Sodium silicate is the common name for a compound sodium
metasilicate, Na2SiO3, also known as water glass or liquid glass.
It is available in aqueous solution and in solid form and is used
in cements, passive fire protection, refractories, textile and
lumber processing, and automobiles. Sodium carbonate and silicon
dioxide react when molten to form sodium silicate and carbon
dioxide:
Na2CO3 + SiO2 → Na2SiO3 + CO2
Anhydrous sodium silicate contains a chain polymeric anion composed
of corner shared {SiO4} tetrahedral, and not a discrete SiO*2−
ion.[1] In addition to the anhydrous form, there are hydrates with
the formula Na2SiO3·nH2O (where n = 5, 6, 8, 9) which contain the
discrete, approximately tetrahedral anion SiO2(OH)*2− with water of
hydration. For example, the commercially available sodium silicate
pentahydrate Na2SiO3·5H2O is formulated as Na2SiO2(OH)2·4H2O and
the nonahydrate Na2SiO3·9H2O is formulated as Na2SiO2(OH)2·8H2O.
