Aluminum oxide characteristics

Microstructurc. Crystal size, porosity, and impurity phases play a major role in fixing the fracture characteristics and toughness of an abrasive grain. As an example, rapidly cooled fused aluminum oxide has a microcrystalline stmcture promoting toughness for heavy-duty grinding appHcations, whereas the same composition cooled slowly has a macrocrystalline stmcture more suitable for medium-duty grinding. 

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). 

Aluminum oxide (AI2O3), also known as alumina, is a highly stable compound with many industrial applications. It is readily obtained by CVD. Its characteristics and properties are summarized in Table 11.1. 

Spent foundry sand can be used as a good source of silica in manufacturing portland cement. Also, the clay fraction of foundry sand is an additional source of iron and aluminum oxides. According to the portland cement industry, spent foundry sand can be beneficially used in the manufacture of Portland cement, as sand possesses the following characteristics ... 

Figure 4.9. Log(/D)-VGS (VDS = 20V) and (inset) /D Vds characteristics for an RF-sputtered ZnO TFT on a spin-coated A1PO dielectric annealed at 300 °C. VGS is stepped from 0 to 40V in 5-V increments for the ID-VDS curves device W/L = 5 L = 100 pm. [Reproduced with permission. Meyers, S. T. Anderson, J. T. Hong, D. Hung, C. M. Wager, J. F. Keszler, D. A. 2007. Solution processed aluminum oxide phosphate thin-film dielectrics. Chem. Mater. 19 4023-4029. Copyright 2007 American Chemical Society.]...

Mitrovic, M. and L. Knezic. 1979. Electrolytic aluminum oxide membranes -a new kind of membrane with reverse osmosis characteristics. Desalination 28 147-56. 

The survey summaries show that zeoHte adsorbents are most often employed for non-aqueous systems. This is because the material generally used as a binder to fabricate an agglomerated zeoHte, is a clay comprising silicon dioxide and aluminum oxide which tends to dissolve in water. This dissolution results in negative changes in physical characteristics of the adsorbent as well as silicon contamination of the solution which manifests itself as turbidity in the product. 

Zhang, H. Zhang, X.-N. (1992) Contribution of iron and aluminum oxides to electrokinetic characteristics of variable charge soils in relation to surface charge. Pedosphere 2 31-42 Zhang, J. Buffle, J. (1995) Kinetics of hematite aggregation by polyacrylic acid Importance of charge neutralization. J. Colloid Interface Sci. 174 500-509... 

Fig. 7 (a) Catechol derivatized tetracenes self-assemble on metal oxide surfaces such as aluminum oxide, (b) Schematic and (c) scanning electron micrographs of FET structures fabricated with a 5-nm aluminum oxide layer on top of a 5-nm thermally oxidized Si wafer to allow self-assembly of the derivatized tetracene between sub-100 nm Au source and drain electrodes, (d) /d-Eds characteristics of the assembled tetracene monolayer FET for a 40 nm channel length showing hole modulation and (inset) an atomic force microscope image of the FET channel... 

As shown in Fig. 12.4, aluminum electrolytic capacitors usually consist of an aluminum foil with a thin film of anodically-formed aluminum oxide (dielectric), an aluminum foil, an electrolyte solution, and a separator. The whole sandwich is compactly rolled and packed in a container. The electrolytic capacitors are in wide use, because of their small sizes, high capacitances, and low prices. However, the characteristics of electrolytic capacitors are apt to deteriorate with time. Recently,... 

HBr + H- H- + Br2 — HBr + Br. properties The characteristics of matter Examples vapor pressure color density temperature, protective oxide An oxide that protects a metal from oxidation. Example aluminum oxide, proton p A positively charged subatomic particle found in the nucleus of an atom, protonation Proton transfer to a Bronsted base. Example 2 H30+(aq) + S2-(s) — ... 

Applications of thermal radiation spectroscopy to expins and pyrots are readily apparent. As a consequence of the highly exothermic nature of explns and flares, significant thermal radiation is emitted which can serve to characterize the reaction processes. The photometric properties of pyrots have been treated in Vol 8, P505-R. In practice, thermal radiation characteristics of explns do not always closely approximate black body properties since the system is non-equilibrium in nature and is time dependent. In addition, some pyrotechnically related materials such as aluminum oxide and magnesium oxide behave as gray bodies with emissivities well below unity. For such systems the radiant emission is reduced as shown in Fig 4... 

Alumina is a porous, high-surface-area form of aluminum oxide. The surface has more polar characteristics than silica gel does therefore, it has both acidic and basic characteristics, reflecting the nature of the metal. Alumina has a high melting point, slightly over 2000°C, which is also a desirable property for a support due to its thermal stability. Alumina is composed of aluminum trihydroxides, Al(OH)3 aluminum oxyhydroxides, AIO(OH) and aluminum oxide, Al203n(H20). 

The vibrational spectrum of 4-pyridine-carboxylic acid on alumina in Fig. 4d is equivalent to an infrared or Raman spectrum and can provide a great deal of information about the structure and bonding characteristics of the molecular layer on the oxide surface. For example, the absence of the characteristic > q mode at 1680 cm 1 and the presence of the symmetric and anti-symmetric O-C-O stretching frequencies at 1380 and 1550 cm indicate that 4-pyridine-carboxylic acid loses a proton and bonds to the aluminum oxide as a carboxylate ion. 

Metals and ceramics (claylike materials) are also used as matrices in advanced composites. In most cases, metal matrix composites consist of aluminum, magnesium, copper, or titanium alloys of these metals or intermetallic compounds, such as TiAl and NiAl. The reinforcement is usually a ceramic material such as boron carbide (B4C), silicon carbide (SiC), aluminum oxide (A1203), aluminum nitride (AlN), or boron nitride (BN). Metals have also been used as reinforcements in metal matrices. For example, the physical characteristics of some types of steel have been improved by the addition of aluminum fibers. The reinforcement is usually added in the form of particles, whiskers, plates, or fibers. 

When the carrier is selected, aluminum oxide should be preferred, because biomimetic sensors on it display higher characteristics (Figure 8.9). Moreover, they are low in price, long lived and stable, and possess high hydrodynamic properties. 

Oxidative stability depends on the adherend surface as well as on the adhesive itself. Some metal adhesive interfaces are chemically capable of accelerating the rate of oxidation. For example, it has been found that nearly all types of structural adhesives exhibit better thermal stability when bonded to glass or aluminum than when bonded to stainless steel or titanium.12 For any given metal, the method of surface preparation can also determine oxide characteristics, and hence bond durability. Thus, the use of primers is common practice with high-temperature structural adhesives. 

Catalysts and catalytic supports are often formulated from aluminas owing to their low cost, and their thermal, chemical and mechanical stability [27], To this end, nonionic surfactant templating with polyethylene oxide surfactants was used to synthesize mesoporous alumina [28], Partially ordered mesoporous materials with wormhole channels were obtained - this seems to be a characteristic of templating with nonionic surfactants. Cationic surfactants have recently been found to template mesoporous aluminum oxide with pore sizes that could be fine-tuned by varying the molar ratio of the reactants [29]. The material obtained was thermally stable to 900 °C and exhibited a narrow pore size distribution. 

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