic nickel powder. For this reason, wick structures with different porosity ranging from 65 to 80% were fabricated by cold pressing sintering process at fixed porosity and their parameters that included porosity, pore radius, and permeability were also measured. According to both the capillary limitation and the present experimental formula of the sintered dendritic nickel powder, the wick structure parameters that would affect the heat transfer capacity of the loop heat pipe (LHP) were analyzed theoretically and then investigated experimentally. The results showed that there exists an optimal combination of wick structure parameters by which the performance of the LHP would achieve optimization. The maximum heat transfer capacity was up to 500 W and the thermal resistance was 0.12°C/W at the allowable working temperature 80°C. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(8): 515,526, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20034 [source] Observation of nanocrystals in porous stain-etched germaniumPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003V. A. Karavanskii Abstract Porous nanocrystalline films were prepared by stain etching and subsequent annealing in hydrogen at 600 °C. The structural properties of the as-etched and annealed films were investigated using Raman scattering and various X-ray techniques. It was shown that the as-etched film had a thickness of ,2 ,m and consisted of two sublayers of different porosity and amorphous-like microstructure The annealing did not change essentially the porosity and thickness but resulted in notable crystallinity transformation. The results of Raman spectroscopy and X-ray measurements and modelling revealed the presence of germanium nanocrystals with mean sizes of about 8,10 nm in the annealed films. [source] Characterization of MOCVD grown GaN on porous SiC templatesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005F. Yun Abstract We have grown GaN layers by MOCVD on a set of nanoporous SiC templates with different porosity and morphology, produced by etching the anodized porous SiC starting material in a H2 environment at temperatures ,1500 °C, in an effort to attain improved films. The hydrogen etching serves to remove surface damage caused during mechanical polishing prior to anodization, remove the skin layer associated with anodization, tune the pore size, and consolidate pore geometry. Growth conditions favoring lateral overgrowth of GaN were employed on this set of samples to obtian GaN to a thickness of 2 µm. Atomically smooth surfaces were obtained for the epitaxial GaN layers. The GaN quality is highly dependent on the specifics of the porous templates used. An intensity increase of up to a factor of 30 was observed in the GaN excitonic peak compared to GaN grown on standard SiC substrate. The I-V data indicated significant reduction in the leakage current (in reverse bias) compared to GaN grown on standard SiC. The dependence of optical properties, crystalline quality, and surface morphology on the particulars of porous SiC templates is discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||