Aluminum oxide/hydroxide layers

Zeolites are aluminosilicates, and considering this, an aluminosilicate composed of silica sheets (SiaOs) bonded to aluminum oxide/hydroxide layers [Al2(OH)4] (China clay with kaolinite composition) is compared with zeolites in LRAM3.56-PP/PER formulations (Figure 6.6). The curves exhibit the same... 

The selective intercalation of guests into solid hosts offers the potential for application in catalysis and separation science. An excellent case in point is zeolites, which exhibit shape and size selective inclusion properties and are used for an enormous variety of processes [44,45]. Additionally, a munber of layered materials have been reported to possess selective intercalation properties, including layered metal phosphonates [46,47], montmorUlonite [48], magnesium aluminum oxide [49], and layered double hydroxides [50-59]. 

The step 1 product (21 g) was dissolved in 210 ml of CH2CI2 and then treated with 77% m-chloroperbenzoic acid (41.6 g) at ambient temperature for 6 hours. The mixture was then poured into a solution of sodium hydroxide (40 g) dissolved in 150 ml of water and 200 ml of hexane and then stirred and cooled to 10°C using an ice bath. The organic layer was isolated and washed once with 100 ml of 5% Na2S204 and three times with 100 ml of 10% KC1 solution. The mixture was concentrated and the residue purified using silica gel column chromatography with hexane/ ethyl acetate, 3 1, respectively. An oil, which was obtained, was dissolved in 100 ml of 10% ethyl acetate in hexane and treated with basic aluminum oxide (3 g) to remove color on the product. After filtration 13 g of product were isolated as a liquid. 

A solution of 1.04 g of 6-chloro-9p,10a-pregna-4,6-diene-3,20-dione and 0.95 g of 2,3-dichlorobenzoquinone in 50 ml of dry benzene was heated to reflux for 10 hours. The reaction mixture was diluted with 70 ml of benzene and extracted three times with 50 ml of 2 N sodium hydroxide solution. The benzene layer was washed with water to neutral, dried with sodium sulfate and evaporated to dryness. The residue (0.7 g) was chromatographed on 20 g Of aluminum oxide (activity II). The fraction eluted with benzene-petroleum ether were combined and recrystallized from acetone. The 6-chloro-9p,10a-pregna-l,4,6-triene-3,20-dione melted at 208-209°C(decomposition), Xmax 229 nm. 

In general, minerals in sedimentary and meta-morphic rocks contain ferrous iron (Velde, 1985) which is destined to become iron oxide under conditions of weathering. Oxidation under surface conditions has a tendency to produce iron in the ferric state. Most often the process takes iron out of the silicates and puts it into an oxide phase. In the uppermost layers of mature soils, iron oxide and various silicates, usually non-iron-bearing, are produced. In silicates containing iron, the majority is in the ferric state. The extent of the transformation of iron oxidation state is a rough measure of the maturity of the soil. In the extremely weathered soils one finds only ferric iron and aluminum oxides and hydroxides. These soils are typically red. 

Because both the black and the green materials contain aluminum oxide or hydroxide, a cause for the black color must be found. The amorphous copper material that shows in the EDAX results but not on the XRD pattern may be this cause. A possible source of the black color in corroded bronze is suggested by Gettens (13) in his study of the corrosion of an ancient Chinese fragment. He attributes a black color in the corrosion layers to the presence of tenorite (CuO) and states that because it is so amorphous, it gives indistinct diffraction patterns or none at all. In a later paper Gettens (14) repeats his belief that the dark product in bronze corrosion is tenorite and stresses the need for further analysis. Plenderleith (15) agrees that the dark material in bronze corrosion is tenorite, but much debate continues as evidenced by a more recently published discussion between corrosion scientists and museum conservators (16). 

Layered double hydroxide carbonates of magnesium and aluminum are called hydrotalcites (e.g., Mg6Al2(OH)i6 CO3-H2O). They can be used as solid bases before or after calcination to produce mixed magnesium-aluminum oxides.74 They have been used to catalyze the addition of alcohols to acrylonitrile 75 the reduction of ketones with iso-... 

Scheckel KG, Scheinost AC, Ford RG, Sparks DL (2000) Stability of layered Ni hydroxide surface precipiates - A dissolution kinetics study. Geochim Cosmochim Acta 64 2727-2735 Scheidegger AM, Lamble GM, Sparks DL (1997) Spectroscopic evidence for the formation of mixed-cation hydroxide phases upon metal sorption on clays and aluminum oxides. J Coll Interf Sci 186 118-128... 

Coatings can form naturally by reaction with the surrounding atmosphere aluminum is quickly covered by an aluminum oxide and hydroxide layer in the presence of oxygen and water. This inert and protective layer can be formed artificially, as is done for window and door frames. A porous layer of alumina can be formed by reaction with oxygen. Pigments can be included in the pores for decorative purposes. After inclusion of the pigments, a suitable treatment of the layer transforms its porous structure to a continuous nonporous one (sealing). These coated frames can withstand relatively harsh conditions for years. 

Stone suggests that catalysis occurs because the ionized carboxylate group of MPT is able to specifically sorb to the positively charged aluminum oxide surface where subsequent attack of hydroxide ions in the diffuse layer occurs. 

For aluminum, the outer surface of the oxide layer in humid environments is considered to be a mixture of aluminum oxide and aluminum hydroxide. After the adsorption of chloride ions, an ion exchange can occur leading to the substitution of hydroxyl ions by chloride ions [179, 180]. After the chemical attack of the oxide, aluminum is electrochemicaUy dissolved. The chloride ions are regenerated after the dissolution of the transitory hydrox-ychloride compounds. Thus, a relatively small amount of chloride ions can result in a progressive attack of the protective layer. Within the head of the filiform filament, the anodic dissolution of aluminum leads to a local acidification of the anolyte due to the hydration of aluminum ions. It has been observed that a secondary cathodic reaction, the reduction of hydrogen ions, can occur. Hydrogen evolution has been observed within the head [166]. 

The aluminum oxide layer was applied to the inner walls of the glass capillary from an aqueous dispersion in the form of aluminum hydroxide and converted In situ into aluminum oxide by heat treatment. By varying heat treatment and by blocking unwanted activities with potassium chloride, adjustment to the desired separation characteristics can be achieved [55]. To prepare the coating suspension, aluminum oxide (particles <2 urn) obtained by calcination of hydroxide is heated for 24 h at 300 °C. 20 g of the alumina is mixed with 70 ml of 5% (w/w) Baymal solution (colloidal aluminum hydroxide) and with 0.3 ml of acetic acid (>96%) and stirred for about 10 min in an ultrasonic bath. Subsequently the mixture is filtered through a wire sieve of 300 mesh and allowed to stand for 24 h for aging. The suspension thus prepared shows thixotropic behavior. 

In the aluminate route to LDH, aluminum salt (113,114), aluminum hydroxide (115,116), or aluminate (117-119) is initially treated with the required amount of base (e.g., six hydroxides for each aluminum if the product is to be of type M(II)2A1(0H)6X), followed by addition of M(II), either in a salt or a carbonate form (113-115,117,119) or in the form of an oxide or hydroxide (116,118,120,121). The pH graph observed for this titration shows endpoints related to the formation of Al(OH)3, aluminate, and LDH. This method of formation yields LDH directly from solution, with no intervening solid phase. The product has an increased degree of order in the metal hydroxide layer and slightly smaller surface area when compared to LDH prepared by other methods, as shown by infrared spectroscopy, powder X-ray diffractometry, scanning electron microscopy, and MAS Al and MAS Cl NMR (113,114,122). 

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