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Composite Ceramics (composite + ceramics)
Selected AbstractsMicrowave Hybrid Post-Heat Treatment of Reaction Sintered Alumina/Lanthanum Hexaaluminate Composite Ceramics,ADVANCED ENGINEERING MATERIALS, Issue 3 2010Zahra Negahdari One of the main problems in development of in situ reaction sintered alumina/lanthanum hexaaluminate composite ceramics is achievement of simultaneous densification and in situ formation of lanthanum hexaaluminate (LHA) platelets inside the matrix. Microwave hybrid post-sintering was investigated as a method to enhance the solid-state reaction of LHA formation and the densification of composite ceramics with 2.8,80 vol% LHA. Comparison of the conventionally and microwave assisted sintered alumina/lanthanum hexaaluminate composite ceramics revealed that utilization of microwave heating in second stage of sintering could enhance the solid-state reaction, the densification, and the anisotropic grain growth of the LHA platelets in ceramics containing more than 20 vol% LHA and for heat treatment at 1500,°C. [source] Microwave Dielectric Properties of Ba3(VO4)2,Mg2SiO4 Composite CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2010Siqin Meng Novel Ba3(VO4)2,Mg2SiO4 microwave dielectric composite ceramics with compositions of (1,x)Ba3(VO4)2,xMg2SiO4 (x=0.50,0.65) have been prepared by firing mixtures of Ba3(VO4)2 and Mg2SiO4. X-ray diffraction and scanning electron microscopy analysis revealed that they coexist without forming secondary phases. Because their resonant frequency temperature coefficients (,f) have opposite signs, the ,f of the composite ceramic can be adjusted passing through zero by changing the relative content of the two phases. Dielectric property measurements were performed using the resonator method at around 11 GHz. Ceramics with Mg2SiO4 55 wt% sintered at 1175°C exhibited microwave dielectric properties of dielectric constant ,r=9.03, Q×f=52 500 GHz, and ,f=0.6 ppm/°C at 11.3 GHz. In this composite ceramic, we observed that the formation of the MgSiO3 secondary phase was suppressed. [source] Microstructure,Dielectric Properties Relationship in Ba0.6Sr0.4TiO3,Mg2SiO4,Al2O3 Composite CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2010Ying Chen 0.60Ba0.6Sr0.4TiO3(BST),(0.40,x)Mg2SiO4(MS),xAl2O3 (x=0, 0.5, 3, 5wt%) composite ceramics exhibit excellent characteristics suitable for tunable device applications. With increasing amount of Al, the dielectric peak can be quantitatively broadened and suppressed; the "phase transition temperature"Tc or (Tm) shifts to a lower temperature. Meanwhile, the tunability is still high in a wider temperature range. Far from Tc, pyroelectric effects are observed by using the Byer and Roundy technology and Slim polarization hysteresis loops are observed under high ac dielectric field at 10Hz. These proved the existence of spontaneous polarization in certain possible orientations in a broad temperature range above Tc in the paraelectric medium and reveal why 0.60BST,(0.40,x)MS,xAl2O3 have such remarkable dielectric nonlinearity. [source] Preparation and Properties of Porous Aluminum Nitride,Silicon Carbide Composite CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2004Eirik Hagen Microporous two-phase AlN,SiC composites were prepared using Al4C3 and either Si (N2 atmosphere) or Si3N4 (Ar atmosphere) as precursors. The reaction mechanisms of the two synthesis routes and the effect of processing conditions on reaction rate and the material microstructures were demonstrated. The exothermic reaction between Si and Al4C3 under N2 atmosphere was shown to be a simple processing route for the preparation of porous two-phase AlN,SiC materials. The homogeneous two-phase AlN,SiC composites had a grain size in the range of 1,5 ,m, and the porosity varied in the range of 36%,45%. The bending strength was 50,60 MPa, in accordance with the high porosity. [source] Super High Threshold Percolative Ferroelectric/Ferrimagnetic Composite Ceramics with Outstanding Permittivity and Initial Permeability,ANGEWANDTE CHEMIE, Issue 12 2010Hui Zheng No abstract is available for this article. [source] Super High Threshold Percolative Ferroelectric/Ferrimagnetic Composite Ceramics with Outstanding Permittivity and Initial Permeability,ANGEWANDTE CHEMIE, Issue 47 2009Hui Zheng Hohe Hemmschwelle: Ferroelektrische/ferrimagnetische Verbundkeramiken mit Perkolationsschwellen von 0.85 bis 0.95 wurden durch einen Sol-Gel-Prozess erhalten, der die leitfähigen Ferritpartikel durch eine ferroelektrische Phase wie BaTiO3 ummantelt und voneinander separiert. Eine derart hohe Schwelle führt zu einem steilen Anstieg von Permittivität , und Anfangspermeabilität ,i bei steigendem Ferrit-Anteil (NZFO=Ni0.5Zn0.5Fe2O4). [source] Microwave Hybrid Post-Heat Treatment of Reaction Sintered Alumina/Lanthanum Hexaaluminate Composite Ceramics,ADVANCED ENGINEERING MATERIALS, Issue 3 2010Zahra Negahdari One of the main problems in development of in situ reaction sintered alumina/lanthanum hexaaluminate composite ceramics is achievement of simultaneous densification and in situ formation of lanthanum hexaaluminate (LHA) platelets inside the matrix. Microwave hybrid post-sintering was investigated as a method to enhance the solid-state reaction of LHA formation and the densification of composite ceramics with 2.8,80 vol% LHA. Comparison of the conventionally and microwave assisted sintered alumina/lanthanum hexaaluminate composite ceramics revealed that utilization of microwave heating in second stage of sintering could enhance the solid-state reaction, the densification, and the anisotropic grain growth of the LHA platelets in ceramics containing more than 20 vol% LHA and for heat treatment at 1500,°C. [source] Strength recovery of machined Al2O3/SiC composite ceramics by crack healingFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 12 2007M. ONO ABSTRACT Alumina is used in various fields as a machine component. However, it has a low fracture toughness, which is a weakness. Thus, countless cracks may be initiated randomly by machining, and these cracks decrease the component's mechanical properties and reliability. To overcome this problem, a crack-healing ability could be a very useful technology. In this study, Al2O3/SiC composite was sintered. This alumina exhibits excellent crack-healing ability. Small specimens for a bending test were made from the Al2O3/SiC. A semicircular groove was machined using a diamond ball-drill. The machining reduced the local fracture stress from approximately 820,300 MPa. The machined specimens were crack-healed under various conditions. The fracture stress of these specimens after crack healing was evaluated systematically from room temperature (RT) to 1573 K. It was found that the local fracture stress of the machined specimen recovered almost completely after crack healing. Therefore, it was concluded that crack healing could be an effective method for improving the structural integrity of machined alumina and reducing machining costs. [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] Microwave Dielectric Properties of Ba3(VO4)2,Mg2SiO4 Composite CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2010Siqin Meng Novel Ba3(VO4)2,Mg2SiO4 microwave dielectric composite ceramics with compositions of (1,x)Ba3(VO4)2,xMg2SiO4 (x=0.50,0.65) have been prepared by firing mixtures of Ba3(VO4)2 and Mg2SiO4. X-ray diffraction and scanning electron microscopy analysis revealed that they coexist without forming secondary phases. Because their resonant frequency temperature coefficients (,f) have opposite signs, the ,f of the composite ceramic can be adjusted passing through zero by changing the relative content of the two phases. Dielectric property measurements were performed using the resonator method at around 11 GHz. Ceramics with Mg2SiO4 55 wt% sintered at 1175°C exhibited microwave dielectric properties of dielectric constant ,r=9.03, Q×f=52 500 GHz, and ,f=0.6 ppm/°C at 11.3 GHz. In this composite ceramic, we observed that the formation of the MgSiO3 secondary phase was suppressed. [source] Centrifugal Gel Casting: A Combined Process for the Consolidation of Homogenous and Reliable CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2010Saeed Maleksaeedi In this work, a combined process, called centrifugal gel casting (CGC), was proposed for the fabrication of homogenous and reliable monolithic and composite ceramics starting from submicrometer-sized powders. This method exploits the advantages of both conventional gel casting (GC) and centrifugal slip casting (CSC), while overcoming the limitations associated with the two methods. Via this process, a relatively low centrifugal force is applied to form a highly concentrated slurry in the mold cavity, which is then followed by in situ polymerization of slurry during gelation. In this work, concentrated alumina slurries with different solid contents from 45 to 65 vol% were consolidated by the three forming methods mentioned above. Various properties of green and fired products were measured and compared. Shorter processing time, lower centrifugal force, higher green strength, and minimal segregation are observed to be the characteristics of CGC in comparison with CSC. In situ elimination of bubbles with no need for degassing and the ability to remove heterogeneities, on top of high reliability and the potential to process higher viscosity slurries, are the main advantages of this method over the conventional GC. [source] Oscillating sliding wear behaviour of SiC, TiC, TiB2, 59SiC,41TiB2 and 52SiC,24TiC,24TiB2 materials up to 750°C in airLUBRICATION SCIENCE, Issue 2 2006R. Wäsche The tribological behaviour of different monolithic and composite ceramics was evaluated in the temperature range between room temperature and 750°C. The test method was oscillating sliding with a ball-on-disk arrangement in an SRV machine. Alumina balls were used as counter body. The friction behaviour was determined on-line, and the wear behaviour was determined from calculations on the basis of wear scar dimensions and profilometric measurements. The friction depends on temperature and shows an increase for most materials for increasing temperature; the smallest friction at all temperatures is found for monolithic TiC. The wear behaviour shows different trends for the different materials. In tests against SiC a maximum of wear is found at 500°C, for TiC at 200°C and for TiB2 at 750°C. The composite ceramics suffer the smallest wear of all materials in the range from 200°C to 500°C. Copyright © 2006 John Wiley & Sons, Ltd. [source] | ||||||||||