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Transformation of calcium sulfate dihydrate (gypsum) into anhydrous calcium sulfate (anhydrite) proceeds slowly in a manganese sulfate/sulfuric acid medium (36 g Mn2+/kg of solution and 36 g H2SO4 ...
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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
Upon further heating above ∼200 °C, the anhydrite becomes less reactive and it consequently hydrates very slowly in contact with water (i.e., β-anhydrite, also known as anhydrite II or dead burnt gypsum [25]). α- and β-bassanite, in contrast, readily react with water and transform into gypsum (i.e., setting of gypsum) [11]. γ-anhydrite ...
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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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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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The lime used was a high purity laboratory Iime and the anhydrite was an industrial by-product containing 97.5% of anhydrite. The superplasticizer used was a sodium salt of a polynaphthalene sulfonate of high quality.The dry powders were first thoroughly mixed in their dry form before adding water. ... ettringite, being formed very slowly ...
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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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In the long-term hydration, the anhydrite-bearing formulations exhibit the highest amount of ettringite, whereas the gypsum-containing samples develop a higher fraction of AFm phases and X-ray amorphous hydrates. This difference may relate to faster dissolution kinetics of gypsum compared to anhydrite in the studied ternary blends.
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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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In addition to the calcium sulfate hydrates, two types of anhydrous calcium sulfate exist, hexagonal (γ-CaSO 4) and orthorhombic (β-CaSO 4) forms . The γ form results from the dehydration of the hydrates and is regarded as the low-temperature species, although it is apparently metastable and even at room temperature very slowly converts to ...
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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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Using the anhydrate formula given to you in lab, and the values from questions 2 and 3, give the formula of your unknown hydrate. Show your calculation. Round the water to the nearest 1/2 or …
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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 to lay. At UK Screeds our …
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Request PDF | Discrimination of bassanite and anhydrite III dehydrated from gypsum at different temperatures | Technical OPC normally contains mixed sulphate carriers in varying amounts. Gypsum ...
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The hydration evolution as well as properties of CSA cement is significantly influenced by curing conditions. A significantly later initial and final setting, a longer dormant period in the calorimetric curves and much lower strength up to 1 day of CSA cement pastes cured at 5 °C are clearly observed compared to 20 °C [5].Generally, curing temperatures do …
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A knowledge of environmental chemistry and aqueous solubility of calcium sulfate and several of its hydrates; anhydrite (CaSO 4), hemihydrate (CaSO 4.0.5H 2 O), and dihydrate (CaSO 4.2H 2 O); in acid and salt-containing media is of huge practical and theoretical importance. In this study, a solubility calculation model was developed based on ...
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The quantity of anhydrite is one of an important factor. Indeed, when the quantity of anhydrite is very high, like in BYF-A-15.5% cement paste, the transformation of the stage Y to the stage BF does not occur even at age 56 days. This is a major reason to explain why there is no further increase of compressive strength of BYF-A-15.5% cement ...
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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 …
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Under normal atmospheric conditions hemihydrate and anhydrite III are metastable, and below 40℃ in the presence of water or water vapor they undergo conversion to the …
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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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However, the phosphoanhydrite, similar to natural anhydrite, is considered non-active and hydrates and hardens very slowly. Although phosphoanhydrite calcined at temperatures of less than 750 ºC set very slowly and gained almost no strength at 3 days, anhydrite calcined at temperatures of 800 ºC could set relatively quickly and gain a certain ...
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The cement clinker was homogenized with 15 wt% of ground limestone and different quantities of natural anhydrite (2.5, 3.5 and 4.5 wt%) to give Portland ... Effect of addition of anhydrite on the hydrate assemblage of a hydrated ... It seems that the slow transformation of hemicarbonate to monocarbonate has a limited impact on the compressive ...
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natural anhydrite is heated from room temperature, has been attributed to the conversion of P-soluble anhydrite to insoluble or natural anhydrite (3). A contradictio~l exists in the literature regarding the presence (8) or absence (4, 5) of a sinlilar exothermic eflect in the case of the a-soluble anhydrite.
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Desalination, 51 (1984) 255-305 255 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands SOLUBILITIES AND SUPERSATURATIONS OF CALCIUM SULFATE AND ITS HYDRATES IN SEAWATER J.A.M. MEIJER* AND G.M. VAN ROSMALEN Delft University of Technology, Department of Chemistry, De Vries van Heystplantsoen 2, 2628 RZ Delft (The …
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Thermodynamic Modeling of Calcium Sulfate Hydrates in the CaSO 4 –H 2 O System from 273.15 to 473.15 K with Extension to 548.15 K ... Anhydrite does not crystallize with a measurable rate ...
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Reactions related to ye'elimite and the formation of ettringite are very fast, causing rapid setting and strength development but at the same time they present a loss of fluidity at early ages and poor workability, that pushes these cements into niche applications [9], [10].This fact is caused by the strong dependence of the final performances on the composition of this …
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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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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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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 also studied by Monte Carlo (MC) simulations. The thermodynamic calculation results reveal that the dehydration mechanism of gypsum significantly depended …
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In aqueous solutions, calcium sulfate forms two hydrates with the chemical names hemihydrate (HH, CaSO 4 ·0.5H 2 O) and dihydrate or gypsum (DH, CaSO 4 ·2H 2 O), in addition to …
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