The dehydration mechanism of natural single crystals of gypsum was investigated in the temperature range 300-430 K by in situ infrared (FTIR) spectroscopy. The thermal evolution of the second-order modes of H 2 O and SO 4 groups in gypsum, in the wavenumber range 4850.5450 cm -1 and 2050.2300 cm -1 respectively, were used …
WhatsApp: +86 18221755073
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 …
WhatsApp: +86 18221755073
The calcium sulphate dihydrate gypsum (CaSO 4 ·2H 2 O) is the most common sulphate evaporite mineral on our planet 1.Sulphate evaporites play an important role in Earth's sulphur cycle and are ...
WhatsApp: +86 18221755073
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 …
WhatsApp: +86 18221755073
It is also worth noting that gypsum is also associated with heave where pyritic materials weather and react with carbonate in ground and surface water producing gypsum (Czerewko et al. 2011 ...
WhatsApp: +86 18221755073
These two experiments clarified that: i) increasing gypsum amount up to 4.5% of binder mass effectively reduced free shrinkage strain subjected to 30 degree of ambient temperature, ii) this free ...
WhatsApp: +86 18221755073
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 ...
WhatsApp: +86 18221755073
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. …
WhatsApp: +86 18221755073
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 ...
WhatsApp: +86 18221755073
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 …
WhatsApp: +86 18221755073
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 ...
WhatsApp: +86 18221755073
The waste gypsum materials studied showed significant differences in the temperatures at which key transformation events occurred; these observations raise …
WhatsApp: +86 18221755073
Calcium sulfate dihydrate has been widely characterized by both differential scanning calorimetry and thermogravimetry (TG). Two dehydration processes were …
WhatsApp: +86 18221755073
We studied the kinetics and mechanism of the dehydration reaction of calcium sulfate dihydrate to hemihydrate under controlled temperature and water vapor partial pressure. From kinetic and reaction rate curves obtained using thermogravimetric analysis (TGA) under isothermal and isobaric conditions, we determined the overall …
WhatsApp: +86 18221755073
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.
WhatsApp: +86 18221755073
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 …
WhatsApp: +86 18221755073
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 …
WhatsApp: +86 18221755073
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 ...
WhatsApp: +86 18221755073
Low-temperature dehydration of gypsum single crystals. Nailia Khasanova. Crystallography Reports, 2008 ... 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 …
WhatsApp: +86 18221755073
Naturally occurring crystals are calcium sulfate dihydrate, CaSO 4 ·2H 2 O, known as gypsum, and anhydrous calcium sulfate, II-CaSO 4. When gypsum is heated, dehydration occurs to form hemihydrates, CaSO 4 ·1/2H 2 O, followed by anhydrite, III-CaSO 4. The hemihydrates and the anhydrite have two modifications, α and β, …
WhatsApp: +86 18221755073
The performance of composite gypsum at elevated temperatures depends on the treatment temperature and reflects the combined effects of gypsum phase change and the filler effects of silica …
WhatsApp: +86 18221755073
As can be seen from Figure 6, the hydration products of gypsum-based composite cementitious materials mainly include gypsum dihydrate (CaSO 4 ·2H 2 O), C-S-H gel, AFt and CH, etc. However, …
WhatsApp: +86 18221755073
When dehydration or decomposition causes a weight change and the DTG signal (TG differential signal) passes over the upper limit threshold, the temperature temporarily stops rising. At this temperature, an isothermal plateau (quasi-isothermal condition) is maintained and the weight change due to dehydration or decomposition is measured.
WhatsApp: +86 18221755073
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 …
WhatsApp: +86 18221755073
Gypsum wallboard has been used for over 100 years as a barrier to the spread of fire in residential and commercial structures. The gypsum molecule, CaSO 4 ·2H 2 O, provides two crystalline waters that are released upon heating providing an endothermic effect. Manufacturers have recognized that the source of the gypsum ore …
WhatsApp: +86 18221755073
The kinetics of the dehydration of gypsum is dependent on the origin of the gypsum and on the impurities in the gypsum samples. ... No hemihydrate was observed. At 60, a very small amount of the hemihydrate is observed, indicating the very slow dehydration of the dihydrate at temperatures below 95 (using a heating rate of 5 …
WhatsApp: +86 18221755073
thermochimica acta ELSEVIER Thermochimica Acta 282/283 (1996) 483-492 The thermal dehydration of natural gypsum and pure calcium sulphate dihydrate (gypsum)' D.L. Hudson-Lamb", C.A. Strydom a, J.H. Potgieter b a Department oJ'Chemistry, University of Pretoria, Pretoria, 0002, South Africa b Technical Services, …
WhatsApp: +86 18221755073
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 …
WhatsApp: +86 18221755073
Measurements have been made of the rate of dehydration of desulphurized gypsum with particle diameters in the range of 35–67 μm in a fluidized bed reactor. Experiments were carried out at bed temperatures of 100 to 170°C. The fluidizing gases were air, with water vapour pressures of between 0.001 atm and 0.35 atm, and carbon …
WhatsApp: +86 18221755073
