Aluminosilicates preparation

A gel is delined as a hydrous metal aluminosilicate prepared from either aqueous solutions, reactive solids, colloidal sols, or reactive aluminosilicates such as the residue structure of metakaolin and glasses. 

A recent article reported the use of strongly acidic mesoporous aluminosilicates prepared from zeolite seeds in the acylation of anisole with octanoyl chloride.[30] The mesoporosity improving the transport of the reactants and the presence of strong acid sites lead to high conversion (>90 %) and high selectivity (100 %). 

Shih, P.-C., Wang, J.-H., Mou, C.-Y. Strongly acidic mesoporous aluminosilicates prepared from zeolite seeds acylation of anisole with octanyl chloride, Catal. Today, 2004, 93-95, 365-370. 

Recently, two kinds of acid sites were proved to exist in nickel oxide-aluminosilicate prepared by a method practically identical with the SHOP method. One was the familiar type known to exist in aluminosilicates in general and the other originated from the combination of nickel oxide with silica and promoted the same reactions described above 14). 

Fig. 24. Palladium on aluminosilicate prepared by cation-exchange method. Palladium content, 1.24 meq/gm.

The MCM-type materials belong to a new family of ordered, mesoporous silicate/aluminosilicate prepared by hydrothermal formation of silica gels in the presence of surfactant templates (Beck et al., 1992). They were discovered only recently, by Beck et al. in 1992, and hold promise for a number of interesting applications. Hence they are included in this chapter. 

Fig. 2. Al MAS NMR spectra of cylindrically shaped aluminosilicates prepared with a Si Al ratio of 20 and functionalised with copper and silver by direct incorporation method.

The occurrence of allophane in rocks is associated with conditions that favor formation of random-structure aluminosilicates. Thus, allophanes of geological origin that occur in fissures of ore veins, on linings of cavities in marl, and in similar locations, appear to have been formed by precipitation at relatively low temperatures and pressures from solutions containing silicon and aluminum. Hydrous aluminosilicates prepared artificially in a similar... 

Table 3. Some Synthetic Zeolites Prepared from Sodium Aluminosilicate Gels...

Sodium alumiaate is widely used in the preparation of alumina-based catalysts. Aluminosilicate [1327-36-2] can be prepared by impregnating siHca gel with alumiaa obtained from sodium alumiaate and aluminum sulfate (41,42). Reaction of sodium alumiaate with siHca or siHcates has produced porous crystalline alumiaosiHcates which are useful as adsorbents and catalyst support materials, ie, molecular sieves (qv) (43,44). 

Multicomponent sol—gel fibers have been successfuUy developed (1,52). The early stages of sol formation and gelation are cmcial for controlling the fiber microstmcture. Aluminosilicates, zirconates, and aluminates (1,18,52) can be prepared by sol—gel methods. MuUite [55964-99-3] 3AI2 O3 -2Si02, fibers... 

After the blends have been prepared (either in the dry or wet process), these materials are fed at a uniform rate into a long rotary kiln. The materials are gradually heated to a liquid state. At temperatures up to about I,600°F the free water evaporates, the clay minerals dehydroxylate and crystallize, and CaCO, decomposes. At temperatures above 1,600°F the CaCO, and CaO react with aluminosilicates and the materials become liquids. Heating is continued to as high as 2,800°F. 

Dental silicate cement was also variously known in the past as a translucent, porcelain or vitreous cement. The present name is to some extent a misnomer, probably attached to the cement in the mistaken belief that it was a silicate cement, whereas we now know that it is a phosphate-bonded cement. It is formed by mixing an aluminosilicate glass with an aqueous solution of orthophosphoric acid. After preparation the cement paste sets within a few minutes in the mouth. It is, perhaps, the strongest of the purely inorganic cements when prepared by conventional methods, with a compressive strength that can reach 300 MPa after 24 hours (Wilson et al, 1972). 

Table 8.1. Properties of aluminosilicate glass cements prepared with various acids in aqueous solution Wilson, 1968)...

An equally simple chemical study was carried out on phytic acid-aluminosilicate cements (Prosser et al., 1983). Phytic acid, myo-inositol hexakis(dihydrogen phosphate), is a naturally occurring substance found in seeds, and it is a stronger acid than phosphoric acid. Cements were prepared using aqueous solutions of phytic acid, concentrated to 50 wt%, and with 5 wt % zinc dissolved in the acid to moderate the rate of reaction with the glass powder. Discs of cement were prepared and these were... 

In a study of dental silicate cements, Kent, Fletcher Wilson (1970) used electron probe analysis to study the fully set material. Their method of sample preparation varied slightly from the general one described above, in that they embedded their set cement in epoxy resin, polished the surface to flatness, and then coated it with a 2-nm carbon layer to provide electrical conductivity. They analysed the various areas of the cement for calcium, silicon, aluminium and phosphorus, and found that the cement comprised a matrix containing phosphorus, aluminium and calcium, but not silicon. The aluminosilicate glass was assumed to develop into a gel which was relatively depleted in calcium. 

Molecular sieves (zeolites) are artificially prepared aluminosilicates of alXali metals. The most common types for gas chromatography are molecular sieve 5A, a calcium aluminosilicate with an effective pore diameter of 0.5 nm, and molecular sieve 13X, a sodium aluminosilicate with an effective pore diameter of 1 nm. The molecular sieves have a tunnel-liXe pore structure with the pore size being dependent on the geometrical structure of the zeolite and the size of the cation. The pores are essentially microporous as the cross-sectional diameter of the channels is of similar dimensions to those of small molecules. This also contrilsutes to the enormous surface area of these materials. Two features primarily govern retention on molecular sieves. The size of the analyte idiich determines whether it can enter the porous... 

Aluminosilicate gel samples having the same composition, Me20-Al203-Si02-H20 (Me = Na, K, Rb and Cs) were prepared by two different procedures ... 

Preparation of the composite materials with the FAU and BEA nanodomains has been reported previously [3,4]. The procedure was based on the impregnation of the parent materials with concentrated template solutions and subsequent recrystallization in the hydrothermal conditions. Amorphous aluminosilicates of chemical composition 13%Al20387%Si02 (13A187Si) and 6%Al20394%Si02 (6A194Si) were used as the parent materials for the FAU and BEA composites, respectively. 

The formation of the microporous phase dispersed in porous, amorphous matrices was followed by XRD and TEM. The XRD patterns of the BEA-composite prepared using the Al-poor aluminosilicate (6A187Si) are shown in Figure 1. BEA was the sole... 

Mesoporous silica was prepared using sodium silicate as silica source and cetyltrimethylammoniumbromide (CTMABr) as template as elsewhere [7]. The aluminosilicates were prepared with a similar procedure by using sodium aluminate as aluminum source, which was dissolved in the surfactant solution as described before [3]. Si/Al molar ratios were of 6, 10, 30 and 80, the impregnated iron amount was 6 wt. 

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