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Author: [[user:Hschwarz|Hans-Jürgen Schwarz]]
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Autor: [[Benutzer:Hschwarz|Hans-Jürgen Schwarz]]<br> <br>
English version by [[user:SLeithaeuser|Sandra Leithäuser]]
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== Abstract  ==
== Abstract  ==
Damaging soluble salts can be transformed into less damaging ones by their conversion into insoluble salts. Two methods can be used. The first one converts soluble salts into poorly soluble or insoluble compounds, thus diminishing the number and degree of crystallization cycles. The second one transforms the less soluble salts into far more soluble ones in order to remove them more easily.


Durch die chemische Salzumwandlung werden zum einen Schadsalze in unlösliche bzw. schwer lösliche Verbindungen überführt, so dass diese nicht mehr schädigend wirken können. Zum anderen wird sie eingesetzt, um schwer lösliche Salze leichter löslich zu machen, um diese anschließend besser entfernen zu können.
== [[Removal of salts by salt conversion]]  ==
 
 
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== [[Entfernen von Salzen durch Salzumwandlung]]  ==


In der Praxis wurden und werden verschiedene Verfahren zur Entfernung schwerlöslicher Salze und Salzkrusten eingesetzt. Vielfach kamen hier früher oft Säuren wie Salzsäure oder auch Essigsäure z.B. zum Entfernen von Calciumcarbonatkrusten zum Einsatz <bib id="Hammer:1996" />, die in vielen Fällen bei nicht optimaler Ausführung weitere Schadensprozesse in Gang setzten. Auch die Verwendung von Hexafluorokieselsäure ist belegt. Zu den Verfahrensschritten der "Gipsumwandlung" gehört auch das Lösen der Gipskruste mit Ammoniumcarbonat. Auch Ionenaustauchser werden seit vielen Jahren zum Entfernen von Krusten eingesetzt<bib id="Pursche:2001" />.
Conservation practice uses various methods for the removal of soluble salts and salt crusts. In the past, acids such as hydrochloric or acetic acid were often used to remove calcium carbonate crusts. However, this can lead to subsequent damages if the correct procedure is not followed diligently.<bib id="Hammer:1996" /> The use of hexafluorosilicic acid has also been documented. The Florentine method <bib id="Matteini:1991"/> of "gypsum transformation" is based on the dissolution of the gypsum crust with ammonium carbonate. Ion exchangers have also been in use for many years to remove crusts.<bib id="Pursche:2001" />


== [[Immobilisierung von Salzen]]  ==
== [[Immobilization of salts]]  ==


Bei der Immobilisierung handelt es sich um eine Umwandlung bzw. den Versuch einer Umwandlung leicht löslicher bauschädlicher Salze in möglichst schwer lösliche oder unlösliche und damit relativ unschädliche Verbindungen. Dies klingt einfach und ist einleuchtend, ist in der Praxis jedoch mit einer Reihe von Problemen verbunden. Zunächst liegt im Mauerwerk nicht nur ein definiertes Salz vor, wie z.B. Calciumnitrat oder ein Magesiumsulfat, sondern man hat es immer mehr oder weniger mit einer Mischung zu tun, die z.T. kristallin, z.T. als Salzlösung vorliegen kann. Meist liegen Carbonat-, Nitrat-, Chlorid- oder Sulfatverbindungen vor. Als Kationen treten hauptsächlich Natrium, Kalium, Magnesium und Calcium auf. Zu berücksichtigen ist, dass Nitratverbindungen nicht in unlösliche Salze umgewandelt werden können, da es keine schwerlöslichen Nitratverbindungen gibt. Es verbleiben uns also nur die Möglichkeiten bei Chloriden, Sulfaten und begrenzt auch bei Carbonaten.  
Immobilization is the conversion of readily soluble salts into poorly soluble or insoluble salts that are therefore less deteriorating compounds. This appears to be simple but the problem is that not all ions form highly insoluble compounds, for example, there are no poorly soluble or insoluble nitrate compounds. Furthermore, masonry usually contains a mixture of ions, not only specific salts, such as calcium nitrate or magnesium sulfate. Thus, even when some salts crystallize out, a solution containing these and other ions will also be present. The most common anions are carbonates, nitrates, chlorides and sulfates, the most common cations are sodium, potassium, magnesium and calcium. This leaves chlorides, sulfates and some limited options for carbonates as the only possibilities for an immobilization treatment.  


Während heute meist Bariumlösungen zum Einsatz kommen <bib id="Friese.etal:1999" />, wurden früher in vielen Fällen Bleihexafluorosilikat verwendet.  
Currently, barium solutions, such as barium hydroxide, are the most frequently employed to immobilize sulfates. In the past, lead hexafluorosilicate was used to immobilize chlorides as well as carbonates, however the fluorosilicate will react with any calcium carbonate in the substrate by turning it into calcium fluoride, and can attack silicate minerals as during the reaction hydroflouric acid is released.  


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= Literatur  =
== Literature ==


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[[Category:Maßnahmen]][[Category:Salzumwandlung]] [[Category:HSchwarz]] [[Category:R-GGrassegger]] [[Category:R-SLaue]] [[Category:Review]]
[[Category:Measures]][[Category:Salt Conversion]] [[Category:Schwarz,Hans-Jürgen]] [[Category:R-SLaue]] [[Category: approved]]

Latest revision as of 10:44, 20 September 2013

Author: Hans-Jürgen Schwarz
English version by Sandra Leithäuser
back to Measures

Abstract

Damaging soluble salts can be transformed into less damaging ones by their conversion into insoluble salts. Two methods can be used. The first one converts soluble salts into poorly soluble or insoluble compounds, thus diminishing the number and degree of crystallization cycles. The second one transforms the less soluble salts into far more soluble ones in order to remove them more easily.

Removal of salts by salt conversion

Conservation practice uses various methods for the removal of soluble salts and salt crusts. In the past, acids such as hydrochloric or acetic acid were often used to remove calcium carbonate crusts. However, this can lead to subsequent damages if the correct procedure is not followed diligently.[Hammer:1996]Title: Salze und Salzbehandlung in der Konservierung von Wandmalerei und Architekturoberfläche.
Author: Hammer, Ivo
Link to Google Scholar
The use of hexafluorosilicic acid has also been documented. The Florentine method [Matteini:1991]Title: In Review: An Assessmant of Florentine Methods of Wall Painting Conservation Based on the Use of Mineral Treatments
Author: Matteini, Mauro
Link to Google Scholar
of "gypsum transformation" is based on the dissolution of the gypsum crust with ammonium carbonate. Ion exchangers have also been in use for many years to remove crusts.[Pursche:2001]Title: Konservierung von Wandmalerei, Reaktive Behandlungsmethoden zur Bestandserhaltung
Link to Google Scholar

Immobilization of salts

Immobilization is the conversion of readily soluble salts into poorly soluble or insoluble salts that are therefore less deteriorating compounds. This appears to be simple but the problem is that not all ions form highly insoluble compounds, for example, there are no poorly soluble or insoluble nitrate compounds. Furthermore, masonry usually contains a mixture of ions, not only specific salts, such as calcium nitrate or magnesium sulfate. Thus, even when some salts crystallize out, a solution containing these and other ions will also be present. The most common anions are carbonates, nitrates, chlorides and sulfates, the most common cations are sodium, potassium, magnesium and calcium. This leaves chlorides, sulfates and some limited options for carbonates as the only possibilities for an immobilization treatment.

Currently, barium solutions, such as barium hydroxide, are the most frequently employed to immobilize sulfates. In the past, lead hexafluorosilicate was used to immobilize chlorides as well as carbonates, however the fluorosilicate will react with any calcium carbonate in the substrate by turning it into calcium fluoride, and can attack silicate minerals as during the reaction hydroflouric acid is released.


Literature

[Hammer:1996]Hammer, Ivo (1996): Salze und Salzbehandlung in der Konservierung von Wandmalerei und Architekturoberfläche.. In: Pursche, Jürgen (eds.): Salzschäden an Wandmalereien, Bayerisches Landesamt für Denkmalpflege, 81-106.Link to Google Scholar
[Matteini:1991]Matteini, Mauro (1991): In Review: An Assessmant of Florentine Methods of Wall Painting Conservation Based on the Use of Mineral Treatments. In: Cather, Sharon (eds.): The Conservation of Wall Paintings: Proceedings of a symposium organized by the Coutrauld Institut of Art and the Getty Conservation Institute, London, July 13-16, 1987, The Getty Conservation Institute, 137-148.Link to Google Scholar
[Pursche:2001]Pursche, Jürgen (eds.) (2001): Konservierung von Wandmalerei, Reaktive Behandlungsmethoden zur Bestandserhaltung, Bayerisches Landesamt für Denkmalpflege, MünchenLink to Google Scholar