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Magnesium silicide
Magnesium silicide
Identifiers
CAS number 22831-39-6 Yes check.svgY
PubChem 89858
Properties
Molecular formula Mg2Si
Molar mass 76.6955 g/mol
Density 1.988 g/cm3
Melting point

1102 °C

Solubility in water reacts
Hazards
EU Index Not listed
Main hazards reacts with water to give silane
Related compounds
Other cations Calcium silicide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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 colour. Silicon dioxide, SiO2, found in sand and glass, when heated with magnesium forms magnesium silicide. The first product in this reaction is silicon, which then reacts further with magnesium to produce Mg2Si:

SiO2 + 2Mg → 2MgO + Si
Si + 2Mg → Mg2Si

Magnesium silicide can also be formed by the reaction between magnesium hydride and silicon with the evolution of hydrogen gas at temperatures above 250°C:

2MgH2+Si→Mg2Si+2H2

This reaction releases 5 wt.% hydrogen and has been considered for hydrogen storage. However, its reversibility has yet to be demonstrated.

Magnesium silicide is used to create aluminium alloys of the 6xxx group, 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.[1]

When magnesium silicide is placed into hydrochloric acid, HCl(aq), the gas silane, SiH4, is produced. This gas is the silicon analogue of methane, CH4, but is more reactive. Silane is pyrophoric, that is, due to the presence of oxygen, it spontaneously combusts in air:

Mg2Si(s) + 4HCl(aq) → SiH4(g) + 2MgCl2(s)
SiH4 + 2O2 → SiO2 + 2H2O

These reactions are typical of a Group 2 silicide. Mg2Si reacts similarly with sulfuric acid. Group 1 silicides are even more reactive. For example, sodium silicide, Na2Si, reacts rapidly with water to yield sodium silicate, Na2SiO3, and hydrogen gas.

References

  1. ^ ASM Handbook, 10th Ed., Vol. 1, Properties and Selection: Non-ferrous Alloys and Special Purpose Materials, 1990, ASM International, Materials Park, Ohio.
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