Grains alumina-based ceramics

Fine Grained Alumina-Based Ceramics Produced Using Magnetic Pulsed Compaction... 

The sintering at reduced down to 1450°C temperatures allowed to obtain the alumina-based ceramics which is 2.5-3 times more resistant to abrasive-erosive wear comparing with the best industrial ceramics with the same composition. Such ceramics combine high density, 0.97, small grain size of the alumina (<300 nm) and MgAl204 spanel (20 nm), high... 

Table 4.1 further shows essential mechanical properties of several products of CeramTec s BIOLOX family of alumina-based materials for femoral heads of hip endoprostheses as well as those of BIONIT manufactured by Mathys Orthopadie GmbH (Bettlach, Switzerland). It is evident that decreasing the grain size of the ceramic precursor powders increases both the flexural strength and the fracture toughness of the material dramatically. 

The asymmetry between tensile and compressive creep is a typical feature of other systems, such as SiC-based and Al203-based ceramics. In fact, this is common in ceramic systems in which an easily deformable glassy phase located at the grain boundaries is present. In contrast, single-phase ceramics such as pure alumina polycrystals and YTZP are reported to be symmetric under both tension and compression. 

Alumina based fibers are subject to creep, even at low temperatures, This phenomenon is exacerbated by the fine grain size of the fibers [20] [54] [67] [70] [73] [79-80]. At 1200°C and with an applied stress of 70 MPa, the strain rate for the fine-grained Nextel 610 a-alumina fiber is higher than that of Fiber FP with a coarser microstructure. Both strain rates are about one order of magnitude higher than that for a bulk alumina ceramic with a grain size of 1.2 jm. The aeep of Nextel 610 is already measurable at a temperature as low as 900 C under an applied stress of 200-500 MPa [70]. 

Utsunomiya et al. [11,12] reported an accumulation-type CTL-based sensor based on this mechanism. The alumina powder (y-Al2()3, 300 mesh in grain size, 30 mg) filled in a glazed ceramic pot (5 mm in diameter) including an electric heater wire was used as a sensor catalyst. First, the catalyst was heated to 500 °C to remove previous adsorbates, then was quenched to room temperature and allowed to adsorb the sample gas for a certain time. 

Detailed HRTEM characterization of the specimens showed that all metal-ceramic interfaces in the two different nanocomposites had thin ( 1 nm thick) amorphous films (see Fig. 11.5). In addition, occluded particles were found inside the alumina grains which also had thin amorphous films at their interfaces with alumina. Analytical microscopy showed the films to contain Ca, Si, and Al.41 Hamaker coefficients were calculated for metal-ceramic interfaces in the presence of a Si02-based film, which indicated that a stronger attractive force is expected for intergranular films at metal-alumina interfaces,... 

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