Sodium silicate

As water glass solidified from a melt, glass-like, ie, amorphous, water-soluble sodium, potassium and lithium silicates or their aqueous solutions respectively. Depending on whether mainly sodium, potassium or lithium silicates are included, one speaks of sodium silicate, potassium or lithium water glass.

History

After Helmond already 1640, the readily soluble pebble humidity discovered the water glass was first produced in 1818 by the chemist and mineralogist Johann Nepomuk von Fuchs; Fuchs gave the new compound its name. " The first major painting with water colors of glass created by the churches and historical painter Josef Schlotthauer (1789-1869) ".

Production

For the preparation of solid water glass ( hard glass ) are mixture of quartz sand and potassium carbonate ( for potassium silicate ) and sodium carbonate ( for sodium silicate ) under CO2 evolution at 1100 ° C to 1200 ° C merged:

Which depends on the composition of the mixture, general formula M 2 O · n SiO2 of industrially important glasses of water is approximately in the range between n = 1 to 4 In general, for a glass of water, the molar or mass ratio of SiO2 to Na2O and SiO2 to K2O specified. Sodium silicate ( see also sodium silicates ) with the molar ratio of 3.4 to 3.5 is the quantitatively most important part.

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

Use

For use comes mostly liquid water glass (liquid Kalium-/Natriumsilicat, Liquid Glass, LIQVOR SILICIVM ). Sodium silicate is not suitable for permanent moisture protection, because it is in contrast to potassium silicate " after some time " gradually dissolves. In the ceramic water glass is used as the electrolyte for the liquefaction of a ceramic mass. Use it also for example as an adhesive ( eg for attaching the ivory plates on piano keys ), as a stabilizer of bleaching liquors in the textile industry and paper industry, as a binder (eg, mineral colors), as an additive in welding electrodes, in detergents to protect components of washing machines from corrosion, as a seal on masonry, landfills and underground work for the protection of natural stones from the weather, in sol- gel processes and as a plant tonic in organic farming. In microbiology, water glass as a substitute for agar is hydrolyzed in the acidic pH range employed in the production of solid nutrient media for growing acid- loving ( acidophilic ) bacteria. In the foundry industry to use water glass for hardening sand molds and cores.

In construction, water glass is traditionally uses

• For consolidating 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 substrate it is diluted with two parts water, for example, and is applied in an amount of about 120 to 380 ml per square meter.
• For even filling of the ( small ) cavities of the concrete surface by lithium water glass
• As an additive for lime paints to improve their adhesion and smudge, and water resistance,
• For the production of an anti- mildew paint, which is still added a 5% borax solution
• For the preservation and reducing the flammability of timber; a sweep is generally complete after a drying time of 2 to 5 days is possible,
• For bonding tiles to walls and tiled stoves. An adhesion can occur after only 10 minutes.

In household water glass can be used for sealing of vases and pottery and as an adhesive for paper to metal and glass.

A common prior to the dissemination of refrigerators preservation method, eg for inserting eggs is also based on water glass: It is stirred for a certain amount of alkali metal silicate solution in water ( usually 1 part water glass to 9 parts water) and proposes the mixture with a whisk on. After a while, the solution is then gelatinous / semi-solid. In this solution, the purified eggs are inserted. The effect of this method of preservation based on the fact that the pores of the egg shell are filled, and the shell is thereby protected against penetration of germs and water or air.

End of the twentieth century water glass was often used (especially as sodium silicate ) in " magic crystal gardens ". These water glass was mixed with various metal salt crystals, with colored stalk -like structure of the crystals grew out. Chemically, this is a consequence of the polymerization of the sodium silicate ions under the influence of the Lewis acid serves as a metal ion; the color of the structure is formed by the substitution of sodium ions by other metal ions. The colored extensions can be both stalaktit as well stalagmitähnlich, depending on whether the crystals sink to the bottom or float on the surface. It should be noted that the structures are similar to the specified stalactite formations only in the form, and that in this case the distribution ( top / bottom) is reversed. The pursuit of these structures grow up, caused by the fact that the polymer acts as a semipermeable membrane, which includes the highly concentrated metallic salt solution; growth arises accordingly by a continuous ' burst ' of this membrane at the point where it is thinnest (top).

In the U.S., the chemical is currently used to make scrapping engines, before using any government scrapping premium actually proven useless ( scrapping compulsory ). This is done by the engine oil is replaced by an aqueous sodium silicate solution.

In April 2011, a sealant on water glass base to seal a leak on the damaged Japanese nuclear power plant Fukushima I was used resigned from the highly contaminated water into the sea.