Activated aluminium oxides

Prokisch et al. [85] described a simple method for determining chromium speciation in soils. Separation of different chromium species was accomplished by the use of acidic activated aluminium oxide. Polarographic methods have been applied in speciation studies on chromium(VI) in soil extracts [86]. Mi-lacic et al. [88] have reviewed methods for the determination of chromium(VI) in soils. 

Phosphaallenes can be synthesized in the same way as 1,3-diaryl-substituted allenes following an aluminium-catalyzed propargyl rearrangement. Using sodium hydroxide-activated aluminium oxide (125), the synthesis is suitable on an enlarged scale without any detectable by-products [Eq. (63)]. A similar proton migration within a coordinated phosphaalkyne was reported recently (126). 

Activated aluminium oxides are commercially available with particle sizes between 2 nun and 10 nun and used for the drying of gases and liqirids (removal of water). This adsorbent is resistant to weak alkaline solutions however, it can be destroyed by acids. 

If arsenic is to be removed from the water, this can be achieved by coprecipitating it on iron or manganese hydroxides, or by filtering the water, after acidification with CO2 (pH 6 - 6.3), over activated aluminium oxide. (W. Fresenius and W. Schneider)... 

The adsorber vessel is filled with zeolitic crystals [2.26] which are bound with ceramic material and formed to spheres of about 3 mm diameter or rods. The crystalline components have pores with diameters in the range of approx. 1 nm. H2O as well as other polar or easily polarizable impurities such as CO2 and various hydrocarbons are retained in the pores. Frequently a thin layer of activated aluminium oxide for H2O adsorption is arranged in front of the zeolitic layer. 

Following such a pretreatment, a controlled, high-energy film of active, aluminium oxide/hydroxide , eminently suitable for structural bonding, will have been grown on the surface of the aluminium. The oxide film can be seen in Fig. 5 at the interface between the alloy and the adhesive. It is a needle-Uke structure growing from the underlying aluminium substrate and has a thickness of about 300 A. It is clear that the adhesive completely wets and penetrates this surface. 

Following such a pretreatment, a controlled, dense, high energy film of active aluminium oxide/hydroxide will have been grown on the surface of the aluminium. The film thickness will be in the region of 3-4 p.m. 

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. 

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

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. 

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]... 

Hitzig et al. have produced a simplified model of the aluminium oxide layer(s) to explain impedance data of specimens prepared under different layer formation and sealing conditionsThe model also gives consideration to the formation of active and passive pits in the oxide layer. Shaw et al. have shown that it is possible to electrochemically incorporate molybdenum into the passive film which, as previously noted, improves the pitting resistance. 

As is well known chemical reactions are accelerated by increasing the temperature. This also applies to heterogeneously catalyzed reactions taking place on the surface of polar sorbents such as aluminium oxide or silica gel (Tables 2.1 and 2.2). Such reactions have also been reported on the moderately polar NH2 layers. Alperin et al. have described the activation of cellulose to yield specific information concerning the substances chromatographed [1]. 

At elevated temperatures in the presence of oxygen the aluminium oxide layer catalyzes the formation of blue fluorescent aluminium oxide surface compounds with 4-hydroxy-3-oxo-A -steroid structures [4]. Aluminium oxide acts as an oxidation catalyst for an activated methylene group. 

A washcoat, which provides a high surface area onto which the active catalyst is impregnated. The washcoat typically consists of a mixture of zirconium, cerium and aluminium oxides. Apart from providing high surface area the washcoat also acts as an oxygen storage system (see below). 

Two contrasting conclusions have been reported in the reactions of lithium aluminium hydride in THF with phosphine oxides and phosphine sulphides respectively. The secondary oxide, phenyl-a-phenylethylphos-phine oxide (42), has been found to be racemized very rapidly by lithium aluminium hydride, and this observation casts some doubt on earlier reports of the preparation of optically active secondary oxides by reduction of menthyl phosphinates with this reagent. A similar study of the treatment of (/ )-(+ )-methyl-n-propylphenylphosphine sulphide (43) with lithium aluminium hydride has revealed no racemization. These results have been rationalized on the basis of the preferred site of attack of hydride on the complexed intermediate (44), which, in the case of phosphine oxides (X = O), is at phosphorus, and in the case of the sulphides (X = S), is at sulphur. Such behaviour is comparable to that observed during the reduction of phosphine oxides and sulphides with hexachlorodisilane. ... 

Freeder, B. G. et al., J. Loss Prev. Process Ind., 1988, 1, 164-168 Accidental contamination of a 90 kg cylinder of ethylene oxide with a little sodium hydroxide solution led to explosive failure of the cylinder over 8 hours later [1], Based on later studies of the kinetics and heat release of the poly condensation reaction, it was estimated that after 8 hours and 1 min, some 12.7% of the oxide had condensed with an increase in temperature from 20 to 100°C. At this point the heat release rate was calculated to be 2.1 MJ/min, and 100 s later the temperature and heat release rate would be 160° and 1.67 MJ/s respectively, with 28% condensation. Complete reaction would have been attained some 16 s later at a temperature of 700°C [2], Precautions designed to prevent explosive polymerisation of ethylene oxide are discussed, including rigid exclusion of acids covalent halides, such as aluminium chloride, iron(III) chloride, tin(IV) chloride basic materials like alkali hydroxides, ammonia, amines, metallic potassium and catalytically active solids such as aluminium oxide, iron oxide, or rust [1] A comparative study of the runaway exothermic polymerisation of ethylene oxide and of propylene oxide by 10 wt% of solutions of sodium hydroxide of various concentrations has been done using ARC. Results below show onset temperatures/corrected adiabatic exotherm/maximum pressure attained and heat of polymerisation for the least (0.125 M) and most (1 M) concentrated alkali solutions used as catalysts. 

Some oxide-type minerals have been found to luminesce when irradiated. A simple example is ruby (aluminium oxide with chromium activator), which emits bright-red light. The phosphors are incorporated into colour television screens to emit the colours blue (silver-activated zinc sulphide), green (manganese-activated zinc orthosilicate), and red (europium-activated yttrium vanadate). 

Aluminium oxide (neutral, activity grade I) available from M. Woelm, Eschwege, Germany, was deactivated by the addition of 7 ml. of water to 1 kg. of the adsorbent before use. 

Another very interesting application of this increased chemical activity of aluminium when amalgamated with mercury is incorporated in a toy which is sometimes seen on sale under the name of" Daddy Tin Whiskers . This toy consists of an aluminium stamping of a face and a pencil, the core of which is filled with a preparation chiefly composed of a mercury salt. It is operated by rubbing the eyebrows and chin with this special pencil. Shortly afterwards white hairs of aluminium oxide (AlsOj) gather wherever the pencil has touched the aluminium. 

Purification of the extract hy filtration through a column with aluminium oxide (activity grade II)... 

Recently, the preparation of metallosilicates with MFI structure, which are composed of silicone oxide and metal oxide substituted isomorphously to aluminium oxide, has been studied actively [1,2]. It is expected that acid sites of different strength from those of aluminosilicate are generated when some tri-valent elements other than aluminium are introduced into the framework of silicalite. The Bronsted acid sites of metallosilicates must be Si(0H)Me, so the facility of heterogeneous rupture of the OH bond should be due to the properties of the metal element. Therefore, the acidity of metallosilicate could be controlled by choosing the metal element. Moreover, the transition-metal elements introduced into the zeolite framework play specific catalytic roles. For example, Ti-silicate with MFI structure has the high activity and selectivity for the hydroxylation of phenol to produce catechol and hydroquinon [3],... 

Aluminium is much cheaper than transition metals, and aluminium oxide is non-toxic. Aluminium residues in a polymer would probably not be harmful. Thus, a catalyst based on aluminium could be extremely attractive, even if it were significantly less active than a transition metal catalyst. This has probably contributed to the continued interest in (potential) aluminium polymerization catalysts. However, such studies are difficult, as even traces of transition metal contamination may lead to erroneous conclusions. According to calculations, insertion barriers at aluminium are typically >10 kcal/mol higher than at transition metal catalysts, corresponding to a reactivity difference of 10, so... 

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