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Here, we report the first solid-like dehydration of gypsum to produce anhydrite at room temperature. Specifically, a 39 nm thick sulfuric acid film (NSF) was fabricated to extract water of crystallization from gypsum and simultaneously enable a phase transformation from gypsum to anhydrite via recrystallization. Using density …
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The dehydration process of gypsum rock was studied under concentrated solar energy by using a Fresnel lens with power density of 260 Wcm 2. Temperatures higher than 700 C were attained for 1 min ...
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Here, we examine the micromechanical status of syn- and post-dehydration gypsum-phases, crucial for understanding intra-crystalline deformation. We micro-indented the (010) planes of natural gypsum crystals from 30 to 140°C at various strain-rates to track mechanical changes during progressive dehydration and phase transition ...
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The first peak that occurred around 125 ℃ can be related to dehydration of water from ettringite. Dehydration of Gypsum was observed at about 150 ℃ in BYF-18GP and BYF-30GP after 2 days but was absent in BYF-9GP. ... The reactivity of α' H-belite was found to be affected by the content of gypsum, as the hydration degree of this phase at ...
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To monitor the degree of cement hydration and microstructural changes, ... When gypsum was added to the CSA cement (Figure 8 b), ettringite was observed after 2 h, as in the B-G0 sample. The ettringite peaks appeared simultaneously with or without the addition of gypsum. However, B-G5 produced strong ettringite peaks owing to the …
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The dehydration products of gypsum under different temperature and water vapor pressure were investigated by thermodynamic theory. Additionally, the rehydration mechanism of soluble anhydrite was ...
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The dehydration reaction of gypsum into bassanite and water induces a large porosity increase, which is partially compacted. The higher the effective stress, the larger the compaction. Application of a …
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during dehydration. In particular, Popp and Kern [1993] observed dramatic decreases in V P, V S and Poisson's ratio during experimental dehydration of lizardite and gypsum. [3] Two challenging problems encountered in addressing the possible importance of dehydration embrittlement in 1Laboratoire de Géologie, École Normale Supérieure, …
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Gypsum hydration: a theoretical and experimental study . Calcium sulphate dihydrate (CaSO4·2H2O or gypsum) is used widely as building material because of its excellent …
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From 550 to 650 °C, the permeability of gypsum slightly increased when the temperature increased; (d) the micro-cracks and porosity obtained from the CT images show a high degree of consistency ...
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The governing equations are integrated numerically using the finite element method. The obtained results show a significant correlation between gypsum dehydration and creation of fluid pathways. The proposed model can be generalised to describe the effects of dehydration in other minerals carrying water in their crystal structures.
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Our study of gypsum dehydration is the first to explore the transition between undrained and drained conditions and to define the material and environmental variables that …
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M. Hofer. Zurich University of Applied Sciences, IMPE, CH 8401 Winterthur, Switzerland. Search for more papers by this author
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Gypsum dehydration has been studied in numerous exper- ... trolled by the degree of interconnectivity of pore space. Prob- ... ment the dehydration of a 2.3 mm diameter cylinder of poly-
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The spectral behavior of gypsum dehydration in the visible to near-infrared (350–2500 nm) wavelength range was investigated by partially dehydrating the four main habits of gypsum (alabaster, satin spar, selenite, and massive) to form bassanite. Powdered samples of gypsum dehydrated at 100–115 °C and hand samples …
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Mass losses vary between 13.7 and 16.5% and heat of dehydration values between 377 and 420 J g −1 for the dehydration of ground and mixed inhomogeneous gypsum samples. As for the dehydration of CaSO 4 ·2H 2 O, the dehydration of synthetic gypsum proceeds via multi-step reactions. Using a heating rate of 5°C min −1, …
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The dehydration of gypsum CaSO 4.2H 2 O has been studied, at negligible water vapour pressure, by in situ infrared (IR) spectroscopy and by thermogravimetry to determine …
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The Simulation and Analysis of Dehydration Process of FGD Gypsum Grouted Wall: ZENG Ziyue 1,2, YANG Jiansen 1, WEI Yongqi 2: 1 School of Civil and Hydraulic Engineering, Ningxia University, Yinchuan 750021, Ningxia, China 2 School of Material Science and Engineering, Tongji University, Shanghai 201804, China
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Soil samples were distilled in two steps: first at 35°C and then at 130°C to separate free and gypsum crystallisation water while ensuring an almost complete dehydration of gypsum (Freyer and ...
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Mass losses vary between 13.7 and 16.5% and heat of dehydration values between 377 and 420 J g −1 for the dehydration of ground and mixed inhomogeneous gypsum samples. As for the dehydration of CaSO 4 ·2H 2 O, the dehydration of synthetic gypsum proceeds via multi-step reactions. Using a heating rate of 5°C min −1, the very …
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Measurements have been made of the rate of dehydration of desulphurized gypsum with particle diameters in the range of 35–67 μm in a fluidized bed reactor. Experiments were carried out at bed temperatures of 100 to 170°C. The fluidizing gases were air, with water vapour pressures of between 0.001 atm and 0.35 atm, and carbon …
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The thermally induced dehydration processes of gypsum, and the corresponding empirical activation energies E a, have been extensively studied in the past, as a function of both temperature and ( P_{{{text{H}}_{ 2} {text{O}}}}, ) using different experimental techniques. As gypsum dehydration has great technological relevance, …
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This article investigates the thermal performance of gypsum boards in the dehydration temperature region, where pronounced chemical reactivity is anticipated. Gypsum board samples were gradually ...
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The striking impact of Δ σ on kinetics is revealed by the conversion curves (Fig. 2i, j, see Methods for definition). At both temperatures, increased Δ σ accelerates the …
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and gypsum dehydration profile, including X-ray diffraction, ... degrees θ. 10 15 20 25 30 35 ... ment, which detected the hemihydrate and an interstitial gypsum.
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The system CaSO(4)-H(2)O, characterized by the three dehydration reactions gypsum-anhydrite, gypsum-bassanite, and bassanite-anhydrite, was reexamined by in situ differential pressure analysis in the temperature range of 60-350 degrees C up to 3.5 GPa pressure. The investigation revealed a fine stru …
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These two experiments clarified that: i) increasing gypsum amount up to 4.5% of binder mass effectively reduced free shrinkage strain subjected to 30 degree of ambient temperature, ii) this free ...
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