Flue gas desulfurization (FGD) gypsum mainly composed of calcium sulfate dihydrate (DH) was used as a raw material to obtain alpha-calcium sulfate hemihydrate ({alpha}-HH) through dehydration in a Ca-Mg-K-Cl-solution medium at 95{sup o}C under atmospheric pressure. The effects of potassium sodium tartrate and sodium citrate on …
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In order to produce α-calcium sulfate hemihydrate (α-CaSO4·0.5H2O) whiskers with high aspect ratios, a minor amount of CuCl2·2H2O was used as the modifying agent in the process of hydrothermal treatment of calcium sulfate dihydrate (CaSO4·2H2O) precursor. The presence of 2.60×10-3 mol/L CuCl2·2H2O resulted in the increase of the …
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The dehydration mechanism of natural single crystals of gypsum was investigated in the temperature range 300–430 K by in situ infrared (FTIR) ... that the dehydration of gypsum directly yields γ-CaSO 4 (anhydrite) without the intermediate formation of hemi-hydrate ... calcium sulphate hemihydrate (CaSO 4 · 0.5H 2 O)
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A readily monitored and controllable hydrothermal system for the facile, cost-effective transformation of FGD gypsum to calcium sulfate hemihydrate whiskers. Particuology, 54 (2021), pp. 173-180. ... Dehydration pathways of gypsum and the rehydration mechanism of soluble anhydrite γ-CaSO 4. ACS Omega, 4 (4) (2019), pp. …
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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 …
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α-Calcium sulfate hemihydrate (α-HH) is an important cementitious material, which can be prepared by hydrothermal method from calcium sulfate dihydrate (DH) in an electrolyte solution. Study of the …
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Under natural conditions, dehydration from gypsum to the hemihydrate/anhydrate phases is slow; hence, low energy is introduced to accelerate this process. Metal-incorporated gypsum was calcined in a muffle furnace at 200–400°C for 2 h and transferred into a desiccator after cooling to approximately 100°C.
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crystallography or mineralogy. α-HH is formed by hydrothermal dehydration of dihydrate, whereas β-HH can be obtained by calcination of gypsum (Christensen et al., 2010; Schmidt et al., 2011). 170 Physicochem. ... Additionally, anhydrite and hemihydrate gypsum are unstable, with the extension of the accumulation time, they slowly hydrate into ...
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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 ...
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The objective of this study was to assess the feasibility of using the plant-source polymer of the matcha powder as a composite admixture for hemihydrate gypsum. Hemihydrate gypsum was mixed with different contents of matcha powder, and then the water requirement for the normal consistency, setting times, density, strength, hydration …
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The influence of impurities on the dehydration and conversion process of calcium sulfate dihydrate to α-calcium sulfate hemihydrate in the two-step wet-process phosphoric acid production ... Sodium cation-mediated crystallization of α-hemihydrate whiskers from gypsum in ethylene glycol–water solutions. Cryst. Growth Des., 18 (11) …
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Calcium sulphate dihydrate (CaSO4·2H2O or gypsum) is used widely as building material because of its excellent fire resistance, aesthetics, and low price. Hemihydrate occurs in …
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The dehydration of gypsum (CaSO4·2H2O) into calcium sulfate hemihydrate (CaSO4·0.5H2O) and anhydrites (γ-CaSO4 and β-CaSO4) was carried …
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Sustainability of gypsum products as a construction material. N. Lushnikova, L. Dvorkin, in Sustainability of Construction Materials (Second Edition), 2016 β-Hemihydrate binder. β-Hemihydrate (also known as plaster of Paris) is the most commonly used gypsum binder in construction.It is produced in an apparatus connected to air. Different equipment is …
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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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1 Introduction . Calcium sulfate hemihydrate [CaCO 4 ∙ 0.5H 2 O(s)] can be found naturally in very dry climate regions in Egypt, Australia, Death valley and Kuwait as bassanite, but in the presence of water or humid atmosphere it can convert to dehydrate [1, 2]. Therefore, the production of hemihydrate industrially has been studied widely through the …
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1. Introduction. Calcium sulfate hemihydrate plaster is considered one of the most popular sustainable binders used in the construction industry due to low production energy, low market price, fire-resistant, and good thermal properties [1 – 5].It is commonly used as an ingredient in paste and mortar plastering and production of some building …
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Their experimental results reveal that gypsum dehydration proceeds through only a single CaSO 4 ·2H 2 O → γ-CaSO 4 step when the ambient water vapor pressure is less than 26664 Pa; ... where P H 2 O(gypsum–hemihydrate) is the equilibrium water vapor pressure of the reaction for the transformation of CaSO 4 ·2H 2 O into β-CaSO 4 …
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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 …
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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 °C. When mixed with water, it dissolves while new gypsum crystals precipitate. Plaster's microstructures affect its reactivity and setting properties, but are poorly understood due …
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Their experimental results reveal that gypsum dehydration proceeds through only a single CaSO 4 ·2H 2 O → γ-CaSO 4 step when the ambient water vapor pressure is less than 26664 Pa; ... where P H 2 O(gypsum–hemihydrate) is the equilibrium water vapor pressure of the reaction for the transformation of CaSO 4 ·2H 2 O into β …
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This work firstly shows that the observed crystallization inside of gypsum during dehydration is the formation of alpha-hemihydrate. Gypsum crystal at (a) 135 • C, and (b) 142 • C. Crystals ...
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The band 3600 cm −1 in hemihydrate is lowered to 3540 cm −1 in gypsum, and the band 3550 cm −1 in hemihydrate to 3400 cm −1 indicates the hydrogen bonding. Hemihydrate contains only one type of water molecule attached to the anion, SO 4 2−, by hydrogen bonding but gypsum contains two types of water molecules out of which one …
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Wolfgang Voigt. Calcium sulfate occurs in nature in form of three different minerals distinguished by the degree of hydration: gypsum (CaSO4·2H2O), hemihydrate (CaSO4·0.5H2O) and anhydrite...
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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...
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The hydration of calcium sulphate hemihydrate (CaSO 4 ·0.5H 2 O) leading to the crystallization of gypsum (calcium sulphate dihydrate – CaSO 4 ·2H 2 O) has been the subject of several investigations over a long period and a vast amount of data is widely distributed throughout in the literature. In this review article an overall picture of the …
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Event/ Capillary environment Open+N2 Open Sealed Sealed + H2O 149 180 200 360 151.5 177 184 375 162.5 208 216 330 166 242 251 291 50% gypsum 50% hemihydrate Inception of major structural change in hemihydrate Formation of g-anhydrite 50% g-anhydrite 50% anhydrite Effect of heating rate on the dehydration of pure gypsum The …
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Negro and Stafferi17,18studied the dehydration of gypsum and hemihydrate. Thegypsum dehydration was nucleation controlled and was modelled using 2d Avrami-Erofe'ev expression. The hemi-hydrate dehydration was expressed as a reaction with anorder of 0.68. Strydom et al.19 studied the dehydration byDTA using up …
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Mexico). Gypsum is one of the softest min-erals and one of the rst minerals to crystal-ize as seawater evaporates. Thus, gypsum is ... ters of its water in a partial dehydration process and becomes hemihydrate gypsum (CaSO 4 •½H 2 O) or calcined gypsum; it is also known as beta gypsum (alpha gypsum is
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Dehydration of α-hemihydrate undergoes conversion to the metastable anhydrite III phase at 180 °C, although this phase does readily take up water and …
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