Gypsum (CaSO 4 ·2H 2 O) dehydration kinetics were investigated through energy dispersive X-ray diffraction (EDXD), under reduced pressure (100 Pa), in the temperature range 313–353 K. The process follows the JMAK (Johnson-Mehl-Avrami Kinetic) model. The fitting procedure of the Arrhenius expression provides an activation …
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previously studied dehydration of synthetic gypsum between 80 and 152 C at a controlled P H 2O. They reported that the dehydration reaction is dominated by both a nucleation and phase boundary mechanisms in the tem-perature range 80–110 C, but at temperature greater than 110 C, the dehydration process is controlled by a diffusion mechanism.
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The pure gypsum, ordinary ed gypsum with different densities (800 kg/m³, 650 kg/m³), ed gypsum with glass fiber or with expanded vermiculite were tested in the temperature range of 25 ...
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Gypsum (calcium sulfate dihydrate) is one of the most used inorganic binding materials in the world. During calcination, calcium sulfate subhydrates are formed and, for technical reasons, are mixed with water to form dihydrate again. Therefore, the dehydration process of gypsum and the rehydration of hemihydrate were investigated. …
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Semantic Scholar extracted view of "The thermal dehydration of synthetic gypsum" by C. Strydom et al. Skip to search form Skip to main content Skip to ... 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 ...
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The dehydration of gypsum to hemihydrate has been studied for decades because it is an important model reaction for understanding fluid-triggered earthquakes, …
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Abstract for 11th GeoRaman International Conference, June 15-19, 2014, St. Louis, Missouri, USA THE MICRO RAMAN SPECTROSCOPY FOR ANALYSIS OF THE GYPSUM DEHYDRATION BY SIMULATED SPACE WEATHERING. Zhongchen Wu1,2, Yuheng Ni1, Zongcheng Ling1, Hong Wu1.1School of Space Science and Physics & …
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The dehydration is an endothermic process, and until the dehydration is finished, the temperature of the gypsum does not exceed 150 °C . However, the dehydration mechanism and the phase transitions in the CaSO 4 – n H 2 O system were not fully described yet, and the literature sources differ.
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With increasing temperature gypsum starts to dehydrate and form calcium sulfates with lower H 2 O content. The dehydration process proceeds stepwise and leads to metastable calcium sulfate phases. Bassanite (calcium sulfate hemihydrate, CaSO 4 ·0.5 H 2 O) is formed at the loss of 1.5 mol H 2 O per formula unit with respect to gypsum ...
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The Cave of Giant Crystals of Naica (Chihuahua, Mexico) is a world geological treasure worth to be preserved. ... Jacques et al. [26] found that the dehydration temperature of waste gypsum is ...
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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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The spectral behavior of gypsum dehydration in the visible to near-infrared (350–2500 nm) wavelength range was investigated by partially. Skip to Main Content. Close. ... 1750, 1945, 2100–2200, and ~2400 nm all decrease with increasing temperature. The samples also underwent visible changes upon dehydration, both at the macroscopic and ...
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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 Received 6 December 2020; accepted 15 December 2020 Published online: 5 January 2021 In order to study the physical and mechanical properties of …
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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 …
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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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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 ...
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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 …
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(2) Under pressure of 99.5% ethyl alcohol saturated vapor, the primary dehydration temperature is raised to 162°C and semihydrated is obtained by heating the sample of dihydrated gypsum at 230°C without the secondary dehydration.
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This article addresses the thermal properties and the microstructure of gypsum boards produced from β-hemihydrate by studying its dehydration process. …
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For the examined dehydration temperatures of 129 °C and 142 °C, the pre-stressed samples dehydrate about two times faster than their low-stress equivalents (Fig. 2, Supplementary Table 1). 3D ...
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The dehydration products of gypsum under different temperature and water vapor pressure were investigated by thermodynamic theory. Additionally, the rehydration …
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The tests were performed at 1 MPa normal stress and a velocity of 1.3 m s −1, while measuring the temperature close to the sliding surface and the relative humidity around the sample. The temperature close to the sliding surface is remarkably stable at ∼100 °C during the dehydration reaction of gypsum.
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At the lower temperatures used gypsum first converts to an amorphous intermediate phase during reaction, but as the temperature is raised to 130 degrees C and above, hydrothermal dehydration to ...
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The above process, known as "dehydration" or "calcination" of gypsum, takes place at the temperature range between ∼80 °C and ∼250 °C, depending on the heating rate, of the gypsum board, and its composition [1], [10], [11].
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Using a heating rate of 5°C min −1, the very slow dehydration of CaSO 4 ·2H 2 O and impurities in the gypsum samples start at temperatures lower than 95°C. The main dehydration of the calcium sulphate dehydrate part of synthetic gypsum occurs between 95 and 170°C (heating rate 5°C min −1 ) and seems to proceed via a process …
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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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In this work, the dehydration pathways of gypsum and the rehydration mechanism of soluble anhydrite were mainly investigated by thermodynamic modeling and MC simulations. The dehydration pathways of gypsum are largely determined by …
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Gypsum board dehydration. 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 …
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Gypsum caprocks' sealing ability is affected by temperature–pressure coupling. Due to the limitations of experimental conditions, there is still a lack of triaxial stress–strain experiments that simultaneously consider changes in temperature and pressure conditions, which limits the accuracy of the comprehensive evaluation of the …
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Corresponding Author. K. Ghazi Wakili. Empa, Swiss Federal Laboratories for Materials Science and Technology, CH-8600 Dübendorf, Switzerland. Correspondence to: K. Ghazi Wakili, Empa, Swiss Federal Laboratories for Materials Science and Technology, CH-8600 Dübendorf, Switzerland.
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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 crystals—a form of gypsum called selenite (CaSO 4 ∙2H 2 O)—took up to a million years to develop within a water-filled, magma-heated cave 300 m below the …
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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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Figure 1: a: Gypsum crystals produced from sodium sulphate and calcium chloride; b: Natural gypsum cut along black lines; c: Gypsum crystals from a, with directions from Figure 2 marked with arrows, on side from Figure 3 marked with yellow, on cleavage plane with red; d: Crystal from a) along c-axis marked in black.
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