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Sodium silicate is a generic name for chemical compounds with the formula or ·, such as sodium metasilicate (), sodium orthosilicate (), and sodium pyrosilicate (). The anions are often . 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 , 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 SiO2:Na2O 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.Gerard Lagaly, Werner Tufar, A. Minihan, A. Lovell "Silicates" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, 2005. Grades with ratio below 2.85:1 are termed alkaline. Those with a higher SiO2:Na2O ratio are described as neutral.
In 1646, Glauber made potassium silicate, which he called liquor silicum, by melting potassium carbonate (obtained by calcination 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. 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). 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).(Glauber, 1647), p. 138
However, it was later claimed that the substances prepared by those alchemists were not waterglass as it is understood today.
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". From page 386: "Ich erhielt es zuerst, vor ungefähr 7 Jahren" (I first obtained it about 7 years ago).
The terms "water glass" and "soluble glass" were used by Leopold Wolff in 1846, by Emil Kopp in 1857,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, 337–349, pages 366–391. and by Hermann Krätzer in 1887.
In 1892, Rudolf Von Wagner distinguished soda glass, 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.Von Wagner, Rudolf (1892; translation of 13th edition by Willian Crookes) Manual of Chemical Technology [6]Von Wagner, Manual of Chemical Technology (1892 translation)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.Morris Schrero (1922): Water-glass: A Bibliography. Published by Carnegie Library, Pittsburgh, Pennsylvania.
Sodium silicates are stable in neutral and alkaline solutions. In acidic solutions, the silicate ions react with hydrogen ions to form , which tend to decompose into silicon dioxide gel. 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 °C.
Sodium silicates can also be obtained by dissolving silicon dioxide (whose melting point is 1713 °C) in molten sodium carbonate (that melts with decomposition at 851 °C):
In 1990, 4 million of alkali metal silicates were produced.
Sodium silicate solutions can also be used as a spin-on adhesive layer to bond glass to glass or a silicon dioxide–covered silicon wafer to one another. Sodium silicate glass-to-glass bonding has the advantage that it is a low-temperature bonding technique, as opposed to fusion bonding. It also requires less processing than glass-to-glass anodic bonding, which requires an intermediate layer such as silicon nitride (SiN) to act as a diffusion barrier for sodium ions. The deposition of such a layer requires a low-pressure chemical vapor deposition step. A disadvantage of sodium silicate bonding, however, is that it is very difficult to eliminate air bubbles. This is in part because the technique does not require a vacuum and also does not use field assistance as in anodic bonding. 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 onto nanofluidic cavity or MEMS elements.
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.
Since the sodium silicate does not burn during casting (it can actually melt at pouring temperatures above 1800 °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 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.
Sodium silicate can be used to fill gaps in the head gasket of an engine. This is especially useful for aluminium alloy Cylinder head, which are sensitive to thermally induced surface deflection. Sodium silicate is added to the cooling system through the radiator and allowed to circulate. When the sodium silicate reaches its "conversion" temperature of , it loses water molecules and forms a glass seal with a re-melting temperature above . 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 precipitate, catastrophically damaging the engine's bearings and pistons within a few minutes.Helliker, Kevin. " The Killer App for Clunkers Breathes Fresh Life Into 'Liquid Glass'" The Wall Street Journal, 4 August 2009. In the United States, this procedure was used to comply with requirements of the Car Allowance Rebate System (CARS) program. Engine Disablement Procedures for the CARS program , cars.gov
Sodium silicate is frequently used in to stabilize and avoid the collapse of borehole walls. It is particularly useful when drill holes pass through argillaceous 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 . This effect aids in reducing water penetration, but has no known effect on reducing water vapor transmission and emission. A chemical reaction occurs with the excess Ca(OH)2 (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 cure has taken place (approximately seven days depending on conditions). These 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.JLR Thompson et al Characterization of Silicate Sealers on Concrete Cement and Concrete Research Vol. 27 No. 10 1997
On June 3, 1958, the 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.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
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. How To Store Fresh Eggs. motherearthnews.com
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 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.SM Tritton (1956) Amateur wine making.
Sodium silicate gel is also used as a substrate for algal growth in aquaculture hatcheries.
Ferrosilicon
Sodium silicate may be produced as a part of hydrogen production by dissolving ferrosilicon in an Aqueous solution sodium hydroxide (NaOH·H2O) solution:
Bayer process
Though unprofitable, Na2SiO3 is a byproduct of Bayer process which is often converted to calcium silicate (Ca2SiO4).
Uses
The main applications of sodium silicates are in detergents, paper industry (as a deinking agent), water treatment, and construction materials.
Adhesives
The adhesive properties of sodium silicate were noted as early as the 1850s and have been widely used at least since the First World War. The largest application of sodium silicate solutions is a cement for producing cardboard. 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.
Coatings
Sodium silicate may be used for various paints and coatings, such as those used on . 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 are needed. The temperature is slowly raised to to dehydrate the film and avoid steaming and blistering. The process must be relatively slow, but infrared lamps may be used at first. In the other method, when high temperatures are not practical, the water resistance may be achieved by chemicals (or ), such as boric acid, phosphoric acid, sodium fluorosilicate, and aluminium phosphate. Before application, an aqueous solution of sodium silicate is mixed with a curing agent.
Water treatment
Sodium silicate is used as an alum coagulant and an iron flocculant in wastewater treatment plants. Sodium silicate binds to molecules, creating larger Flocculation 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.
Foundries, refractories and pottery
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.
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.
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.
Construction
A mixture of sodium silicate and sawdust has been used in between the double skin of certain . This not only makes them more Fireproofing, but also makes cutting them open with an oxyacetylene torch extremely difficult due to the smoke emitted.
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. 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 Daiichi nuclear power plant in Japan in April, 2011. Press Release (TEPCO:2011.4.6) The residual heat carried by the water used for cooling the damaged reactors accelerated the setting of the injected mixture.
Firearms
A historical use of the adhesive properties of sodium silicates is the production of 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. Similarly, sodium silicate was also used to cement the top wad into brass , 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
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.
See also
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