magnesium silicide
{{Chembox
| Watchedfields = changed
| verifiedrevid = 451686130
| ImageFile1 = Antifluorite_Structure.jpg
| ImageFile2 = Magnesium silicide.jpg
| ImageName = Sample of magnesium silicide as powder
| PIN = Magnesium silicide
|Section1={{Chembox Identifiers
| CASNo = 22831-39-6
| CASNo_Ref = {{cascite|correct|CAS}}
| PubChem = 89858
| ChemSpiderID = 81111
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| EINECS = 245-254-5
| UNNumber = 2624
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 475E6FMG3K
| SMILES = [Mg]=[Si]=[Mg]
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/2Mg.Si
| InChI = 1/2Mg.Si/rMg2Si/c1-3-2
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = YTHCQFKNFVSQBC-UHFFFAOYSA-N
| InChIKey = YTHCQFKNFVSQBC-GEBTXNJDAA
}}
|Section2={{Chembox Properties
| Mg=2 | Si=1
| Appearance = Gray cubic crystals
| Density = 1.99 g cm−3{{RubberBible92nd|page=4.74}}
| MeltingPtC = 1102
| Solubility = reacts}}
|Section3={{Chembox Structure
| CrystalStruct = Antifluorite (cubic), cF12
| SpaceGroup = Fm{{overline|3}}m, #225
| Coordination =
| LattConst_a = 0.6351 nm
| LattConst_b =
| LattConst_c =
| LattConst_alpha =
| LattConst_beta =
| LattConst_gamma =
| MolShape =
| OrbitalHybridisation =
| Dipole =
| UnitCellFormulas = 4
}}
|Section7={{Chembox Hazards
| ExternalSDS =
| GHSPictograms = {{GHS02}}
| GHSSignalWord = Warning
| HPhrases = {{H-phrases|261}}
| PPhrases = {{P-phrases|231+232|280|370+378|402+404|501}}
| MainHazards = reacts with water to produce pyrophoric silane
| NFPA-H =
| NFPA-F =
| NFPA-R =
| NFPA-S =
| FlashPt =
| AutoignitionPt = }}
|Section8={{Chembox Related
| OtherAnions =
| OtherCations = Calcium silicide
| OtherFunction =
| OtherFunction_label =
| OtherCompounds = }}
}}
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.
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.
Synthesis
File:04. Добивање на аморфен силициум и магнезиум силицид.webm
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,{{cite book |last1=Ehrlich |first1=P. |editor1-last=Brauer |editor1-first=Georg |translator-last1=Riley |translator-last2=Reed F. |title=Handbook of Preparative Inorganic Chemistry |date=1963 |publisher=Academic Press, Inc. |location=New York |isbn=978-0121266011 |page=921 |volume=1 |edition=2nd |url=https://archive.org/download/Preperative_Inorganic_Chemistry_Brauer/Preperative_Inorganic_Chemistry_Brauer.pdf |access-date=26 September 2024 |language=English |chapter=17}} even explosively.{{cite journal |doi=10.1002/cber.19160490114|title=Siliciumwasserstoffe. I. Die aus Magnesiumsilicid und Säuren entstehenden Siliciumwasserstoffe|year=1916|last1=Stock|first1=Alfred|last2=Somieski|first2=Carl|journal=Berichte der Deutschen Chemischen Gesellschaft|volume=49|pages=111–157|url=https://zenodo.org/record/1426597}}
Reactions
File:05. Реакција на магнезиум силицид во солна киселина.webm
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.
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."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}}.
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.
References
{{Commons category|Magnesium silicide}}
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{{Magnesium compounds}}
{{Silicides}}