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Structural evolution during the dehydration of gypsum materials

Published online by Cambridge University Press:  05 July 2018

S. D. M. Jacques ,
A. González-Saborido ,
O. Leynaud ,
J. Bensted ,
M. Tyrer ,
R. I. W. Greaves  and
P. Barnes
S. D. M. Jacques*
Affiliation:
Department of Chemistry, University College London, 20 Gordon Street, London WC1H OAJ, UK and School of Crystallography, Birkbeck College, Malet Street, London WC1E 7HX, UK
A. González-Saborido
Affiliation:
Department of Chemistry, University College London, 20 Gordon Street, London WC1H OAJ, UK and School of Crystallography, Birkbeck College, Malet Street, London WC1E 7HX, UK
O. Leynaud
Affiliation:
Department of Chemistry, University College London, 20 Gordon Street, London WC1H OAJ, UK and School of Crystallography, Birkbeck College, Malet Street, London WC1E 7HX, UK
J. Bensted
Affiliation:
Department of Chemistry, University College London, 20 Gordon Street, London WC1H OAJ, UK and School of Crystallography, Birkbeck College, Malet Street, London WC1E 7HX, UK
M. Tyrer
Affiliation:
Department of Materials, Imperial College, Prince Consort Road, South Kensington, London SW7 2BP, UK
R. I. W. Greaves
Affiliation:
Department of Materials, Imperial College, Prince Consort Road, South Kensington, London SW7 2BP, UK
P. Barnes
Affiliation:
Department of Chemistry, University College London, 20 Gordon Street, London WC1H OAJ, UK and School of Crystallography, Birkbeck College, Malet Street, London WC1E 7HX, UK
*
* E-mail: s.jacques@mail.cryst.bbk.ac.uk
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Abstract

The dehydration of pure and waste gypsums has been examined using in situ synchrotron angledispersive X-ray diffraction. Pure gypsum was studied under a number of defined environments; various industrial waste gypsums were also studied under a common standard environment. It is found that the dehydration of gypsum to anhydrite proceeds via the hemihydrate and γ-anhydrite phases and the interplay and behaviour of these phases has been determined by full structural ‘Rietveld’ refinement. In the study of the pure gypsum system, the hemihydrate structure is shown to be preserved as water is lost. A ‘zero-water hemihydrate’ is observed before refinement in the higher symmetry γ-anhydrite cell is possible. The waste gypsum materials studied showed significant differences in the temperatures at which key transformation events occurred; these observations raise implications concerning the re-use of by-product gypsum materials. Finally, high temperature data are re-examined in the search for a variation of the anhydrite structure.

Keywords

gypsumdehydration.
Type
Research Article
Information
Mineralogical Magazine , Volume 73 , Issue 3 , June 2009 , pp. 421 - 432
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2009

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