New insights on high-pressure behaviour of microporous materials from X-ray single-crystal data
Articolo
Data di Pubblicazione:
2003
Citazione:
New insights on high-pressure behaviour of microporous materials from X-ray single-crystal data / G.D. Gatta, P. Comodi, P.F. Zanazzi. - In: MICROPOROUS AND MESOPOROUS MATERIALS. - ISSN 1387-1811. - 61:1-3(2003), pp. 105-115. ((Intervento presentato al 6. convegno Occurence, Properties and Utilization of Natural Zeolites tenutosi a Thessaloniki nel 2002.
Abstract:
The main deformation mechanisms induced by pressure on different structural types of zeolites were analysed by comparing experimental data and theoretical models. Data of single-crystal X-ray diffraction obtained with the sample in a Merrill-Bassett diamond anvil cell on a four-circle diffractometer were collected at different pressures for samples of heulandite, scolecite and bikitaite, using non-penetrating pressure transmitting media (glycerol or silicon oil), up to 5 GPa. The results indicated that, at first approximation, the theoretical approach reproduces the structural evolution of zeolites under pressure. However, the flexibility possessed by framework microporous silicates resulted more complex than that which can be modelled by undeformable "rigid-unit modes", being completely flexible in the oxygen hinges. Moreover, the compressibility of the zeolites under study does not appear to be directly related to the microporosity represented by the framework density (FD): The bulk moduli (simply defined as the inverse of volume compressibility coefficients) of heulandite (27.5(2) GPa) and scolecite (54.6(3) GPa) were different even though their FD's were quite similar. Single crystal data have shown that the structural evolution of the open-framework silicates, is strongly controlled by the framework, whereas the role of the extra-framework content was less important. In all three zeolites the position of the extra-framework water molecules and cations was maintained approximately and their coordination numbers remained unchanged within the pressure range investigated.
Tipologia IRIS:
01 - Articolo su periodico
Keywords:
natural zeolites; single-crystal X-ray diffraction; high-pressure; comparative compressibility
Elenco autori:
G.D. Gatta, P. Comodi, P.F. Zanazzi
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