|
| ||
|
|
||
Ceramic Components (ceramic + component)
Selected AbstractsImproving SOFC Ceramic Components: A Multi-faceted Scientific and Technological ChallengeFUEL CELLS, Issue 5 2008Fillipo Maglia No abstract is available for this article. [source] Direct Laser Sintering of Al2O3,SiO2 Dental Ceramic Components by Layer-Wise Slurry DepositionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2006André Gahler This publication presents a solid freeform fabrication technique for ceramics in the alumina,silica system by layering binder-free, high-loaded ceramic slurries, followed by selective laser sintering. The low melting silica phase and the reaction sintering between silica and alumina favor the rapid prototyping of pure ceramic parts. On the basis of electroacoustic and viscosity measurements, stable slurries from Al2O3/SiO2 powder mixtures and water with a high fluidity have been prepared for the layer deposition with a doctor blade like in tape casting. Layers with a thickness of about 100 ,m were processed. It was found in laser parameter studies that ceramic parts can only be obtained using special alumina contents and laser parameters. But the biphasic approach may allow greater flexibility in the processing regime than is afforded by the use of just one material. The microstructure of these parts depends mainly on the temperature gradient induced by the laser absorption and thermal conduction. The wet shaping facilitates laser-sintered parts with a relatively high density, which could be increased by a thermal post-treatment. [source] Ink-Jet Printing of Binders for Ceramic ComponentsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2002Jooho Moon Layered manufacturing methods for fabricating ceramic components can involve selective deposition of binder using ink-jet printing. Selection of a proper binder plays a critical role in fabricating parts with good surface finish, dimensional accuracy, and high resolution. Several polymeric solution-phase binders were investigated in terms of their physical properties, printing performance, and binder-powder bed interaction. It was observed that the molecular weight should be <15 000 for the binder to be penetrated into dense powder compacts. Binder infiltration kinetics and printed line width were also significantly influenced by powder-bed characteristics, such as surface roughness and pore size, as well as the physical properties of the binder, such as viscosity and surface tension. [source] A new methodology to guarantee the structural integrity of Al2O3/SiC composite using crack healing and a proof testFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 7 2007M. ONO ABSTRACT Structural ceramics are brittle and sensitive to flaws. As a result, the structural integrity of a ceramic component may be seriously affected by inherent flaws. Self-crack-healing is an excellent answer to this problem. At the moment, however, there is no technique to heal embedded flaws. Therefore, a technique to guarantee the reliability of ceramic components is demanded, and thus a technique using crack healing followed by proof test was developed by K. Ando et al. to accomplish this. With this technique, testing the mechanical behaviour of the crack-healed zone is very important for ensuring the structural integrity of a ceramic component. In this study, first Al2O3/SiC composite with an excellent crack-healing ability was sintered. Second, a crack was introduced on the sample (3 mm × 4 mm × 36 mm), which reduced the bending strength by about 80%, and subsequently the crack was healed. Third, a proof test was carried out on the crack-healed sample. Last, using the crack-healed and proof-tested sample, a fracture test was carried out up to 1373 K. The measured minimum fracture stress (,Fmin) was compared with the theoretical minimum strength (,G) from room temperature (R.T.) to 1373 K. It was concluded that ,G showed good agreement with ,Fmin up to 1373 K and that the crack healing followed by proof test was an excellent technique to increase the survival probability by administering a proof test and to guarantee the reliability of Al2O3/SiC composite. [source] Crack-healing and mechanical behaviour of Al2O3/SiC composites at elevated temperatureFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 7 2004K. ANDO ABSTRACT Alumina/silicon carbide (Al2O3/SiC) composite ceramics with large self-crack-healing ability, high strength and high heat-resistance limit temperature for strength were developed and subjected to three-point bending. A semicircular surface crack 100 ,m in diameter was made on each sample. Crack-healing behaviour was systematically studied, as functions of crack-healing temperature and healing time, and the fatigue strengths of the crack-healed sample at room temperature and 1373 K were investigated. Four main conclusions were drawn from the present study. (1) Al2O3/SiC composite ceramics have the ability to heal after cracking from 1273to 1673 K in air. (2) The heat-resistance limit temperature for strength of the crack-healed sample is ,1573 K, and ,68% of the samples fractured from outside the crack-healed zone in the testing-temperature range 873,1573 K. (3) The crack-healed sample exhibited very high fatigue limit at room temperature and also 1373 K. (4) The large self-crack-healing ability is a desirable technique for the high structural integrity of ceramic component. [source] A new methodology to guarantee the structural integrity of Al2O3/SiC composite using crack healing and a proof testFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 7 2007M. ONO ABSTRACT Structural ceramics are brittle and sensitive to flaws. As a result, the structural integrity of a ceramic component may be seriously affected by inherent flaws. Self-crack-healing is an excellent answer to this problem. At the moment, however, there is no technique to heal embedded flaws. Therefore, a technique to guarantee the reliability of ceramic components is demanded, and thus a technique using crack healing followed by proof test was developed by K. Ando et al. to accomplish this. With this technique, testing the mechanical behaviour of the crack-healed zone is very important for ensuring the structural integrity of a ceramic component. In this study, first Al2O3/SiC composite with an excellent crack-healing ability was sintered. Second, a crack was introduced on the sample (3 mm × 4 mm × 36 mm), which reduced the bending strength by about 80%, and subsequently the crack was healed. Third, a proof test was carried out on the crack-healed sample. Last, using the crack-healed and proof-tested sample, a fracture test was carried out up to 1373 K. The measured minimum fracture stress (,Fmin) was compared with the theoretical minimum strength (,G) from room temperature (R.T.) to 1373 K. It was concluded that ,G showed good agreement with ,Fmin up to 1373 K and that the crack healing followed by proof test was an excellent technique to increase the survival probability by administering a proof test and to guarantee the reliability of Al2O3/SiC composite. [source] Texture Analysis and Finite Element Modeling of Operational Stresses in Ceramic Injection Molding Components for High-Pressure PumpsINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 4 2005Martin Wenzelburger Texturization of microstructures in ceramic components during injection of thermoplastic feedstocks into the mold is a well-known problem in ceramic injection molding (CIM) technology. The influences of textures on the mechanical properties of components with anisotropic properties, which depend on crystallite structure and orientation, usually involve weakening of the structure by the formation of separation planes and accumulation of stresses, which can lead to crack initiation and subcritical failure. A light optical texture analysis technique was developed for the analysis of thin section preparations from optically anisotropic ceramic materials. An internal Al2O3 gear rim for high-pressure gear pumps that is manufactured by CIM was chosen for the evaluation of this technique. Components were produced from thermoplastic ceramic feedstocks with different rheological behavior. Thin sections were prepared from the sintered parts. The texture was analyzed by polarized transmission light microscopy of the thin sections and colorimetric analysis of the crystal orientation. For the evaluation of the component properties, function, and lifetime, operating tests on a test bench were carried out as well as finite element (FE) simulation of the stress distribution in the components under operational load with regard to the texturization. The results were used for the localization of stress gradients and their comparison and correlation to the texturization. The functionality of this texture analysis method was proved by the tests, and it is expected to be a convenient novel method for the analysis and optimization of the parameters in CIM processes and the design of injection gate and mold. [source] Polymer-Derived Ceramics: 40 Years of Research and Innovation in Advanced CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2010Paolo Colombo Preceramic polymers were proposed over 30 years ago as precursors for the fabrication of mainly Si-based advanced ceramics, generally denoted as polymer-derived ceramics (PDCs). The polymer to ceramic transformation process enabled significant technological breakthroughs in ceramic science and technology, such as the development of ceramic fibers, coatings, or ceramics stable at ultrahigh temperatures (up to 2000°C) with respect to decomposition, crystallization, phase separation, and creep. In recent years, several important advances have been achieved such as the discovery of a variety of functional properties associated with PDCs. Moreover, novel insights into their structure at the nanoscale level have contributed to the fundamental understanding of the various useful and unique features of PDCs related to their high chemical durability or high creep resistance or semiconducting behavior. From the processing point of view, preceramic polymers have been used as reactive binders to produce technical ceramics, they have been manipulated to allow for the formation of ordered pores in the meso-range, they have been tested for joining advanced ceramic components, and have been processed into bulk or macroporous components. Consequently, possible fields of applications of PDCs have been extended significantly by the recent research and development activities. Several key engineering fields suitable for application of PDCs include high-temperature-resistant materials (energy materials, automotive, aerospace, etc.), hard materials, chemical engineering (catalyst support, food- and biotechnology, etc.), or functional materials in electrical engineering as well as in micro/nanoelectronics. The science and technological development of PDCs are highly interdisciplinary, at the forefront of micro- and nanoscience and technology, with expertise provided by chemists, physicists, mineralogists, and materials scientists, and engineers. Moreover, several specialized industries have already commercialized components based on PDCs, and the production and availability of the precursors used has dramatically increased over the past few years. In this feature article, we highlight the following scientific issues related to advanced PDCs research: (1) General synthesis procedures to produce silicon-based preceramic polymers. (2) Special microstructural features of PDCs. (3) Unusual materials properties of PDCs, that are related to their unique nanosized microstructure that makes preceramic polymers of great and topical interest to researchers across a wide spectrum of disciplines. (4) Processing strategies to fabricate ceramic components from preceramic polymers. (5) Discussion and presentation of several examples of possible real-life applications that take advantage of the special characteristics of preceramic polymers. Note: In the past, a wide range of specialized international symposia have been devoted to PDCs, in particular organized by the American Ceramic Society, the European Materials Society, and the Materials Research Society. Most of the reviews available on PDCs are either not up to date or deal with only a subset of preceramic polymers and ceramics (e.g., silazanes to produce SiCN-based ceramics). Thus, this review is focused on a large number of novel data and developments, and contains materials from the literature but also from sources that are not widely available. [source] Cross-linked Polyvinyl Alcohol as a Binder for Gelcasting and Green MachiningJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2008France Chabert Submicrometer alumina suspensions, dispersed in aqueous acidic solutions of polyvinyl alcohol (PVA) and 2,5-dimethoxy-2,5-dihydrofuran, have been evaluated for suitability as a cross-linkable binder system for casting complex-shaped ceramic components. Suspensions of up to 50 vol% solids have rheological behavior, which is suitable for pouring and filling molds. Complex-shaped green bodies are then formed by heating the suspension in the mold for a period of time (typically 15,60 min) at moderate temperature (60°,80°C) to gel the suspension. High green densities (58%,62% of full density) can be obtained. The dried green bodies have strength in excess of 1 MPa and may be readily machined. No more than 1,3 wt% PVA per weight of alumina is necessary, ensuring burnout that minimizes generation of flaws. The ceramic components can be fired to >96% of full density when fired for 2 h at 1400°,1450°C. Cross-linkable PVA may receive more widespread acceptance in ceramic processing than previous gelcasting formulations because PVA is already a common processing additive. [source] Determination of the Minimum Time for Binder Removal and Optimum Geometry for Three-Dimensional Porous Green BodiesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2003Stephen J. Lombardo A model is developed to optimize two aspects of the thermal removal of binder from green ceramic components. The model, which accounts for flow in porous media arising from the thermal decomposition of binder in three-dimensional bodies with anisotropic permeability, describes the pressure within the body as a function of position, time, and temperature during the heating cycle. The model is used with variational calculus to predict the heating profile that minimizes the cycle time for the thermal removal of binder. The model is also used to determine which body geometry maximizes the buildup of pressure in parallelepipeds, a common shape of multilayer ceramic capacitors. [source] Ultrasonic Velocity Technique for Nondestructive Quantification of Elastic Moduli Degradation during Creep in Silicon NitrideJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2003Franti, ek Lofaj The ultrasonic velocity technique was used for nondestructive quantification of creep damage during interrupted tensile creep tests at 1400°C in an advanced silicon nitride to investigate the possibilities of this technique for creep damage monitoring in ceramic components. The longitudinal and shear wave velocities, Poisson's ratio, and Young's, shear, and bulk moduli linearly decreased with strain. Precise density change measurements indicated a linear relationship with a coefficient of proportionality of 0.69 between the volume fraction of cavities and tensile strain. Cavitation was identified as the main creep mechanism in the studied silicon nitride and the reason for ultrasonic velocity and elastic moduli degradation. The measurement of just the longitudinal wave velocity changes was found to be sufficient for quantification of cavitation during creep. The capability of the ultrasonic velocity technique for simple, sensitive, and reliable nondestructive monitoring of creep damage during intermittent creep was demonstrated in silicon nitride. [source] Ink-Jet Printing of Binders for Ceramic ComponentsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2002Jooho Moon Layered manufacturing methods for fabricating ceramic components can involve selective deposition of binder using ink-jet printing. Selection of a proper binder plays a critical role in fabricating parts with good surface finish, dimensional accuracy, and high resolution. Several polymeric solution-phase binders were investigated in terms of their physical properties, printing performance, and binder-powder bed interaction. It was observed that the molecular weight should be <15 000 for the binder to be penetrated into dense powder compacts. Binder infiltration kinetics and printed line width were also significantly influenced by powder-bed characteristics, such as surface roughness and pore size, as well as the physical properties of the binder, such as viscosity and surface tension. [source] Al2O3/TiC Based Metal Cutting Tools by Microwave Sintering Followed by Hot Isostatic PressingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2000Adrian Goldstein The feasibility of producing Al2O3/TiC metal cutting tools by fast microwave sintering followed by hot isostatic pressing was examined. Microwave heating profiles able to ensure near-full densification of Al2O3/TiC ceramic components were determined. Simple-shape specimens could be sintered to a bulk density of 97% theoretical density (TD) while in the case of tool-shaped ones maximal densification levels attained were somewhat lower, i.e., ,95% TD. Temperature uniformization,within the heating chamber,by using a particulate SiC susceptor noticeably reduced tool cracking propensity. Densification levels in the range acceptable for commercial tool manufacturing (,98% TD) were achieved by hot isostatic pressing of the microwave-sintered parts. The isostatically pressed parts exhibited a Vickers hardness Hv, 2000 kg/mm2 and a fracture toughness KIC, 4.3 MPa·m1/2. [source] | ||||||||||