Armstrongite at non ambient conditions: An in-situ high temperature single crystal X-ray diffraction study

Lacalamita, Maria; Cametti, Georgia; Mesto, Ernesto; Schingaro, Emanuela (2019). Armstrongite at non ambient conditions: An in-situ high temperature single crystal X-ray diffraction study. Microporous and mesoporous materials, 275, pp. 180-190. Elsevier 10.1016/j.micromeso.2018.08.008

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The dehydration process of armstrongite, CaZr[Si6O15]·2H2O, from Khan Bogdo deposit (Gobi, Mongolia) was studied by in-situ High Temperature Single Crystal X-ray Diffraction (HT SCXRD) in air from 25 to 500 °C and in N2 atmosphere from 25 to 375 °C. An abrupt discontinuity in the trend of the a and b parameters and of the unit-cell volume was observed at T = 275 °C in dry condition and at T = 450 °C in air. This discontinuity is associated to dehydration and to a first-order transition. When compared to RT armstrongite, the dehydrated phase structure (obtained at 275 °C only under dry conditions) is characterized by the same space group (C2/m), cell volume decrease of ~7.5%, compatible with the loss of the two water molecules, positional disorder of Ca over three sites, splitting of some of the heteropolyhedral framework oxygen atoms, tilting of Zr octahedra and Si tetrahedral and, distortion of four-, six- and eight-membered channels. Differently from other Zr-silicate structures, the channels dimension of the dehydrated structure (defined as the ratio between the longest and shortest diagonals of the channels) allowed the armstrongite structure to completely recover the structural water after 21 days exposure to humid conditions.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Institute of Geological Sciences > Mineralogy
08 Faculty of Science > Institute of Geological Sciences

UniBE Contributor:

Cametti, Georgia

Subjects:

500 Science > 550 Earth sciences & geology

ISSN:

1387-1811

Publisher:

Elsevier

Language:

English

Submitter:

Georgia Cametti

Date Deposited:

11 Jun 2019 16:52

Last Modified:

24 Oct 2019 04:27

Publisher DOI:

10.1016/j.micromeso.2018.08.008

BORIS DOI:

10.7892/boris.130013

URI:

https://boris.unibe.ch/id/eprint/130013

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