Difference between revisions of "Saturated salt solutions"

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== Description ==
 
== Description ==
  
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In a closed environment, saturated salt solutions can maintain an equilibrium with the moisture in the air. At low humidities, fully hydrated (liquid) salts can volatilize water. The solid salts can absorb moisture when the humidity is high.  
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In a closed environment, saturated salt solutions can maintain an equilibrium with the moisture in the air. At low humidity, fully hydrated (liquid) salts can volatilize water. The solid salts can absorb moisture when the humidity is high. Saturated salt solutions are a low maintenance method to provide a constant humidity level within a display case (Eggert 2022).  Unlike silica gel, which requires reconditioning, the saturated salt solutions only need supplemental distilled water added once a year.
  
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Percent relative humidities produced at 20 C (Greenspan 1977):
 
  
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- lithium chloride = 12.4  
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'''Relative Humidity % at Selected Temperatures'''
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{| class="wikitable"
 +
|-
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| Saturated Salt Solution
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| Chemical Formula
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| 68°F
 +
| 77°F
 +
| 86°F
 +
|-
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| [[Lithium chloride]]
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| LiCl H2O
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| 12. 4%
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| 12. 0%
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| 11.8%
 +
|-
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| [[Potassium acetate]]
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| CH3CO2K
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| 23. 3%
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| 22. 7%
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| 22.0%
 +
|-
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| [[Magnesium chloride]]
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| MgCl2 6H2O
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| 33. 6%
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| 33. 2%
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| 32.8%
 +
|-
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| [[Potassium carbonate]]
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| K2CO3 2H2O
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| 44. 0%
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| 43. 8%
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| 43.5%
 +
|-
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| [[Potassium nitrate]]
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| KNO3
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| 49. 0%
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| 48. 1%
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| 47.2%
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|-
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| [[Magnesium nitrate]]
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| Mg(NO3)2 6H20
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| 54. 9%
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| 53. 4%
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| 52.0%
 +
|-
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| [[Sodium nitrate]]
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| NaNO3
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| 65. 3%
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| 64. 3%
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| 63.3%
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|-
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| [[Sodium chloride]]
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| NaCl
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| 75. 5%
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| 75. 8%
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| 75.6%
 +
|-
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| [[Ammonium sulfate]]
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| (NH4)2SO4
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| 80. 6%
 +
| 80. 3%
 +
| 80.0%
 +
|-
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| [[Potassium nitrate]]
 +
| KNO3
 +
| 93. 2%
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| 92. 0%
 +
| 90.7%
 +
|-
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| [[Potassium sulfate]]
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| K2SO4
 +
| 97. 2%
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| 96. 9%
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| 96.6%
 +
|}
  
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- potassium acetate = 23.3
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Table obtained from Technical Bulletin No. 5, Creating and Maintaining Humidities by Salt Solutions. Hygrodynamics, Inc.
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- magnesium chloride = 33.6
 
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- potassium carbonate = 44
 
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- potassium nitrite = 49
 
−
 
 
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- magnesium nitrate = 54.9
 
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- sodium nitrite = 65.3
 
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- sodium chloride = 75.5  
 
−
 
 
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- ammonium sulfate = 80.6
 
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- potassium nitrate = 93.2
 
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- potassium sulfate = 97.2
 
  
 
== Synonyms and Related Terms ==
 
== Synonyms and Related Terms ==
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salt solutions
 
salt solutions
  
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== Additional Information ==
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==Collection Risks==
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L. Greenspan "Humidity Fixed Points of Binary Saturated Aqueous Solutions" ''J. Research of the NBS'', Vol 81A, No. 1 1977.
 
  
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== Authority ==
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* Magnesium chloride can release chlorine
  
 +
== Resources and Citations ==
 +
* G. Eggert, "Saturated salt solutions in showcases: humidity control and pollutant absorption", ''Herit Sci'' 10, 54 (2022). https://doi.org/10.1186/s40494-022-00689-3
 +
* AIC Conservation Wiki: [https://www.conservation-wiki.com/wiki/Category:Exhibit_Technical_Notes Exhibit Technical Notes: Environmental Control]
 +
* Exhibit Guidelines Technical Note: [https://www.conservation-wiki.com/wiki/Conditioning_Silica_Gel_with_a_Saturated_Salt_Solution Conditioning Silica Gel with a Saturated Salt Solution]
 +
* L. Greenspan "Humidity Fixed Points of Binary Saturated Aqueous Solutions" ''J. Research of the NBS'', Vol 81A, No. 1 1977.
 
* Hermann Kuhn, ''Conservation and Restoration of Works of Art and Antiquities'', Butterworths, London, 1986
 
* Hermann Kuhn, ''Conservation and Restoration of Works of Art and Antiquities'', Butterworths, London, 1986
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* Pam Hatchfield, ''Pollutants in the Museum Environment'', Archetype Press, London, 2002
 
* Pam Hatchfield, ''Pollutants in the Museum Environment'', Archetype Press, London, 2002
  
  
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[[Category:Materials database]][[Category: MWG]][[Category: Climate/Environment]]
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[[Category:Materials database]]
 

Latest revision as of 10:42, 20 July 2023

Description

In a closed environment, saturated salt solutions can maintain an equilibrium with the moisture in the air. At low humidity, fully hydrated (liquid) salts can volatilize water. The solid salts can absorb moisture when the humidity is high. Saturated salt solutions are a low maintenance method to provide a constant humidity level within a display case (Eggert 2022). Unlike silica gel, which requires reconditioning, the saturated salt solutions only need supplemental distilled water added once a year.


Relative Humidity % at Selected Temperatures

Saturated Salt Solution Chemical Formula 68°F 77°F 86°F
Lithium chloride LiCl H2O 12. 4% 12. 0% 11.8%
Potassium acetate CH3CO2K 23. 3% 22. 7% 22.0%
Magnesium chloride MgCl2 6H2O 33. 6% 33. 2% 32.8%
Potassium carbonate K2CO3 2H2O 44. 0% 43. 8% 43.5%
Potassium nitrate KNO3 49. 0% 48. 1% 47.2%
Magnesium nitrate Mg(NO3)2 6H20 54. 9% 53. 4% 52.0%
Sodium nitrate NaNO3 65. 3% 64. 3% 63.3%
Sodium chloride NaCl 75. 5% 75. 8% 75.6%
Ammonium sulfate (NH4)2SO4 80. 6% 80. 3% 80.0%
Potassium nitrate KNO3 93. 2% 92. 0% 90.7%
Potassium sulfate K2SO4 97. 2% 96. 9% 96.6%

Table obtained from Technical Bulletin No. 5, Creating and Maintaining Humidities by Salt Solutions. Hygrodynamics, Inc.

Synonyms and Related Terms

salt solutions

Collection Risks

  • Magnesium chloride can release chlorine

Resources and Citations

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