Magnesium silicide
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| Magnesium silicide | |
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| IUPAC name | Magnesium silicide |
| Identifiers | |
| CAS number | [22831-39-6] |
| Properties | |
| Molecular formula | Mg2Si |
| Molar mass | 76.70 g mol−1 |
| Density | 2.56 g cm−3 |
| Melting point |
778 °C |
| Hazards | |
| NFPA 704 |
 0
2
0
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| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references |
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Magnesium silicide, Mg2Si, is an inorganic compound consisting of magnesium and silicon. 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 is used to create aluminum 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.
[edit] 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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