In-situ dehydration studies of fully K-, Rb-, and Cs-exchanged natrolites

Lee, Yongmoon, Seoung, Donghoon, Liu, Dan, Park, Min Bum, Hong, Suk Bong, Chen, Haiyan, Bai, Jianming, Kao, Chi-Chang, Vogt, Thomas and Lee, Yongjae 2011, In-situ dehydration studies of fully K-, Rb-, and Cs-exchanged natrolites, American mineralogist, vol. 96, no. 2-3, pp. 393-401, doi: 10.2138/am.2011.3678.

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Title In-situ dehydration studies of fully K-, Rb-, and Cs-exchanged natrolites
Author(s) Lee, Yongmoon
Seoung, Donghoon
Liu, DanORCID iD for Liu, Dan
Park, Min Bum
Hong, Suk Bong
Chen, Haiyan
Bai, Jianming
Kao, Chi-Chang
Vogt, Thomas
Lee, Yongjae
Journal name American mineralogist
Volume number 96
Issue number 2-3
Start page 393
End page 401
Total pages 9
Publisher Mineralogical Society of America
Place of publication Chantilly, Va.
Publication date 2011-02
ISSN 0003-004X
Keyword(s) Cs-natrolite
rietveld refinement
Summary In-situ synchrotron X-ray powder diffraction studies of K-, Rb-, and Cs-exchanged natrolites between room temperature and 425 °C revealed that the dehydrated phases with collapsed frameworks start to form at 175, 150, and 100 °C, respectively. The degree of the framework collapse indicated by the unit-cell volume contraction depends on the size of the non-framework cation: K-exchanged natrolite undergoes an 18.8% unit-cell volume contraction when dehydrated at 175 °C, whereas Rb- and Cs-exchanged natrolites show unit-cell volume contractions of 18.5 and 15.2% at 150 and 100 °C, respectively. In the hydrated phases, the dehydration-induced unit-cell volume reduction diminishes as the cation size increases and reveals increasingly a negative slope as smaller cations are substituted into the pores of the natrolite structure. The thermal expansion of the unit-cell volumes of the dehydrated K-, Rb-, and Cs-phases have positive thermal expansion coefficients of 8.80 × 10−5 K−1, 1.03 × 10−4 K−1, and 5.06 × 10−5 K−1, respectively. Rietveld structure refinements of the dehydrated phases at 400 °C reveal that the framework collapses are due to an increase of the chain rotation angles, ψ, which narrow the channels to a more elliptical shape. Compared to their respective hydrated structures at ambient conditions, the dehydrated K-exchanged natrolite at 400 °C shows a 2.2-fold increase in ψ, whereas the dehydrated Rb- and Cs-natrolites at 400 °C reveal increases of ψ by ca. 3.7 and 7.3 times, respectively. The elliptical channel openings of the dehydrated K-, Rb-, to Cs-phases become larger as the cation size increases. The disordered non-framework cations in the hydrated K-, Rb-, and Cs-natrolite order during dehydration and the subsequent framework collapse. The dehydrated phases of Rb- and Cs-natrolite can be stabilized at ambient conditions.
Language eng
DOI 10.2138/am.2011.3678
Field of Research 020406 Surfaces and Structural Properties of Condensed Matter
040306 Mineralogy and Crystallography
020503 Nonlinear Optics and Spectroscopy
Socio Economic Objective 970104 Expanding Knowledge in the Earth Sciences
HERDC Research category C1.1 Refereed article in a scholarly journal
Copyright notice ©2011, Mineralogical Society of America
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