This article addresses the thermal properties and the microstructure of gypsum boards produced from β-hemihydrate by studying its dehydration process. …
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 …
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 …
We studied the kinetics and mechanism of the dehydration reaction of calcium sulfate dihydrate to hemihydrate under controlled temperature and water vapor partial pressure.
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.
e ect is influenced by wide equilibrium temperature ranges in the process of the transformation of dihydrate gypsum into semi-aqueous gypsum and anhydrite. In the process of the dehydration of phases, the instability of the CaSO4-H2O system occurs at a temperature of 45 C. The first intense dehydration of the dihydrate into hemihydrate …
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 …
The dehydration of pure and waste gypsums has been examined using in situ synchrotron angledispersive X-ray diffraction. Pure gypsum was studied under a …
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 ...
It can be seen from Figure 8 that gypsum dihydrate was the mineral in the hydrated gypsum matrix without thermal treatment (25 °C). After the thermal treatment at 200 °C, the gypsum dihydrate lost one and a half moles of water and transformed into gypsum hemihydrate (with half a mole of water left).
(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 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 …
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 …
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 ...
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, …
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 thus leaves a significant …
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 …
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 ...
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 ...
The dehydration of gypsum to hemihydrate has been studied for decades because it is an important model reaction for understanding fluid-triggered earthquakes, …
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 …
Mass losses vary between 13.7 and 16.5% and heat of dehydration values between 377 and 420 J g −1 for the dehydration of ground and mixed inhomogeneous gypsum samples. 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 …
Abstract. The core composition of gypsum wallboard is calcium sulfate dihydrate (CaSO 4 ·2H 2 O) with varying impurities, additives, or both. This study compares here two commercially calcined sources of hemihydrate (CaSO 4 ·½H 2 O) from a natural source and a synthetic by-product of flue gas desulfurization and neutralization …
Temperature measurements at pre-selected board locations indicated three distinct stages of gypsum dehydration; free moisture evaporation, transformation of calcium sulfate dihydrate to calcium ...
1. Introduction. As a part of the continuing study of gypsum plaster [] 1 the properties of calcium sulfate dihydrate (CaSO 4 · 2H 2 O) and calcium sulfate hemihydrate (CaSO4 · 1/2H 2 O) were studied by differential thermal analysis, thermogravimetry, and differential scanning calorimetric techniques.These investigations were undertaken in order to gain …
In the low-temperature and high water vapor zone above curve AB in Figure Figure2 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 increased, gypsum undergoes a two-step dehydration process (CaSO 4 ·2H 2 O → γ …
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 …
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 ...
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 …
Structural evolution during the dehydration of gypsum materials - Volume 73 Issue 3 ... Jorgensen, J.D. and Hinks, D.G. (1984) A crystallographic study of the low-temperature dehydration products of gypsum, CaSO 4-2H 2 O; hemihydrate CaSO 4-0.5H 2 O, and γ-CaSO 4. American Mineralogist, ... Thermal dehydration of calcium …
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. …
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 …
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 .
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.
