Aluminate sodalites

A slightly different linear relationship was found by Weller et al. (1994) between 8iso and the mean tetrahedral Al-O-Al bond angles in a series of 7 aluminate sodalites... 

The data of Weller et al. (1994) for 7 aluminate sodalites have also been found to show a linear relationship between Xq and li l... 

Fig. 13. Schematic drawing (top) of the VPI-5 structure and the plot (bottom) of the quadru-pole coupling constants, of Al as a fimction of the shear strain parameter of AIO4 tetra-hedra in aluminate sodalites (A, V), feldspars ( ), and VPI-5 ( ) [112,113]...

Depmeier, W. (1987), "Aluminate sodalites. A family of inclusion compounds with strong host-guest interactions", J. Incl. Phen., 5,279-282. 

W. DEPMEIER / Aluminate Sodalites - a Family of Inclusion Compounds with Strong Host-Guest... 

ALUMINATE SODALITES - A FAMILY OF INCLUSION COMPOUNDS WITH STRONG HOST-GUEST INTERACTIONS... 

Aluminate sodalites belong to a structural family which, in principle, has been known for quite a long time and which is closely related to various zeolites. Naturally occurring sodalites belong to the class of aluminosilicates (e.g., sodalite in the proper sense has the idealized formula Nag [A1 pSig02i ] CI2) 5 whereas aluminate sodalites have a composition Mg [a1 2 24 2 (pseudo-)cubic cell... 

It is also of interest to use MAS NMR for the study of the thermal treatment of zeolites which are not in the ammonium-exchanged form. In an X-ray study, Pluth and Smith (179) found electron density at the center of the sodalite cages in dehydrated zeolites Ca-A and Sr-A and attributed this to a partial occupancy of these sites by a four-coordinated aluminous species. No such effect was found in zeolite A exchanged with monovalent cations. Corbin et al. (180) used 27A1 MAS NMR to examine commercial samples of K-A, Na-A and (Ca,Na)-A, as received (see Fig. 41). For K-A and Na-A, only framework tetrahedral Al species were observed, with chemical shifts of 57 and 52 ppm respectively. However, in (Ca,Na)-A an additional intense resonance at 78 ppm, typical of AlfOH) but definitely not due to framework aluminum, was also found (see Fig. 41). A much weaker signal, also at 78 ppm, was detected in zeolite Sr-A its intensity increased greatly on heating the sample to 550°C. Freude et al. (183) came to very similar conclusions in their NMR study of heat-treated zeolite Ca-A. They found that maximum framework dealumination occurs at 500°C and corresponds to ac. 17% of total Al. 

Water and hydroxyl ion are the classic mineralisers in hydrothermal synthesis, firstly because aqueous alkali dissolves amphoteric oxides and so promotes mobility and mixing of molecular and ionic species as a pre-requisite for reaction. A second vital role is that of molecular water which (see below) stabilises aluminous zeolites by filling channels and cavities. This role can be shared or taken over by organic molecules (e.g. in porosils, silica-rich zeolites or AlPO s), and by salts (e.g. in scapolites, sodalite and cancrinite). 

In preparation series b the addition of 20 wL% AI(P03)3 constitutes an amount of 3/4 of the binder mass in fact. There is a surplus of added AI(P03)3. Corresponding to the above three steps of reaction, the amount of crystalline by-products NatP207 and Na2HP04 increases also with an increase in added AI(P03)3 in this preparation series b of note is the observation of the crystalline aluminosilicate, sodalite. This fact can be valued as a hint for introduction of aluminate in the formed network. Evaluations of the balance of components show a distinct dominance of the silicate for the amorphous phase (Reference ). 

Fukui et al. [33] have investigated the effects of NaOH concentration on the crystal stracture and the rate of reaction of the synthesized zeolite from fly ash with a hydrothermal treatment method. They have reported that fly ash or the mixture of fly ash and silica powder results in an increase in the reaction rates with the increase of NaOH concentration due to increase of the dissolution rate of silicate ion and aluminate ion. It has been clarified that the NaOH concentration also affects the crystal structure of synthesized zeolites. It has been concluded that the proportion of Phillipsite continues to be lower than the increasing proportion of Hydroxy-sodalite in the product with the increase in the concentration of NaOH. 

Fukui et al. [8] have utilized NaCl for synthesis of Phillipsite from fly ash by hydrothermal treatment with microwave heating. It has been reported that the crystallinity of Philhpsite can be increased by addition of NaCl in the hydrothermal reaction matrix with low concentration of NaOH, whereas no effects have been reported in case of high concentration of NaOH. However, microwave heating has been a favorable tool for the generation of Hydroxy-sodalite. It has been demonstrated that the substitution of NaCl by NaOH can reduce the rate of dissolution of aluminate and silicate ions from fly ash. As such, the rate of generation of aluminosilicate gel can be enhanced by employing microwave heating of the solution. 

Shigemoto et al. [9] have reported about selective formation of Na-X zeolite from a mixture of coal fly ash procured from two different sources. It has been reported that most of the fly ash particles got converted into silicates and aluminates of sodium during 1 h of fusion at 773 K, whereas the hydrothermal activation for 6 h of the fused product, crystallized into Na-X, Na-A, Na-Pl and Hydroxy-sodalite zeolites in different proportions based on Na/Fly ash ratio (i.e., 1.2-1.8) employed and Al content of fly ash. It has been opined that fly ash enriched with aluminium, can be crystallized to zeolite Na-A in place of Na-X. 

Gmtzeckand Siemer [45] have investigated the synthesis of zeolites from a mixture of class-F fly ash and slurry of sodium aluminate prepared in proportion of 3 1 (i.e., Na Al). They have reported that a class-F fly ash reacts with the slurry to synthesize zeolites from a highly alkaline waste stream. The reaction has been studied as a function of mixture (i.e., fly ash slurry) composition (3 2, 1 1, and 1 2), time (1, 3, and 7 days), and temperature (80, 130, and 180 °C). The X-ray diffraction analysis of the products has indicated that the reaction between fly ash and sodium aluminate can result final yield as zeolite A, Na-Pl, and Hydroxy-sodalite at 80, 130 and 180 °C, respectively. It has been clarified that the bulk of the sodium has been incorporated into the zeolitic phases. 

Compositional ranges reported for particular zeolites are illustrated in Table IV. One of the most remarkable examples of isomorphous replacement for a given framework topology is found with sodalite. The framework exists as a pure Ca-aluminate (Si/Al = 0) as a normal sodalite at the Lowenstein limit (Si/Al = 1) as a silica-rich form. 

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