Alumina material properties

However, the extent of the activity enhancement cannot be related to the higher surface area of this material. Two possible explanations were proposed to account for the effect of mirror plane composition on combustion activity one is related to the different oxidation state of the cation in the mirror plane the other is associated with the crystal structure of layered-alumina materials (i.e., magne-toplumbite and (3-Al203) which have different population and co-ordination of the ions in the mirror planes. Both these electronic and structural factors can, in principle, affect the redox properties. 

In order to evaluate correctly the textural properties a carefully selection of calculation method is necessary. Evaluation of micropore volume in ERS-8 and SA calculated with Dubinin-Radushkevich and DFT are consistent, instead an overestimate value is observed with Horvath-Kavazoe method. The pore size distribution of MSA, MCM-41, HMS and commercial silica-alumina materials have been evaluated by BJH and DFT method. Only DFT model is effective, in particular for evaluation in the border line range between micro and mesopores. 

The materials containing La or Ba exhibit high resistance to sintering and maintain a large surface area after calcination. Moreover, the crystal phase of alumina remains unchanged. Nevertheless, Ba and La, which have a strong effect on the thermal stability of alumina material, negatively affect the catalytic properties of supported Pd catalysts in complete oxidation of methane. The conversion of methane over supported Pd catalyst is lower when the support is modified by addition of rare-earth species. 

However, as the density decreases, other properties like strength and morphology might be adversely affected ref Fig. 4. Here the upper curve depicts the behavior of a standard alumina material, whereas the next one shows that a stronger material can be made, even for a high pore volume support. The other lines illustrate how proper treatment may increase the attrition resistance further. One factor that may influence the strength is any inclusions or second phases as illustrated in Fig. 5, although the detailed correlations can be difficult to unravel. 

New trends in the development and application of hard ceramic grinding and cutting materials will be discussed in this Chapter. For both groups of tools, modern technical demands drive the development of submicrometer microstruc-tures that exhibit significantly increased hardness and reliability. Manufacturing approaches and resulting properties will be described for both advanced single phase sintered alumina materials and for composite ceramics. 

This class of materials was developed to combine the chemical stability of alumina and properties of Si3N4 with ease of sintering. A beta Sialon is formed by substitution of Al and O ions for Si and N in Si3N4 lattice, as Sie-zAlzOzNg-z- The resultant structure contains elongated beta-Sialon grains, typically with some intergranular phase, which could be amorphous or crystalline. Substitution of alumina adds to the chemical stability... 

Various material properties (e. g. thermal diffiisivity, air permeability) have been determined for WHIPOX CMCs. Reliable data are important for potential applications such as thermal insulators, filters or burners. Thermal conductivity perpendicular to fiber orientation is about IW/mK. Closer inspection reveals lower conductivity if a mullite matrix is employed instead of alumina. Thermal conductivity in fiber direction, on the other hand, is about three times higher as perpendicular to the fiber direction, reflecting the non-isotropic structure of the composite (Figure 11). 

The ceramic materials investigated in this paper are hot-pressed silicon nitride (HPSN), reaction-bonded silicon nitride (RBSN), zirconia-toughened alumina (AI2O3), and porous SiC. The available material properties for these ceramics are given in Table 4.3. The HPSN and zirconia-toughened alumina ceramics were in the shape of flexural strength test bars cut from billets. The RBSN ceramic was molded into bars of the shape of flexural test specimens. The porous SiC ceramic was provided in the shape of flexural test specimens. 

The low temperature shift catalyst functions 100-200°C below the temperature of the high temperature system and is operated between 210 and 240°C. The catalysts used in this process are copper/zinc oxide/alumina materials. The composition and method of preparation of the copper-based precursors are crucial in determining the final properties of the catalyst. The typical composition of a commercial copper/zinc oxide/alumina catalyst may be 33% CuO, 34% ZnO, and 33% AI2O3. Although the ability of copper/zinc oxides to catalyze the WGS reaction was recognized in the late 1920s, routine usage in commercial plants did not occur until 1963. Until that time, the susceptibility of the catalyst to... 

Because of the variation of alumina surface properties with hydroxyl concentration and type, adsorption behavior can be modified in numerous ways on the materials. A relatively easy method, for example, is thermal dehydroxylation. As shown in Figure 4 for two levels of hydroxyl content, the acidic and basic site concentrations can be made quite different. This trend is summarized in Figure 5 for transition aluminas as a function of final activation temperature in the synthesis process. Higher temperatures tend to eliminate surface hydroxyls, which increase the number of Lewis acid sites, thus increasing total acid sites on a surface area basis. 

In an attempt to marry the best characteristics of HTCC and LTCC, Kyocera has developed an intermediate-firing cofired ceramic, designated as A0600. This alumina material employs copper-based conductors. Thus, this composition enjoys the low electrical resistivity of Cu metallization along with the superior mechanical and thermal properties of alumina. A "broad-brush" comparison of this material to standard 92% alumina and a generic LTCC formulation is presented in Table 6.4. 

A single selected experiment with glass and a single experiment with alumina, both conducted at mild thermal conditions, were used to adjust the collision frequency pre-factor Tcoii- In this way, the value of Fcoii = 10m (/coll = 1.6 s ) was obtained for glass, and Fcoii = 45 m (/cou = 4.1 s ) for alumina. Once this parameter was fitted, it was used without further change for comparison with all other data gained with the respective material. A deeper discussion on the effect of the number of collisions on model response, more details about equipment and material properties, and a full documentation of the experimental results can be found in Terrazas-Velarde (2010). Here, just a few comparisons with measured data are presented to show that the model can reliably describe the influence of process parameters. 

Mishra, R. S. Mukherjee, A. K. Electric pulse assisted rapid consolidation of ultrafine grained alumina matrix composites. Materials Science Engineering, A Structural Materials Properties, Microstructure and Processing A287,178-182 (2000). 

The material used for all the simulations is alumina, whose properties are as follows Young s modulus E = 400GPa, Poisson s ratio v = 0.27 and density... 

Example 3 Alumina In Static Fatigue - Material Properties Changing With Time... 

The data shown in Table 2 have been extracted from experimental results of e and as a function of the frequency with typical variations shown in Figures 8 and 9 for various ceramics. In Figure 8 pronounced dipolar relaxations occur for the titanate ceramics such as barium or barium/strontium titanate in the frequency range 10 MHz - 100 GHz. The effective loss factors of these two ceramics at 2.45 GHz are 0.2 and 0.3 respectively indicating that both these materials will readily absorb microwave radiation at this industrial allocated frequency. Lime alumina silicate, steatite and calcium titanate on the other hand have loss factors below 0.02 and as such are not obvious candidates for microwave heating. Figure 10 shows the material properties of a family of ferrites, some types can have extremely high loss factors. 

Refractoriness (Melting Temperature). Instantaneous grinding temperatures may exceed 3500°C at the interface between an abrasive and the workpiece being ground (14). Hence melting temperature is an important property. Additionady, for alumina, sdicon carbide, B C, and many other materials, hardness decreases rapidly with increasing temperature (7). Fortunately, ferrous metals also soften with increasing temperatures and do so even more rapidly than abrasives (15). 

Traditional adsorbents such as sihca [7631 -86-9] Si02 activated alumina [1318-23-6] AI2O2 and activated carbon [7440-44-0], C, exhibit large surface areas and micropore volumes. The surface chemical properties of these adsorbents make them potentially useful for separations by molecular class. However, the micropore size distribution is fairly broad for these materials (45). This characteristic makes them unsuitable for use in separations in which steric hindrance can potentially be exploited (see Aluminum compounds, aluminum oxide (ALUMINA) Silicon compounds, synthetic inorganic silicates). 

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