Calcium disilicide (CaSi2) is an inorganic compound, a silicide of calcium. It is a whitish or dark grey to black solid matter with melting point 1033 °C. It is insoluble in water, but may decompose when subjected to moisture, evolving hydrogen and producing calcium hydroxide. Decomposes in hot water. It is flammable and may ignite spontaneously in air.
hR9 unit cell
|Molar mass||96.249 g/mol|
|Melting point||1,040 °C (1,900 °F; 1,310 K)|
|R3m, No. 166|
a = 0.38295/0.3855 nm, c = 1.5904/3.06 nm
Formula units (Z)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
At ambient conditions calcium disilicide exists in two 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 tetragonal phase. The tetragonal phase is a superconductor with a transition temperature of 1.37 K.
In pyrotechnics, it is used as fuel to make special mixtures, e.g. for production of smokes, in flash compositions, and in percussion caps. 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 explosive bolts, hand grenades, and infrared decoys. Smoke compositions often contain hexachloroethane; during burning they produce silicon tetrachloride, which, like titanium tetrachloride used in smoke-screens, reacts with air moisture and produces dense white fog. Gum arabic is used in some mixtures to inhibit calcium silicide decomposition.
- Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). Boca Raton, FL: CRC Press. p. 4.56. ISBN 1439855110.
- Evers, Jürgen (1979). "Transformation of three-connected silicon nets in CaSi2". Journal of Solid State Chemistry. 28 (3): 369. Bibcode:1979JSSCh..28..369E. doi:10.1016/0022-4596(79)90087-2.
- Evers, J; Oehlinger, G; Ott, H.R (1980). "Superconductivity of SrSi2 and BaGe2 with the α-ThSi2-type structure". Journal of the Less Common Metals. 69 (2): 389. doi:10.1016/0022-5088(80)90297-0.
- Calvert, J. B. (2004) Flash! Bang! Whiz! An introduction to propellants, explosives, pyrotechnics and fireworks. University of Denver