— 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 opportunities afforded by this methodology are illustrated with the example of gypsum dehydration. The remainder of this article is structured as follows. First, the basic principles of SAXS/WAXS are elucidated. We proceed with a brief synopsis of the relevance and current knowledge of gypsum dehydration. The experimental cell is …
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— The dehydration of gypsum can be observed using thermo-gravimetric measurement and differential scanning calorimetry. Depending on the parameters of measurement, a two-step process can be observed. The formation of beta-hemihydrate starts at around 85°C and is shifted into the formation of anhydrite III. Due to this, it is …
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— The kinetics of the dehydration of gypsum was investigated by powder diffraction methods. Using the incoherent scattering effect of H with the neutron beam, the background intensity as a measure of the water content was checked in the temperature range 295–623 K.
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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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— In this study, we reported an unprecedented VMs extraction approach through a two-step phase transition strategy involving dehydration–rehydration of gypsum with …
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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 whether intermediate phases (CaSO 4. n H 2 O) exist, other than the hemihydrate with n =0.5, and also to compare the mechanism of the dehydration process when measured …
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low-temperature dehydration of gypsum has been inves-tigated for many years. The rst analysis of the process is attributed to Flörke (1952), which indicated a two-step process CaSO 4 ·2H 2 O CaSO 4 ·0.5H 2 O -CaSO 4.An early study of the kinetics of dehydration of gypsum was performed, in vacuo, by Molony & Ridge (1968) whose
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— The numerous reports [1] dealing with the morphological changes accompanying the dehydration of gypsum contain several interesting descriptions of the main morphological features of the pseudomorphs. Though, they only refer to the consequences of the cracking of the crystals as they appear on the free external faces …
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— The plaster is an aerial binder obtained through the dehydration of gypsum (CaSo4 2H2O) and forming semyhidrated calcium sulphate (CaSO4 ½ H2O) at temperatures ranging between 85 – 120 degrees ...
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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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— 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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Gypsum plaster is an inorganic binder that is prepared in a two-step process. The first step is dehydration: heated to 100-200 • C, gypsum (CaSO 4 ⋅2H 2 O) releases water as vapor [1, 2] and ...
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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 …
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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...
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— 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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— First study of gypsum single crystal dehydration using X-ray absorption tomography. • Evidence and mechanism of a multi-scale crack pattern due to structure …
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Thermogravimetric and Calorimetric Analysis Dynamic kinetic measurements for the dehydration of gypsum were performed with a Netzsch STA 409 simultaneous TG-DSC instrument and analysed by means of a multivariant non-linear regression developed by Netzsch. Thermogravimetric and calorimetric data were collected in a dynamic nitrogen …
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— Abstract The dehydration of pure and waste gypsums has been examined using in situ synchrotron angle-dispersive X-ray diffraction. Pure gypsum was studied under a number of defined environments; various industrial waste gypsums were also studied under a common standard environment. It is found that the dehydration of gypsum to …
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— In order to study the physical and mechanical properties of gypsum rock samples in three states (natural, high-temperature dehydration and hydration time), natural gypsum rock was put into high-temperature condition of 220°C for dehydration treatment, and then the high-temperature dehydrated gypsum rock was treated with different …
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— Gypsum dehydration affects matrix morphology; the porosity changes due to the decrease of solid volume and increase of fluid content. In addition, the increase of pore pressure affects the compaction within the porous material. Therefore, the intrinsic permeability varies with respect to porosity, and it can be estimated based as follows: ...
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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 …
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The effect of dehydration on the strength of gypsum was chosen for investigation partly because of the known occurrence of evaporites along many thrust faults but chiefly because this dehydration was considered to be typical of, but more tractable o t laboratory investigation than, the hydrous-anhydrous reactions of many metamorphic rocks. ...
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— Because gypsum contains water in its structure, it can accommodate large shear deformation under external load. Laboratory experiments show that during gypsum dehydration, the escaping water weakens the rock, facilitating deformation. In our study, we employ microindentation tests to examine the micromechanics of gypsum during …
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— the dehydration of gypsum due to the effects. of high pressure and temperature during. burial. However, Sonnenfeld (1984) suggested that high pressure and temperature.
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Calcium sulphate dihydrate (CaSO4·2H2O or gypsum) is used widely as building material because of its excellent fire resistance, aesthetics, and low price. Hemihydrate occurs in …
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— The dehydration process of a synthetic gypsum indicates that it has an interstitial gypsum phase dehydrating in a similar way to the interstitial phase found in the Terra Alba gypsum.
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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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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 conversion of gypsum to anhydrite upon burial and heating is accompanied by about a 39% volume decrease, a four-fold increase in thermal conductivity, and consumption of heat. Accurate "back-stripping" of an evaporite basin and tracking its thermal evolution requires a knowledge of the depth of the gypsum-anhydrite transition. …
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