Boride

	Email		Print
	Bookmark		Link

Boride

In chemistry a boride is a chemical compound between boron

Boron

Boron is a chemical element with atomic number 5 and the chemical symbol B. Boron is a trivalent metalloid element which occurs abundantly in the evaporite ores borax and ulexite....
and a less electronegative

Electronegativity

Electronegativity, symbol χ, is a chemical property that describes the ability of an atom to attract electrons towards itself in a covalent bond....
element. This is a very large group of compounds that are generally high melting and are not ionic in nature. Some borides exhibit very useful physical properties. The term boride is also loosely applied to compounds such as B₁₂As₂ (N.B. Arsenic has an electronegativity higher than boron) that is often referred to as icosahedral boride

Boron arsenide

Boron arsenide is a chemical compound of boron and arsenic. It is a cubic semiconductor with a lattice constant of 0.4777 nm and an indirect bandgap of roughly 1.5 eV....
.

borides can be classified loosely as boron rich or metal rich, for example the compound YB₆₆ at one extreme through to Nd₂Fe₁₄B at the other.

Discussion

Ask a question about 'Boride'

Start a new discussion about 'Boride'

Answer questions from other users

Full Discussion Forum

Encyclopedia

In chemistry a boride is a chemical compound between boron

Boron

Electronegativity

Boron arsenide

Boron arsenide is a chemical compound of boron and arsenic. It is a cubic semiconductor with a lattice constant of 0.4777 nm and an indirect bandgap of roughly 1.5 eV....
.

Ranges of compounds

The borides can be classified loosely as boron rich or metal rich, for example the compound YB₆₆ at one extreme through to Nd₂Fe₁₄B at the other. The generally accepted definition is that if the ratio of boron atoms to metal atoms is 4 : 1 or more the compound is boron rich, if it is less then it is metal rich.

Boron rich borides (B:M 4:1 or more)

The main group metals, lanthanide

Lanthanide

According to the IUPAC terminology, the lanthanoid series comprises the fifteen chemical elements with atomic numbers 57 through 71, from lanthanum to lutetium....
s and actinide

Actinide

According to IUPAC nomenclature, the actinoid series encompasses the 15 chemical elements that lie between actinium and lawrencium included on the periodic table, with atomic numbers 89 - 103....
s form a wide variety of boron-rich borides, with metal:boron ratios up to YB₆₆.

The properties of this group vary from one compound to the next, and includes examples of compounds that are semi conductors, superconductors, diamagnetic

Diamagnetism

Diamagnetism is the property of an object which causes it to create a magnetic field in opposition of an externally applied magnetic field, thus causing a repulsive effect....
, paramagnetic

Paramagnetism

Paramagnetism is a form of magnetism which occurs only in the presence of an externally applied magnetic field. Paramagnetic materials are attracted to magnetic fields, hence have a relative magnetic permeability greater than 1 ....
, ferromagnetic

Ferromagnetism

Ferromagnetism is the basic mechanism by which certain materials form permanent magnets and/or exhibit strong interactions with magnets; it is responsible for most phenomena of magnetism Magnet#Common uses of magnets ....
or anti-ferromagnetic

Antiferromagnetism

In materials that exhibit antiferromagnetism, the magnetic moments of atoms or molecules, usuallyrelated to the spins of electrons, align in a regular pattern with neighboring spin s pointing in opposite directions....
.. They are mostly stable and refractory.

Some metallic dodecaborides contain boron icosahedra, others (for example yttrium

Yttrium

Yttrium is a chemical element with symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanoids and has historically been classified as a rare earth element....
, zirconium

Zirconium

Zirconium is a chemical element with the symbol Zr and atomic number 40. It is a lustrous, gray-white, strong transition metal that resembles titanium....
and uranium

Uranium

Uranium is a silvery-gray metallic chemical element in the actinide series of the periodic table that has the chemical symbol U and atomic number 92....
) have the boron atoms arranged in cuboctahedra

Cuboctahedron

In geometry, a cuboctahedron is a polyhedron with eight triangular faces and six square faces. A cuboctahedron has 12 identical vertices, with two triangles and two squares meeting at each, and 24 identical edges, each separating a triangle from a square....
.

LaB₆

Lanthanum hexaboride

Lanthanum hexaboride is an inorganic chemical, a boride of lanthanum. It is a refractory ceramic material that has a melting point of 2210 ?C, is insoluble in water and hydrochloric acid....
is an inert refractory

Refractory

A refractory material is one that retains its strength at high temperatures. ASTM International C71 defines refractories as "non-metallic materials having those chemical and physical properties that made them applicable for structures, or as components of systems, that are exposed to environments above 1000 ?F "....
compound, used in hot cathodes because of its low work function for emission of electrodes; YB₆₆ crystals are used as monochromator

Monochromator

A monochromator is an optics device that transmits a mechanically selectable narrow band of wavelengths of light or other radiation chosen from a wider range of wavelengths available at the input....
s for low-energy synchrotron

Synchrotron

A synchrotron is a particular type of cyclic particle accelerator in which the magnetic field and the electric field are carefully synchronized with the travelling particle beam....
X-rays. describes the production of the crystals by a indirect-heating floating zone method, their characterisation and their use on the beamline.

Metal rich borides (B:M less than 4:1)

The transition metals tend to form metal rich borides. Metal-rich borides as a group are high melting and inert. Some are easily formed and this explains their use in making turbine blades, rocket nozzles etc. Some examples include AlB₂

Aluminium diboride

Aluminium diboride is a chemical compound made from the metal aluminium and the non-metal boron. It is one of two compounds of aluminium and boron, the other being aluminium dodecaboride that are both commonly referred to as aluminium boride....
and TiB₂

Titanium boride

Titanium diboride is an extremely hard ceramic compound composed of titanium and boron which has excellent wear resistance . TiB2 is also a reasonable electrical conductor , so it can be used as an anode material in aluminium smelting and can also be shaped by electrical discharge machining....
. Recent investigations into this class of borides have revealed a wealth of interesting properties such as super conductivity at 39 K in MgB₂

Magnesium diboride

Magnesium diboride is an inexpensive and simple superconductor. Its superconductivity was announced in the journal Nature in March 2001. Its critical temperature#Superconductivity of is the highest amongst conventional superconductors....
and the ultra-incompressibility of OsB₂ and ReB₂

Rhenium diboride

Rhenium diboride is a synthetic superhard material. It was discovered by a team at University of California, Los Angeles and announced in Science in April 2007....

Boride structures

The boron rich borides contain 3-dimensional frameworks of boron atoms that can include boron polyhedra. The metal rich borides contain single boron atoms, B₂ units, boron chains or boron sheets/layers.

Examples of the different types of borides are :-

isolated boron atoms, example Mn₄B
B₂ units, example V₃B
chains of boron atoms, example FeB
sheets or layers of boron atoms CrB₂
3-dimensional boron frameworks that include boron polyhedra, example NaB₁₅ with boron icosahedra

Boride

Ranges of compounds

Boron rich borides (B:M 4:1 or more)

Metal rich borides (B:M less than 4:1)

Boride structures

See also

General References

Footnotes