Hemihydrate gypsum is found in two forms: α-hemihydrate gypsum (α-CaSO 4 ⋅0.5H 2 O) and β-hemihydrate gypsum (β-CaSO 4 ⋅0.5H 2 O) [8]. The α-hemihydrate gypsum is produced by the autoclaving and salt solution method whereas β-hemihydrate gypsum is obtained through calcination at temperature lower than 200 °C. …
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The current mapped extent of gypsum soils in the United States, based on the Gridded SSURGO (gSSURGO) product (Soil Survey Staff, 2013), indicates a total of 10,916 km 2 (Figure 1).For this compilation, "gypsum soils" are considered to include soil map units in which "gyp" is included in the taxonomic classification of the named soil …
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The results showed that as soon as a stable gypsum nucleus is formed, hemihydrate hydration will proceed to its end and all the hemihydrate will become …
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The synthesis of α-calcium sulfate hemihydrate (α-CSH) from flue gas desulfurization (FGD) gypsum is a good way to realize the comprehensive utilization of FGD gypsum. To obtain α-CSH with the satisfactory performances, a facile hydrothermal-aging pretreatment process for FGD gypsum raw materials was proposed, where FGD …
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This study combined inorganic α-hemihydrate gypsum (α-HHG) with organic polyacrylamide (PAM) hydrogel to create a novel α-HHG/PAM composite material. Through this facile composite strategy, this fabricated material exhibited a significantly longer initial setting time and higher mechanical strength compared to α-HHG. The …
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Alpha high‐strength hemihydrate gypsum (CaSO 4 ·0.5H 2 O, α‐HH) with a large‐size columnar crystal (average size: 135.31 µm, maximum size: 500 µm) is successfully prepared via a NaCl ...
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The gypsum in Fig. 9 a and b was prepared with a w 0 /h 0 of 0.65 and 0.80, respectively. It is clear that the crystals in Fig. 9 a are much tighter and homogeneous than that in Fig. 9 b. This shows that the gypsum produced with a lower water content has a better bonding between the gypsum crystals which should lead better mechanical …
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During hemihydrate gypsum hydration, the proportion of free P was higher, which mainly existed as H3PO4 and H2PO4⁻, but P species on dihydrate gypsum surface contained a higher HPO4² ...
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Why is Calcium Sulphate hemihydrate called plaster of Paris?. Ans: Hint: Calcium Sulphate hemihydrate is a white- yellowish chemical substance which is present in finely divided powder and it is an odourless powder. ... It is also known as Gypsum plaster. Complete answer: So, as we know that, Calcium Sulphate hemihydrate has the …
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The apparent empirical activation energies (Ea) suggest that the transition from gypsum to hemihydrate is mainly controlled by nucleation and growth mechanism, while the transition from gypsum to γ-anhydrite is mostly followed by phase boundary mechanism. ... Impact of limestone fineness on cement hydration at early age. Cement …
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The calcium sulphate dihydrate gypsum (CaSO 4 ·2H 2 O) is the most common sulphate evaporite mineral on our planet 1.Sulphate evaporites play an important role in Earth's sulphur cycle and are ...
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In this study, phosphogypsum (PG) is simulated by doping fluorine and phosphorus ions in an analytically pure reagent of gypsum dihydrate. The influence of fluorine and phosphorus impurity and content on the dehydration reaction process of phosphogypsum and its crystalline micromorphology is assessed during the preparation …
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The main focus of the paper is on the formation of alpha-hemihydrate inside of a gypsum crystal during formation of beta-hemihydrate by heating up the gypsum crystal. Inside or on one gypsum …
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The applications of gypsum in China are primarily twofold: the preparation of high-strength gypsum, construction gypsum, composite cementing materials, and others, and the preparation of gypsum building products like gypsum board and gypsum blocks. Among these, α-hemihydrate gypsum (α-HH) is a high-end gypsum product, mainly …
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Calcium sulfate hemihydrate whiskers (CSHWs) were prepared from high-purity salt gypsum in a glycerol–water system. The effects of the glycerol/water ratio, reaction temperature, reaction time, and stirring speed on the crystal morphology of the CSHWs were investigated.
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this condition the slump is zero which indicates the minim water/hemihydrate should be 0.55 to promise a fluid gypsum plaster which is in line with the sprinkling method result. The deformation coefficient (Ep, the slope of the trend line) indicates the sensitivity of the tested materials to the water on the workability.
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ALPHA SPECIAL GYPSUMS - FROM FGD GYPSUM TO HEMIHYDRATE They prove their benefits day to day particularly in the building materials industry, and have been incorporated in Knauf products for decades. Even customers from other sectors have come to appreciate their excellent product properties. With Blaine values of ≥ 1700 to ≥ 2900 …
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Keywords: α-calcium sulfate hemihydrate, industrial by-product gypsum, FGD gypsum, phosphogypsum, preparation method 1. Introduction 1.1. α-calcium sulfate hemihydrate Calcium sulfate hemihydrate generally exists in two forms, i.e., α- and β-forms. As an important building material, the industrial production and application of β-form began ...
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Alpha-calcium sulfate hemihydrate (α-HH) has been prepared from flue gas desulfurization (FGD) gypsum with salt solution method under atmospheric pressure. X-ray diffraction (XRD), thermogravimetry and differential scanning calorimetry (TG-DSC), optical micrograph, X-ray photoelectron spectroscopy (XPS), energy dispersive spectrometry …
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Nucleation of hemihydrate is common within the vacancy-rich water layer of the (010)-plane in the gypsum parent, especially where this plane intersects crystal …
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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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In this study, the effect of sulphonated naphthalene formaldehyde condensate (SNF) and polycarboxylate (PC) superplasticizers on the performance of β-calcium sulphate hemihydrate plaster has been discussed. A considerable improvement in the properties of β-hemihydrate plaster was observed with an increase in …
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Calcium sulfate exists in three forms, namely dihydrate or gypsum (CaSO4·2H2O), anhydrite (CaSO4), and hemihydrate or bassanite (CaSO4·0.5H2O) depending on temperature, pressure, pH, and formation conditions. The formation of calcium sulfates occurs widely in nature and in many engineering settings. Herein, a …
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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 omongwaite.
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It was also found that gypsum is stable in the low-temperature and high water vapor pressure region and does not dehydrate to form any calcium sulfate …
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DOI: 10.1016/j.scitotenv.2023.166405 Corpus ID: 261023588; Revealing maleic acid role in the preparation of α-hemihydrate gypsum from titanium gypsum through experiments and DFT calculations.
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Flue gas gypsum may be converted to α-hemihydrate by suspending the starting material in inorganic salt solutions of high concentration or in diluted sulfuric acid and maintaining the suspension ...
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The effects of phosphoric acid (H3PO4) in pressurized aqueous solution on the dehydration of CaSO4·2H2O to form α-hemihydrate gypsum (α-HH) phase and the regulation of crystal shape were studied in this paper in order to provide guidance for the low-cost and high-value utilization of phosphogypsum. The results showed that H3PO4 …
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Phosphogypsum can be used to prepare β-hemihydrate gypsum (β-CaSO4·1/2H2O) plaster. A prerequisite for any effective reuse of phosphogypsum is to understanded the act by which impurities in ...
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