temperature dehydrated gypsum rock was treated with different hydration time, and the gypsum rock samples in three states were subjected to ultrasonic test, density test and uniaxial compression test. The results show that the main components of natural gypsum minerals were gypsum dihydrate (71%), dolomite (27%) and potassium chloride (2%). The ...
Request PDF | Structural evolution of gypsum (CaSO4·2H2O) during thermal dehydration | Herein, an in situ high-temperature synchrotron X-ray diffraction study of gypsum is performed in the ...
The dehydration process of gypsum rock was studied under concentrated solar energy by using a Fresnel lens with power density of 260 Wcm 2. Temperatures higher than 700 C were attained for 1 min ...
Dihydrate gypsum is the dominant phase composition in PG, it is a stable phase at room temperature but can be converted into α-hemihydrate gypsum (α-CaSO 4 ·0.5H 2 O) [16] and β-hemihydrate gypsum (β-CaSO 4 ·0.5H 2 O), also called building gypsum [17] according to different heating methods. α-hemihydrate gypsum is prepared in a ...
In this paper, the effect of two thermal drying regimes of hardened FGD gypsum specimens, with the maximum temperatures of 40 °C and 80 °C and at atmospheric pressure, on the measured …
Effects of heat flux, exposure time, and temperature on gypsum dehydration. ... Gypsum (Calcium Sulfate Dihydrate) forms naturally when calcium sulfate is hydrated by groundwater and as a …
Gypsum of chemical formula CaSO 4 ·2H 2 O, also called calcium sulfate dihydrate, is a versatile material used in several sectors of activity such as cement industry, plaster manufacturing and agriculture [1, 2].It is also found in the formulation of many useful products like paper, glass and paints [3, 4].Gypsum production is carried out in two different …
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.
The thermodynamic calculation results reveal that the dehydration mechanism of gypsum significantly depended on ambient temperature and water vapor pressure.
Temperature measurements at pre-selected board locations indicated three distinct stages of gypsum dehydration; free moisture evaporation, transformation of calcium sulfate dihydrate to calcium ...
Dihydrate gypsum is the dominant phase composition in PG, it is a stable phase at room temperature but can be converted into α-hemihydrate gypsum ... PG was subjected to calcination at relatively low temperatures, and the effect of calcination temperature and time on dehydration behaviour of PG are shown in Fig. 4. The crystal water content ...
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.
The temperature at which the gypsum binder (calcium sulfate hemihydrate) is industrially produced, between 80 and 180 °C, is often mentioned in the literature [14,15,16,17].However, dehydration from gypsum to basanite (CaSO 4 ·0.5H 2 O) starts at a much lower temperature. The dehydration temperature depends on the measurement method, the …
Keywords: Gypsum, Hemihydrate, Soluble anhydrite, Dehydration, In situ high–temperature synchrotron X– ray diffraction INTRODUCTION Calcium sulfate dihydrate, gypsum CaSO 4·2H 2O, is the most common sulfate mineral. Therefore, considerable attention has been paid to the dehydration of gypsum. Numerous studies on the mechanisms and products of
During the calcination process of the dihydrate gypsum, there was an occurrence of two dehydration reactions in a temperature range from 120 °C to 360 °C. The first step was the conversion of CaSO 4 ·2H 2 O into CaSO 4 ·1/2H 2 O, followed by dehydration of CaSO 4 ·1/2H 2 O to CaSO 4 [ 39 ].
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 …
It has been determined that α-hemihydrate gypsum can be obtained from FGD gypsum under hydrothermal conditions at 125 °C and 130°C. The compressive strength of gypsum samples is …
Abstract: 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 ...
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 …
(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.
THE differential thermograms of calcium sulphate dihydrates (gypsums) show two relatively large endothermic effects in close sequence below 250° C. There is general agreement1,2 that these two effects represent the two-step decomposition of the dihydrate to hemihydrate and to soluble anhydrite. A third small endothermic effect, which is always associated with the second …
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 ambient temperature and …
This article addresses the thermal properties and the microstructure of gypsum boards produced from b-hemihydrate by studying its dehydration process. Dehydration reaction of gypsum …
The dehydration of gypsum to hemihydrate has been studied for decades because it is an important model reaction for understanding fluid-triggered earthquakes, and due to the global use of plaster ...
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 ...
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 …
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,
The crystal lattice of raw gypsum, i.e., calcium sulfate dihydrate (CaSO 4 ·2H 2 O) contains approximately 21% by weight chemically bound ... This study was the first CFD simulation effort to account for the two main macroscopic effects of gypsum dehydration, namely, the temperature-dependent GP thermophysical properties and the production and ...
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 ...
Herein, an in situ high–temperature synchrotron X–ray diffraction study of gypsum is performed in the temper-ature range of 30 –200 °C to investigate the continuous structural change from …
A microscope study has been made of the development of crystals of calcium sulphate hemihydrate produced on, or in, sheets of the dihydrate in the form of selenite by calcining under controlled conditions. The crystal forms were shown to be strongly dependent upon both temperature and ambient water vapour pressure. A mechanism for the nucleation and growth …
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.
Gypsum (calcium sulfate dihydrate, CaSO 4 ·2H 2 O) is the most aqueous phase in the system CaSO 4 –H 2 O and, besides anhydrite II, the stable phase under ambient atmospheric conditions. With increasing temperature gypsum starts to dehydrate and form calcium sulfates with lower H 2 O content. The dehydration process proceeds stepwise and ...
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.
Calcium sulfate hemihydrate, also known as bassanite or Plaster of Paris, is one of the most extensively produced inorganic materials worldwide. Nowadays, bassanite is mainly obtained by thermal dehydration of calcium sulfate dihydrate (gypsum) – a process that consumes considerable amounts of energy and thu