What is "sodium silicate"

n. a viscous glass consisting of sodium silicate in solution; used as a cement or as a protective coating and to preserve eggs [syn: soluble glass, water glass]

Sodium silicate is the common name for compounds with the formula Na(SiO)O. A well-known member of this series is sodium metasilicate, NaSiO. Also known as waterglass or liquid glass, these materials are available in aqueous solution and in solid form. The pure compositions are colourless or white, but commercial samples are often greenish or blue owing to the presence of iron-containing impurities.

They are used in cements, passive fire protection, textile and lumber processing, refractories, and automobiles. Sodium carbonate and silicon dioxide react when molten to form sodium silicate and carbon dioxide:

Anhydrous sodium silicate contains a chain polymeric anion composed of corner-shared {SiO} tetrahedral, and not a discrete SiO ion. In addition to the anhydrous form, there are hydrates with the formula NaSiO·nHO (where n = 5, 6, 8, 9) which contain the discrete, approximately tetrahedral anion SiO(OH) with water of hydration. For example, the commercially available sodium silicate pentahydrate NaSiO·5HO is formulated as NaSiO(OH)·4HO and the nonahydrate NaSiO·9HO is formulated as NaSiO(OH)·8HO.

In industry, the various grades of sodium silicate are characterized by their SiO:NaO weight ratio (weight ratios can be converted to molar ratios by multiplication with 1.032), which can vary between 2:1 and 3.75:1. Grades with this ratio below 2.85:1 are termed alkaline. Those with a higher SiO:NaO ratio are described as neutral.