Aluminosilicate gel

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

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

Aluminide alloys, 13 530 Aluminium powder, 10 738. See also Aluminum entries Aluminohydride derivatives, 13 624 Aluminohydrides, 13 621-624 Aluminophosphate zeolites, 14 98 Aluminosilicate gels, 16 830 Aluminosilicate glass, matrix for... 

Sodium aluminate, 2 345t, 358-359 analysis, 2 275-276 economic aspects, 2 275 health and safety factors, 2 276 manufacture, 2 274-275 neutralization, 2 424 physical and chemical properties of, 2 273-274 uses of, 2 276-277 in water treatment, 26 111 Sodium aluminosilicate gels, synthetic zeolites prepared from, 16 831t Sodium aluminosilicates, 12 578 Sodium aluminum hydride, 13 621, 623-624... 

M ions (among which Na+ from NaCl) interact with the aluminosilicate gel (and eventually direct its structure towards a zeolite framework by template effect), more readily than the Na+ which were originally associated with the silicate anions. 

The general behaviour of the alkali cations in presence of aluminosilicate gels and their influence on zeolite nucleation and crystallization rates has been discussed in detail elsewhere (26). Their specific role in the formation of the various (M)ZSM-5 zeolites can be depicted on the basis of the above described observations. ... 

In basic medium, negative A1 species appear and condense with the remaining silicate entities, as to yield an Al-rich aluminosilicate gel. A few Al-richer nuclei can then form and yield a small amount of Al-richer ZSM-5 particles at the end of the process. 

Alkanes—Continued reactions—Continued with ozonide ions, 135 with superoxide ions, 134-35 role of oxygen ions in oxidation. 138-41 Alkenes, reactions with oxygen ions, 134 with ozonide ions, 135 with superoxide ions, 134-35 Aluminosilicate gels, alkali cations, 241... 

The method developed by Milton in the late 1940s, involves the hydrothermal crystallization of reactive alkali metal aluminosilicate gels at high pH and low temperatures and pressures, typically 100°C and ambient pressure. Milton, Breck and coworkers synthesis work led to over 20 zeolitic materials with low to intermediate Si/Al ratios (1-5) [86]. Chapter 3 and references [1] and [25] provide more detailed discussion of synthesis. 

Flanigen monitored the changes in the IR spectra that occur during the synthesis of NaX zeolite from a sodium aluminosilicate gel. The appearance of absorption bands due to the formation of structural units in the zeoUte as the crystallization of NaX proceeded were observed [93]. In particular, the growth of a band around 575 cm indicated the formation of double six-rings which is one of the structural sub-units of X zeolite. 

The aqueous chemistry of aluminum(III) above pH 6 differs from that of silicates in that the only important species, other than solid Al(OH)3 at pH 5-8, is Al(OH)4, which, although isoelectronic with Si(OH)4, shows no tendency to catenate. On the other hand, below pH 5 Alm, unlike the poorly soluble Si(OH)4, is freely soluble as Al3+(aq) [actually Al(OH2)63+, Section 13.2], while at intermediate pH hydrolytic A1 species, including the ion Ali304(0H)24(0H2)127+ referred to above, predominate in solution. However, Al(OH)4 units can readily insert themselves into silicate anion species in solution. The result is usually the prompt precipitation of an aluminosilicate gel (a typical zeolite precursor), although over some limited Al, Si, and OH- concentration ranges quite high concentrations of dissolved aluminosilicates can be maintained over many months.9... 

A previous examination of a synthetic calcium mordenite 15) revealed an orthorhombic cell. A synthetic strontium mordenite 16) had a C-centered orthorhombic cell although Kerr 12) reported that a few crystals giving electron diffraction patterns corresponding approximately to the body-centered structure Immm) have been synthesized hydro-thermally from aluminosilicate gels containing strontium similar to those gels which yielded a strontium-mordenite. ... 

Barrer and Mainwaring (20) report the use of metakaolin as the aluminosilicate raw material for reaction with the hydroxides of K and Ba as well as the binary base systems Ba-K and Ba-TMA to form zeolites. Zeolite phases previously synthesized in the analogous hydrous aluminosilicate gel systems were crystallized with KOH, including phillipsite-, chabazite-, K-F-, and L-type structures. The barium system yielded two unidentified zeolite phases (Ba-T and Ba-N) and a species Ba-G,L with a structural resemblance to Linde zeolite L. Ba-G,L was reported previously by Barrer and Marshall (21) as Ba-G. Similar phases were formed in the Ba-K system and in the TMA-Ba system where, in addition, erionite-type phases were formed. The L-type structures are said to represent aluminous analogs of the zeolite L previously reported (22). 

Crystallization was followed by analyzing the solid product quantitatively by x-ray powder diffraction. Prepared mixtures of a standard sample of mordenite and the amorphous substrate of mordenite composition were used to establish a calibration curve for the quantity of mordenite based on the summation of x-ray peak intensities. For zeolites A and X, the unreacted aluminosilicate gel was used to prepare mixtures with standard samples of zeolites A and X for quantitative phase identification. 

The crystallization of zeolites from alkaline aluminosilicate gels was studied by luminescence and Raman spectroscopy. Trace amounts of Fe3+ ions substituted for Al3+in the tetrahedral aluminosilicate gel framework exhibit characteristic phosphorescence spectra, which have been used to follow the buildup of the zeolite framework. Phosphorescence spectra of exchanged Eui+ cations and Raman spectra of (CH N+ cations present in the solid phase of the gel indicate that no zeolitic cages exist in this phase during the induction period. Raman spectra of the liquid phase of the gel system show only the presence of Si02-(0H)2 and Al(OH)a anions. Our results demonstrate that crystallization of zeolites occurs within the solid phase of the gel, which is believed to consist of amorphous tetrahedral alumino-... 

Several proposals have been advanced for this mechanism. On the basis of electron microscopy studies and chemical analysis of aluminosilicate gels Breck and Flanigen concluded that crystallization occurs from the solid gel phase (3, 4) The induction period was postulated to be a time... 

Zeolite formation depends on reaction conditions 2-4). It is generally believed that most zeolites are formed as metastable phases. According to Barrer (3), the course of the synthesis, beginning with the type of starting material, determines the structure of the zeolite formed. The studies of Zhdanov 2, 5) on the composition of liquid and solid phases of hydrogels indicate that the kind and composition of the zeolite formed depend on the hydrogel composition and that the results of crystallization of aluminosilicate gels obtained in the same way are reproducible. 

Zeolite Na-A was synthesized in our laboratory. After crystallization from the sodium aluminosilicate gel, the zeolite was carefully washed with deionized water in order to remove occluded impurities without causing H30+ ion exchange. It was then stored in a desiccator containing saturated NH4CI solution. 

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