Sodium silicate is the common name for compounds with the formula Na2(SiO2)nO. A well known member of this series is sodium metasilicate, Na2SiO3. 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 carbonateand silicon dioxide react when molten to form sodium silicate and carbon dioxide:
Na2CO3 + SiO2 → Na2SiO3 + CO2
Sodium carbonate and sodium sulfate melt at temperatures far below that of silica. (<900 °C vs >1600 °C) Either is melted, and silica dissolved into the molten material, where it reacts to form sodium silicate.
Na2CO3 + x SiO2 → (Na2O)•(SiO2)x + CO2
2 Na2SO4 + C + 2 SiO2 → 2 Na2SiO3 + 2 SO2 + CO2