Gypsum Dehydration Temperature
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- Gypsum Dehydration Temperature
of the dehydration of calcium sulfate hemihydrate. J. Am. Chem. Soc. 58:1261–1265. Fig. 6. Comparisons between the gypsum content (percentage by. ... (temperature at which gypsum becomes anhydrite).
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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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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 at a point ...
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KINETICS OF GYPSUM DEHYDRATION D. Fatu Department of Physical Chemistry, Blv. Elisabeta 4-12 Bucharest, 70346 Romania (Received June 6, 2000; in revised form January 25, 2001) ... low heating rate (2 K minŒ1), the temperature and mass gradients are lower, so the consecutive decomposition stages are better separated. For the kinetic analysis of ...
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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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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 heated up to 300°C, using a low heating rate. Temperature measurements at pre-selected board locations indicated three distinct stages of gypsum ...
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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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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.
WhatsApp: +86 18221755073The dehydration (transition from gypsum through bassanite to anhydrite) was characterized by a mass loss (caused by water vapor release) and started at a temperature of …
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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 dehydrates to γ-anhydrite at 488 K. …
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The dehydration temperature and humidity affects the resulting calcium sulphates. Anhydrite exists in different polymorphs (anhydrite I-III) of which anhy- ... The dehydration of high purity gypsum (calcium sulphate dihydrate, Fluka, 99.9% purity) was performed in chamber furnaces at 85 °C up to 550 °C in air. The initial high purity gyp-
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Depending on the mill temperature, the gypsum becomes partially or completely dehydrated to hemihydrate or anhydrite respectively. According to [8] the temperatures at which gypsum dehydration to hemihydrate can take place lie between 95 and 170 °C. The results of [9] indicate that gypsum dehydration can even begin at temperatures below 70 °C.
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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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Dehydration of gypsum in drained conditions induces a decrease in Vp and Vs Acoustic emissions indicate pore collapse Poisson's ratio decreases due to microcracks and solid phases replacement ... [51] As stated in section 1, Volterra gypsum has been chosen as a low-temperature analogue of serpentinites. The extrapolation of our observations on ...
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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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The decomposition of gypsum (dehydration) was studied in the pressure range 7.5-60 kbar and the temperature range 75—400 °C using a belt type apparatus. Surprisingly, gypsum is rather stable even at pressures greater than 20 kbar contradicting the results of a calculation of the space requirement of the competing phases (AII—CaSO4 + H2O ...
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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 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 by two techniques with …
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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 °C. When …
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Using the DVS Vacuum, we investigated the influence of relative humidity on gypsum dehydration between 25 °C and 60 °C. The mass loss observed by DVS indicated the …
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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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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 muffle furnace at ...
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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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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 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, the ...
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For example, Yang et al. found that the dehydration temperature of gypsum gradually increased with the rise in pressure, and the dehydration boundary between gypsum and bassanite was determined to ...
WhatsApp: +86 18221755073The thermodynamic calculation results reveal that the dehydration mechanism of gypsum significantly depended on ambient temperature and water vapor pressure.
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during experimental dehydration of lizardite and gypsum. [3] Two challenging problems encountered in addressing the possible importance of dehydration embrittlement in ... high-pressure and high-temperature tests is to study gypsum as an analogue of serpentine-rich rocks at depth [Ko et al., 1997; Milsch and Scholz, 2005]. Gypsum undergoes brittle-
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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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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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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 results revealed smaller mass loss of high-temperature calcined gypsum products during dry-wet cycles between 50°C and 70°C, indicating superior waterproofing capabilities. ... Notably, the dehydration temperature of PG doped with sulfuric acid converting to anhydrite remained below 180°C, with the minimum calcination temperature ...
WhatsApp: +86 18221755073DOI: 10.2298/SOS1002233L Corpus ID: 135642604; Influence of the gypsum dehydration temperature and alkali additives on the properties of anhydrite cement @article{Leskeviciene2010InfluenceOT, title={Influence of the gypsum dehydration temperature and alkali additives on the properties of anhydrite cement}, author={V. Leskeviciene and I. …
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The orientation of the crystallographic axes of the studied gypsum crystal was determined on an Enraf Nonius CAD-4 automatic four-circle diffractometer. The unit- 806 LOW-TEMPERATURE DEHYDRATION OF GYPSUM SINGLE CRYSTALS 807 (a) (a) (b) Li a O2 O1 O1 O2 O2 OW O2 b O2 X O2 Z S Y H2 H1 O1 c (b) Li Fig. 2.
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1. Ultrasonic results indicate gypsum hydration reaction consists of two stages: the dissolution of hemihydrate in the first stage and the nucleation and precipitation of dihydrate in the second stage. 2. Gypsum hydration is strongly influenced by water amount. Spread flow test is suitable to determine the water demand for gypsum hydration.
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gypsum dehydration process at 124.3 °C under different water vapor partial pressures. Their experimental results reveal that gypsum dehydration proceeds through only a single CaSO 4· …
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