Salts Resulting from Restoration Materials: Difference between revisions

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Many restoration materials contribute to the salt contamination of objects. Sometimes they can even be the main source of damage.   
Many restoration materials contribute to the salt contamination of objects. Sometimes they can even be the main source of damage.   


Difficult are alkaline and acidic cleaning or restoration products such as:
The most relevant are the alkaline and acidic cleaning or restoration products such as:




=== Water glass ===
=== Water glass ===


Water glass is used to consolidate surfaces. The following reactions can be visualized schematically:  
Water glass was used in the past to consolidate surfaces and was the precursor to the current silicate esters based consolidans. Water glass is a sodium (or potassium) silicate and the following reactions can be visualized schematically:


  Na<sub>2</sub>SiO<sub>3</sub> (Na-water glass) <nowiki>+</nowiki> CO<sub>2</sub> <nowiki>+</nowiki> H<sub>2</sub>O&nbsp; → SiO<sub>2</sub> <sub>Gel</sub> <nowiki>+</nowiki> Na<sub>2</sub>CO<sub>3</sub>  
  Na<sub>2</sub>SiO<sub>3</sub> (Na-water glass) <nowiki>+</nowiki> CO<sub>2</sub> <nowiki>+</nowiki> H<sub>2</sub>O&nbsp; → SiO<sub>2</sub> <sub>Gel</sub> <nowiki>+</nowiki> Na<sub>2</sub>CO<sub>3</sub>  
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  K<sub>2</sub>SiO<sub>3 </sub><sup></sup>(K-water glass)<sup></sup> + CO<sub>2</sub> + H<sub>2</sub>O → SiO<sub>2</sub> <sub>Gel</sub> + K<sub>2</sub>CO<sub>3</sub>  
  K<sub>2</sub>SiO<sub>3 </sub><sup></sup>(K-water glass)<sup></sup> + CO<sub>2</sub> + H<sub>2</sub>O → SiO<sub>2</sub> <sub>Gel</sub> + K<sub>2</sub>CO<sub>3</sub>  


The resulting sodium carbonate can constitute up to 30% of water glass substance, the potassium carbonate up to 20%.
The resulting sodium carbonate can constitute up to 30% of the deposited material, and the potassium carbonate up to 20%.
 
Potassium water glass: potassium carbonate is very hygroscopic and it is hardly ever found in its crystalline form. A subsequent reaction into potassium nitrate in contrast nearly always leads to efflorescence.  


Potassium carbonate is very hygroscopic and it is hardly ever found in its crystalline form. A subsequent reaction into potassium nitrate will lead to efflorescence of this latter salt.


=== Acids  ===
=== Acids  ===


Some acids are used to clean surfaces, e.g. hydrochloric acid, acetic acid, formic acid and hydrofluoric acid. Accordingly, these lead to the formation of salts.
Some acids are used to clean surfaces <bib id="Wihr:1986"/>, e.g., hydrochloric acid, acetic acid, formic acid and hydrofluoric acid. These can lead to the formation of salts as the acid reacts with the substrate material.


=== Alkaline cleaning agents ===
=== Alkaline cleaning agents ===
   
   
These include sodium and ammonium bicarbonate and Na or K lye.   
These include sodium and ammonium bicarbonate and Na or K lye, i.e., sodium or potassium hydroxide.   


Carbonates may form due the application of alkaline agents. These then point to the corresponding salts. Further reactions, in the presence of [[nitrate]] and [[sulfate]], may also point to the related salts.  
Carbonates may form due to the application of alkaline agents such as sodium or potassium hydroxide that will react with the CO<sub>2</sub> from the atmosphere. These alkaline carbonates may react further in the presence or  [[nitrate]] and [[sulfate]], forming the corresponding salts.  


The presence of an alkali-containing building material may be concealed in the presence of "[[gypsum]]" within the pore solution, because, due to calcite precipitation, no [[natrite]] or [[thermonatrite]] efflorescence occurs, but [[thenardite]]/[[mirabilite]] efflorescence occurs instead. The simplified reaction has been approximately summarized in the following equation
The presence of an alkali-containing building material may be concealed in the presence of "[[gypsum]]" within the pore solution, because, due to calcite precipitation, no [[natrite]] or [[thermonatrite]] efflorescence occurs, but [[thenardite]]/[[mirabilite]] efflorescence occurs instead. The simplified reaction can represented by the following equation


Na<sub>2</sub>CO<sub>3</sub> + CaSO<sub>4</sub> → CaCO<sub>3</sub> ↓ + Na<sub>2</sub>SO<sub>4</sub>
Na<sub>2</sub>CO<sub>3</sub> + CaSO<sub>4</sub> → CaCO<sub>3</sub> ↓ + Na<sub>2</sub>SO<sub>4</sub>
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=== Neutralization reaction ===
=== Neutralization reaction ===


Neutralization is often carried out in the process of cleaning objects with alkaline detergents (or respectively acids). Hydrochloric acid, for example, is used for neutralizing some alkaline detergents. Apart from the fact that it is difficult to determine the success of neutralization on every part of the object, this process causes the formation of easily soluble salts, for example following this reaction:
Neutralization is often carried out in the process of cleaning objects with alkaline detergents (or respectively acids). Hydrochloric acid, for example, is used for neutralizing some alkaline detergents. Apart from the fact that it is difficult to determine the success of neutralization on every part of the object, this process causes the formation of easily soluble salts, such as sodium chloride as shown by the following reaction:


  NaOH + HCl → NaCl + H<sub>2</sub>O
  NaOH + HCl → NaCl + H<sub>2</sub>O
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<biblist/>
<biblist/>


[[Category:Origin of Salt]] [[Category:Schwarz,Hans-Jürgen]] [[Category:R-HSiedel]] [[Category:R-SLaue]] [[Category:inReview]]
[[Category:Origin of Salt]] [[Category:Schwarz,Hans-Jürgen]] [[Category:R-HSiedel]] [[Category:R-SLaue]] [[Category:approved]]

Latest revision as of 08:37, 2 December 2012

Author:Hans-Jürgen Schwarz
English Translation by Sandra Leithäuser


back to Origin of Salts

Restoration materials[edit]

Many restoration materials contribute to the salt contamination of objects. Sometimes they can even be the main source of damage.

The most relevant are the alkaline and acidic cleaning or restoration products such as:


Water glass[edit]

Water glass was used in the past to consolidate surfaces and was the precursor to the current silicate esters based consolidans. Water glass is a sodium (or potassium) silicate and the following reactions can be visualized schematically:

Na2SiO3 (Na-water glass) + CO2 + H2O  → SiO2 Gel + Na2CO3 


K2SiO3 (K-water glass) + CO2 + H2O → SiO2 Gel + K2CO3 

The resulting sodium carbonate can constitute up to 30% of the deposited material, and the potassium carbonate up to 20%.

Potassium carbonate is very hygroscopic and it is hardly ever found in its crystalline form. A subsequent reaction into potassium nitrate will lead to efflorescence of this latter salt.

Acids[edit]

Some acids are used to clean surfaces [Wihr:1986]Title: Restaurierung von Steindenkmälern. Ein Handbuch für Restauratoren, Steinbildhauer, Architekten und Denkmalpfleger.
Author: Wihr, Rolf
Link to Google Scholar
, e.g., hydrochloric acid, acetic acid, formic acid and hydrofluoric acid. These can lead to the formation of salts as the acid reacts with the substrate material.

Alkaline cleaning agents[edit]

These include sodium and ammonium bicarbonate and Na or K lye, i.e., sodium or potassium hydroxide.

Carbonates may form due to the application of alkaline agents such as sodium or potassium hydroxide that will react with the CO2 from the atmosphere. These alkaline carbonates may react further in the presence or nitrate and sulfate, forming the corresponding salts.

The presence of an alkali-containing building material may be concealed in the presence of "gypsum" within the pore solution, because, due to calcite precipitation, no natrite or thermonatrite efflorescence occurs, but thenardite/mirabilite efflorescence occurs instead. The simplified reaction can represented by the following equation

Na2CO3 + CaSO4 → CaCO3 ↓ + Na2SO4

Neutralization reaction[edit]

Neutralization is often carried out in the process of cleaning objects with alkaline detergents (or respectively acids). Hydrochloric acid, for example, is used for neutralizing some alkaline detergents. Apart from the fact that it is difficult to determine the success of neutralization on every part of the object, this process causes the formation of easily soluble salts, such as sodium chloride as shown by the following reaction:

NaOH + HCl → NaCl + H2O

Literature[edit]

[Wihr:1986] Wihr, Rolf (1986): Restaurierung von Steindenkmälern. Ein Handbuch für Restauratoren, Steinbildhauer, Architekten und Denkmalpfleger., München: CallweyLink to Google Scholar