Calcium silicides

Calcium silicides , also called calcium silicon, are a group of intermetallic compounds of calcium with silicon .

Occurrence and manufacture

Calcium silicides can be produced on the one hand by melting calcium carbide (CaC ₂ ) and silicon dioxide (SiO ₂ ), on the other hand by reducing silicon dioxide, calcium oxide or calcium carbide with carbon in an electric furnace. They can also be obtained directly from the elements at 1300 ° C or 1050 ° C.

${\displaystyle \mathrm {Ca+Si\longrightarrow CaSi} }$

${\displaystyle \mathrm {2\ Ca+Si\longrightarrow Ca_{2}Si} }$

Calcium disilicide can be obtained by reacting calcium hydride or calcium monosilicide with silicon at about 1000 ° C.

${\displaystyle \mathrm {CaH_{2}+2\ Si\longrightarrow CaSi_{2}+H_{2}} }$

${\displaystyle \mathrm {CaSi+Si\longrightarrow CaSi_{2}} }$

Properties and use

Like many other silicides , calcium silicides also have good electrical conductivity. However, this is strongly dependent on the modification, for example dicalcium silicide (Ca ₂ Si) is a semiconductor . When poured over with dilute hydrochloric acid, CaSi decomposes vigorously with formation of self-igniting silanes and leaving behind white silica . Calcium disilicide is in the form of hexagonal tablets of a lead-gray color and a vivid metallic sheen. It dissolves quietly in hydrochloric acid with the separation of the yellow siloxene characteristic of the disilicide .

Calcium silicides are used, for example, in metal processing. There they are used, among other things, as a deoxidizer for steels because of their strongly reducing properties .

List of calcium silicides and their modifications

Surname	Molecular formula	CAS no.	Status	molar mass	density	Schoenflies symbolism	Hermann Mauguin symbolism	Size of the unit cell in pm	source
Calcium disilicide	CaSi 2		firmly			${\displaystyle C_{3v}^{6}}$	${\displaystyle R{\bar {3}}c}$	a = 386.3 c = 3071.0
Calcium disilicide (high pressure and temperature)	CaSi 2	12013-56-8	firmly	96.25	2.50	${\displaystyle D_{4h}^{19}}$	${\displaystyle I4_{1}/amd}$	a = 428.3 c = 1352
Calcium monosilicide	CaSi	12737-18-7	firmly	68.17	2.32	${\displaystyle D_{2h}^{17}}$	${\displaystyle Cmcm}$	a = 391 b = 459 c = 1079.5
Dicalcium silicide	Ca 2 Si	12049-73-9				${\displaystyle D_{2h}^{16}}$	${\displaystyle Pnma}$	a = 766.7 b = 479.9 c = 900.2
	Ca 3 Si 4					${\displaystyle C_{6h}^{2}}$	${\displaystyle P6_{3}/m}$	a = 854.1 c = 1490.6
Pentacalcium trisilicide	Ca 5 Si 3					${\displaystyle D_{4h}^{18}}$	${\displaystyle I4/mcm}$	a = 764 c = 1462
	Ca 14 Si 19	174879-69-7			2.44	${\displaystyle C_{3v}^{6}}$	${\displaystyle R{\bar {3}}c}$	a = 867.85 (6) b = 867.85 (6) c = 6852.8 (8)

literature

• P. Manfrinetti, ML Fornasini, A. Palenzona: The phase diagram of the Ca-Si system . In: Intermetallics . tape 8 , no. 3 , March 2000, p. 223-228 , doi : 10.1016 / S0966-9795 (99) 00112-0 .

Individual evidence

1. ↑ ^{a b c} Georg Brauer (ed.), With the collaboration of Marianne Baudler a . a .: Handbook of Preparative Inorganic Chemistry. 3rd, revised edition. Volume I, Ferdinand Enke, Stuttgart 1975, ISBN 3-432-02328-6 , p. 933.
2. ↑ ^{a b} P. Manfrinetti, ML Fornasini, A. Palenzona: The phase diagram of the Ca-Si system . In: Intermetallics . tape 8 , no. 3 , March 2000, p. 223-228 , doi : 10.1016 / S0966-9795 (99) 00112-0 .
3. ^ ^{A b} Jean D'Ans, Ellen Lax: Paperback for chemists and physicists. Volume 3. Elements, Inorganic Compounds and Materials, Minerals . Springer, 1998, ISBN 978-3-540-60035-0 , pp. 358-359 .
4. ↑ P. Eckerlin, E. Wölfel: The crystal structure of Ca ₂ Si and Ca ₂ Ge . In: Journal of Inorganic and General Chemistry . tape 280 , no. 5-6 , 1955, pp. 321-331 , doi : 10.1002 / zaac.19552800509 .
5. ^ O. Madelung, U. Rössler, M. Schulz: Ca ₂ Si, Ca ₂ Sn, Ca ₂ Pb crystal structure, physical properties . In: Non-tetrahedrally Bonded Elements and Binary Compounds I . 41C. Springer-Verlag, Berlin / Heidelberg 1998, ISBN 3-540-64583-7 , doi : 10.1007 / 10681727_135 .
6. ↑ B. Eisenmann, H. Schäfer: The crystal structures of the compounds Ca ₅ Si ₃ and Ca ₅ Ge ₃ . In: Journal of Nature Research B . 29, 1974, pp. 460-463 ( PDF , free full text). Quoted from: P. Manfrinetti, ML Fornasini, A. Palenzona: The phase diagram of the Ca – Si system . In: Intermetallics . tape 8 , no. 3 , March 2000, p. 223-228 , doi : 10.1016 / S0966-9795 (99) 00112-0 .
7. ↑ A. Currao, S. Wengert, R. Nesper, J. Curda, H. Hillebrecht: Ca ₁₄ Si ₁₉ - a Zintl phase with a Novel Twodimensional silicone Framework . In: Z.anorg.allg.Chem . tape 622 , 1996, pp. 501-508 , doi : 10.1002 / zaac.19966220319 .