Cation-dependent anomalous compression of gallosilicate zeolites with CGS topology: A high-pressure synchrotron powder diffraction study
- Department of Earth System Sciences, Yonsei University, Seoul 120-749 (Korea, Republic of)
- Pohang Accelerator Laboratory, POSTECH, Pohang 790-784 (Korea, Republic of)
- Nano-Materials Research Center, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of)
- National Synchrotron Light Source, Brookhaven National Laboratory, Upton, NY 11973 (United States)
The high-pressure compression behaviour of 3 different cation forms of gallosilicate zeolite with CGS topology has been investigated using in situ synchrotron X-ray powder diffraction and a diamond-anvil cell technique. Under hydrostatic conditions mediated by a nominally penetrating pressure-transmitting medium, unit-cell lengths and volume compression is modulated by different degrees of pressure-induced hydration and accompanying channel distortion. In a Na-exchanged CGS (Na{sub 10}Ga{sub 10}Si{sub 22}O{sub 64}.16H{sub 2}O), the unit-cell volume expands by ca. 0.6% upon applying hydrostatic pressure to 0.2 GPa, whereas, in an as-synthesized K-form (K{sub 10}Ga{sub 10}Si{sub 22}O{sub 64}.5H{sub 2}O), this initial volume expansion is suppressed to ca. 0.1% at 0.16 GPa. In the early stage of hydrostatic compression below {approx}1 GPa, relative decrease in the ellipticity of the non-planar 10-rings is observed, which is then reverted to a gradual increase in the ellipticity at higher pressures above {approx}1 GPa, implying a change in the compression mechanism. In a Sr-exchanged sample (Sr{sub 5}Ga{sub 10}Si{sub 22}O{sub 64}.19H{sub 2}O), on the other hand, no initial volume expansion is observed. Instead, a change in the slope of volume contraction is observed near 1.5 GPa, which leads to a 2-fold increase in the compressibility. This is interpreted as pressure-induced rearrangement of water molecules to facilitate further volume contraction at higher pressures. - Graphical abstract: Three different cation forms of gallosilicate CGS zeolites have been investigated using synchrotron X-ray powder diffraction and a diamond-anvil cell. Under hydrostatic conditions, unit-cell lengths and volume show anomalous compression behaviours depending on the non-framework cation type and initial hydration level, which implies different modes of pressure-induced hydration and channel distortion.
- OSTI ID:
- 21128240
- Journal Information:
- Journal of Solid State Chemistry, Vol. 181, Issue 4; Other Information: DOI: 10.1016/j.jssc.2008.01.017; PII: S0022-4596(08)00025-X; Copyright (c) 2008 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
- Country of Publication:
- United States
- Language:
- English
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