Calcium disilicide: Difference between revisions

| Watchedfields = changed

| verifiedrevid = 428831186

| ImageFile = CaSi2.png

| ImageSize =

| ImageCaption = hR9 unit cell

| IUPACName =

| OtherNames =

|Section1={{Chembox Identifiers

| CASNo_Ref = {{cascite|correct|??}}

| CASNo = 12013-56-8

| PubChem = 57647918

| ChemSpiderID = 26499946

| SMILES =

|Section2={{Chembox Properties

| Formula = CaSi₂

| MolarMass = 96.249 g/mol<ref name=b92>{{RubberBible92nd|page=4.56}}</ref>

| Appearance = grey solid<ref name=b92/>

| Density = 2.50 g/cm³<ref name=b92/>

| MeltingPtC = 1040

| MeltingPt_ref =<ref name=b92/>

| BoilingPt =

| Solubility = insoluble

| Section3 = {{Chembox Structure

| 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 disilicide''' ([[Calcium|Ca]][[Silicon|Si]]₂) is an inorganic compound, a [[silicide]] of [[calcium]]. It is a whitish or dark grey to black solid matter with melting point 1033&nbsp;°C. It is insoluble in water, but may decompose when subjected to moisture, evolving [[hydrogen]] and producing [[calcium hydroxide]]. It decomposes in hot water, and is flammable and may ignite spontaneously in air.

==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&nbsp;°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 CaSi₂|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 SrSi₂ and BaGe₂ with the α-ThSi₂-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 AlB₂-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==

===Alloys===

Calcium silicide is used for manufacture of special metal [[alloy]]s, e.g. for removing [[phosphorus]] and as a [[deoxidizer]].

===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://mysite.du.edu/~jcalvert/phys/bang.htm Flash! Bang! Whiz! An introduction to propellants, explosives, pyrotechnics and fireworks]. [[University of Denver]]</ref>

==References==

<references />

{{Silicides}}