Formation and transformation of five different phases in the CaSO4-H2O system: Crystal structure of the subhydrate beta-CaSO4 center dot 0.5H(2)O and soluble anhydrite CaSO4
(2008) In Chemistry of Materials 20(6). p.2124-2132- Abstract
- At least five crystalline-phases can be found in the CaSO4-H2O system, which are gypsum CaSO4 center dot 2H(2)O, the subhydrates alpha- and beta-CaSO4 center dot 0.5H(2)O, and the soluble and insoluble anhydrite CaSO4. The formation of these five phases in the CaSO4-H2O system and their transformations were investigated by in situ time-resolved synchrotron radiation powder X-ray diffraction (SR-PXD) in this study. Furthermore, revised structural models for beta-CaSO4 center dot 0.5H(2)O and soluble anhydrite CaSO4 are presented. The hydration of alpha-CaSO4 center dot 0.5H(2)O was studied at 25 degrees C and showed that the reaction with H2O started immediately after mixing the two reactants and that the formation of CaSO4 center dot... (More)
- At least five crystalline-phases can be found in the CaSO4-H2O system, which are gypsum CaSO4 center dot 2H(2)O, the subhydrates alpha- and beta-CaSO4 center dot 0.5H(2)O, and the soluble and insoluble anhydrite CaSO4. The formation of these five phases in the CaSO4-H2O system and their transformations were investigated by in situ time-resolved synchrotron radiation powder X-ray diffraction (SR-PXD) in this study. Furthermore, revised structural models for beta-CaSO4 center dot 0.5H(2)O and soluble anhydrite CaSO4 are presented. The hydration of alpha-CaSO4 center dot 0.5H(2)O was studied at 25 degrees C and showed that the reaction with H2O started immediately after mixing the two reactants and that the formation of CaSO4 center dot 2H(2)O was coupled to the depletion of alpha-CaSO4 center dot 0.5H(2)O. The thermal decomposition of CaSO4 center dot 2H(2)O was investigated in the temperature range of 25-500 degrees C and showed the fon-nation of alpha-CaSO4 center dot 0.5H(2)O followed by the formation of soluble anhydrite AIII-CaSO4, which was gradually converted to insoluble anhydrite AII-CaSO4. The thermal decomposition of alpha-CaSO4 center dot 0.5D(2)O was investigated in the temperature range of 25-500 degrees C and showed successive phase transformations to beta-CaSO4 center dot 0.5D(2)O, soluble anhydrite AIII-CaSO4, and insoluble anhydrite AII-CaS04. The two polymorphs of anhydrite coexist in the investigated temperature range of 200-500 degrees C. The hydrothermal decomposition of CaSO4 center dot 2H(2)O was investigated in the temperature range of 25-200 degrees C using a 1 M HNO3 or a 1 M LiCl solution, and in both experiments, CaSO4 center dot 2H(2)O was converted to alpha-CaSO4 center dot 0.5H(2)O and further to insoluble anhydrite AII-CaSO4. A structural model for beta-CaSO4 center dot 0.5H(2)O is proposed on the basis of SR-PXD data and a trigonal unit cell (in hexagonal setting) a = 6.93145(3), c = 12.736 17(4) angstrom, Z = 6, and space group P3(1). A structural model for soluble anhydrite AIII-CaSO4 is also proposed on the basis of powder neutron diffraction data, and a hexagonal unit cell parameters are a = 6.9687(1), c = 6.3004(1) angstrom, Z = 3, and space group P6(2)22. (Less)
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https://lup.lub.lu.se/record/1185111
- author
- Norlund Christensen, Axel ; Olesen, Maja ; Cerenius, Yngve LU and Jensen, Torben R
- organization
- publishing date
- 2008
- type
- Contribution to journal
- publication status
- published
- subject
- in
- Chemistry of Materials
- volume
- 20
- issue
- 6
- pages
- 2124 - 2132
- publisher
- The American Chemical Society (ACS)
- external identifiers
-
- wos:000254128800015
- scopus:41749120978
- ISSN
- 0897-4756
- DOI
- 10.1021/cm7027542
- language
- English
- LU publication?
- yes
- id
- ea7dce38-065c-4b8e-addb-51bd6f51ff45 (old id 1185111)
- date added to LUP
- 2016-04-01 11:58:29
- date last changed
- 2022-03-28 18:23:07
@article{ea7dce38-065c-4b8e-addb-51bd6f51ff45,
abstract = {{At least five crystalline-phases can be found in the CaSO4-H2O system, which are gypsum CaSO4 center dot 2H(2)O, the subhydrates alpha- and beta-CaSO4 center dot 0.5H(2)O, and the soluble and insoluble anhydrite CaSO4. The formation of these five phases in the CaSO4-H2O system and their transformations were investigated by in situ time-resolved synchrotron radiation powder X-ray diffraction (SR-PXD) in this study. Furthermore, revised structural models for beta-CaSO4 center dot 0.5H(2)O and soluble anhydrite CaSO4 are presented. The hydration of alpha-CaSO4 center dot 0.5H(2)O was studied at 25 degrees C and showed that the reaction with H2O started immediately after mixing the two reactants and that the formation of CaSO4 center dot 2H(2)O was coupled to the depletion of alpha-CaSO4 center dot 0.5H(2)O. The thermal decomposition of CaSO4 center dot 2H(2)O was investigated in the temperature range of 25-500 degrees C and showed the fon-nation of alpha-CaSO4 center dot 0.5H(2)O followed by the formation of soluble anhydrite AIII-CaSO4, which was gradually converted to insoluble anhydrite AII-CaSO4. The thermal decomposition of alpha-CaSO4 center dot 0.5D(2)O was investigated in the temperature range of 25-500 degrees C and showed successive phase transformations to beta-CaSO4 center dot 0.5D(2)O, soluble anhydrite AIII-CaSO4, and insoluble anhydrite AII-CaS04. The two polymorphs of anhydrite coexist in the investigated temperature range of 200-500 degrees C. The hydrothermal decomposition of CaSO4 center dot 2H(2)O was investigated in the temperature range of 25-200 degrees C using a 1 M HNO3 or a 1 M LiCl solution, and in both experiments, CaSO4 center dot 2H(2)O was converted to alpha-CaSO4 center dot 0.5H(2)O and further to insoluble anhydrite AII-CaSO4. A structural model for beta-CaSO4 center dot 0.5H(2)O is proposed on the basis of SR-PXD data and a trigonal unit cell (in hexagonal setting) a = 6.93145(3), c = 12.736 17(4) angstrom, Z = 6, and space group P3(1). A structural model for soluble anhydrite AIII-CaSO4 is also proposed on the basis of powder neutron diffraction data, and a hexagonal unit cell parameters are a = 6.9687(1), c = 6.3004(1) angstrom, Z = 3, and space group P6(2)22.}},
author = {{Norlund Christensen, Axel and Olesen, Maja and Cerenius, Yngve and Jensen, Torben R}},
issn = {{0897-4756}},
language = {{eng}},
number = {{6}},
pages = {{2124--2132}},
publisher = {{The American Chemical Society (ACS)}},
series = {{Chemistry of Materials}},
title = {{Formation and transformation of five different phases in the CaSO4-H2O system: Crystal structure of the subhydrate beta-CaSO4 center dot 0.5H(2)O and soluble anhydrite CaSO4}},
url = {{http://dx.doi.org/10.1021/cm7027542}},
doi = {{10.1021/cm7027542}},
volume = {{20}},
year = {{2008}},
}