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, …
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However only - 35 % of natural gypsum is calcium sulphate dihydrate. Thus on calculating, 35% of the heat of dehydration of the calcium sulphate dihydrate value gives a heat of dehydration of the calcium sulphate dihydrate in natural gypsum of - …
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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 …
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The core composition of gypsum wallboard is calcium sulfate dihydrate (CaSO 4 ·2H 2 O) with varying impurities, additives, or both. ... The analysis supports the hypothesis that minor components in the cast have an effect on the high temperature performance of gypsum casts. The analysis is enhanced when the differential thermal …
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@article{Preturlan2020KineticsAM, title={Kinetics and Mechanism of the Dehydration of Calcium Sulfate Dihydrate: A Comprehensive Approach for Studying the Dehydration of Ionic Hydrates under Controlled Temperature and Water Vapor Pressure}, author={Jo{~a}o G. D. Preturlan and Laetitia Vieille and Sara Quiligotti and Lo{"i}c …
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The dehydration products of gypsum under different temperature and water vapor pressure were investigated by thermodynamic theory. Additionally, the rehydration mechanism of …
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The dehydration temperatures related to calcium chloride (during complete dehydration) was ... and dihydrate (CaCl2·2H2O, unit cell volume: 530 Å3) are the major hydrated forms of calcium chloride available at around 25 °C (Fig. 1a). The majority of calcium chloride occupied as tetrahydrate rather than dihydrate (Table 1). The X-ray .
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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 …
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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 ...
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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 …
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Soil samples were distilled in two steps: first at 35°C and then at 130°C to separate free and gypsum crystallisation water while ensuring an almost complete dehydration of gypsum (Freyer...
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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, …
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Calcium sulfate dihydrate has been widely characterized by both differential scanning calorimetry and thermogravimetry (TG). Two dehydration processes were reported to be partially overlapping. High resolution TG and water vapor self generated atmosphere pin-hole lid strategies were used to increase the resolution of both …
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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 …
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At 2.5 GPa, gypsum starts to dehydrate around 428 K, by forming bassanite, CaSO 4 hemihydrate, which completely dehydrates to γ-anhydrite at 488 K.
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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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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 …
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Gypsum (calcium sulfate dihydrate, Fluka, 99.9% purity) samples were dehydrated at temperatures from 85 up to 800 °C 25 g of substance was weighed in corundum crucibles of 60 ml size and dehydrated in two different furnace types to cover the complete temperature range. The furnaces were calibrated with thermo elements.
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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 …
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Abstract The dehydration of gypsum CaSO4.2H2O has been studied, at negligible water vapour pressure, by in situ infrared (IR) spectroscopy and by thermogravimetry to determine whether intermediate phases (CaSO4.nH2O) exist, other than the hemihydrate with n=0.5, and also to compare the mechanism of the …
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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 ...
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The variations in the mass-loss process of the thermal dehydration of CS-DH under isothermal conditions with temperatures and p(H 2 O) values agreed with those reported previously by Preturlan et ...
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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 …
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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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Synthetic and Naturally Mined Gypsum (Calcium Sulfate Dihydrate) [CAS No. 1] Supporting Nomination for Toxicological Evaluation by the National Toxicology Program January 2006 Prepared by: Integrated Laboratory Systems, Inc. Research Triangle Park, NC Under Contract No. N01-ES-35515
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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 …
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Based on Fig. 32.3, the intensity of gypsum in each sample after undergoing different heating processes can be observed, indicating that heat treatment also helps in the rehydration process as at higher heating temperature, the intensity peak of anhydrite at 25.43° [200] slowly diminishes while the intensity peak of gypsum at 11.61° [020 ...
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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 carbon footprint. Towards a more sustainable future, alternative technologies for bassanite production at low temperatures are therefore …
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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. ... Low-temperature dehydration of gypsum single crystals. 2008 • Nailia Khasanova. Download Free PDF View PDF.
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Gypsum has five phases, namely dihydrate gypsum (CaSO 4 ·2H 2 O), hemihydrate gypsum (CaSO 4 ·0.5H 2 O), ... 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 remains unchanged …
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However only - 35% of natural gypsum is calcium sulphate dihydrate. Thus on calculating, 35% of the heat of dehydration of the calcium sulphate dihydrate value gives a heat of dehydration of the calcium sulphate dihydrate in natural gypsum of - 140-175 J g- r.
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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 …
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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. …
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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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