Pressure-induced over-hydration of thomsonite: A synchrotron powder diffraction study

Anna Yu. Likhacheva 1 , Yuriy V. Seryotkin 1 , Andrey Yu. Manakov 2 , Sergey V. Goryainov 1 , Aleksey I. Ancharov 3  and Mikhail A. Sheromov 4
  • 1 Institute of Geology and Mineralogy SibD RAS, pr.ak.Koptyuga 3, 630090 Novosibirsk, Russia
  • 2 Institute of Inorganic Chemistry SibD RAS, ac.Lavrentieva av. 3, 630090 Novosibirsk, Russia
  • 3 Institute of Solid State Chemistry SibD RAS, Kutateladze st. 18, 630218 Novosibirsk, Russia
  • 4 Budker Institute of Nuclear Physics SibD RAS, ac.Lavrentieva av. 11, 630090 Novosibirsk, Russia

Abstract

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.

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