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
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

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 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

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, 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 be 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]