Water glass

The title of this article is ambiguous. Water glass can also refer to a drinking vessel, see drinking glass .

Sample of sodium metasilicate Na ₂ SiO ₃

Section from the chain structure of sodium metasilicate

When water glass is solidified from a melt glassy, ie amorphous , water-soluble sodium , potassium and lithium silicate or referred to their aqueous solutions. Depending on whether predominantly sodium, potassium or lithium silicates are included, one speaks of sodium silicate , potassium silicate or lithium water glass .

The drying of an aqueous solution of water glass begins with the evaporation of water and is followed by the formation of water-insoluble silica (silicification). The silicification of water glass is irreversible, which means that water glass is not created again by adding water to the silica.

history

After von Helmond discovered the more easily soluble silica moisture in 1640 , the water glass was first produced in 1818 by the chemist and mineralogist Johann Nepomuk von Fuchs ; Fuchs also gave the new connection its name. Together with Franz Xaver Pettenkofer , during the reconstruction of the Royal Court and National Theater , which burned down in 1823, he developed a process to reduce the flammability of wood. They came up with the idea of ​​covering decorations and scaffolding with water glass. Later they also treated painted backdrops with the fire retardant, but found that it caused paint damage. So they set about mixing waterglass with inorganic color pigments . The new painting process was later named stereochromy . “The church and history painter Josef Schlotthauer (1789–1869) created the first larger paintings with water glass paints”.

Manufacturing

To produce solid water glasses ( solid glasses ) , mixtures of quartz sand and potassium carbonate (for potash water glass ) or sodium carbonate (for soda water glass ) are fused with CO ₂ evolution at 1100 ° C to 1200 ° C:

${\displaystyle \mathrm {M_{2}CO_{3}+{\mathit {n}}\ SiO_{2}\longrightarrow M_{2}O\cdot {\mathit {n}}\ SiO_{2}+CO_{2}\uparrow } }$ ... (M = alkali metal)

The general formula M ₂ O · n SiO _2, which is dependent on the composition of the mixture, is technically important water glasses in the range between n equals 1 to 4. As a rule, the molar or mass ratio of SiO ₂ to Na ₂ O for a water glass or SiO _{2 given} to K ₂ O. Soda waterglass (see also sodium silicates ) with a molar ratio of 3.4 to 3.5 is the most important part in terms of quantity. The density is still often given in the outdated unit degree Baumé .

The cooled glass is ground to a powder. By dissolving it in water at high temperatures (e.g. 150 ° C at 5 bar pressure), liquid water glass ( liquid glass ) is obtained as a clear, colloidal alkaline solution or as an alkaline gel (gelatinous to solid mass).

use

Liquid water glass ( liquid potassium / sodium silicate , liquid glass , liquor silicon ) is mostly used . Soda water glass is not suitable for permanent moisture protection because, unlike potassium water glass, it gradually dissolves after a long period of time. In ceramics , water glass serves as an electrolyte to liquefy a ceramic mass . It is also used as an adhesive (e.g. for sticking ivory plates on piano keys), as a stabilizer for bleaching liquors in the textile and paper industry , as a binder (e.g. for mineral paints ), as an additive in welding electrodes , in detergents To protect components of washing machines from corrosion , as a seal for masonry, landfills and underground construction , to protect natural stones from the weather, in sol-gel processes and as a plant strengthener in organic agriculture . In microbiology , water glass is used as a substitute for agar , which hydrolyzes in the acidic pH range , in the production of solid nutrient media for the cultivation of acidophilic bacteria. In foundry technology, water glass is used to harden sand molds and cores.

Water glass is traditionally used in construction

• for hardening and sealing of plaster and masonry as well as for the protection of natural stones from the weather by silicification . Depending on the absorbency of the surface, it is diluted with two parts of water, for example, and applied in an amount of approx. 120 to 380 ml per square meter.
• to close the pores of the near-surface layers of screed and concrete. The wear resistance can be increased by up to 15%, the formation of dust is reduced and the capillary water absorption decreases by around 80%. Lithium water glass is significantly more expensive than sodium or potassium water glass, but has the following advantages: Its water solubility and alkalinity are lower. This reduces the likelihood that silica will separate from the cement paste and cause expansion through the formation of alkali silicate or calcium silicate hydrate gel, which leads to the loosening of the surface and the formation of cracks. The viscosity is lower, which increases the depth of penetration. The silicate structures are larger and network more completely, which improves the sealing of the concrete surface. The reaction with hydrated lime takes place more slowly, which means that the lithium waterglass can be distributed more evenly in the pores.
• As an additive for lime paints to improve their adhesion as well as smear and water resistance on substrates containing silicate
• for the production of an anti-mold paint to which a five percent borax solution is added
• as a wood preservative and reducing the flammability of construction timber; painting over is generally possible after a drying time of two to five days
• for gluing tiles to walls and tiled stoves; Adhesion can already occur after 10 minutes

In the preservation and restoration of wall paintings , stone sculptures and objects, water glass was used as a strengthening agent. Due to its often low penetration depth and the possible formation of salts (alkali carbonates in connection with carbon dioxide from the air), it is no longer used to strengthen stone. Potassium silicate is still used as a binding agent for strongly colored, water-resistant paints and coatings (mineral paints) on substrates containing silicate.

In foundry technology , water glass can be used as a binder for sand molds . The hardening is usually accelerated by artificial fumigation with carbon dioxide .

In dental technology , water glass is used as a binding agent in the production of fine investment materials for casting model cast prostheses .

In the home, water glass can be used to seal vases and pottery and as an adhesive for paper on metal and glass.

A common method of preservation before the proliferation of refrigerators , e.g. B. for laying eggs , is also based on water glass: You stir a certain amount of the alkali silicate solution in water (usually 1 part water glass to 9 parts water) and whip the mixture with a whisk . After a while the solution will become gelatinous / semi-solid. The cleaned eggs are laid in this solution. The effect of this preservation method is based on the fact that the pores of the egg shell are filled, so that the egg is protected from the ingress of water, air and microorganisms.

Water glass (especially as sodium silicate) can be used to create “ magical crystal gardens ”. To do this, water glass is mixed with various metal salt crystals. As a result, colored, stem-like structures grow out of the crystals. From a chemical point of view this is a consequence of the polymerization of the sodium silicate ions under the influence of the metal ions serving as Lewis acids ; the color of the structure is created by the substitution of sodium ions by other metal ions. The colored projections can be similar to stalactite or stalagmite , depending on whether the crystals sink or float on the surface. It should be noted that the shape of the structures is roughly reminiscent of the stalactite formations given and that the distribution (top / bottom) is reversed. The upward growth of these structures is due to the fact that the polymer acts like a semi-permeable membrane that encloses the highly concentrated metal salt solution; the growth accordingly results from the continuous tearing of this membrane at the point where it is thinnest (above).

In the USA , the chemical is currently used to demonstrably make combustion engines to be scrapped unusable before claiming a state scrapping bonus ( scrapping obligation ). It does this by replacing the motor oil with an aqueous sodium silicate solution.

Water glass is a component of the so-called smoke paste , with which the head bore of many tobacco pipes made of briar is lined in order to protect the wood the first time you smoke.

In April 2011, a water glass-based sealant was used to close a leak at the damaged Japanese nuclear power plant Fukushima I , from which highly contaminated water leaked into the sea.

Web links

Wiktionary: water glass  - explanations of meanings, word origins, synonyms, translations

• Water glass. Entry in Meyer's Large Konversations-Lexikon , 6th edition, 1905–1909, available online at Zeno.org
• Safety data sheet Potash water glass (PDF; 323 kB)
• Safety data sheet soda water glass (PDF)
• OECD : Screening Information Dataset (SIDS) Initial Assessment Report (SIAR) for Disodium silicate, pentahydrate

Individual evidence

1. ↑ ^{a b} water glass. In: Angela Weyer et al. (Ed.): EwaGlos. European Illustrated Glossary Of Conservation Terms For Wall Paintings And Architectural Surfaces . English Definitions with translations into Bulgarian, Croatian, French, German, Hungarian, Italian, Polish, Romanian, Spanish and Turkish. Michael Imhof, Petersberg 2015, ISBN 978-3-7319-0260-7 , p. 402 , doi : 10.5165 / hawk-hhg / 233 ( download ).
2. ^ Zeno.org: pebble moisture
3. ↑ Fraunhofer IRB: Chemistry and Properties of Water Glass ( Memento from January 4, 2012 in the Internet Archive )
4. ↑ Entry on water glass. In: Römpp Online . Georg Thieme Verlag, accessed on April 9, 2011.
5. ^ Walter Ackermann: Johann Nepomuk Fuchs (1774-1856). Mineralogist and chemist. Die Oberpfalz, 2018, 106th year, pp. 92–96.
6. ↑ Salzgitter aktuell: Water glass: Binder for mortar and concrete ( Memento from April 26, 2014 in the Internet Archive )
7. ↑ Soluble Silicate Manufacture (English) ( Memento of October 14, 2008 in the Internet Archive ) (PDF; 26 kB)
8. ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 91st – 100th, improved and greatly expanded edition. Walter de Gruyter, Berlin 1985, ISBN 3-11-007511-3 , p. 779.
9. ↑ SA Wyrzgol: What you should know about water glass ( Memento from July 17, 2013 in the Internet Archive ) (PDF; 176 kB), Obtego AG, Neufahrn
10. ↑ B.‐Y. Youn, Final Report Assessment of the Effectiveness of Water Glass to Improve the Wear Resistance of Industrial Floors , Chair for Building Materials Technology, Ruhr University Bochum, Fraunhofer IRB Verlag, 2010.
11. ↑ F. Gaboriaud et al., J. Phys. Chem. B 1999, 103, 2091-2099
12. ↑ DerStandard : Killer Chemistry Brings New Market to Life, August 11, 2009.
13. ↑ Water glass seals leak in Fukushima. Report to Deutschlandfunk from April 6, 2011.
14. ↑ Out flow of fluid containing radioactive materials to the ocean from areas near intake channel of Fukushima Daiichi Nuclear Power Station Unit 2 (continued report) ( Memento from April 24, 2011 on WebCite ) (English, pdf). Tepco, April 6, 2011, archived from the original , retrieved May 17, 2011.