(PDF) A new calcium sulfate hemi-hydrate

At least five crystalline phases can be found in the CaSO 4 -H 2 O system, which are gypsum CaSO 4 • 2H 2 O, the subhydrates Rand β-CaSO 4 • 0.5H 2 O, and the soluble and insoluble anhydrite CaSO 4 . The formation of these five phases in the CaSO 4

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Application of thermodynamic modeling to predict the stable hydrate

Thermodynamic modeling was used to predict the stable hydrate phase assemblages in a ternary CSA-OPC-anhydrite system. On the basis of this modeling, five systems with diverging expected hydrate ...

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Hydrate vs. Anhydrate — What's the Difference?

Yes, an anhydrate can absorb water to become a hydrate, a process that depends on the environmental conditions and the compound.

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Conversion of gypsum to anhydrite in aqueous salt solutions

Using X-ray diffraction patterns the dihydrate, hemi-hydrate, soluble anhydrite, and natural anhydrite can be identified. The a- and /3-forms of hemi- hydrate and of soluble anhydrite are not distinguishable from powder diagrams. Natural or insoluble anhydrite has the lowest solubility above 40 of any calcium sulfate modification.

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(PDF) Solubility of anhydrite and gypsum at temperatures below …

Thus, a long-standing discussion about the thermodynamic aspect of the gypsum-anhydrite conversion can be closed, not the kinetic part. Comparison of the data selection of Shen et al. (2019) and ...

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The gypsum–anhydrite paradox revisited

Three crystalline phases are known in the CaSO 4 –H 2 O system, distinguishable by their degree of hydration: gypsum (CaSO 4 ·2H 2 O), bassanite (CaSO 4 ·0.5H 2 O), and anhydrite (CaSO 4).On Earth, calcium sulfate is mainly encountered as gypsum or anhydrite related with evaporitic environments (e.g. Buick and Dunlop, 1990, Warren, 2006), although …

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Calcium sulphate hydrates : a review | Semantic Scholar

The evidence for and against various possible calcium sulphate hydrates is reviewed. The hydrates that exist are calcium sulphate dihydrate CaSO 4 .2H 2 O, calcium sulphate hemihydrate CaSO 4 .1/2H 2 O, and three anhydrous phases : soluble calcium sulphate anhydrite, insoluble calcium sulphate anhydrite, and a high temperature calcium sulphate anhydrite phase. The α- …

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Guide to tiling onto anhydrite screeds | Tiling Tips

The binder comes as either an alpha hemi-hydrate (a stronger and harder crystalline form) or anhydrous Calcium Sulfate. When water is added the binders will form calcium Sulfate dihydrate – more commonly known as Gypsum. ... BAL DPM can be used on anhydrite screeds up to 87% RH. As a general rule thumb the drying time for a Calcium Sulfate ...

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The hydrothermal decomposition of calcium monosulfoaluminate 14-hydrate

The calcium aluminate monosulfate hydrates Ca 4 Al 2 O 6 (SO 4)·nH 2 O (where n=8–14) are ternary layered double hydroxides [1] with structures related to brucite, hydrotalcite and hydrocalumite. These materials are of particular interest because of their rich intercalation chemistry and structural diversity [2], [3].The best characterized is the 12-hydrate which occurs …

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Must anhydrite screeds be sanded?

There can be a propensity to over-sand, or even grind the screed, to provide a very rough surface or in an attempt to expose coarse aggregate, in the mistaken belief this will help bond strengths for final floorcoverings. Anhydrite screeds contain no coarse aggregate so this in itself is clearly a paradoxical practice doomed to failure.

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Anhydrite screeds: Handle with care

FOLLOWING my November column in CFJ on subfloor moisture, I received a call from a reader asking for advice on dealing with moisture in calcium sulphate (ie. anhydrite or alpha-hemihydrate) screeds. When it comes to calcium sulphate screeds, the most common question I am asked is about drying times and what to do if a

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Frontiers | Solubility of anhydrite and gypsum at …

Vice versa anhydrite can exist metastable below the transition temperature due to low rates of gypsum nucleation under conditions of not too high supersaturation ... of tedious dilatometric and tensiometric measurements of …

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Anhydrite: The mineral anhydrite information and pictures

Anhydrite and Gypsum are chemically similar, except Gypsum has the addition of water. In fact, the name of Anhydrite is derived from " An " and " Hydra " - meaning "without water" - in …

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Hydrate vs. Anhydrate — What's the Difference?

Heating gypsum produces anhydrite, used in drywall. 15. Hydrate. Requires specific conditions to retain water molecules. Hydrate storage conditions must prevent water loss. 7. ... A lotion can hydrate the skin. Hydrate (slang) …

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Calcium sulfate hemihydrate | 1

ChEBI: Calcium sulfate hemihydrate is a calcium salt and a hydrate. General Description. Gypsum is a naturally hydrated calcium sulfate. It can also be easily synthesized in a partially hydrated or anhydrous form. The partially hydrated form is called hemihydrate calcium sulfate, while the anhydrous form is called anhydrite (Jorgensen 1994).

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Gypsum and Anhydrite | Rock & Gem Magazine

In low temperatures and the presence of available water, anhydrite can hydrate (or rehydrate) and convert to gypsum. Conversely, in …

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Dehydration Pathways of Gypsum and the …

Direct precipitation of anhydrite from a solution results in the formation of the calcium sulphate polymorph β-anhydrite (β-CaSO4; insoluble), which is thermodynamically stable (Tang et al ...

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‪Abubakar Isah‬

Influence of rock wettability on THF hydrate saturation and distribution in sandstones. GR Abbasi, A Al-Yaseri, A Isah, A Keshavarz, S Iglauer ... Multiscale Wettability Characterization of Anhydrite-Rich Carbonate Rocks: Insights into Zeta Potential, Flotation, and Contact Angle Measurements. ... The system can't perform the operation now. Try ...

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Anhydrite

Rarely, anhydrite can be associated with smoky quartz and calcite on Alpine type veins (Alpine clefts/fissures). Naming and Discovery. Anhydrite was first discovered in 1794 in the Hall salt mine near Innsbruck, Austria, and named then or shortly after by Abraham Gottlob Werner. The depth of the occurrence was critical to the discovery, because ...

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Application of thermodynamic modeling to predict the stable hydrate

Thermodynamic modeling was used to predict the stable hydrate phase assemblages in a ternary CSA-OPC-anhydrite system. On the basis of this modeling, five systems with diverging expected hydrate phases were chosen for experimental examination via QXRD and TGA.The aim of this study was to examine whether and to which extent the predicted …

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Calcium Carbonate and Ettringite Induced Efflorescence in CAC

We focused on the efflorescence induced microstructural evolution of ettringite-rich systems prepared with calcium aluminate cement (CAC) and anhydrite. The effects of anhydrite on the visible efflorescence, and the corresponding capillary absorption of CAC-anhydrite mortars were revealed. The composition and microstructure of efflorescence-causing substances were …

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What you Need To Know About Anhydrite Screeds Before Laying Flooring

Over the last 15 years or so, calcium sulphate, or anhydrite, screeds have grown considerably in popularity and today account for about one quarter of all screeds installed in new buildings. There are several advantages that they have over and above traditional sand and cement screeds, not the least of which is that they are very quick and easy ...

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Anhydrite Mineral | Uses and Properties

Anhydrite is an evaporite mineral that occurs in extensive layered deposits in sedimentary basins where large volumes of sea water have been evaporated. …

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Gas hydrate reservoir identification based on rock physics …

The load-bearing type gas hydrate and pore-filling type gas hydrate (figure 1) are two common occurrence states considered in rock physics investigations; the former implies that a gas hydrate is a part of the rock skeleton, while the latter implies that a gas hydrate fills in the pore space (Waite et al. 2004; Dong et al. 2018; Ma et al. 2019 ...

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Caminite: a new magnesium-hydroxide-sulfate-hydrate mineral …

As laboratory experiments predict, a Mg-hydroxide-sulfate-hydrate mineral, here named caminite, precipitates in nature from seawater heated in an active submarine hydrothermal system. ... large volumes of convecting seawater headed above approximately 240C may precipitate abundant caminite and anhydrite. Formation of abundant caminite can ...

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Mechanism and kinetics of gypsum–anhydrite

Calcium sulfate can be precipitated as dihydrate (DH) or gypsum (CaSO 4 ·2H 2 O) at low temperatures and as hemihydrate (HH) (CaSO 4 ·0.5H 2 O) or anhydrite (AH) (CaSO 4) at elevated temperatures (Li and Demopoulos, 2005).All calcium sulfate hydrates are relatively insoluble and they are formed wherever calcium and sulfate occur together after the …

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Hydration of anhydrite

Hydration of anhydrite Hydration is the incorporation of water mole-cule(s) into a mineral, which results in a structural as well as chemical change. This can drastically weaken the stability of a mineral, and make it very susceptible to other forms of chemical weathering. For example, hydration of anhydrite results in the formation of gypsum ...

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Process for the conversion of anhydrite into gypsum

Gypsum and gypsum plaster products can be made from an anhydrite or mixed anhydrite and gypsum starting material, of natural origin or derived chemically as a byproduct, by mixing the powdered anhydrite with part or all (but not more) of the water necessary for complete hydration to gypsum, compressing the mixture into compacted blocks or other bodies, and allowing the …

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Discrimination of bassanite and anhydrite III dehydrated from …

Anhydrite exists in different polymorphs (anhydrite I-III) of which anhy- ... hydrate (with exactly 0.5 mole water), the amount of bassanite in the dehydrated samples could be recalculated by using equation (1). 0.5 ( ) ( ) 2 4 2 2 M H O M CaSO mBassanite m m H O H O = + ...

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Anhydrite Floor Screed: A Comprehensive Guide to Installation

What is Anhydrite Screed? Anhydrite screed, also known as calcium sulfate screed, is a self-leveling floor screed that consists of anhydrous calcium sulfate binder, aggregates, and water. It offers a smooth, level surface that is ideal for a variety of …

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