Home About us Contact
|
Home About us Contact | ||
|
|
||
Al2O3 Particles (al2o3 + particle)
Selected AbstractsTailoring Materials Properties by Accumulative Roll Bonding,ADVANCED ENGINEERING MATERIALS, Issue 8 2010Tina Hausöl Accumulative roll bonding (ARB) as a method of severe plastic deformation (SPD) is an interesting established process to produce ultrafine-grained (UFG) sheet materials with high potential for light weight constructions. The ARB process offers a high flexibility for tailored material design. Al2O3 particles, carbon fibers and titanium foils are used as reinforcement of aluminum sheets introduced during accumulative roll bonding. Furthermore multicomponent materials are produced by cladding of different aluminum alloys. These sandwich-like structures allow to combine desired properties of the materials involved. Post-ARB heat treatment offers another possibility for tailoring materials properties of graded structures as shown by formation of TiAl3 in Al/Ti laminates. The tailored materials are investigated by means of SEM, EDX, nanoindentation experiments and tensile testing. [source] Neutron Diffraction Measurement of Residual Stresses in Friction Stir Processed Nanocomposite Surface Layer,ADVANCED ENGINEERING MATERIALS, Issue 8 2009Hanbing Xu FSP is used to introduce Al2O3 nano-sized particles to an Al 6061 alloy surface to form a hard, strong, and wear-resistant Al-Al2O3 nanocomposite layer. The residual stresses in the FSP zones (with and without Al2O3 particles) have been quantitatively analyzed using neutron diffraction. Results indicated tensile macro-level residual stresses in all three directions with peak values around 100 MPa longitudinally. [source] THIS ARTICLE HAS BEEN RETRACTED Effect of Silica Sol on the Properties of Alumina-Based Duplex Ceramic CoresINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 1 2008Yexia Qin A series of alumina-based ceramic cores sintered at 1300°C, 1400°C, and 1500°C for 5 h were prepared, and the phases and microstructures were characterized by X-ray diffraction and scanning electron microscopy. The effect of colloidal silica sols on the properties of ceramic core was discussed. The properties of these materials were determined. The results indicated that the microstructure of the core is characterized by the presence of substantially unreacted Al2O3 particles having a polycrystalline composition consisting essentially of in situ synthesized 3Al2O3·2SiO2 on the surface of the Al2O3 particles. The colloidal silica sol contents do not have an appreciable effect on the densification and shrinkage of the alumina ceramic core. The ceramic cores of 5 wt% colloidal silica sol contents sintered at 1500°C for 5 h showed the smallest creep deformation in the present research. [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, Microstructure, and Mechanical Properties of a Novel Ti2AlC/TiC/Al2O3In Situ CompositeJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2006D. L. Zhang This paper describes a novel process for synthesizing a Ti2AlC/TiC/Al2O3in situ composite. This route utilizes TiO2, carbon, and Al powders as raw materials, and involves high-energy mechanical milling and powder sintering. The Ti2AlC/TiC/Al2O3 bulk in situ composite produced has a phase composition of Ti2AlC,20 vol% TiC,35 vol% Al2O3 with fine Al2O3 particles (size: 0.5,15 ,m) embedded in a Ti2AlC/TiC matrix. The Ti2AlC grains exhibit a nanometer scale lamellar structure, and most of the Al2O3 grains contain fine cubic TiOmC1,m precipitates (size: 10,200 nm). The average hardness and bending strength of the composite are in the ranges of 11,12.5 GPa and 380,440 MPa, respectively. Here we have demonstrated that the mechanical performance (mainly hardness and bending strength) of the composite is directly correlated with the size of the Al2O3 particles present in the as-fabricated in situ composite. [source] Tribological Properties of Polycrystalline Ti3SiC2 and Al2O3 -Reinforced Ti3SiC2 CompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2006Chunfeng Hu Tribological properties of Ti3SiC2 and Al2O3 -reinforced Ti3SiC2 composites (10 and 20 vol% Al2O3) were investigated by using an AISI-52100 bearing steel ball dryly sliding on a linear reciprocating athletic specimen. The friction coefficients were found varying only in a range of 0.1 under the applied loads (2.5, 5, and 10 N), and the wear rates of the composites decreased with increasing Al2O3 content. The enhanced wear resistance is mainly attributed to the hard Al2O3 particles nail the surrounding soft matrix and decentrale the shear stresses under the sliding ball to reduce the wear losses. [source] Room-Temperature Freeze Casting for Ceramics with Nonaqueous Sublimable Vehicles in the Naphthalene,Camphor Eutectic SystemJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2004Kiyoshi Araki Freeze casting for Al2O3 was accomplished at room temperature with nonaqueous sublimable vehicles in the naphthalene,camphor eutectic system with a eutectic temperature of 31°C. A fully dense sintered body (>99.5% of theoretical density (T.D.)) was obtained with a eutectic composition vehicle, whereas at most 90% T.D. was obtained with an off-eutectic (i.e., hypo- or hypereutectic) composition vehicle due to formation of large uniquely shaped voids. Microstructural observation suggested that growing pro-eutectic crystals rejected the suspended Al2O3 particles to form large voids during the solidification process. At the eutectic composition, formation of fine lamellar microstructure in a solidified vehicle is considered to inhibit particle rejection resulting in large voids. [source] The Role of Functional Parameters for Topographical Characterization of Bone-Anchored ImplantsCLINICAL IMPLANT DENTISTRY AND RELATED RESEARCH, Issue 2 2006Anna Arvidsson MSc ABSTRACT Background, The surface topographical characterization of bone-anchored implants has been recommended to be based on amplitude, spatial, and hybrid parameters. There are also functional parameters that have the potential to describe characteristics important for a specific application. Purpose, The aim of the present study was to evaluate if parameters that have been described as functional in engineering applications are also relevant in the topographical characterization of bone-anchored implants. Materials and Methods, The surface topography of threaded titanium implants with different surface roughness (Sa, Sds, and Sdr) was analyzed with an optical interferometer, and five candidating functional parameters (Sbi, Sci, Svi, Sm, and Sc) were calculated. Examples of the same parameters for five commercially available dental implants were also calculated. Results, The highest core fluid retention index (Sci) was displayed by the turned implants, followed by fixtures blasted with 250- and 25-,m particles, respectively. Fixtures blasted with 75-,m Al2O3 particles displayed the lowest Sci value. This is the inverse order of the bone biological ranking based on earlier in vivo studies with the experimental surfaces included in the present study. Conclusion, A low core fluid retention index (Sci) seems favorable for bone-anchored implants. Therefore, it is suggested to include Sci to the set of topographical parameters for bone-anchored implants to possibly predict the biological outcome. [source] Retrievability of implant-retained crowns following cementationCLINICAL ORAL IMPLANTS RESEARCH, Issue 12 2008Christian Mehl Abstract Objectives: The purpose of this study was to assess the retrievability of cemented implant crowns using two different removal devices. The influence of five cement types and two cement application techniques was evaluated. Methods: Forty copings were cast from a CoCr alloy for 40 tapered titanium abutments (5° taper, 4.3 mm diameter, 6 mm height, Camlog, Germany). Twenty copings were modeled as single crowns, whereas 20 copings were modeled with an extension to simulate fixed partial dentures (FPDs). Before cementation, the inner surfaces of the copings were air-abraded (50 ,m Al2O3 particles at 2.5 bars), while the abutments were used as delivered with machined surfaces. Copings were cemented with eugenol-free zinc oxide (Freegenol), zinc phosphate (Harvard), glass ionomer (Ketac Cem), polycarboxylate (Durelon) and so-called self-adhesive resin (RelyX Unicem) cement. Cement was applied in a thin film band of 1 or 3 mm to the cervical margin of the inner surface of the copings, respectively. After cementation, specimens were stored in saline solution for 24 h. The Coronaflex and a standardized custom-made removal device were used to remove the copings from the abutments. Results: Using the same cement, no statistically significant influence with regard to the type of restoration (crown/FDP), cement application mode and device was detected (P>0.05). Therefore, data of specimens cemented with the same cement were pooled. Median attempts to remove the copings were: zinc oxide: 3, self-adhesive resin: 3, zinc phosphate: 5, glass ionomer: 16 and polycarboxylate: 58. Four levels of significance (P<0.0001) were found: (1) zinc oxide/self-adhesive resin; (2) zinc phosphate; (3) glass ionomer; and (4) polycarboxylate. Conclusions: Zinc phosphate and glass ionomer cement might be suitable for a so-called ,semipermanent' (=retrievable) cementation, while polycarboxylate seems to provide the most durable cementation. [source] | |||||||||||||