Powder alumina-based ceramics

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. 

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. 

The possibility to obtain a uniformly dispersed composite powder was shown for the a-Fe-Al203 system where metal particles with an average size of 55 nm were formed in an amorphous/nano alumina matrix.18 Other studies attempting to obtain dense bulk composites based on the sol-gel route using conventional pressure-assisted sintering ( 1400°C and an applied force of 10 MPa) resulted in a coarse microstructure.16 However, if reaching theoretical density is not a necessary requirement, a porous ceramic microstructure containing nanometer-sized metal particles can be used as a catalytic material.19 Certain combinations of composite materials demand... 

LNA, which is an acid, can adsorb on alumina via acid-base interaction or hydrogen bonding. The structural formula of LNA and those of other organic dispersants are given in Fig. 2. The interaction between the solvent and LNA cannot be responsible for the viscosity curves because the most basic solvent, tetrahydrofuran (THF) [11], would interact with LNA the most. The acid-base interaction is based on Drago s work on Lewis acid-base interaction energies [12]. Fowkes [2,13,14] expanded the concept to ceramic processing. The relative acidity and basicity of solvents used are listed in Table 1. The ceramic powders used are listed in Table 2. 

Co-extrusion processing using thermoplastic binder systems for ceramic bodies has been described by Van Hoy [Hoy 98]. The major binder component used in this study was ethylene vinyl acetate, and methoxypoly-ethylene glycol was used as a plasticizer. Feedstocks of alumina, a piezoelectric ceramic powder and carbon black were repeatedly co-extruded to form an array of fine M -shaped structures. With this method the size of the alumina M shapes could be reduced by a factor of 915. In this example the use of solvent-based binders would have been problematical because of drying of the feedstocks and extrudates during the co-extrusion process and during handling. 

The present study aims at investigating the Reaction Bonded Silicon Carbide (RBSC) process to produce porous mullite-bonded SiC ceramics. Wu and Claussen (1991) reported a technique to produce mullite ceramics starting from Al, SiC and AI2O3 powder mixtures. However for the purpose of this study it was decided to use only SiC and Al 03 as the precursor powders with SiC as the major component so that after completion of the reaction the microstructure would be SiC bonded with mullite phase, with no residual alumina. This material was then tested for its mechanical properties like Young s modulus. Modulus of Rupture. Properties of Silicate-based SiC refractories have been reported to a certain extent by Reddy and others. Its potential use as a refractory material has been evaluated by measuring its thermal shock resistance. A sample refractory that has been designed in the... 

Ceramics can often be bonded with epoxy or acrylic adhesives, but there are limitations in their use at high temperatures. Few organic adhesives can perform >250 °C, and inorganic adhesives have been developed for ceramics that offer a service temperature of >2000 °C. These are based on inorganic binding compounds such as sodium silicates and various metal phosphates, with carbon, alumina, silica, magnesia or zirconia powder fillers. Ceramic adhesives can be... 

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