Magnesium silicide, Mg₂Si, is an

inorganic compound An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''. Inorgan ...

consisting of

magnesium Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...

and

silicon Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...

. As-grown Mg₂Si usually forms black crystals; they are

semiconductor A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities (" doping") to its crystal structure. When two regions with different doping level ...

s with n-type conductivity and have potential applications in

thermoelectric generator A thermoelectric generator (TEG), also called a Seebeck generator, is a solid state device that converts heat (driven by temperature differences) directly into electrical energy through a phenomenon called the '' Seebeck effect'' (a form of the ...

Crystal structure

Mg₂Si crystallizes in the antifluorite structure. In the

face-centered cubic In crystallography, the cubic (or isometric) crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals. There are three main varieties o ...

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

It can be produced by heating

silicon dioxide Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundan ...

, SiO₂, found in

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is usually defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural ...

, with excess

. The process first forms silicon metal and

magnesium oxide Magnesium oxide (MgO), or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium (see also oxide). It has an empirical formula of MgO and consists of a lattice of Mg2+ ions and O2− ions ...

, 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, even explosively.

Reactions

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 Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...

silane Silane (Silicane) is an inorganic compound with chemical formula . It is a colorless, pyrophoric gas with a sharp, repulsive, pungent smell, somewhat similar to that of acetic acid. Silane is of practical interest as a precursor to elemental ...

(SiH₄) and

magnesium chloride Magnesium chloride is an inorganic compound with the formula . It forms hydrates , where ''n'' can range from 1 to 12. These salts are colorless or white solids that are highly soluble in water. These compounds and their solutions, both of which ...

are produced: :Mg₂Si + 4 HCl → SiH₄ + 2 MgCl₂

Sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...

can be used as well. These protonolysis reactions are typical of a

group 2 The term Group 2 may refer to: * Alkaline earth metal The alkaline earth metals are six chemical elements in group (periodic table), group 2 of the periodic table. They are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (B ...

(

alkaline earth metal The alkaline earth metals are six chemical elements in group (periodic table), group 2 of the periodic table. They are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).. The elements have very similar p ...

) and

group 1 Group 1 may refer to: * Alkali metal, a chemical element classification for Alkali metal * Group 1 (motorsport), a regulation set of the FIA for series-production touring cars used in motorsport. * Group One Thoroughbred horse races, the leading e ...

(

alkali metal The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K),The symbols Na and K for sodium and potassium are derived from their Latin names, ''natrium'' and ''kalium''; these are still the origins of the names ...

)

silicide A silicide is a type of chemical compound that combines silicon and a usually more electropositive element. Silicon is more electropositive than carbon. In terms of their physical properties, silicides are structurally closer to borides than t ...

s. 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. . 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

References

{{Silicides Alkaline earth silicides Magnesium compounds Fluorite crystal structure