Dehydration behaviors and properties of anhydrite II prepared by
The addition of sulfuric acid reduced the dehydration temperature, accelerating the nucleation of anhydrous calcium sulfate and increasing the number of crystal nuclei, resulting in the formation of small anhydrite gypsum crystals. ... In Fig. 10 g, long columnar dihydrate gypsum crystals formed in HPG280–40 % at 7 days, with some ...
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Thermal Analysis & Rheology THERMAL SOLUTIONS
Stucco is formed by partial dehydration of gypsum (calcium sulfate dihydrate), a naturally occurring mineral. ... of temperature, should provide a convenient method for ... Weight Loss Profile For Calcium Sulfate Dihydrate - Open Pan TS-29 0 50 100 150 200 250 300 350 75 80 85 90 95 100 105-0.2 0.0 0.2 0.4 0.6
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The dihydrate‐hemihydrate transformation in gypsum
Dehydration experiments revealed that the most important variables that control the rate of the gypsum-to-bassanite transformation are temperature and water vapour pressure (Ball & 2 Norwood, 1969 ...
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Discrimination of bassanite and anhydrite III dehydrated from …
Gypsum (calcium sulphate dihydrate, CaSO4 ·2 H2O) is added to the clinker before the mill-ing process and dehydrates partially to bassanite (calcium sulphate hemihydrate, CaSO4 ·0.5 …
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Dissolution and conversions of gypsum and anhydrite
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. ... dihydrate: Jour. Inorg. Nucl. Chem., v. 33,
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The Mechanism of the First Hydration‐Dehydration Cycle of Pure …
The DSC signals of the generated dihydrate indicate the phase transformation from dihydrate to soluble anhydrite through a two-step dehydration process of CaSO 4 · 2H 2 O CaSO 4 · 0.5H 2 O γCaSO 4 as displayed in Figure 11 . Moreover, the TG curves are compatible with the theoretical stochiometric percentage mass loss of water (21%).
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Scrutinizing Gypsum Board Thermal Performance at Dehydration Temperatures
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 3008C, using a low heating rate. ... [18], the energy needed for the dehydration of pure calcium sulfate dihydrate (gf ¼ 0%, mc ¼ 20.9% ...
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The thermal dehydration of synthetic gypsum
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 with an ...
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Gypsum hydration: a theoretical and experimental study
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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Synthesis of large plate-like gypsum dihydrate from waste gypsum …
Dehydration of gypsum dihydrate to gypsum hemihydrate in liquid phase can be understood in terms of solubility. The cross point of solubility of gypsum dihydrate and hemihydrate are at 97 ± 1 °C in pure water. 9 The hemihydrate is hardly formed, even if the dihydrate is heated in water at 100 °C (Fig. 2). Therefore, it is necessary to use ...
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Dehydrating Time & Temperature Guide: Fruits, Vegetables, Meat…
Whether you are dehydrating fruits or vegetables, herbs or spices, there is a difference in the dehydration time, because food is farmed and harvested in different quantities and contains differing levels of moisture and fats. ... An internal temperature of 160 degrees F is necessary for eliminating disease-causing bacteria. Using a calibrated ...
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Raman spectroscopy of the dehydration process of gypsums
occurrence of dihydrate dehydration at this temperature was detected, evidenced by the disappearance of multiple dih ydrate peaks, especially the peak at 1002 cm 1 .
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Fast in-situ X-ray scattering reveals stress sensitivity of …
he calcium sulphate dihydrate gypsum (CaSO 4·2H 2O) is the most common sulphate evaporite mineral on our planet1. Sulphate evaporites play an important role in ... dehydration temperatures, 129 ...
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Dehydration behavior of FGD gypsum by simultaneous TG and
Methods. The dehydration process of FGD gypsum was performed with simultaneous TG/DSC analysis (NETZSCH STA 409 Luxx, Selb/Bavaria, Germany) at N 2 atmosphere with a gas flow of 20 mL min −1.Non-isothermal analysis was carried out at different heating rate (2−20 K min −1).Isothermal analysis was conducted in the temperature range of …
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In situ IR spectroscopic and thermogravimetric study of the dehydration
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 …
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Dehydration Pathways of Gypsum and the …
In this work, the dehydration pathways of gypsum and the rehydration mechanism of soluble anhydrite were mainly investigated by …
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(PDF) Dehydration Pathways of Gypsum and the …
The thermodynamic calculation results reveal that the dehydration mechanism of gypsum significantly depended on ambient temperature and water vapor pressure.
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Dehydration Pathways of Gypsum and the Rehydration …
The dehydration products of gypsum under different temperature and water vapor pressure were investigated by thermodynamic theory. Additionally, the rehydration mechanism …
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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 fire resistance, aesthetics, and low price. Hemihydrate occurs in two formations of α- and β-type. Among them β-hemihydrate is mainly used to produce gypsum plasterboard since the hydration product of the α-hemihydrate is too brittle to be used as …
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Scrutinizing Gypsum Board Thermal Performance at Dehydration Temperatures
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.
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The thermal dehydration of synthetic gypsum
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.
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Effect of sodium fluoride on the crystal regulation of high-strength …
As one of the extensively used inorganic cementitious material, hemihydrate gypsum (HH, CaSO 4 ·0.5H 2 O) has two forms, namely β-HH and α-HH. β phase is a dehydration product of calcium sulfate dihydrate (DH, CaSO 4 ·2H 2 O) in dry air at 105–180 °C and has a longer history of application, whilst α-HH can be produced by wet calcination …
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From atom level to macroscopic scale: Structural mechanism of …
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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Dehydration Temperature of Gypsum
(1) 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.
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Dehydration of Gypsum Rock by Solar Energy: Preliminary Study
The stability of bassanite and the mechanism of dehydration of natural gypsum were investigated by in situ micro-Raman spectroscopy in the temperature range 300-380 K and 300-450 K. From the thermal evolution of the sulphate (940-1200 cm -1 ) and water (3250-3750 cm -1 ) molecular stretching (ν ν 1 and ν ν 3 ) modes, it was evident that the ...
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KINETIC STUDIES OF THERMAL DEHYDRATION OF …
4-1 Temperature Change in Drying and Dehydration of Gypsum in a Fluidized Bed Fig. 2 illustrates a typical change of interior tempera-tures with time during the drying and dehydration of gypsum in the shape of circular plate (Run G-18, To-184°C). There are some significant observations which werecommonto these entire series of runs:
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Properties of Building Gypsum
The hydration product of gypsum is dihydrate gypsum, while the dehydration temperature of dihydrate gypsum is low, about 120 ℃. When the air humidity is low, the dihydrate gypsum …
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Structural evolution during the dehydration of gypsum materials
(a) Surface plot of angle-dispersive diffraction patterns (collected at station 6.2, SRS, UK, using a wavelength of 1.4000(2) A ˚ ) obtained during the dehydration of a pure gypsum system within ...
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Low-temperature dehydration of gypsum single crystals
On the basis of the analysis of the electron spin resonance spectrum of the radical ion, it is established that the transformation of gypsum (CaSO 4 • 2H 2 O) into bassanite (CaSO 4 • 0.5H 2 O) with partial removal of water molecules occurs through
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Formation of α-Hemihydrate Inside of a Gypsum Crystal during …
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 ...
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