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Waterglass

Sodium silicate
Structural formula of polymeric sodium silicate
Ball and stick model of polymeric sodium silicate
Sample of sodium silicate in a vial
Names
IUPAC name
Sodium metasilicate
Other names
Liquid glass
Waterglass
Identifiers
6834-92-0 YesY
3D model (Jmol) Interactive image
Abbreviations E550
ChEBI CHEBI:60720 YesY
ChemSpider 21758 YesY
ECHA InfoCard 100.027.193
EC Number 229-912-9
MeSH Sodium+metasilicate
PubChem 23266
RTECS number VV9275000
UN number 3253
Properties
Na2SiO3
Appearance White to greenish opaque crystals
Density 2.61 g/cm3
Melting point 1,088 °C (1,990 °F; 1,361 K)
22.2 g/100 ml (25 °C)
160.6 g/100 ml (80 °C)
Solubility insoluble in alcohol
1.52
Thermochemistry
111.8 J/(K·mol)
113.71 J/(K·mol)
−1561.43 kJ/mol
−1427 kJ/mol
Hazards
Safety data sheet Avantor Performance Materials
Corrosive C
R-phrases R34, R37
S-phrases (S1/2), S13, S24/25, S36/37/39, S45
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Lethal dose or concentration (LD, LC):
LD50 (median dose)
1153 (rat, oral)
Related compounds
Other anions
Sodium carbonate
Other cations
Potassium silicate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
YesY  (what is YesYN ?)
Infobox references

Sodium silicate is the common name for compounds with the formula (Na2SiO2)nO. A well-known member of this series is sodium metasilicate, Na2SiO3. Also known as waterglass or liquid glass, these materials are available in aqueous solution and in solid form. The pure compositions are colourless or white, but commercial samples are often greenish or blue owing to the presence of iron-containing impurities.

They are used in cements, passive fire protection, textile and lumber processing, refractories, and automobiles. Sodium carbonate and silicon dioxide react when molten to form sodium silicate and carbon dioxide:

Anhydrous sodium silicate contains a chain polymeric anion composed of corner-shared {SiO4} tetrahedral, and not a discrete SiO32− ion. In addition to the anhydrous form, there are hydrates with the formula Na2SiO3·nH2O (where n = 5, 6, 8, 9), which contain the discrete, approximately tetrahedral anion SiO2(OH)22− with water of hydration. For example, the commercially available sodium silicate pentahydrate Na2SiO3·5H2O is formulated as Na2SiO2(OH)2·4H2O, and the nonahydrate Na2SiO3·9H2O is formulated as Na2SiO2(OH)2·8H2O.

In industry, the various grades of sodium silicate are characterized by their SiO2:Na2O weight ratio (weight ratios can be converted to molar ratios by multiplication with 1.032), which can vary between 2:1 and 3.75:1. Grades with this ratio below 2.85:1 are termed alkaline. Those with a higher SiO2:Na2O ratio are described as neutral.

Water glass was defined in Von Wagner's Manual of Chemical Technology (1892 translation) as any of the soluble alkaline silicates, first observed by Jean Baptist van Helmont around 1640 as a fluid substance made by melting sand with excess alkali.Glauber made what he termed "liquor silicum" in 1646 from potash and silica.Johann Nepomuk von Fuchs, in 1818, obtained what is now known as water glass by treating silicic acid with an alkali, the result being soluble in water, "but not affected by atmospheric changes". Von Wagner distinguished soda, potash, double (soda and potash), and fixing (i.e., stabilizing) as types of water glass. The fixing type was "a mixture of silica well saturated with potash water glass and a sodium silicate" used to stabilize inorganic water color pigments on cement work for outdoor signs and murals.


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