Sodium Silicate: Overview and Applications

Sodium silicate, commonly known as waterglass, is a chemical compound with the general formula Na_2xSi_yO_{2y x} or (Na_2O)_x·(SiO₂)_y. This compound family includes sodium metasilicate (Na₂SiO₃), sodium orthosilicate (Na₄SiO₄), and sodium pyrosilicate (Na₆Si₂O₇). These compounds are typically colorless transparent solids or white powders that dissolve in water to varying extents. Sodium silicate solutions and solids are widely used in various industrial applications.

Historical Background

The study and use of sodium silicate date back to the 1500s when European alchemists began to explore alkali metal silicates. Notable early observations include Giambattista della Porta's 1567 finding that tartaric acid could melt quartz at lower temperatures and Johann Nepomuk von Fuchs's 1818 preparation of waterglass as understood today.

Properties

Sodium silicates are colorless or white crystalline solids that dissolve readily in water, forming alkaline solutions. They are stable in neutral and alkaline environments but form silicic acids in acidic solutions, which decompose into hydrated silicon dioxide gel. This gel can be heated to produce silica gel, a desiccant that withstands temperatures up to 1100°C.

Production

Sodium silicates are produced by combining silica (sand), caustic soda, and water in a reactor under hot steam. Alternatively, they can be synthesized by dissolving silica in molten sodium carbonate or from sodium sulfate with a reducing agent like carbon.

Applications

Industrial Uses

Adhesives: Sodium silicate is used as a cement for cardboard production and as a spin-on adhesive for bonding glass and silicon oxide surfaces.

Coatings: Sodium silicate serves as a binder for various paints and coatings, which can be cured by heating or chemical agents to improve water resistance.

Drilling Fluids: It stabilizes borehole walls and prevents collapse when drilling through argillaceous formations.

Concrete Treatment: Sodium silicate solutions reduce porosity in concrete, enhancing durability and water repellency.

Detergents: It is used as a detergent auxiliary to coat and strengthen detergent granules.

Water Treatment: As a flocculant, sodium silicate aids in coagulating and removing impurities from water.

Refractory and Foundry Applications

Refractory Use: It acts as a binder in high-temperature insulation boards and adhesives for refractory applications.

Foundry: Sodium silicate is used as a binder in sand casting molds, providing rapid production of strong molds through carbon dioxide gassing, ester addition, or microwave heating.

Miscellaneous Uses

Dye Fixative: It is used to fix dyes on textiles by providing a high pH environment.

Metal and Automotive Repair: Sodium silicate paste repairs exhaust systems and fills head gasket gaps. It also disables engines for recycling purposes.

Safe Construction: Mixed with sawdust, it enhances the fire resistance of safes.

Crystal Gardens: Used in toys and educational sets to create stalagmites of colored metal silicates.

Pottery: Sodium silicate acts as a deflocculant in casting slips and creates crackle effects in pottery.

Sealing Leaks: It seals leaks in water-containing structures, such as the Fukushima Daiichi nuclear plant.

Firearm Cartridges: Historically used to seal paper cartridges for black powder revolvers.

Food and Medicine

Cosmetics: Sodium silicate is an ingredient in wrinkle remover creams, providing temporary skin tightening.

Food Preservation: It preserves eggs by forming an airtight coating, allowing storage for up to five months.

Brewing: Used to clarify wine and beer by precipitating colloidal particles.

Aquaculture: Sodium silicate gel supports algal growth in hatcheries.

Sodium Silicate Powder

Sodium Silicate Powder is a fine, white powder with a SiO2 to Na2O ratio of 3.22, similar to liquid sodium silicates. When dissolved, it forms a hazy, colorless colloidal solution. This SSG sodium silicate is used for specialized refractory compounds and acid-resistant cements. It functions as a binder for powdered materials intended for mixing with water, suitable for high-temperature and/or acid-resistant applications. It ships within 7 business days and is available for export only from the United States.

Sodium Silicate