Sodium sulfate heptahydrate

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Author: Amelie Stahlbuhk
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Sodium sulfate heptahydrate
Mineralogical name
Chemical name sodium sulfate heptahydrate
Trivial name
Chemical formula Na2SO4•7H2O
Other forms Na2SO4•10H2O (Mirabilite)
Crystal system
Crystal structure
Deliquescence humidity 20°C 89.1 %
Solubility (g/l) at 20°C 3.143 mol/kg
Density (g/cm³)
Molar volume
Molar weight 268,14 g/mol
Transparency
Cleavage
Crystal habit
Twinning
Phase transition
Chemical behavior
Comments
Crystal Optics
Refractive Indices
Birefringence
Optical Orientation
Pleochroism
Dispersion
Used Literature
[Steiger.etal:2008]Title: Crystallization of sodium sulfate phases in porous materials: The phase diagram Na2SO4–H2O and the generation of stress
Author: Steiger, Michael; Asmussen, Sönke
Link to Google Scholar


Introduction

Sodium sulfate heptahydrate is a metastable phase of sodium sulfate. Its formation can be observed during the rapid cooling of a solution that is saturated at 40 °C [Gans:1978]Title: Thermodynamic stability of sodium sulfate heptahydrate
Author: Gans W.
Link to Google Scholar

Solubility


Figure 1: Solubility of Na2SO4 in water, according to : [Steiger.etal:2008]Title: Crystallization of sodium sulfate phases in porous materials: The phase diagram Na2SO4–H2O and the generation of stress
Author: Steiger, Michael; Asmussen, Sönke
Link to Google Scholar



The solubility of the heptahydrate at 20 °C is 3.145 mol/kg [Steiger.etal:2008]Title: Crystallization of sodium sulfate phases in porous materials: The phase diagram Na2SO4–H2O and the generation of stress
Author: Steiger, Michael; Asmussen, Sönke
Link to Google Scholar
. Figure 1 idicates that, eventhough it is a metastable phase, the heptahydrate is more relevant at lower temperatures.

Hygroscopicity


Figure 2:Deliquescence of Na2SO4, according to: [Steiger.etal:2008]Title: Crystallization of sodium sulfate phases in porous materials: The phase diagram Na2SO4–H2O and the generation of stress
Author: Steiger, Michael; Asmussen, Sönke
Link to Google Scholar


At 20 °C the deliquescence humidity lies at 89.1 %. The values are higher at lower temperatures (table 1).


Table 1: Deliquescnece humidity of sodium sulfate heptahydrate at different round temperatures, according to [Steiger.etal:2008]Title: Crystallization of sodium sulfate phases in porous materials: The phase diagram Na2SO4–H2O and the generation of stress
Author: Steiger, Michael; Asmussen, Sönke
Link to Google Scholar
0°C 10°C 20°C
96.1%r.h. 93.3%r.h. 89.1%r.h.


The importance of the heptahydrate in the damage process

see [Saidov:2012]Title: Sodium sulfate heptahydrate in weathering phenomena of porous materials
Author: Saidov, Tamerlan
Link to Google Scholar

Weblinks

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Literature

[Gans:1978]Gans W. (19778): Thermodynamic stability of sodium sulfate heptahydrate. Z. Phys. Chem. NF, 111 (), 39-46Link to Google Scholar
[Saidov:2012]Saidov, Tamerlan (2012): Sodium sulfate heptahydrate in weathering phenomena of porous materials. dissertation, Eindhoven: Technische Universiteit Eindhoven, Url, http://dx.doi.org/10.6100/IR737583Link to Google Scholar
[Steiger.etal:2008]Steiger, Michael; Asmussen, Sönke (2008): Crystallization of sodium sulfate phases in porous materials: The phase diagram Na2SO4–H2O and the generation of stress. Geochimica et Cosmochimica Acta, 72 (17), 4291-4306, 10.1016/j.gca.2008.05.053Link to Google Scholar