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Alumina Ceramics (alumina + ceramics)
Selected AbstractsProcessing of Bulk Alumina Ceramics Using Laser Engineered Net ShapingINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 3 2008Vamsi Krishna Balla Application of rapid prototyping (RP) in ceramics manufacturing is motivated by advances in engineering ceramics where attaining complex shapes using traditional processing is difficult. Laser Engineered Net Shaping (LENSÔ), a commercial RP process, is used to fabricate dense, net-shaped structures of ,-Al2O3. Shapes such as cylinder, cube, and gear have been fabricated successfully with 10,25 mm section sizes. As-processed structures show anisotropy in mechanical properties with a high compressive strength normal to the build direction and columnar grains along the build direction. Heat treatment did not alter strength and anisotropy, but increased the grain size from 6 to 200 ,m and hardness from 1550 to 1700 Hv. [source] Hydraulic Alumina Binder for Extrusion of Alumina CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2007Takaaki Nagaoka The present work describes the effect of hydraulic alumina (HA) as a new inorganic binder on extrusion of alumina ceramics. The addition of a small amount of HA imparted significant flowability and rigidity to the extruded alumina. Under optimum processing conditions such as amounts of HA and water, and curing period, alumina rods and tubes were successfully extruded using a single screw extruder. Sintered specimens have achieved a relative density of 97% after sintering at 1600°C for 2 h. Dense alumina samples prepared using organic and inorganic binders had similar mechanical properties, that is, Young's modulus >380 GPa and Hv>2000. These results suggest that HA is a new kind of inorganic binder applicable to the extrusion of ceramics. [source] Chemically Bonded Phosphate Ceramics: II, Warm-Temperature Process for Alumina CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2003Arun S. Wagh This is the second of three papers on a dissolution model that describes the formation of chemically bonded phosphate ceramics. In this paper, we discuss the kinetics of formation of aluminum phosphate ceramics between 100° and 150°C. Using basic thermodynamic formulations, we calculated the temperatures of maximum solubility of alumina and its hydrated phases and predicted the temperatures of formation of ceramics. Differential thermal and X-ray diffraction analyses on samples made in the laboratory confirm these temperatures. The resulting ceramics of alumina bonded with aluminum phosphate (berlinite) show a high compressive strength of 16 000 psi. We have concluded that rapid evaporation of excess water in the slurry generates porosity in the ceramics, and that better processing methods are needed. A consolidation model is presented that describes the microstructure of the ceramic. It predicts that a very small amount of alumina must be converted to form the bonding phase; hence, the product is mostly alumina with a thin coating of berlinite on the surface of alumina particles. [source] Surface Finishing of Alumina Ceramics by Means of Abrasive Jet MachiningJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2002Manabu Wakuda Abrasive jet machining (AJM) is proposed as a new approach to surface finishing of structural ceramics. The effect of AJM on the material removal behavior of a commercially available alumina ceramic, and its effect on mechanical properties, was characterized and compared with identical material subjected to conventional finishing processes. Conventional grinding of the ceramic resulted in a surface that was dominated by intergranular fracture, whereas, during AJM, impact by the abrasives led to material removal in a manner resembling ductile behavior, and the resulting surface appearance was much smoother. A significant improvement in flexural strength was attained, compared with the strength of both the ground and lapped samples, because of an induced compressive residual stress. [source] Effect of Ultrasonication on the Microstructure and Tensile Elongation of Zirconia-Dispersed Alumina Ceramics Prepared by Colloidal ProcessingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2001Tohru S. Suzuki To obtain dense, fine-grained ceramics, fine particles and advanced powder processing, such as colloidal processing, are needed. Al2O3 and ZrO2 particles are dispersed in colloidal suspensions by electrosteric repulsion because of polyelectrolyte absorbed on their surfaces. However, additional redispersion treatment such as ultrasonication is required to obtain dispersed suspensions because fine particles tend to agglomerate. The results demonstrate that ultrasonication is effective in improving particle dispersion in suspensions and producing a homogeneous fine microstructure of sintered materials. Superplastic tensile ductility is improved by ultrasonication in preparing suspensions because of the dense and homogeneous fine microstructure. [source] Thermal Shock Performance of Fine Grained Al2O3 Ceramics With TiO2 and ZrO2 Additions for Refractory Applications,ADVANCED ENGINEERING MATERIALS, Issue 6 2010Christos G. Aneziris Abstract Due to zirconia and titania additions carbon-free fine grained alumina ceramics are produced with superior thermal shock performance. The decomposition of Al2TiO5 in the alumina doped matrix dominates during thermal shock attack and leads to higher strengths in comparison to the as sintered samples after thermal shock. EDX, EBSD, and XRD investigations describe the phase evolution before and after quenching the samples from 950 to 1200,°C in water, respectively. [source] Faceted Surface Grain Morphology of Rapidly Solidified Alumina: Characterization and Potential Applications,ADVANCED ENGINEERING MATERIALS, Issue 12 2009Sandip P. Harimkar Abstract The study reports on the formation of regular multi-faceted surface grains during laser surface modification of alumina ceramics. The formation of such faceted morphology of the grains can be strongly correlated with the formation of crystallographic texture. Such evolution of crystallographically-textured, multi-faceted grains opens up new avenues for laser surface modification, where regular three dimensional surface features are formed through solidification processing. [source] Percolative Mechanism of Aging in Zirconia-Containing Ceramics for Medical Applications,ADVANCED MATERIALS, Issue 6 2003C. Pecharromán For biomedical applications, zirconia-toughened alumina ceramics (see Figure) would be very appropriate materials, provided that the zirconia content is kept below the percolation threshold (upper limit of 16 vol.-% 3Y-TZP inside an alumina matrix). That the concept of a percolation threshold is relevant when talking about aging degradation, is demonstrated by comparing specular IR reflectance measurements with aging experiments. [source] Hydraulic Alumina Binder for Extrusion of Alumina CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2007Takaaki Nagaoka The present work describes the effect of hydraulic alumina (HA) as a new inorganic binder on extrusion of alumina ceramics. The addition of a small amount of HA imparted significant flowability and rigidity to the extruded alumina. Under optimum processing conditions such as amounts of HA and water, and curing period, alumina rods and tubes were successfully extruded using a single screw extruder. Sintered specimens have achieved a relative density of 97% after sintering at 1600°C for 2 h. Dense alumina samples prepared using organic and inorganic binders had similar mechanical properties, that is, Young's modulus >380 GPa and Hv>2000. These results suggest that HA is a new kind of inorganic binder applicable to the extrusion of ceramics. [source] Microwave Dielectric Properties of Sintered Alumina Using Nano-Scaled Powders of , Alumina and TiO2JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2007Cheng-Liang Huang The microstructure and the microwave dielectric properties of nano-scaled , alumina (,-Al2O3) ceramics with various added amounts of nano-scaled TiO2 have been investigated. The sintering temperature of nano-scaled , alumina can be effectively lowered by increasing the TiO2 content. The Q×f values of nano-scaled , alumina could be tremendously boosted by adding an appropriate amount of TiO2. However, introducing excessive TiO2 into the alumina ceramics would instead lead to a decrease in the Q×f values. The phases of TiO2 and Al2TiO5 co-existed at 1350°C, and the maximum Q×f value appeared right after the eradication of TiO2 phase at 1400°C. Consequently, increasing the TiO2 content to 0.5 wt% yielded a Q×f value of 680 000 GHz (measured at 14 GHz) for nano-scaled , alumina prepared at 1400°C for duration of 4 h. In addition, a very low loss tangent (tan ,) of 2 × 10,5 was also obtained at 14 GHz. The ,f value is strongly correlated to the compositions and can be controlled through the existing phases. In fact, ,f could be adjusted to near zero by adding 8 wt% TiO2 to , alumina ceramics. A dielectric constant (,r) of 10.81, a high Q×f value of 338 000 GHz (measured at 14 GHz), and a temperature coefficient of resonant frequency (,f) of 1.3 ppm/°C were obtained for nano-scaled , alumina with 8 wt% TiO2 sintered at 1350°C for 4 h. Sintered ceramic samples were also characterized by X-ray diffraction and scanning electron microscopy. [source] Transparent Polycrystalline Alumina Ceramic with Sub-Micrometre Microstructure by Means of Electrophoretic DepositionMATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 4 2006A. Braun Abstract The optical quality attainable in coarse-grained polycrystalline alumina is severely limited by grain-boundary scattering, which is inherent to non-cubic materials. The optical properties of sub-micrometre polycrystalline alumina are of growing interest triggered by the fact that a decrease in the grain sizes of the final sintered material yields an improvement in the optical quality while the scattering mechanism changes as the grain size becomes comparable with the wavelength of light. To achieve transparent alumina ceramics with a fine-grained microstructure, however, porosity and other defects must be avoided. This necessitates the optimization of processing and sintering procedures. Electrophoretic deposition (EPD) is a colloidal process in which ceramic bodies are directly shaped from a stable suspension by application of an electric field. Electrophoretic deposition enables the formation of homogeneous, uniform green microstructures with high density, which can be sintered to transparency. It is a simple and precise technique to synthesize not only monoliths, but also composites with complex geometries [1]. Alumina green bodies were deposited from stabilized aqueous suspensions with and without doping. Green alumina compacts were evaluated based on their pore size distribution and density. Densification behaviour was characterized by dilatometric studies conducted at constant heating rate. Samples were sintered at different temperatures with subsequent post-densification by hot isostatic pressing. Transparency was evaluated by means of spectroscopic measurements. The measured in-line transmission of the samples at 645 nm was more than 50,% and that is 58,% of the value of sapphire. The influence of dopings on transparency was investigated. The mechanical properties of the samples were tested. [source] | ||||||||||||||||||||||