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| Watchedfields = changed
| verifiedrevid = 428831186
| ImageFile = CaSi2.png
| ImageSize =
| ImageCaption = hR9 unit cell
|
| OtherNames =
|Section1={{Chembox Identifiers
| CASNo_Ref = {{cascite|correct|??}}
| CASNo = 12013-56-8
| PubChem = 57647918
| ChemSpiderID = 26499946
| SMILES =
}}
|Section2={{Chembox Properties
| Formula = CaSi<sub>2</sub>
| MolarMass = 96.
| Appearance =
| Density = 2.
| MeltingPtC =
| MeltingPt_ref =<ref name=b92/>
| BoilingPt =
| Solubility = insoluble
}}
| Section3 = {{Chembox
| Structure_ref =<ref name=str/>
| CrystalStruct = Trigonal, [[Pearson symbol|hR9/hR18]],
| SpaceGroup = R{{overline|3}}m, No. 166
| PointGroup =
}}▼
| LattConst_a = 0.38295/0.3855 nm
| LattConst_b =
| LattConst_c = 1.5904/3.06 nm
| LattConst_alpha =
| LattConst_beta =
| LattConst_gamma =
| LattConst_ref =
| LattConst_Comment =
| UnitCellVolume =
| UnitCellFormulas = 3/6
| Coordination =
| MolShape =
| OrbitalHybridisation =
| Dipole =
}}
'''Calcium
Industrial calcium silicide usually contains [[iron]] and [[aluminium]] as the primary contaminants, and low amounts of [[carbon]] and [[sulfur]].
==Properties==
At ambient conditions calcium disilicide exists in two [[polymorphism (materials science)|polymorphs]], hR9 and hR18; in the hR18 structure the hR9 [[unit cell]] is stacked twice along the c axis. Upon heating to 1000 °C at a pressure of ca. 40 kBar, calcium disilicide converts to a (semi-stable) [[tetragonal]] phase.<ref name=str>{{cite journal|doi=10.1016/0022-4596(79)90087-2|title=Transformation of three-connected silicon nets in CaSi<sub>2</sub>|journal=Journal of Solid State Chemistry|volume=28|issue=3|pages=369–377|year=1979|last1=Evers|first1=Jürgen|bibcode=1979JSSCh..28..369E}}</ref> The tetragonal phase is a [[superconductor]] with a transition temperature of 1.37 K<ref>{{cite journal|doi=10.1016/0022-5088(80)90297-0|title=Superconductivity of SrSi<sub>2</sub> and BaGe<sub>2</sub> with the α-ThSi<sub>2</sub>-type structure|journal=Journal of the Less Common Metals|volume=69|issue=2|pages=389|year=1980|last1=Evers|first1=J|last2=Oehlinger|first2=G|last3=Ott|first3=H.R}}</ref> to 1.58 K.<ref>{{cite journal | last=McWhan | first=D.B. | last2=Compton | first2=V.B. | last3=Silverman | first3=M.S. | last4=Soulen | first4=J.R. | title=Crystal structure and superconductivity of a high-pressure phase of CaSi2 | journal=Journal of the Less Common Metals | publisher=Elsevier BV | volume=12 | issue=1 | year=1967 | issn=0022-5088 | doi=10.1016/0022-5088(67)90073-2 | pages=75–76}}</ref> Although there is no observable superconducting transition temperature for the trigonal/rhombohedral (i.e. hR9 and hR18 unit cells) at ambient pressure, under high pressure (>12 GPa/120 kbar) this phase has been observed exhibit superconducting transition.<ref>{{cite journal |last1=Sanfilippo |first1=S. |last2=Elsinger |first2=H. |last3=Nunez-Regueiro |first3=M. |last4=Laborde |first4=O. |last5=LeFloch |first5=S. |last6=Affronte |first6=M. |last7=Olcese |first7=G. L. |last8=Palenzona |first8=A. |title=Superconducting high pressure CaSi2 phase with Tc up to 14K |journal=Physical Review B |date=2000 |volume=61 |issue=6 |page=R3800 |doi=10.1103/PhysRevB.61.R3800 |bibcode=2000PhRvB..61.3800S |url=https://journals.aps.org/prb/abstract/10.1103/PhysRevB.61.R3800 |accessdate=20 April 2020}}</ref> When the trigonal phase is placed under pressures exceeding 16 GPa, there is a phase transition to an AlB<sub>2</sub>-like phase.<ref>{{cite journal |last1=Bordet |first1=P. |last2=Affronte |first2=M. |last3=Sanfilippo |first3=S. |last4=Nunez-Regueiro |first4=M. |last5=Laborde |first5=O. |last6=Olcese |first6=G. L. |last7=Palenzona |first7=A. |last8=LeFloch |first8=S. |last9=Levy |first9=D. |last10=Hanfland |first10=M. |title=Structural phase transitions in CaSi2 under high pressure |journal=Physical Review B |date=2000 |volume=62 |issue=17 |page=11392 |doi=10.1103/PhysRevB.62.11392 |bibcode=2000PhRvB..6211392B |url=https://journals.aps.org/prb/abstract/10.1103/PhysRevB.62.11392 |accessdate=20 April 2020}}</ref>
==Uses==
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===Pyrotechnics===
In [[pyrotechnics]], it is used as fuel to make special mixtures, e.g. for production of [[smoke]]s, in flash compositions, and in [[percussion cap]]s. Specification for pyrotechnic calcium silicide is MIL-C-324C. In some mixtures it may be substituted with [[ferrosilicon]]. Silicon-based fuels are used in some time delay mixtures, e.g. for controlling of [[Pyrotechnic fastener|explosive bolts]], hand grenades, and infrared decoys.{{citation needed | date = May 2009}} Smoke compositions often contain [[hexachloroethane]]; during burning they produce [[silicon tetrachloride]], which, like [[titanium tetrachloride]] used in [[smoke-screen]]s, reacts with air moisture and produces dense white fog. [[Gum arabic]] is used in some mixtures to inhibit calcium silicide decomposition.
===Heating food===
[[Self-heating can]]s of military food rations developed during WWII used a [[thermite]]-like mixture of 1:1 [[iron(II,III) oxide]] and calcium silicide. Such mixture, when ignited, generates moderate amount of heat and no gaseous products.<ref>Calvert, J. B. (2004) [https://web.archive.org/web/20110810182006/http://
==References==▼
<references />▼
{{Calcium compounds}}
{{Silicides}}
▲==References==
▲<references />
[[Category:Alkaline earth silicides]]
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