Magnesium silicide

Magnesium silicide, Mg2Si, is an inorganic compound consisting 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]

Magnesium silicide
Names
Preferred IUPAC name
Magnesium silicide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.041.125
EC Number
  • 245-254-5
UNII
UN number 2624
  • InChI=1S/2Mg.Si checkY
    Key: YTHCQFKNFVSQBC-UHFFFAOYSA-N checkY
  • InChI=1/2Mg.Si/rMg2Si/c1-3-2
    Key: YTHCQFKNFVSQBC-GEBTXNJDAA
  • [Mg]=[Si]=[Mg]
Properties
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]
reacts[1]
Structure[2]
Antifluorite (cubic), cF12
Fm3m, #225
a = 0.6351 nm
4
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 reacts with water to produce pyrophoric silane
GHS labelling:
GHS02: Flammable
Warning
H261
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).
checkY verify (what is checkY☒N ?)
Infobox references

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

It can be produced by heating silicon dioxide, SiO2, found in sand, with excess magnesium. The process first forms silicon metal and magnesium oxide, and, if an excess of SiO2 is used, then elemental silicon is formed:

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 silicon:

2 Mg + Si → Mg2Si

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

Reactions

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, both resulting in increased strength of the alloy.[6]

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

References
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  1. Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). Boca Raton, FL: 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 Mg2Si1−xGex (x=0.0~0.4) Solid Solution Semiconductors". Mater. Trans., JIM. 33 (9): 845–850. doi:10.2320/matertrans1989.33.845.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  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.open access
  4. Ehrlich, P. (1963) "Alkaline Earth Metals", p. 920 in Handbook of Preparative Inorganic Chemistry, 2nd ed., Vol. 1. G. Brauer (ed.). Academic Press, New York.
  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.
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