hemihydrate gypsum dihydrate gypsum

a-Hemihydrate Gypsum from Flue Gas Desulphurization …

2013-5-23 · FGD gypsum is produced as a by-product during the process of desulphurization of exhaust gas emitted in power stations heated by fuel containing sulphur. It has been determined that α-hemihydrate gypsum can be obtained from FGD gypsum under hydrothermal conditions at 125 °C and 130 °C. The compressive strength of gypsum samples is 13 MPa ...

Determination of Calcium Sulfate Dihydrate and …

Gypsum in the form of the dihydrate (CaSO4·2H20) or the hemihydrate (CaSO4 ·½ H20) is an important additive in cement is. It serves to retard the setting and hardening of the cement. In the quality control of cement, it is therefore important to know the exact

Preparation of Whitening Dihydrate Gypsum and Short …

2017-8-29 · Using FGD gypsum as the raw material, whitening and large prismatic dihydrate gypsum can be obtained by dissolution‐crystallization and decoloring process with α‐hemihydrate gypsum whiskers prepared in MgSO 4 ‐CaCl 2 ‐H 2 O solution, which can transform into whitening short columnar α‐hemihydrate gypsum. The effects of aging temperature, pH, …

Availability of density measuring methods estimating …

As a result, it was found that the dihydrate gypsum is changed into the hemihydrate gypsum under thermal condition of 90°C and the hemihydrate gypsum is changed into anhydrite under that of 120°C with heating of 24 hours. The followings are clarified in this paper: (1) The cement density measuring method was available in order to measure the ...

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Reuse of phosphogypsum as hemihydrate gypsum: The …

2021-11-1 · The main phases of phosphogypsum and natural gypsum are the same as those of dihydrate gypsum (CaSO 4 •2H 2 O), and even the CaSO 4 •2H 2 O content in phosphogypsum is higher than that in natural gypsum. It is thus feasible to prepare gypsum plaster by calcining phosphogypsum instead of natural gypsum.

The dihydrate‐hemihydrate transformation in gypsum

2007-5-4 · A microscope study has been made of the development of crystals of calcium sulphate hemihydrate produced on, or in, sheets of the dihydrate in the form of selenite by calcining under controlled conditions. The crystal forms were shown to be strongly dependent upon both temperature and ambient water vapour pressure. A mechanism for the nucleation and growth …

Crystallization of gypsum from hemihydrate in presence of …

1999-3-1 · The crystallization of gypsum (CaSO 4 ·2H 2 O) from a suspension of calcium sulphate hemihydrate is well-known as the setting of plaster. In this paper we present results concerning the crystallization of gypsum in the presence of different acids. The influence of additives on the crystallization kinetics and on the morphology of gypsum ...

Calcium sulphate hemihydrate hydration leading to …

2007-3-1 · 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 subject is presented.

Why is the hemihydrate gypsum (CaSO4 …

At temperatures above 200 degree C, the dihydrate phase transforms to anhydrite. The anhydrite phase can absorb the moisture and transform to hemihydrate phase again.

Effect of Gypsum-Hemihydrate Ratio in Cement on …

1997-3-1 · In the present paper, the results of an experimental investigation on the effect of the gypsum-hemihydrate ratio in cement on the rheological properties of fresh concrete are presented. For the most reactive type of cement with a high content of both C3A and alkalies, a reduced gypsum-hemihydrate ratio from 80/20 to 20/80 reduced the yield ...

Study on conversion of dihydrate gypsum to hemihydrate …

Depending on the preparation process, α-type hemihydrate gypsum or β-type hemihydrate gypsum can be obtained. The performance of the two has obvious differences. The former has a dense crystal structure, the latter is an irregular, loose crystal. The crystal form of hemihydrate gypsum is a key factor affecting the strength of the product.

Reuse of phosphogypsum as hemihydrate gypsum: The ...

2021-8-10 · The results indicates that H 3 PO 4 accelerated hemihydrate gypsum dissolution and dihydrate gypsum precipitation, which included route I, involving Ca 2+ and SO 4 2-, and route II, involving [CaSO 4] 0. However, when the content of H 3 PO 4 was ≥0.5%, the 3

Gypsum dihydrate

The process is highly adaptable—one of three forms of calcium sulfate [gypsum (dihydrate), plaster of paris (hemihydrate), or anhydrate]—may be used. The advantage of this process is the avoidance of a sulfuric acid intermediary. In a broad temperature range gypsum dihydrate, CaS04 >2H20, is thermodynamically more stable than semihydrate ...

Activation of anhydrate phosphogypsum by K2SO4 and …

2011-12-20 · 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 …

Estimation of gypsum hemihydrate content in recycled …

2014-10-24 · In order to utilize reclaimed gypsums (gypsum board waste) derived from waste plasterboards as geo-materials, thermal behaviors of the reclaimed gypsums and reagent gypsum are investigated in this paper. Furthermore, simple density measuring method of judging quality of the reclaimed gypsums is examined to determine the gypsum hemihydrate content. As the …

Preparation of α-hemihydrate gypsum from …

Flue gas desulfurization (FGD) gypsum mainly composed of calcium sulfate dihydrate (DH) was used as a raw material to obtain -calcium sulfate hemihydrate (-HH) through dehydration in …

Gypsum hydration: a theoretical and experimental study

2019-12-3 · 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 formations of α- and β-type. Among them β-hemihydrate is mainly used to produce gypsum plasterboard since the hydration product of the α-hemihydrate is too

Availability of Density Measuring Methods Estimating …

2014-5-22 · As a result, it was found that the dihydrate gypsum is changed into the hemihydrate gypsum under thermal condition of 90°C and the hemihydrate gypsum is changed into anhydrite under that of 120°C with heating of 24 hours. The followings are clarified in this paper: (1) The cement density measuring method was available in order to measure the ...

Gypsum hemihydrate–cement blends to improve renderings …

Calcium sulphate hemihydrate hydration leading to gypsum

A new precipitation pathway for calcium sulfate …

This work investigates the early stages of precipitation of calcium sulfate from aqueous solution at room temperature and shows for the first time that amorphous calcium sulfate (ACS) and calcium sulfate hemihydrate are …

Hemihydrate

Depending on the process these products are: gypsum dihydrate, gypsum hemihydrate or anhydrite with more or less calcium sulfite or calcium sulfite hemihydrate. • At high amount of sulfites in waste materials used to produce the binder (even more then 50% S in sulfite) the retardation of H 2 release takes place. •

Production of gypsum hemihydrate with waste heat, …

OSTI.GOV Patent: Production of gypsum hemihydrate with waste heat, aqueous H/sub 2/SO/sub 4/ and sulfuric acid salts ...

Effect of pH on the Preparation of {alpha}-Calcium Sulfate …

2009-12-15 · @article{osti_21261829, title = {Effect of potassium sodium tartrate and sodium citrate on the preparation of {alpha}-calcium sulfate hemihydrate from flue gas desulfurization gypsum in a concentrated electrolyte solution}, author = {Shen, Z X and Guan, B H and Fu, H L and Yang, L C}, abstractNote = {Flue gas desulfurization (FGD) gypsum mainly composed of …

Modification on the Performance of the Hemihydrate …

2018-12-29 · Hemihydrate gypsum with more matcha powder had the higher water requirement, longer setting times and lower density. Less than 1% matcha powder had slight impact on the strength of hardened paste, but more than 1% matcha powder had a remarkable one. ... The Crystal Growth of Calcium Sulfate Dihydrate in the Presence of Additives[J]. Journal of ...

Calcium Sulphate Hemihydrate Hydration Leading to …

2022-6-11 · 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 ...

Method for hydrating hemihydrate gypsum

A gypsum mold having good water absorbing properties, which is suitable for cast molding pottery, can be prepared by stirring a mixture of hemihydrate gypsum cooled to -40° to 5° C. and water to form a slurry of gypsum in water having a temperature of -5° to 10° C., pouring it into a water-impermeable mold, maintaining it therein until the setting reaction thereof is completed …

Method for preparing α-hemihydrate gypsum

2020-7-9 · (22) 07.09.2020 (43) 24.06.2021 (57) Disclosed is a method for preparing α-hemihydrate gypsum, the method involving using citric acid as a crystal transformation agent to prepare dihydrate gypsum, and then subjecting the dihydrate gypsum to crystal transformation under the excitation effect of an α-hemihydrate gypsum seed to prepare α50 grade α …

the difference between dihydrate gypsum and …

2021-7-25 · Calcium Sulfate Dihydrate - An Overview. cs cements begin as gypsum, or calcium sulfate dihydrate (caso 4 · 2h 2 o), which is either mined from the earth or produced through more controlled chemical processes (randolph, 1971). gypsum and its products differ in purity and form, but the major feature of this material is the fact that its water of hydration can be driven off …

PROCESS FOR PRODUCING ALPHA-HEMIHYDRATE …

2008-2-14 · What is claimed is: 1. A process for producing alpha-hemihydrate gypsum from dihydrate gypsum, comprising: feeding a slurry comprising the dihydrate gypsum and water into a heating tube; heating the heating tube at a temperature effective to generate steam and pressure from the water, wherein the steam and pressure are effective to convert the dihydrate gypsum …

Crystallization Kinetics of α-Hemihydrate Gypsum …

2021-7-21 · 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 conversion kinetics of DH to α-HH in NaCl solution is helpful for understanding the control process. In this paper, X-ray diffraction (XRD) patterns were applied …

Gypsum

The transition temperature in aqueous solution for the gypsum-bassanite (dihydrate to hemihydrate) is in the 40°C-66°C range. Under normal climatic conditions, on monuments, the precipitation of calcium sulfate from aqueous solution will therefore be predominantly gypsum. Anhydrite forms when the temperature in solution is higher than 40°-60°C.