Aluminium oxide

The thermodynamically stable form of alumina (a-Al203 or corundum) consists of a hexagonal close-packed sublattice of oxygen anions with 2/3 of the octahedral interstices occupied by A1 cations in an ordered array. The octahedral NMR resonance has the parameters 8iso = ca.l6 ppm, Xq = 2.38 MHz (Jakobsen et al. 1989). 

Even though the differences between the Al NMR spectra of the transition aluminas are subtle, the technique has been used to smdy the thermal transformation sequences of the hydrated aluminas gibbsite, Al(OH)3 (Slade et al. 1991, Meinhold et al. 1993), boehmite, 7-AIOOH (Slade e a/. 1991a, Meinhold era/. 1993, Pecharromm eta/. 1999), pseudoboehmite (Meinhold et al. 1993) and bayerite, Al(OH)3 (Meinhold et al. 1993, Pecharroman et al. 1999). 

On the basis of the presence of a NMR resonance at ca. 30 ppm, aluminium in 5-fold coordination has been reported in some transition aluminas, particularly the amorphous P-AI2O3 (Slade et al. 1991, Meinhold et al. 1993). Amorphous precursors of T1-AI2O3 derived from hydrolysis of aluminium in solution show strong resonances at ca. 35 ppm, attributed to 5-coordinate aluminium arising from the movement of Al from octahedral to tetrahedral sites with the creation of oxygen anion vacancies adjacent to occupied octahedral sites (Wood et al. 1990). 

A similar but very weak resonance reported at 30 ppm in 7-AI2O3 heated at 600°C has been attributed to 5-coordinated aluminium atoms on the surface of the oxide particles (Pecharroman et al. 1999). Cross-polarisation experiments between Al NMR and the protons from surface-adsorbed pyridine (Morris and Ellis 1989) or ammonia (Coster et al. 1994) have been used to investigate the surface state of cat-alytically active 7-AI2O3. No NMR evidence has been found of the hypothetical 3-coordinated Al theoretically predicted to occur at the alumina surface. Even assuming for this species a 8iso of 95-100 ppm, a Xq of 10 MHz and an t value of one, Coster et al. (1994) found no experimental evidence for its existence, prompting a recent explanation based on density functional calculations that the 3-coordinated surface Al atoms 

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A pletliora of different SA systems have been reported in tire literature. Examples include organosilanes on hydroxylated surfaces, alkanetliiols on gold, silver, copper and platinum, dialkyl disulphides on gold, alcohols and amines on platinum and carboxyl acids on aluminium oxide and silver. Some examples and references can be found in [123]. More recently also phosphonic and phosphoric esters on aluminium oxides have been reported [124, 125]. Only a small selection out of tliis number of SA systems can be presented here and properties such as kinetics, tliennal, chemical and mechanical stability are briefly presented for alkanetliiols on gold as an example. 

Finally, in 1985, the results of an extensive investigation in which adsorjDtion took place onto an aluminium oxide layer fonned on a film of aluminium deposited in vacuo onto a silicon wafer was published by Allara and Nuzzo 1127, 1281. Various carboxylic acids were dissolved in high-purity hexadecane and allowed to adsorb from this solution onto the prepared aluminium oxide surface. It was found that for chains with more than 12 carbon atoms, chains are nearly in a vertical orientation and are tightly packed. For shorter chains, however, no stable monolayers were found. The kinetic processes involved in layer fonnation can take up to several days. 

Tredgold R FI, Jones S D, Evans S D and Williams P I 1986 Aluminium oxide as a substrate for the deposition of Langmuir-Blodgett films J. Mol. Electron. 2 147-9... 

Early calculations of a similar kind indicated that the compound AlCl is unlikely to exist but at temperatures above about HOOK aluminium oxide AI2O3 and the trichloride AICI3 react to form the compound AlCl on cooling this disproportionates to give the trichloride and aluminium metal... 

Aluminium is obtained on a large scale by the electrolysis of the oxide, dissolved in fused cryolite The oxide, occurring naturally as bauxite, AI2O3.2H2O, usually contains silica and iron(III) oxide as impurities. These must be removed first, since aluminium, once prepared, cannot be freed of other metals (which will be deposited on electrolysis) by refining it. The crude oxide is dissolved under pressure in caustic soda solution the aluminium oxide and silica dissolve and the ironflll) oxide is left ... 

Aluminium oxide occurs naturally as emery (an impure form) and as corundum. Corundum is a crystalline form which may be coloured by traces of impurity, for example as ruby (red) and sapphire (blue). Small synthetic rubies and sapphires have been made by heating alumina with the colouring oxide in an oxy-hydrogen flame. 

Aluminium oxide may be prepared in the laboratory by heating the hydroxide (p. 151) or by heating powdered aluminium in air, when the oxide is formed together with some nitride. The reaction ... 

Aluminium oxide is a white solid, insoluble in water, with a very high melting point. If heated above red heat, it becomes insoluble in acids and alkalis, and can only be brought into solution by first fusing it with sodium or potassium hydroxide when an aluminate is formed. 

Sheet aluminium can be given a colour by a similar process. The aluminium is first made the anode in a bath of chromic acid (p. 377) when, instead of oxygen being evolved, the aluminium becomes coated with a very adherent film of aluminium oxide which is very adsorbent. If a dye is added to the bath the oxide film is coloured, this colour being incorporated in a film which also makes the remaining aluminium resistant to corrosion. This process is called anodising aluminium. 

Aluminium nitride can also be prepared by heating a mixture of aluminium oxide and carbon in nitrogen in an electric arc furnace ... 

It is a green powder, insoluble in water and in acids (cf. aluminium oxide, AI2O3). It is not reduced by hydrogen. 

Aluminium oxide. The commercial material, activated alumina, is made from aluminium hydroxide it will absorb 15-20 per cent, of its weight of water, can be re-activated by heating at 175° for about seven hours, and does not appreciably deteriorate with repeated use. Its main application is as a drying agent for desiccators. 

Cyclopentadiene (2.5) was prepared from its dimer (Merck-Schuchardt) immediately before use. Dimineralised water was distilled twice in a quartz distillation unit. Ethanol (Merck) was of the highest purity available. Acetonitrile (Janssen) was mn over basic aluminium oxide prior to use. 2,2,2-Trifluoroethanol (Acros) was purified by distillation (bp 79 - C). Co(N03)2 6H20,... 

AI2O3 (aluminium oxide) in ruby laser, 346 in titanium-sapphire laser, 348 3142 (cyclic) interstellar, 120 3142 (linear) interstellar, 120... 

ALUMDJUMCOMPOUNDS - ALUMINIUM OXIDE (ALUMNA) - CALCINED, TABULAR, AND ALUMINATECETffiNTS] (Vol 2)... 

ALUMDIUMCOMPOUNDS - ALUMINIUM OXIDE (ALUMDIA) - ACTIVATED] (Vol2)... 

Composition materials ineluding indieator reagent and bearer have been investigated as sensor materials. It has been found out that nature of beai er (sorbent or polymer film) is of the main signifieanee. Siliea gel, aluminium oxide, porous glass, polyurethane, polyvinylehloride ete have been investigated as beai ers. 

Alumina powder is made from bauxite, a hydrated aluminium oxide with the formula AlfOH), of which there are large deposits in Australia, the Caribbean and Africa. After crushing and purification, the bauxite is heated at 1150°C to decompose it to alumina, which is then milled and sieved... 

Aluminium oxide Hydrotreating petroleum feedstocks Fluid cracking Autoexhausts Nuisance... 

Desiccant grade activated alumina is a highly porous form of aluminium oxide. It has the appearance of white chalky beads. Standard stock sizes have 2 - 5 mm or 5 - 8 mm. beads. An adsorbent from liquids and gases it is supplied usually in bulk packs. 

Shaver s disease A disease of the lungs found in workers exposed to fumes or dusts containing aluminium oxide. It is a type of pneumoconiosis and results in interstitial fibrosis and decreased lung function. 

Organic fluorescence indicators for aluminium oxide, silica gel and cellulose layers (code F366, UV366) include ... 

Silica gel and aluminium oxide layers are highly active stationary phases with large surface areas which can, for example, — on heating — directly dehydrate, degrade and, in the presence of oxygen, oxidize substances in the layer This effect is brought about by acidic silanol groups [93] or is based on the adsorption forces (proton acceptor or donor effects, dipole interactions etc) The traces of iron in the adsorbent can also catalyze some reactions In the case of testosterone and other d -3-ketosteroids stable and quantifiable fluorescent products are formed on layers of basic aluminium oxide [176,195]... 

Aluminium oxide deoxynivalenol in wheat 7 mm at 120 °C, yields a fluorescent derivative under UV light (i = 365 nm) [193, 196]... 

It is known that not all reactions proceed in the same manner on all adsorbent layers because the material in the layer may promote or retard the reaction. Thus, Ganshirt [209] was able to show that caffeine and codeine phosphate could be detected on aluminium oxide by chlorination and treatment with benzidine, but that there was no reaction with the same reagent on silica gel. Again the detection of amino acids and peptides by ninhydrin is more sensitive on pure cellulose than it is on layers containing fluorescence indicators [210]. The NBP reagent (. v.) cannot be employed on Nano-Sil-Ci8-100-UV2S4 plates because the whole of the plate background becomes colored. 

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