Experimental Study on Physical and Mechanical Properties …
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 ...
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Gypsum board reaction kinetics at elevated temperatures
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].
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Structural evolution during the dehydration of gypsum materials
The waste gypsum materials studied showed significant differences in the temperatures at which key transformation events occurred; these observations raise implications concerning the re-use of by-product gypsum materials. Finally, high temperature data are re-examined in the search for a variation of the anhydrite structure.
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Thermal analysis of calcium sulfate dihydrate sources used to
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 is a factor that affects all …
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Investigation of the impurity effect on the kinetics of thermal
Calcium sulfate gypsum dihydrate CaSO 4 ·2H 2 O is a typical ... °C correspond to dehydration of gypsum; in the temperature range (400–900) °C decomposition and dissociation of ... It follows from the experimental data that the isothermal high-temperature decomposition of anhydrite in natural samples in the air atmosphere is a complex and ...
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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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Formation of α-Hemihydrate Inside of a Gypsum Crystal during …
The formation of beta-hemihydrate is an endothermic reaction as well. During the phase decomposition of dihydrate to hemihydrate, the temperature inside of the crystal should not increase above the decomposition temperature in which …
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Scrutinizing Gypsum Board Thermal Performance at Dehydration Temperatures
Temperature measurements at pre-selected board locations indicated three distinct stages of gypsum dehydration; free moisture evaporation, transformation of calcium sulfate dihydrate to calcium ...
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Physicomechanical Properties of Gypsum with Mineral Additions …
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 flour or talc powder. ... There was tremendous pore water loss, and gypsum dehydration happened at 100 °C and 200 °C, leading to a porous structure that ...
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(PDF) Experimental Study on Physical and Mechanical …
In order to study the physical and mechanical properties of gypsum rock samples in three states (natural, high-temperature dehydration and hydration time), natural gypsum rock was put into high ...
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Structural evolution of gypsum (CaSO4·2H2O) during …
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
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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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Formation of α-Hemihydrate Inside of a …
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 …
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Changes in structure and composition of gypsum paste at …
The structure and composition of the gypsum at elevated temperatures were studied by means of scanning electron microscopy, X-ray diffraction (XRD) and thermogravimetry (TG). The gypsum paste samples were heated to the temperatures from 50 to 1000 °C. The changes in the structure of gypsum were in good accordance with the changes in properties. …
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KINETIC STUDIES OF THERMAL DEHYDRATION OF …
Drying and thermal dehydration of gypsum in the shape of thick circular plate and sphere ware investigated, especially by using a fluidized bed to reduce the film resistance for heat transfer. …
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Influence of the Calcination Temperature of Synthetic Gypsum on …
dehydration of natural gypsum stone (dihydrate calcium sulphate) from an opencast gypsum mine. It is characterized by the quick growth of mechanical strength and short time of binding.
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Novel approach to thermal degradation kinetics of gypsum: application
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 …
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Thermal properties and microstructure of gypsum board and its
This article addresses the thermal properties and the microstructure of gypsum boards produced from β-hemihydrate by studying its dehydration process. Dehydration …
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(PDF) Study of Gypsum Dehydration by Controlled …
The dehydration of gypsum (CaSO 4 • 2H 2 O) into calcium sulfate hemihydrate (CaSO 4 • 0.5H 2 O) and anhydrites (-CaSO 4 and-CaSO 4) was carried out by heating under a constant pressure of water vapor using Controlled …
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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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Mechanical strength, hydration products, and microstructure of …
It is commonly acknowledged that the dehydration of dihydrate gypsum typically results in complete decomposition into anhydrite within the temperature range of 100 °C to 150 °C [50]. Nevertheless, when subjected to a slow heating rate, the decomposition interval for dihydrate gypsum decreases.
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Calcium sulfate dihydrate, dehydration
We will quote as an example the dehydration of calcium sulfate dihydrate (gypsum) into plaster, which is, in fact, a sohd solution of water in calcium sulfate whose composition varies practically from 0 to 0.66 and which takes value of 0.5 under normal conditions of temperature and moisture from where the name of semi-hydrate comes, which is ...
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Fast in-situ X-ray scattering reveals stress sensitivity of gypsum
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 ...
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Effect of high temperatures on gypsum-based composites
Calcined gypsum (commonly known as a Plaster of Paris) in powder form consists mainly of calcium sulphate hemihydrate CaSO 4 ·1/2H 2 O, which is prepared by dehydration of calcium sulphate dihydrate CaSO 4 ·2H 2 O (natural gypsum rock or an industrial by-product, e.g. from flue gas desulphurization of coal power plants or from phosphoric acid ...
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Structures of a) gypsum, b) hemihydrate, and c) insoluble …
As can be seen in Fig. 11 the dehydration temperature of the hemihydrate increases with sodium content. ... which can be found as calcium sulfate dihydrate or gypsum (CaSO 4 ⋅2H 2 O ...
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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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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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Dehydration Pathways of Gypsum and the Rehydration …
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 …
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Structural evolution of gypsum (CaSO4·2H2O) during thermal dehydration
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 ...
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Thermal analysis of calcium sulfate dihydrate sources used to
An ore of calcium sulfate dihydrate should exhibit four distinct thermal reactions evident in the DTA and TGA evaluations; 1) the first is an endotherm ending ∼105 °C where the adsorbed water is driven off, 2) a second endotherm ending ∼175 °C where 75% of the crystalline water is driven off to achieve the metastable phase, CaSO 4 ·½H 2 O (commonly …
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