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{{Infobox_Salt
|Footnote            = <ref>http://webmineral.com/data/Thenardite.shtml  viewed on 29/07/2010</ref><ref>http://www.mindat.org/min-3935.html  viewed on 29/07/2010</ref>
|photo                = [[File:HJS-Na2SO4-111703-02-10x.jpg|300px]]
|mineralogical_Name  = Thenardite
|chemical_Name        = Sodium sulfate
|Trivial_Name        = Pyrotechnite
|chemical_Formula      = Na<sub>2</sub>SO<sub>4</sub>
|Hydratforms          = [[Mirabilite]] (Na<sub>2</sub>SO<sub>4</sub>•10H<sub>2</sub>O)<br>Sodiumsulfate heptahydrate (Na<sub>2</sub>SO<sub>4</sub>•7H<sub>2</sub>O)
|Crystal_System      = orthorhombic
|Crystal_Structure    =
|Deliqueszenzhumidity = 81.7% (25°C)
|Solubility          = 162 g/l
|Density              = 2.689 g/cm³
|MolVolume            = 53.11 cm<sup>3</sup>/mol
|Molweight            = 142.04 g/mol
|Transparency        = transparent to translucent
|Cleavage            = perfect
|Crystal_Habit        =
|Twinning            =
|Refractive_Indices  = n<sub>x</sub> = 1.468<br> n<sub>y</sub> = 1.473<br> n<sub>z</sub> = 1.483
|Birefringence        = Δ = 0.015
|optical_Orientation  = positive
|Pleochroism          =
|Dispersion          =
|Phase_Transition    =
|chemBehavior        =
|Comments            = soluble in water and glycerin,<br> not soluble in pure alcohol
}}


Authors: [[user:Hschwarz|Hans-Jürgen Schwarz ]], Michael Steiger, [[user:TMueller|Tim Müller]] <br>
English translation by [[user:MAngeli|Matthieu Angeli]] <br>
back to [[Sulfate]]
= Sodium sulfate and thenardite =
__TOC__
== Abstract  ==
Sodium sulfate and its phases thenardite, mirabilite and heptahydrate are described. Heptahydrate´s role as a major source of damage is also explained .
== Occurrence ==
Both thenardite and [[mirabilite]] occur as natural minerals. In nature sodium sulfate occurs in mineral waters in the form of double salts, as deposits of former salt lakes. Knowledge of the hydrated sodium sulfate dates back to the 16th Century. Its first description has been written by Glauber in 1658 in which he described it as "sal mirable". It is also quite common to read the name "Glauber's salt" for [[mirabilite]] in the literature.
== Information on the origin and formation of thenardite / mirabilite in monuments  ==
With the entry of materials that contain soluble sodium compounds, the mineral system of a monument may create sodium sulfate as salt efflorescence, when reacting with various sources of sulfate for example air contaminated with sulphurous gases. In Germany cement exhibits a high content of sodium ions, because the German standardization institute (DIN) allows for a content of up to 0.5 %  soluble alkalis. This means that 100 kg of Portland cement containing only 0.1% soluble Na<sub>2</sub>O can form 520g of [[Mirabilite]] when in contact with air containing sulfuric acid [calculation by Arnold/Zehnder 1991]. Sodium ions can also enter into monuments from a plethora of cleaning materials and especially older restoration products (such as water glass). Ground water and surface water are also a possible source of Na<sup>+</sup>-ions. Road salt consists to a large extent of slightly soluble [[Halite|sodium chloride]]. Finally, in the coastal areas, sea water is a significant source of [[Halite|NaCl]].
== Solubility behavior  ==
[[file:Na2SO4_sol.jpg|thumb|350px|right|'''Figure1''': Solubility of Na2SO4 in water, Graph: M. Steiger]]<br>
The structures of both thenardite and [[mirabilite]] belong to the group of easily soluble salts and therefore they are easily mobilized (see table [[hygroscopicity of the salts and ERH]]). The solubility of sodium sulfate is highly dependent on temperature. For this reason, a rapid drop of temperature is highly likely to yield very high supersaturation and salt crystallization.<br>
== Hygroscopicity  ==
[[file:Na2SO4_aw.jpg|thumb|350px|right|'''Figure2''':Deliquescence of Na2SO4, Graph: M. Steiger]]
The temperature effect on the deliquescence points of thenardite and mirabilite is shown below. The striking features here are the opposite curve transitions. In the presence of other ions (in salt mixtures), the parameters of the equilibrium moisture content, as well as the necessary temperature and humidity conditions for recrystallization, change significantly. The following table shows experimental data of equilibrium moisture for different salt mixtures at different temperatures.It turns out that all the values of equilibrium moisture content are lower than those of the pure salt mirabilite (see table [[equilibrium moisture content as a function of temperature]]). <br>
<br clear="all">
{|border="2" cellspacing="0" cellpadding="4" width="52%" align="left" class="wikitable"
|+''Table 1''' - Information about the equilibrium moisture of saturated solid solutions (mixing ratio: saturated sol.A / saturated sol.B = 1:1) <bib id="Vogt.etal:1993"/>''                   
|-
|bgcolor = "#F0F0F0" |
|bgcolor = "#F0F0F0" align="center"| '''MgSO<sub>4</sub>'''
|bgcolor = "#F0F0F0" align="center"| '''Ca(NO<sub>3</sub>)<sub>2</sub>'''
|bgcolor = "#F0F0F0" align="center"| '''KNO<sub>3</sub>'''
|-
|bgcolor = "#F7F7F7" | '''Na<sub>2</sub>SO<sub>4</sub> • 10H<sub>2</sub>O'''
|bgcolor = "#FFFFEO" align="center"| 87(21°C)
|bgcolor = "#FFFFEO" align="center"| 74 (21°C)
|bgcolor = "#FFFFEO" align="center"| 81(21°C)
|}
<br clear="all">
'''Water vapor sorption: '''
[[file:Deliqueszenz Mirabilit, Thenardit .JPG|thumb|350px|right|'''Figure 3''': Deliquescence points of pure salts thenardite and mirabilite <bib id="Arnold.etal:1991"/>]]
The table below shows additional information for estimating the hygroscopicity of sodium sulfate for the sorption behavior of pure salt and the mixture with [[Halite|halite]] at different relative humidity levels:
<br>
{|border="2" cellspacing="0" cellpadding="4" width="52%" align="center" class="wikitable"
|+''Table 2''': Moist sorption of sodium sulphate in M.% after 56 days of storage [after <bib id="Vogt.etal:1993"/>]''
|-
|bgcolor = "#F0F0F0" | '''Air humidity'''
|bgcolor = "#F0F0F0" align="center"| '''87% r.F.'''
|bgcolor = "#F0F0F0" align="center"| '''81% r.F.'''
|bgcolor = "#F0F0F0" align="center"| '''79% r.F.'''
|-
|bgcolor = "#F7F7F7" | '''Na<sub>2</sub>SO<sub>4</sub>''' 
|bgcolor = "#FFFFEO" align="center"| 79
|bgcolor = "#FFFFEO" align="center"| 0 
|bgcolor = "#FFFFEO" align="center"| 0
|-
|bgcolor = "#F7F7F7" | '''Na<sub>2</sub>SO<sub>4</sub>+NaCl''' (1:1 molar mixture)
|bgcolor = "#FFFFEO" align="center"| 157
|bgcolor = "#FFFFEO" align="center"| 32
|bgcolor = "#FFFFEO" align="center"| 15
|}
== Crystallization pressure  ==
When crystallizing from an aqueous solution, the crystallization pressure of thenardite lies in the 29.2-34.5 N/mm<sup>2</sup> range. These values are higher that those calculated for other building-damaging salts <bib id="Winkler:1975"/>.
== Hydration behavior  ==
[[file:Mirabilit Thenardit.ogg|thumb|400px|right|Conversion of mirabilite (?) into thenardite]]
The Na<sub>2</sub>SO<sub>4</sub> – H<sub>2</sub>O system:
The only stable forms of sodium sulfate are the decahydrate ([[Mirabilite|mirabilite]]) and the anhydrite (thenardite). The generation of mirabilite by recrystallization of the salt from an aqueous supersaturated solution occurs at 32.4°C. In particular, the transition from thenardite to mirabilite and the incorporation of 10 water molecules in the crystal lattice causes a volume expansion of 320%. This transition happens at a relatively low temperature (32-35°C), the damage caused by this salt is highly dependent on the temperature and thus on the environment. This temperature range is given as a guide, because this transition could happen for example at 25°C at 80% relative humidity, or even at 0°C at 60.7% relative humidity [information from Gmelin]. Due to this strong dependence on the environmental parameters, an estimate of the damage caused on buildings by crystallization and hydration of sodium sulfate are very difficult to obtain.
<!--
== The importance of the heptahydrate in the damage process ==
== Hydration pressure  ==
Der Hydratationsdruck, der beim Übergang von Thenardit zu [[Mirabilit]] aufgebaut wird, ist stark abhängig von den bestehenden Luftfeuchte- und Temperatur-verhältnissen, was in der nachstehenden Tabelle verdeutlicht ist:
<br clear="all">
{|border="2" cellspacing="0" cellpadding="4" width="52%" align="left" class="wikitable"
|+''Tabelle 3''': Hydratationsdruck Thenardit-[[Mirabilit]] nach <bib id="Winkler.etal:1970"/>''                   
|-
|bgcolor = "#F0F0F0" align=center| '''rel. Feuchte %'''
|bgcolor = "#F0F0F0" align=center|  '''20.0 °C'''
|bgcolor = "#F0F0F0" align=center|  '''25.0 °C'''
|bgcolor = "#F0F0F0" align=center|  '''30.0 °C'''
|-
|bgcolor = "#F7F7F7" align=center| '''100'''
|bgcolor = "#FFFFEO" align="center"| 48.9 N/mm<sup>2</sup>
|bgcolor = "#FFFFEO" align="center"| 40.5 N/mm<sup>2</sup>
|bgcolor = "#FFFFEO" align="center"| 28.9 N/mm<sup>2</sup>
|-
|bgcolor = "#F7F7F7" align=center| '''95,0'''
|bgcolor = "#FFFFEO" align="center"| 41.3 N/mm<sup>2</sup>
|bgcolor = "#FFFFEO" align="center"| 32.7 N/mm<sup>2</sup>
|bgcolor = "#FFFFEO" align="center"| 23.3 N/mm<sup>2</sup>
|-
|bgcolor = "#F7F7F7" align="center"| '''90,0'''
|bgcolor = "#FFFFEO" align="center"| 33.5 N/mm<sup>2</sup>
|bgcolor = "#FFFFEO" align="center"| 24.9 N/mm<sup>2</sup>
|bgcolor = "#FFFFEO" align="center"| 13.7 N/mm<sup>2</sup>
|-
|bgcolor = "#F7F7F7" align="center"| '''85,0'''
|bgcolor = "#FFFFEO" align="center"| 25.5 N/mm<sup>2</sup>
|bgcolor = "#FFFFEO" align="center"| 16.0 N/mm<sup>2</sup>
|bgcolor = "#FFFFEO" align="center"| 5.1 N/mm<sup>2</sup>
|-
|bgcolor = "#F7F7F7" align="center"| '''80,0'''
|bgcolor = "#FFFFEO" align="center"| 16.4 N/mm<sup>2</sup>
|bgcolor = "#FFFFEO" align="center"| 7.8 N/mm<sup>2</sup>
|bgcolor = "#FFFFEO" align="center"| 0.0
|-
|bgcolor = "#F7F7F7" align="center"| '''75.0'''
|bgcolor = "#FFFFEO" align="center"| 6.7 N/mm<sup>2</sup>
|bgcolor = "#FFFFEO" align="center"| 0.0
|bgcolor = "#FFFFEO" align="center"|  -
|}
<br clear=all>
Die Volumenveränderung, die beim Phasenübergang stattfindet, ist mit ca. 320% anzugeben <bib id="Sperling.etal:1980"/>.
== Analytical detection  ==
=== Microscopy<br>  ===
'''Laboruntersuchung:'''<br>Durch mikroskopische Beobachtungen des Lösungsverhaltens sind die gute Wasserlöslichkeit und Ethanolunlöslichkeit zu verifizieren. Thenardit und [[Mirabilit]] besitzen keine morphologische Charakterisitka, die bei einfachen Rekristallisationsversuchen zur Identifizierung beitragen können. Vielmehr ist eine große Bandbreite unterschiedlichster Erscheinungsformen beobachtbar.<br>
'''Brechungsindizes:''' &nbsp;&nbsp; n<sub>x</sub> = 1.468; n<sub>y</sub> =1,473; n<sub>z</sub> =1.483<br>'''Doppelbrechung''':&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Δ = 0.015<br>'''Kristallklass'''e:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; orthorhombisch<br>
<br>
'''[[Polarisationsmikroskopie|Polarisationsmikroskopische]] Investigation:'''<br>
In Abhängigkeit von den vorliegenden Luftfeuchte- und Temperaturbedingungen verändern Kristalle des Rohprobematerials und des rekristallisierten Präparates ihren Kristallwassergehalt. An trockner Luft (mit r.F. &lt; 80% und Raumtemperatur) verliert [[Mirabilit]] sein Kristallwasser und geht in Thenardit über. Dieser Vorgang kann mikroskopisch klar nachvollzogen werden, wenn der Prozess der Rekristallisation beobachtet wird. [[Mirabilit]] weist charakteristische anormale Interferenzfarbe auf, im Zuge des Wasserverlustes und Entstehen von Thenardit schwächen sich die anormalen Interferenzphänomene zunehmend ab.<br><br>Die Zuweisung der Brechungsindizes von Thenardit erfolgt entsprechend der Immersionsmethode. Aufgrund der niedrigen maximalen Doppelbrechung zeigt Thenardit zumeist graue Interferenzfarben. Die Auslöschung ist parallel oder symmetrisch.
<br>'''Verwechslungsmöglichkeiten:'''
Generell ist die Unterscheidung einer bestimmten Anzahl von Sulfaten (die unten aufgelistet sind und wozu Thenardit zählt) ohne mikrochemische Bestimmung der Anionen problematisch, da die Brechungsindizes der Salze dicht beieinander liegen und alle Salze eine niedrige Doppelbrechung aufweisen. Hilfreich ist die Verwendung eines Immersionsmittels mit einem n<sub>D</sub>-Wert von 1,48. Eine Differenzierung innerhalb dieser Gruppe wird damit möglich. Außerdem können die unten genannten Eigenschaften als Abgrenzungskriterien hinzugezogen werden.
Eindeutig bestimmbar wird Thenardit durch die Möglichkeit, nach Auflösung des Probematerials im Zuge der Rekristallisation das Phänomen anormaler Interferezfarben beobachten zu können, sprich [[Mirabilit]] in der hohen Hydratstufe zu identifizieren und somit indirekt Thenardit nachzuweisen.
{|border="2" cellspacing="0" cellpadding="4" width="100%" align="left" class="wikitable"
|+''Tabelle 3''': Unterscheidungsmerkmale zu anderen Sulfaten''
|-
|bgcolor = "#F0F0F0"| '''Salzphase'''
|bgcolor = "#F0F0F0"| '''Unterscheidungsmerkmal'''
|-
|bgcolor = "#F7F7F7"| '''[[Boussingaultit]]''' (NH<sub>4</sub>)<sub>2</sub>Mg(SO)<sub>4</sub> • 6H<sub>2</sub>0
|bgcolor = "#FFFFEO"| keine anormalen Interferenzfarben / schiefe Auslöschung
|-
|bgcolor = "#F7F7F7"| '''[[Schönit|Pikromerit]]''' K<sub>2</sub>Mg(SO<sub>4</sub>)<sub>2</sub> • 6H<sub>2</sub>0
|bgcolor = "#FFFFEO"| keine anormalen Interferenzfarben / schiefe Auslöschung
|-
|bgcolor = "#F7F7F7"|'''[[Astrakanit|Bloedit]]''' Na<sub>2</sub>Mg(SO<sub>4</sub>)<sub>2</sub> • 6H<sub>2</sub>0
|bgcolor = "#FFFFEO"| alle Indizes &gt;1.48 / keine anormalen Interferenzfarben / schiefe Auslöschung / optisch negativ orientiert.
|-
|bgcolor = "#F7F7F7"| '''[[Aphthitalit|Glaserit]]''' K<sub>3</sub>Na(SO<sub>4</sub>)<sub>2</sub>
|bgcolor = "#FFFFEO"| alle Indizes &gt;1.48 / keine anormalen Interferenzfarben/schiefe Auslöschung
|-
|bgcolor = "#F7F7F7"| '''[[Arcanit]]''' K<sub>2</sub>SO<sub>4</sub>
|bgcolor = "#FFFFEO"| alle Indizes &gt;1.48 / keine anormalen Interferenzfarben
|-
|bgcolor = "#F7F7F7"| '''[[Magnesiumformiat]]''' Mg(HCO<sub>2</sub>)<sub>2</sub> • 2H<sub>2</sub>O
|bgcolor = "#FFFFEO"| vergleichsweise hohe Doppelbrechung / keine anormalen Interfernzfarben / schiefe Auslöschung
|}
<br>
'''Betrachtung von Mischsystemen:'''
Mischsystem Na<sup>+</sup>– Ca<sup>2+</sup>– SO<sub>4</sub> <sup>2-</sup>: Der Ausfall von [[Gips]] erfolgt im Zuge der Rekristallisation entsprechend der geringeren Löslichkeit desselben zuerst. Der charakteristische nadelige Habitus von einzelnen Gipskristallen wie auch von Aggregaten bleibt bestehen. Der Ausfall von Natriumsulfat erfolgt später, das eigentliche Kristallwachstum vollzieht sich merklich schneller. Die Morphologie ist unspezifisch.
Mischsystem Na<sup>+</sup>– SO<sub>4</sub> <sup>2-</sup>– Cl<sup>-</sup>: Der Ausfall der beiden Partikelsorten beginnt etwa zeitgleich. Halit mit charakteristischer Morphologie, Natriumsulfat in extrem variierender Gestalt.
=== X-ray diffractometry  ===
=== Raman-Spectroscopy  ===
=== DTA / TG  ===
=== IR-Spectroscopy  ===
<br>
<br>
<br>
-->
== Pictures of salt and salt damage  ==
=== In the field ===
<gallery caption="Thenardite efflorescences" widths="200px" heights="150px" perrow="3">
Image:Idensen,_Thenardit_ausbluehung_aussen.jpg|Thenardite crystals on a wall in the old church in Idensen,Germany
Image:Eilsumpudrigeausbluehungen.jpg|Thenardite efforesceneces in the Ev. Ref. church in Eilsum, Germany
</gallery>
=== Under the polarizing microscope  ===
<gallery caption="Sodium sulfate crystals between to glass plates " widths="200px" heights="150px" perrow="3">
Image:HJS Na2SO4-slides-6.jpg  |plain polarized light
Image:HJS Na2SO4-slides-1.jpg| crossed polarisers,  red I
Image: |         
Image:HJS Na2SO4-slides-110703-10x-3.jpg|plain polarized light
Image:HJS Na2SO4-slides-110703-10x-2.jpg| crossed polarisers
Image:HJS Na2SO4-slides-110703-10x-1.jpg|  crossed polarisers,  red I
Image:HJS Na2SO4-slides-2-110603.jpg|plain polarized light
Image:HJS Na2SO4-slides-1-110603.jpg|  crossed polarisers,  red I
Image: |
Image:HJS-Na2SO4-111703-02-10x.jpg|plain polarized light
Image:HJS-Na2SO4-111703-04-10x.jpg|plain polarized light
Image:HJS-Na2SO4-111703-01-10x.jpg| crossed polarisers,  red I
</gallery>
<br>
<gallery caption="Sodium sulfate crystals, crystallised out of a water extraction of a real sample" widths="200px" heights="150px" perrow="3">
Image:HJS Na2SO4 092503-3.jpg|plain polarized light
Image:HJS Na2SO4 092503-4.jpg|plain polarized light
</gallery>
<!--
=== Under the Scanning Electron Microscope ===
-->
== Weblinks<br>  ==
<references />
== Literature  ==
<biblist/>
[[Category:Thenardite]][[Category:Sulphate]][[Category:Salt]][[Category:InProgress]][[Category:Sulfate]]
[[User:SLeithaeuser|SLeithaeuser]] 15:22, 6 May 2012 (CEST)
[[User:SLeithaeuser|SLeithaeuser]] 15:22, 6 May 2012 (CEST)

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SLeithaeuser 15:22, 6 May 2012 (CEST)

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