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Dehydration and rehydration of vermiculites: III. Phlogopitic Sr- and Ba-vermiculite

Published online by Cambridge University Press:  09 July 2018

H. Graf v. Reichenbach
Affiliation:
Institute of Soil Science and SFB 173, University of Hannover, 30419 Hannover, Germany
J. Beyer
Affiliation:
Institute of Soil Science and SFB 173, University of Hannover, 30419 Hannover, Germany

Abstract

Dehydration and rehydration of a phlogopitic vermiculite saturated with either Sr2+ or Ba2+ were studied by thermoanalysis (TG, DSC, DTA) and by in situ X-ray powder diffractometry. A detailed analysis of the relationship between temperature and state of hydration of the vermiculites close to equilibrium at atmospheric pressure was rendered possible by use of low heating rates in combination with a fast recording position-sensitive detector. For Sr-vermiculite, the results reveal the existence of a number of distinct states of hydration characterized by basal spacings of 1.54, 1.51, 1.49, 1.23, 1.21 and 0.96 nm. The Ba-vermiculite failed to develop a two-layer hydrate even in contact with water. Its one-layer hydrate (1.24 nm) was reversibly transformed into an incompletely dehydrated ordered ‘mica-structure’ (1.00-0.99 urn), before an irreversibly dehydrated structure was attained at temperatures exceeding 700°C The formation of regular 1:1 interstratification was confirmed for all transformations characterized by a change in the number of water layers. The concluding compilation summarizes basal spacings, stacking orders, layer translations and specific water contents for all discrete states of hydration observed in our experiments at saturation of vermiculite with different alkaline earth cations.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1997

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