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The dehydration of gypsum to hemihydrate has been studied for decades because it is an important model reaction for understanding fluid-triggered earthquakes, and due to the global use of plaster ...
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α-Hemihydrate gypsum (α-HH) is known as high strength gypsum, the strength of α-HHs is three times larger than that of building gypsum, ... Effect of ionic impurities on the crystallization of gypsum in wet-process phosphoric acid. Ind. Eng. Chem. Res., 40 (5) (2001) Google Scholar [17]
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Preparation of α-hemihydrate gypsum crystal is an approach for utilization of phosphogypsum (PG), but the soluble phosphorus impurities in PG have a crucial …
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The preparation process of α-hemihydrate gypsum (α-HH) using flue gas desulphurization (FGD) gypsum and concentrated brine is illustrated in Fig. 2. This study aims to validate the feasibility of this approach and understand the influence of various brine components on the overall process [18].
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The hydration of calcium sulphate hemihydrate (CaSO 4 ·0.5H 2 O) leading to the crystallization of gypsum (calcium sulphate dihydrate – CaSO 4 ·2H 2 O) has been the subject of several investigations over a long period and a vast amount of data is widely distributed throughout in the literature. In this review article an overall picture of the …
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The hydration of hemihydrate phosphogypsum in the alkaline environment was investigated aiming to recycle phosphogypsum-a promising gypsum resource in …
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Hemihydrate Kelley, Southard and Anderson' have shown that the thermodynamic properties of calcium sulphate hemihydrate depend on whether the ... facture of gypsum plaster by the kettle process) is
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The main synthetic materials are α-hemihydrate gypsum dihydrate, calcium carbonate, adsorption materials and composite material (Wang et al., ... In the process of controlling the hemihydrate gypsum phase and crystalline form, a crystallization regulator can be added to adjust and control its crystalline form and the quantity of fine whiskers ...
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Moulding gypsums are products made of calcium sulphate hemihydrate with optional factory additives, where very pure brilliant raw gypsum is used in their manufacture. Physically different hemihydrates are produced depending on the calcination process used: Alpha hemihydrate in the autoclave, or beta hemihydrate in the boiler plant or in the ...
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Here, a dynamic method, or an improved autoclaved process, was used to produce α-calcium sulfate hemihydrate from FGD gypsum. In this process, the attachment water of the mixture of FGD gypsum ...
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The detailed dissolution process of hemihydrates were revealed: surface dissolution and particle fragmentation. • Gypsum precipitates at the beginning, …
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In this article, tricalcium aluminate (C 3 A) was utilized as addition agent for hemihydrate gypsum (HHG) to improve the performance of gypsum pastes, and on that basis, the optimal dosage group of C 3 A was selected for further study on the composite effect with nano-silica (NS). HHG plasters with 0–5% content of C 3 A and besides …
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The detailed dissolution process of hemihydrates were revealed: surface dissolution and particle fragmentation. • Gypsum precipitates at the beginning, crystallizes rapidly after 20 min hydration and tends to be stable after 2 h hydration. • The hydration reaction of hemihydrate is a process of particle size reduction.
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When gypsum is heated at about 150–160 °C, it loses approximately three-quarters of its water in a partial dehydration process and becomes hemihydrate gypsum (CaSO 4 •½H 2 O) or calcined gypsum; it is also known as beta gypsum (alpha gypsum is made by processing batches of gypsum under elevated pressure). Calcined gypsum or …
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What is gypsum? What is hemihydrate gypsum? Define gypsum plaster and gypsum plasterboard. Where do gypsum deposits are located? List the different …
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The Influences of soluble phosphorus on hydration process and mechanical properties of hemihydrate gypsum under deep retarding condition. Materials 15 (7), 2680 (2022).
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Using solar energy to dehydrate gypsum to produce β-hemihydrate is one way to improve the carbon footprint 13,14 . Alternatively, α-hemihydrate is produced from gypsum using an autoclave process ...
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Phosphogypsum (PG) is a massive industrial solid waste. In this paper, PG was purified by flotation method, and α-hemihydrate gypsum (α-HH) was prepared by the autoclaving method. The morphology ...
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Phospho-gypsum is an industrial solid waste discharged from the phosphate production process. The waste includes complex impurities such as phosphoric acid and its salts, fluoride, and organics. Usually, retarders are mixed in gypsum-based building materials to extend setting time. Although the effects of the impurities on hydration …
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1. Introduction. Gypsum plaster, or stucco or `plaster of Paris', is the material made by the hydration of calcium sulfate hemihydrate (CaSO 4 ·0.5H 2 O) resulting in the formation of calcium sulfate dihydrate, or gypsum (CaSO 4 ·2H 2 O). Gypsum plaster has been used as a construction material since the Neolithic period (de …
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Median hemidihydrate process requirements are given in Table 2. Dihydrate-Hemihydrate Process (DHH) Although the attack and digestion sections are run under dihydrate conditions, it is not desirable to effect a very high degree of P 2 O 5 recovery during the separation of the acid from the dihydrate because the succeeding dehydration …
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The first describes the process of water leaving the structure of gypsum to form hemihydrate or anhydrite. The second depicts the temperature-dependent …
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consumption of hemihydrate and formation of dihydrate. 1. Ultrasonic results indicate gypsum hydration reaction consists of two stages: the dissolution of hemihydrate in the first stage and the nucleation and precipitation of dihydrate in the second stage. 2. Gypsum hydration is strongly influenced by water amount. Spread flow test is
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The dihydrate–hemihydrate process, based on recrystallization, enhances the total recovery of P 2 O 5 and yields hemihydrate PG with a remarkably high degree of purity, comparable to natural gypsum. In this study, the new dihydrate–hemihydrate process was employed.
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Another way is a recrystallization process at around 100 °C in an autoclave filled with gypsum slurry. In this process, larger hemihydrate crystals can grow with fewer surface defects. A comparable process …
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There is no steady state between hemihydrate dissolution and gypsum growth even in the first stages of the hydration process. The growth rate laws are either quadratic or linear according to ...
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An industrially feasible process was proposed to produce α-calcium sulfate hemihydrate (α-HH) from FGD gypsum without any additives. In this process, an AlCl 3 solution was used to promote the …
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wallboard, gypsum must be partially dehydrated or calcined to produce calcium sulfate hemihydrate (CaSO4 ½H 2O), commonly called stucco. A flow diagram for a typical gypsum process producing both crude and finished gypsum products is shown in Figure 11.16-1. In this process gypsum is crushed, dried, ground, and calcined.
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8.4 Calcined Gypsum Manufacturing Process – 203 8.5 Properties of Gypsum – 205 8.5.1 Fire Properties – 206 8.5.2 Acoustic Properties – 207 ... The slurry form of hemihydrate gypsum plaster may be poured between two adhesive layers to manufacture wallboard, placed into molds, or can be used to ll cracks. Thus, cur -
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The hydration mechanism of hemihydrate was proved to be dissolution and precipitation via in-situ ESEM observation.. The detailed dissolution process of hemihydrates were revealed: surface dissolution and particle fragmentation.. Gypsum precipitates at the beginning, crystallizes rapidly after 20 min hydration and tends to be …
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