Magnesium silicide, Mg₂Si, is an

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

consisting of

magnesium Magnesium is a chemical element with the 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 of the periodic ...

and

silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ...

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

semiconductor A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way ...

s with n-type conductivity and have potential applications in thermoelectric generators.

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 of ...

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 , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

, SiO₂, found in

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

, with excess

. The process first forms silicon metal and

magnesium oxide Magnesium oxide ( Mg O), 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� ...

, 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,Ehrlich, P. (1963) "Alkaline Earth Metals", p. 920 in ''Handbook of Preparative Inorganic Chemistry'', 2nd ed., Vol. 1. G. Brauer (ed.). Academic Press, New York. 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, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the dige ...

silane Silane is an inorganic compound with chemical formula, . It is a colourless, pyrophoric, toxic gas with a sharp, repulsive smell, somewhat similar to that of acetic acid. Silane is of practical interest as a precursor to elemental silicon. Sila ...

(SiH₄) and

magnesium chloride Magnesium chloride is the family of inorganic compounds with the formula , where x can range from 0 to 12. These salts are colorless or white solids that are highly soluble in water. These compounds and their solutions, both of which occur in natu ...

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

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

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

Group 2 The term Group 2 may refer to: * Alkaline earth metal, a chemical element classification * Astronaut Group 2, also known as The New Nine, the second group of astronauts selected by NASA in 1962 * Group 2 (racing) The Group 2 racing class referred ...

alkaline earth metal The alkaline earth metals are six chemical elements in 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 properties: they are all ...

and

Group 1 Group 1 may refer to: * Alkali metal, a chemical element classification for Alkali metal * Group 1 (racing), a historic (until 1981) classification for Touring car racing, applied to standard touring cars. Comparable to modern FIA Group N * Group On ...

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. Silicides are structurally closer to borides than to carbides. Similar to borides and carb ...

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 Narrow-gap semiconductors are semiconducting materials with a band gap that is comparatively small compared to that of silicon, i.e. smaller than 1.11 eV at room temperature. They are used as infrared detectors or thermoelectrics. List of narrow- ...

. Its as-grown crystal exhibit n-type conductivity, but it can 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

{{Silicides Alkaline earth silicides Magnesium compounds Fluorite crystal structure