Silicon-aluminum ratio formula

There are several crystal phases and each has some flexibility in the chanical composition [106,168,169]. The most frequently used formula is Na6[(A102)6Si02)io]-12-15H20 [106,109,126]. The silicon to aluminum ratio may vary between 1.0-2.5 [66,106,168,169] and 1.6-2.7 [106], respectively. 

Silicon atoms in the zeoHte framework are tetrahedrally coordinated (Q ), resulting in five different silicon environments denoted as Si(nAl) units, where n corresponds to the number of aluminum atoms in the second coordination sphere. Each type of Si( Al) unit ( =0,1,2,3 or 4) yields Si MAS NMR signals in a well-defined range of chemical shifts [1,56-58]. These ranges are summarized for the various siHcon units in Fig. 6. The Si MAS NMR spectra of zeolites consisting of sihcon atoms on crystallographically equivalent T-sites, e.g., zeolite X and Y, are only a function of framework composition (Fig. 7). Therefore, the framework s/ Ai ratio of these materials may be calculated directly from the Si MAS NMR intensities using the formula ... 

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