Magnesium silicide

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Magnesium silicide
CaF2 polyhedra.png
Magnesium silicide.jpg
Names
Preferred IUPAC name
Magnesium silicide
Identifiers
22831-39-6 YesY
ChemSpider 81111 YesY
EC number 245-254-5
Jmol-3D images Image
PubChem 89858
Properties
Mg2Si
Molar mass 76.69 g·mol−1
Density 1.988 g cm−3
Melting point 1,102 °C (2,016 °F; 1,375 K)
Hazards
Main hazards reacts with water to give silane
R-phrases R23, R24, R25, R34
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).
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Infobox references

Magnesium silicide, Mg2Si, is an inorganic compound consisting of magnesium and silicon. As a powder magnesium silicide is dark blue or slightly purple in color.

Synthesis[edit]

The material is prepared by combining silicon and magnesium in a 2:1 proportion. 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 magnesium is used, the silicide 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 via:

2 Mg + Si → Mg2Si

Hence, the overall reaction for the formation of magnesium silicide from a 4:1 Mg:SiO2 molar ratio may be represented as:

4 Mg + SiO2 → 2 MgO + Mg2Si

These reactions proceed exothermically.[1]

Uses[edit]

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.[2]

Reactions[edit]

Magnesium silicide can be viewed as consisting of Si4− ions. As such it is reactive toward acids. Thus, when magnesium silicide is placed into hydrochloric acid, HCl (aq), the gas silane, SiH4, is produced:

Mg2Si + 4 HCl → SiH4 + 2 MgCl2

Sulfuric acid can be used as well. These protonolysis reactions are typical of a Group 2 silicide. Group 1 silicides are even more reactive. For example, sodium silicide, Na2Si, reacts rapidly with water to yield sodium silicate, Na2SiO3, and hydrogen gas.

Crystal Structure[edit]

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.[3]

References[edit]

  1. ^ P. Ehrlich "Alkaline Earth Metals" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 920.
  2. ^ ASM Handbook, 10th Ed., Vol. 1, Properties and Selection: Non-ferrous Alloys and Special Purpose Materials, 1990, ASM International, Materials Park, Ohio.
  3. ^ A. Kato et al. J. Phys: Condens. Matter 21 (2009) 205801.