The Mechanism of the Dehydration of Calcium Sulfate Hemihydrate

Weiser, Harry B.; Milligan, W. O.; Ekholm, W. C.

doi:10.1021/ja01298a050

Cited by 39 publications

(18 citation statements)

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“…This is consistent with the structural determinations by Wooster [1] showing that gypsum has a layer lattice and layers are held together by hydrogen explored [11,12] .…”

Section: Scanning Electron Microgramssupporting

confidence: 92%

The calcium sulfate-water system:

Clifton¹

1970

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“…This is consistent with the structural determinations by Wooster [1] showing that gypsum has a layer lattice and layers are held together by hydrogen explored [11,12] .…”

Section: Scanning Electron Microgramssupporting

confidence: 92%

The calcium sulfate-water system:

Clifton¹

1970

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“…Th e transformation of gypsum by releasing constitutional water is well known (Weiser et al, 1936), and has been proposed by Nelson et al (1978), Artieda et al (2006), and others as a method for gypsum determination. Th ermo-gravimetric (TG) methods require very simple lab equipment and are free of errors arising from the presence of soluble salts.…”

Section: Thermogravimetrymentioning

confidence: 99%

Gypsum, a Tricky Material

Herrero

Artieda

Hudnall

2009

Soil Science Soc of Amer J

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The familiarity of mankind with gypsum and its simple composition are in contrast with the frequent mistakes reported for its behavior and role in nature. Gypsum has been studied as a raw material, as a rock constituent, as an indicator of geological and archaeological conditions, and from other points of view. However, its role in Earth surface processes, its relationship to life through calcium in the equilibrium of carbonates and its structural water molecules, seems overlooked. Moreover, errors of gypsum formulation, analysis, and behavior obscure some of its roles within nature. The semi‐solubility of gypsum explains its actions in many soils. The softness, fragility, and crystal water of gypsum are often not considered. Routinely drying at 105°C and pulverizing samples for lab analyses casts suspicion on all analytical results because gypsum becomes anhydrite and/or bassanite at this temperature. Specific physicochemical models are needed to predict the behavior of soils mainly composed of gypsum.

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“…Although this suggests that a product having a still more negative heat of solution might be obtained at a still higher temperature, nevertheless, this is doubtful because of the dissociation which will occur at higher temperatures. Marchal [28] has determined the dissociation pressure of CaS04 at 1,000, 1,100, and 1,230 0 C and found it to be 8,24, and 97 mm of Hg, respectively. Since the heat of solution of 1.5 g of CaO in 640 g of 2.09 molal HCl in this calorimeter is +834 calfg [29], it is evident that any dissociation of CaS04 will result in an increase in the heat of solution.…”

mentioning

confidence: 99%

Heats of hydration and transition of calcium sulfate

Newman¹,

Wells²

1938

J. RES. NATL. BUR. STAN.

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The heats of solution at 25° C in 2.09 molal HCI of gypsum, hemihydrate, natural anhydrite, and anhydrous CaS04, prepared by heating gypsum at various temperatures, have been determined. From these values the heats evolved in the hydration to gypsum of hemihydrate, and of anhydrite prepared at 1,000° C, were calculated to be 4,100 ±30 and 3,990 ±20 cal/mole, r espectively. The heat evolved in the hydration to gypsum of soluble anhydrite prepared by dehydrating gypsum at 75° C is not less than 6,990 cal/mole . In the course of this work X-ray and microscopic studies gave no indication of the existence of more than two forms of anhydrous calcium sulfate: Soluble anhydrite a nd a modification formed rapidly at high temperatures, the latter being identical with natural anhydrite. The heat evolved in the transition of soluble anhydrit e to natural anhydrite is not less than 3,000 cal/mole. I.

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The Mechanism of the Dehydration of Calcium Sulfate Hemihydrate

Cited by 39 publications

References 0 publications

The calcium sulfate-water system:

The calcium sulfate-water system:

Gypsum, a Tricky Material

Heats of hydration and transition of calcium sulfate

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