The Low Pressure Dehydration of Magnesium Sulphate Heptahydrate and Cobaltous Chloride Hexahydrate

Ford, R. W.; Frost, G. B.

doi:10.1139/v56-082

Cited by 17 publications

(10 citation statements)

References 3 publications

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“…Catalysis of both stages I and I1 by low water vapor pressures has been observed in other salt hydrate systems (17,18), the magnitude of the pressures required in this work presumably being due t o the less efficient transport of water molecules to and from the reaction site in processes a t atmospheric pressure, compared to those carried out in Can. J. Chem.…”

Section: Discussionmentioning

confidence: 59%

THE EFFECT OF WATER VAPOR UPON THE DEHYDRATION OF CaSO_4•2H₂O

McAdie¹

1964

Can. J. Chem.

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Kinetics of the two-stage dehydration of CaS04.2HzO have been examined under controlled water vapor pressures up to one atmosphere. For both stages water vapor initially accelerated the rate of dehydration and subsequently retarded it. Separate, temperature-dependent water vapor pressures were noted above which each stage could be suppressed.The hemihydrate was clearly defined either as a change in the rate of weight loss during dehydration or, a t higher water vapor pressures, as a fixed composition. The heat of solution of the hemihydrate increased linearly with the partial water vapor pressure present during its formation, but was independent of the formation temperature over the range studied. *\ctivation energy and pre-exponential factor for the dihydrate -+ hemihydrate process also increased linearly with water vapor pressure. Hemihydrates produced a t the extremes of water vapor pressure corresponded to the a-and 6-modifications, as defined thermodynamically, and the production of a hemihydrate series with properties varying linearly from one extreme t o the other is discussed.The dehydration of calcium sulphate dihydrate (gypsum) has been studied for decades by many investigators, few of whoin have made provision for controlling the partial water vapor pressure during dehydration. No systematic study of its kinetic influence has been reported, although Weiser and co-workers (1, 2) clearly demonstrated the importance of such isobaric studies to a proper understanding of the system. Despite earlier controversy (3) the combination of evidence now available (1, 2 , 4-8) has established the existence of the hemihydrate as the lower hydrate in the CaS04-H20 system. However, the composition in terms of water of hydration can be variable over rather wide liinits and has led to speculation that there inay exist a zeolitic type of structure rather than that of a true hydrate. Clarification has recently been obtained from nuclear magnetic resonance results (5), showing the hemihydrate to contain definite crystal water as well as a variable quantity of relatively free water "occluded" within the crystal lattice. Two modifications of the hemihydrate are known, differing in thermodynamic properties (4), although being structurally quite similar (9, 10). Speculation that these differences reflect the degree of crystal lattice perfection has recently received support (6). This paper will describe a syste~natic study of the influence of water vapor pressure upon the kinetics of the dehydration process and upon the thermodynamic properties of the heinihydrates obtained. Previous studies of these properties involved hemihydrates produced a t the extreme conditions, i.e. under essentially anhydrous conditions or in an atmosphere saturated with water vapor, plus some commercial plasters produced under undefined partial water vapor pressures (-1, 11). A later paper ~vill discuss the influence of partial water vapor pressure upon such practical properties of the hemihydrate as gauging water requirement. E X P E R I M E...

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Section: Discussionmentioning

confidence: 59%

THE EFFECT OF WATER VAPOR UPON THE DEHYDRATION OF CaSO_4•2H₂O

McAdie¹

1964

Can. J. Chem.

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“…MgSO 4 •1.25H 2 O or the five fourth hydrates or also called synthetic kieserite was synthetized by Emons [7]. Grindrod has analyzed a sample supplied as nominally 97% pure monohydrate of magnesium sulfate by Sigma-Aldrich but bulk composition significantly differed from MgSO 4 •1H 2 O [17]. Exact water content was determined by thermo-gravimetric analysis.…”

Section: Mgso 4 (S) + 7h 2 O (G) ↔ Mgso 4 • 7h 2 O (S)mentioning

confidence: 99%

“…However, it seems that this process is typical only for large particles and is not found for small particles (<200 µm). In another study, the influence of low water vapor pressure on the kinetic rate of dehydration has been carried out [17]. It seems that the formation of the lower crystalline hydrates of magnesium sulfate is possible in special conditions like high relative humidity.…”

Section: Mgso 4 (S) + 7h 2 O (G) ↔ Mgso 4 • 7h 2 O (S)mentioning

confidence: 99%

Thermodynamic study of MgSO4 – H2O system dehydration at low pressure in view of heat storage

et al. 2017

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Study about magnesium sulfatewater vapor equilibrium proved to be very interesting especially on the use of dehydration-hydration reactions for the heat storage application in recent research. Heat is realized by hydration of lower hydrates as this reaction is exothermic. Therefore, reversible reaction, endothermic thermal dehydration of higher hydrates, is used for charging of system and in this state the energy can be stored over long time. Even if magnesium sulfate appears as promising candidate with high theoretical energy density of 2.8 GJ/m-3 , technological process is rather complicated. The main problem that thermodynamic and kinetic data are poorly understood to present. In these study salt hydrates equilibrium of magnesium sulfate was investigated by new approach. It makes possible to understand the dehydration reaction of MgSO 4 •6H 2 O for heat storage application. Dehydration reaction under various water vapor pressures and temperatures were investigated by thermogravimetric analysis. The result showed that water content in the solid phase is a function of temperature for given water vapor pressure. So, we can conclude that this magnesium sulfatewater vapor system is bivariant and some hydrates appear as the non-stoichiometric hydrates.

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“…[4] The dehydration rate and pathways are further dependent on the water vapour pressure. [5,6] The structural changes during dehydration are identified and possible metastable states at different temperatures and vapour pressures are characterised. [7 -10] These give better understandings and predictions about the dehydration process at larger scales.…”

Section: Introductionmentioning

confidence: 99%

Molecular dynamics study on thermal dehydration process of epsomite (MgSO₄·7H₂O)

Zhang

Iype

Nedea

et al. 2013

Molecular Simulation

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The Low Pressure Dehydration of Magnesium Sulphate Heptahydrate and Cobaltous Chloride Hexahydrate

Cited by 17 publications

References 3 publications

THE EFFECT OF WATER VAPOR UPON THE DEHYDRATION OF CaSO_4•2H₂O

THE EFFECT OF WATER VAPOR UPON THE DEHYDRATION OF CaSO_4•2H₂O

Thermodynamic study of MgSO4 – H2O system dehydration at low pressure in view of heat storage

Molecular dynamics study on thermal dehydration process of epsomite (MgSO₄·7H₂O)

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The Low Pressure Dehydration of Magnesium Sulphate Heptahydrate and Cobaltous Chloride Hexahydrate

Cited by 17 publications

References 3 publications

THE EFFECT OF WATER VAPOR UPON THE DEHYDRATION OF CaSO4•2H2O

THE EFFECT OF WATER VAPOR UPON THE DEHYDRATION OF CaSO4•2H2O

Thermodynamic study of MgSO4 – H2O system dehydration at low pressure in view of heat storage

Molecular dynamics study on thermal dehydration process of epsomite (MgSO4·7H2O)

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THE EFFECT OF WATER VAPOR UPON THE DEHYDRATION OF CaSO_4•2H₂O

THE EFFECT OF WATER VAPOR UPON THE DEHYDRATION OF CaSO_4•2H₂O

Molecular dynamics study on thermal dehydration process of epsomite (MgSO₄·7H₂O)