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Si-Al disorder and solid solutions in analcime, chabazite, and wairakite by Philip S. Neuhoff; Jonathan F. Stebbins; Dennis K. Bird is a Earth and Planetary Sciences article available to read on EtoBox.

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Quantitative determination of the abundance of Si(nAl) tetrahedral structural units (where n = 0, 1, 2, 3, or 4) through analysis of 29 Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectra was used to assess the state of Si-Al disorder in the zeolites analcime [(NaAl) x Si 48-x O 96 •16H 2 O], chabazite [(Ca 0.5 ,Na,K) x Al x Si 12-x O 24 •12H 2 O], and wairakite [CaAl 2 Si 4 O 12 •2H 2 O]. Short-range Si-Al ordering in chabazite and analcime is a regular function of Al mol fraction and is fully consistent with Al avoidance, as has generally been reported for zeolites not subjected to heat treatment. The results of this study and previously reported 29 Si MAS NMR spectra suggest that natural analcime samples are more Si-Al ordered than either their synthetic counterparts or chabazite. Cluster variation method (CVM) calculations were used to calculate the configurational entropy (S CON ) due to Si-Al disorder in chabazite and analcime. The calculations predict that long-range Si-Al ordering develops when Al occupies 5 out of 12 tetrahedral sites in chabazite and synthetic analcime and 17 out of every 48 tetrahedral sites in natural analcime. The difference between th

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Author

Philip S. Neuhoff; Jonathan F. Stebbins; Dennis K. Bird

Publisher

Mineralogical Society of America

Published

2003

Language

EN

Field

Earth and Planetary Sciences (Physical Sciences)