| Autor: |
Lee, Yongjae, Vogt, Thomas, Hriljac, Joseph A., Parise, John B., Hanson, Jonathan C., Kim, Sun Jin |
| Předmět: |
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| Zdroj: |
Nature; 12/5/2002, Vol. 420 Issue 6915, p485, 5p |
| Abstrakt: |
Zeolites crystallize in a variety of three-dimensional structures in which oxygen atoms are shared between tetrahedra containing silicon and/or aluminium, thus yielding negatively charged tetrahedral frameworks that enclose cavities and pores of molecular dimensions occupied by charge-balancing metal cations and water molecules. Cation migration in the pores and changes in water content associated with concomitant relaxation of the framework have been observed in numerous variable-temperature studies, whereas the effects of hydrostatic pressure on the structure and properties of zeolites are less well explored. The zeolite sodium aluminosilicate natrolite was recently shown to undergo a volume expansion at pressures above 1.2 GPa as a result of reversible pressure-induced hydration; in contrast, a synthetic analogue, potassium gallosilicate natrolite, exhibited irreversible pressure-induced hydration with retention of the high-pressure phase at ambient conditions. Here we report the structure of the high-pressure recovered phase and contrast it with the high-pressure phase of the sodium aluminosilicate natrolite. Our findings show that the irreversible hydration behaviour is associated with a pronounced rearrangement of the non-framework metal ions, thus emphasizing that they can dearly have an important role in mediating the overall properties of zeolites. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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