Sodium sulfate heptahydrate

Author: Amelie Stahlbuhk
back to Sulfate

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

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.

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

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
. Figure 1 indicates 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

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

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

For more informations see [Saidov:2012]Title: Sodium sulfate heptahydrate in weathering phenomena of porous materials
Author: Saidov, Tamerlan Adamovich

Literature

[Gans:1978]	Gans, W. (1978): Thermodynamic stability of sodium sulfate heptahydrate. In: Zeitschrift für Physikalische Chemie, 111 (1), 39-46, Url
[Saidov:2012]	Saidov, Tamerlan Adamovich (2012): Sodium sulfate heptahydrate in weathering phenomena of porous materials. dissertation, Technische Universiteit Eindhoven, Url
[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. In: Geochimica et Cosmochimica Acta, 72 (17), 4291-4306, Url

A phase is a physically distinctive form of matter and is characterized by having relatively uniform chemical and physical properties.

the relative humidity, above which a material, e.g. a salt, absorbes humidity from the air and dissolves.