Preparation of α-High-Strength Hemihydrate …
An industrially feasible process was proposed to produce α-calcium sulfate hemihydrate (α-HH) from FGD gypsum without any additives. In this process, an AlCl3 solution was used to promote the …
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Gypsum hydration: A theoretical and experimental study
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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Calcium Sulphate Hemihydrate Hydration Leading to Gypsum
The mechanism of hydration of calcium sulfate hemihydrate (CaSO 4 ·0.5H 2 O) to form gypsum (CaSO 4 ·2H 2 O) was studied by combining scanning 3D X-ray diffraction (s3DXRD) and phase contrast ...
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Crystallization Kinetics of -Hemihydrate Gypsum …
gypsum (CaSO4 2H2O), hemihydrate gypsum (CaSO4 0.5H2O), and anhydrite (CaSO4) [1–3]. Phosphogypsum (PG) is mainly composed of calcium sulfate dihydrate (DH), which is a byproduct from the wet process of phosphoric acid production. It is estimated that every ton of phosphoric acid produces about 4.5 to 5.5 tons of PG [4,5] in the world. A large
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Alpha Gypsum: k-sentials
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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Hemihydrate and Two-Stage Processes
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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Understanding gypsum in 3 diagrams
According to Lavoisier and Le Chatelier, 9 the reaction is a process of dissolving hemihydrate to create a super saturated solution of gypsum, from which gypsum is formed. This is possible due to the lower solubility of gypsum compared to hemihydrate. This theory is proven by Figure 4a - 4i and it shows why gypsum can act …
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Dehydration Pathways of Gypsum and the Rehydration …
The dehydration of gypsum (Gy) was studied, at negligible water vapor pressure, by in situ IR spectroscopy and by thermogravimetry to det. whether intermediate phases (CaSO4.nH2O) exist, other than the hemihydrate with n = 0.5, and also to compare the mechanism of the dehydration process when measured by 2 techniques with very …
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Hydration reaction and microstructural characteristics of hemihydrate
The crystal of hemihydrate and gypsum in Fig. 12 was marked as number 1 and 2, respectively. After 2 min hydration, the particles were mainly hemihydrate, and a few fibrous gypsum crystals were observed under different hydration condition, which confirmed that gypsum precipitated at the very beginning. ... The process of gypsum …
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The Influences of Soluble Phosphorus on Hydration …
Gypsum specimens were prepared according to GB/T 28627-2012 [29]. Briefly, - CaSO 4 1/2H 2 O was slowly transferred into water in 30 s and then left for 30 s.
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11.16 Gypsum Manufacturing
soil conditioner, industrial and building plasters, and gypsum wallboard. To produce plasters or 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 ...
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Materials | Free Full-Text | Experimental Study and …
Flue-gas desulphurization (FGD) gypsum is a highly prevalent industrial by-product worldwide, which can be an excellent alternative to natural gypsum due to its high content of CaSO4·2H2O. The preparation of α-calcium sulfate hemihydrate is a high-value pathway for the efficient use of FGD gypsum. Here, a dynamic method, or an improved …
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Autoclave‐Free Formation of α‐Hemihydrate …
Here, a dynamic method, or an improved autoclaved process, was used to produce α-calcium sulfate hemihydrate from FGD gypsum. In this process, the …
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Revealing maleic acid role in the preparation of α-hemihydrate gypsum …
Titanium gypsum (TG) is rarely used to produce α-hemihydrate gypsum (α-HH) because of its poor crystallinity and high impurity and moisture contents. Here, a method is proposed to prepare α - HH by adjusting the reaction temperature, CaCl 2 solution concentration and maleic acid dosage based on acid leaching and heat-treated …
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Preparation of α-High Strength Gypsum from Flue Gas …
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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Process for producing alpha-hemihydrate gypsum
One process of forming alpha-hemihydrate gypsum involves placing calcium sulfate dihydrate in an autoclave in the presence of saturated steam at elevated pressure over an extended period of time. This method can be used for autoclaving of lump or ground gypsum. Typical pressures for the autoclave can be from atmospheric to …
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Effect of modifiers on crystalizing habit and
This process can disrupt the original structure of hemihydrate gypsum. The addition of maleic acid to the salt solution was found to foster anhydrous gypsum formation. In contrast, succinic acid can decrease the crystals' aspect ratio, resulting in the growth of short columns, thereby enhancing the product's strength performance.
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Crystallization kinetics of large-sized columnar α-hemihydrate gypsum …
Direct production of high-strength α-calcium sulfate hemihydrate (α-HH) with no additives was accomplished by the reaction of aluminum sulfate and waste CaCl 2 discarded from Solvay soda plant. For scaling-up this new process, the crystallization kinetics of α-HH was experimentally investigated under varying conditions including …
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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 …
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No. 4710 February 6, 1960 NATURE 375
A sample of hemihydrate was prepared by heating 800 gm. of a washed natural gypsum for 5 hr. in a glass container filled to a depth of. 3 in. (oven temp. 170° C.). The sample was cooled and then ...
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The effect of retarders on the setting process in industrially …
The study by Schneider [11] on the effects of retarders focused on the configuration process for hemihydrate gypsum, using citric acid and tartaric acid as additives. In this case, mechanical ...
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Fast in-situ X-ray scattering reveals stress sensitivity …
The gypsum-hemihydrate transformation has been long studied as a laboratory analogue for seismogenic dehydration reactions during subduction 8,9 and as …
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Formation of α-Hemihydrate Inside of a Gypsum …
Gypsum (calcium sulfate dihydrate) is one of the most used inorganic binding materials in the world. During calcination, calcium sulfate subhydrates are formed and, for technical reasons, are mixed with water to form dihydrate again. Therefore, the …
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Revealing maleic acid role in the preparation of α-hemihydrate gypsum …
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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Utilization of phosphogypsum to synthesize α-hemihydrate gypsum …
Phosphogypsum (PG) is a kind of industrial solid waste with high impurity content and low utilization rate. In this study, α-hemihydrate gypsum (α-HH) was synthesized from PG in H 3 PO 4 –H 2 O solution (wet-process phosphoric acid solution and phosphoric acid solution) under atmospheric pressure. The crystal morphology of α …
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Gypsum hydration: a theoretical and experimental study
Gypsum hydration: a theoretical and experimental study. Calcium sulphate dihydrate (CaSO4·2H2O or gypsum) is used widely as building material because of its excellent …
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Hydration characteristics and mechanism analysis of β
The production of gypsum plaster starts from the thermal dehydration of gypsum (CaSO 4 ·2H 2 O, calcium sulfate dihydrate), at about 100–180 °C. During the process of heating, 75% crystallization water in calcium sulfate dihydrate is lost, and calcium sulfate hemihydrate (CaSO 4 ·0.5H 2 O) is finally formed, which is also referred …
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Hydration characteristics and mechanism analysis of β
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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Microstructure and mechanical properties of β …
Therefore topics such as the hydration induced properties, and especially the behavior of the β-hemihydrate upon hydration to produce gypsum (plasterboard) is still …
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ALPHA GYPSUM POWDER VS BETA GYPSUM POWDER – …
1.Hemihydrate gypsum has two forms: α and β, both of which are rhombic crystals, but their physical properties are different. α-type hemihydrate gypsum has good crystallinity and firmness. β-type hemihydrate gypsum is a flaky and cracked crystal with excellent crystals. Its specific surface area is much larger than that of α-type ...
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