Pressure-induced over-hydration of thomsonite; a synchrotron powder diffraction study

The structural behavior of thomsonite compressed in aqueous medium up to 3 GPa was studied by means of in situ synchrotron powder diffraction with a diamond anvil cell. In the range between 0.0001 and 2 GPa, the compressibility of thomsonite is markedly lower than that reported previously, where a n...

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Published inThe American mineralogist Vol. 92; no. 10; pp. 1610 - 1615
Main Authors Likhacheva, Anna Yu, Seryotkin, Yuriy V, Manakov, Andrey Yu, Goryainov, Sergey V, Ancharov, Aleksey I, Sheromov, Mikhail A
Format Journal Article
LanguageEnglish
Published Washington Mineralogical Society of America 01.10.2007
De Gruyter
Walter de Gruyter GmbH
Subjects
Aqueous solutions
compressibility
Crystal structure
Diamonds
Diffraction
framework silicates
high pressure
Hydration
Mineralogy
Minerals
natrolite
over-hydration
phase transition
Phase transitions
powder method
pressure
silicates
Structural behavior
synchrotron radiation
thomsonite
Water pressure
X-ray diffraction data
Zeolite
zeolite group
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Summary:The structural behavior of thomsonite compressed in aqueous medium up to 3 GPa was studied by means of in situ synchrotron powder diffraction with a diamond anvil cell. In the range between 0.0001 and 2 GPa, the compressibility of thomsonite is markedly lower than that reported previously, where a non-penetrating medium (with only 6% H2O) was used. This indicates a pressure-induced hydration (PIH), which results in the transition to an over-hydrated phase observed at 2 GPa. The structure of over-hydrated thomsonite contains one additional, half-occupied H2O position, coordinated by the calcium at the Ca2 site, with a scolecite-like coordination [CaO4(H2O)3]. The appearance of new H2O position causes a 4.5% volume expansion through the cooperative rotation of [T2O5]∞ chains, leading to the enlargement of the cross-section of the main channels parallel to c axis. The observed deformation mechanism is similar to that found in high-hydrated and super-hydrated natrolite, although only a half of the channels are affected by PIH. The present data indicate that the over-hydration effect in fibrous zeolites strongly depends on the partial water pressure in compressing medium.
ISSN:0003-004X
1945-3027
DOI:10.2138/am.2007.2566