Water channel structure of bassanite at high air humidity: crystal structure of CaSO4·0.625H2O

Schmidt, Horst; Paschke, Iris; Freyer, Daniela; Voigt, Wolfgang

doi:10.1107/s0108768111041759

Cited by 37 publications

(34 citation statements)

References 24 publications

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“…Many authors wrote extensive reviews on these points as, for example, Bezou 10 , Freyer and Voigt 11 , Christensen et al 12,13 , Ballirano 14 , and Schmidt et al 15 . Calcium sulfate dihydrate dehydrates to hemihydrate or anhydrite (CaSO % ) depending on temperature and humidity conditions.…”

Section: Introductionmentioning

confidence: 99%

“…1,16,17 The hemihydrate has also been reported to increase its structural water content to form a higher hydrate of the form CaSO % ⋅ 0.625H + O (0.625-H). 15 Three kinds of anhydrites have been reported: soluble anhydrite (AIII-CaSO % ), insoluble anhydrite (AII-CaSO % ), and anhydrite I (AI-CaSO % ). AIII-CaSO % is known to be unstable and hydrate back to hemihydrate under atmospheric conditions.…”

Section: Introductionmentioning

confidence: 99%

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Comprehensive Thermodynamic Study of the Calcium Sulfate–Water Vapor System. Part 1: Experimental Measurements and Phase Equilibria

Preturlan

Vieille

Quiligotti

et al. 2019

Ind. Eng. Chem. Res.

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The calcium sulfate–water vapor system is of great scientific and technological importance due to its applications in several fields such as the construction materials industry, geology, and planetary sciences. While much effort has been concentrated during the past decades on characterizing the crystallographic structure of the different calcium sulfate polymorphs, some questions concerning their thermodynamic aspects as phase equilibria and their capability to increase their overall water content continuously beyond structural water content seem to have been left aside. Nevertheless, the comprehension of these aspects is of the utmost importance if we want to understand this chemical system fully. The present two-part work investigates these phenomena experimentally and by a thermodynamic modeling approach. In this first part, we develop a rigorous experimental protocol by thermogravimetric analysis under controlled temperature and water vapor partial pressure. We use this protocol to obtain thermodynamic equilibrium values for the overall water content of calcium sulfate hydrates. To ensure that the equilibrium was reached, we verified that these values could be obtained by distinct thermodynamic paths. With the equilibrium data, we were able to propose an updated equilibrium curve between soluble anhydrite AIII-CaSO4 and CaSO4·0.5H2O and estimate the thermodynamic parameters Δr H° = (35.5 ± 1.0) kJ·mol–1 and Δr S° = (80.0 ± 2.8) J·mol–1·K–1. After that, we were able to quantify the extent of water adsorption as a function of (T, P H2O), and we observed that it could represent a significant part of the overall water content of calcium sulfates.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Comprehensive Thermodynamic Study of the Calcium Sulfate–Water Vapor System. Part 1: Experimental Measurements and Phase Equilibria

Preturlan

Vieille

Quiligotti

et al. 2019

Ind. Eng. Chem. Res.

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“…A wealth of studies was conducted to understand in which gypsum, upon heating to temperatures higher than ∼373 K, first dehydrates into the metastable hemihydrate, which then dehydrates into γ -anhydrite (Bezou et al, 1995;Singh and Middendorf, 2007;Christensen et al, 2008;Jacques et al, 2009). The existence of a subhydrate CaSO 4 ×xH 2 O has been discussed for some time, and recently Schmidt et al (2011) proved that hemihydrate reacts to CaSO 4 ×0.625H 2 O in moist conditions. The dehydration of gypsum is an anomalously slow process compared to the dehydration of other compounds containing crystal water (Charola et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

Pore formation during dehydration of polycrystalline gypsum observed and quantified in a time-series synchrotron radiation based X-ray micro-tomography experiment

Fußeis¹,

Schrank²,

Liu³

et al. 2011

Preprint

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We conducted an in-situ X-ray micro-computed tomography heating experiment at the Advanced Photon Source (USA) to dehydrate an unconfined 2.3 mm diameter cylinder of Volterra Gypsum. We used a purpose-built X-ray transparent furnace to heat the sample to 388 K for a total of 310 min to acquire a three-dimensional time-series tomography dataset comprising nine time steps. The voxel size of 2.2 μm3 proved sufficient to pinpoint reaction initiation and the organization of drainage architecture in space and time. We observed that dehydration commences across a narrow front, which propagates from the margins to the centre of the sample in more than four hours. The advance of this front can be fitted with a square-root function, implying that the initiation of the reaction in the sample can be described as a diffusion process. Novel parallelized computer codes allow quantifying the geometry of the porosity and the drainage architecture from the very large tomographic datasets (6.4 × 109 voxel each) in unprecedented detail. We determined position, volume, shape and orientation of each resolvable pore and tracked these properties over the duration of the experiment. We found that the pore-size distribution follows a power law. Pores tend to be anisotropic but rarely crack-shaped and have a preferred orientation, likely controlled by a pre-existing fabric in the sample. With on-going dehydration, pores coalesce into a single interconnected pore cluster that is connected to the surface of the sample cylinder and provides an effective drainage pathway. Our observations can be summarized in a model in which gypsum is stabilized by thermal expansion stresses and locally increased pore fluid pressures until the dehydration front approaches to within about 100 μm. Then, the internal stresses are released and dehydration happens efficiently, resulting in new pore space. Pressure release, the production of pores and the advance of the front are coupled in a feedback loop. We discuss our findings in the context of previous studies

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“…In the article by Schmidt et al (2011), the correspondence author is incorrectly given as Horst Schmidt. The correct correspondence author is Daniela Freyer as given above.…”

mentioning

confidence: 99%

“…The correspondence author in the paper by Schmidt et al [(2011), Acta Cryst. B67, 467-475] is corrected.…”

mentioning

confidence: 99%

Water channel structure of bassanite at high air humidity: crystal structure of CaSO₄·0.625H₂O. Corrigendum

Schmidt

Paschke

Freyer

et al. 2012

Acta Crystallogr Sect B

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Water channel structure of bassanite at high air humidity: crystal structure of CaSO₄·0.625H₂O

Cited by 37 publications

References 24 publications

Comprehensive Thermodynamic Study of the Calcium Sulfate–Water Vapor System. Part 1: Experimental Measurements and Phase Equilibria

Comprehensive Thermodynamic Study of the Calcium Sulfate–Water Vapor System. Part 1: Experimental Measurements and Phase Equilibria

Pore formation during dehydration of polycrystalline gypsum observed and quantified in a time-series synchrotron radiation based X-ray micro-tomography experiment

Water channel structure of bassanite at high air humidity: crystal structure of CaSO₄·0.625H₂O. Corrigendum

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Water channel structure of bassanite at high air humidity: crystal structure of CaSO4·0.625H2O

Cited by 37 publications

References 24 publications

Comprehensive Thermodynamic Study of the Calcium Sulfate–Water Vapor System. Part 1: Experimental Measurements and Phase Equilibria

Comprehensive Thermodynamic Study of the Calcium Sulfate–Water Vapor System. Part 1: Experimental Measurements and Phase Equilibria

Pore formation during dehydration of polycrystalline gypsum observed and quantified in a time-series synchrotron radiation based X-ray micro-tomography experiment