Geometrical Constraints of Thermal Dehydration of β-Calcium Sulfate Hemihydrate Induced by Self-Generated Water Vapor

2021 ◽  
Author(s):  
Shun Iwasaki ◽  
Yuto Zushi ◽  
Nobuyoshi Koga
Keyword(s):  
Water Vapor ◽  
Calcium Sulfate ◽  
Reaction Pathway ◽  
Water Vapor Pressure ◽  
Atmospheric Condition ◽  
Thermal Dehydration ◽  
Reaction Behavior ◽  
Calcium Sulfate Dihydrate ◽  
Geometrical Constraints ◽  
Calcium Sulfate Hemihydrate

The thermal dehydration of calcium sulfate dihydrate exhibits complex reaction behavior, in which the reaction pathway and kinetics vary depending on water vapor pressure (p(H2O)) applied as the atmospheric condition...

Thermal dehydration of calcium sulfate dihydrate: physico-geometrical kinetic modeling and the influence of self-generated water vapor

2020 ◽  
Vol 22 (39) ◽  
pp. 22436-22450
Author(s):  
Shun Iwasaki ◽  
Nobuyoshi Koga
Keyword(s):  
Water Vapor ◽  
Kinetic Modeling ◽  
Calcium Sulfate ◽  
Reaction Pathway ◽  
The Self ◽  
Thermal Dehydration ◽  
Calcium Sulfate Dihydrate ◽  
Kinetics Of

The reaction pathway and kinetics of thermal dehydration is regulated by the self-generated water vapor.

EFFECT OF WATER VAPOR ON THE FORMATION OF MODIFICATIONS

1965 ◽  
Vol 43 (9) ◽  
pp. 2522-2529 ◽  
Author(s):  
R. A. Kuntze
Keyword(s):  
Water Vapor ◽  
Vapor Pressure ◽  
Atmospheric Pressure ◽  
Calcium Sulfate ◽  
Water Vapor Pressure ◽  
Exothermic Peak ◽  
Vapor Pressures ◽  
Ambient Water ◽  
Rate Of Heating ◽  
Calcium Sulfate Hemihydrate

The two recognized forms of calcium sulfate hemihydrate can be identified by the position of a relatively small exothermic peak in their differential thermograms. Hemihydrates prepared at various water vapor pressures up to 760 mm Hg were found to produce this exothermic peak in a position which is characteristic for the β-form. These results indicate that α-hemihydrate cannot be made at atmospheric pressure, as was previously suggested on the basis of heat solution measurements. The typical differential thermogram of α-hemihydrate is only obtained with material made by dehydration in solution or by autoclaving. The effect of ambient water vapor pressure on the position of the three peaks that occur in the differential thermogram of CaSO4•2H2O has also been studied. It was found that the incipient temperature of the second endothermic peak, corresponding to the transition of hemihydrate to soluble anhydrite, is displaced independent of the rate of heating from 145 °C to 187 °C with increasing water vapor pressures up to 760 mm Hg. This indicates that, for each temperature, a threshold water vapor pressure exists, above which soluble anhydrite cannot be formed.

The Kinetics and Mechanism of Formation of Calcium Sulfate Scale Minerals—The Influence of Inhibitors

CORROSION ◽  
1979 ◽  
Vol 35 (7) ◽  
pp. 304-308 ◽  
Author(s):  
GEORGE H. NANCOLLAS ◽  
WESLEY WHITE ◽  
FELIX TSAI ◽  
LARRY MAS LOW
Keyword(s):  
Calcium Sulfate ◽  
Mechanism Of Formation ◽  
Seeded Growth ◽  
Langmuir Adsorption ◽  
Calcium Sulfate Dihydrate ◽  
Calcium Sulfate Scale ◽  
Rate Of Reaction ◽  
Growth Method ◽  
Kinetics Of ◽  
Calcium Sulfate Hemihydrate

Abstract A seeded growth method has been used to study the kinetics of crystallization of calcium sulfate dihydrate at various temperatures and at ionic strengths up to 0.6M. Under all conditions, the rate of reaction is proportional to the square of the relative supersaturation and is controlled by a surface process. The same kinetics are applicable for the growth of calcium sulfate hemihydrate at temperatures above 110 C. The organic phosphonates effectively retard scale formation, and diethylenetriaminepenta (methylenephosphonic acid), when present at a concentration as low as 10−7M, completely inhibits the growth of calicum sulfate hemihydrate at 120 C. By assuming that the inhibitor molecules are adsorbed on growth sites on the surface of the crystals, the inhibition can be interpreted in terms of a simple Langmuir adsorption isotherm.

Fabrication of Spherical Carbonate Apatite Using Calcium Sulfate as a Precursor by W/O Emulsion Method

2012 ◽  
Vol 529-530 ◽  
pp. 78-81 ◽  
Author(s):  
Shunsuke Nomura ◽  
Kanji Tsuru ◽  
Shigeki Matsuya ◽  
Ichiro Takahashi ◽  
Ishikawa Kunio
Keyword(s):  
Calcium Sulfate ◽  
Single Phase ◽  
Carbonate Content ◽  
Carbonate Apatite ◽  
X Ray Diffraction ◽  
Emulsion Method ◽  
Calcium Sulfate Dihydrate ◽  
Hydrogen Carbonate ◽  
Diffraction Patterns ◽  
Calcium Sulfate Hemihydrate

We fabricated spherical carbonate apatite from spherical calcium sulfate which was prepared by w/o emulsion method. Calcium sulfate hemihydrate slurry was dropped in oil under continuous stirring and was kept at room temperature for 60 min to obtain set spherical calcium sulfate dihydrate (CaSO42H2O) with approximately 1 mm in diameter. The spherical CaSO42H2O was hydrothermally-treated at 120°C for 24 hours in the presence of 0.4 mol.L-1 disodium hydrogen phosphate and sodium hydrogen carbonate aqueous solution. X-ray diffraction patterns assigned to apatite single phase could be detected from the obtained spheres. Carbonate content in apatitic structure was found to be approximately 6.5wt%.

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