Magnesium silicide

Magnesium silicide

Names
Preferred IUPAC name Magnesium silicide
Identifiers
CAS Number	22831-39-6  Y
3D model (JSmol)	Interactive image
ChemSpider	81111  Y
ECHA InfoCard	100.041.125
EC Number	245-254-5
PubChem CID	89858
UNII	475E6FMG3K  Y
UN number	2624
CompTox Dashboard (EPA)	DTXSID4066830
InChI InChI=1S/2Mg.Si Y Key: YTHCQFKNFVSQBC-UHFFFAOYSA-N Y InChI=1/2Mg.Si/rMg2Si/c1-3-2 Key: YTHCQFKNFVSQBC-GEBTXNJDAA
SMILES [Mg]=[Si]=[Mg]
Properties
Chemical formula	Mg2Si
Molar mass	76.695 g·mol−1
Appearance	Gray cubic crystals [1]
Density	1.99 g cm−3 [1]
Melting point	1,102 °C (2,016 °F; 1,375 K) [1]
Solubility in water	reacts [1]
Structure [2]
Crystal structure	Antifluorite (cubic), cF12
Space group	Fm3m, #225
Lattice constant	a = 0.6351 nm
Formula units (Z)	4
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	reacts with water to produce pyrophoric silane
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H261
Precautionary statements	P231+P232, P280, P370+P378, P402+P404, P501
Related compounds
Other cations	Calcium silicide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y  verify  (what is  YN ?) Infobox references

Magnesium silicide, Mg₂Si, is an inorganic compound of magnesium and silicon. As-grown Mg₂Si usually forms black crystals; they are semiconductors with n-type conductivity and have potential applications in thermoelectric generators. ^[3]

Crystal structure

Mg₂Si crystallizes in the antifluorite structure. In the face-centered cubic lattice, Si centers occupy the corners and face-centered positions of the unit cell, and Mg centers occupy eight tetrahedral sites in the interior of the unit cell. The coordination numbers of Si and Mg are eight and four, respectively. ^[2]

Synthesis

The reaction of powdered sand with magnesium powder.

It can be produced by heating silicon dioxide, SiO₂, found in sand, with excess magnesium. The process first forms elemental silicon and magnesium oxide:

2 Mg + SiO₂ → 2 MgO + Si

If an excess of Mg is present, Mg₂Si is formed from the reaction of the remaining magnesium with the elemental silicon:

2 Mg + Si → Mg₂Si

If there is an excess of SiO₂, then elemental silicon remains.

These reactions proceed exothermically, ^[4] even explosively. ^[5]

Reactions

The reaction of magnesium silicide with 10% hydrochloric acid.

Magnesium silicide can be viewed as consisting of Si⁴⁻ ions. As such, it is reactive toward acids. Thus, when magnesium silicide is treated with hydrochloric acid, silane (SiH₄) and magnesium chloride are produced:

Mg₂Si + 4 HCl → SiH₄ + 2 MgCl₂

Sulfuric acid can be used as well. These protonolysis reactions are typical of a group 2 (alkaline earth metal) and group 1 (alkali metal) silicides. The early development of silicon hydrides relied on this reaction. ^[5]

Uses

Magnesium silicide is used to create aluminium alloys of the 6000 series, containing up to approximately 1.5% Mg₂Si. An alloy of this group can be age-hardened to form Guinier-Preston zones and a very fine precipitate, resulting in increased alloy strength. ^[6]

Magnesium silicide is a narrow-gap semiconductor. Its as-grown crystal exhibits n-type conductivity, but it can be changed to p-type by doping with Ag, Ga, Sn and possibly Li (at high doping levels). The major potential electronic application of Mg₂Si is in thermoelectric generators. ^{[3] [7]}

References

1. Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). Boca Raton, Florida: CRC Press. p. 4.74. ISBN   1-4398-5511-0.
2. Noda Y., Kon H., Furukawa Y., Otsuka N., Nishida I.A., Masumoto K. (1992). "Preparation and Thermoelectric Properties of Mg₂Si_1−xGe_x (x=0.0~0.4) Solid Solution Semiconductors". Mater. Trans., JIM. 33 (9): 845–850. doi: 10.2320/matertrans1989.33.845 .
3. Hirayama, Naomi (2019). "Substitutional and interstitial impurity p-type doping of thermoelectric Mg₂Si: a theoretical study". Sci. Technol. Adv. Mater. 20 (1): 160–172. Bibcode:2019STAdM..20..160H. doi:10.1080/14686996.2019.1580537. PMC   6419642 . PMID   30891103.
4. Ehrlich, P. (1963). "17". In Brauer, Georg (ed.). Handbook of Preparative Inorganic Chemistry (PDF). Vol. 1. Translated by Riley; Reed F. (2nd ed.). New York: Academic Press, Inc. p. 921. ISBN   978-0121266011 . Retrieved 26 September 2024.
5. Stock, Alfred; Somieski, Carl (1916). "Siliciumwasserstoffe. I. Die aus Magnesiumsilicid und Säuren entstehenden Siliciumwasserstoffe". Berichte der Deutschen Chemischen Gesellschaft. 49: 111–157. doi:10.1002/cber.19160490114.
6. "Properties and Selection: Non-ferrous Alloys and Special Purpose Materials" in ASM Handbook, 10th ed., Vol. 1, 1990, ASM International, Materials Park, Ohio. ISBN   0871703785.
7. Borisenko, Victor E. (2013). Semiconducting Silicides: Basics, Formation, Properties. Springer Science & Business Media. pp. 187, 287. ISBN   978-3-642-59649-0.