Temperature and humidity dependent formation of CaSO4·xH2O (x = 0...2) phases

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Title:Main Title: Temperature and humidity dependent formation of CaSO4·xH2O (x = 0...2) phases
Description:Abstract: The temperature and humidity dependent formation of different crystalline phases CaSO4·xH2O with 0 ≤ x ≤ 2 was investigated by in situ X-ray powder diffraction using a Bruker D8 diffractometer equipped with an Anton Paar CHC+ cryo−/ humidity chamber. By isothermal measurements over time ranges up to 60 h at temperatures between 76 °C and 140 °C the dehydration of gypsum (CaSO4·2H2O) to bassanite (CaSO4·½H2O) and γ-anhydrite (γ-CaSO4) was studied under low relative humidity of<7% and under consideration of the dependence of the dehydration process on particle size. β-anhydrite (β-CaSO4, mineral anhydrite) was not found as dehydration product up to 140 °C, but only in small amounts as dehydration product of bassanite after 6 months at 80 °C. Rehydration of previously formed bassanite between 30° and 10 °C at relative humidity of 95% (without free H2O in the sample) was investigated analogously to the dehydration study. With quantitative phase analysis by the Rietveld method of the isothermal X-ray powder diffraction measurements fraction of conversion versus time curves were derived and the applicability of kinetic models is discussed. From the results it can be concluded that gypsum dehydration/rehydration under climatic conditions present in the Atacama Desert is unlikely to occur over diurnal cycles, however, very small fractions of gypsum dehydrated to bassanite and subsequently rehydrated to gypsum are conceivable over very extended time scales in the top layer of the soil surface. Faster dehydration and slower rehydration for small particle size (< 20 μm) could favor a minor accumulation of gypsum dehydration products. However, the formation of large amounts of β-anhydrite (which is found, besides gypsum, as main sulfate constituent of ‘gypsum crust’ in the Atacama Desert) by gypsum/bassanite dehydration under climatic conditions in the Atacama Desert, is unlikely for the pure CaSO4·xH2O system without gypsum/ bassanite nucleation-inhibiting additives.
Responsible Party
Creators:Laura Ritterbach (Author), Petra Becker-Bohatý (Author)
Publisher:Global and Planetary Change
Publication Year:2021
CRC1211 Topic:Surface
Related Subproject:C4
Subject:Keyword: Kinetics
Geogr. Information Topic:Environment
File Details
Data Type:Data Paper - Publication
File Size:2.2 MB
Date:Accepted: 29.07.2021
Mime Type:application/pdf
Data Format:PDF
Download Permission:Only Project Members (Download Embargo will be lifted after project end)
General Access and Use Conditions:According to the CRC1211DB data policy agreement.
Access Limitations:According to the CRC1211DB data policy agreement.
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Specific Information - Publication
Publication Status:Accepted
Review Status:Peer reviewed
Publication Type:Article
Article Type:Electronic
Source:Global and Planetary Change
Number of Pages:11 (1 - 11)
Metadata Details
Metadata Creator:Benedikt Ritter
Metadata Created:16.07.2021
Metadata Last Updated:27.01.2022
Funding Phase:2
Metadata Language:English
Metadata Version:V50
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