Intermetallics
Encyclopedia
Intermetallics or intermetallic compounds is a term that is used in a number of different ways. Most commonly it refers to solid-state phases involving metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...

s. There is a "research definition" adhered to generally in scientific publications, and a wider "common use" term. There is also a completely different use in coordination chemistry, where it has been used to refer to complexes containing two or more different metals.

Although the term intermetallic compounds, as it applies to solid phases, has been in use for many years, its introduction was regretted, for example by Hume-Rothery in 1955.

Note that many intermetallic compounds are often simply called alloys, even though strictly speaking they are not. For example, complex metallic alloys
Complex metallic alloys
Complex metallic alloys are intermetallic compounds characterized by the following structural features:#large unit cells, comprising some tens up to thousands of atoms,...

 are intermetallic compounds with large unit cells.

Research definition

This was stated by Schulze in 1967, and defines intermetallic compounds as solid phases containing two or more metallic elements, with optionally one or more non-metallic elements, whose crystal structure differs from that of the other constituents. Under this definition the following are included
  • Electron (or Hume-Rothery) compounds
  • Size packing phases. e.g. Laves phase
    Laves phase
    Laves phases are intermetallic phases that have composition AB2 and are named for Fritz Laves who first described them. The phases are classified on the basis of geometry alone. There are three different classification classes: cubic, hexagonal MgZn2, and hexagonal MgNi2. The latter two classes...

    s, Frank-Kaspar phases and Nowotny phase
    Nowotny phase
    A Nowotny chimney ladder phase in inorganic chemistry is a particular intermetallic crystal structure found with certain binary compounds. NLC phases are generally tetragonal and are composed of two separate sublattices. The first is a tetragonal array of transition metal atoms, generally from...

    s
  • Zintl phase
    Zintl phase
    In chemistry a Zintl phase is the product of a reaction between*group 1 or group 2 and*post transition metals or metalloids from group 13, 14, 15 or 16....

    s

The definition of a metal is taken to include:
  • the so-called poor metals, i.e. aluminium, gallium, indium, thallium, tin and lead
  • some, if not all, of the metalloid
    Metalloid
    Metalloid is a term used in chemistry when classifying the chemical elements. On the basis of their general physical and chemical properties, each element can usually be classified as a metal or a nonmetal. However, some elements with intermediate or mixed properties can be harder to characterize...

    s, e.g. silicon, germanium, arsenic, antimony and tellurium.


Alloys, which are a homogeneous mixture of metals, and interstitial compound
Interstitial compound
An interstitial compound or interstitial alloy is a compound that is formed when an atom of sufficiently small radius sits in an interstitial “hole” in a metal lattice. Examples of small atoms are hydrogen, boron, carbon and nitrogen...

s such as the carbide
Carbide
In chemistry, a carbide is a compound composed of carbon and a less electronegative element. Carbides can be generally classified by chemical bonding type as follows: salt-like, covalent compounds, interstitial compounds, and "intermediate" transition metal carbides...

s and nitride
Nitride
In chemistry, a nitride is a compound of nitrogen where nitrogen has a formal oxidation state of −3. Nitrides are a large class of compounds with a wide range of properties and applications....

s are excluded under this definition. However, interstitial intermetallic compounds are included as are alloys of intermetallic compounds with a metal.

Common use

In common use of the research definition, including poor metals and metalloids, is extended to include compounds such as cementite
Cementite
Cementite, also known as iron carbide, is a chemical compound of iron and carbon, with the formula Fe3C . By weight, it is 6.67% carbon and 93.3% iron. It has an orthorhombic crystal structure. It is a hard, brittle material, normally classified as a ceramic in its pure form, though it is more...

, Fe3C. These compounds, sometimes termed interstitial compound
Interstitial compound
An interstitial compound or interstitial alloy is a compound that is formed when an atom of sufficiently small radius sits in an interstitial “hole” in a metal lattice. Examples of small atoms are hydrogen, boron, carbon and nitrogen...

s can be stoichiometric, and share similar properties to the intermetallic compounds defined above.

Complexes

The term intermetallic is used to describe compounds involving two or more metals such as the cyclopentadienyl complex Cp6Ni2Zn4.

Intermetallics involving two or more metallic elements

Intermetallic compounds are generally brittle and high melting. They often offer a compromise between ceramic
Ceramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...

 and metallic properties when hardness and/or resistance to high temperatures is important enough to sacrifice some toughness
Toughness
In materials science and metallurgy, toughness is the ability of a material to absorb energy and plastically deform without fracturing; Material toughness is defined as the amount of energy per volume that a material can absorb before rupturing...

 and ease of processing. They can also display desirable magnetic
Magnetism
Magnetism is a property of materials that respond at an atomic or subatomic level to an applied magnetic field. Ferromagnetism is the strongest and most familiar type of magnetism. It is responsible for the behavior of permanent magnets, which produce their own persistent magnetic fields, as well...

, superconducting and chemical properties, due to their strong internal order and mixed (metallic
Metallic bond
Metallic bonding is the electrostatic attractive forces between the delocalized electrons, called conduction electrons, gathered in an "electron sea", and the positively charged metal ions...

 and covalent
Covalent bond
A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding....

/ionic
Ionic bond
An ionic bond is a type of chemical bond formed through an electrostatic attraction between two oppositely charged ions. Ionic bonds are formed between a cation, which is usually a metal, and an anion, which is usually a nonmetal. Pure ionic bonding cannot exist: all ionic compounds have some...

) bonding, respectively. Intermetallics have given rise to various novel materials developments. Some examples include alnico
Alnico
Alnico is an acronym referring to iron alloys which in addition to iron are composed primarily of aluminium , nickel and cobalt , hence al-ni-co, with the addition of copper, and sometimes titanium. Alnico alloys are ferromagnetic, with a high coercivity and are used to make permanent magnets...

 and the hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 storage materials in nickel metal hydride batteries. 3, which is the hardening phase in the familiar nickel-base superalloy
Superalloy
A superalloy, or high-performance alloy, is an alloy that exhibits excellent mechanical strength and creep resistance at high temperatures, good surface stability, and corrosion and oxidation resistance. Superalloys typically have a matrix with an austenitic face-centered cubic crystal structure. ...

s, and the various titanium
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....

 aluminides have also attracted interest for turbine blade applications, while the latter is also used in very small quantities for grain refinement of titanium alloy
Titanium alloy
Titanium alloys are metallic materials which contain a mixture of titanium and other chemical elements. Such alloys have very high tensile strength and toughness , light weight, extraordinary corrosion resistance, and ability to withstand extreme temperatures...

s.

Properties and examples

  • magnetic materials e.g. alnico
    Alnico
    Alnico is an acronym referring to iron alloys which in addition to iron are composed primarily of aluminium , nickel and cobalt , hence al-ni-co, with the addition of copper, and sometimes titanium. Alnico alloys are ferromagnetic, with a high coercivity and are used to make permanent magnets...

    ; sendust
    Sendust
    Sendust is a magnetic metal powder that was invented at Tohoku Imperial University in Sendai, Japan, about 1936 as an alternative to permalloy in inductor applications for telephone networks. Sendust composition is typically 85% iron, 9% silicon and 6% aluminum. The powder is sintered into cores...

    ; Permendur, FeCo
  • superconductors e.g. A15 phases
    A15 phases
    The A15 phases are series of intermetallic compounds with the chemical formula A3B and a specific structure...

    ; niobium-tin
    Niobium-tin
    Niobium-tin or triniobium-tin is a metallic chemical compound of niobium and tin , used industrially as a type II superconductor. This intermetallic compoundis a A15 phases superconductor...

  • hydrogen storage
    Hydrogen storage
    Hydrogen storage describes the methods for storing H2 for subsequent use. The methods span many approaches, including high pressures, cryogenics, and chemical compounds that reversibly release H2 upon heating...

     e.g. AB5 compounds (nickel metal hydride batteries)
  • shape memory alloy
    Shape memory alloy
    A shape-memory alloy is an alloy that "remembers" its original, cold-forged shape: returning the pre-deformed shape by heating. This material is a lightweight, solid-state alternative to conventional actuators such as hydraulic, pneumatic, and motor-based systems...

    s e.g. Cu-Al-Ni (alloys of Cu3Al and nickel); Nitinol (NiTi)
  • coating materials e.g. NiAl
  • high temperature structural materials e.g. nickel aluminide
    Nickel aluminide
    Nickel aluminide is an intermetallic material with properties similar to both a ceramic and a metal.There are three materials called nickel aluminide:* NiAl, CAS number 12003-78-0 * NiAl3, CAS number 12004-71-6* Ni3Al-Ni3Al:...

    , Ni3Al
  • dental amalgams which are alloys of intermetallics Ag3Sn and Cu3Sn


The formation of intermetallics can cause problems. Intermetallics of gold and aluminium
Gold-aluminium intermetallics
A gold-aluminium intermetallic is an intermetallic compound of gold and aluminium that occurs at contacts between the two metals. These intermetallics have different properties than the individual metals which can cause problems in wire bonding in microelectronics...

 are a significant cause of wire bond
Wire bonding
Wire bonding is the primary method of making interconnections between an integrated circuit and a printed circuit board during semiconductor device fabrication. Although less common, wire bonding can be used to connect an IC to other electronics or to connect from one PCB to another...

 failures in semiconductor devices and other microelectronics
Microelectronics
Microelectronics is a subfield of electronics. As the name suggests, microelectronics relates to the study and manufacture of very small electronic components. Usually, but not always, this means micrometre-scale or smaller,. These devices are made from semiconductors...

 devices. There are 5 of them. AuAl2 is known as "purple plague". Au5Al2 is known as "white plague".

History

Examples of intermetallics through history include:
  • Roman yellow brass
    Brass
    Brass is an alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties.In comparison, bronze is principally an alloy of copper and tin...

    , CuZn
  • Chinese high tin bronze
    Bronze
    Bronze is a metal alloy consisting primarily of copper, usually with tin as the main additive. It is hard and brittle, and it was particularly significant in antiquity, so much so that the Bronze Age was named after the metal...

    , Cu31Sn8
  • type metal
    Type metal
    In printing, type metal refers to the metal alloys used in traditional typefounding and hot metal typesetting. Lead is the main constituent of these alloys...

     SbSn

German type metal is described as breaking like glass, not bending, softer than copper but more fusible than lead. The chemical formula does not agree with the one above; however, the properties match with an intermetallic compound or an alloy of one.

See also

  • Alloy
    Alloy
    An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...

  • Complex metallic alloys
    Complex metallic alloys
    Complex metallic alloys are intermetallic compounds characterized by the following structural features:#large unit cells, comprising some tens up to thousands of atoms,...

  • Kirkendall effect
    Kirkendall effect
    The Kirkendall effect is the motion of the boundary layer between two metals that occurs as a consequence of the difference in diffusion rates of the metal atoms...

  • Maraging steel
    Maraging steel
    Maraging steels are steels which are known for possessing superior strength and toughness without losing malleability, although they cannot hold a good cutting edge. Aging refers to the extended heat-treatment process...

  • Metallurgy
    Metallurgy
    Metallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their mixtures, which are called alloys. It is also the technology of metals: the way in which science is applied to their practical use...

  • Superalloy
    Superalloy
    A superalloy, or high-performance alloy, is an alloy that exhibits excellent mechanical strength and creep resistance at high temperatures, good surface stability, and corrosion and oxidation resistance. Superalloys typically have a matrix with an austenitic face-centered cubic crystal structure. ...


External links

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