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Open Porosity (open + porosity)
Selected AbstractsBulk Nanoporous Metal for ActuationADVANCED ENGINEERING MATERIALS, Issue 8 2010Hai-Jun Jin Abstract Nanoporous metals prepared by controlled chemical or electrochemical corrosion of alloys can provide prototypical manifestations of bulk nanostructured material. Samples are readily prepared with dimensions at the millimeter or centimeter scale, while at the same time the microstructure is a homogeneous array of interpenetrating solid skeleton phase and pore channels with a characteristic size that can reach down to below 5,nm. The interest in nanoporous metals as functional materials derives from recent observations of unique materials behavior resulting from their extremely small structure size and their open porosity with large volume-specific surface area. As an example, this article discusses the possible use of nanoporous metal for actuation. [source] Manufacture of Biomorphic SiC Components with Homogeneous Properties from Sawdust by Reactive Infiltration with Liquid SiliconJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2010Noelia R. Calderon Biomorphic SiC components with homogeneous properties were manufactured from sawdust using a novel method to produce preforms, without addition of any extra binder, but with enough mechanical strength to be carbonized up to 1400°C without deformation. Reactive infiltration of carbon preforms of an adequate open porosity with liquid silicon has been successfully used to prepare biomorphic components. Moreover, the modification of bioSiC properties induced by the structural rearrangement of carbon preforms when they are further heat treated at 2500°C was additionally studied. BioSiC components showed a maximum in bending strength when the material is processed from carbon preforms exhibiting around 40% of open porosity, which seems to be the optimum value for carbon preforms treated at 1400° and 2500°C. However, the heat treatment of the carbon preforms at 2500°C produced bioSiC components with a finer and more homogeneous microstructure than those obtained from carbon preforms treated at 1400°C, improving their bending strength up to 22%. [source] Effects of Oxidation Curing and Sintering Additives on the Formation of Polymer-Derived Near-Stoichiometric Silicon Carbide FibersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2008Lifu Chen The effects of oxygen pick-up and sintering additives on the formation of silicon carbide (SiC) fibers from polyaluminocarbosilane are studied. It has been found that the strict control of oxygen pick up during the oxidation curing is essential to produce near-stoichiometric SiC fibers. When the molar ratio of oxygen to excess carbon in the pyrolyzed fibers (SiCxOy) is slightly over 1 (O/CExcess=y/(x,1)>1), the excess carbon is eliminated during the subsequent sintering as CO and CO2 as a result of the decomposition of SiCxOy; the remaining oxygen is removed as SiO and CO vapor, leaving near-stoichiometric SiC as the residue. However, with still increasing oxygen pick up, the final ceramic fibers become more porous and rich in silicon. The evolution of CO, CO2, and SiO generates high porosity in the absence of a sintering additive, leading to low fiber density. The inter-connected and open porosity favors the formation of CO. In contrast, for the fibers containing aluminum (Al) or Al/B sintering additives, the pores are much smaller and essentially closed, favoring the formation of CO2. Therefore, after sintering at 1800°C, the fibers without sintering additives contain excess silicon, while those with sintering additives are near stoichiometric. Al is beneficial to the densification but it alone cannot produce fibers of high density. When B is added in addition to Al, the fibers can be sintered to nearly full density. [source] Preparation of a Porous Cermet SOFC Anode Substrate by Gelcasting of NiO,YSZ PowdersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2007Kuttan Prabhakaran A porous NiO,YSZ substrate for anode-supported solid oxide fuel cells has been prepared by gelcasting of NiO,YSZ powders using urea,formaldehyde monomers, followed by humidity-controlled drying, binder removal, and sintering of the gelled bodies. The gelled bodies had sufficient strength to remove even 2-mm-thick samples from the mold immediately after gelation. A gelcast NiO,YSZ sample sintered at 1450°C for 2 h showed an open porosity of ,53 vol%, and the porosity increased to ,58% upon reduction with hydrogen. Pore sizes measured on the scanning electron microscopy photomicrograph of NiO,YSZ and Ni,YSZ cermet substrates are in the range of 2,5 ,m. Urea,formaldehyde polymer, present in a high amount (,13 wt%) in the gelcast body, acts as a template for pores. [source] Sintering Behavior and Properties of Iron-Rich Glass-CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2004Alexander Karamanov Iron-rich glass-ceramics were obtained by the sintering of two glass powders, labeled G1 and G2, at heating rates of 5° and 20°C/min followed by an isothermal step in the 850°,1050°C temperature interval. The sintering process was evaluated by the linear shrinkage; the closed porosity was estimated by density measurements; the structure and the morphology of the glass ceramics were observed by scanning electron microscopy. The bending strength, the Young modulus, and Vickers hardness of the glass-ceramics materials were evaluated. The results showed that the sintering process and morphology of the glass-ceramics depends on the amount of magnetite and pyroxene formed. With a low percentage of crystal phase formed (25%,30% typical of G1) the structure is characterized by closed porosity; at higher crystallization (45%,50% typical of G2) open porosity is mainly formed. The properties of the glass-ceramics were not influenced by the heating rate but improved with an increase in the degree of crystallization. [source] Alkoxide Sol-Gel-Processed Cordierite FiberJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2002Mu-Tsun Tsai An alkoxide sol-gel route was developed to prepare stoichometric cordierite fibers. The influences of the aging treatment and heating rate on the sinterability of the gel fibers were also examined. X-ray diffraction analysis revealed that the unaged and aged fibrous gels all remained amorphous <800&, but began crystallization into ,-cordierite and ,-cordierite at ,900°C and 1050°C, respectively; single-phase ,-cordierite fibers were obtained at 1300°C. Heating the unaged fibers yielded denser microstructures, with fine grain sizes of ,0.2,0.4 ,m, whereas the aged fibers exhibited porous microstructures following heating at 1300°C. A higher heating rate and aging treatment resulted in a higher open porosity of the fired fiber. [source] | ||||||||||