dehydrated hemihydrate gypsum in Mexico

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Calcium Sulfate Hemihydrate

Calcium Sulfate Hemihydrate, also known as plaster of Paris, is a material made from gypsum that has been used for centuries in construction and various medical applications, including bone repair and growth factor release. ... When gypsum is heated, dehydration occurs to form hemihydrates, CaSO 4 ·1/2H 2 O, followed by anhydrite, III-CaSO 4.

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Dehydration Pathways of Gypsum and the Rehydration …

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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Preparation of α-calcium sulfate hemihydrate from …

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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Modification on the Performance of the Hemihydrate Gypsum …

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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From atom level to macroscopic scale: Structural mechanism of gypsum

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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Synthesis of calcium sulfate hemihydrate whiskers from high …

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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Structural evolution during the dehydration of gypsum …

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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Effect of sodium fluoride on the crystal regulation of high …

As one of the extensively used inorganic cementitious material, hemihydrate gypsum (HH, CaSO 4 ·0.5H 2 O) has two forms, namely β-HH and α-HH. β phase is a dehydration product of calcium sulfate dihydrate (DH, CaSO 4 ·2H 2 O) in dry air at 105–180 °C and has a longer history of application, whilst α-HH can be produced …

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Ingenious approach for retrieving valuable metals from gypsum …

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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Gypsum Products

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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Direct formation of the γ-CaSO4 phase in dehydration …

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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Gypsum hydration: a theoretical and experimental study

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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Structural characteristic and formation mechanism of hemihydrate …

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 Kinetics of Gypsum in a Fluidized Bed Reactor

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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In situ micro-Raman investigation of dehydration …

dehydration of gypsum showed that the dehydration was sequential first to hemihydrate (bassanite) and then to anhydrate. Hemihydrate is known to be thermodynami cally unstable at all temperatures; however it is available in nature, although rarely and its existence and formation are difficult to understand. The objective of the present

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No. 4710 February 6, 1960 NATURE 375

thermal analysis in a sample of hemihydrate prepared by calcining gypsum under conditions simulating ... dehydrated sample of this hemihydrate is shown in Fig. l, curve a.

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Crystallization Kinetics of α-Hemihydrate …

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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Hemihydrate

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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Structural evolution during the dehydration of …

Unit-cell expansion of the hemihydrate phase during the dehydration study of pure gypsum within a sealed capillary with an excess of water: (A) a, b and c unit-cell parameters; (B) b unit-cell angle.

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Structures of a) gypsum, b) hemihydrate, and c) …

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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Understanding gypsum in 3 diagrams

Learn how gypsum, hemihydrate and anhydrite react with water and change their crystal structure and solubility. See thermal analysis, dilatometry and …

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Hydration mechanism of a sodium-doped phosphogypsum-based hemihydrate

The mass loss in the temperature range of 81.6 ℃∼137.1 ℃ is caused by the dehydration of gypsum into hemihydrate gypsum, which is in accordance with ref [40]. As the temperature continues to increase to 297.5 °C, the mass loss reaches 5.80 %. This is the result of the removal of crystal water from hemihydrate gypsum and …

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Fast in-situ X-ray scattering reveals stress sensitivity of …

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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Thermal properties and microstructure of gypsum board and …

This article addresses the thermal properties and the microstructure of gypsum boards produced from β-hemihydrate by studying its dehydration process. …

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Calcium sulphate hemihydrate hydration leading to gypsum

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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Preparation of α-calcium sulfate hemihydrate

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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Formation of α-Hemihydrate Inside of a Gypsum Crystal …

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 …

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Direct formation of the γ-CaSO4 phase in dehydration process of gypsum

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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Structural evolution during the dehydration of gypsum …

It is found that the dehydration of gypsum to anhydrite proceeds via the hemihydrate and γ-anhydrite phases and the interplay and behaviour of these phases …

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Dehydration Pathways of Gypsum and the Rehydration …

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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2 Gypsum dehydration during cement production

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 …

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Influence of dehydration method on the morphology of hemihydrate gypsum

Influence of dehydration method on hemihydrate gypsum, hemihydrate phosphogypsum and processed hemihydrate phosphogypsum crystal morphology was researched. Gypsum raw material dehydration in dry ...

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Formation of α-Hemihydrate Inside of a Gypsum Crystal …

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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Thermal behaviour and kinetics of dehydration of gypsum …

Thermal behaviour and kinetics of dehydration of gypsum in air have been investigated using in situ real-time laboratory parallel-beam X-ray powder diffraction data evaluated by the Rietveld method. Thermal expansion has been analysed from 298 to 373 K. The high-temperature limits for the cell edges and for the cell volume, calculated …

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Dehydration Pathways of Gypsum and the Rehydration

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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Gypsum Soils—Their Morphology, Classification, Function, …

Dehydration of α-hemihydrate undergoes conversion to the metastable anhydrite III phase at 180 °C, although this phase does readily take up water and …