calcium silicate

{{Short description|Chemical compound naturally occurring as the mineral larnite}}

{{Chembox

|ImageFile = Ca2SiO4simple.svg

| ImageSize =

| ImageAlt =

| IUPACName =

| Verifiedfields = changed

| Watchedfields = changed

| verifiedrevid = 477002240

| PIN = Calcium silicate

| SystematicName = Dicalcium silicate

| OtherNames = {{unbulleted list

| Belite

| Calcium monosilicate

| Calcium hydrosilicate

| Calcium metasilicate

| Calcium orthosilicate

| Micro-cell

| Silene

| Silicic acid calcium salt

}}

|Section1={{Chembox Identifiers

| CASNo = 1344-95-2

| CASNo_Ref = {{cascite|correct|CAS}}

| CASNo1 = 111811-33-7

| CASNo1_Comment = hydrate

| CASNo1_Ref = {{cascite|correct|??}}

| CASNo2 = 12168-85-3

| CASNo2_Comment = calcium oxide

| CASNo2_Ref = {{cascite|correct|CAS}}

| PubChem = 14941

| PubChem1 = 44154858

| PubChem1_Comment = hydrate

| PubChem2 = 25523

| PubChem2_Comment = calcium oxide

| ChemSpiderID = 14235

| ChemSpiderID_Ref = {{chemspidercite|changed|chemspider}}

| ChemSpiderID1 = 23811

| ChemSpiderID1_Comment = calcium oxide

| ChemSpiderID1_Ref = {{chemspidercite|correct|chemspider}}

| ChEBI = 190294

| UNII = S4255P4G5M

| UNII_Ref = {{fdacite|correct|FDA}}

| UNII1_Ref = {{fdacite|correct|FDA}}

| UNII1 = 404G39282C

| UNII1_Comment = calcium oxide

| EINECS = 235-336-9

| KEGG_Ref = {{keggcite|changed|kegg}}

| KEGG = D03309

| MeSHName = Calcium+silicate

| SMILES = [Ca++].[Ca++].[O-][Si]([O-])([O-])[O-]

| StdInChI_Ref = {{stdinchicite|changed|chemspider}}

| StdInChI = 1S/2Ca.O4Si/c;;1-5(2,3)4/q2*+2;-4

| StdInChIKey_Ref = {{stdinchicite|changed|chemspider}}

| StdInChIKey = JHLNERQLKQQLRZ-UHFFFAOYSA-N}}

|Section2={{Chembox Properties

| Ca=2 | Si=1 | O=4

| Appearance = White crystals

| MeltingPtC = 2130R. B. Heimann, Classic and Advanced Ceramics: From Fundamentals to Applications, Wiley, 2010 {{ISBN|352763018X}}

| Solubility = 0.01% (20 °C)

| Density = 2.9 g/cm³ (solid)

}}

|Section3={{Chembox Structure

| CrystalStruct =

}}

|Section5={{Chembox Thermochemistry

| DeltaHf = −1630 kJ/mol{{cite book| author = Zumdahl, Steven S.|title =Chemical Principles 6th Ed.| publisher = Houghton Mifflin Company| year = 2009| isbn = 978-0-618-94690-7|page=A21}}

| Entropy = 84 J/(mol·K)

}}

|Section6={{Chembox Pharmacology

| ATCCode_prefix = A02

| ATCCode_suffix = AC02

}}

|Section7={{Chembox Hazards

| ExternalSDS = {{cite web |url=http://www.bnzmaterials.com/msds/msds218.html |title=SDS Sheet Library |publisher=BNZ Materials |access-date=2017-07-19 |archive-url=https://web.archive.org/web/20120304071621/http://www.bnzmaterials.com/msds/msds218.html |archive-date=2012-03-04 |url-status=dead }}

| MainHazards = Irritant

| FlashPt = Not applicable

| NFPA-H = 2

| NFPA-F = 0

| NFPA-R = 0

| PEL = TWA 15 mg/m³ (total) TWA 5 mg/m³ (resp){{PGCH|0094}}

| IDLH = N.D.

| REL = TWA 10 mg/m³ (total) TWA 5 mg/m³ (resp)

}}

|Section8={{Chembox Related

| OtherAnions =

}}

Calcium silicate can refer to several silicates of calcium including:

CaO·SiO₂, wollastonite (CaSiO₃)
2CaO·SiO₂, larnite (Ca₂SiO₄)
3CaO·SiO₂, alite or (Ca₃SiO₅)
3CaO·2SiO₂, (Ca₃Si₂O₇).

This article focuses on Ca₂SiO₄, also known as calcium orthosilicate, or by the shortened trade name Cal-Sil/Calsil. All calcium silicates are white free-flowing powders. Being strong, cheap and nontoxic, they are components of important structural materials.

Production and occurrence

Calcium silicates are produced by treating calcium oxide and silica in various ratios. Their formation is relevant to Portland cement.H. F. W. Taylor, Cement Chemistry, Academic Press, 1990, {{ISBN|0-12-683900-X}}, p. 33–34.

Calcium silicate is a byproduct of the Pidgeon process, a major route to magnesium metal. The process converts a mixture of magnesium and calcium oxides as represented by the following simplified equation:{{cite book |doi=10.1002/14356007.a15_559 |chapter=Magnesium |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2003 |last1=Amundsen |first1=Ketil |last2=Aune |first2=Terje Kr. |last3=Bakke |first3=Per |last4=Eklund |first4=Hans R. |last5=Haagensen |first5=Johanna Ö. |last6=Nicolas |first6=Carlos |last7=Rosenkilde |first7=Christian |last8=Van Den Bremt |first8=Sia |last9=Wallevik |first9=Oddmund |isbn=978-3-527-30385-4 }}

:{{chem2|MgO*CaO +Si -> 2 Mg + Ca2SiO4}}

The calcium oxide combines with silicon as the oxygen scavenger, yielding the very stable calcium silicate and releasing volatile (at high temperatures) magnesium metal.

Via the carbonate–silicate cycle, carbonate rocks convert into silicate rocks by metamorphism and volcanism and silicate rocks convert to carbonates by weathering and sedimentation.{{Cite journal |last1=Berner|first1=Robert |last2=Lasaga|first2=Antonio |last3=Garrels|first3=Robert |date=1983 |title=The carbonate-silicate geochemical cycle and its effect on atmospheric carbon dioxide over the past 100 million years |journal=American Journal of Science|volume=283|issue=7|pages=641–683 |bibcode=1983AmJS..283..641B |doi=10.2475/ajs.283.7.641|doi-access=free}}{{Cite journal|last1=Walker|first1=James C. G.|last2=Hays|first2=P. B.|last3=Kasting|first3=J. F. |date=1981 |title=A negative feedback mechanism for the long-term stabilization of Earth's surface temperature|journal=Journal of Geophysical Research: Oceans|language=en|volume=86|issue=C10|pages=9776–9782 |bibcode=1981JGR....86.9776W |doi=10.1029/JC086iC10p09776 |issn=2156-2202}}

The production of sulfuric acid from anhydrous calcium sulfate produces calcium silicates.[https://www.cementkilns.co.uk/cement_kiln_whitehaven.html Whitehaven Cement Plant] Upon being mixed with shale or marl, and roasted at 1400 °C, the sulfate liberates sulfur dioxide gas, a precursor to sulfuric acid. The resulting calcium silicate is used in cement clinker production.[https://www.cementkilns.co.uk/cemkilndoc054.html Anhydrite Process]

:{{chem2|2 CaSO4 + 2 SiO2 + C → 2 CaSiO3 + 2 SO2 + CO2}}

Structure

File:963-ICSD.png of {{chem2|Ca2SiO4}}. Color code: red (O), blue (Ca), gold (Si).|left]]

As verified by X-ray crystallography, calcium silicate is a dense solid consisting of tetrahedral orthosilicate (SiO₄^4-) units linked to Ca²⁺ via Si-O-Ca bridges. There are two calcium sites. One is seven coordinate and the other is eight coordinate.{{cite journal |doi=10.1107/S0567740877006918 |title=Redetermination of the structure of β-dicalcium silicate |date=1977 |last1=Jost |first1=K. H. |last2=Ziemer |first2=B. |last3=Seydel |first3=R. |journal=Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry |volume=33 |issue=6 |pages=1696–1700 |bibcode=1977AcCrB..33.1696J }}

Use

=As a component of cement=

Calcium silicates are the major ingredients in Portland cements.{{cite book |doi=10.1002/14356007.a05_489.pub2 |chapter=Cement |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2008 |last1=Sprung |first1=Siegbert |isbn=978-3-527-30385-4 }}

class=wikitable \|+ Typical constituents of portland clinker plus gypsum showing cement chemist notation (CCN) ! Clinker ! CCN ! Mass ! Mineral
Tricalcium silicate (CaO)₃ · SiO₂	C₃S	25–50%	alite
Dicalcium silicate (this article) (CaO)₂ · SiO₂	C₂S	20–45%	belite
Tricalcium aluminate (CaO)₃ · Al₂O₃	C₃A	5–12%
Tetracalcium aluminoferrite (CaO)₄ · Al₂O₃ · Fe₂O₃	C₄AF	6–12%
CaSO₄ · 2 H₂O	CS̅H₂	2–10%	gypsum

=High-temperature insulation=

File:Calcium silicate cladding 2of2.jpg board being clad around steel structure in order to achieve a fire-resistance rating]]

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 and 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=

File:Promat signum tray cladding 1.jpg 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.]]

It is used in passive fire protection and fireproofing as calcium silicate brick or in roof tiles. It is one of the most successful materials in fireproofing in Europe because of regulations and fire safety guidelines for commercial and residential building codes. Where North Americans use spray fireproofing plasters, Europeans are more likely to use cladding made of calcium silicate. {{why|date=December 2012}} 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.{{citation needed|date=July 2017}}

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.{{citation needed|date=July 2017}}

=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.{{cite web|last=Ziemkiewicz|first=Paul|title=The Use of Steel Slag in Acid Mine Drainage Treatment and Control|url=http://wvmdtaskforce.com/proceedings/98/98zie/98zie.htm|website=Wvmdtaskforce.com|access-date=25 April 2011|url-status=dead|archive-url=https://web.archive.org/web/20110720064631/http://wvmdtaskforce.com/proceedings/98/98zie/98zie.htm|archive-date=20 July 2011}}

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),{{cite web|last=Skousen|first=Jeff|title=Chemicals|url=http://www.wvu.edu/~agexten/landrec/chemtrt.htm#Chemicals|work=Overview of Acid Mine Drainage Treatment with Chemicals|publisher=West Virginia University Extension Service|access-date=29 March 2011|url-status=dead|archive-url=https://web.archive.org/web/20110524070234/http://www.wvu.edu/~agexten/landrec/chemtrt.htm#Chemicals|archive-date=24 May 2011}} calcium silicate effectively precipitates heavy metals and does not armor over, prolonging its effectiveness in AMD systems.{{cite journal|last=Hammarstrom|first=Jane M.|author2=Philip L. Sibrell|author3=Harvey E. Belkin|title=Characterization of limestone reacted with acid-mine drainage|journal=Applied Geochemistry|issue=18|pages=1710–1714|url=http://mine-drainage.usgs.gov/pubs/AG_18-1705-1721.pdf|access-date=30 March 2011|archive-date=5 June 2013|archive-url=https://web.archive.org/web/20130605231303/http://mine-drainage.usgs.gov/pubs/AG_18-1705-1721.pdf|url-status=dead}}

=As a product of sealants=

It is used as a sealant in roads or on the shells of fresh eggs: when sodium silicate is applied as a sealant to cured concrete or egg shells, it chemically reacts with calcium hydroxide or calcium carbonate to form calcium silicate hydrate, sealing micropores with a relatively impermeable material.{{cite journal | last1 = Giannaros | first1 = P. | last2 = Kanellopoulos | first2 = A. | last3 = Al-Tabbaa | first3 = A. | year = 2016 | title = Sealing of cracks in cement using microencapsulated sodium silicate | journal = Smart Materials and Structures | volume = 25 | issue = 8| page = 8 | doi = 10.1088/0964-1726/25/8/084005 | bibcode = 2016SMaS...25h4005G | doi-access = free }}{{cite journal | last1 = Passmore | first1 = S. M. | year = 1975 | title = Preserving eggs | journal = Nutrition & Food Science | volume = 75 | issue = 4| pages = 2–4 | doi = 10.1108/eb058634 }}

=Agriculture=

Calcium silicate is often used in agriculture as a plant available source of silicon. It is "applied extensively to Everglades mucks and associated sands planted to sugarcane and rice" {{cite journal|last=Gascho|first=Gary J.|title=Chapter 12 Silicon sources for agriculture|journal=Studies in Plant Science|volume=8|issue=8|pages=197–207|doi=10.1016/S0928-3420(01)80016-1|year=2001|isbn=9780444502629}}

=Other=

Calcium silicate is used as an anticaking agent in food preparation, including table salt[http://www.mortonsalt.com/faqs/food_salt_faq.html#q6] {{webarchive|url=https://web.archive.org/web/20081225045630/http://www.mortonsalt.com/faqs/food_salt_faq.html|date=2008-12-25}} and as an antacid. It is approved by the United Nations' FAO and WHO bodies as a safe food additive in a large variety of products.

{{cite web| title = Food Additive Details: Calcium silicate| url = http://www.codexalimentarius.net/gsfaonline/additives/details.html?id=315| access-date = July 28, 2013| archive-url = https://web.archive.org/web/20120605054550/http://www.codexalimentarius.net/gsfaonline/additives/details.html?id=315| archive-date = June 5, 2012

}} 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. It has the E number reference E552.