Bases Alumina

Ziogas et al. [28] performed catalyst screening with this reactor with catalysts coatings, which were made of various base aluminas such as corundum, boehmite and y-alumina. Testing of Cu/Cr and Cu/Mn catalysts based on the different coatings for methanol steam reforming revealed differences in activity which were ascribed... 

Silver-alumina type catalysts are by far the most widely used, especially since they are the main catalytic source in the epoxidation of ethylene. Therefore, they are readily available and already have undergone extensive studies. Many systems have sought to utilize the presence of NO (another harmful environmental species) in gas feeds. In this case, the NO species would be reduced to N2, causing oxidation of the hydrocarbon with the support of the catalyst. Studies have helped to elucidate the active species on the catalyst surface at varying temperatures and species leading to the desired products (31). Results from a recent study point to the active silver species being a [Ag O Al] bound intermediate that leads to N2 formation (32). If the silver is present in nanoparticle form, it is simply believed to be a spectator. Other work showed mixed results on the benefit of silver-based alumina systems for the oxidation of methane and higher hydrocarbons. The effect is dependent on the type of reactor system prepared (33,34). 

FIGURE 16.30 AFM images of the copper surface after polishing in (a) a DI water based alumina slurry, (b) a DI water based silica slurry, (c) a citric acid-based alumina slurry, and (d) a citric acid based silica slurry at pH 6. 

Effect of Chemical Addition In order to insure that surfactants are compatible with the commercial slurries containing chemical reagents, two slurry chemistries (ferric nitrate and hydrogen peroxide) were employed to test the efficiency of the selected surfactants in the presence of chemicals. The results showed that the effect of surfactant on stability and removal rate is not influenced by the presence of the chemicals. Both hydrogen peroxide and ferric nitrate based chemistries were added to Brij 35 based alumina slurries. 

Figure 4a and 4b AFM scans of a copper wafer polished with plain and surfactant based alumina slurry (average roughness = 9 nm for 4a and =4 nm for 4b). 

Bases Alumina, see p-Toluenesulfonylhydrazine. Dehydroabietylamine. 1,5-Diazabicyclo [4.3.0]nonene-5. 1,4-Diazabicyclo[2.2.2]octane. l,S-Diazabicyclot5.4.0]undecene-5. 2,6-Di-/-butylpyridine. N,N,-Diethylglycine ethyl ester, see /-Amyl chloroformate. 2,6-Dimethyl-piperidine. Ethanolamine. Lithium diisopropylamide, see Diphenylsulfonium isopropylide. Lithium nitride. Magnesium methoxide. N-Methylmorpholine. Piperidine. Potassium amide. Potassium hydroxide. Potassium triethylmethoxide. Pyridine. Pyrrolidine. Sodium methoxide. Sodium 2-methyl-2-butoxide. Sodium thiophenoxide. Thallous ethoxide. Triethyla-mine. Triphenylphosphine, see l-Methyl-2-pyrrolidone. 

Another interesting feature of alkoxide based aluminas is their ability to form colloidal systems, also known as alumina dispersions or sols. Through chemical attack, usually by acids in combination with shear energy (although basic systems are also known), the agglomerated powder particles can be broken down into the so-called primary aggregates (figure 10). 

B. A. Pint "Study of the Reactive Element Effect in ODS Iron-Base Alumina-Formers, Materials Science Forum, in press (1996). 

S. L. Morissette, and J. A. Lewis, Chemorheology of aqueous based alumina-poly(vinyl alcohol) gelcasting suspension, J. Am. Ceram. Soc., 82, 521-8 (1999). 

Basic refractories (e.g. chromite, graphite, carbide etc.) These are used in areas where slags and atmosphere are either acidic or basic and are chemically stable to both acids and bases. Alumina Manufactured from burnt bauxite, electro cast bauxite. 

MOR depends on whether the silver is reduced. Table 14.9 summarizes the solid adsorbents available for iodine capture. The silver-based alumina, silica, and mordenite adsorbents have comparable characteristics and are the currently preferred sorbents. An advantage of the mordenite is that the regeneration of the sorbent is possible, thereby utilizing the silver over the course of several cycles. The stripped iodine is then available for sorption using a cheaper metal or conversion to a waste form preferred for long-term storage. 

Babel, A.K., Mackay, R.A., 1999. Surfactant based alumina slurries for copper CMP. In Babu, S.V., Danyluk., S., Krishnan, M., Tsijimura, M. (Eds.), Chemical-mechanical polishing — fundamentals and challenges symposium held April 5—9, San Erandsco, California, USA, pp. 135-142. 

Because the variety of chemical functional groups that can be adsorbed on aluminas is so diverse, a third group of surface modifications is becoming more popular. They involve chemical treatment of the alumina surface in order to introduce new functionalities which can enhance adsorption. An example of such a modification is given in Figure 10. A transition alumina surface is silanized through a condensation reaction with a commercial triethoxysilane. The synthesized surface exhibits quite different properties than the base alumina and can be used for applications such as reversed phase chromatography. 

Typical sorbents for normal-phase SPE are silica, cyano, did, NHz (all silica based), alumina (AI2O3 based), and Florisil (MgSi03 based) (Table 9.3). 

Hawthorne H.M., Neville A., Troczynski T., Hu X., Thammachart M., Xie Y., Fu J., Yang Q. Characterization of chemically bonded composite sol-gel based alumina coatings on steel substrates. Surf. Coat. Technol. 2004 176 243-252... 

Reinforcements that have been used for CMCs include continuous fibers, discontinuous fibers, whiskers, and particles. Key continuous fibers used in CMCs include carbon, silicon carbide-based, alumina-based, alumina-boiia-sihca, quartz, and alkah-resistant glass. Steel wires are also used. Discontinuous CMC fibers are primarily silica based. Silicon carbide is the key whisker reinforcement. Particulate reinforcements include silicon carbide, zirconium carbide, hafnium carbide, hafnium diboiide, and zirconium diboride. 

W. J. Quadakkers and M. J. Bennett, Oxidation induced lifetime limits of thin walled, iron based, alumina fonning, oxide dispersion strengthened aUoy components. Materials Science and Technology, 10, 126-131 (1994). 

Quadakkers W J and Bennett M J (1994), Oxidation Induced Lifetime Limits of Thin Walled, Iron Based, Alumina Forming, Oxide Dispersion Strengthened Alloy Components, Mater Sci Tech, 10, 126-131. 

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