Sodium silicate
From Free net encyclopedia
| Sodium metasilicate | |
|---|---|
| Image:Sodium silicate.jpg | |
| General | |
| Other names | Waterglass |
| Molecular formula | Na2SiO3 |
| Molar mass | 122.06 g/mol |
| Appearance | colorless solid |
| CAS number | [6834-92-0] |
| Properties | |
| Density and phase | 2.4 g/cm3, solid |
| Solubility in water | Soluble |
| Melting point | 1088 °C |
| Boiling point | ? °C (? K) |
| Thermodynamic data | |
| Standard enthalpy of formation ΔfH°solid | −1519 kJ/mol |
| Standard molar entropy S°solid | 113.8 J.K−1.mol−1 |
| Hazards | |
| EU classification | not listed |
| NFPA 704 | |
| Supplementary data page | |
| Structure and properties | n, εr, etc. |
| Thermodynamic data | Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| Regulatory data | Flash point, RTECS number, etc. |
| Related compounds | |
| Other anions | Sodium carbonate Sodium germanate Sodium stannate Sodium plumbate |
| Other cations | Potassium silicate |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references | |
Sodium silicate, also known as water glass or liquid glass, is a compound used in cements, textile and lumber processing.
Contents |
Properties
Sodium carbonate and silicon dioxide react when molten to form sodium silicate and carbon dioxide.
Sodium silicate is a white solid that is soluble in water, producing an alkaline solution. There are many kinds of this compound, including sodium orthosilicate, Na4SiO4; sodium metasilicate, Na2SiO3; sodium polysilicate, (Na2SiO3)n; sodium pyrosilicate, Na6Si2O7, and others. All are glassy, colourless and dissolve in water.
Sodium silicate is stable in neutral and alkaline solutions. In acidic solutions, the silicate ion reacts with hydrogen ions to form silicic acid, which when heated and roasted forms silica gel, a hard, glassy substance that absorbs water readily.
Metal repair
Sodium silicate is used, along with magnesium silicate in muffler repair paste. When dissolved in water, both sodium silicate, and magnesium silicate 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 somewhat permanent, brittle repair.
Automotive Repair
Sodium silicate can be used in older automobiles to seal leaks in the cooling system. A jar of "liquid glass" is poured into the radiator and allowed to circulate. Minute holes and gaps are sealed, often curing radiator leaks and faulty cylinder-head gaskets. This approach is often used by disreputable used-car salespersons.
Food preservation
Sodium silicate was also used as an egg preservation agent in the early 20th Century with large success. When fresh eggs are immersed in it, bacteria which cause the eggs to spoil are kept out and water is kept in. Eggs can be kept fresh using this method for up to nine months. When boiling eggs preserved this way, it is well advised to pin-prick the egg to allow steam to escape because the shell is no longer porous.
Timber Treatment
The use of sodium silicate as a timber treatment for pressure-treated wood actually began some time in the 19th century. It is suggested as an alternative for using silicate of potash (Potassium silicate), but that it is more expensive in a book called "Handy Farm Devices and How to Make Them" by Rolfe Cobleigh, published in 1910. Its use has become more well-known again in 2005, when an environmental scientist developed a method for rendering sodium silicate insoluable once the lumber has been treated with it. With or without the additonal process, treating wood with Sodium Silicate preserves wood from moisture and insects and possesses some flame-retardant properties. Sodium silicate treated lumber is considered a safer alternative to chromated copper arsenate (CCA), restricted by the EPA in 2004, and alkaline copper quaternary (ACQ), which corrodes non-galvanized nails and screws.
Concrete and General Masonry Treatment
Concrete treated with a Sodium Silicate solution helps to significantly reduce porosity in most masonry products such as concrete, stucco, plasters. A chemical reaction occurs with the excess CaOH in the concrete that permanently binds the silicates with the surface making them far more wearable and water repellent. It is generally advised to apply only after initial cure has taken place (7 days or so depending on conditions).