Boron is a chemical element. It has the

symbol A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise very different conc ...

B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous

metalloid A metalloid is a type of chemical element which has a preponderance of material property, properties in between, or that are a mixture of, those of metals and nonmetals. There is no standard definition of a metalloid and no complete agreement on ...

; in its

amorphous In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid, glassy solid) is a solid that lacks the long-range order that is characteristic of a crystal. Etymology The term comes from the Greek ''a'' ("wi ...

form it is a brown powder. As the lightest element of the boron group it has three valence electrons for forming

covalent bond A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atoms ...

s, resulting in many compounds such as boric acid, the mineral sodium borate, and the ultra-hard crystals of

boron carbide Boron carbide (chemical formula approximately B4C) is an extremely hard boron–carbon ceramic, a covalent material used in tank armor, bulletproof vests, engine sabotage powders, as well as numerous industrial applications. With a Vickers hard ...

and boron nitride. Boron is synthesized entirely by cosmic ray spallation and

supernova A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when ...

s and not by

stellar nucleosynthesis Stellar nucleosynthesis is the creation (nucleosynthesis) of chemical elements by nuclear fusion reactions within stars. Stellar nucleosynthesis has occurred since the original creation of hydrogen, helium and lithium during the Big Bang. As a ...

, so it is a low-abundance element in the Solar System and in the

Earth's crust Earth's crust is Earth's thin outer shell of rock, referring to less than 1% of Earth's radius and volume. It is the top component of the lithosphere, a division of Earth's layers that includes the crust and the upper part of the mantle. The ...

. It constitutes about 0.001 percent by weight of Earth's crust. It is concentrated on Earth by the water-solubility of its more common naturally occurring compounds, the borate minerals. These are mined industrially as evaporites, such as borax and

kernite Kernite, also known as rasorite, is a hydrated sodium borate hydroxide mineral with formula . It is a colorless to white mineral crystallizing in the monoclinic crystal system typically occurring as prismatic to acicular crystals or granular mass ...

. The largest known deposits are in Turkey, the largest producer of boron minerals. Elemental boron is a

that is found in small amounts in meteoroids, but chemically uncombined boron is not otherwise found naturally on Earth. Industrially, the very pure element is produced with difficulty because of contamination by carbon or other elements that resist removal. Several allotropes exist:

boron is a brown powder; crystalline boron is silvery to black, extremely hard (9.3 on the

Mohs scale The Mohs scale of mineral hardness () is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. The scale was introduced in 1812 by th ...

), and a poor electrical conductor at room temperature (1.5 × 10^-6 Ω^-1 cm^-1 room temperature electrical conductivity). The primary use of the element itself is as boron filaments with applications similar to

carbon fibers Carbon fibers or carbon fibres (alternatively CF, graphite fiber or graphite fibre) are fibers about in diameter and composed mostly of carbon atoms. Carbon fibers have several advantages: high stiffness, high tensile strength, high stren ...

in some high-strength materials. Boron is primarily used in chemical compounds. About half of all production consumed globally is an additive in fiberglass for insulation and structural materials. The next leading use is in polymers and ceramics in high-strength, lightweight structural and heat-resistant materials. Borosilicate glass is desired for its greater strength and thermal shock resistance than ordinary soda lime glass. As sodium perborate, it is used as a

bleach Bleach is the generic name for any chemical product that is used industrially or domestically to remove color (whitening) from a fabric or fiber or to clean or to remove stains in a process called bleaching. It often refers specifically, to ...

. A small amount is used as a dopant in semiconductors, and

reagent In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...

intermediates in the synthesis of organic fine chemicals. A few boron-containing organic pharmaceuticals are used or are in study. Natural boron is composed of two stable isotopes, one of which ( boron-10) has a number of uses as a neutron-capturing agent. The intersection of boron with biology is very small. Consensus on it as essential for mammalian life is lacking. Borates have low toxicity in mammals (similar to table salt) but are more toxic to arthropods and are occasionally used as

insecticide Insecticides are substances used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. Insecticides are used in agriculture, medicine, industry and by consumers. Insecticides are claimed to b ...

s. Boron-containing organic antibiotics are known. Although only traces are required, it is an essential

plant nutrient Plant nutrition is the study of the chemical elements and compounds necessary for plant growth and reproduction, plant metabolism and their external supply. In its absence the plant is unable to complete a normal life cycle, or that the element i ...

History

The word ''boron'' was coined from '' borax'', the mineral from which it was isolated, by analogy with ''carbon'', which boron resembles chemically. Sassolite

Borax in its mineral form (then known as tincal) first saw use as a glaze, beginning in

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...

circa 300 AD. Some crude borax traveled westward, and was apparently mentioned by the alchemist Jabir ibn Hayyan around 700 AD.

Marco Polo Marco Polo (, , ; 8 January 1324) was a Venetian merchant, explorer and writer who travelled through Asia along the Silk Road between 1271 and 1295. His travels are recorded in ''The Travels of Marco Polo'' (also known as ''Book of the Marv ...

brought some glazes back to Italy in the 13th century. Georgius Agricola, in around 1600, reported the use of borax as a flux in

metallurgy Metallurgy is a domain of materials science and engineering that studies the physical and chemical behavior of metallic elements, their inter-metallic compounds, and their mixtures, which are known as alloys. Metallurgy encompasses both the sc ...

. In 1777, boric acid was recognized in the hot springs (

soffioni Soffioni (sometimes spelt ''suffioni''), a name applied in Italy to certain volcanic vents which emit jets of steam, generally associated with hydrogen sulfide and carbon dioxide, sometimes also with a little ammonia and marsh gas. The soffioni a ...

) near Florence, Italy, at which point it became known as ''sal sedativum'', with ostensible medical benefits. The mineral was named sassolite, after

Sasso Pisano Sasso Pisano is a village in Tuscany, central Italy, administratively a frazione of the comune of Castelnuovo di Val di Cecina, province of Pisa. At the time of the 2001 census its population was 213.European borax from 1827 to 1872, when

American American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the "United States" or "America" ** Americans, citizens and nationals of the United States of America ** American ancestry, pe ...

sources replaced it. Boron compounds were relatively rarely used until the late 1800s when Francis Marion Smith's Pacific Coast Borax Company first popularized and produced them in volume at low cost. Boron was not recognized as an element until it was isolated by Sir Humphry Davy and by Joseph Louis Gay-Lussac and

Louis Jacques Thénard Louis Jacques Thénard (4 May 177721 June 1857) was a French chemist. Life He was born in a farm cottage near Nogent-sur-Seine in the Champagne district the son of a farm worker. In the post-Revolution French educational system , most boys rec ...

. In 1808 Davy observed that electric current sent through a solution of borates produced a brown precipitate on one of the electrodes. In his subsequent experiments, he used potassium to

reduce Reduction, reduced, or reduce may refer to: Science and technology Chemistry * Reduction (chemistry), part of a reduction-oxidation (redox) reaction in which atoms have their oxidation state changed. ** Organic redox reaction, a redox react ...

boric acid instead of

electrolysis In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from n ...

. He produced enough boron to confirm a new element and named it ''boracium''. Gay-Lussac and Thénard used iron to reduce boric acid at high temperatures. By oxidizing boron with air, they showed that boric acid is its oxidation product.

Jöns Jacob Berzelius Baron Jöns Jacob Berzelius (; by himself and his contemporaries named only Jacob Berzelius, 20 August 1779 – 7 August 1848) was a Swedish chemist. Berzelius is considered, along with Robert Boyle, John Dalton, and Antoine Lavoisier, to be on ...

identified it as an element in 1824. Pure boron was arguably first produced by the American chemist Ezekiel Weintraub in 1909.

Preparation of elemental boron in the laboratory

Some early routes to elemental boron involved the reduction of

boric oxide Boron trioxide or diboron trioxide is the oxide of boron with the formula . It is a colorless transparent solid, almost always glassy (amorphous), which can be crystallized only with great difficulty. It is also called boric oxide or boria. It h ...

with metals such as magnesium or aluminium. However, the product was often contaminated with borides of those metals. Pure boron can be prepared by reducing volatile boron halides with hydrogen at high temperatures. Ultrapure boron for use in the semiconductor industry is produced by the decomposition of diborane at high temperatures and then further purified by the zone melting or Czochralski processes. The production of boron compounds does not involve the formation of elemental boron, but exploits the convenient availability of borates.

Characteristics

Allotropes

Boron is similar to carbon in its capability to form stable covalently bonded molecular networks. Even nominally disordered (

) boron contains regular boron

icosahedra In geometry, an icosahedron ( or ) is a polyhedron with 20 faces. The name comes and . The plural can be either "icosahedra" () or "icosahedrons". There are infinitely many non- similar shapes of icosahedra, some of them being more symmetrica ...

which are bonded randomly to each other without long-range order. Crystalline boron is a very hard, black material with a melting point of above 2000 °C. It forms four major

allotrope Allotropy or allotropism () is the property of some chemical elements to exist in two or more different forms, in the same physical state, known as allotropes of the elements. Allotropes are different structural modifications of an element: the ...

s: α-rhombohedral and β-rhombohedral (α-R and β-R), γ-orthorhombic (γ) and β-tetragonal (β-T). All four phases are stable at ambient conditions, and β-rhombohedral is the most common and stable. An α-tetragonal phase also exists (α-T), but is very difficult to produce without significant contamination. Most of the phases are based on B₁₂ icosahedra, but the γ phase can be described as a

rocksalt Halite (), commonly known as rock salt, is a type of salt, the mineral (natural) form of sodium chloride ( Na Cl). Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, p ...

-type arrangement of the icosahedra and B₂ atomic pairs. It can be produced by compressing other boron phases to 12–20 GPa and heating to 1500–1800 °C; it remains stable after releasing the temperature and pressure. The β-T phase is produced at similar pressures, but higher temperatures of 1800–2200 °C. The α-T and β-T phases might coexist at ambient conditions, with the β-T phase being the more stable. Compressing boron above 160 GPa produces a boron phase with an as yet unknown structure, and this phase is a superconductor at temperatures below 6–12 K. Borospherene ( fullerene-like B₄₀ molecules) and borophene (proposed graphene-like structure) were described in 2014.

Chemistry of the element

Elemental boron is rare and poorly studied because the pure material is extremely difficult to prepare. Most studies of "boron" involve samples that contain small amounts of carbon. The chemical behavior of boron resembles that of silicon more than aluminium. Crystalline boron is chemically inert and resistant to attack by boiling hydrofluoric or hydrochloric acid. When finely divided, it is attacked slowly by hot concentrated hydrogen peroxide, hot concentrated nitric acid, hot

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 formu ...

or hot mixture of sulfuric and chromic acids. The rate of oxidation of boron depends on the crystallinity, particle size, purity and temperature. Boron does not react with air at room temperature, but at higher temperatures it burns to form boron trioxide: :4 B + 3 O₂ → 2 B₂O₃ Tetraborate-xtal-3D-balls

Boron undergoes halogenation to give trihalides; for example, :2 B + 3 Br₂ → 2 BBr₃ The trichloride in practice is usually made from the oxide.

Atomic structure

Boron is the lightest element having an electron in a

p-orbital In atomic theory and quantum mechanics, an atomic orbital is a Function (mathematics), function describing the location and wave-like behavior of an electron in an atom. This function can be used to calculate the probability of finding any electr ...

in its ground state. Unlike most other p-elements, it rarely obeys the octet rule and usually places only six electrons (in three molecular orbitals) onto its valence shell. Boron is the prototype for the boron group (the IUPAC group 13), although the other members of this group are metals and more typical p-elements (only aluminium to some extent shares boron's aversion to the octet rule). Boron also has much lower electronegativity than subsequent

period 2 element A period 2 element is one of the chemical elements in the second row (or period) of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behavior of th ...

s. For the latter, lithium salts are common e.g. lithium fluoride, lithium hydroxide, lithium amide, and methyllithium, but lithium boryllides are extraordinarily rare.Bethany Halford ''Boron Attacks Electropositive element pressed into action as nucleophilic boryllithium'' '' Chemical & Engineering News'' 2006; Volume 84(41): 1
Link
Strong bases do not deprotonate a borohydride R₂BH to the boryl anion R₂B⁻, instead forming the octet-complete adduct R₂HB-base.''Boronic Acids: Preparation, Applications in Organic Synthesis and Medicine''. Dennis G. Hall

Chemical compounds

In the most familiar compounds, boron has the formal oxidation state III. These include oxides, borates, sulfides, nitrides, and halides. The trihalides adopt a planar trigonal structure. These compounds are

Lewis acid A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any sp ...

s in that they readily form adducts with electron-pair donors, which are called

Lewis base A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any sp ...

s. For example, fluoride (F⁻) and

boron trifluoride Boron trifluoride is the inorganic compound with the formula BF3. This pungent, colourless, and toxic gas forms white fumes in moist air. It is a useful Lewis acid and a versatile building block for other boron compounds. Structure and bondin ...

(BF₃) combined to give the tetrafluoroborate anion, BF₄⁻. Boron trifluoride is used in the petrochemical industry as a catalyst. The halides react with water to form boric acid. It is found in nature on Earth almost entirely as various oxides of B(III), often associated with other elements. More than one hundred borate minerals contain boron in oxidation state +3. These minerals resemble silicates in some respect, although it is often found not only in a tetrahedral coordination with oxygen, but also in a trigonal planar configuration. Unlike silicates, boron minerals never contain it with coordination number greater than four. A typical motif is exemplified by the tetraborate anions of the common mineral borax, shown at left. The formal negative charge of the tetrahedral borate center is balanced by metal cations in the minerals, such as the sodium (Na⁺) in borax. The tourmaline group of borate-silicates is also a very important boron-bearing mineral group, and a number of borosilicates are also known to exist naturally.

=Boranes

Deltahedral-borane-cluster-array-numbered-3D-bs-17

Boranes are chemical compounds of boron and hydrogen, with the generic formula of B_xH_y. These compounds do not occur in nature. Many of the boranes readily oxidise on contact with air, some violently. The parent member BH₃ is called borane, but it is known only in the gaseous state, and dimerises to form diborane, B₂H₆. The larger boranes all consist of boron clusters that are polyhedral, some of which exist as isomers. For example, isomers of B₂₀H₂₆ are based on the fusion of two 10-atom clusters. The most important boranes are diborane B₂H₆ and two of its pyrolysis products, pentaborane B₅H₉ and decaborane B₁₀H₁₄. A large number of anionic boron hydrides are known, e.g. ₁₂H₁₂sup>2−. The formal

oxidation number In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. Co ...

in boranes is positive, and is based on the assumption that hydrogen is counted as −1 as in active metal hydrides. The mean oxidation number for the borons is then simply the ratio of hydrogen to boron in the molecule. For example, in diborane B₂H₆, the boron oxidation state is +3, but in decaborane B₁₀H₁₄, it is ⁷/₅ or +1.4. In these compounds the oxidation state of boron is often not a whole number.

=Boron nitrides

= The boron nitrides are notable for the variety of structures that they adopt. They exhibit structures analogous to various

allotropes of carbon Carbon is capable of forming many allotropy, allotropes (structurally different forms of the same element) due to its Valence (chemistry), valency. Well-known forms of carbon include diamond and graphite. In recent decades, many more allotrope ...

, including graphite, diamond, and nanotubes. In the diamond-like structure, called cubic boron nitride (tradename

Borazon Borazon is a brand name of a cubic form of boron nitride (cBN). Its color ranges from black to brown and gold, depending on the chemical bond. It is one of the hardest known materials, along with various forms of diamond and kinds of boron nitride ...

), boron atoms exist in the tetrahedral structure of carbon atoms in diamond, but one in every four B-N bonds can be viewed as a

coordinate covalent bond In coordination chemistry, a coordinate covalent bond, also known as a dative bond, dipolar bond, or coordinate bond is a kind of two-center, two-electron covalent bond in which the two electrons derive from the same atom. The bonding of metal io ...

, wherein two electrons are donated by the nitrogen atom which acts as the

to a bond to the

ic boron(III) centre. Cubic boron nitride, among other applications, is used as an abrasive, as it has a hardness comparable with diamond (the two substances are able to produce scratches on each other). In the BN compound analogue of graphite, hexagonal boron nitride (h-BN), the positively charged boron and negatively charged nitrogen atoms in each plane lie adjacent to the oppositely charged atom in the next plane. Consequently, graphite and h-BN have very different properties, although both are lubricants, as these planes slip past each other easily. However, h-BN is a relatively poor electrical and thermal conductor in the planar directions.

=Organoboron chemistry

= A large number of organoboron compounds are known and many are useful in

organic synthesis Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...

. Many are produced from hydroboration, which employs diborane, B₂H₆, a simple borane chemical, or carboboration. Organoboron(III) compounds are usually tetrahedral or trigonal planar, for example, tetraphenylborate, (C₆H₅)₄sup>− vs.

triphenylborane Triphenylborane, often abbreviated to BPh3 where Ph is the phenyl group C6H5-, is a chemical compound with the formula B(C6H5)3. It is a white crystalline solid and is both air and moisture sensitive, slowly forming benzene and triphenylboroxin ...

, B(C₆H₅)₃. However, multiple boron atoms reacting with each other have a tendency to form novel dodecahedral (12-sided) and icosahedral (20-sided) structures composed completely of boron atoms, or with varying numbers of carbon heteroatoms. Organoboron chemicals have been employed in uses as diverse as

(see below), a complex very hard ceramic composed of boron-carbon cluster anions and cations, to

carborane Carboranes are electron-delocalized (non-classically bonded) clusters composed of boron, carbon and hydrogen atoms.Grimes, R. N., ''Carboranes 3rd Ed.'', Elsevier, Amsterdam and New York (2016), . Like many of the related boron hydrides, these cl ...

s, carbon-boron cluster chemistry compounds that can be halogenated to form reactive structures including

carborane acid Carborane acids (X, Y, Z = H, Alk, F, Cl, Br, CF3) are a class of superacids, some of which are estimated to be at least one million times stronger than 100% pure sulfuric acid in terms of their Hammett acidity function values (''H''0 ≤ –1 ...

, a

superacid In chemistry, a superacid (according to the classical definition) is an acid with an acidity greater than that of 100% pure sulfuric acid (), which has a Hammett acidity function (''H''0) of −12. According to the modern definition, a superacid ...

. As one example, carboranes form useful molecular moieties that add considerable amounts of boron to other biochemicals in order to synthesize boron-containing compounds for

boron neutron capture therapy Neutron capture therapy (NCT) is a type of radiotherapy for treating locally invasive malignant tumors such as primary brain tumors, recurrent cancers of the head and neck region, and cutaneous and extracutaneous melanomas. It is a two-step proc ...

for cancer.

=Compounds of B(I) and B(II)

= As anticipated by its hydride clusters, boron forms a variety of stable compounds with formal oxidation state less than three. B₂F₄ and B₄Cl₄ are well characterized. Magnesium-diboride-3D-balls

Binary metal-boron compounds, the metal borides, contain boron in negative oxidation states. Illustrative is

magnesium diboride Magnesium diboride is the inorganic compound with the formula MgB2. It is a dark gray, water-insoluble solid. The compound has attracted attention because it becomes superconductor, superconducting at 39 K (−234 °C). In terms of its ...

(MgB₂). Each boron atom has a formal −1 charge and magnesium is assigned a formal charge of +2. In this material, the boron centers are trigonal planar with an extra double bond for each boron, forming sheets akin to the carbon in graphite. However, unlike hexagonal boron nitride, which lacks electrons in the plane of the covalent atoms, the delocalized electrons in magnesium diboride allow it to conduct electricity similar to isoelectronic graphite. In 2001, this material was found to be a high-temperature superconductor. It is a superconductor under active development. A project at

CERN The European Organization for Nuclear Research, known as CERN (; ; ), is an intergovernmental organization that operates the largest particle physics laboratory in the world. Established in 1954, it is based in a northwestern suburb of Gene ...

to make MgB₂ cables has resulted in superconducting test cables able to carry 20,000 amperes for extremely high current distribution applications, such as the contemplated high luminosity version of the

Large Hadron Collider The Large Hadron Collider (LHC) is the world's largest and highest-energy particle collider. It was built by the European Organization for Nuclear Research (CERN) between 1998 and 2008 in collaboration with over 10,000 scientists and hundred ...

. Certain other metal borides find specialized applications as hard materials for cutting tools. Often the boron in borides has fractional oxidation states, such as −1/3 in

calcium hexaboride Calcium hexaboride (sometimes calcium boride) is a compound of calcium and boron with the chemical formula CaB6. It is an important material due to its high electrical conductivity, hardness, chemical stability, and melting point. It is a black, ...

(CaB₆). From the structural perspective, the most distinctive chemical compounds of boron are the hydrides. Included in this series are the cluster compounds dodecaborate (),

decaborane Decaborane, also called decaborane(14), is the borane with the chemical formula B10 H14. This white crystalline compound is one of the principal boron hydride clusters, both as a reference structure and as a precursor to other boron hydrides. It ...

(B₁₀H₁₄), and the

s such as C₂B₁₀H₁₂. Characteristically such compounds contain boron with coordination numbers greater than four.

Isotopes

Boron has two naturally occurring and stable isotopes, ¹¹B (80.1%) and ¹⁰B (19.9%). The mass difference results in a wide range of δ¹¹B values, which are defined as a fractional difference between the ¹¹B and ¹⁰B and traditionally expressed in parts per thousand, in natural waters ranging from −16 to +59. There are 13 known isotopes of boron; the shortest-lived isotope is ⁷B which decays through proton emission and alpha decay with a half-life of 3.5×10⁻²² s. Isotopic fractionation of boron is controlled by the exchange reactions of the boron species B(OH)₃ and (OH)₄sup>−. Boron isotopes are also fractionated during mineral crystallization, during H₂O phase changes in hydrothermal systems, and during hydrothermal alteration of

rock Rock most often refers to: * Rock (geology), a naturally occurring solid aggregate of minerals or mineraloids * Rock music, a genre of popular music Rock or Rocks may also refer to: Places United Kingdom * Rock, Caerphilly, a location in Wales ...

. The latter effect results in preferential removal of the sup>10B(OH)₄sup>− ion onto clays. It results in solutions enriched in ¹¹B(OH)₃ and therefore may be responsible for the large ¹¹B enrichment in seawater relative to both oceanic crust and continental crust; this difference may act as an isotopic signature. The exotic ¹⁷B exhibits a nuclear halo, i.e. its radius is appreciably larger than that predicted by the liquid drop model. The ¹⁰B isotope is useful for capturing thermal neutrons (see neutron cross section#Typical cross sections). The nuclear industry enriches natural boron to nearly pure ¹⁰B. The less-valuable by-product, depleted boron, is nearly pure ¹¹B.

Commercial isotope enrichment

Because of its high neutron cross-section, boron-10 is often used to control fission in nuclear reactors as a neutron-capturing substance. Several industrial-scale enrichment processes have been developed; however, only the fractionated vacuum distillation of the

dimethyl ether Dimethyl ether (DME; also known as methoxymethane) is the organic compound with the formula CH3OCH3, (sometimes ambiguously simplified to C2H6O as it is an isomer of ethanol). The simplest ether, it is a colorless gas that is a useful precursor ...

adduct of

(DME-BF₃) and column chromatography of borates are being used.

Enriched boron (boron-10)

Enriched boron or ¹⁰B is used in both radiation shielding and is the primary nuclide used in

neutron capture therapy of cancer Neutron capture therapy (NCT) is a type of radiotherapy for treating locally invasive malignant tumors such as primary brain tumors, recurrent cancers of the head and neck region, and cutaneous and extracutaneous melanomas. It is a two-step proc ...

. In the latter ("boron neutron capture therapy" or BNCT), a compound containing ¹⁰B is incorporated into a pharmaceutical which is selectively taken up by a malignant tumor and tissues near it. The patient is then treated with a beam of low energy neutrons at a relatively low neutron radiation dose. The neutrons, however, trigger energetic and short-range secondary alpha particle and lithium-7 heavy ion radiation that are products of the boron-neutron nuclear reaction, and this ion radiation additionally bombards the tumor, especially from inside the tumor cells. In nuclear reactors, ¹⁰B is used for reactivity control and in emergency shutdown systems. It can serve either function in the form of

borosilicate Borosilicate glass is a type of glass with silica and boron trioxide as the main glass-forming constituents. Borosilicate glasses are known for having very low coefficients of thermal expansion (≈3 × 10−6 K−1 at 20 °C), ma ...

control rods or as boric acid. In pressurized water reactors, ¹⁰B boric acid is added to the reactor coolant after the plant is shut down for refueling. When the plant is started up again, the boric acid is slowly filtered out over many months as fissile material is used up and the fuel becomes less reactive. In future crewed interplanetary spacecraft, ¹⁰B has a theoretical role as structural material (as boron fibers or BN nanotube material) which would also serve a special role in the radiation shield. One of the difficulties in dealing with cosmic rays, which are mostly high energy protons, is that some secondary radiation from interaction of cosmic rays and spacecraft materials is high energy

spallation Spallation is a process in which fragments of material (spall) are ejected from a body due to impact or stress. In the context of impact mechanics it describes ejection of material from a target during impact by a projectile. In planetary p ...

neutrons. Such neutrons can be moderated by materials high in light elements, such as polyethylene, but the moderated neutrons continue to be a radiation hazard unless actively absorbed in the shielding. Among light elements that absorb thermal neutrons, ⁶Li and ¹⁰B appear as potential spacecraft structural materials which serve both for mechanical reinforcement and radiation protection.

Depleted boron (boron-11)

= Radiation-hardened semiconductors

Cosmic radiation Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own ...

will produce secondary neutrons if it hits spacecraft structures. Those neutrons will be captured in ¹⁰B, if it is present in the spacecraft's semiconductors, producing a gamma ray, an alpha particle, and a lithium ion. Those resultant decay products may then irradiate nearby semiconductor "chip" structures, causing data loss (bit flipping, or single event upset). In

radiation-hardened Radiation hardening is the process of making electronic components and circuits resistant to damage or malfunction caused by high levels of ionizing radiation (particle radiation and high-energy electromagnetic radiation), especially for environm ...

semiconductor designs, one countermeasure is to use ''depleted boron'', which is greatly enriched in ¹¹B and contains almost no ¹⁰B. This is useful because ¹¹B is largely immune to radiation damage. Depleted boron is a byproduct of the nuclear industry (see above).

= Proton-boron fusion

= ¹¹B is also a candidate as a fuel for aneutronic fusion. When struck by a proton with energy of about 500 k eV, it produces three alpha particles and 8.7 MeV of energy. Most other fusion reactions involving hydrogen and helium produce penetrating neutron radiation, which weakens reactor structures and induces long-term radioactivity, thereby endangering operating personnel. The

alpha particles Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay, but may also be prod ...

from ¹¹B fusion can be turned directly into electric power, and all radiation stops as soon as the reactor is turned off.

NMR spectroscopy

Both ¹⁰B and ¹¹B possess

nuclear spin In atomic physics, the spin quantum number is a quantum number (designated ) which describes the intrinsic angular momentum (or spin angular momentum, or simply spin) of an electron or other particle. The phrase was originally used to describe th ...

. The nuclear spin of ¹⁰B is 3 and that of ¹¹B is . These isotopes are, therefore, of use in nuclear magnetic resonance spectroscopy; and spectrometers specially adapted to detecting the boron-11 nuclei are available commercially. The ¹⁰B and ¹¹B nuclei also cause splitting in the resonances of attached nuclei.

Occurrence

Boron is rare in the Universe and solar system due to trace formation in the

Big Bang The Big Bang event is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological models of the Big Bang explain the evolution of the observable universe from the ...

and in stars. It is formed in minor amounts in cosmic ray spallation nucleosynthesis and may be found uncombined in cosmic dust and meteoroid materials. In the high oxygen environment of Earth, boron is always found fully oxidized to borate. Boron does not appear on Earth in elemental form. Extremely small traces of elemental boron were detected in Lunar regolith. Although boron is a relatively rare element in the Earth's crust, representing only 0.001% of the crust mass, it can be highly concentrated by the action of water, in which many borates are soluble. It is found naturally combined in compounds such as borax and boric acid (sometimes found in volcanic spring waters). About a hundred borate minerals are known. On 5 September 2017, scientists reported that the ''Curiosity'' rover detected boron, an essential ingredient for life on Earth, on the planet Mars. Such a finding, along with previous discoveries that water may have been present on ancient Mars, further supports the possible early habitability of Gale Crater on Mars.

Production

Economically important sources of boron are the minerals

colemanite Colemanite (Ca2B6O11·5H2O) or (CaB3O4(OH)3·H2O) is a borate mineral found in evaporite deposits of alkaline lacustrine environments. Colemanite is a secondary mineral that forms by alteration of borax and ulexite. It was first described in 18 ...

, rasorite (

), ulexite and tincal. Together these constitute 90% of mined boron-containing ore. The largest global borax deposits known, many still untapped, are in Central and Western Turkey, including the provinces of Eskişehir,

Kütahya Kütahya () (historically, Cotyaeum or Kotyaion, Ancient Greek, Greek: Κοτύαιον) is a city in western Turkey which lies on the Porsuk River, Porsuk river, at 969 metres above sea level. It is inhabited by some 578,640 people (2022 estimate) ...

and Balıkesir. Global proven boron mineral mining reserves exceed one billion metric tonnes, against a yearly production of about four million tonnes. Turkey and the United States are the largest producers of boron products. Turkey produces about half of the global yearly demand, through

Eti Mine Works Eti Maden is a Turkish state-owned mining and chemicals company focusing on boron products. It holds a government monopoly on the mining of borate minerals in Turkey, which possesses 72% of the world's known deposits. In 2012, it held a 47% share o ...

( tr, Eti Maden İşletmeleri) a

Turkish Turkish may refer to: *a Turkic language spoken by the Turks * of or about Turkey ** Turkish language *** Turkish alphabet ** Turkish people, a Turkic ethnic group and nation *** Turkish citizen, a citizen of Turkey *** Turkish communities and mi ...

state-owned State ownership, also called government ownership and public ownership, is the ownership of an industry, asset, or enterprise by the state or a public body representing a community, as opposed to an individual or private party. Public ownersh ...

mining and chemicals company focusing on boron products. It holds a government monopoly on the mining of borate minerals in Turkey, which possesses 72% of the world's known deposits. In 2012, it held a 47% share of production of global borate minerals, ahead of its main competitor,

Rio Tinto Group Rio Tinto Group is an Anglo-Australian Multinational corporation, multinational company that is the world's second-largest metals and mining corporation (behind BHP). The company was founded in 1873 when of a group of investors purchased a mine ...

. Almost a quarter (23%) of global boron production comes from the single

Rio Tinto Borax Mine The Rio Tinto Boron Mine (formerly the U.S. Borax Boron Mine) in Boron, California is California's largest open-pit mine and the largest borax mine in the world, producing nearly half the world's borates. Ore reserves are sufficient for produ ...

(also known as the U.S. Borax Boron Mine) near Boron, California.

Market trend

The average cost of crystalline elemental boron is US$5/g. Elemental boron is chiefly used in making boron fibers, where it is deposited by

chemical vapor deposition Chemical vapor deposition (CVD) is a vacuum deposition method used to produce high quality, and high-performance, solid materials. The process is often used in the semiconductor industry to produce thin films. In typical CVD, the wafer (substra ...

on a tungsten core (see below). Boron fibers are used in lightweight composite applications, such as high strength tapes. This use is a very small fraction of total boron use. Boron is introduced into semiconductors as boron compounds, by ion implantation. Estimated global consumption of boron (almost entirely as boron compounds) was about 4 million tonnes of B₂O₃ in 2012. As compounds such as borax and kernite its cost was US$377/tonne in 2019. Boron mining and refining capacities are considered to be adequate to meet expected levels of growth through the next decade. The form in which boron is consumed has changed in recent years. The use of ores like

has declined following concerns over arsenic content. Consumers have moved toward the use of refined borates and boric acid that have a lower pollutant content. Increasing demand for boric acid has led a number of producers to invest in additional capacity. Turkey's state-owned

opened a new boric acid plant with the production capacity of 100,000 tonnes per year at Emet in 2003.

increased the capacity of its boron plant from 260,000 tonnes per year in 2003 to 310,000 tonnes per year by May 2005, with plans to grow this to 366,000 tonnes per year in 2006. Chinese boron producers have been unable to meet rapidly growing demand for high quality borates. This has led to imports of sodium tetraborate ( borax) growing by a hundredfold between 2000 and 2005 and boric acid imports increasing by 28% per year over the same period. The rise in global demand has been driven by high growth rates in glass fiber, fiberglass and

glassware production. A rapid increase in the manufacture of reinforcement-grade boron-containing fiberglass in Asia, has offset the development of boron-free reinforcement-grade fiberglass in Europe and the US. The recent rises in energy prices may lead to greater use of insulation-grade fiberglass, with consequent growth in the boron consumption. Roskill Consulting Group forecasts that world demand for boron will grow by 3.4% per year to reach 21 million tonnes by 2010. The highest growth in demand is expected to be in Asia where demand could rise by an average 5.7% per year.

Applications

Nearly all boron ore extracted from the Earth is destined for refinement into boric acid and sodium tetraborate pentahydrate. In the United States, 70% of the boron is used for the production of glass and ceramics. The major global industrial-scale use of boron compounds (about 46% of end-use) is in production of glass fiber for boron-containing insulating and structural fiberglasses, especially in Asia. Boron is added to the glass as borax pentahydrate or boron oxide, to influence the strength or fluxing qualities of the glass fibers. Another 10% of global boron production is for borosilicate glass as used in high strength glassware. About 15% of global boron is used in boron ceramics, including super-hard materials discussed below. Agriculture consumes 11% of global boron production, and bleaches and detergents about 6%.

Elemental boron fiber

Boron fibers (boron filaments) are high-strength, lightweight materials that are used chiefly for advanced aerospace structures as a component of composite materials, as well as limited production consumer and sporting goods such as golf clubs and

fishing rod A fishing rod is a long, thin rod used by angling, anglers to fishing, catch fish by manipulating a fishing line, line ending in a fish hook, hook (formerly known as an ''angle'', hence the term "angling"). At its most basic form, a fishing ...

s. The fibers can be produced by

of boron on a tungsten filament. Boron fibers and sub-millimeter sized crystalline boron springs are produced by laser-assisted

. Translation of the focused laser beam allows production of even complex helical structures. Such structures show good mechanical properties ( elastic modulus 450 GPa, fracture strain 3.7%, fracture stress 17 GPa) and can be applied as reinforcement of ceramics or in micromechanical systems.

Boronated fiberglass

Fiberglass is a fiber reinforced polymer made of plastic reinforced by glass fibers, commonly woven into a mat. The glass fibers used in the material are made of various types of glass depending upon the fiberglass use. These glasses all contain silica or silicate, with varying amounts of oxides of calcium, magnesium, and sometimes boron. The boron is present as borosilicate, borax, or boron oxide, and is added to increase the strength of the glass, or as a fluxing agent to decrease the melting temperature of silica, which is too high to be easily worked in its pure form to make glass fibers. The highly boronated glasses used in fiberglass are E-glass (named for "Electrical" use, but now the most common fiberglass for general use). E-glass is alumino-borosilicate glass with less than 1% w/w alkali oxides, mainly used for glass-reinforced plastics. Other common high-boron glasses include C-glass, an alkali-lime glass with high boron oxide content, used for glass staple fibers and insulation, and D-glass, a borosilicate glass, named for its low dielectric constant. Not all fiberglasses contain boron, but on a global scale, most of the fiberglass used does contain it. Because of the ubiquitous use of fiberglass in construction and insulation, boron-containing fiberglasses consume over half the global production of boron, and are the single largest commercial boron market.

Borosilicate glass

Borosilicate glass, which is typically 12–15% B₂O₃, 80% SiO₂, and 2% Al₂O₃, has a low coefficient of thermal expansion, giving it a good resistance to thermal shock. Schott AG's "Duran" and Owens-Corning's trademarked Pyrex are two major brand names for this glass, used both in laboratory glassware and in consumer cookware and bakeware, chiefly for this resistance.

Boron carbide ceramic

Several boron compounds are known for their extreme hardness and toughness.

Boron carbide Boron carbide (chemical formula approximately B4C) is an extremely hard boron–carbon ceramic, a covalent material used in tank armor, bulletproof vests, engine sabotage powders, as well as numerous industrial applications. With a Vickers hard ...

is a ceramic material which is obtained by decomposing B₂O₃ with carbon in an electric furnace: :2 B₂O₃ + 7 C → B₄C + 6 CO Boron carbide's structure is only approximately B₄C, and it shows a clear depletion of carbon from this suggested stoichiometric ratio. This is due to its very complex structure. The substance can be seen with empirical formula B₁₂C₃ (i.e., with B₁₂ dodecahedra being a motif), but with less carbon, as the suggested C₃ units are replaced with C-B-C chains, and some smaller (B₆) octahedra are present as well (see the boron carbide article for structural analysis). The repeating polymer plus semi-crystalline structure of boron carbide gives it great structural strength per weight. It is used in tank armor,

bulletproof vest A bulletproof vest, also known as a ballistic vest or a bullet-resistant vest, is an item of body armor that helps absorb the impact and reduce or stop penetration to the torso from firearm-fired projectiles and fragmentation from explosions. T ...

s, and numerous other structural applications. Boron carbide's ability to absorb neutrons without forming long-lived

radionuclide A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transfer ...

s (especially when doped with extra boron-10) makes the material attractive as an absorbent for neutron radiation arising in nuclear power plants. Nuclear applications of boron carbide include shielding, control rods and shut-down pellets. Within control rods, boron carbide is often powdered, to increase its surface area.

High-hardness and abrasive compounds

Boron carbide and cubic boron nitride powders are widely used as abrasives. Boron nitride is a material isoelectronic to carbon. Similar to carbon, it has both hexagonal (soft graphite-like h-BN) and cubic (hard, diamond-like c-BN) forms. h-BN is used as a high temperature component and lubricant. c-BN, also known under commercial name

borazon Borazon is a brand name of a cubic form of boron nitride (cBN). Its color ranges from black to brown and gold, depending on the chemical bond. It is one of the hardest known materials, along with various forms of diamond and kinds of boron nitride ...

, is a superior abrasive. Its hardness is only slightly smaller than, but its chemical stability is superior, to that of diamond.

Heterodiamond Heterodiamond is a superhard material containing boron, carbon, and nitrogen (BCN). It is formed at high temperatures and high pressures, e.g., by application of an explosive shock wave to a mixture of diamond and cubic boron nitride (c-BN). The he ...

(also called BCN) is another diamond-like boron compound.

Metallurgy

Boron is added to

boron steel Boron steel refers to steel alloyed with a small amount of boron, usually less than 1%. The addition of boron to steel greatly increases the hardenability of the resulting alloy. Description Boron is added to steel as ferroboron (~12-24% B). As ...

s at the level of a few parts per million to increase hardenability. Higher percentages are added to steels used in the nuclear industry due to boron's neutron absorption ability. Boron can also increase the surface hardness of steels and alloys through boriding. Additionally metal borides are used for coating tools through

or physical vapor deposition. Implantation of boron ions into metals and alloys, through ion implantation or ion beam deposition, results in a spectacular increase in surface resistance and microhardness. Laser alloying has also been successfully used for the same purpose. These borides are an alternative to diamond coated tools, and their (treated) surfaces have similar properties to those of the bulk boride. For example,

rhenium diboride Rhenium diboride (ReB2) is a synthetic superhard material. It was first synthesized in 1962 and re-emerged recently due to hopes of achieving high hardness comparable to that of diamond. The reported ultrahigh hardness has been questioned, althou ...

can be produced at ambient pressures, but is rather expensive because of rhenium. The hardness of ReB₂ exhibits considerable anisotropy because of its hexagonal layered structure. Its value is comparable to that of tungsten carbide, silicon carbide, titanium diboride or zirconium diboride. Similarly, AlMgB₁₄ + TiB₂ composites possess high hardness and wear resistance and are used in either bulk form or as coatings for components exposed to high temperatures and wear loads.

Detergent formulations and bleaching agents

Borax is used in various household laundry and cleaning products, including the "

20 Mule Team Borax 20 Mule Team Borax is a brand of cleaner manufactured in the United States by The Dial Corporation, a subsidiary of Henkel.Hildebrand, G. H. (1982) "Borax Pioneer: Francis Marion Smith." San Diego: Howell-North Books. The product primarily con ...

" laundry booster and "

Boraxo 20 Mule Team Borax is a brand of cleaner manufactured in the United States by The Dial Corporation, a subsidiary of Henkel.Hildebrand, G. H. (1982) "Borax Pioneer: Francis Marion Smith." San Diego: Howell-North Books. The product primarily co ...

" powdered hand soap. It is also present in some tooth bleaching formulas. Sodium perborate serves as a source of active oxygen in many

detergent A detergent is a surfactant or a mixture of surfactants with cleansing properties when in dilute solutions. There are a large variety of detergents, a common family being the alkylbenzene sulfonates, which are soap-like compounds that are more ...

s, laundry detergents, cleaning products, and laundry bleaches. However, despite its name, "Borateem" laundry bleach no longer contains any boron compounds, using sodium percarbonate instead as a bleaching agent.

Insecticides

Boric acid is used as an insecticide, notably against ants, fleas, and cockroaches.

Semiconductors

Boron is a useful dopant for such semiconductors as silicon,

germanium Germanium is a chemical element with the symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid in the carbon group that is chemically similar to its group neighbors s ...

, and silicon carbide. Having one fewer valence electron than the host atom, it donates a hole resulting in p-type conductivity. Traditional method of introducing boron into semiconductors is via its atomic diffusion at high temperatures. This process uses either solid (B₂O₃), liquid (BBr₃), or gaseous boron sources (B₂H₆ or BF₃). However, after the 1970s, it was mostly replaced by ion implantation, which relies mostly on BF₃ as a boron source. Boron trichloride gas is also an important chemical in semiconductor industry, however, not for doping but rather for plasma etching of metals and their oxides. Triethylborane is also injected into vapor deposition reactors as a boron source. Examples are the plasma deposition of boron-containing hard carbon films, silicon nitride–boron nitride films, and for doping of diamond film with boron.

Magnets

Boron is a component of

neodymium magnet A hard_disk_drive.html"_;"title="Nickel-plated_neodymium_magnet_on_a_bracket_from_a_hard_disk_drive">Nickel-plated_neodymium_magnet_on_a_bracket_from_a_hard_disk_drive_ file:Nd-magnet.jpg.html" ;"title="hard_disk_drive_.html" ;"title="hard_disk_d ...

s (Nd₂Fe₁₄B), which are among the strongest type of permanent magnet. These magnets are found in a variety of electromechanical and electronic devices, such as

magnetic resonance imaging Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio wave ...

(MRI) medical imaging systems, in compact and relatively small motors and

actuator An actuator is a component of a machine that is responsible for moving and controlling a mechanism or system, for example by opening a valve. In simple terms, it is a "mover". An actuator requires a control device (controlled by control signal) a ...

s. As examples, computer HDDs (hard disk drives), CD (compact disk) and DVD (digital versatile disk) players rely on neodymium magnet motors to deliver intense rotary power in a remarkably compact package. In mobile phones 'Neo' magnets provide the magnetic field which allows tiny speakers to deliver appreciable audio power.

Shielding and neutron absorber in nuclear reactors

Boron shielding is used as a control for nuclear reactors, taking advantage of its high

cross-section Cross section may refer to: * Cross section (geometry) ** Cross-sectional views in architecture & engineering 3D *Cross section (geology) * Cross section (electronics) * Radar cross section, measure of detectability * Cross section (physics) **Ab ...

for neutron capture. In pressurized water reactors a variable concentration of boronic acid in the cooling water is used as a neutron poison to compensate the variable reactivity of the fuel. When new rods are inserted the concentration of boronic acid is maximal, and is reduced during the lifetime.

Other nonmedical uses

* Because of its distinctive green flame, amorphous boron is used in pyrotechnic flares. * In the 1950s, there were several studies of the use of boranes as energy-increasing " Zip fuel" additives for jet fuel. *

Starch Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human diets ...

and casein-based adhesives contain sodium tetraborate decahydrate (Na₂B₄O₇·10 H₂O). * Some anti-corrosion systems contain borax. * Sodium borates are used as a

flux Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications to physics. For transport ph ...

for soldering silver and gold and with ammonium chloride for welding ferrous metals. They are also fire retarding additives to plastics and rubber articles. * Boric acid (also known as orthoboric acid) H₃BO₃ is used in the production of textile fiberglass and flat panel displays and in many

PVAc Polyvinyl acetate (PVA, PVAc, poly(ethenyl ethanoate)), commonly known as wood glue, PVA glue, white glue, carpenter's glue, school glue, or Elmer's glue in the US, is a widely available adhesive used for porous materials like wood, paper, and ...

- and

PVOH Poly(vinyl alcohol) (PVOH, PVA, or PVAl) is a water- soluble synthetic polymer. It has the idealized formula H2CH(OH)sub>''n''. It is used in papermaking, textile warp sizing, as a thickener and emulsion stabilizer in polyvinyl acetate (PVAc) a ...

-based adhesives. * Triethylborane is a substance which ignites the JP-7 fuel of the Pratt & Whitney J58 turbojet/ ramjet engines powering the Lockheed

SR-71 Blackbird The Lockheed SR-71 "Blackbird" is a long-range, high-altitude, Mach 3+ strategic reconnaissance aircraft developed and manufactured by the American aerospace company Lockheed Corporation. It was operated by the United States Air Force ...

. It was also used to ignite the F-1 Engines on the Saturn V Rocket utilized by NASA's Apollo and Skylab programs from 1967 until 1973. Today

SpaceX Space Exploration Technologies Corp. (SpaceX) is an American spacecraft manufacturer, launcher, and a satellite communications corporation headquartered in Hawthorne, California. It was founded in 2002 by Elon Musk with the stated goal of ...

uses it to ignite the engines on their Falcon 9 rocket.Mission Status Center, June 2, 2010, 1905 GMT
, '' SpaceflightNow'', accessed 2010-06-02, Quotation: "The flanges will link the rocket with ground storage tanks containing liquid oxygen, kerosene fuel, helium, gaseous nitrogen and the first stage ignitor source called triethylaluminum-triethylborane, better known as TEA-TEB." Triethylborane is suitable for this because of its pyrophoric properties, especially the fact that it burns with a very high temperature. Triethylborane is an industrial

initiator An initiator can refer to: * A person who instigates something. * Modulated neutron initiator, a neutron source used in some nuclear weapons ** Initiator, an Explosive booster ** Initiator, the first Nuclear chain reaction * Pyrotechnic initiator, ...

radical Radical may refer to: Politics and ideology Politics *Radical politics, the political intent of fundamental societal change *Radicalism (historical), the Radical Movement that began in late 18th century Britain and spread to continental Europe and ...

reactions, where it is effective even at low temperatures. * Borates are used as environmentally benign wood preservatives.

Pharmaceutical and biological applications

Boron plays a role in pharmaceutical and biological applications as it is found in various bacteria-produced antibiotics, such as

boromycin Boromycin is a bacteriocidal polyether-macrolide antibiotic. It was initially isolated from the '' Streptomyces antibioticus'', and is notable for being the first natural product found to contain the element boron. It is effective against most G ...

s, aplasmomycins, borophycins, and tartrolons. These antibiotics have shown inhibitory effects on certain bacteria, fungi, and protozoa growth. Boron is also being studied for its potential medicinal applications, including its incorporation into biologically active molecules for therapies like boron neutron capture therapy for brain tumors. Some boron-containing biomolecules may act as signaling molecules interacting with cell surfaces, suggesting a role in cellular communication. Boric acid has antiseptic, antifungal, and antiviral properties and, for these reasons, is applied as a water clarifier in swimming pool water treatment. Mild solutions of boric acid have been used as eye antiseptics.

Bortezomib Bortezomib, sold under the brand name Velcade among others, is an anti-cancer medication used to treat multiple myeloma and mantle cell lymphoma. This includes multiple myeloma in those who have and have not previously received treatment. It is ...

(marketed as Velcade and Cytomib). Boron appears as an active element in the organic pharmaceutical bortezomib, a new class of drug called the proteasome inhibitor, for treating myeloma and one form of lymphoma (it is currently in experimental trials against other types of lymphoma). The boron atom in bortezomib binds the catalytic site of the

26S proteasome Proteasomes are protein complexes which degrade unneeded or damaged proteins by proteolysis, a chemical reaction that breaks peptide bonds. Enzymes that help such reactions are called proteases. Proteasomes are part of a major mechanism by whi ...

with high affinity and specificity. * A number of potential boronated pharmaceuticals using boron-10, have been prepared for use in

(BNCT). * Some boron compounds show promise in treating

arthritis Arthritis is a term often used to mean any disorder that affects joints. Symptoms generally include joint pain and stiffness. Other symptoms may include redness, warmth, swelling, and decreased range of motion of the affected joints. In som ...

, though none have as yet been generally approved for the purpose.

Tavaborole Tavaborole, sold under the brand name Kerydin, is a topical antifungal medication for the treatment of onychomycosis, a fungal infection of the nail and nail bed with a complete clearance rate of 6-7% and partial clearance rate of 23-24% in ind ...

(marketed as Kerydin) is an Aminoacyl tRNA synthetase inhibitor which is used to treat toenail fungus. It gained FDA approval in July 2014. Dioxaborolane chemistry enables radioactive

fluoride Fluoride (). According to this source, is a possible pronunciation in British English. is an inorganic, monatomic anion of fluorine, with the chemical formula (also written ), whose salts are typically white or colorless. Fluoride salts typ ...

( ¹⁸F) labeling of

antibodies An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the ...

or red blood cells, which allows for

positron emission tomography Positron emission tomography (PET) is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in Metabolism, metabolic processes, and in other physiological activities including bl ...

(PET) imaging of cancer and hemorrhages, respectively. A Human-Derived, Genetic, Positron-emitting and Fluorescent (HD-GPF) reporter system uses a human protein, PSMA and non-immunogenic, and a small molecule that is positron-emitting (boron bound ¹⁸ F) and fluorescence for dual modality PET and fluorescent imaging of genome modified cells, e.g. cancer,

CRISPR/Cas9 Cas9 (CRISPR associated protein 9, formerly called Cas5, Csn1, or Csx12) is a 160 kilodalton protein which plays a vital role in the immunological defense of certain bacteria against DNA viruses and plasmids, and is heavily utilized in genetic e ...

, or CAR T-cells, in an entire mouse. The dual-modality small molecule targeting PSMA was tested in humans and found the location of primary and metastatic

prostate cancer Prostate cancer is cancer of the prostate. Prostate cancer is the second most common cancerous tumor worldwide and is the fifth leading cause of cancer-related mortality among men. The prostate is a gland in the male reproductive system that sur ...

, fluorescence-guided removal of cancer, and detects single cancer cells in tissue margins. In neutron capture therapy (BNCT) for malignant brain tumors, boron is researched to be used for selectively targeting and destroying tumor cells. The goal is to deliver higher concentrations of the non-radioactive boron isotope (¹⁰B) to the tumor cells than to the surrounding normal tissues. When these ¹⁰B-containing cells are irradiated with low-energy thermal neutrons, they undergo nuclear capture reactions, releasing high linear energy transfer (LET) particles such as α-particles and lithium-7 nuclei within a limited path length. These high-LET particles can destroy the adjacent tumor cells without causing significant harm to nearby normal cells. Boron acts as a selective agent due to its ability to absorb thermal neutrons and produce short-range physical effects primarily affecting the targeted tissue region. This binary approach allows for precise tumor cell killing while sparing healthy tissues. The effective delivery of boron involves administering boron compounds or carriers capable of accumulating selectively in tumor cells compared to surrounding tissue. BSH and BPA have been used clinically, but research continues to identify more optimal carriers. Accelerator-based neutron sources have also been developed recently as an alternative to reactor-based sources, leading to improved efficiency and enhanced clinical outcomes in BNCT. By employing the properties of boron isotopes and targeted irradiation techniques, BNCT offers a potential approach to treating malignant brain tumors by selectively killing cancer cells while minimizing the damage caused by traditional radiation therapies. BNCT has shown promising results in clinical trials for various other malignancies, including glioblastoma, head and neck cancer, cutaneous melanoma, hepatocellular carcinoma, lung cancer, and extramammary Paget's disease. The treatment involves a nuclear reaction between nonradioactive boron-10 isotope and low-energy thermal or high-energy epithermal neutrons to generate α particles and lithium nuclei that selectively destroy DNA in tumor cells. The primary challenge lies in developing efficient boron agents with higher content and specific targeting properties tailored for BNCT. Integration of tumor-targeting strategies with BNCT could potentially establish it as a practical personalized treatment option for different types of cancers. Ongoing research explores new boron compounds, optimization strategies, theranostic agents, and radiobiological advances to overcome limitations and cost-effectively improve patient outcomes.

Research areas

Magnesium diboride Magnesium diboride is the inorganic compound with the formula MgB2. It is a dark gray, water-insoluble solid. The compound has attracted attention because it becomes superconductor, superconducting at 39 K (−234 °C). In terms of its ...

is an important superconducting material with the transition temperature of 39 K. MgB₂ wires are produced with the

powder-in-tube Superconducting wires are electrical wires made of superconductive material. When cooled below their transition temperatures, they have zero electrical resistance. Most commonly, conventional superconductors such as niobium-titanium are used, ...

process and applied in superconducting magnets. Amorphous boron is used as a melting point depressant in nickel-chromium braze alloys. Hexagonal boron nitride forms atomically thin layers, which have been used to enhance the

electron mobility In solid-state physics, the electron mobility characterises how quickly an electron can move through a metal or semiconductor when pulled by an electric field. There is an analogous quantity for holes, called hole mobility. The term carrier mobili ...

in graphene devices. It also forms nanotubular structures ( BNNTs), which have high strength, high chemical stability, and high thermal conductivity, among its list of desirable properties. Boron has multiple applications in nuclear fusion research. It is commonly used for conditioning the walls in fusion reactors by depositing boron coatings on plasma-facing components and walls to reduce the release of hydrogen and impurities from the surfaces. It is also being used for the dissipation of energy in the fusion plasma boundary to suppress excessive energy bursts and heat fluxes to the walls.

Biological role

Boron is an essential plant

nutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...

, required primarily for maintaining the integrity of cell walls. However, high soil concentrations of greater than 1.0 ppm lead to marginal and tip necrosis in leaves as well as poor overall growth performance. Levels as low as 0.8 ppm produce these same symptoms in plants that are particularly sensitive to boron in the soil. Nearly all plants, even those somewhat tolerant of soil boron, will show at least some symptoms of boron toxicity when soil boron content is greater than 1.8 ppm. When this content exceeds 2.0 ppm, few plants will perform well and some may not survive. There exist several known boron-containing natural

antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention of ...

s. The first one found was

, isolated from

streptomyces ''Streptomyces'' is the largest genus of Actinomycetota and the type genus of the family Streptomycetaceae. Over 500 species of ''Streptomyces'' bacteria have been described. As with the other Actinomycetota, streptomycetes are gram-positive, ...

in the 1960s. Others are tartrolons, a group of antibiotics discovered in the 1990s from culture broth of the

myxobacterium The myxobacteria ("slime bacteria") are a group of bacteria that predominantly live in the soil and feed on insoluble organic substances. The myxobacteria have very large genomes relative to other bacteria, e.g. 9–10 million nucleotides except ...

'' Sorangium cellulosum''. In 2013, chemist and synthetic biologist Steve Benner suggested that the conditions on Mars three billion years ago were much more favorable to the stability of

RNA Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carbohydra ...

and formation of oxygen-containing boron and molybdenum catalysts found in life. According to Benner's theory, primitive life, which is widely believed to have originated from RNA, first formed on Mars before migrating to Earth.

In human health

It is thought that boron plays several essential roles in animals, including humans, but the exact physiological role is poorly understood. Boron deficiency has only been clearly established in livestock; in humans, boron deficiency may affect

bone mineral density Bone density, or bone mineral density, is the amount of bone mineral in bone tissue. The concept is of mass of mineral per volume of bone (relating to density in the physics sense), although clinically it is measured by proxy according to optica ...

, though it has been noted that additional research on the effects of bone health is necessary. Boron is not classified as an essential human nutrient because research has not established a clear biological function for it. The U.S.

Food and Nutrition Board The Dietary Reference Intake (DRI) is a system of nutrition recommendations from the National Academy of Medicine (NAM) of the National Academies (United States). It was introduced in 1997 in order to broaden the existing guidelines known as Reco ...

(FNB) found the existing data insufficient to derive a

Recommended Dietary Allowance The Dietary Reference Intake (DRI) is a system of nutrition recommendations from the National Academy of Medicine (NAM) of the National Academies (United States). It was introduced in 1997 in order to broaden the existing guidelines known as Reco ...

(RDA), Adequate Intake (AI), or

Estimated Average Requirement The Dietary Reference Intake (DRI) is a system of nutrition recommendations from the National Academy of Medicine (NAM) of the National Academies (United States). It was introduced in 1997 in order to broaden the existing guidelines known as Reco ...

(EAR) for boron and the U.S. Food and Drug Administration (FDA) has not established a daily value for boron for food and dietary supplement labeling purposes. While low boron status can be detrimental to health, probably increasing the risk of

osteoporosis Osteoporosis is a systemic skeletal disorder characterized by low bone mass, micro-architectural deterioration of bone tissue leading to bone fragility, and consequent increase in fracture risk. It is the most common reason for a broken bone ...

, poor immune function, and cognitive decline, high boron levels are associated with cell damage and toxicity. Still, studies suggest that boron may exert beneficial effects on reproduction and development, calcium metabolism, bone formation, brain function,

insulin Insulin (, from Latin ''insula'', 'island') is a peptide hormone produced by beta cells of the pancreatic islets encoded in humans by the ''INS'' gene. It is considered to be the main anabolic hormone of the body. It regulates the metabolism o ...

and energy substrate metabolism, immunity, and

steroid A steroid is a biologically active organic compound with four rings arranged in a specific molecular configuration. Steroids have two principal biological functions: as important components of cell membranes that alter membrane fluidity; and a ...

hormone (including estrogen) and vitamin D function, among other functions. A small human trial published in 1987 reported on postmenopausal women first made boron deficient and then repleted with 3 mg/day. Boron supplementation markedly reduced urinary calcium excretion and elevated the serum concentrations of 17 beta-estradiol and testosterone. Environmental boron appears to be

inversely correlated In mathematics, two sequences of numbers, often experimental data, are proportional or directly proportional if their corresponding elements have a constant ratio, which is called the coefficient of proportionality or proportionality constant ...

with

. The exact mechanism by which boron exerts its physiological effects is not fully understood, but may involve interactions with adenosine monophosphate (ADP) and S-adenosyl methionine (SAM-e), two compounds involved in important cellular functions. Furthermore, boron appears to inhibit cyclic ADP-ribose, thereby affecting the release of calcium ions from the

endoplasmic reticulum The endoplasmic reticulum (ER) is, in essence, the transportation system of the eukaryotic cell, and has many other important functions such as protein folding. It is a type of organelle made up of two subunits – rough endoplasmic reticulum ( ...

and affecting various biological processes. Some studies suggest that boron may reduce levels of inflammatory biomarkers.

Congenital endothelial dystrophy type 2 Congenital hereditary corneal dystrophy (CHED) is a form of corneal endothelial dystrophy that presents at birth. CHED was previously subclassified into two subtypes: CHED1 and CHED2. However in 2015, the International Classification of Corneal ...

, a rare form of corneal dystrophy, is linked to mutations in SLC4A11 gene that encodes a transporter reportedly regulating the intracellular concentration of boron. In humans, boron is usually consumed with food that contains boron, such as fruits,

leafy vegetables Leaf vegetables, also called leafy greens, pot herbs, vegetable greens, or simply greens, are plant leaves eaten as a vegetable, sometimes accompanied by tender petioles and shoots. Leaf vegetables eaten raw in a salad can be called salad gre ...

, and

nuts Nut often refers to: * Nut (fruit), fruit composed of a hard shell and a seed, or a collective noun for dry and edible fruits or seeds * Nut (hardware), fastener used with a bolt Nut or Nuts may also refer to: Arts, entertainment, and media Com ...

. Foods that are particularly rich in boron include avocados, dried fruits such as raisins, peanuts, pecans, prune juice, grape juice, wine and chocolate powder. According to 2-day food records from the respondents to the Third National Health and Nutrition Examination Survey (NHANES III), adult dietary intake was recorded at 0.9 to 1.4 mg/day.Boron. IN
Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Copper
. National Academy Press. 2001, pp. 510–521.

Analytical quantification

For determination of boron content in food or materials, the colorimetric '' curcumin method'' is used. Boron is converted to boric acid or borates and on reaction with curcumin in acidic solution, a red colored boron- chelate complex,

rosocyanine Rosocyanine and rubrocurcumin are two red colored materials, which are formed by the reaction between curcumin and borates. Application The color reaction between borates and curcumin is used within the spectrophotometrical determination and qu ...

, is formed.

Health issues and toxicity

Elemental boron, boron oxide, boric acid, borates, and many organoboron compounds are relatively nontoxic to humans and animals (with toxicity similar to that of table salt). The LD₅₀ (dose at which there is 50% mortality) for animals is about 6 g per kg of body weight. Substances with an LD50 above 2 g/kg are considered nontoxic. An intake of 4 g/day of boric acid was reported without incident, but more than this is considered toxic in more than a few doses. Intakes of more than 0.5 grams per day for 50 days cause minor digestive and other problems suggestive of toxicity. Boric acid is more toxic to insects than to mammals, and is routinely used as an insecticide. However, it has been used in

neutron capture therapy Neutron capture therapy (NCT) is a type of radiotherapy for treating locally invasive malignant tumors such as primary brain tumors, recurrent cancers of the head and neck region, and cutaneous and extracutaneous melanomas. It is a two-step pro ...

alongside other boron compounds such as

sodium borocaptate Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable isot ...

and

boronophenylalanine Phenylalanine (symbol Phe or F) is an essential α-amino acid with the formula . It can be viewed as a benzyl group substituted for the methyl group of alanine, or a phenyl group in place of a terminal hydrogen of alanine. This essential amino aci ...

with reported low toxicity levels. The boranes (boron hydrogen compounds) and similar gaseous compounds are quite poisonous. As usual, boron is not an element that is intrinsically poisonous, but the toxicity of these compounds depends on structure (for another example of this phenomenon, see phosphine). The boranes are also highly flammable and require special care when handling, some combinations of boranes and other compounds are highly explosive. Sodium borohydride presents a fire hazard owing to its reducing nature and the liberation of hydrogen on contact with acid. Boron halides are corrosive. Boron toxicity (2313046082)

Boron is necessary for plant growth, but an excess of boron is toxic to plants, and occurs particularly in acidic soil. It presents as a yellowing from the tip inwards of the oldest leaves and black spots in barley leaves, but it can be confused with other stresses such as magnesium deficiency in other plants.

Notes

References

External links

Boron
at The Periodic Table of Videos (University of Nottingham) * J. B. Calvert
Boron
2004, private website

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