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Ceramic Particles (ceramic + particle)
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] Design and Nanofabrication of Superconductor Ceramic Strands and Customized LeadsINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 2 2004Anatoly E. Rokhvarger We made possible an engineering application of the 18-year-old Nobel Prize-winning discovery of High Temperature Superconductor (HTS) ceramic particles. Guided by certain theories of physics and nano-science, we created the ceramic-silicone nanofabrication method where a silicone additive controls both the nanostructural evolution of the magnetically oriented HTS ceramic nano-grains by a 3D polymeric matrix scaffold and thermally induced nano-phase transformation. These result in the sintered granular superconductor ceramic composite material with the desirable superconducting nano-phase composition and 3D nanostructure including vortex-pinning network. The prototype HTS samples were nanofabricated in the form of adhesion substrate coated strands or surfaces or variously shaped bulk leads. [source] Differential apoptotic response of J774 macrophages to alumina and ultra-high-molecular-weight polyethylene particlesJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 1 2002Alain Petit We recently identified apoptosis in in vitro wear particle-stimulated macrophages. The recent explosion of interest in apoptosis lies in the fact that it is under positive and negative regulation through evolutionary conserved biochemical pathways. It may also be possible to modulate macrophage apoptosis in the treatment of periprosthetic osteolysis. The purpose of this study was to compare the macrophage response to identically sized particles of alumina ceramic (Al2O3) and ultra-high-molecular-weight polyethylene (UHMWPE) in terms of TNF-, release and induction of apoptosis. J774 mouse macrophages were incubated for 0,24 h in the presence of Al2O3 and UHMWPE particles. TNF-, release was measured by ELISA; Poly(ADP-ribose)polymerase (PARP) and caspase-3 expression was analyzed by Western blot; DNA fragmentation (DNA laddering) was visualized on agarose gel containing ethidium bromide. Al2O3 particles induced TNF-, release after 4 h incubation with concentrations reaching 483 and 800 pg/ml after 24 h with 125 and 250 particles/macrophage, respectively (control = 161 pg/ml) (P < 0.05 vs. control). The same concentrations of UHMWPE particles induced a much larger and significant TNF-, release after only 1 h incubation, increasing up to 6250 pg/ml after 24 h (P < 0.05 vs. control). Western blot analysis demonstrated that the active caspase-3 fragment (17 kDa) and the proteolytic PARP fragment (85 kDa) were expressed after 2 h incubation with 125 and 250 Al2O3 particles/macrophage. The active caspase-3 and the PARP fragment had lower expression and appeared after a longer incubation time (8 h) with 125 and 250 UHMWPE particles/macrophage. Finally, DNA fragmentation (DNA laddering) was observed after 16 h with 125 and 250 particles of Al2O3 per macrophage whereas no laddering was induced by UHMWPE particles even after 24 h incubation. This study shows that although both Al2O3 and UHMWPE particles induce TNF-, release, this stimulation was much greater (8,10 times higher) with UHMWPE than A12O3 (P < 0.05 vs. control). As well, the induction of apoptosis, as measured by activation of caspase-3, PARP cleavage and DNA laddering, is different for these two particles, being faster and more important with Al2O3 than UHMWPE. We hypothesize that the ability of Al2O3 to induce macrophage apoptosis may explain the lower TNF-, release observed with these particles and explain the differences seen in osteolysis patterns of ceramic,ceramic (CC) vs. metal,polyethylene (Mpe) articulations. In conclusion, apoptosis may be a major internal mechanism to decrease macrophage activity and may be a desired therapeutic endpoint. The identification of an apoptosis-related pathway in the macrophage response to ceramic particles provides crucial data for a rational approach in the treatment and/or prevention of periprosthetic osteolysis. © 2002 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved. [source] Synthesis of silicon nitride based ceramic nanoparticles by the pyrolysis of silazane block copolymer micellesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2006Kozo Matsumoto Abstract Diblock copolymer poly(1,1,3,N,N,-pentamethyl-3-vinylcyclodisilazane)- block- polystyrene (polyVSA- b -polySt) and triblock copolymer poly(1,1,3,N,N,-pentamethyl-3-vinylcyclodisilazane)- block- polystyrene- block -poly(1,1,3,N,N,-pentamethyl-3-vinylcyclodisilazane) (polyVSA- b -polySt- b -polyVSA), consisting of silazane and nonsilazane segments, were prepared by the living anionic polymerization of 1,1,3,N,N,-pentamethyl-3-vinylcyclodisilazane and styrene. PolyVSA- b -polySt formed micelles having a poly(1,1,3,N,N,-pentamethyl-3-vinylcyclodisilazane) (polyVSA) core in N,N -dimethylformamide, whereas polyVSA- b -polySt and polyVSA- b -polySt- b -polyVSA formed micelles having a polyVSA shell in n -heptane. The micelles with a polyVSA core were core-crosslinked by UV irradiation in the presence of diethoxyacetophenone as a photosensitizer, and the micelles with a polyVSA shell were shell-crosslinked by UV irradiation in the presence of diethoxyacetophenone and 1,6-hexanedithiol. These crosslinked micelles were pyrolyzed at 600 °C in N2 to give spherical ceramic particles. The pyrolysis process was examined by thermogravimetry and thermogravimetry/mass spectrometry. The morphologies of the particles were analyzed by atomic force microscopy and transmission electron microscopy. The chemical composition of the pyrolysis products was analyzed by X-ray fluorescence spectroscopy and Raman scattering spectroscopy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4696,4707, 2006 [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] Thick Nb-Doped Bismuth Titanate Film with Controllable Grain OrientationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2006Weiwu Chen In the current work, we reported a potential approach to obtain thick ceramic films with controllable grain orientation based on magnetic alignment and polymerization techniques. The slurry containing 40 vol% Bi4Ti2.96Nb0.04O12 (BINT) ceramic powder, monomer, initiator, and catalyst was drop coated on a Pt substrate and then moved into a vertical 10 T magnetic field. In 1,2 min, the ceramic particles were aligned by a strong magnetic force in slurry and then in situ locked by polymerization on the substrate. After sintering at 1000°C, a BINT ceramic film (50,80 ,m in thickness) with a highly a/b plane orientation was obtained. Theoretically, the grain orientation in the films can be easily controlled by adjusting the magnetic field direction. This approach is readily applicable to other materials with a non-cubic structure and is expected to facilitate the fast preparation of grain-oriented thick films. [source] Green Machining of a Thermoplastic Ceramic-Ethylene Ethyl Acrylate/Isobutyl Methacrylate CompoundJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2004Young-Hag Koh The machinability of a thermoplastic compound that consisted of 52 vol% ceramic particles and 48 vol% thermoplastic binders was investigated. To investigate the machining mechanisms, various blends of a ductile polymer (ethylene ethyl acrylate (EEA)) and a brittle polymer (isobutyl methacrylate (IBMA)) were used as thermoplastic binders. The fraction of IBMA to EEA in the blend was increased from 0 to 50 vol%. As the IBMA content was increased, the thermoplastic compound exhibited a stiffer stress versus strain response under compression because of the brittle nature of the IBMA polymer. The machinability of the thermoplastic compound was remarkably improved with increased IBMA content because of the mitigation of the extensive deformation of the thermoplastic compound. [source] Fabrication of Ceramic,Polymer Photonic Crystals by Stereolithography and Their Microwave PropertiesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2002Soshu Kirihara Three-dimensional photonic crystals with periodic variations in the dielectric constant were fabricated using a stereolithographic rapid prototyping method. The structures were composed of millimeter-scale ordered epoxy lattices in which ceramic particles with high dielectric constants (such as silica and titania) were dispersed. These crystals were designed to reflect microwaves via the formation of photonic band gaps in a gigahertz range. The attenuation of transmission amplitude through the photonic crystals, which was measured as a function of frequency using a network analyzer, clearly showed the formation of band gaps in the microwave range. [source] Analytical Electron Microscopy Study of Green Ceramics Formed from Aqueous Suspensions Using the Hydrolysis-Assisted Solidification ProcessJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2002a Novak During the hydrolysis-assisted solidification (HAS) of aqueous ceramic suspensions, aluminum hydroxides are formed that bind the ceramic particles into a stiff wet body. Transmission electron microscopy investigations of HAS-processed Al2O3 and ZrO2 green parts after drying revealed that the secondary phase is amorphous and distributed uniformly around the host ceramic particles. The estimated thickness of this layer was 3,5 nm. Moreover, areas of a few tens of nanometers in size were found at three-particle junctions that contained an amorphous phase and individual nanocrystals of boehmite. [source] Selective laser sintering of aluminium- and titanium-based composites: processing and characterisationPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2003S. Vaucher Abstract Metal matrix composites have been processed by selective laser sintering of metal-ceramic powder blends. The feasibility of manufacturing Al- and Ti-based composites reinforced with various ceramic particles has been assessed. The resulting microstructures are strongly dependent on the laser power and metal-ceramic reactivity. High laser power results in improved density. In-situ grown carbides develop during sintering in AlMg12,SiC and Ti-graphite systems. On the contrary, no discernible reaction has been observed in AlSi20,SiC and Ti-diamond systems. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Conductive composites of UHMWPE and ceramics based on the segregated network conceptPOLYMER ENGINEERING & SCIENCE, Issue 1 2000J. Bouchet The manufacturing of composites of ultra high molecular weight polyethylene and ceramics with conductive properties has been investigated. Attention has been focused on the lowering of the amount of filler necessary to achieve low resistivity. Using segregated networks, mixing large polymer particles and submicron metal or conductive ceramic particles may be an interesting route, provided that the processing method enables to generate the desired structures. Because sintering avoids the intimate blending of the components, it is a suitable technique for this aim. The combined effects of temperature, pressure and sintering time have been investigated. The influence of the blending of the solids on the covering of the polyethylene particles before the sintering has also been pointed out. The typical features related to the concept of a segregated network are discussed in connection with the morphologies of the polymer and ceramic particles. The successful application of the reduction of the percolation threshold by a segregated network in conductive composites of polymer and metallic particles is described. [source] A Method for the Detection of Defluidized Zones in Slurry Bubble ColumnsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003Ahad Emami Abstract The formation of defluidized zones was studied in a laboratory slurry bubble column equipped with heat transfer probes. The probes were small thermistors 2.4 mm in diameter. Dionized water and air were used as a liquid and gas phase, respectively. Solids were fine ceramic particles with mean size of 19.2 ,m and density of 2244 kg/m3. The effects of solids holdup (up to 30 wt% on gas free basis), gas superficial velocity (0.01-0.09 m/s), sparger height (0.01-0.09 m) on defluidized zones formation was studied. Cycle analysis of the local heat transfer fluctuations reliably detected the local formation of defluidized zones for each condition. La formation de zones défluidisées a été étudiée dans une colonne à bulles avec bouillie, équipée de sondes de transfert de chaleur. Les sondes étaient des petits thermistors de 2.4 mm de diamètre. De l'eau déionisée et de l'air constituaient les phases liquide et gazeuse. Les solides étaient des fines particules en céramique avec une taille moyenne de 19.2 µm et une densité de 2244 kg/m3. Les effets de la rétention solide (jusqu'à 30 % en masses sur base sans gaz), de la vitesse superficielle du gaz (0.01-0.09 m/s) et de la hauteur du distributeur de gaz ont été étudiés. L'analyse de cycle du transfert de local de chaleur a détecté de façon fiable la formation locale de zones défluidisées pour chaque condition. [source] Histomorphometric analysis of the osseointegration of four different implant surfaces in the femoral epiphyses of rabbitsCLINICAL ORAL IMPLANTS RESEARCH, Issue 11 2008Laurent Le Guehennec Abstract Objectives: The surface properties of titanium dental implants are key parameters for rapid and intimate bone,implant contact. The osseointegration of four implant surfaces was studied in the femoral epiphyses of rabbits. Material and methods: Titanium implants were either grit-blasted with alumina or biphasic calcium phosphate (BCP) ceramic particles, coated with a thin octacalcium phosphate (OCP) layer, or prepared by large-grit sand blasting and acid-etched (SLA). After 2 and 8 weeks of implantation, the bone-implant contact and bone growth inside the chambers were compared. Scanning electron microscopy (SEM) and profilometry showed distinct microtopographies. Results: The alumina-Ti, BCP-Ti and OCP-Ti groups had similar average surface roughness in the 1,2 ,m range whereas the SLA surface was significantly higher with a roughness averaging 4.5 ,m. Concerning the osseointegration, the study demonstrated a significantly greater bone-to-implant contact for both the SLA and OCP-Ti surfaces as compared with the grit-blasted surfaces, alumina- and BCP-Ti at both 2 and 8 weeks of healing. Conclusion: In this animal model, a biomimetic calcium phosphate coating gave similar osseointegration to the SLA surface. This biomimetic coating method may enhance the apposition of bone onto titanium dental implants. [source] | ||||||||||||||||||||||