Particular aluminum oxide

This isotope ofO does notalways occur in all natural samples in its usual proportion. In particular, aluminum oxides in meteorites usually reveal an excess of the l60 isotope. In such refractory minerals, the lS0/170 ratio stays almost unchanged, and for that... 

At high temperatures, aluminum reduces many oxygen-containing compounds, particularly metal oxides. These reactions, of the type shown in equation 6, are used in the manufacture of certain metals and alloys, as well as in the thermite welding process. ... 

According to Faraday s law, one Faraday (26.80 Ah) should deposit one gram equivalent (8.994 g) of aluminum. In practice only 85—95% of this amount is obtained. Loss of Faraday efficiency is caused mainly by reduced species ( Al, Na, or A1F) dissolving or dispersing in the electrolyte (bath) at the cathode and being transported toward the anode where these species are reoxidized by carbon dioxide forming carbon monoxide and metal oxide, which then dissolves in the electrolyte. Certain bath additives, particularly aluminum fluoride, lower the content of reduced species in the electrolyte and thereby improve current efficiency. 

The poor efficiencies of coal-fired power plants in 1896 (2.6 percent on average compared with over forty percent one hundred years later) prompted W. W. Jacques to invent the high temperature (500°C to 600°C [900°F to 1100°F]) fuel cell, and then build a lOO-cell battery to produce electricity from coal combustion. The battery operated intermittently for six months, but with diminishing performance, the carbon dioxide generated and present in the air reacted with and consumed its molten potassium hydroxide electrolyte. In 1910, E. Bauer substituted molten salts (e.g., carbonates, silicates, and borates) and used molten silver as the oxygen electrode. Numerous molten salt batteiy systems have since evolved to handle peak loads in electric power plants, and for electric vehicle propulsion. Of particular note is the sodium and nickel chloride couple in a molten chloroalumi-nate salt electrolyte for electric vehicle propulsion. One special feature is the use of a semi-permeable aluminum oxide ceramic separator to prevent lithium ions from diffusing to the sodium electrode, but still allow the opposing flow of sodium ions. 

The results presented here for silicas and aluminas illustrate that there is a wealth of structural information in the infrared spectra that has not previously been recognized. In particular, it was found that adsorbed water affects the lattice vibrations of silica, and that particle-particle Interactions affect the vibrations of surface species. In the case of alumina, it was found that aluminum oxides and hydroxides could be distinguished by their infrared spectra. The absence of spectral windows for photoacoustic spectroscopy allowed more complete band identification of adsorbed surface species, making distinctions between different structures easier. The ability to perform structural analyses by infrared spectroscopy clearly indicates the utility of photoacoustic spectroscopy. 

Aluminum oxides, similar to silica gels, are available as bulk materials and as precoated plates, to be used not only for straight phase adsorption chromatography, but also for partition PLC (see Table 3.3 and Table 3.4). In particular, the aluminum oxide type 150 (i.e., mean pore diameter 150 A [15 tun]) is suitable for partition chromatographic purposes. 

Anodic oxidation of valve metals, particularly, aluminum, has attracted considerable attention because of its wide application in various fields of technology. Traditionally, aluminum is anodized in order to protect the metal against corrosion, to improve its abrasion and adsorption properties, etc.1 The more recent and rapidly growing applications of anodic aluminas in electronics are due to their excellent dielectric properties, perfect planarity, and good reproducibility in production. Finally, ways have recently been found to use the energy potential of aluminum oxidation for chemical power sources of the metal-air type2,3 and other electrochemical applications. 

A particularly simple example would be the energy of a sample of aluminum metal in air. The surface of the metal is covered with a continuous layer of aluminum oxide which may be less than 20 angstroms in thickness in a dry atmosphere but will be much thicker in moist air or after contact with hot water. Consequently, the... 

A variation of this method was used to control the surface properties of aluminum oxide particles, particularly the surface density of Lewis acid sites. Instead of using a long-chain amine surfactant, the solution of aluminum alkoxide precursor was mixed with a small amine to convert the alkoxide dimer (or oligomer in general) into monomeric alkoxide-amine adduct. Controlled hydrolysis of this adduct produces an aluminum oxyhydroxide in which the surface A1 ions are coordinated to amine... 

The catalytic activity of aluminas are mostly related to the Lewis acidity of a small number of low coordination surface aluminum ions, as well as to the high ionicity of the surface Al-O bond [67,92]. The number of such very strong Lewis sites present on aluminum oxide surfaces depends on the dehydroxylation degree and on the particular phase and preparation. Depending on the activation temperature, the density of the strongest Lewis acid sites tends to decrease as the calcination temperature of the alumina increases (i.e., upon the sequence y — 5 —> 9, which is also a sequence of decreasing surface area and increasing catalyst stability). 

The metal has very little commercial use. In elemental form it is a laser source, a portable x-ray source, and as a dopant in garnets. When added to stainless steel, it improves grain refinement, strength, and other properties. Some other applications, particularly in oxides mixed with other rare earths, are as carbon rods for industrial hghting, in titanate insulated capacitors, and as additives to glass. The radioactive isotope ytterbium-169 is used in portable devices to examine defects in thin steel and aluminum. The metal and its compounds are used in fundamental research. 

Of particular interest is the syn-l,6-imino-8,13-methano[14]annulene (59) which represents the first authenticated example of a stable 1H-azepine with a free NH group (80AG(E)1015). The annulene with aluminum oxide undergoes a remarkable isomerization to the anti isomer (61). Investigation shows that the isomerization is not a thermal reaction but involves alumina-catalyzed proto tropic shifts via the 3/7-azepine tautomer (60). This system is unique in that it is the first example of a 3H -> 1H azepine tautomerism, and is a consequence of the high degree of strain in the anti-Bredt 3iT-azepine (60). 

However, in the particular airburst event analyzed, the condensable metallic system was essentially two component. That is, roughly equivalent masses of aluminum and iron constituted the principle amount of condensable material. Aluminum oxides would condense earlier than iron oxides so that it is not inconceivable that a two-component particle... 

The term cermet derives from the combination of ceramic and melal. Cermets are produced by powder metallurgy techniques and represent Ihe bonding of two or more metals. They are particularly useful at high temperatures (850- I250"C). Chromium is used in several cermet combinations, including chromium-bonded aluminum oxide, metal-bonded chromium carbide, and metal-bonded chromium horide. 

The sonophotocatalytic system is effective for overall water splitting as shown in Fig. 12.2 and Table 12.1. This system requires, properly, a photocatalyst such as particulate Ti02. As ultrasonic waves pass through the solution, the properties of the solution influence a sonochemical reaction. In particular, negative effects are considered in the presence of powdered photocatalysts. The effects of fine particles in the solution on the sonochemical reaction have been noted so far. For example, Yasuda et al.19) reported the effects of insoluble particles, such as silicon oxide (Si02) or aluminum oxide (Al203), in the reactant solution on the sonochemical reaction and demonstrated that the reaction rate constant depended on particle properties, particle size and number of particles. It is assumed that a powdered photocatalyst suspended in the solution obstructs the transmission of ultrasonic waves. In this section, the influence of the photocatalyst powder suspended in solution on the sonochemical reaction is examined. 

In its inorganic form, P is a nutrient showing low solubility and mobility in the soil, because it easily reacts with the soil mineral components (clay, iron and aluminum oxides, and carbonates) (Stevenson, 1986). The P content in humic substances ranges from 0.1% to 1.0% and is particularly abundant in humic acids. By using 31P NMR, it was shown that different forms of P can be associated with humic fractions... 

Reactions of this type are so strongly exothermal that the metal is melted and settles to the bottom of the crucible, while the aluminum oxide floats on top of the melt. Goldschmidt reduction is particularly useful when one wishes to prepare metals free from carbon, but it is a relatively expensive method. 

Cava and Pollack s elegant synthesis of benzo[c]thiophene52 has been extended to the synthesis of, for example, naphtho[l,2-c]thio-phene (47),52 methyl benzo[c]thiophene-5-carboxylate,54 and 1,3-dimethyl- (48)55 and l,3,4,6-tetraphenylthieno[3,4-c]thiophene (49).56 The last compound is of particular interest because it is a remarkably stable (cf. compound 48 which only exists transiently) nonclassical thiophene containing ten n electrons for which the only uncharged resonance structure (49) contains a tetravalent sulfur atom. When the sulfoxide (50) is pyrolyzed over aluminum oxide, it gives the parent cyclic sulfide and 51 by disproportionation.57 However, when 50 is heated in acetic anhydride in the presence of iV-phenylmaleimide,... 

Anodizing is an electrolytic method involving aluminum alloy as the anode, which is converted to an aluminum oxide layer of 5-30 pm thickness. Anodic coatings obtained in sulfuric acid, when properly sealed, are particularly effective against discoloration. Anodic coatings are used in the case of alloys used in architecture and as well as paint bases. 

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