Calcium silicate

Calcium silicate
Calcium silicate passive fire protection board being clad around steel structure in order to achieve a fire-resistance rating.
Calcium silicate
CAS number 1344-95-2 YesY, 111811-33-7 hydrate YesY, 12168-85-3 calcium oxide YesY
PubChem 14941, 44154858 hydrate, 25523 calcium oxide
ChemSpider 14235 N, 23811 calcium oxide YesY
UNII S4255P4G5M YesY
EC number 235-336-9
KEGG D03309 N
MeSH Calcium+silicate
ATC code A02AC02
Jmol-3D images Image 1
Molecular formula Ca2O4Si
Molar mass 172.24 g mol−1
Exact mass 171.881767331 g mol-1
Appearance White crystals
Melting point

1540 °C, 1813 K, 2804 °F

MSDS [1]
Main hazards Irritant
NFPA 704
NFPA 704.svg
Flash point Not applicable
 N silicate (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Calcium silicate (often referred to by its shortened trade name Cal-Sil or Calsil) is the chemical compound Ca2SiO4, also known as calcium orthosilicate and sometimes formulated 2CaO.SiO2. It is one of group of compounds obtained by reacting calcium oxide and silica in various ratios[1] e.g. 3CaO.SiO2, Ca3SiO5; 2CaO.SiO2, Ca2SiO4; 3CaO.2SiO2, Ca3Si2O7 and CaO.SiO2, CaSiO3. Calcium orthosilicate is a white powder with a low bulk density and high physical water absorption. It is used as an anti-caking agent and an antacid. A white free-flowing powder derived from limestone and diatomaceous earth, calcium silicate has no known adverse effects to health[citation needed]. It is used in roads, insulation, bricks, roof tiles, table salt[2] and occurs in cements, where it is known as belite (or in cement chemist notation C2S).


High temperature insulation

Calcium silicate is commonly used as a safe alternative to asbestos for high temperature insulation materials. Industrial grade piping and equipment insulation is often fabricated from calcium silicate. Its fabrication is a routine part of the curriculum for insulation apprentices. Calcium silicate competes in these realms against rockwool as well as proprietary insulation solids, such as perlite mixture and vermiculite bonded with sodium silicate. Although it is popularly considered an asbestos substitute, early uses of calcium silicate for insulation still made use of asbestos fibers.

Passive fire protection

Circuit integrity fireproofing of cable trays in Lingen/Ems, Germany using calcium silicate board system qualified to DIN 4102. Other methods for exterior protection of electrical circuits include boards made of sodium silicate bonded and pressed vermiculite and flexible wraps made of ceramic fibre and rockwool.

One of the most successful materials in fireproofing in Europe is calcium silicate. Where North Americans use spray fireproofing plasters, Europeans are more likely to use cladding made of calcium silicate. Calcium silicate is easily damaged by water. Therefore, silicone treated sheets are available to fabricators to mitigate potential harm from high humidity or general presence of water. Fabricators and installers of calcium silicate in passive fire protection often also install firestops.

Acid mine drainage remediation

Calcium silicate is also a constituent of the slag that is produced when molten iron is made from iron ore and calcium carbonate in a blast furnace. When this material is processed into a highly refined, repurposed calcium silicate aggregate, it is used in the remediation of acid mine drainage (AMD) on active and passive mine sites.[3] Calcium silicate neutralizes active acidity in AMD systems by removing free hydrogen ions from the bulk solution, thereby increasing pH. As its silicate anion captures H+ ions (raising the pH), it forms monosilicic acid (H4SiO4), a neutral solute. Monosilicic acid remains in the bulk solution to play other important roles in correcting the adverse effects of acidic conditions. As opposed to limestone (a popular remediation material),[4] calcium silicate effectively precipitates heavy metals and does not armor over, prolonging its effectiveness in AMD systems.[3][5]

As a product of sealants

When sodium silicate is applied as a sealant to cured concrete or the shells of fresh eggs, it chemically reacts with calcium hydroxide or carbonate to form calcium silicate hydrate, sealing pores with a relatively impermeable material.


  1. ^ H F W Taylor, Cement Chemistry, Academic Press, 1990, ISBN 0-12-683900-X, p 33-34
  2. ^
  3. ^ a b Ziemkiewicz, Paul. "The Use of Steel Slag in Acid Mine Drainage Treatment and Control". Retrieved 25 April 2011. 
  4. ^ Skousen, Jeff. "Chemicals". Overview of Acid Mine Drainage Treatment with Chemicals. West Virginia University Extension Service. Retrieved 29 March 2011. 
  5. ^ Hammarstrom, Jane M.; Philip L. Sibrell; Harvey E. Belkin. "Characterization of limestone reacted with acid-mine drainage". Applied Geochemistry (18): p.1710–1714. Retrieved 30 March 2011. 

See also

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