Calcium disilicide (CaSi2) is an inorganic compound, asilicide ofcalcium. 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, evolvinghydrogen and producingcalcium hydroxide. It decomposes in hot water, and is flammable and may ignite spontaneously in air.
 hR9 unit cell | |
| Identifiers | |
|---|---|
| ChemSpider | |
| ECHA InfoCard | 100.031.431 |
| Properties | |
| CaSi2 | |
| Molar mass | 96.249 g/mol[1] |
| Appearance | grey solid[1] |
| Density | 2.50 g/cm3[1] |
| Melting point | 1,040 °C (1,900 °F; 1,310 K)[1] |
| insoluble | |
| Structure[2] | |
| Trigonal,hR9/hR18, | |
| R3m, No. 166 | |
a = 0.38295/0.3855 nm,c = 1.5904/3.06 nm | |
Formula units (Z) | 3/6 |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Industrial calcium silicide usually containsiron andaluminium as the primary contaminants, and low amounts ofcarbon andsulfur.
Properties
editAt ambient conditions calcium disilicide exists in twopolymorphs, hR9 and hR18; in the hR18 structure the hR9unit 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.[2] The tetragonal phase is asuperconductor with a transition temperature of 1.37 K[3] to 1.58 K.[4] 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.[5] When the trigonal phase is placed under pressures exceeding 16 GPa, there is a phase transition to an AlB2-like phase.[6]
Uses
editAlloys
editCalcium silicide is used for manufacture of special metalalloys, e.g. for removingphosphorus and as adeoxidizer.
Pyrotechnics
editInpyrotechnics, it is used as fuel to make special mixtures, e.g. for production ofsmokes, in flash compositions, and inpercussion caps. Specification for pyrotechnic calcium silicide is MIL-C-324C. In some mixtures it may be substituted withferrosilicon. Silicon-based fuels are used in some time delay mixtures, e.g. for controlling ofexplosive bolts, hand grenades, and infrared decoys.[citation needed] Smoke compositions often containhexachloroethane; during burning they producesilicon tetrachloride, which, liketitanium tetrachloride used insmoke-screens, reacts with air moisture and produces dense white fog.Gum arabic is used in some mixtures to inhibit calcium silicide decomposition.
Heating food
editSelf-heating cans of military food rations developed during WWII used athermite-like mixture of 1:1iron(II,III) oxide and calcium silicide. Such mixture, when ignited, generates moderate amount of heat and no gaseous products.[7]
References
edit- ^abcdHaynes, William M., ed. (2011).CRC Handbook of Chemistry and Physics (92nd ed.). Boca Raton, Florida:CRC Press. p. 4.56.ISBN 1-4398-5511-0.
- ^abEvers, Jürgen (1979). "Transformation of three-connected silicon nets in CaSi2".Journal of Solid State Chemistry.28 (3):369–377.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.
- ^McWhan, D.B.; Compton, V.B.; Silverman, M.S.; Soulen, J.R. (1967). "Crystal structure and superconductivity of a high-pressure phase of CaSi2".Journal of the Less Common Metals.12 (1). Elsevier BV:75–76.doi:10.1016/0022-5088(67)90073-2.ISSN 0022-5088.
- ^Sanfilippo, S.; Elsinger, H.; Nunez-Regueiro, M.; Laborde, O.; LeFloch, S.; Affronte, M.; Olcese, G. L.; Palenzona, A. (2000)."Superconducting high pressure CaSi2 phase with Tc up to 14K".Physical Review B.61 (6): R3800.Bibcode:2000PhRvB..61.3800S.doi:10.1103/PhysRevB.61.R3800. Retrieved20 April 2020.
- ^Bordet, P.; Affronte, M.; Sanfilippo, S.; Nunez-Regueiro, M.; Laborde, O.; Olcese, G. L.; Palenzona, A.; LeFloch, S.; Levy, D.; Hanfland, M. (2000)."Structural phase transitions in CaSi2 under high pressure".Physical Review B.62 (17): 11392.Bibcode:2000PhRvB..6211392B.doi:10.1103/PhysRevB.62.11392. Retrieved20 April 2020.
- ^Calvert, J. B. (2004)Flash! Bang! Whiz! An introduction to propellants, explosives, pyrotechnics and fireworks.University of Denver