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Authors:  [[user:Hschwarz|Hans-Jürgen Schwarz]], [[user:TMueller|Tim Müller]], Nils Mainusch
<br>English Translation by Sandra Leithäuser
<br>
back to [[Sulfate]]
{{Infobox_Salt
{{Infobox_Salt
|Footnote            =<ref>http://webmineral.com/data/Epsomite.shtml seen on 29.072010</ref><ref>http://www.mindat.org/min-1393.html seen on 29.072010</ref>
|Footnote            =<ref>http://webmineral.com/data/Epsomite.shtml seen on 29.072010</ref><ref>http://www.mindat.org/min-1393.html seen on 29.072010</ref><ref><bib id="Steiger.etal:2011"></ref><ref><bib id="Lide:1995"></ref>
|photo                = [[File:HJS MgSO4 092503-2.jpg|300px]]
|photo                = [[File:HJS MgSO4 092503-2.jpg|300px]]
|mineralogical_Name  = Epsomite
|mineralogical_Name  = Epsomite
|chemical_Name        = Magnesiumsulfate Heptahydrate
|chemical_Name        = Magnesium sulfate heptahydrate
|Trivial_Name        =Bitter Salts, Reichardtite, Seelandite
|Trivial_Name        = Bitter Salts, reichardtite, seelandite
|chemical_Formula    = MgSO<sub>4</sub>•7H<sub>2</sub>O  
|chemical_Formula    = MgSO<sub>4</sub>•7H<sub>2</sub>O  
|Hydratforms          =[[Kieserite]] (MgSO<sub>4</sub>•H<sub>2</sub>O)<br>[[Sanderite]] (MgSO<sub>4</sub>•2H<sub>2</sub>O)<br>[[Starkeyite]] (MgSO<sub>4</sub>•4H<sub>2</sub>O)<br>[[Pentahydrite]](MgSO<sub>4</sub>•5H<sub>2</sub>O)  <br>[[Hexahydrite]] (MgSO<sub>4</sub>•6H<sub>2</sub>O)<br>[[Meridianite]] (MgSO<sup>4</sup>•11H<sub>2</sub>O)<br>[[Magnesium 12-Hydrate]]
|Hydratforms          = [[Kieserite]] (MgSO<sub>4</sub>•H<sub>2</sub>O)<br>[[Sanderite]] (MgSO<sub>4</sub>•2H<sub>2</sub>O)<br>[[Starkeyite]] (MgSO<sub>4</sub>•4H<sub>2</sub>O)<br>[[Pentahydrite]](MgSO<sub>4</sub>•5H<sub>2</sub>O)  <br>[[Hexahydrite]] (MgSO<sub>4</sub>•6H<sub>2</sub>O)<br>[[Meridianiite]] (MgSO<sub>4</sub>•11H<sub>2</sub>O)<br>[[Magnesium 12-Hydrate]]
|Crystal_System      = orthorhombic
|Crystal_System      = orthorhombic
|Crystal_Structure    =
|Crystal_Structure    =
|Deliqueszenzhumidity = 90.1% (20°C), 94% (30°C)
|Deliqueszenzhumidity = 91.3 %
|Solubility          = 710 g/l
|Solubility          = 2.893 mol/kg
|Density              = 146.8 cm<sup>3</sup>/mol
|Density              = 1.68 g/cm<sup>3</sup>
|MolVolume            = 246.48 g/mol  
|MolVolume            = 146.8 cm<sup>3</sup>/mol  
|Molweight            =1.67 g/cm<sup>3</sup>
|Molweight            = 246.48 g/mol
|Transparency        = transparent to translucent
|Transparency        = transparent to translucent
|Cleavage            = perfect
|Cleavage            = clear to perfect
|Crystal_Habit        =
|Crystal_Habit        = small, acicular, fibre like crystals, granular agregates, crusts
|Twinning            =
|Twinning            = rare
|Refractive_Indices  = n<sub>x</sub> = 1.433<br>n<sub>y</sub> = 1.455<br>n<sub>z</sub> = 1.461
|Refractive_Indices  = n<sub>x</sub> = 1.432<br>n<sub>y</sub> = 1.453<br>n<sub>z</sub> = 1.4609
|Birefringence        = Δ = 0.028
|Birefringence        = Δ = 0.0284
|optical_Orientation  = biaxial negative
|optical_Orientation  = biaxial negative
|Pleochroism          =
|Pleochroism          = none
|Dispersion          =
|Dispersion          =51.1°
|Phase_Transition    =
|Phase_Transition    =
|chemBehavior        =
|chemBehavior        =
|Comments            = can by produced from an aqueous solution under 50°C
|Comments            = can be produced from an aqueous solution under 50°C
|Literature            =<bib id="Steiger.etal:2011"/> <bib id="Lide:1995"/> <bib id="Dana:1951"/>
}}
}}


<bibimport/>
Authors:  [[user:Hschwarz|Hans-Jürgen Schwarz]], [[user:TMueller|Tim Müller]], Nils Mainusch
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back to [[Sulfate]]
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== Einleitung  ==


== Introduction  ==


== Vorkommen von Epsomit ==
== Occurrence of epsomite ==


Als natürliches Mineral wurde Epsomit im Jahr 1695 erstmalig aus den Mineralwässern des Ortes Epsom (bei London) gewonnen, woher die mineralogische Namensgebung rührt. Ebenso wie [[Kieserit]] (Magnesiumsulfatmonohydrat) treten Einzelkristalle in der Natur selten auf. Beide Magnesiumsalze wie auch weitere Hydratstufen werden in alpinen Lagerstätten abgebaut und erscheinen zusammen mit [[Sylvin]] und [[Halit|Steinsalz]] in Norddeutschland und in den Abraumsalzen des Staßfurter Gebietes (bei Magdeburg).
The natural mineral epsomite was first extracted in 1695, from the mineral waters near Epsom (London), where the mineral name was derived from. Just as [[kieserite]] (magnesium sulfate mono hydrate), single crystals rarely occur in nature. Both magnesium salts, as well as their hydrate forms are extracted from alpine deposits and occur together with [[sylvite]] and [[halite|rock salt]] in north Germany, and in the top layer of salt deposits by Staßfurt (near Magdeburg).


== Angaben zu Herkunft und Bildung von Epsomit an Baudenkmalen  ==
== Information on the origin and formation of epsomite on monuments ==


Die Bildung von Magnesiumsulfaten an Denkmalen setzt das Vorhandensein löslicher Magnesiumverbindungen, bzw. von Magnesiumionen voraus. An historischen Bauten können unterschiedliche Materialien Verwendung finden, in denen Magnesiumverbindungen enthalten sind. Einige Beispiele seien nachfolgend aufgeführt:<br>  
The formation of magnesium sulfate on monuments requires the presence of soluble magnesium compounds, and magnesium ions. Different building materials on historic structures can contain magnesium compounds. Some examples are listed below:<br>   
*'''Utilization of lime with dolomite  components''': [[Dolomite]] (CaMg(CO<sub>3</sub>)<sub>2</sub> ) is a double salt.  If lime stone containing dolomite components is heated, slaked and used as mortar, CaCO<sub>3</sub> and MgCO<sub>3</sub>·xH<sub>2</sub>O  form through this process (e.g. [[Nesquehonite]] MgCO<sub>3</sub>·3H<sub>2</sub>O including the molecules from the water of crystallization). The water solubility of MgCO<sub>3</sub>·3H<sub>2</sub>O  at 1,76 g/l, is significantly above the solubility of [[calcite]] (0,014 g/l) and [[dolomite]] (0,078 g/l). If magnesium ions have been dissolved by moisture, they can form several different magnesium salts in the presents of the corresponding anions. The formation of magnesium sulfate can occur if, in connection with dolomite containing plasters, [[gypsum]] was used for stucco or plaster, readily supplying sulfates. 
*'''Utilization of magnesia containing binder''': Magnesia binder consists essentially of  MgO and MgCl<sub>2</sub> or magnesium sulfate. The fully cured and solidified binder can contain highly hygroscopic magnesium salts, which can be converted to magnesium sulfate.
*'''Utilization of cement''': According to the German standard, DIN 1164 <bib id="DIN1164:1994"/> a maximum content MgO of 5 M.% is tolerated in cements. Apart from the possibility of causing damage by delayed quenching, due to the expansion of the magnesia, magnesium ions can theoretically be released and cause the formation of magnesium sulfate. 


*'''Verwendung von Kalk mit dolomitischem Anteil''': [[Dolomit]] ist ein Doppelsalz der Zusammensetzung CaMg(CO<sub>3</sub>)<sub>2</sub>. Wird dolomithaltiger Kalk gebrannt, gelöscht und als Mörtelmischung verwendet, liegt nach dem Prozess der Carbonatisierung sowohl CaCO<sub>3</sub> wie auch MgCO<sub>3</sub>·xH<sub>2</sub>0 vor (beispielsweise in Form von [[Nesquehonit]], also mit drei Kristallwassermolekülen in der Form MgCO<sub>3</sub>·3H<sub>2</sub>0). Die Wasserlöslichkeit von MgCO<sub>3</sub>·3H<sub>2</sub>0 liegt mit ca. 1,76 g/l deutlich über den Löslichkeiten von [[Calcit]] (0,014 g/l) und [[Dolomit]] (0,078 g/l). Durch Feuchteeinwirkung gelöste Magnesiumionen können mit entsprechenden Anionen verschiedene Magnesiumsalze bilden. Die Bildung von Magnesiumsulfat kann forciert erfolgen, wenn in Verbindung mit dolomithaltigem Verputz Stuckgips oder Gipsputz am Objekt verwendet wurde und somit Sulfat im Überschuss vorliegt.
Deicing salt can be another source of magnesium sulfate, it often contains a small proportion of readily soluble MgCl<sub>2</sub>. Furthermore, the magnesium supply can occur through constant soil leaching in connection with rising damp.
*'''Verwendung von Magnesiabinder''': Magnesiabinder besteht im wesentlichen aus MgO und MgCl<sub>2</sub> oder Magnesiumsulfat. Das ausreagierte und verfestigte Bindemittel kann stark hygroskopische Magnesiumsalze enthalten, welche zu Magnesiumsulfat umgebildet werden können.
*'''Verwendung von Zement''': Nach DIN 1164 <bib id="DIN1164:1994"/> ist in Zementen eine Höchstgehalt an MgO von 5 M.% zugelassen. Außer der Möglichkeit bei zeitverzögert verlaufendem Ablöschen durch sogenanntes „Magnesiatreiben“ Schäden zu verursachen, können theoretisch Magnesiumionen freigesetzt werden und zur Bildung von Magnesiumsulfat führen.


Als weitere Quelle einer möglichen Magnesiumsulfatbildung ist Streusalz anzuführen, welches oft einen geringen Anteil des leichtlöslichen MgCl<sub>2</sub> enthält. Weiterhin kann eine Magnesiumzufuhr durch stete Bodenauslaugung bei aufsteigender Feuchte erfolgen.
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<br>
== Solubility properties ==


== Solibiliy properties ==
[[file:S MgSO4.jpg|thumb|800 px|left|'''Figure 1:''' Solubilities in the system MgSO<sub>4</sub>-H<sub>2</sub>O and its temperature dependence. The molality ''m'' [n(MgSO<sub>4</sub>•xH<sub>2</sub>O)•kg(H<sub>2</sub>O)<sup>-1</sup>] is plotted versus the temperature. Equilibria of the different hydrated forms can be distiguished by the different colours of the curves. Dotted lines represent the metastable equilibria. In addition to the solubilities, freezing and boiling points are given. According to <bib id="Steiger.etal:2011a"/>.]]
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[[file:MgSO4_s.jpg|thumb|350px|right|'''>Figure 1''': Solubility of MgSO<sub>4</sub> in water (Diagram: Michael Steiger)]]


[[fil:Loeslichkeit Epsomit 01.JPG|thumb|350px|right|'''Figure 2''': Darstellung der temperaturabhängigen Veränderung der Löslichkeit von Epsomit im Vergleich mit anderen Salzphasen (nach <bib id=Stark.etal:1996/>)]]
The solubility of the above magnesium sulfate forms is significantly above 100 g/l (20°C), and they are part of the group of easily soluble salts. In principle, this leads to a great mobility of the salt and frequent shifting of the accumulation zones inside the material fabric. Due to the influence of temperature on solubility, there is a risk of precipitation of the dissolved salts in combination with rapid temperature drops.  
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Alle oben beschriebenen Magnesiumsulfathydratformen zählen mit einer Löslichkeit von deutlich über 100 g/l (bei 20°C) zur Gruppe der leichtlöslichen Salze. Damit ist im Prinzip eine große Mobilität des Salzes und eine häufige Verschiebung der Anreicherungszonen im Materialgefüge verbunden. Mit dem Temperatureinfluss auf die Löslichkeit kann die Gefahr eines Ausfallens gelöster Salze bei raschem Temperaturabfall verbunden sein.
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<br>


== Hygroscopicity  ==
== Hygroscopicity  ==
<!--
 
Die geringe Hygroskopizität des Reinsalzes Epsomit, die in dem hohen Wert der Gleichgewichtsfeuchte im Bereich 88-90 % r.F. deutlich wird, kann nicht isoliert betrachtet werden. In Mischsystemen, d.h. unter dem Einfluss von Fremdionen, liegt der Sorptionspunkt tiefer (siehe Tab.). Die Möglichkeit der hygroskopischen Feuchteaufnahme mit den damit verbundenen Problematiken ist trotz des hohen Deliqueszenzpunktes durchaus gegeben. <br>
The low hygroscopicity of the pure salt epsomite which becomes evident in the high value of the equilibrium moisture content in the range of 88-90% RH, cannot be considered in isolation. In mixed systems, i.e. under the influence of foreign ions the sorption point is lower (see table). The possibility of hygroscopic moisture uptake with the connected difficulties is still possible despite the high [[deliquescence|Deliquescence]] point. <br>  
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[[file:MgSO4_a.jpg|thumb|350px|left|'''Figure 1:''' The system MgSO<sub>4</sub>/H<sub>2</sub> form -30°C to 80°C , (Diagram: Michael Steiger)]]
 
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[[File:D MgSO4 e.jpg|thumb|800px|left|'''Figure 2:''' Deliquescence behaviour in the system MgSO<sub>4</sub>-H<sub>2</sub>O. The water activity ''a<sub>w</sub>'' is plotted versus the temperature. Different colours label equilibrium and deliquescence humidities of the different phases of the system. Dotted lines represent metastable equilibria. According to <bib id="Steiger.etal:2011a"/>.]]
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{|border="2" cellspacing="0" cellpadding="4" width="52%" align="left" class="wikitable"
{|border="2" cellspacing="0" cellpadding="4" width="52%" align="left" class="wikitable"
|+''Table 1:Deliquescence points at different temperatures [after <bib id=Arnold.etal:1991/>]''                    <!-- Tabellenüberschrift einfügen -->
|+''Table 1:Deliquescence humidities at different temperatures [according to <bib id="Steiger.etal:2011a"/>]''                     
|-
|-
|bgcolor = "#F0F0F0" align=center| 10°C  
|bgcolor = "#F0F0F0" align=center| 10°C  
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|bgcolor = "#F0F0F0" align=center| 30°C
|bgcolor = "#F0F0F0" align=center| 30°C
|-
|-
|bgcolor = "#FFFFEO" align=center| 86,9% r.F.  
|bgcolor = "#FFFFEO" align=center| 93.7% r.h.  
|bgcolor = "#FFFFEO" align=center| 90,1% r.F.  
|bgcolor = "#FFFFEO" align=center| 91.3% r.h.  
|bgcolor = "#FFFFEO" align=center| 88,3% r.F.  
|bgcolor = "#FFFFEO" align=center| 90.3% r.h.  
|bgcolor = "#FFFFEO" align=center| 88,0% r.F.
|bgcolor = "#FFFFEO" align=center| 89.1% r.h.
|}
|}
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<br clear="all">  


===Sorption of moisture===
===Moisture Sorption===
{|border="2" cellspacing="0" cellpadding="4" width="52%" align="left" class="wikitable sortable"
{|border="2" cellspacing="0" cellpadding="4" width="52%" align="left" class="wikitable sortable"
|+''Tabele 2: Behavior concerning moisture sorption of magnesium sulfate [after <bib id=Vogt.etal:1993/>]''
|+''Tabele 2: Behavior concerning moisture sorption of magnesium sulfate [according to <bib id="Vogt.etal:1993"/>]''
|-
|-
|bgcolor = "#F0F0F0"| '''Moisture sorption at'''  
|bgcolor = "#F0F0F0"| '''Moisture sorption at'''  
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|bgcolor = "#FFFFEO" align=center| 27
|bgcolor = "#FFFFEO" align=center| 27
|-
|-
|bgcolor = "#F7F7F7"| '''MgSO<sub>4</sub> + NaCl'''<br>(1:1 molare mixture)  
|bgcolor = "#F7F7F7"| '''MgSO<sub>4</sub> + NaCl'''<br>(1:1 molar mixture)  
|bgcolor = "#FFFFEO" align=center| 240  
|bgcolor = "#FFFFEO" align=center| 240  
|bgcolor = "#FFFFEO" align=center| 146  
|bgcolor = "#FFFFEO" align=center| 146  
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== Kristallisationsdruck  ==


Aufgrund der leichten Löslichkeit des Salzes treten bei entsprechenden Feuchteverhältnissen Lösungs- und Rekristallisationsvorgänge ein. Der dabei (theoretisch berechenbare) Kristallisationsdruck liegt bei Epsomit zwischen 10,5-12,5 N/mm<sup>2 </sup>und bei [[Hexahydrit]] zwischen 11,8- 14,1 N/mm<sup>2</sup>. Im Vergleich mit anderen bauschädlichen Salzen liegen diese Werte somit im unteren Drittel einer berechneten Werteskala, die insgesamt von 7,2 bis 65,4 N/mm<sup>2</sup> reicht [nach <bib id=Winkler:1975/>]
== Crystallization pressure  ==
 
Due to the high solubility of the salt, dissolving  and recrystallization processes take place under the appropriate humidity conditions. In theory the occurring crystallization pressure can be calculated and ranges between 10,5-12,5 N/mm<sup>2 </sup> for epsomite and between 11,8- 14,1 N/mm<sup>2</sup> for [[hexahydrite]]. Compared to other damaging salts these values are thus to be found in the lower third of a calculated scale of values, alltogether ranging from  7,2 bis 65,4 N/mm<sup>2</sup> [according to <bib id="Winkler:1975"/>].


== Hydratationsverhalten ==
== Hydration behavior ==


Das System MgSO<sub>4</sub> – H<sub>2</sub>O: Als stabile Verbindungen sind die oben aufgelisteten sechs Hydratstufen des Magnesiumsulfates belegt. Mit der Ausnahme des Magnesiumsulfat-12-Hydrates wurden alle oben aufgeführten Kristallwasserstufen des Magnesiumsulfates an Baudenkmalen nachgewiesen, wobei im wesentlichen jedoch nur Epsomit, [[Hexahydrit]], [[Pentahydrit]] und [[Kieserit]] auftreten.  
The system MgSO<sub>4</sub> – H<sub>2</sub>O: the listed hydrate stages of magnesium sulfates are known to be stable compounds. With the exception of magnesium sulfate- 12- hydrate, all the above stages of the chemically combined water of magnesium sulfate on monuments are visible, but essentially only epsomite, [[hexahydrite]], [[pentahydrite]] and [[kieserite]] occur.


Epsomit stellt bei Raumtemperatur und einer relativen Feuchte im Bereich von 50%-90% die beständigste Hydratstufe dar. Sinkt die relative Feuchte bei Raumtemperatur deutlich unter 50%, dann kommt es zu Kristallwasserabgabe und der Bildung niedrigerer Hydratstufen. [[Hexahydrit]] (MgSO<sub>4</sub><sub></sub> × 6H<sub>2</sub>O) ist als Reinsalz theoretisch nur im Temperaturbereich zwischen ca. 48°C und 67,5 °C stabil. [[Pentahydrit]] wird in der Literatur als an der Luft metastabil, bzw. instabil bezeichnet, trotzdem ist die Existenz dieser beiden Salzphasen an Bauwerken röntgenografisch nachgewiesen. Das Austreiben des Hydratwassers bis zum Erhalt von [[Kieserit]] kann bei erhöhten Temperaturen stattfinden.
At room temperature and an RH between 50%-90%, epsomite is the most stable hydrate stage. If the RH drops significantly lower than 50% at room temperature, the chemically combined water is released and lower hydrate stages are formed. Hexahydrite (MgSO<sub>4</sub><sub></sub> × 6H<sub>2</sub>O) as pure salt is only stable at a temperature range of approx. 48°C to 67,5 °C.
Pentahydrite has been thought to be metastable or unstable when exposed to the air, nevertheless the existence of these two salt phases has been detected by X-ray diffraction on building structures. The expulsion of the hydrate water can occur up to the formation of kieserite at elevated temperatures.


== Hydratationsdruck ==
== Hydration pressure ==


Die Möglichkeit der Veränderung des Kristallwassergehaltes von Magnesiumsulfaten an Bauwerken ist erwiesen, und es ist anzunehmen, dass Wechsel im Bereich der Kristallwasserstufen [[Pentahydrit]], [[Hexahydrit]] und Epsomit (in Abhängigkeit von klimatischen Veränderungen) in situ durchlaufen werden. Der Einbau eines Wassermoleküles in das Kristallgitter des [[Hexahydrit]] und der Umbildung zu Epsomit ist mit einer Volumenzunahme von rund 10% verbunden. Der daraus resultierende Hydratationsdruck kann bei einer Temperatur von 0-20°C und einer r.F. von ca. 70% mit Werten zwischen 6,8 –9,7 N/mm<sup>2</sup> angegeben werden. Für die Umwandlung von [[Kieserit]] zu [[Hexahydrit]] ist eine Volumenzunahme von ca. 140% anzugeben [nach <bib id=Stark.etal:1996/>].
Possible variations in magnesium sulfate´s content of chemically combined water on constructions are a fact, and it is likely, that changes in the hydrate stages [[pentahydrite]], [[hexahydrite]] and epsomite (subject to climatic fluctuations) are taking place in situ. The addition of a water molecule into the crystal lattice of hexahydrite, resulting in the transformation to epsomite, is associated with an increase in volume of around 10%. At temperatures from 0-20°C and 70% RH the resulting hydration pressure can be specified at values between 6,8 –9,7 N/mm<sup>2</sup>. The conversion from kieserite to hexahydrite causes an increase in volume of approx. 140%   [according to <bib id="Stark.etal:1996"/>].


== Umwandlungsreaktionen ==
== Conversion reaction ==


Als Beispiel für das Schädigungspotential, das mit der Bildung von Epsomit verbunden ist, sei ein Fall dargestellt: Liegt Magnesiumcarbonat (als [[Magnesit]]) im Materialgefüge eines Denkmales vor, so kann durch die Einwirkung von Schwefelsäure Epsomit entstehen. Mit dieser Umwandlung ist eine Volumenzunahme von über 400% verbunden nach <bib id=Stark.etal:1996/>.
The following case is a good example for the potential damage connected with the formation of epsomite: if magnesium carbonate (as [[magnesite]]) is present in the material structure of a monument, epsomite can form through the influence of sulfuric acid. According to <bib id="Stark.etal:1996"/> this conversion is linked to an increase in volume of over 400%.
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== Analytischer Nachweis ==
== Analytical identification ==


Kristallisiertes Magnesiumsulfat, welches an einem Objekt vorliegt, kann in unterschiedlichen Morphologien erscheinen, wobei bestimmte Erscheinungsformen vorzugsweise auftreten. Bei einem im Rahmen der Diplomarbeit von Mainusch <bib id= Mainusch:2001/> untersuchten Objekt stellte sich die Ausbildung eines Gemisches von Epsomit und [[Hexahydrit]] in situ als lockere Kruste einer opaken, grauweißlichen Substanz dar. In Form “körniger Krusten” ist Epsomit in der Klosterkirche St. Johann in Müstair belegt, Magnesiumsulfatausblühungen in Form von Salz-Whiskern wurden in der St. Georgskirche in der Steiermark in Österreich nachgewiesen.  
On objects, crystallized magnesium sulfate can appear in differing morphologies, but specific forms appear more frequently. One examined object displayed a loose crust of an opaque, gray to yellow substance in situ, which was a mixture of epsomite and hexahydrite (part of the thesis by Mainusch <bib id= "Mainusch:2001"/>). At the monastery church St. Johann at Müstair epsomite appeared as “granular crusts”. Magnesium sulfate efflorescence in the shape of salt whiskers was detected at St. Georgs church in Steiermark (Styria).  
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=== Mikrochemie ===
=== Micro- chemistry ===
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=== Mikroskopie  ===
'''Laboruntersuchung:'''


Behauchen einer überwiegend magnesiumsulfathaltigen Ausblühung bewirkt keine makroskopisch beobachtbaren Veränderungen. Charakteristisch hingegen ist das gute Lösungsverhalten in Wasser, ein pH-Wert um 7 und die Ausbildung eines mit bloßem Auge erkennbaren, ringförmigen und leicht erhabenen Saumes bzw. einer transparenten Schicht, die nach dem Verdampfen des wässrigen Lösemittels verbleibt.
=== Microscopy  ===


Im Labor sind die Ergebnisse der Objekttests unter Zuhilfenahme des Mikroskops zu überprüfen. Die Betrachtung einerseits des Rohprobematerials, wie auch des rekristallisierten Salzes zeigt: Magnesiumsulfatkristalle treten im Probematerial in sehr unspezifischen Erscheinungsformen auf. Versuche, gut ausgebildete Magnesiumsulfat-Einzelkristalle auf dem Wege der Rekristallisation aus wässriger Lösung zu erstellen, erweisen sich als sehr schwierig, da eine starke Verwachsungstendenz besteht. So bildet sich in der Regel der erwähnte auffällige, ringförmige Saum von flach ineinander verwachsenen Kristallen, wenn eine überwiegend magnesiumsulfathaltige Lösung vorsichtig eingedampft wird. Epsomit zeigt eine geringe Löslichkeit in wasserfreiem Ethanol und in Glyzerin, was unter dem Mikroskop gut zu beobachten ist.
'''Laboratory examination:'''


Die Tendenz von Magnesiumsulfat, beim Rekristallisieren aus wässriger Lösung kaum äquidimensionale oder elongierte Einzelkristalle auszubilden, erschwert die Erstellung guter Präparate für die weitergehende [[Polarisationsmikroskopie|polarisationsmikroskopische]] Untersuchung beträchtlich. Die geringe Ethanollöslichkeit ermöglicht es allerdings, durch sehr dosierte, eventuell mehrfache Zugabe auf das rekristallisierte Material Einzelpartikel zu isolieren. Sowohl am Ausgangsmaterial, wie auch am rekristallisierten Präparat ist die weiterfolgende Untersuchung am [[polarisationsmikroskopie|Polarisationsmikroskop]] durchzuführen.<br>  
Breathing onto a (predominantly) magnesium sulfate efflorescence, causes no observable macroscopic changes. However, characteristics are: the good solubility in water, a pH of 7, the formation of a ring-shaped slightly raised seam (visible by the naked eye), or a transparent layer that remains in place after the evaporation of the aqueous solvent.
In laboratory tests on objects the results should be double checked with the microscope. Observations of the raw sample material and the recrystallized salt, show that magnesium sulfate crystals appear in unspecific forms in sample material.  
Experiments to produce well-shaped, single magnesium sulfate crystals, by recrystallization in aqueous solution have not been very successful, because of a strong tendency for intergrowth. Usually the previously mentioned, distinct, ring-shaped seam of intergrown crystals forms, when the magnesium sulfate containing solute is evaporated. Epsomite shows a low solubility in anhydrous ethanol and glycerin under the microscope.
For further examinations using [[polarized light microscopy|polarized light microscopy]], a considerable difficulty is the creation of good preparations, due to the tendency of magnesium sulfate to form only few equidimensional or elongated single crystals.  The low solubility in ethanol, nevertheless allows to isolate single particles by repeatedly adding recrystallized material. Both on the base material as well as the recrystallized product, examination using polarized light microscopy should be carried out.<br>  


'''Brechungsindizes''':&nbsp; n<sub>X</sub> = 1,433, n<sub>y</sub> = 1,455, n<sub>z</sub> <br>
'''Refractive indices''':&nbsp; n<sub>X</sub> = 1,433, n<sub>y</sub> = 1,455, n<sub>z</sub> <br>
'''Doppelbrechung: &nbsp;&nbsp; '''Δ = max.&nbsp; 0,028 <br>
'''Birefringence: &nbsp;&nbsp; '''Δ = max.&nbsp; 0,028 <br>
'''Kristallklasse:''' &nbsp; &nbsp; &nbsp; &nbsp;&nbsp; orthorhombisch
'''Crystal class:''' &nbsp; &nbsp; &nbsp; &nbsp;&nbsp; orthorhombic
<br>
<br>
<br>
<br>


'''[[Polarisationsmikroskopie|Polarisationsmikroskopische Untersuchung:]]'''<br>  
'''[[Polarized light microscopy|Polarized light microscopic examination:]]'''<br>  
 


Die Zuweisung der Brechungsindizes von Epsomit erfolgt entsprechend der Immersionsmethode (sukzessive mittels der Einbettmedien n<sub>D</sub>=1,518; n<sub>D</sub>=1,47; n<sub>D</sub>=1,46). Bei der Verwendung eines Immersionsmediums mit Brechungsindex n<sub>D</sub>=1,45 ist bei vielen Einzelpartikeln ein geringer, jedoch klarer Wechsel im Relief bei der Rotation erkennbar. Da Epsomit zur Klasse der orthorhombischen Kristalle zählt, tritt keine schiefe, sondern stets parallele und symmetrische Auslöschung auf. Neben Epsomit bildet sich zumeist auch Hexahydrit, welches monoklin ist und nahezu identische Brechungsindizes wie Epsomit aufweist. Zwischen diesen beiden Hydratformen des Magnesiumsaulfates ist eine Unterscheidung nur über die Zuweisung der Kristallklasse möglich. Aufgrund des geringen Gangunterschiedes zeigen Epsomitkristalle in der Regel nur niedrige Interferenzfarben im Bereich der ersten Ordnung.  
The allocation of epsomite to the refractive indices is carried out according to the immersion method (successively by means of embedding media n<sub>D</sub>=1,518; n<sub>D</sub>=1,47; n<sub>D</sub>=1,46). When using an immersion medium with a refractive index of n<sub>D</sub>=1,45 on many single particles a slight but distinct variation in relief is visible at rotation. Because epsomite belongs to the class of orthorhombic crystals, it never appears in an oblique but always in a parallel symmetrical extinction. Beside epsomite, hexahydrite often forms, which is monoclinic and has nearly identical refractive indices. A distinction between these two hydrate stages of magnesium sulfate is only possible through the allocation of the crystal class. Due to the low path difference epsomite crystals usually only show low inference colors in the range of the first order.  


'''Verwechslungsmöglichkeiten:'''<br>  
'''Possibility for mistakes:'''<br>  


Epsomit/[[Hexahydrit]] sind zuzuweisen, sofern die unteren Untersuchungskriterien eindeutig geklärt sind:
Epsomite/[[hexahydrite]] are to be allocated, once the examination criteria below have been clarified:  


*gute Wasserlöslichkeit
*good water solubility
*charakteristisches Erscheinungsbild bei der Rekristallisation&nbsp;  
*characteristic appearance at recrystallization&nbsp;  
*geringe Doppelbrechung
*low birefringence


<br>
<br>
-->
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== Röntgendiffraktometrie ==
== X- Ray diffraction ==


== Raman-Stektroskopie ==
== Raman-Spectroscopiy ==


== DTA / TG  ==
== DTA / TG  ==


== IR-Spektroskopie ==
== IR-Spectroscopy ==


= <br>Umgang mit Epsomitschäden  =
= <br>Umgang mit Epsomitschäden  =
Line 185: Line 186:
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== Salts and deteriotion pattern  ==
== Salts and deterioration pattern  ==


=== On objects  ===
=== On objects  ===


=== Under the polarising microscope  ===
=== Under the polarising microscope  ===
 
<gallery caption="Crystallized on monuments " widths="200px" heights="150px" perrow="3">
Image:0141 0010 Bb440um 0021.JPG|Sample of a salt crust of magnesium sulfate whiskers (image width 440 um)
</gallery>


<gallery caption="Crystallized from a water solution on a glass slide " widths="200px" heights="150px" perrow="3">
<gallery caption="Crystallized from a water solution on a glass slide " widths="200px" heights="150px" perrow="3">


Image:0141 0010 Bb440um 0021.JPG|Sample of a salt crust of magnesium sulfate whiskers
Image:CeS 221209-02-10x-01.JPG|Sample of magnesium sulfate re-crystallized from water solution on a glass slide
Image:CeS 221209-02-10x-01.JPG|Real sample with magnesium sulfate salts, crystallized from a water solution on a glass slide
Image:CeS 221209-02-10x-02.JPG|Sample of magnesium sulfate re-crystallized from water solution on a glass slide  
Image:CeS 221209-02-10x-02.JPG|Real sample with magnesium sulfate salts, crystallized from a water solution on a glass slide  
Image:CeS 221209-04-2,5kx-01.JPG|Sample of magnesium sulfate re-crystallized from water solution on a glass slide  
Image:CeS 221209-04-2,5kx-01.JPG|Real sample with magnesium sulfate salts, crystallized from a water solution on a glass slide  
Image:CeS 221209-04-2,5kx-02.JPG|Sample of magnesium sulfatere-crystallized from water solution on a glass slide   
Image:CeS 221209-04-2,5kx-02.JPG|Real sample with magnesium sulfate salts, crystallized from a water solution on a glass slide   
Image:CeS 221209-04-2,5kx-03.JPG|Sample of magnesium sulfate re-crystallized from water solution on a glass slide  
Image:CeS 221209-04-2,5kx-03.JPG|Real sample with magnesium sulfate salts, crystallized from a water solution on a glass slide  
Image:MGSO4 4.5.2006 (11).JPG|Magnesium- sulfate, crystallized from a water solution on a glass slide  
Image:MGSO4 4.5.2006 (11).JPG|Magnesium- sulfate, crystallized from a water solution on a glass slide  
Image:MGSO4 4.5.2006 (12).JPG|Magnesium sulfate, crystallized from a water solution on a glass slide  
Image:MGSO4 4.5.2006 (12).JPG|Magnesium sulfate, crystallized from a water solution on a glass slide  
Line 217: Line 219:
<references/>
<references/>


[[Category:Epsomite]][[Category:Sulphate]][[Category:Salt]][[Category:InProgress]][[Category:Sulfate]]
 
 
== Literature ==
 
<biblist/>
 
 
 
[[Category:Epsomite]][[Category:Sulphate]][[Category:Salt]][[Category:approved]][[Category:Sulfate]][[Category:List]]

Latest revision as of 10:43, 3 May 2023

Authors: Hans-Jürgen Schwarz, Tim Müller, Nils Mainusch
English Translation by Sandra Leithäuser
back to Sulfate

Epsomite[1][2][3][4]
HJS MgSO4 092503-2.jpg
Mineralogical name Epsomite
Chemical name Magnesium sulfate heptahydrate
Trivial name Bitter Salts, reichardtite, seelandite
Chemical formula MgSO4•7H2O
Other forms Kieserite (MgSO4•H2O)
Sanderite (MgSO4•2H2O)
Starkeyite (MgSO4•4H2O)
Pentahydrite(MgSO4•5H2O)
Hexahydrite (MgSO4•6H2O)
Meridianiite (MgSO4•11H2O)
Magnesium 12-Hydrate
Crystal system orthorhombic
Crystal structure
Deliquescence humidity 20°C 91.3 %
Solubility (g/l) at 20°C 2.893 mol/kg
Density (g/cm³) 1.68 g/cm3
Molar volume 146.8 cm3/mol
Molar weight 246.48 g/mol
Transparency transparent to translucent
Cleavage clear to perfect
Crystal habit small, acicular, fibre like crystals, granular agregates, crusts
Twinning rare
Phase transition
Chemical behavior
Comments can be produced from an aqueous solution under 50°C
Crystal Optics
Refractive Indices nx = 1.432
ny = 1.453
nz = 1.4609
Birefringence Δ = 0.0284
Optical Orientation biaxial negative
Pleochroism none
Dispersion 51.1°
Used Literature
[Steiger.etal:2011]Title: Weathering and Deterioration
Author: Steiger, M.; Charola, A. E.; Sterflinger, K.
Link to Google Scholar
[Lide:1995]Title: CRC Handbook of Chemistry and Physics
Author: Lide D.R.
Link to Google Scholar
[Dana:1951]Title: Dana's System of Mineralogy
Author: Dana J.D.
Link to Google Scholar



Introduction[edit]

Occurrence of epsomite[edit]

The natural mineral epsomite was first extracted in 1695, from the mineral waters near Epsom (London), where the mineral name was derived from. Just as kieserite (magnesium sulfate mono hydrate), single crystals rarely occur in nature. Both magnesium salts, as well as their hydrate forms are extracted from alpine deposits and occur together with sylvite and rock salt in north Germany, and in the top layer of salt deposits by Staßfurt (near Magdeburg).

Information on the origin and formation of epsomite on monuments[edit]

The formation of magnesium sulfate on monuments requires the presence of soluble magnesium compounds, and magnesium ions. Different building materials on historic structures can contain magnesium compounds. Some examples are listed below:

  • Utilization of lime with dolomite components: Dolomite (CaMg(CO3)2 ) is a double salt. If lime stone containing dolomite components is heated, slaked and used as mortar, CaCO3 and MgCO3·xH2O form through this process (e.g. Nesquehonite MgCO3·3H2O including the molecules from the water of crystallization). The water solubility of MgCO3·3H2O at 1,76 g/l, is significantly above the solubility of calcite (0,014 g/l) and dolomite (0,078 g/l). If magnesium ions have been dissolved by moisture, they can form several different magnesium salts in the presents of the corresponding anions. The formation of magnesium sulfate can occur if, in connection with dolomite containing plasters, gypsum was used for stucco or plaster, readily supplying sulfates.
  • Utilization of magnesia containing binder: Magnesia binder consists essentially of MgO and MgCl2 or magnesium sulfate. The fully cured and solidified binder can contain highly hygroscopic magnesium salts, which can be converted to magnesium sulfate.
  • Utilization of cement: According to the German standard, DIN 1164 [DIN1164:1994]Title: DIN 1164-1: Zement Teil 1, Zusammensetzung und Anforderungen
    Author: DIN
    Link to Google Scholar
    a maximum content MgO of 5 M.% is tolerated in cements. Apart from the possibility of causing damage by delayed quenching, due to the expansion of the magnesia, magnesium ions can theoretically be released and cause the formation of magnesium sulfate.

Deicing salt can be another source of magnesium sulfate, it often contains a small proportion of readily soluble MgCl2. Furthermore, the magnesium supply can occur through constant soil leaching in connection with rising damp.


Solubility properties[edit]

Figure 1: Solubilities in the system MgSO4-H2O and its temperature dependence. The molality m [n(MgSO4•xH2O)•kg(H2O)-1] is plotted versus the temperature. Equilibria of the different hydrated forms can be distiguished by the different colours of the curves. Dotted lines represent the metastable equilibria. In addition to the solubilities, freezing and boiling points are given. According to [Steiger.etal:2011a]Title: Decomposition reactions of magnesium sulfate hydrates and phase equilibria in the MgSO4-H2O and Na+-Mg2+-Cl--SO42--H2O systems with implications for Mars
Author: Steiger, Michael; Linnow, Kirsten; Ehrhardt, Dorothee; Rohde, Mandy
Link to Google Scholar
.



The solubility of the above magnesium sulfate forms is significantly above 100 g/l (20°C), and they are part of the group of easily soluble salts. In principle, this leads to a great mobility of the salt and frequent shifting of the accumulation zones inside the material fabric. Due to the influence of temperature on solubility, there is a risk of precipitation of the dissolved salts in combination with rapid temperature drops.

Hygroscopicity[edit]

The low hygroscopicity of the pure salt epsomite which becomes evident in the high value of the equilibrium moisture content in the range of 88-90% RH, cannot be considered in isolation. In mixed systems, i.e. under the influence of foreign ions the sorption point is lower (see table). The possibility of hygroscopic moisture uptake with the connected difficulties is still possible despite the high Deliquescence point.



Figure 2: Deliquescence behaviour in the system MgSO4-H2O. The water activity aw is plotted versus the temperature. Different colours label equilibrium and deliquescence humidities of the different phases of the system. Dotted lines represent metastable equilibria. According to [Steiger.etal:2011a]Title: Decomposition reactions of magnesium sulfate hydrates and phase equilibria in the MgSO4-H2O and Na+-Mg2+-Cl--SO42--H2O systems with implications for Mars
Author: Steiger, Michael; Linnow, Kirsten; Ehrhardt, Dorothee; Rohde, Mandy
Link to Google Scholar
.



Table 1:Deliquescence humidities at different temperatures [according to [Steiger.etal:2011a]Title: Decomposition reactions of magnesium sulfate hydrates and phase equilibria in the MgSO4-H2O and Na+-Mg2+-Cl--SO42--H2O systems with implications for Mars
Author: Steiger, Michael; Linnow, Kirsten; Ehrhardt, Dorothee; Rohde, Mandy
Link to Google Scholar
]
10°C 20°C 25°C 30°C
93.7% r.h. 91.3% r.h. 90.3% r.h. 89.1% r.h.


Moisture Sorption[edit]

Tabele 2: Behavior concerning moisture sorption of magnesium sulfate [according to [Vogt.etal:1993]Title: Der Einfluss hygroskopischer Salze auf die Gleichgewichtsfeuchte und Trocknung anorganischer Baustoffe
Author: Vogt, R.; Goretzki, Lothar
Link to Google Scholar
]
Moisture sorption at 87%r.F. 81%r.F. 70%r.F. 61%r.F. 50%r.F.
MgSO4 76 75 70 71 27
MgSO4 + NaCl
(1:1 molar mixture)
240 146 75 50 20


Crystallization pressure[edit]

Due to the high solubility of the salt, dissolving and recrystallization processes take place under the appropriate humidity conditions. In theory the occurring crystallization pressure can be calculated and ranges between 10,5-12,5 N/mm2 for epsomite and between 11,8- 14,1 N/mm2 for hexahydrite. Compared to other damaging salts these values are thus to be found in the lower third of a calculated scale of values, alltogether ranging from 7,2 bis 65,4 N/mm2 [according to [Winkler:1975]Title: Stone: Properties, Durability in Man´s Environment
Author: Winkler, Erhard M.
Link to Google Scholar
].

Hydration behavior[edit]

The system MgSO4 – H2O: the listed hydrate stages of magnesium sulfates are known to be stable compounds. With the exception of magnesium sulfate- 12- hydrate, all the above stages of the chemically combined water of magnesium sulfate on monuments are visible, but essentially only epsomite, hexahydrite, pentahydrite and kieserite occur.

At room temperature and an RH between 50%-90%, epsomite is the most stable hydrate stage. If the RH drops significantly lower than 50% at room temperature, the chemically combined water is released and lower hydrate stages are formed. Hexahydrite (MgSO4 × 6H2O) as pure salt is only stable at a temperature range of approx. 48°C to 67,5 °C. Pentahydrite has been thought to be metastable or unstable when exposed to the air, nevertheless the existence of these two salt phases has been detected by X-ray diffraction on building structures. The expulsion of the hydrate water can occur up to the formation of kieserite at elevated temperatures.

Hydration pressure[edit]

Possible variations in magnesium sulfate´s content of chemically combined water on constructions are a fact, and it is likely, that changes in the hydrate stages pentahydrite, hexahydrite and epsomite (subject to climatic fluctuations) are taking place in situ. The addition of a water molecule into the crystal lattice of hexahydrite, resulting in the transformation to epsomite, is associated with an increase in volume of around 10%. At temperatures from 0-20°C and 70% RH the resulting hydration pressure can be specified at values between 6,8 –9,7 N/mm2. The conversion from kieserite to hexahydrite causes an increase in volume of approx. 140% [according to [Stark.etal:1996]Title: Bauschädliche Salze
Author: Stark, Jochen; Stürmer, Sylvia
Link to Google Scholar
].

Conversion reaction[edit]

The following case is a good example for the potential damage connected with the formation of epsomite: if magnesium carbonate (as magnesite) is present in the material structure of a monument, epsomite can form through the influence of sulfuric acid. According to [Stark.etal:1996]Title: Bauschädliche Salze
Author: Stark, Jochen; Stürmer, Sylvia
Link to Google Scholar
this conversion is linked to an increase in volume of over 400%.


Analytical identification[edit]

On objects, crystallized magnesium sulfate can appear in differing morphologies, but specific forms appear more frequently. One examined object displayed a loose crust of an opaque, gray to yellow substance in situ, which was a mixture of epsomite and hexahydrite (part of the thesis by Mainusch [Mainusch:2001]Title: Erstellung einer Materialsammlung zur qualitativen Bestimmung bauschädlicher Salze für Fachleute der Restaurierung
Author: Mainusch, Nils
Link to Google Scholar
). At the monastery church St. Johann at Müstair epsomite appeared as “granular crusts”. Magnesium sulfate efflorescence in the shape of salt whiskers was detected at St. Georgs church in Steiermark (Styria).

Microscopy[edit]

Laboratory examination:

Breathing onto a (predominantly) magnesium sulfate efflorescence, causes no observable macroscopic changes. However, characteristics are: the good solubility in water, a pH of 7, the formation of a ring-shaped slightly raised seam (visible by the naked eye), or a transparent layer that remains in place after the evaporation of the aqueous solvent. In laboratory tests on objects the results should be double checked with the microscope. Observations of the raw sample material and the recrystallized salt, show that magnesium sulfate crystals appear in unspecific forms in sample material. Experiments to produce well-shaped, single magnesium sulfate crystals, by recrystallization in aqueous solution have not been very successful, because of a strong tendency for intergrowth. Usually the previously mentioned, distinct, ring-shaped seam of intergrown crystals forms, when the magnesium sulfate containing solute is evaporated. Epsomite shows a low solubility in anhydrous ethanol and glycerin under the microscope. For further examinations using polarized light microscopy, a considerable difficulty is the creation of good preparations, due to the tendency of magnesium sulfate to form only few equidimensional or elongated single crystals. The low solubility in ethanol, nevertheless allows to isolate single particles by repeatedly adding recrystallized material. Both on the base material as well as the recrystallized product, examination using polarized light microscopy should be carried out.

Refractive indices:  nX = 1,433, ny = 1,455, nz
Birefringence:    Δ = max.  0,028
Crystal class:          orthorhombic

Polarized light microscopic examination:


The allocation of epsomite to the refractive indices is carried out according to the immersion method (successively by means of embedding media nD=1,518; nD=1,47; nD=1,46). When using an immersion medium with a refractive index of nD=1,45 on many single particles a slight but distinct variation in relief is visible at rotation. Because epsomite belongs to the class of orthorhombic crystals, it never appears in an oblique but always in a parallel symmetrical extinction. Beside epsomite, hexahydrite often forms, which is monoclinic and has nearly identical refractive indices. A distinction between these two hydrate stages of magnesium sulfate is only possible through the allocation of the crystal class. Due to the low path difference epsomite crystals usually only show low inference colors in the range of the first order.

Possibility for mistakes:

Epsomite/hexahydrite are to be allocated, once the examination criteria below have been clarified:

  • good water solubility
  • characteristic appearance at recrystallization 
  • low birefringence


Salts and deterioration pattern[edit]

On objects[edit]

Under the polarising microscope[edit]


Weblinks[edit]

  1. http://webmineral.com/data/Epsomite.shtml seen on 29.072010
  2. http://www.mindat.org/min-1393.html seen on 29.072010
  3. <bib id="Steiger.etal:2011">
  4. <bib id="Lide:1995">


Literature[edit]

[DIN1164:1994]DIN (1994): DIN 1164-1: Zement Teil 1, Zusammensetzung und Anforderungen.Link to Google Scholar
[Dana:1951]Dana E.S. (eds.) Dana J.D. (1951): Dana's System of Mineralogy, 7, Wiley & SonsLink to Google Scholar
[Lide:1995]Lide D.R. (eds.) Lide D.R. (1995): CRC Handbook of Chemistry and Physics, CRC PressLink to Google Scholar
[Mainusch:2001]Mainusch, Nils (2001): Erstellung einer Materialsammlung zur qualitativen Bestimmung bauschädlicher Salze für Fachleute der Restaurierung, Diplomarbeit, HAWK Hochschule für angewandte Wissenschaft und Kunst Hildesheim/Holzminden/Göttingen, file:Diplomarbeit Nils Mainusch.pdfLink to Google ScholarFulltext link
[Stark.etal:1996] Stark, Jochen; Stürmer, Sylvia (1996): Bauschädliche Salze, Bauhaus-Univ. WeimarLink to Google Scholar
[Steiger.etal:2011]Steiger, M.; Charola, A. E.; Sterflinger, K. (2011): Weathering and Deterioration. In: Siegesmund, Siegfried; Snethlage, Rolf (eds.): Stone in Architecture - Properties, Durability, Springer, 227-316.Link to Google Scholar
[Steiger.etal:2011a]Steiger, Michael; Linnow, Kirsten; Ehrhardt, Dorothee; Rohde, Mandy (2011): Decomposition reactions of magnesium sulfate hydrates and phase equilibria in the MgSO4-H2O and Na+-Mg2+-Cl--SO42--H2O systems with implications for Mars. In: Geochimica et Cosmochimica Act, 75 (12), 3600-3626, 10.1016/j.gca.2011.03.038,Link to Google Scholar
[Vogt.etal:1993]Vogt, R.; Goretzki, Lothar (1993): Der Einfluss hygroskopischer Salze auf die Gleichgewichtsfeuchte und Trocknung anorganischer Baustoffe, unveröffentlichter Bericht.Link to Google Scholar
[Winkler:1975] Winkler, Erhard M. (1975): Stone: Properties, Durability in Man´s Environment, Springer Verlag, WienLink to Google Scholar