Calcium silicate

Calcium silicate

Names
Preferred IUPAC name Calcium silicate
Systematic IUPAC name Dicalcium silicate
Other names Belite Calcium monosilicate Calcium hydrosilicate Calcium metasilicate, Calcium orthosilicate Grammite Micro-cell Silene Silicic acid calcium salt
Identifiers
CAS Number	1344-95-2 111811-33-7 hydrate 12168-85-3 calcium oxide
ChemSpider	14235 23811 calcium oxide
EC Number	235-336-9
Jmol 3D model	Interactive image
KEGG	D03309
MeSH	Calcium+silicate
PubChem	14941 44154858 hydrate 25523 calcium oxide
UNII	S4255P4G5M
InChI InChI=1S/2Ca.O4Si/c;;1-5(2,3)4/q2*+2;-4 Key: JHLNERQLKQQLRZ-UHFFFAOYSA-N
SMILES [Ca++].[Ca++].[O-][Si]([O-])([O-])[O-]
Properties
Chemical formula	Ca2O4Si
Molar mass	172.24 g·mol^−1
Appearance	White crystals
Density	0.29 g/cm^3 (solid)[1]
Melting point	1,540 °C (2,800 °F; 1,810 K)
Solubility in water	0.01% (20 °C)[1]
Thermochemistry
Std molar entropy (S^o298)	84 J·mol^−1·K^−1[2]
Std enthalpy of formation (ΔfH^o298)	−1630 kJ·mol^−1[2]
Pharmacology
ATC code	A02AC02 (WHO)
Hazards
Main hazards	Irritant
Safety data sheet	[3]
NFPA 704	0 2 0
Flash point	Not applicable
US health exposure limits (NIOSH):
PEL (Permissible)	TWA 15 mg/m^3 (total) TWA 5 mg/m^3 (resp)[1]
REL (Recommended)	TWA 10 mg/m^3 (total) TWA 5 mg/m^3 (resp)[1]
IDLH (Immediate danger)	N.D.[1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Calcium silicate passive fire protection board being clad around steel structure in order to achieve a fire-resistance rating.

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 a group of compounds obtained by reacting calcium oxide and silica in various ratios^[4] e.g. 3CaO•SiO₂, Ca₃SiO₅; 2CaO•SiO₂, Ca₂SiO₄; 3CaO•2SiO₂, Ca₃Si₂O₇ and CaO•SiO₂, CaSiO₃. Calcium silicate is a white free-flowing powder derived from limestone and diatomaceous earth. It has a low bulk density and high physical water absorption. It is used in roads, insulation, bricks, roof tiles, table salt^[5] and occurs in cements, where it is known as belite (or in cement chemist notation C₂S).

It is used as an anti-caking agent in food preparation and an antacid. It is approved by the United Nations' FAO and WHO bodies as a safe food additive in a large variety of products.^[6]

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. High performance calcium silicate boards retain their excellent dimensional stability even in damp and humid conditions and can be installed at an early stage in the construction program, before wet trades are completed and the building is weather-tight. For sub-standard products, 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.

While the best possible Reaction to Fire Classifications are A1 (construction applications) and A1Fl (flooring applications) respectively, both of which mean "non-combustible" according to EN 13501-1: 2007, as classified by a notified laboratory in Europe, some calcium silicate boards only come with Fire Classification of A2 (limited combustibility) or even lower classifications (or no classification), if they are tested at all.

Acid mine drainage remediation

Calcium silicate, also known as slag, is produced when molten iron is made from iron ore, silicon dioxide and calcium carbonate in a blast furnace. When this material is processed into a highly refined, re-purposed calcium silicate aggregate, it is used in the remediation of acid mine drainage (AMD) on active and passive mine sites.^[7] 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),^[8] calcium silicate effectively precipitates heavy metals and does not armor over, prolonging its effectiveness in AMD systems.^[7][9]

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.

See also

• Alite
• Belite
• Jaffeite
• Fireproofing
• Firestop
• Passive fire protection
• Plaster
• Perlite
• Sodium silicate
• Vermiculite

References

1. "NIOSH Pocket Guide to Chemical Hazards #0094". National Institute for Occupational Safety and Health (NIOSH).
2. Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A21. ISBN 0-618-94690-X.
3. http://www.bnzmaterials.com/msds/msds218.html
4. H F W Taylor, Cement Chemistry, Academic Press, 1990, ISBN 0-12-683900-X, p 33-34
5. http://www.mortonsalt.com/faqs/food_salt_faq.html#q6
6. "Food Additive Details: Calcium silicate". Retrieved July 28, 2013. Codex General Standard for Food Additives (GSFA) Online Database, FAO/WHO Food Standards Codex alimentarius, published by the Food and Agricultural Organization of the United Nations / World Health Organization, 2013.
7. Ziemkiewicz, Paul. "The Use of Steel Slag in Acid Mine Drainage Treatment and Control". Retrieved 25 April 2011.
8. Skousen, Jeff. "Chemicals". Overview of Acid Mine Drainage Treatment with Chemicals. West Virginia University Extension Service. Retrieved 29 March 2011.
9. Hammarstrom, Jane M.; Philip L. Sibrell; Harvey E. Belkin. "Characterization of limestone reacted with acid-mine drainage" (PDF). Applied Geochemistry (18): 1710–1714. Retrieved 30 March 2011.