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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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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 also studied by Monte Carlo (MC) simulations.
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A systematic study was conducted to investigate the correlation between the dehydration of gypsum and the time and temperature of calcination as well as the grain size of the starting material.It was found that the proposed formula may be considered as a real expression of the dehydration raction throughtout the major part of α. However, the …
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The dependence of the solubility of gypsum on temperature is nonlinear, reaching a maximum at 43°C. ... the dehydration of gypsum due to the effects. of high pressure and temperature during ...
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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. ... No consistent relationship was observed between dehydration temperature and grain size or ...
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Plaster, made of calcium sulfate hemihydrate (CaSO 4 •½H 2 O) and/or γ -anhydrite (CaSO 4) is obtained by dehydration of gypsum (CaSO 4 ·2H 2 O) at 100–200 …
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The first step is dehydration: heated to 100-200 • C, gypsum (CaSO 4 ⋅2H 2 O) releases water as vapor [1, 2] and, depending on temperature and water vapor partial pressure (p …
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Dehydration Temperature of Gypsum. Keiichi MURAKAMI, Yosihisa SHIMAMURA, Hirobumi TANAKA. Author information ... In an atomsphere, the primary dehydration temperature of natual dihydrated gypsum used as a test sample is 133°C while its secondary dehydration temperature being 192°C. Under pressure of saturated water …
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Gypsum (calcium sulfate dihydrate, Fluka, 99.9% purity) samples were dehydrated at temperatures from 85 up to 800 °C 25 g of substance was weighed in corundum crucibles of 60 ml size and dehydrated in two different furnace types to cover the complete temperature range.The furnaces were calibrated with thermo elements.
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The commercial rock gypsum studied generates both hemihydrate and anhydrite at 128°C, and its impurities do not dehydrate until the temperature is increased to 500°C.
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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 also studied by Monte Carlo (MC) simulations. The thermodynamic calculation results reveal that the dehy …
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The test results of water absorption during high-temperature dehydration gypsum rock immersion and hydration are shown in Figure 9a. It can be seen that the hydration water absorption rate increased rapidly within 0–20 min, and the water absorption amount and the water absorption time were in a logarithmic relationship; after 20 min, …
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The effects of pressure on the dehydration of gypsum materials were investigated up to 633 K and 25 GPa by using Raman spectroscopy and synchrotron X-ray diffraction with an externally heated diamond anvil cell. At 2.5 GPa, gypsum starts to dehydrate around 428 K, by forming bassanite, CaSO4 hemihydrate, which completely …
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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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Abstract The dehydration of gypsum CaSO4.2H2O has been studied, at negligible water vapour pressure, by in situ infrared (IR) spectroscopy and by thermogravimetry to determine whether intermediate phases (CaSO4.nH2O) exist, other than the hemihydrate with n=0.5, and also to compare the mechanism of the …
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Thermal conductivity of gypsum boards beyond dehydration temperature. K. Ghazi Wakili, Corresponding Author. K. Ghazi Wakili. Empa, Swiss Federal Laboratories for Materials Science and Technology, CH-8600 Dübendorf, Switzerland.
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The performance of composite gypsum at elevated temperatures depends on the treatment temperature and reflects the combined effects of gypsum phase change and the filler effects of silica flour or talc powder. ... There was tremendous pore water loss, and gypsum dehydration happened at 100 °C and 200 °C, leading to a porous …
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Although high-temperature calcination (≥800°C) could destroy the gypsum structure [10] to release the incorporated metals ... Under natural conditions, dehydration from gypsum to the hemihydrate/anhydrate phases is slow; hence, low energy is introduced to accelerate this process. Metal-incorporated gypsum was calcined in a …
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DEHYDRATION OF GYPSUM. Studies of the dehydration of gypsum in dry air atmospheres have shown that the hemihydrate of calcium sulfate is not a stable phase in the temperature range 90-140 deg C. The final product of dehydration was always anhydrous. Discontinuities in the weight loss versus time curves for powdered gypsum …
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of Gypsum Rock During High-Temperature Dehydration–Hydration Expansion Sijiang Wei,1,2 Yushun Yang,3,5 Chongbang Xu,4 Meng Wang,1,2 Wenlong Shen,1,2 and Chengdong Su1,2 ... temperature dehydrated gypsum rock was treated with different hydration time, and the gypsum rock samples in three states were subjected to …
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When gypsum is subjected to a high temperature environment, water molecules bound in its crystal lattice are released and transferred through its mass; this "gypsum dehydration" (GD) process is highly endothermic, thus enhancing the fire resistance of the overall structure [5]. Despite the widespread use of GP wall assemblies …
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kinetic parameters that are needed to predict dehydration and thermal degradation of gypsum board using a set of Arrhenius equations. Specimens of a Type C board were tested in a TGA apparatus in nitrogen at four heating rates; 5, 10, 20 and 60 °C/min. ... If the temperature ranges for the reactions of the different components are separated, ...
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The degree of dehydration depends on the temperature and duration of heating. Partial Dehydration: When gypsum is partially dehydrated, it forms a material known as "plaster of Paris" or "calcined gypsum." Plaster of Paris is a white, powdery substance that can be mixed with water to create a workable plaster paste, used in …
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Structural evolution during the dehydration of gypsum materials - Volume 73 Issue 3. ... J.D. and Hinks, D.G. (1984) A crystallographic study of the low-temperature dehydration products of gypsum, CaSO 4-2H 2 O; hemihydrate CaSO 4-0.5H 2 O, and γ-CaSO 4. American Mineralogist, 69, 910—919.Google Scholar.
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DOI: 10.1002/fam.2234 Corpus ID: 135782591; Thermal conductivity of gypsum boards beyond dehydration temperature @article{GhaziWakili2015ThermalCO, title={Thermal conductivity of gypsum boards beyond dehydration temperature}, author={Karim Ghazi Wakili and Matthias M. Koebel and T. Glaettli and Marco Hofer}, journal={Fire and …
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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 …
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The dehydration kinetics of gypsum strongly depend on temperature and water vapour pressure. Here, we perform fast, time- ... effect of mechanical stress on gypsum dehydration kinetics is not well ...
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One way to overcome part of the technical difficulties when dealing with high-pressure and high-temperature tests is to study gypsum as an analogue of serpentine-rich rocks at depth [Ko et al., 1997; ... allowing us to visualize in situ the microstructural changes occurring during the dehydration of gypsum. [33] Figures 11a, ...
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Synthetic anhydrite is obtained when gypsum is dehydrated at the temperature of 600 to 800ºC [7]. There is little knowledge about the influence of the dehydration temperature on
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Low-temperature dehydration of gypsum single crystals. ... By isothermal measurements over time ranges up to 60 h at temperatures between 76 °C and 140 °C the dehydration of gypsum (CaSO4·2H2O ...
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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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changes (1-2 min) as a function of temperature. a b Figure 1. a) Dehydration of gypsum at 85 °C and 17.6% RH. Reaction starts in <1 hr and is complete after 5.6 hr. b) Dehydration of gypsum at 85 °C and 47% RH. Reaction starts after 6.6 hr and is close to completion after 50 hr. Lunar and Planetary Science XXXVIII (2007) 1432.pdf
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At 2.5 GPa, gypsum starts to dehydrate around 428 K, by forming bassanite, CaSO4 hemihydrate, which completely dehydrates to c-anhydrite at 488 K.
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Abstract. An in situ dehydration kinetics study of gypsum under water-saturated condition was performed in the temperature and pressure ranges of 383–423 K and 343–1085 MPa by using a hydrothermal diamond anvil cell and Raman spectroscopy. Kinetic analysis shows that the dehydration rate k increases with pressure, suggesting …
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Gypsum board dehydration takes place at the temperature range between ∼80 °C and 250 °C, depending on the heating rate and the composition of the gypsum board [1], [10], [16], [17]. During this process the chemically bound water dissociates from the crystal mesh and, together with the free moisture content, evaporates.
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The thermodynamic calculation results reveal that the dehydration mechanism of gypsum significantly depended on ambient temperature and water vapor pressure.
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