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Dehydration Pathways of Gypsum and the …
The dehydration products of gypsum under different temperature and water vapor pressure were investigated by thermodynamic theory. …
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QUANTITATIVE IN-SITU X-RAY DIFFRACTION ANALYSIS …
the slow changes in phase composition during hydration and leads to more stable values of the phase development. Refined parameters are lattice parameters and crystallite size for the hydrate
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Formation of ettringite in Portland cement/calcium aluminate cement
To explore the formation of ettringite at lower temperatures in the Portland cement/calcium aluminate cement/calcium sulfate ternary system hydrates, the effect of calcium sulfate variety on the setting time of the ternary system and the strength development of its mortars at 0, 5, 10 and 20 °C were investigated.The formation of ettringite was further …
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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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The ternary system Portland cement–calcium
The hydration processes of ordinary Portland cement (OPC) and of calcium sulphoaluminate cement (CSA) are very well documented. The OPC clinker is mainly composed of four phases, two calcium silicates C 3 S and C 2 S, one calcium aluminate C 3 A, and ferrite C 4 AF, to which calcium sulphate is added to control setting. C 3 S and C 3 A mainly contribute …
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On the hydration process of the slag-anhydrite-lime system: A
A mixture of slag and anhydrite (without lime) reacted to produce C-S-H and ettringite, but the initiation time of reaction was very long-as much as 400 h. In this case, the calcium oxide/silica (CaO/SiO2) ratio of the calcium-silicate-hydrate was considered as low as 0•6 to 0•8.
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The hydrothermal decomposition of calcium monosulfoaluminate 14-hydrate
We apply in-situ synchrotron X-ray diffraction to study the transformation of calcium monosulfoaluminate 14-hydrate Ca4Al2O6(SO4)·14H2O [monosulfate-14] to hydrogarnet Ca3Al2(OH)12 on the ...
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Thermodynamic Modeling of Calcium Sulfate Hydrates in a CaSO
The data sets by Cameron and Breazeale 19 are very scattered and show larger values than other researchers' data and the calculated values of this work. 4.3.2. Anhydrite. The calculated solubility curves of anhydrite in sulfuric acid solutions are shown in …
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ANHYDRITE – CaSO
ANHYDRITE – CaSO 4 Anhydrite is a very common anhydrous sulfate, an important constituent of evaporitic sequences and related deposits. It is a very important ore. Anhydrite is usually very pure, but ma y contain Sr and Ba. It has fusibility 2 (melts in the candle flame). Anhydrite crystals reach 15 cm in length, with 40 recognized combined ...
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How to dissolve anhydrite, is it soluble in HCL?
Anhydrite (powdered) is soluble in hydrochloric acid (HCl), but only with little effect in water. It hydrates over longer period of time < 42°C and turns into …
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(PDF) Solubility of anhydrite and gypsum at temperatures below …
The extremely slow crystallization kinetics of anhydrite at T < 90°C prevents a direct determination of this transition temperature. In the present work the different approaches to fix this ...
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Hydration of anhydrite of gypsum (CaSO 4.II) in a ball mill
After the formation of anhydrite III, continued heating leads to less soluble anhydrite (anhydrite II). Under ambient conditions, CaSO4.II reacts very slowly with water; hence, the …
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Calcium sulfate
Calcium sulfate (or calcium sulphate) is the inorganic compound with the formula CaSO 4 and related hydrates.In the form of γ-anhydrite (the anhydrous form), it is used as a desiccant.One particular hydrate is better known as plaster of Paris, and another occurs naturally as the mineral gypsum.It has many uses in industry. All forms are white solids that are poorly soluble in …
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Difference Between Gypsum and Anhydrite
Anhydrite usually occurs in arid places forming from the dehydration of gypsum. When exposed to water, anhydrite slowly turns into gypsum. It is sometimes used as an ornamental stone or as a soil conditioner.
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Hydration of anhydrite of gypsum (CaSO4.II) in a ball mill
The ability of anhydrite to react with water, converting itself into gypsum, is the basis of its use as a construction material. However, this process, known as setting, is very slow. …
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Hydrothermal Preparation of a Gehlenite Hydrate
Hydrothermal treatment of synthetic gehlenite (2CaO.Al 2 O 3.SiO 2) or of various mixtures of oxides, hydrates, etc., approximating the composition of gehlenite, at 260 to 650° C, produced a hitherto unreported compound having the composition 2CaO.Al 2 O 3.SiO 2.H 2 O. Other phases, usually hydrogarnet, were always present in small amounts. A natural gehlenite containing Fe …
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Gypsum and Anhydrite | Rock & Gem Magazine
And while anhydrite can hydrate into gypsum, gypsum can dehydrate into anhydrite. Therefore, these two minerals often form mutual pseudomorphs, with gypsum exhibiting the external orthorhombic shape of anhydrite and anhydrite exhibiting the external monoclinic shape of gypsum. ... An interesting side-by-side example of these two forms of ...
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(PDF) Hydration of Portland cement with additions of …
In the OPC_ACA, gypsum is consumed within 1.5 h, as well as the main part of anhydrite (8 wt.% from total 10 wt.%), followed by a slow decrease up to one day when all anhydrite is consumed. The amount of ettringite reaches a plateau …
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Hydration of anhydrite of gypsum (CaSO4.II) in a ball mill
Various forms of calcium sulphate hydrate have been reviewed by Hand [1]. Depending on the temperature, calcium sulphate exists as anhydrite (CaSO 4), subhydrate ([2]; CaSO 4.xH 2 O, 0
The thermal behaviour of γ-CaSO 4
Within the 343–383 K thermal range, γ-anhydrite has been found to partially re-hydrate to bassanite CaSO4·0.5H2O. At 455 K the transformation γ-CaSO4 → β-CaSO4, insoluble anhydrite, starts ...
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Hydration mechanisms of super sulphated slag …
For the calculations it was considered that the slag dissolves uniformly and KOH, anhydrite and water equilibrate fast while the dissolution of the slag is very slow. Thus, the composition of the hydrate assemblage was calculated as a function …
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Investigations of anhydrite in CFBC fly ash as cement retarders
We can conclude that the linear expansion and compressive strength can develop in coordination with the addition of sodium sulfate. e desulfurization slag contains SO 3 in a form of anhydrite, and ...
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Study of aluminum sulfate and anhydrite on cement hydration process
The hydrates amorphous fraction is composed of different phases and its chemical composition is changing over time. During early hydration, it is mainly composed of aluminium hydroxide and strätlingite, while in the anhydrite-bearing system it can additionally contain some monosulphoaluminate.
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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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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 of soluble anhydrite was ...
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Understanding hydration reactions, mechanical properties, …
Calcium sulfates such as gypsum and anhydrite are abundant and readily available in the Earth's crust [1, 2]mon uses of the minerals are related to fire resistance, easy availability, and low cost [3, 4], leading to many applications in building materials, medicinal chemistry, energy storage, and geotechnical engineering [5, 6].The usual phases of calcium sulfates include …
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Mechanisms of early ettringite formation in ternary CSA–OPC–anhydrite
Ettringite is the major hydrate phase precipitated in the early stages of hydration in these systems and may be formed by three different main reaction pathways. To investigate the process of these mechanisms, the hydration of four different ternary blends were examined by means of heat flow calorimetry, in situ X-ray diffraction, and ...
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Hydration mechanisms of super sulphated slag cement
The activation of GGBFS by sulphates was first described by Kühl in 1909 [1].Generally, the super sulphated cements (SSC) consist of 80–85 wt.% of slag with 10–15 wt.% of anhydrite and an alkaline activator, often Portland cement clinker [2].The main hydration products are ettringite and C–S–H [3], [4].SSC shows an increased resistance to sulphate …
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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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Dehydration Pathways of Gypsum and the Rehydration …
where r ij and σ ij are the actual and reference distances between atoms i and j, respectively; ε o is the permittivity of free space (ε o = 8.8543 × 10 –12 C 2 J –1 m –1); ε ij is the potential well-depth; and q i and q j are the value of the charge on atoms i and j.The LJ interactions between unlike atoms are treated with the sixth-order mixing rule. 20 The atom-based summation ...
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