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 …

The paper assesses the influence of the calcination temperature of synthetic gypsum binder on the binding properties of innovative gypsum pastes, as well as on masonry and plastering mortars. The calcination process of gypsum binder was carried out at four different temperatures ranging from 170 to 190 °C. The specimens for testing …

In order to achieve the resourceful, large-scale and high-value utilization of bulk industrial solid wastes such as flue gas desulfurization gypsum (FGDG), fly ash (FA) and ground blast furnace slag (GGBS), and to reduce the dosage of cementitious materials, orthogonal experimental methods were used to prepare composite cementitious …

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 …

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 …

We report on changes in rock permeability induced by devolatilization reactions using gypsum as a reference analog material. Cylindrical samples of natural alabaster were dehydrated in air (dry) for up to 800 h at ambient pressure and temperatures between 378 and 423 K. Subsequently, the reaction kinetics, so induced …

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 …

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 …

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 …

In the low-temperature and high water vapor zone above curve AB in Figure 2, gypsum is thermodynamically stable; in the ABC zone, CaSO 4 ·2H 2 O will partially dehydrate its crystal water to form β-CaSO 4 ·0.5H 2 O, and as the temperature is …

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) …

Introduction. 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, depending on temperature and water vapor partial pressure (p H2O) [3,4] forms either hemihydrate (CaSO 4 •½H 2 O) or γ-anhydrite …

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; ...

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, ...

After the 300 °C treatment, the dehydration of gypsum was likely completed, forming a more robust anhydrate phase that increased the strength of the gypsum matrix …

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 ...

In the high-temperature and low water vapor pressure region, gypsum dehydrates to form γ-CaSO 4 in a single-step process (CaSO 4 ·2H 2 O → γ-CaSO 4 ); with increasing water vapor pressure ...

M. Koebel. Empa, Swiss Federal Laboratories for Materials Science and Technology, CH-8600 Dübendorf, Switzerland. Search for more papers by this author

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 …

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].

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 …

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.

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 …

The Simulation and Analysis of Dehydration Process of FGD Gypsum Grouted Wall ZENG Ziyue 1,2, YANG Jiansen 1, WEI Yongqi 2 1 School of Civil and Hydraulic Engineering, Ningxia University, Yinchuan 750021, Ningxia, China 2 School of Material Science and Engineering, Tongji University, Shanghai 201804, China

(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.

The thermal conductivity of the gypsum board reduces after the dehydration (in the temperature region of 3008C), in some cases almost 50% [7], due to absence of bound water and despite the increase of the porosity.

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. (a) Projection of the gypsum structure on the (001) plane. The periodicity b is determined by two double layers, between which water molecules are concentrated. ...

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 …

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 slow dehydration of CaSO 4 ·2H 2 O and impurities in the gypsum samples start at temperatures lower than 95°C.