Gypsum Hemihydrate Monohydrate Gypsum And Dihydrate Gypsum
Calcium Sulfate Dihydrate
The plaster of Paris is prepared from gypsum (calcium sulfate dihydrate (CSD): CaSO 4 ⋅ 2H 2 O) which is mined from the earth or synthesized. When heated at about 160 °C, gypsum is converted in its hemihydrate form (CSH) which is used in plaster of Paris. The chemical reaction responsible for the setting and hardening of calcium sulfate ...
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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. Additionally, the rehydration mechanism of soluble anhydrite was also studied …
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Effect of Soluble Phosphorus on the Mechanical Properties …
Preparation of α-hemihydrate gypsum crystal is an approach for utilization of phosphogypsum (PG), but the soluble phosphorus impurities in PG have a crucial influence on the performance of α-hemihydrate gypsum. In this article, different forms of soluble phosphorus (H3PO4, H2PO4− and HPO42−) on the setting time and mechanical properties of α …
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Preparation of Medium–Low Strength Hemihydrate Gypsum …
This study explored the production of a medium–low strength α-hemihydrate gypsum (α-HH) from phosphogypsum using an autoclaved method. The influence of slurry …
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High-quality gypsum binders based on synthetic calcium …
A XRD pattern of β-calcium sulfate hemihydrate (Fig. 1, a), a SEM image (Fig. 1, b), and the dependence of the strength of gypsum on the temperature of its dehydration (Fig. 1, c) are shown in Fig. 1.The XRD pattern of β-calcium sulfate hemihydrate is fully assigned by the XRD pattern of hemihydrate as reported in reference [26].From Fig. 1, c it follows that the …
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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. ... dihydrate and hemihydrate processes ...
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Formation of α-Hemihydrate Inside of a Gypsum Crystal …
Gypsum crystal partly dehydrated, cleaved along cleavage plane, with observable dihydrate, α-hemihydrate and β-hemihydrate. Yellow circle = still dihydrate, blue circle = alpha hemihydrate, red ...
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Preparation of α-calcium sulfate hemihydrate from …
sulfate. And the classical dihydrate technique is the main process to produce phosphoric acid in fertilizer industries. Additionally, anhydrite and hemihydrate gypsum are unstable, with the extension of the accumulation time, they slowly hydrate into dihydrate gypsum. Therefore, the main component of PG is calcium sulfate dihydrate (CaSO
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The dihydrate‐hemihydrate transformation in gypsum
Download Citation | The dihydrate‐hemihydrate transformation in gypsum | A microscope study has been made of the development of crystals of calcium sulphate hemihydrate produced on, or in ...
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Calcium Sulphate Hemihydrate Hydration Leading to Gypsum
The hydration of calcium sulphate hemihydrate (CaSO4·0.5H2O) leading to the crystallization of gypsum (calcium sulphate dihydrate – CaSO4·2H2O) has been the subject of several investigations ...
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Influencing the Morphology of Gypsum | SpringerLink
Gypsum is a well-known mineral that is obtained from natural resources or from technological processes. Gypsum (calcium sulfate dihydrate) is burned to calcium sulfate …
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Preparation of Medium–Low Strength Hemihydrate Gypsum …
Moreover, the percentage content of hemihydrate gypsum and dihydrate gypsum in the gypsum specimens were assessed using the oven method specified in GB/T36141-2018 "Analysis method of phase composition of construction gypsum". The assessment of the mechanical properties of α-HH followed the JC/T2038-2010 "α-high-strength gypsum" standard.
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Formation of α-Hemihydrate Inside of a Gypsum Crystal …
Figure 7. Gypsum crystal partly dehydrated, cleaved along cleavage plane, with observable dihydrate, α β α-hemihydrate and β-hemihydrate. Yellow circle = still dihydrate, blue circle = alpha hemihydrate, red circle = beta hemihydrate, black arrow = alpha hemihydrate growing direction of a needle like crystal.
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(PDF) Estimation of gypsum hemihydrate content in …
It has been reported that gypsum plasterboard wastes can be recycled in a sequential process by crushing, separating, and burning to transform the dihydrate into the hemihydrate phase [17].
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The setting of gypsum plaster
2) Calcium sulfate hemihydrate was formed by the rehydration of gypsum dehydrated in vacuo. This hemihydrate showed the proton resonance spectrum corresponding to the signal of three spin type ...
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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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Activation of anhydrate phosphogypsum by K2SO4 and hemihydrate gypsum …
Lime pretreated phosphogypsum(PG) was calcined at 500 °C to produce anhydrate gypsum cement. Due to the slow hydration of anhydrate gypsum, additives, K2SO4 and hemihydrate gypsum were selected to accelerate the hydration of anhydrate. The hydration characteristics, the resistance to hydrodynamic water, and the mineralogical studies were …
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Autoclave-Free Formation of α-Hemihydrate Gypsum
The crystal morphology of the produced α-hemihydrate gypsum and, thus, its quality depend significantly on the composition of the liquid phase. Additions of different carbonic acids may improve the quality of the product distinctly. Under optimal working conditions the quality of the formed α-hemihydrate gypsum is similar to that of a ...
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(PDF) The thermal dehydration of natural gypsum and pure …
thermochimica acta ELSEVIER Thermochimica Acta 282/283 (1996) 483-492 The thermal dehydration of natural gypsum and pure calcium sulphate dihydrate (gypsum)l a,*, C.A. Strydom D.L. Hudson-Lamb aDepurtment of Chemistry, University of Pretoria, a, J.H. Potgieter b Pretoriu, 0002, South Africa b Technical Services, PPC, PO Box 40073, Cleveland 2022, …
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Innovative synthesis of high-strength α-hemihydrate gypsum…
High-strength gypsum is the recognized designation for α-hemihydrate gypsum, often referred to as α-HH (CaSO 4 ·0.5H 2 O), which is a cementitious material with low water requirement and high strength [8].The strength of α-HH is generally between 25 and 50 N/mm 2, which is three times that of ordinary building plaster, and has superior working performance. α …
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Hydration reaction and microstructural characteristics of hemihydrate
The phase change of hemihydrate to dihydrate gypsum at different pH was followed by XRD. As shown in Fig. 10, the typical diffraction peak (2-theta = 14.82°, PDF card No. 41-0224) of hemihydrate was outstanding in early hydration time at all pH. It was about 30 min that the peak of hemihydrate disappeared in the reference sample.
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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 by wet calcination …
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Eco-friendly, high-toughness gypsum prepared using hemihydrate
Hemihydrate phosphogypsum (HPG), formed by direct PG dehydration at temperatures around 180 ℃, is mainly composed of calcium sulfate hemihydrate (CaSO 4 · 0.5 H 2 O) [8], [9].When hydrated from CaSO 4 · 0.5 H 2 O to CaSO 4 · 2 H 2 O, HPG exhibits obvious self-hardening properties and can be used as a cementitious material. HPG is a …
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Recycling of waste gypsum from αlpha-hemihydrate …
The main crystal phase in WG powder is dihydrate gypsum (DH), which is consistent with the characteristic vibration peak in FTIR. In addition, the content of DH in WG powder is about 90%, and it also exits a small amount of hemihydrate gypsum (HH), SiO 2 and other impurities. From the comprehensive analyses of WG powder, it can be found that ...
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Microstructure and mechanical properties of β-hemihydrate …
1. Introduction. Gypsum (CaSO 4 ·2H 2 O, also known as dihydrate) plaster is one of the earliest building materials elaborated by mankind, and gypsum plasterboard is used …
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Influence of calcination and GGBS addition in preparing β-hemihydrate …
This is because the main composition of PG is dihydrate gypsum (CaSO 4 ⋅2H 2 O), which can be dehydrated to form synthetic hemihydrate gypsum, like natural mineral gypsum. Depending on the temperature and condition of the dehydration process, natural gypsum exists in four different phases, namely hemihydrate gypsum (CaSO 4 ⋅0.5H 2 O), III ...
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Mechanism and kinetics of gypsum–anhydrite …
Contrary to the gypsum behavior at 90 °C, in the experiments performed at elevated temperatures inside the autoclave, the transformation process proceeded faster, and a different transformation mechanism was observed.In the experiments performed at 150 °C, more than 90% of gypsum transformed to hemihydrate after 2 h retention time, but no anhydrite …
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Synthesis and Characterisation of Hemihydrate Gypsum…
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 effects of the addition amount and …
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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 two …
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Autoclave‐Free Formation of α‐Hemihydrate Gypsum
On comparing the solubility of calcium sulfate dihydrate and α-calcium sulfate hemihydrate in the formamide aqueous solution, it was found that the solubility of α-calcium sulfate hemihydrate is ...
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