View source for Sodium silicate

{{Short description|Hygroscopic chemical compound of variable Na2O/SiO2 ratio precursor of waterglass}}
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[[File:Křemičitan sodný.PNG|thumb|Na<sub>2</sub>SiO<sub>3</sub>]]

'''Sodium silicate''' is a generic name for [[chemical compound]]s with the formula {{chem|Na|2''x''|Si|''y''|O|2''y''+''x''}} or {{chem|(|Na|2|O|)|''x''}}·{{chem|(SiO|2|)|''y''}}, such as [[sodium metasilicate]] ({{chem|Na|2|SiO|3}}), [[sodium orthosilicate]] ({{chem|Na|4|Si|O|4}}), and [[sodium pyrosilicate]] ({{chem|Na|6|Si|2|O|7}}). The anions are often [[polymer]]ic. These compounds are generally colorless transparent solids or white powders, and soluble in water in various amounts.

Sodium silicate is also the technical and common name for a mixture of such compounds, chiefly the metasilicate, also called '''waterglass''', '''water glass''', or '''liquid glass'''. The product has a wide variety of uses, including the formulation of [[cement]]s, coatings, [[passive fire protection]], textile and lumber processing, manufacture of [[refractory]] ceramics, as [[adhesives]], and in the production of [[silica gel]]. The commercial product, available in [[water solution]] or in solid form, is often greenish or blue owing to the presence of iron-containing impurities.

In industry, the various grades of sodium silicate are characterized by their SiO<sub>2</sub>:Na<sub>2</sub>O weight ratio (which can be converted to molar ratio by multiplication with 1.032). The ratio can vary between 1:2 and 3.75:1.<ref name=Ullmann>Gerard Lagaly, Werner Tufar, A. Minihan, A. Lovell "Silicates" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, 2005. {{doi|10.1002/14356007.a23_661}}</ref> Grades with ratio below 2.85:1 are termed alkaline. Those with a higher SiO<sub>2</sub>:Na<sub>2</sub>O ratio are described as neutral.

==History==
Soluble silicates of [[alkali]] metals (sodium or [[potassium]]) were observed by European [[alchemy|alchemists]] in the 16th century. [[Giambattista della Porta]] observed in 1567 that ''tartari salis'' (cream of tartar, [[potassium bitartrate]]) caused powdered ''crystallum'' (quartz) to melt at a lower temperature.<ref>{{cite book |last1=della Porta |first1=Giambattista |title=Magia naturalis sive de miraculis rerum naturalium, libri iiii |trans-title=Natural magic or on the miracles of nature, in four books |date=1569 |publisher=Guillaume Rouillé (Gulielmum Rovillium) |location=Lyon (''Lugdunum''), France |pages=290–291 |language=Latin}} See [https://books.google.com/books?id=Z9j1m8oXBlEC&pg=PA302 pp. 290–291], "''Crystallus, ut fusilis fiat''" (Quartz, so made molten)]</ref> Other possible early references to alkali silicates were made by [[Basil Valentine]] in 1520,<ref>{{cite journal |last1=Kohn |first1=C. |title=Die Erfindung des Wasserglas im Jahre 1520 |journal=Zeitschrift des Österreichischen Ingenieur-Vereines |trans-journal=Journal of the Austrian Engineer Association |date=1862 |volume=14 |pages=229–230 |trans-title=The invention of waterglass in the year 1520 |language=German |url=http://digital.onb.ac.at/OnbViewer/viewer.faces?doc=ABO_%2BZ228846906 }}</ref> and by [[Georgius Agricola|Agricola]] in 1550. Around 1640, [[Jan Baptist van Helmont]] reported the formation of alkali silicates as a soluble substance made by melting sand with excess alkali, and observed that the silica could be precipitated quantitatively by adding acid to the [[Solution (chemistry)|solution]].<ref>{{cite book |last1=van Helmont |first1=Johannes |title=Opuscula medica inaudita |date=1644 |publisher=Jost Kalckhoven (Jodocum Kalcoven) |location=Cologne, Germany |page=53 |language=Latin}} In Part I:  ''De Lithiasi'', [https://archive.org/details/bub_gb_GWOFpC0fDcAC/page/n51 page 53], van Helmont mentions that alkalis dissolve silicates:  "''Porro lapides, gemmae, arenae, marmora, silices, &c. adjuncto alcali, vitrificantur: sin autem plure alcali coquantur, resolvuntur in humido quidem: ac resoluta, facili negotio acidorum spirituum, separantur ab alcali, pondere pristini pulveris lapidum''." (Furthermore, stone, gems, sand, marble, silica, etc., become glassy by the addition of alkali: but if roasted with more alkali, they are dissolved in moisture: and the former weight of the stone powder is separated from the alkali and released by simply adding acid.)</ref>

In 1646, [[Johann Rudolf Glauber|Glauber]] made [[potassium silicate]], which he called ''liquor silicum'', by melting [[potassium carbonate]] (obtained by [[calcination|calcinating]] cream of tartar) and sand in a crucible, and keeping it molten until it ceased to bubble (due to the release of [[carbon dioxide]]). The mixture was allowed to cool and then was ground to a fine powder.<ref>{{cite book |last1=Glauber |first1=Johann Rudolf |title=Furni Novi Philosophici |trans-title=New Philosophical Furnace|date=1647 |publisher=Johann Fabel |location=Amsterdam, Netherlands |volume=2 |pages=136–137 |url=https://books.google.com/books?id=f-GomMQpnqYC&pg=PA136 |language=German}} See: ''"Wie durch Hülff eines reinen Sandes oder Kißlings auß Sale Tartari ein kräfftiger Spiritus kan erlanget werden."'' (How with the help of a pure sand or silica a powerful solution can be gotten from cream of tartar).</ref> When the powder was exposed to moist air, it gradually formed a viscous liquid, which Glauber called "''Oleum oder Liquor Silicum, Arenæ, vel Crystallorum''" (i.e., oil or solution of silica, sand or quartz crystal).<ref>(Glauber, 1647), [https://books.google.com/books?id=f-GomMQpnqYC&pg=PA138 p. 138]</ref>

However, it was later claimed that the substances prepared by those alchemists were not waterglass as it is understood today.<ref>{{cite journal |last1=Anon. |title=Die Erfindung des Wasserglases im Jahre 1520 |journal=Kunst- und Gewerbe-Blatt |date=1863 |volume=49 |pages=228–230 |url=https://books.google.com/books?id=ew8AAAAAMAAJ&pg=RA1-PA227 |trans-title=The invention of waterglass in the year 1520 |language=German}}
* Reprinted in:  {{cite journal |last1=Anon. |title=Die Erfindung des Wasserglases im Jahre 1520 |journal=Polytechnisches Journal |date=1863 |volume=168 |pages=394–395 |url=https://books.google.com/books?id=AAQ1AAAAMAAJ&pg=PA394 |trans-title=The invention of waterglass in the year 1520 |language=German}}
* Reprinted in:  {{cite journal |last1=Anon. |title=Die angebliche Erfindung des Wasserglases im Jahre 1520 |journal=Neues Repertorium für Pharmacie |date=1863 |volume=12 |pages=271–273 |url=https://books.google.com/books?id=uwQ9AAAAcAAJ&pg=PA27 |trans-title=The alleged invention of waterglass in the year 1520 |language=German}}</ref> That would have been prepared in 1818 by [[Johann Nepomuk von Fuchs]], by treating [[silicic acid]] with an alkali; the result being soluble in water, "but not affected by atmospheric changes".<ref>{{cite journal |last1=Nepomuk von Fuchs |first1=Johann |title=Ueber ein neues Produkt aus Kieselerde und Kali |journal=Archiv für die gesammte Naturlehre |date=1825 |volume=5 |issue=4 |pages=385–412 |url=https://books.google.com/books?id=-aE8AAAAYAAJ&pg=PA385 |trans-title=On a new product from silica and potash |language=German}} From page 386: ''"Ich erhielt es zuerst, vor ungefähr 7 Jahren"'' (I first obtained it about 7 years ago). 
* Reprinted in:  {{cite journal |last1=Nepomuk Fuchs |first1=Joh. |title=Ueber ein neues Produkt aus Kieselerde und Kali; und dessen nüzliche Anwendung als Schuzmittel gegen schnelle Verbreitung des Feuers in Theatern, als Bindemittel, firnißartigen Anstrichen u.s.w. |journal=Polytechnisches Journal |date=1825 |volume=17 |pages=465–481 |url=https://books.google.com/books?id=zbs-AAAAcAAJ&pg=PA465 |trans-title=On a new product from silica and potash; and its useful application as a protection against the rapid spread of fire in theaters, as a glue, varnish, etc. |language=German}}</ref>

The terms "water glass" and "soluble glass" were used by [[Leopold Wolff]] in 1846,<ref>{{cite book |last1=Wolff |first1=Leopold |title=Das Wasserglas: Seine Darstellung, Eigenschaften und seine mannichfache Anwendung in den technischen Gewerben |trans-title=Water-glass: its preparation, properties, and its manifold uses in technical commerce |date=1846 |publisher=Gottfried Basse |location=Quedlinburg and Leipzig, Germany |url=https://books.google.com/books?id=ajdkAAAAcAAJ |language=German}}</ref> by [[Emil Kopp|Émile Kopp]] in 1857,<ref>Emile Kopp (1857): "Sur la préparation et les propriétés du verre soluble ou des silicates de potasse et de soude; analyse de tous les travaux publiés jusqu'a ce jour sur ce sujet" (On the preparation and properties of soluble glass or the silicates of potash and soda; analysis of all works published until today on this subject). ''Le Moniteur scientifique'', volume 1, [https://books.google.com/books?id=zS5EAAAAYAAJ&pg=PA337 337–349], [https://books.google.com/books?id=zS5EAAAAYAAJ&pg=PA337 pages 366–391].</ref> and by [[Hermann Krätzer]] in 1887.<ref>{{cite book |last1=Krätzer |first1=Hermann |title=Wasserglas und Infusorienerde, deren Natur und Bedeutung für Industrie, Technik und die Gewerbe |trans-title=Water-glass and soluble earths, their nature and significance for industry, technology, and commerce |date=1887 |publisher=Hartleben |location=Vienna, Austria |url=https://books.google.com/books?id=CCZaAAAAYAAJ |language=German}}</ref>

In 1892, Rudolf Von Wagner distinguished [[soda glass|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.<ref>Von Wagner, Rudolf (1892; translation of 13th edition by Willian Crookes) ''Manual of Chemical Technology'' [https://archive.org/details/manualchemicalt00croogoog]</ref><ref>Von Wagner, ''Manual of Chemical Technology'' (1892 translation)</ref><ref>Hermann Mayer (1925): ''Das Wasserglas; Sein Eigenschaften, Fabrikation und Verwendung auf Grund von Erfahrungen und Mitteilungen der Firma Henkel & Cie''. (The Water-glass: Its properties, production, and application on the basis of experiences and communications of the firm of Henkel & Co.) Published by Vieweg, Braunschweig, Germany.</ref><ref>Morris Schrero (1922): [https://archive.org/details/waterglassabibl00schrgoog/page/n2 <!-- pg=1 --> ''Water-glass: A Bibliography'']. Published by Carnegie Library, Pittsburgh, Pennsylvania.</ref>

==Properties==
Sodium silicates are colorless glassy or crystalline solids, or white powders. Except for the most silicon-rich ones, they are readily soluble in water, producing [[alkaline]] solutions.{{Citation needed|date=September 2023}} When dried up it still can be rehydrated in water.<ref name=":0">{{Citation |title=The OxyChem Sodium Silicate Handbook |date=2019 |url=https://www.oxy.com/siteassets/documents/chemicals/products/other-essentials/silicate.pdf}}</ref>

Sodium silicates are stable in [[pH|neutral]] and [[alkaline]] solutions. In [[acidic]] solutions, the [[silicate]] ions react with hydrogen ions to form [[silicic acid]]s, which tend to decompose into [[hydrate]]d silicon dioxide [[gel]].{{citation needed|date=February 2024}} Heated to drive off the water, the result is a hard translucent substance called [[silica gel]], widely used as a [[desiccant]]. It can withstand temperatures up to 1100&nbsp;°C.{{Citation needed|date=September 2023}}

==Production==
Solutions of sodium silicates can be produced by treating a mixture of [[silica]] (usually as [[quartz sand]]), [[caustic soda]], and water, with hot steam in a [[chemical reactor|reactor]]. The overall reaction is
: 2''x'' NaOH + {{chem|Si|O|2}} → {{chem|(|Na|2|O|)|''x''}}·{{chem|SiO|2}} + ''x'' {{chem|H|2|O}}

Sodium silicates can also be obtained by dissolving [[silicon dioxide|silica]] {{chem|Si|O|2}} (whose [[melting point]] is 1713&nbsp;°C) in molten [[sodium carbonate]] (that melts with decomposition at 851&nbsp;°C):<ref name = "Greenwood">{{Greenwood&Earnshaw}}</ref>
: ''x'' {{chem|Na|2|CO|3}} + {{chem|SiO|2}} → {{chem|(|Na|2|O|)|''x''}}·{{chem|SiO|2}} + ''x'' {{chem|CO|2}}
The material can be obtained also from [[sodium sulfate]] (melting point 884&nbsp;°C) with [[carbon]] as a reducing agent:
: 2''x'' {{chem|Na|2|SO|4}} + C + 2 {{chem|SiO|2}} → 2 {{chem|(|Na|2|O|)|''x''}}·{{chem|Si|O|2}} + 2 {{chem|SO|2}} + {{chem|CO|2}}

In 1990, 4 million [[ton]]s of alkali metal silicates were produced.<ref name=Ullmann/>

=== Ferrosilicon ===
{{Further|Ferrosilicon#Hydrogen production}}
Sodium silicate may be produced as a part of [[hydrogen production]] by dissolving ferrosilicon in an [[Aqueous solution|aqueous]] [[sodium hydroxide]] (NaOH·H<sub>2</sub>O) solution:<ref>{{Cite journal |last1=Brack |first1=Paul |last2=Dann |first2=Sandie E. |last3=Wijayantha |first3=K. G. Upul |last4=Adcock |first4=Paul |last5=Foster |first5=Simon |date=November 2015 |title=An old solution to a new problem? Hydrogen generation by the reaction of ferrosilicon with aqueous sodium hydroxide solutions |journal=Energy Science & Engineering |language=en |volume=3 |issue=6 |pages=535–540 |doi=10.1002/ese3.94|s2cid=54929253 |doi-access=free |bibcode=2015EneSE...3..535B }}</ref>

: 2NaOH + Si + H<sub>2</sub>O → Na<sub>2</sub>SiO<sub>3</sub> + 2H<sub>2</sub>

=== Bayer process ===
Though unprofitable, Na<sub>2</sub>SiO<sub>3</sub> is a byproduct of [[Bayer process]] which is often converted to [[calcium silicate]] (Ca<sub>2</sub>SiO<sub>4</sub>).

== Uses ==
{{More citations needed section|date=December 2022}}

The main applications of sodium silicates are in detergents, paper industry (as a [[deinking]] agent), water treatment, and construction materials.<ref name=Ullmann/>

=== Adhesives ===

The adhesive properties of sodium silicate were noted as early as the 1850s<ref>{{Cite book |last=Commerce |first=Royal Society for the Encouragement of Arts, Manufactures and |url=https://books.google.com/books?id=wj1JAAAAcAAJ&pg=PA523 |title=Journal |date=1859 |publisher=RSA |language=en}}</ref> and have been widely used at least since the [[First World War]].<ref>{{Cite journal |last=Furness |first=Rex |date=1922-09-30 |title=Sodium silicate as an adhesive |url=https://onlinelibrary.wiley.com/doi/10.1002/jctb.5000411801 |journal=Journal of the Society of Chemical Industry |language=en |volume=41 |issue=18 |pages=381R–384R |doi=10.1002/jctb.5000411801|url-access=subscription }}</ref> The largest application of sodium silicate solutions is a cement for producing [[cardboard]].<ref name=Ullmann/> When used as a paper cement, the sodium silicate joint tends to crack within a few years, at which point it no longer holds the paper surfaces cemented together.

Sodium silicate solutions can also be used as a spin-on adhesive layer to bond glass to glass<ref name="Wang-1997">{{Cite journal|date=1997-12-15|title=Low temperature bonding for microfabrication of chemical analysis devices|url=https://www.sciencedirect.com/science/article/abs/pii/S0925400597002943|journal=Sensors and Actuators B: Chemical|language=en|volume=45|issue=3|pages=199–207|doi=10.1016/S0925-4005(97)00294-3|issn=0925-4005|last1=Wang|first1=H.Y|last2=Foote|first2=R.S|last3=Jacobson|first3=S.C|last4=Schneibel|first4=J.H|last5=Ramsey|first5=J.M|bibcode=1997SeAcB..45..199W |url-access=subscription}}</ref> or a silicon dioxide–covered silicon wafer to one another.<ref name="Puers-1997">{{Cite journal|last1=Puers|first1=R|last2=Cozma|first2=A|date=1997-09-01|title=Bonding wafers with sodium silicate solution|url=https://iopscience.iop.org/article/10.1088/0960-1317/7/3/008|journal=Journal of Micromechanics and Microengineering|volume=7|issue=3|pages=114–117|doi=10.1088/0960-1317/7/3/008|bibcode=1997JMiMi...7..114P|s2cid=250822654|issn=0960-1317|url-access=subscription}}</ref> Sodium silicate glass-to-glass bonding has the advantage that it is a low-temperature bonding technique, as opposed to fusion bonding.<ref name="Wang-1997" /> It also requires less processing than glass-to-glass anodic bonding,<ref name="Berthold-2000">{{Cite journal|date=2000-05-15|title=Glass-to-glass anodic bonding with standard IC technology thin films as intermediate layers|url=https://www.sciencedirect.com/science/article/abs/pii/S0924424799003763|journal=Sensors and Actuators A: Physical|language=en|volume=82|issue=1–3|pages=224–228|doi=10.1016/S0924-4247(99)00376-3|issn=0924-4247|last1=Berthold|first1=A.|last2=Nicola|first2=L.|last3=Sarro|first3=P.M.|author3-link=Lina Sarro|last4=Vellekoop|first4=M.J|bibcode=2000SeAcA..82..224B |url-access=subscription}}</ref> which requires an intermediate layer such as [[silicon nitride]] (SiN) to act as a diffusion barrier for sodium ions.<ref name="Berthold-2000" /> The deposition of such a layer requires a low-pressure chemical vapor deposition step.<ref name="Berthold-2000" /> A disadvantage of sodium silicate bonding, however, is that it is very difficult to eliminate air bubbles.<ref name="Puers-1997" /> This is in part because the technique does not require a vacuum and also does not use field assistance{{clarification needed|reason=define technical term "field assistance"|date=March 2024}} as in anodic bonding.<ref name="Springer US-2008">{{Cite book|url=https://doi.org/10.1007/978-0-387-48998-8|title=Encyclopedia of Microfluidics and Nanofluidics|date=2008|publisher=Springer US|isbn=978-0-387-32468-5|editor-last=Li|editor-first=Dongqing|location=Boston, MA|language=en-gb|doi=10.1007/978-0-387-48998-8}}</ref> This lack of field assistance can sometimes be beneficial, because field assistance can provide such high attraction between wafers as to bend a thinner wafer and collapse<ref name="Springer US-2008" /> onto nanofluidic cavity or MEMS elements.

=== Coatings ===

Sodium silicate may be used for various paints and coatings, such as those used on [[welding rod]]s. Such coatings can be cured in two ways. One method is to heat a thin layer of sodium silicate into a gel and then into a hard film. To make the coating water-resistant, high temperatures of {{convert|100|C|F K}} are needed.<ref name=":0" /> The temperature is slowly raised to {{convert|150|C|F K}} to dehydrate the film and avoid steaming and blistering. The process must be relatively slow, but infrared lamps may be used at first.<ref name=":0" /> In the other method, when high temperatures are not practical, the water resistance may be achieved by chemicals (or [[ester]]s), such as [[boric acid]], [[phosphoric acid]], [[sodium fluorosilicate]], and [[aluminium phosphate]].<ref name=":0" /> Before application, an aqueous solution of sodium silicate is mixed with a curing agent.<ref name=":0" />

It is used in detergent auxiliaries such as complex sodium disilicate and modified sodium disilicate. The detergent granules gain their ruggedness from a coating of silicates.<ref name=Ullmann/>

=== Water treatment ===

Sodium silicate is used as an alum coagulant and an iron [[flocculant]] in [[wastewater treatment]] plants. Sodium silicate binds to [[colloid]]al molecules, creating larger [[Flocculation|aggregates]] that sink to the bottom of the water column. The microscopic negatively charged particles suspended in water interact with sodium silicate. Their [[electrical double layer]] collapses due to the increase of [[ionic strength]] caused by the addition of sodium silicate (doubly negatively charged anion accompanied by two sodium cations) and they subsequently aggregate. This process is called [[coagulation]].<ref name=Ullmann/>

=== Foundries, refractories and pottery ===
{{Main|Sand casting#Sodium silicate}}
{{See also|Calcium silicate}}

It is used as a binder of the sand when doing [[sand casting]] of all common metals. It allows for the rapid production of a strong mold or core by three main methods.{{Citation needed|date=September 2023}}

* Method 1 requires passing carbon dioxide gas through the mixture of sand and sodium silicate in the sand molding box or core box. The carbon dioxide reacts with the sodium silicate to form solid silica gel and sodium carbonate.{{citation needed|date=March 2024}} This provides adequate strength to remove the now hardened sand shape from the forming tool. Additional strength occurs as any unreacted sodium silicate in the sand shape dehydrates.
* Method 2 requires adding an [[ester]] (reaction product of an acid and an alcohol) to the mixture of sand and sodium silicate before it is placed into the molding box or core box. As the ester hydrolyzes from the water in the liquid sodium silicate, an acid is released which causes the liquid sodium silicate to gel. Once the gel has formed, it will dehydrate to a glassy phase as a result of [[Syneresis (chemistry)|syneresis]]. Commonly used esters include acetate esters of glycerol and ethylene glycol as well as carbonate esters of propylene and ethylene glycol. The higher the water solubility of the ester, the faster the hardening of the sand.{{Citation needed|date=September 2023}}
* Method 3 requires microwave energy to heat and dehydrate the mixture of sand and sodium silicate in the sand molding box or core box. The forming tools must pass through microwaves for this to work well. Because sodium silicate has a high dielectric constant, it absorbs microwave energy very rapidly. Fully dehydrated sand shapes can be produced within a minute of microwave exposure. This method produces the highest strength of sand shapes bonded with sodium silicate.{{Citation needed|date=August 2024}}

Since the sodium silicate does not burn during casting (it can actually melt at pouring temperatures above 1800&nbsp;°F), it is common to add organic materials to provide for enhanced sand breakdown after casting. The additives include sugar, starch, carbons, wood flour and phenolic resins.

Water glass is a useful binder for solids, such as [[vermiculite]] and [[perlite]]. When blended with the latter lightweight fraction, water glass can be used to make hard, high-temperature insulation boards used for refractories, [[passive fire protection]], and high-temperature insulations, such as in moulded pipe insulation applications. When mixed with finely divided mineral powders, such as vermiculite dust (which is common scrap from the exfoliation process), one can produce high temperature adhesives. The intumescence{{clarification needed|reason=what intumescence? This has not previously been referred to|date=March 2024}} disappears in the presence of finely divided mineral dust, whereby the waterglass becomes a mere matrix. Waterglass is inexpensive and abundantly available, which makes its use popular in many refractory applications.

Sodium silicate is used as a [[deflocculant]] in casting slips helping reduce [[viscosity]] and the need for large amounts of water to liquidize the clay body. It is also used to create a crackle effect in pottery, usually wheel-thrown. A vase or bottle is thrown on the wheel, fairly narrow and with thick walls. Sodium silicate is brushed on a section of the piece. After five minutes, the wall of the piece is stretched outward with a rib or hand. The result is a wrinkled or cracked look.

It is also the main agent in "magic water", which is used when joining clay pieces, especially if the moisture level of the two differs.<ref>{{cite web | url=http://lakesidepottery.com/HTML%20Text/Tips/pottery-magic-mud-magic-water-paper-clay.htm | title=Ceramic, Pottery, Sculpture and Kintsugi Repair &#124; China repair and restoration }}</ref>

=== Dyes ===

Sodium silicate solution is used as a fixative for hand dyeing with [[reactive dyes]] that require a high pH to react with the textile fiber. After the dye is applied to a cellulose-based fabric, such as cotton or rayon, or onto silk, it is allowed to dry, after which the sodium silicate is painted on to the dyed fabric, covered with plastic to retain moisture, and left to react for an hour at room temperature.<ref>{{ cite web | last = Burch | first = Paula | title = Sodium silicate as a fixative for dyeing | date = March 22, 2010 | url = http://www.pburch.net/dyeing/FAQ/sodium_silicate.shtml | access-date = March 22, 2010}}</ref>

=== Repair work ===

Sodium silicate is used, along with [[magnesium silicate]], in [[muffler]] repair and fitting paste. Magnesium silicate can be mixed with a solution of sodium silicate to form a thick paste that is easy to apply. When the [[exhaust system]] of an internal combustion engine heats up to its [[operating temperature]], the heat drives out all of the excess water from the paste. The [[silicate]] compounds that are left over have glass-like properties, making a temporary, brittle repair that can be reinforced with glass fibre.{{citation needed|date=November 2024}}

Sodium silicate can be used to fill gaps in the [[head gasket]] of an engine. This is especially useful for [[aluminium alloy]] [[Cylinder head|cylinder heads]], which are sensitive to thermally induced surface deflection. Sodium silicate is added to the cooling system through the [[Radiator (engine cooling)|radiator]] and allowed to circulate. When the sodium silicate reaches its "conversion" temperature of {{Convert|100-105|C|F}}, it loses water molecules and forms a glass seal with a re-melting temperature above {{Convert|810|C|F}}. This repair can last two years or longer, and symptoms disappear instantly. However, this repair works only when the sodium silicate reaches its "conversion" temperature. Also, sodium silicate (glass particulate) contamination of lubricants is detrimental to their function, and contamination of engine oil is a serious possibility in situations in which a coolant-to-oil leak is present.

Sodium silicate solution is used to inexpensively, quickly, and permanently disable automobile engines. Running an engine with half a U.S. gallon (or about two liters) of a sodium silicate solution instead of [[motor oil]] causes the solution to [[Precipitated silica|precipitate]], catastrophically damaging the engine's bearings and pistons within a few minutes.<ref name="helliker">Helliker, Kevin. "[https://www.wsj.com/articles/SB124934376942503053#mod=loomia?loomia_si=t0:a16:g2:r5:c0.077553:b26935024 The Killer App for Clunkers Breathes Fresh Life Into 'Liquid Glass']" ''The Wall Street Journal'', 4 August 2009.</ref> In the United States, this procedure was used to comply with requirements of the [[Car Allowance Rebate System|Car Allowance Rebate System (CARS)]] program.<ref name="helliker" /><ref>[http://www.cars.gov/files/disposal-salvage/engine-disablement-procedures.pdf Engine Disablement Procedures for the CARS program] {{webarchive|url=https://web.archive.org/web/20101019102043/http://cars.gov/files/disposal-salvage/engine-disablement-procedures.pdf |date=2010-10-19 }}, cars.gov</ref>

=== Construction ===

A mixture of sodium silicate and [[sawdust]] has been used in between the double skin of certain [[safe]]s. This not only makes them more [[Fireproofing|fire resistant]], but also makes cutting them open with an [[oxyacetylene torch]] extremely difficult due to the [[smoke]] emitted.

Sodium silicate is frequently used in [[drilling fluid]]s to stabilize and avoid the collapse of [[borehole]] walls. It is particularly useful when drill holes pass through [[argillaceous]] [[Formation (stratigraphy)|formations]] containing swelling [[clay minerals]] such as [[smectite]] or [[montmorillonite]].

[[Concrete]] treated with a sodium silicate solution helps to reduce [[porosity]] in most [[masonry]] products such as [[concrete]], [[stucco]], and [[plaster]]s. This effect aids in reducing water penetration, but has no known effect on reducing water vapor transmission and emission.<ref>{{Cite web|url=http://www.sgh.com/sites/default/files/downloads/technicalbrief_alkali_silicate_based_admixtures.pdf|title=Home|access-date=2018-08-09|archive-date=2018-08-10|archive-url=https://web.archive.org/web/20180810011332/http://www.sgh.com/sites/default/files/downloads/technicalbrief_alkali_silicate_based_admixtures.pdf|url-status=dead}}</ref> A chemical reaction occurs with the excess Ca(OH)<sub>2</sub> ([[portlandite]]) present in the concrete that permanently binds the silicates with the surface, making them far more durable and water repellent. This treatment generally is applied only after the initial [[curing (chemistry)|cure]] has taken place (approximately seven days depending on conditions). These [[coating]]s are known as [[silicate mineral paint]]. An example of the reaction of sodium silicate with the calcium hydroxide found in concrete to form [[calcium silicate hydrate]] (CSH) gel, the main product in hydrated Portland cement, follows.<ref>JLR Thompson et al Characterization of Silicate Sealers on Concrete Cement and Concrete Research Vol. 27 No. 10 1997</ref>

:{{chem|Na|2|SiO|3}} + {{chem|y H|2|O|}} + {{chem|x Ca(OH)|2}} → {{chem|x CaO.SiO|2|.y H|2|O|}} + {{chem|2NaOH}}

=== Crystal gardens ===

When crystals of a number of metallic salts are dropped into a solution of water glass, simple or branching [[stalagmites]] of colored metal silicates are formed. This phenomenon has been used by manufacturers of toys and chemistry sets to provide instructive enjoyment to many generations of children from the early 20th century until the present. An early mention of crystals of metallic salts forming a "[[chemical garden]]" in sodium silicate is found in the 1946 ''Modern Mechanix'' magazine.<ref>{{cite journal|url=http://blog.modernmechanix.com/2006/07/21/magic-garden/|journal=Mechanix Illustrated|date=April 1946|page=88|title=Magic garden|access-date=2007-04-30|archive-date=2012-02-10|archive-url=https://web.archive.org/web/20120210145543/http://blog.modernmechanix.com/2006/07/21/magic-garden/|url-status=dead}}</ref>  Metal salts used included the sulfates and/or chlorides of copper, cobalt, iron, nickel, and manganese.

=== Sealants ===

Sodium silicate with additives was injected into the ground to harden it and thereby to prevent further leakage of highly radioactive water from the [[Fukushima I Nuclear Power Plant|Fukushima Daiichi nuclear power plant]] in Japan in April, 2011.<ref>[http://www.tepco.co.jp/en/press/corp-com/release/11040601-e.html Press Release] (TEPCO:2011.4.6)</ref> The residual heat carried by the water used for cooling the damaged reactors accelerated the setting of the injected mixture.

On June 3, 1958, the [[USS Nautilus (SSN-571)|USS ''Nautilus'']], the world's first nuclear submarine, visited Everett and Seattle. In Seattle, crewmen dressed in civilian clothing were sent in to secretly buy 140 quarts (160 liters) of an automotive product containing sodium silicate (originally identified as Stop Leak) to repair a leaking condenser system. The ''Nautilus'' was en route to the North Pole on a top secret mission to cross the North Pole submerged.<ref>Commander William R. Anderson with Clay Blair Jr., Nautilus 90 North (Cleveland and New York: The World Publishing Co., 1959), pp. 133–137; Commander William R. Anderson with Clay Blair Jr., Nautilus 90 North (New York: The New American Library, 1959), 89–90</ref>

=== Firearms ===

A historical use of the adhesive properties of sodium silicates is the production of [[paper cartridge]]s for black powder revolvers produced by [[Colt's Manufacturing Company]] between 1851 and 1873, especially during the [[American Civil War]]. Sodium silicate was used to seal combustible nitrated paper together to form a conical paper cartridge to hold the black powder, as well as to cement the lead ball or conical bullet into the open end of the paper cartridge. Such sodium silicate cemented paper cartridges were inserted into the cylinders of revolvers, thereby speeding the reloading of cap-and-ball black powder revolvers. This use largely ended with the introduction of Colt revolvers employing brass-cased cartridges starting in 1873.<ref name=kelley>{{Cite web |url=http://www.civilwarguns.com/9508.html |title=Making and using combustible paper pistol cartridges |author=Tom Kelley |date=August 1995 |access-date=2010-12-17 |archive-date=2008-03-27 |archive-url=https://web.archive.org/web/20080327194822/http://www.civilwarguns.com/9508.html |url-status=dead }}</ref><ref name=Kirst>{{cite book |author=Kirst, W.J. |title=Self consuming paper cartridges for the percussion revolver |place=Minneapolis, Minnesota |publisher=Northwest Development Co. |year=1983}}</ref> Similarly, sodium silicate was also used to cement the top wad into brass [[shotgun shell]]s, thereby eliminating any need for a crimp at the top of the brass shotgun shell to hold a shotgun shell together. Reloading brass shotgun shells was widely practiced by self-reliant American farmers during the 1870s, using the same waterglass material that was also used to preserve eggs. The cementing of the top wad on a shotgun shell consisted of applying from three to five drops of waterglass on the top wad to secure it to the brass hull. Brass hulls for shotgun shells were superseded by paper hulls starting around 1877. The newer paper-hulled shotgun shells used a roll crimp in place of a waterglass-cemented joint to hold the top wad in the shell. However, whereas brass shotshells with top wads cemented with waterglass could be reloaded nearly indefinitely (given powder, wad, and shot, of course), the paper hulls that replaced the brass hulls could be reloaded only a few times.

=== Food and medicine ===
[[File:"Raise More Poultry...on Farms and Back Yards...More Eggs and Poultry Will save Beef and Pork." - NARA - 512571.tif|thumb|World War I poster suggesting the use of waterglass to preserve eggs]]

Sodium silicate and other silicates are the primary components in "instant" wrinkle remover creams, which temporarily tighten the skin to minimize the appearance of wrinkles and under-eye bags. These creams, when applied as a thin film and allowed to dry for a few minutes, can present dramatic results. This effect is not permanent, lasting from a few minutes up to a couple of hours. It works like water cement, once the muscle starts to move, it cracks and leaves white residues on the skin.

Waterglass has been used as an egg preservative with large success, primarily when refrigeration is not available. Fresh-laid eggs are immersed in a solution of sodium silicate (waterglass). After being immersed in the solution, they are removed and allowed to dry. A permanent air tight coating remains on the eggs. If they are then stored in appropriate environment, the majority of bacteria which would otherwise cause them to spoil are kept out and their moisture is kept in. According to the cited source, treated eggs can be kept fresh using this method for up to five months. When boiling eggs preserved that way, the shell is no longer permeable to air, and the egg will tend to crack unless a hole in the shell is made (e.g., with a pin) in order to allow steam to escape.<ref>[https://www.motherearthnews.com/real-food/how-to-store-fresh-eggs-zmaz77ndzgoe How To Store Fresh Eggs]. motherearthnews.com</ref>

Sodium silicate's [[flocculant]] properties are also used to clarify wine and beer by precipitating colloidal particles. As a clearing agent, though, sodium silicate is sometimes confused with [[isinglass]] which is prepared from [[collagen]] extracted from the dried [[swim bladder]]s of [[sturgeon]] and other fishes. Eggs can be preserved in a bucket of waterglass gel, and their shells are sometimes also used (baked and crushed) to clear wine.<ref>SM Tritton (1956) ''Amateur wine making''.</ref>

Sodium silicate gel is also used as a substrate for algal growth in [[aquaculture]] hatcheries.<ref>{{Cite journal | doi=10.1021/j150528a013| title=Polymerization and Properties of Dilute Aqueous Silicic Acid from Cation Exchange| journal=The Journal of Physical Chemistry| volume=59| issue=6| pages=532–541| year=1955| last1=Bechtold| first1=M. F.}}</ref>

==See also==
* [[Precipitated silica]]
* [[Sodium carbonate]]
* [[Sodium stannate]]
* [[Sodium germanate]]

==References==
{{Reflist}}

==Further reading==
*Ashford's Dictionary of Industrial Chemicals, third edition, 2011, page 8369.

==External links==
{{Commons category|Sodium silicates}}
*[http://www.cees-silicates.eu Centre Européen d'Etudes des Silicates]
*[http://www.inchem.org/documents/icsc/icsc/eics1137.htm International Chemical Safety Card 1137]
*[http://chemsub.online.fr/name/silicic_acid,_sodium_salt.html ChemSub Online : Silicic acid, sodium salt]
*[http://chemsub.online.fr/name/sodium_metasilicate.html ChemSub Online : Sodium metasilicate]

{{Sodium compounds}}
{{Silicon compounds}}
{{Oxygen compounds}}
{{Glass science}}
{{Authority control}}

{{DEFAULTSORT:Sodium Silicate}}
[[Category:Cement]]
[[Category:Concrete]]
[[Category:Drilling technology]]
[[Category:Glass compositions]]
[[Category:Inorganic silicon compounds]]
[[Category:Sodium compounds]]
[[Category:Silicates]]