Boron chemical element

Boron ( /?b??r?n/) is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. Sony VAIO VGN-FW160E/H Battery

However, boron is concentrated on Earth by the water-solubility of its more common naturally occurring compounds, the borate minerals. These are mined industrially as evaporate ores, such as borax and kernite.

Chemically uncombined boron is not found naturally on Earth. Industrially, very pure isolated boron is produced with difficulty, as boron tends to form refractory materials containing small amounts of carbon or other elements.Sony VAIO VGN-FW160F/E Battery

Several allotropes of boron exist: amorphous boron is a brown powder and crystalline boron is black, extremely hard (about 9.5 on Mohs' scale), and a poor conductor at room temperature. Elemental boron is used as a dopant in the semiconductor industry.

The major industrial-scale uses of boron compounds are in sodium perborate bleaches, and the borax component of fiberglass insulation.Sony VAIO VGN-FW170J/H Battery

Boron polymers and ceramics play specialized roles as high-strength lightweight structural and refractory materials. Boron compounds are used in silica-based glasses and ceramics to give them resistance to thermal shock. Boron-containing reagents are used for the synthesis of organic compounds, as intermediate in the synthesis of fine chemicals. Sony VAIO VGN-FW180AE Battery

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.

In biology, borates have low toxicity in mammals (similar to table salt), but are more toxic to arthropods and are used as insecticides.Sony VAIO VGN-FW180D Battery

Boric acid is mildly antimicrobial, and a natural boron-containing organic antibiotic is known. Boron is essential to life. Small amounts of boron compounds play a strengthening role in the cell walls of all plants, making boron necessary in soils. Experiments indicate a role for boron as an ultratrace element in animals, but the nature of its role in animal physiology is unknown.Sony VAIO VGN-FW180E Battery

History and etymology

The name boron originates from the Arabic word ???? buraq or the Persian word ???? burah;[6] which are names for the mineral borax.

Boron compounds were known thousands of years ago. Borax was known from the deserts of western Tibet, where it received the name of tincal, derived from the Sanskrit.Sony VAIO VGN-FW180E/H Battery

Borax glazes were used in China from AD300, and some tincal even reached the West, where the Persian alchemist J?bir ibn Hayy?n seems to mention it in 700. Marco Polo brought some glazes back to Italy in the 13th century. Agricola, around 1600, reports the use of borax as a flux in metallurgy. Sony VAIO VGN-FW180FU Battery

In 1777, boric acid was recognized in the hot springs (soffioni) near Florence, Italy, and became known as sal sedativum, with mainly medical uses. The rare mineral is called sassolite, which is found at Sasso, Italy. Sasso was the main source of European borax from 1827 to 1872, at which date American sources replaced it.Sony VAIO VGN-FW190EBH Battery

Boron compounds were relatively rarely used chemicals until the late 1800s when Francis Marion Smith's Pacific Coast Borax Company first popularized these compounds and made them in volume and hence cheap

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 Sony VAIO VGN-FW190ECH Battery

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 boric acid instead of electrolysis. He produced enough boron to confirm a new element and named the element boracium.Sony VAIO VGN-FW190EDH Battery

Gay-Lussac and Thénard use iron to reduce boric acid at high temperatures. They showed by oxidizing boron with air that boric acid is a oxidation product of boron.[12][13] Jöns Jakob Berzelius identified boron as an element in 1824.[14] Pure boron was arguably first produced by the American chemist Ezekiel Weintraub in 1909.Sony VAIO VGN-FW190NAH Battery

Allotropes

Boron is similar to carbon in its capability to form stable covalently bonded molecular networks. Even nominally disordered (amorphous) boron contains regular boron icosahedra which are, however, bonded randomly to each other without long-range order.Sony VAIO VGN-FW190NBH Battery

Crystalline boron is a very hard, black material with a high melting point of above 2000 °C. It exists in four major polymorphs: ?, ?, ? and T. Whereas ?, ? and T phases are based on B12 icosahedra, the ?-phase can be described as a rocksalt-type arrangement of the icosahedra and B2 atomic pairs.Sony VAIO VGN-FW190NCH Battery

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 T phase is produced at similar pressures, but higher temperatures of 1800–2200 °C. As to the ? and ? phases, they might both coexist at ambient conditions with the ? phase being more stable.Sony VAIO VGN-FW190NDH Battery

Compressing boron above 160 GPa produces a boron phase with an as yet unknown structure, and this phase is a superconductor at temperatures 6–12 K.

Chemistry of the element

Elemental boron is rare and poorly studied because the material is extremely difficult to prepare. Most studies on "boron" involve samples that contain small amounts of carbon.Sony VAIO VGN-FW190NEH Battery

Chemically, boron behaves more closely to silicon than to 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 or hot mixture of sulfuric and chromic acids.Sony VAIO VGN-FW198U/H Battery

The rate of oxidation of boron depends upon 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

Ball-and-stick model of tetraborate anion, [B4O5(OH)4]2?, as it occurs in crystalline borax, Na2[B4O5(OH)4]·8H2O. Sony VAIO VGN-FW260J/B Battery

Boron atoms are pink, with bridging oxygens in red, and four hydroxyl hydrogens in white. Note two borons are trigonally bonded sp2 with no formal charge, while the other two borons are tetrahedrally bonded sp3, each carrying a formal charge of ?1. The oxidation state of all borons is III.Sony VAIO VGN-FW280J/H Battery

This mixture of boron coordination numbers and formal charges is characteristic of natural boron minerals.

Boron undergoes halogenation to give trihalides, for example:

2 B + 3 Br2 ? 2 BBr3

These trihalides in practice are usually made from the oxides. Sony VAIO VGN-FW290JRB Battery

Chemical compounds

In its most familiar compounds, boron has the formal oxidation state III. These include oxides, sulfides, nitrides, and halides.

The trihalides adopt a planar trigonal structure. These compounds are Lewis acids in that they readily form adducts with electron-pair donors, which are called Lewis bases. Sony VAIO VGN-FW290JTB Battery

For example, fluoride (F-) and boron trifluoride (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.

Boron is found in nature on Earth entirely as various oxides of B(III), often associated with other elements. Sony VAIO VGN-FW290JTH Battery

The more than one hundred borates all feature boron in oxidation state +3. These mineral resemble silicates in some respect, although boron is often found not only in a tetrahedral coordination with oxygen, but also in a trigonal planar configuration. Unlike silicates, the boron minerals never feature boron with coordination number greater than four. Sony VAIO VGN-FW290JTW Battery

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 centers is balanced by metal cations in the minerals, such as the sodium (Na+) in borax.

The boron nitrides are notable for the variety of structures that they adopt. Sony VAIO VGN-FW355J/H Battery

They adopt structures analogous to various allotropes of carbon, including graphite, diamond, and nanotubes. In the diamond-like structure called cubic boron nitride (tradename Borazon), boron atoms exist in the tetrahedral structure of carbons atoms in diamond, but one in every four B-N bonds can be viewed as a coordinate covalent bond, Sony VAIO VGN-FW373J/B Battery

wherein two electrons are donated by the nitrogen atom which acts as the Lewis base to a bond to the Lewis acidic 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). Sony VAIO VGN-FW30B Battery

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: both are lubricants, as these planes slip past each other. Sony VAIO VGN-FW50B Battery

However, h-BN is a relatively poor electrical and thermal conductor in the planar direction.

Organoboron chemistry

A large number of organoboron compounds are known and many are useful in organic synthesis. Organoboron(III) compounds are usually tetrahedral or trigonal planar, for example, tetraphenylborate (B(C6H5)4-) vs triphenylborane (B(C6H5)3). Many are produced from hydroboration, which employs diborane (B2H6).Sony VAIO VGN-FW51B/W Battery

Although these are not found on Earth naturally, boron forms a variety of stable compounds with formal oxidation state less than three. As for many covalent compounds, formal oxidation states are often of little meaning in boron hydrides and metal borides. The halides also form derivatives of B(I) and B(II). Sony VAIO VGN-FW51MF Battery

BF, isoelectronic with N2, is not isolable in condensed form, but B2F4 and B4Cl4 are well characterized.

Binary metal-boron compounds, the metal borides, feature boron in oxidation state less than III. Illustrative is magnesium diboride (MgB2). Each boron has a formal ?1 charge and magnesium is assigned a formal charge of 2+. Sony VAIO VGN-FW51MF/H Battery

In this material, the boron centers are trigonal planar, with an extra double bond for each boron, with the boron atoms forming sheets akin to the carbon in graphite. However, unlike the case with hexagonal boron nitride which by comparison lacks electrons in the plane of the covalent atoms,Sony VAIO VGN-FW51ZF Battery

the delocalized electrons in the plane of magnesium diboride allow it to conduct electricity similar to isoelectronic graphite. In addition, in 2001 this material was found to be a high-temperature superconductor.

Certain other metal borides find specialized applications as hard materials for cutting tools.Sony VAIO VGN-FW51ZF/H Battery

From the structural perspective, the most distinctive chemical compounds of boron are the hydrides. Included in this series are the cluster compounds dodecaborate (B12H122-), decaborane (B10H14), and the carboranes such as C2B10H12. Characteristically such compounds feature boron with coordination numbers greater than four.Sony VAIO VGN-FW52JB Battery

Isotopes

Ball-and-stick model of superconductor magnesium diboride. Boron atoms lie in hexagonal aromatic graphite-like layers, with a charge of ?1 per boron. Magnesium (II) ions lie between layers

Boron has two naturally occurring and stable isotopes, 11B (80.1%) and 10B (19.9%).Sony VAIO VGN-FW54FB Battery

The mass difference results in a wide range of ?11B 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. Sony VAIO VGN-FW70DB Battery

It has 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 [B(OH)4]?. Boron isotopes are also fractionated during mineral crystallization, during H2O phase changes in hydrothermal systems, and during hydrothermal alteration of rock. Sony VAIO VGN-FW71DB/W Battery

The latter effect results in preferential removal of the 10B(OH)4 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.Sony VAIO VGN-FW72JGB Battery

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 good at capturing thermal neutrons. Natural boron is about 20% 10B and 80% 11B. The nuclear industry enriches natural boron to nearly pure 10B. The less-valuable by-product, depleted boron, is nearly pure 11B.Sony VAIO VGN-FW73JGB Battery

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 adduct of boron trifluoride (DME-BF3) and column chromatography of borates are being used.Sony VAIO VGN-FW74FB Battery

Enriched boron (boron-10)

Enriched boron or 10B is used in both radiation shielding and in boron neutron capture therapy. In the latter, a compound containing 10B is attached to a muscle near a tumor. The patient is then treated with a relatively low dose of thermal neutrons. This causes energetic and short range alpha radiation from the boron to bombard the tumor.Sony VAIO VGN-FW81HS Battery

In nuclear reactors, 10B is used for reactivity control and in emergency shutdown systems. It can serve either function in the form of borosilicate control rods or as boric acid. In pressurized water reactors, boric acid is added to the reactor coolant when the plant is shut down for refueling. Sony VAIO VGN-FW81NS Battery

It is then slowly filtered out over many months as fissile material is used up and the fuel becomes less reactive.

In future manned 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.Sony VAIO VGN-FW81S Battery

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 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.Sony VAIO VGN-FW82DS Battery

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)

Cosmic radiation will produce secondary neutrons if it hits spacecraft structures. Sony VAIO VGN-FW82JS Battery

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. These resultant decay products may then irradiate nearby semiconductor 'chip' structures, causing data loss (bit flipping, or single event upset). Sony VAIO VGN-FW82XS Battery

In radiation hardened semiconductor designs, one countermeasure is to use depleted boron which is greatly enriched in 11B and contains almost no 10B. 11B is largely immune to radiation damage. Depleted boron is a by-product of the nuclear industry.

11B is also a candidate as a fuel for aneutronic fusion.Sony VAIO VGN-FW83DS Battery

When struck by a proton with energy of about 500 keV, 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. Sony VAIO VGN-FW83JS Battery

Whereas, the alpha particles 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. The nuclear spin of 10B is 3 and that of 11B is 3/2. Sony VAIO VGN-FW83XS Battery

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 a relatively rare element in the Earth's crust, representing only 0.001%. Sony VAIO VGN-FW90HS Battery

The worldwide commercial borate deposits are estimated at 10 million tonnes. Turkey and the United States are the world's largest producers of boron.[50][51] Turkey has almost 72% of the world’s boron reserves. Boron does not appear on Earth in elemental form but is found combined in borax, boric acid, colemanite, kernite, ulexite and borates. Sony VAIO VGN-FW90NS Battery

Boric acid is sometimes found in volcanic spring waters.

Ulexite is one of over a hundred borate minerals; it is a fibrous crystal where individual fibers can guide light like optical fibers.

Economically important sources of boron are rasorite (kernite) and tincal (borax ore). Sony VAIO VGN-FW90S Battery

They are both found in the Mojave Desert of California, but the largest borax deposits are in Central and Western Turkey including the provinces of Eski?ehir, Kütahya and Bal?kesir.

Production

The production of boron compounds does not involve formation of elemental boron, but exploits the convenient availability of borates.Sony VAIO VGN-FW91NS Battery

The earliest routes to elemental boron involved reduction of boric oxide with metals such as magnesium or aluminium. However the product is almost always contaminated with metal borides. Pure boron can be prepared by reducing volatile boron halides with hydrogen at high temperatures. Sony VAIO VGN-FW91S Battery

Ultrapure boron, for the use in semiconductor industry, is produced by the decomposition of diborane at high temperatures and then further purified with the zone melting or Czochralski processes.

Market trend

Estimated global consumption of boron rose to a record 1.8 million tonnes of B2O3 in 2005, following a period of strong growth in demand from Asia, Europe and North America.Sony VAIO VGN-FW92DS Battery

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 colemanite has declined following concerns over arsenic content. Consumers have moved towards the use of refined borates and boric acid that have a lower pollutant content. The average cost of crystalline boron is $5/g.Sony VAIO VGN-FW92JS Battery

Increasing demand for boric acid has led a number of producers to invest in additional capacity. Eti Mine Company of Turkey opened a new boric acid plant with the production capacity of 100,000 tonnes per year at Emet in 2003. Rio Tinto Group increased the capacity of its boron plant from 260,000 tonnes per year in 2003 to 310,000 tonnes per year by May 2005,Sony VAIO VGN-FW93DS Battery

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.Sony VAIO VGN-FW93JS Battery

The rise in global demand has been driven by high growth rates in fiberglass and borosilicate production. A rapid increase in the manufacture of reinforcement-grade fiberglass in Asia with a consequent increase in demand for borates has offset the development of boron-free reinforcement-grade fiberglass in Europe and the USA. Sony VAIO VGN-FW93XS Battery

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.Sony VAIO VGN-FW94FS Battery]

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. Sony VAIO VGN-FW94GS Battery

Glass and ceramics

Borosilicate glassware. Displayed are two beakers and a test tube.

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. Duran and Pyrex are two major brand names for this glass, used both in laboratory glassware and in consumer cookware and bakeware, chiefly for this resistance.Sony VAIO VGN-FW94HS Battery

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 rods. The fibers can be produced by chemical vapor deposition of boron on a tungsten filament.Sony VAIO VGN-G118CN Battery

Boron fibers and sub-millimeter sized crystalline boron springs are produced by laser-assisted chemical vapor deposition. Translation of the focused laser beam allows to produce 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. Sony VAIO VGN-G118GN/B Battery

Detergent formulations and bleaching agents

Borax is used in various household laundry and cleaning products, including the well-known "20 Mule Team Borax" laundry booster and "Boraxo" powdered hand soap. It is also present in some tooth bleaching formulas.Sony VAIO VGN-G118GN/T Battery

Sodium perborate serves as a source of active oxygen in many detergents, 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.Sony VAIO VGN-G118TN/B Battery

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, and silicon carbide. Having one fewer valence electron than the host atom, it donates a hole resulting in p-type conductivity. Sony VAIO VGN-G118TN/S Battery

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 1970s, it was mostly replaced by ion implantation, which relies mostly on BF3 as a boron source.Sony VAIO VGN-G11VN/T Battery

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.Sony VAIO VGN-G11VN/TC Battery

Magnets

Boron is a component of neodymium magnets (Nd2Fe14B), which are the strongest type of permanent magnet. They are found in a variety of domestic and professional electromechanical and electronic devices, such as magnetic resonance imaging (MRI), various motors and actuators, computer HDDs, CD and DVD players, mobile phones, timer switches, speakers, and so on.Sony VAIO VGN-G11XN/B Battery

High-hardness and abrasive compounds

Boron carbide is used for inner plates of ballistic vests

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

Boron carbide and cubic boron nitride powders are widely used as abrasives. Metal borides are used for coating tools through chemical vapor deposition or physical vapor deposition. Sony VAIO VGN-G1AAPS Battery

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.Sony VAIO VGN-G1AAPSA Battery

Boron carbide

Boron carbide is a ceramic material which is obtained by decomposing B2O3 with carbon in the electric furnace:

2 B2O3 + 7 C ? B4C + 6 CO

Boron carbide's stucture 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. Sony VAIO VGN-G1AAPSB Battery

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 B-C chains, and there are smaller (B6) octahedra present as well. (See the article for structural analysis).Sony VAIO VGN-G1AAPSC Battery

The repeating polymer plus semi-crystalline structure of boron carbide gives it great structural strength per weight. It is used in tank armor, bulletproof vests, and numerous other structural applications.

Boron carbide's ability to absorb neutrons without forming long-lived radionuclides (especially when doped with extra boron-10) makes the material attractive as an absorbent for neutron radiation arising in nuclear power plants. Sony VAIO VGN-G1ABNS Battery

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.[75]

Mechanical properties of BCN solids [76] and ReB2[77]

Material Diamond cubic-BC2N cubic-BC5 cubic-BN B4C ReB2

Vickers hardness (GPa) 115 76 71 62 38 22

Fracture toughness (MPa m1/2) 5.3 4.5 9.5 6.8 3.5

Other superhard boron compounds

Heterodiamond (also called BCN); Sony VAIO VGN-G1KAP Battery

Boron nitride. This material is 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,[78] is a superior abrasive.Sony VAIO VGN-G1KBN Battery

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

Rhenium diboride 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.Sony VAIO VGN-G1KBNA Battery

Its value is comparable to that of tungsten carbide, silicon carbide, titanium diboride or zirconium diboride.

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.

Shielding in nuclear reactors

Boron shielding is used as a control for nuclear reactors, taking advantage of its high cross-section for neutron capture.Sony VAIO VGN-G1LAP Battery

Other nonmedical uses

Boron-containing emergency flare

Launch of Apollo 15 Saturn V rocket, using triethylborane ignitor

Because of its distinctive green flame, amorphous boron is used in pyrotechnic flares.[80]*Starch and casein-based adhesives contain sodium tetraborate decahydrate (Na2B4O7•10 H2O) Sony VAIO VGN-G1LBN Battery

Some anti-corrosion systems contain borax.[81]

Sodium borates are used as a flux for soldering silver and gold and with ammonium chloride for welding ferrous metals.[82] 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 [63][84] and in many PVAc and PVOH based adhesives.Sony VAIO VGN-G218LN/T Battery

Triethylborane is a substance which ignites the JP-7 fuel of the Pratt & Whitney J58 turbojet/ramjet engines powering the Lockheed SR-71 Blackbird.[85] 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. Sony VAIO VGN-G218N/B Battery

Triethylborane is suitable for this because of its pyrophoric properties, especially the fact that it burns with a very high temperature.[86] Triethylborane is an industrial initiator in radical reactions, where it is effective even at low temperatures.

Research areas

Magnesium diboride is an important superconducting material with the transition temperature of 39 K. MgB2 wires are produced with the powder-in-tube process and applied in superconducting magnets.Sony VAIO VGN-G21XP/B Battery

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 graphene devices. It also forms nanotubular structures (BNNTs), which have with high strength, high chemical stability, and high thermal conductivity, among its list of desirable properties.Sony VAIO VGN-G2AANS Battery

Biological role

There is a boron-containing natural antibiotic, boromycin, isolated from streptomyces.Boron is an essential plant nutrient, required primarily for maintaining the integrity of cell walls. Conversely, high soil concentrations of > 1.0 ppm can cause marginal and tip necrosis in leaves as well as poor overall growth performance. Sony VAIO VGN-G2AAPS Battery

Levels as low as 0.8 ppm can cause these same symptoms to appear in plants particularly sensitive to boron in the soil. Nearly all plants, even those somewhat tolerant of boron in the soil, will show at least some symptoms of boron toxicity when boron content in the soil is greater than 1.8 ppm. Sony VAIO VGN-G2AAPSA Battery

When this content exceeds 2.0 ppm, few plants will perform well and some may not survive. When boron levels in plant tissue exceed 200 ppm symptoms of boron toxicity are likely to appear. Sony VAIO VGN-G2AAPSC Battery

As an ultratrace element, boron is necessary for the optimal health of rats, although it is necessary in such small amounts that ultrapurified foods and dust filtration of air is necessary to induce boron deficiency, which manifest as poor coat or hair quality.Sony VAIO VGN-G2AAPSB Battery

Presumably, boron is necessary to other mammals. No deficiency syndrome in humans has been described. Small amounts of boron occur widely in the diet, and the amounts needed in the diet would, by analogy with rodent studies, be very small. The exact physiological role of boron in the animal kingdom is poorly understood.Sony VAIO VGN-G2KAN Battery

Boron occurs in all foods produced from plants. Since 1989 its nutritional value has been argued. It is thought that boron plays several biochemical roles in animals, including humans. The U.S. Department of agriculture conducted an experiment in which postmenopausal women took 3 mg of boron a day. Sony VAIO VGN-G2KANA Battery

The results showed that supplemental boron reduced excretion of calcium by 44%, and activated estrogen and vitamin D, suggesting a possible role in the suppression of osteoporosis. However, whether these effects were conventionally nutritional, or medicinal, could not be determined. The US National Institutes of Health quotes this source:Sony VAIO VGN-G2KBNA Battery

Total daily boron intake in normal human diets ranges from 2.1–4.3 mg boron/day.

Analytical quantification

For determination of boron content in food or materials the colorimetric curcumin method is used. Boron has to be transferred to boric acid or borates and on reaction with curcumin in acidic solution, a red colored boron-chelate complex, rosocyanine, is formed.Sony VAIO VGN-NR160E/S Battery

Boron pharmaceuticals and biologicals

Boric acid has antiseptic, antifungal, and antiviral properties and for this reasons is applied as a water clarifier in swimming pool water treatment. Mild solutions of boric acid have been used as eye antiseptics.

A number of potential boronated pharmaceuticals using boron-10, have been prepared for use in boron neutron capture therapy (BNCT). Sony VAIO VGN-NR160E/T Battery

Some boron compounds show promise in treating arthritis, though none have as yet been generally approved for the purpose.

Boron is used as an intermediate in pharmaceutical synthesis, but it appeared as an active element in its first-approved organic pharamaceutical in bortezomib, a new class of drug called proteasome inhibitors, which are active in myeloma and one form of lymphoma.Sony VAIO VGN-NR160E/W Battery

The boron atom in bortezomib binds the catalytic site of the 26S proteasome[106] with high affinity and specificity.

Health issues

Elemental boron, boron oxide, boric acid, borates, and many organoboron compounds are non-toxic to humans and animals (approximately similar to table salt). Sony VAIO VGN-NR180E/S Battery

The LD50 (dose at which there is 50% mortality) for animals is about 6 g per kg of body weight. Substances with LD50 above 2 g are considered non-toxic. The minimum lethal dose for humans has not been established, but an intake of 4 g/day was reported without incidents, and medical dosages of 20 g of boric acid for neutron capture therapy caused no problems.Sony VAIO VGN-NR180E/T Battery

Fish have survived for 30 min in a saturated boric acid solution and can survive longer in strong borax solutions.Boric acid is more toxic to insects than to mammals, and is routinely used as an insecticide.

The boranes and similar gaseous compounds are quite poisonous. As usual, it is not an element that is intrinsically poisonous, but toxicity depends on structure.Sony VAIO VGN-NR290E/S Battery

The boranes (boron hydrogen compounds) are toxic as well as highly flammable and require special care when handling. Sodium borohydride presents a fire hazard due to its reducing nature, and the liberation of hydrogen on contact with acid. Boron halides are corrosive.Sony VAIO VGN-NR290E/T Battery

Congenital endothelial dystrophy type 2, a rare form of corneal dystrophy, is linked to mutations in SLC4A11 gene that encodes a transporter reportedly regulating the intracellular concentration of boron.

Elemental boron can exist in several allotropes, the most common of which are crystalline boron and brown amorphous boron.Sony VAIO VGN-NR298E/S Battery

Crystalline boron has four major polymorphs: ?, ?, ? and T. Whereas the ? phase is most stable and others are metastable, the transformation rate is negligible at room temperature, and thus all those phases can exist at ambient conditions.

Crystalline boron is a very hard (Vickers hardness comparable to that of cubic boron nitride), black, diamagnetic material with a melting point of 2080 °C.Sony VAIO VGN-NR460E/L Battery

Pure elemental boron is difficult to extract. The earliest methods involved reduction of boric oxide with metals such as magnesium or aluminum. However the product is almost always contaminated with metal borides. Pure boron can be prepared by reducing volatile boron halides with hydrogen at high temperatures.Sony VAIO VGN-NR460E/P Battery

Very pure boron, for the use in semiconductor industry, is produced by the decomposition of diborane at high temperatures and then further purified with the zone melting or Czochralski processes.[4] Even more difficult is to prepare pure single crystals of pure boron phases, because of polymorphism, reactivity of boron with impurities, etc.; typical crystal size is ~0.1 mm.Sony VAIO VGN-NR498E/L Battery

?-rhombohedral boron

?-rhombohedral boron has a unit cell of twelve boron atoms. The structure consists of B12 icosahedra in which each boron atom has five nearest neighbors within the icosahedron. If the bonding were the conventional covalent type then each boron would have donated 5 electrons. Sony VAIO VGN-NR498E/S Battery

However, boron has only 3 valence electrons, and it is thought that the bonding in the B12 icosahedra is achieved by the so-called 3-center electron-deficient bonds where the electron charge is accumulated at the center of a triangle formed by 3 adjacent atoms.

The isolated B12 icosahedra are not stable; thus boron is not a molecular solid, but the icosahedra in it are connected by strong covalent bonds.Sony VAIO VGN-NR498E/T Battery

?-rhombohedral boron

?-rhombohedral boron has a subcell containing 105–108 atoms — or a unit cell of 320 atoms. Many atoms form B12 icosahedra, but there are also a large number of non-icosahedral atoms as well. For long time, it was unclear whether the ? or ? phase is most stable at ambient conditions;Sony VAIO VGN-NR498E/W Battery

however, gradually a consensus was reached that ? phase as the thermodynamically stable allotrope.

?-boron

The ?-phase can be described as a NaCl-type arrangement of two types of clusters, B12 icosahedra and B2 pairs.Sony VAIO VGN-NR50 Battery

It can be produced by compressing other boron phases to 12–20 GPa, heating to 1500–1800 0C and is quenchable to ambient conditions. There is evidence of significant charge transfer from B2 pairs to the B12 icosahedra in this structure;[6] in particular, lattice dynamics suggests the presence of significant long-range electrostatic interactions.Sony VAIO VGN-NR50B Battery

This phase was reported by Wentorf in 1965, however neither structure nor chemical composition were established. The structure was solved using ab initio crystal structure prediction calculations[6] and confirmed using single crystal X-ray diffraction.Sony VAIO VGN-NR51 Battery

Tetragonal boron phases

Two tetragonal phases have been reported, T-50 (or ?-tetragonal boron)[17] and T-192 (or ß-tetragonal boron) with 50 and 192 atoms in the unit cell, respectively. Whereas T-50 has been assigned to a compound (nitride (B50N2) or carbide (B50C2)),[8] T-192 is a genuine pure boron phase. Sony VAIO VGN-NR51B Battery

It was produced in 1960 by hydrogen reduction of BBr3 on hot tungsten, rhenium or tantalum filaments at temperatures 1270–1550 °C (i.e. chemical vapor deposition).[9] Further studies have reproduced the synthesis and confirmed the absence of impurities in this phase.Sony VAIO VGN-NR52 Battery

High-pressure superconducting phase

Compressing boron above 160 GPa produces a boron phase with an as yet unknown structure. Contrary to other phases, which are semiconductors, this phase is a metal and becomes a superconductor with a critical temperature increasing from 4 K at 160 GPa to 11 K at 250 GPa.Sony VAIO VGN-NR52B Battery

This structural transformation occurs at pressures at which theory predicts the icosahedra to dissociate.

Amorphous boron

Amorphous boron contains B12 regular icosahedra that are randomly bonded to each other without long range order.Sony VAIO VGN-NR71B Battery

Pure amorphous boron can be produced by thermal decomposition of diborane at temperatures below 1000 °C. Annealing at 1000 °C converts amorphous boron to ?-rhombohedral boron. Amorphous boron nanowires (30–60 nm thick) or fibers[28] can be produced by magnetron sputtering and laser-assisted chemical vapor deposition, respectively;Sony VAIO VGN-NR71B2 Battery

and they also convert to ?-rhombohedral boron nanowires upon annealing at 1000 °C.

Boron nitride is a chemical compound with chemical formula BN, consisting of equal numbers of boron and nitrogen atoms. BN is isoelectronic to a similarly structured carbon lattice and thus exists in various crystalline forms. Sony VAIO VGN-NR72B Battery

The hexagonal form corresponding to graphite is the most stable and softest among BN polymorphs, and is therefore used as a lubricant and an additive to cosmetic products. The cubic (sphalerite structure) variety analogous to diamond is called c-BN. Its hardness is inferior only to diamond, but its thermal and chemical stability is superior. Sony VAIO VGN-NS10E/S Battery

The rare wurtzite BN modification is similar to lonsdaleite and may even be harder than the cubic form.

Boron nitride is not found in nature and is therefore produced synthetically from boric acid or boron trioxide. The initial product is amorphous BN powder, which is converted to crystalline h-BN by heating in nitrogen flow at temperatures above 1500 °C. c-BN is made by annealing h-BN powder at higher temperatures, under pressures above 5 GPa. Sony VAIO VGN-NS10J/S Battery

Contrary to diamond, larger c-BN pellets can be produced by fusing (sintering) relatively cheap c-BN powders. As a result, c-BN is widely used in mechanical applications.

Because of excellent thermal and chemical stability, boron nitride ceramics are traditionally used as parts of high-temperature equipment. Sony VAIO VGN-NS10L/S Battery

Boron nitride has a great potential in nanotechnology. Nanotubes of BN can be produced that have a structure similar to that of carbon nanotubes, i.e. graphene (or BN) sheets rolled on themselves, however the properties are very different: whereas carbon nanotubes can be metallic or semiconducting depending on the rolling direction and radius,Sony VAIO VGN-NS110E/L Battery

a BN nanotube is an electrical insulator with a wide bandgap of ~5.5 eV (same as in diamond), which is almost independent of tube chirality and morphology. Similar to other BN forms, BN nanotubes are more thermally and chemically stable than carbon nanotubes which favors them for some applications.Sony VAIO VGN-NS110E/S Battery

Structure

Boron nitride has been produced in an amorphous (a-BN) and crystalline forms. The most stable crystalline form is the hexagonal one, also called h-BN, ?-BN, or g-BN (graphitic BN). It has a layered structure similar to graphite. Sony VAIO VGN-NS110E/W Battery

Within each layer, boron and nitrogen atoms are bound by strong covalent bonds, whereas the layers are held together by weak van der Waals forces. The interlayer "registry" of these sheets differs, however, from the pattern seen for graphite, because the atoms are eclipsed, with boron atoms lying over and above nitrogen atoms.Sony VAIO VGN-NS115N/S Battery

This registry reflects the polarity of the B-N bonds. Still, h-BN and graphite are very close neighbors and even the BC6N hybrids have been synthesized where carbon substitutes for some B and N atoms.

As diamond is less stable than graphite, cubic BN is less stable than h-BN, but the conversion rate between those forms is negligible at room temperature. Sony VAIO VGN-NS11ER/S Battery

The cubic form has the sphalerite crystal structure, same as diamond structure, and is also called ?-BN or c-BN. The wurtzite BN form (w-BN) has similar structure as lonsdaleite, rare hexagonal polymorph of carbon. In both c-BN and w-BN boron and nitrogen atoms are grouped into tetrahedra, but the angles between neighboring tetrahedra are different.Sony VAIO VGN-NS11E/S Battery

The partly ionic structure of BN layers in h-BN reduces covalency and electrical conductivity, whereas the interlayer interaction increases resulting in higher hardness of h-BN relative to graphite. The reduced electron-delocalization in hexagonal-BN is also indicated by its absence of color and a large band gap.Sony VAIO VGN-NS11J/S Battery

Very different bonding – strong covalent within the basal planes (planes where boron and nitrogen atoms are covalently bonded) and weak between them – causes high anisotropy of most properties of h-BN.

For example, the hardness, electrical and thermal conductivity are much higher within the planes than perpendicular to them. On the contrary, the properties of c-BN and w-BN are more homogeneous.Sony VAIO VGN-NS11L/S Battery

Those materials are extremely hard, with the hardness of c-BN being slightly smaller and w-BN even higher than that of diamond.[10] Because of much better stability to heat and metals, c-BN surpasses diamond in mechanical applications.[11] The thermal conductivity of BN is among the highest of all electric insulators (see table).Sony VAIO VGN-NS11MR/S Battery

Boron nitride can be doped p-type with Be and n-type with boron, sulfur, silicon or if co-doped with carbon and nitrogen. Both hexagonal and cubic BN are wide-gap semiconductors with a band gap energy corresponding to the UV region. If voltage is applied to h-BN or c-BN, then it emits UV light in the range 215–250 nm and therefore can potentially be used as light emitting diodes (LEDs) or lasers.Sony VAIO VGN-NS11M/S Battery

Little is known on melting behavior of boron nitride. It sublimates at 2973 °C at normal pressure releasing nitrogen gas and boron, but melts at elevated pressure.

Thermal stability

Hexagonal and cubic (and probably w-BN) BN show remarkable chemical and thermal stabilities. Sony VAIO VGN-NS11SR/S Battery

For example, h-BN is stable to decomposition in temperatures up to 1000 °C in air, 1400 °C in vacuum, and 2800 °C in an inert atmosphere. The reactivity of h-BN and c-BN is relatively similar, and the data for c-BN are summarized in the table below.

Chemical stability

Boron nitride is insoluble in usual acids, but is soluble in alkaline molten salts and nitrides, such as LiOH, KOH, NaOH-Na2CO3, NaNO3, Li3N, Mg3N2, Sr3N2, Ba3N2 or Li3BN2, which are therefore used to etch BN.Sony VAIO VGN-NS11S/S Battery

Thermal conductivity

The theoretical thermal conductivity of hexagonal Boron nitride nanoribbons (BNNRs) can approach 1700–2000 W/(m·K), which has the same order of magnitude as the experimental measured value for graphene, and can be comparable to the theoretical calculations for graphene nanoribbons.Sony VAIO VGN-NS11ZR/S Battery

Moreover, the thermal transport in the BNNRs is anisotropic. The thermal conductivity of zigzag-edged BNNRs is about 20% larger than that of armchair-edged nanoribbons at room temperature.

The resulting disordered (amorphous) boron nitride contains 92–95% BN and 5–8% B2O3. Sony VAIO VGN-NS11Z/S Battery

The remaining B2O3 can be evaporated in a second step at temperatures >1500 °C in order to achieve BN concentration >98%. Such annealing also crystallizes BN, the size of the crystallites increasing with the annealing temperature.

h-BN parts can be fabricated inexpensively by hot-pressing with subsequent machining.Sony VAIO VGN-NS12M/S Battery

The parts are made from boron nitride powders adding boron oxide for better compressibility. Thin films of boron nitride can be obtained by chemical vapor deposition from boron trichloride and nitrogen precursors. Combustion of boron powder in nitrogen plasma at 5500 °C yields ultrafine boron nitride used for lubricants and toners.Sony VAIO VGN-NS12M/W Battery

Boron nitride reacts with iodine fluoride in trichlorofluoromethane at ?30 °C to produce an extremely sensitive contact explosive, NI3, in low yield.

Intercalation of hexagonal BN

Similar to graphite, various molecules, such as NH3 or alkali metals, can be intercalated into hexagonal boron nitride, that is inserted between its layers. Both experiment and theory suggest the intercalation is much more difficult for BN than for graphite.Sony VAIO VGN-NS12S/S Battery

Preparation of cubic BN

Synthesis of c-BN uses same methods as that of diamond: Cubic boron nitride is produced by treating hexagonal boron nitride at high pressure and temperature, much as synthetic diamond is produced from graphite. Sony VAIO VGN-NS21M/P Battery

Direct conversion of hexagonal boron nitride to the cubic form has been observed at pressures between 5 and 18 GPa and temperatures between 1730 and 3230 °C, that is similar parameters as for direct graphite-diamond conversion. The addition of a small amount of boron oxide can lower the required pressure to 4–7 GPa and temperature to 1500 °C. Sony VAIO VGN-NS21M/W Battery

As in diamond synthesis, to further reduce the conversion pressures and temperatures, a catalyst is added, such as lithium, potassium, or magnesium, their nitrides, their fluoronitrides, water with ammonium compounds, or hydrazine. Other industrial synthesis methods, again borrowed from diamond growth, Sony VAIO VGN-NS21S/S Battery

use crystal growth in a temperature gradient, or explosive shock wave. The shock wave method is used to produce material called heterodiamond, a superhard compound of boron, carbon, and nitrogen.

Low-pressure deposition of thin films of cubic boron nitride is possible. As in diamond growth, the major problem is to suppress the growth of hexagonal phases (h-BN or graphite, respectively). Sony VAIO VGN-NS21S/W Battery

Whereas in diamond growth this is achieved by adding hydrogen gas, boron trifluoride is used for c-BN. Ion beam deposition, plasma-enhanced chemical vapor deposition, pulsed laser deposition, reactive sputtering, and other physical vapor deposition methods are used as well.Sony VAIO VGN-NS21Z/S Battery

Preparation of wurtzite BN

Wurtzite BN can be obtained via static high-pressure or dynamic shock methods.[33] The limits of its stability are not well defined. Both c-BN and w-BN are formed by compressing h-BN, but formation of w-BN occurs at much lower temperatures close to 1700 °C.Sony VAIO VGN-NS31M/P Battery

Production statistics

Whereas the production and consumption figures for the raw materials used for BN synthesis, namely boric acid and boron trioxide, are well known (see boron), the corresponding numbers for the boron nitride are not listed in statistical reports. An estimate for the 1999 world production is 300 to 350 metric tons. Sony VAIO VGN-NS31M/W Battery

The major producers and consumers of BN are located in the United States, Japan, China and Germany. In 2000, prices varied from about $75/kg to $120/kg for standard industrial-quality h-BN and were about up to $200–$400/kg for high purity BN grades.Sony VAIO VGN-NS31S/S Battery

Hexagonal BN

Hexagonal BN is the most widely used polymorph. It is a good lubricant at both low and high temperatures (up to 900 °C, even in an oxidizing atmosphere). h-BN lubricant is particularly useful when the electrical conductivity or chemical reactivity of graphite (alternative lubricant) would be problematic. Sony VAIO VGN-NS31Z/P Battery

Another advantage of h-BN over graphite is that its lubricity does not require water or gas molecules trapped between the layers. Therefore, h-BN lubricants can be used even in vacuum, e.g. in space applications. The lubricating properties of fine-grained h-BN are used in cosmetics, paints, dental cements, and pencil leads.Sony VAIO VGN-NS31Z/S Battery

Hexagonal BN was first used in cosmetics around 1940 in Japan. However, because of its high price, h-BN was soon abandoned for this application. Its use was revitalized in the late 1990s with the optimization h-BN production processes, and currently h-BN is used by nearly all leading producers of cosmetic products for foundations, Sony VAIO VGN-NS31Z/W Battery

make-up, eye shadows, blushers, kohl pencils, lipsticks and other skincare products.

Because of its excellent thermal and chemical stability, boron nitride ceramics are traditionally used as parts of high-temperature equipment. h-BN can be included in ceramics, alloys, resins, plastics, rubbers, and other materials, giving them self-lubricating properties. Sony VAIO VGN-NS38M/P Battery

Such materials are suitable for construction of e.g. bearings and in steelmaking. Plastics filled with BN have less thermal expansion as well as higher thermal conductivity and electrical resistivity. Due to its excellent dielectric and thermal properties, BN is used in electronics e.g. as a substrate for semiconductors, microwave-transparent windows, and as a structural material for seals.Sony VAIO VGN-NS38M/W Battery

Hexagonal BN is used in xerographic process and laser printers as a charge leakage barrier layer of the photo drum. In the automotive industry, h-BN mixed with a binder (boron oxide) is used for sealing oxygen sensors, which provide feedback for adjusting fuel flow. The binder utilizes the unique temperature stability and insulating properties of h-BN.Sony VAIO VGN-NS130E/L Battery

Parts can be made of h-BN by hot pressing. Union Carbide Corporation produces three grades of BN. HBN, with boron oxide binder, usable to 550–850 °C in oxidizing atmosphere and up to 1600 °C in vacuum, but due to the boron oxide content is sensitive to water. HBR uses calcium borate binder and is usable at 1600 °C. HBC grade uses no binder and can be used to 3000 °C.Sony VAIO VGN-NS130E/S Battery

Cubic boron nitride

Cubic boron nitride (CBN or c-BN) is widely used as an abrasive. Its usefulness arises from its insolubility in iron, nickel, and related alloys at high temperatures, whereas diamond is soluble in these metals to give carbides. Polycrystalline c-BN (PCBN) abrasives are therefore used for machining steel, whereas diamond abrasives are preferred for aluminum alloys, ceramics, and stone. Sony VAIO VGN-NS130E/W Battery

When in contact with oxygen at high temperatures, BN forms a passivation layer of boron oxide. Boron nitride binds well with metals, due to formation of interlayers of metal borides or nitrides. Materials with cubic boron nitride crystals are often used in the tool bits of cutting tools. Sony VAIO VGN-NS140E/L Battery

For grinding applications, softer binders, e.g. resin, porous ceramics, and soft metals, are used. Ceramic binders can be used as well. Commercial products are known under names "Borazon" (by Diamond Innovations), and "Elbor" or "Cubonite" (by Russian vendors).Sony VAIO VGN-NS140E/S Battery

Similar to diamond, the combination in c-BN of highest thermal conductivity and electrical resistivity is ideal for heat spreaders. Contrary to diamond, large c-BN pellets can be produced in a simple process (called sintering) of annealing c-BN powders in nitrogen flow at temperatures slightly below the BN decomposition temperature. Sony VAIO VGN-NS140E/W Battery

This ability of c-BN and h-BN powders to fuse allows cheap production of large BN parts.

As cubic boron nitride consists of light atoms and is very robust chemically and mechanically, it is one of the popular materials for X-ray membranes: low mass results in small X-ray absorption, and good mechanical properties allow usage of thin membranes, thus further reducing the absorption.Sony VAIO VGN-NS190J/L Battery

Amorphous boron nitride

Layers of amorphous boron nitride (a-BN) are used in some semiconductor devices, e.g. MISFETs. They can be prepared by chemical decomposition of trichloroborazine with caesium, or by thermal chemical vapor deposition methods. Thermal CVD can be also used for deposition of h-BN layers, or at high temperatures, c-BN.Sony VAIO VGN-NS190J/S Battery

Other BN forms -Boron nitride fibers

Hexagonal BN can be prepared in the form of fibers, structurally similar to carbon fibers, by thermal decomposition of extruded borazine (B3N3H6) fibers with addition of boron oxide in a nitrogen atmosphere at 1800 °C. Sony VAIO VGN-NS190J/W Battery

An alternative method is thermal decomposition of cellulose fibers impregnated with boric acid or ammonium tetraborate in an atmosphere of ammonia and nitrogen above 1000 °C. Boron nitride fibers are used as reinforcement in composite materials, with the matrix materials ranging from organic resins to ceramics to metals (see Metal matrix composites). Sony VAIO VGN-NS235J/L Battery

Boron nitride nanomesh

Boron nitride nanomesh is an inorganic nanostructured two-dimensional material. It consists of a single BN layer, which forms by self-assembly a highly regular mesh after high-temperature exposure of a clean rhodium or ruthenium surface to borazine under ultra-high vacuum. Sony VAIO VGN-NS235J/P Battery

The nanomesh looks like an assembly of hexagonal pores. The distance between 2 pore centers is 3.2 nm and the pore diameter is ~2 nm.

The boron nitride nanomesh is not only stable to decomposition under vacuum, air and some liquids, but also up to temperatures of 800 °C.Sony VAIO VGN-NS235J/S Battery

In addition, it shows the extraordinary ability to trap molecules and metallic clusters which have similar sizes to the nanomesh pores, forming a well-ordered array. These characteristics promise interesting applications of the nanomesh in areas like nanocatalysis, surface functionalisation, spintronics, quantum computing and data storage media like hard drives.Sony VAIO VGN-NS235J/W Battery

Boron nitride nanotubes

Boron nitride nanotubes were theoretically predicted in 1994 ] and experimentally discovered in 1995. They can be imagined as a rolled up sheet of boron nitride. Structurally, it is a close analog of the carbon nanotube, Sony VAIO VGN-NS240E/L Battery

namely a long cylinder with diameter of several to hundred nanometers and length of many micrometers, except carbon atoms are alternately substituted by nitrogen and boron atoms. However, the properties of BN nanotubes are very different: whereas carbon nanotubes can be metallic or semiconducting depending on the rolling direction and radius,Sony VAIO VGN-NS290J/L Battery

a BN nanotube is an electrical insulator with a bandgap of ~5.5 eV, basically independent of tube chirality and morphology. In addition, a layered BN structure is much more thermally and chemically stable than a graphitic carbon structure.

All well-established techniques of carbon nanotube growth, such as arc-discharge, Sony VAIO VGN-NS290J/S Battery

laser ablation and chemical vapor deposition, are used to synthesize BN nanotubes. BN nanotubes can also be produced by ball milling of amorphous boron, mixed with a catalyst: iron powder, under NH3 atmosphere. Subsequent annealing at ~1100 °C in nitrogen flow transforms most of the product into BN.Sony VAIO VGN-NS50B/L Battery

Electrical and field emission properties of the thus prepared nanotubes can be tuned by doping with gold atoms via sputtering of gold on the nanotubes. Doping rare-earth atoms of europium turns a BN nanotube into a phosphor material emitting visible light under electron excitation.Sony VAIO VGN-NS50B/W Battery

Like BN fibers, boron nitride nanotubes show promise for aerospace applications where integration of boron and in particular the light isotope of boron (10B) into structural materials improves their radiation-shielding properties; the improvement is due to strong neutron absorption by 10B. Sony VAIO VGN-NS51B/L Battery

Such 10BN materials are of particular theoretical value as composite structural materials in future manned interplanetary spacecraft, where absorption-shielding from cosmic ray spallation neutrons is expected to be a particular asset in light construction materials.Sony VAIO VGN-NS51B/P Battery

Composites containing BN

Addition of boron nitride to silicon nitride ceramics improves the thermal shock resistance of the resulting material. For the same purpose, BN is added also to silicon nitride-alumina and titanium nitride-alumina ceramics.Sony VAIO VGN-NS51B/W Battery

Other materials being reinforced with BN are, e.g., alumina and zirconia, borosilicate glasses, glass ceramics, enamels, and composite ceramics with titanium boride-boron nitride and titanium boride-aluminium nitride-boron nitride and silicon carbide-boron nitride composition.Sony VAIO VGN-NS52JB/L Battery

Boron neutron capture therapy (BNCT) is an experimental form of radiotherapy that uses a neutron beam that interacts with boron injected into a patient. BNCT depends on the interaction of slow neutrons with boron-10 to produce alpha particles and lithium nuclei, without producing other types of ionizing radiation.Sony VAIO VGN-NS52JB/P Battery

Patients are first given an intravenous injection of a boron-10 containing chemical that preferentially binds to tumor cells. In clinical trials performed so far the neutrons are created in a nuclear reactor, but particle accelerators may also be used to collide protons into targets made of lithium or beryllium.Sony VAIO VGN-NS52JB/W Battery

The neutrons pass through a neutron moderator, which shapes the neutron energy spectrum suitable for BNCT treatment. Before entering the patient the neutron beam is shaped by a beam collimator. While passing through the tissue of the patient, the neutrons are slowed by collisions and become low energy thermal neutrons. Sony VAIO VGN-NS70B/W Battery

The thermal neutrons undergo reaction with the boron-10 nuclei, forming a compound nucleus (excited boron-11) which then promptly disintegrates to lithium-7 and an alpha particle. Both the alpha particle and the lithium ion produce closely spaced ionizations in the immediate vicinity of the reaction, with a range of approximately 5-9 micrometres, Sony VAIO VGN-NS71B/W Battery

or roughly the thickness of one cell diameter. This technique is advantageous since the radiation damage occurs over a short range and thus normal tissues can be spared.

BNCT has been experimentally tested primarily as an alternative treatment for malignant brain tumors called glioblastoma multiforme as well as recurrent, locally advanced head and neck cancer. Sony VAIO VGN-NS72JB/W Battery

Although there are reports of some successful outcomes, this approach has not yet been shown to be superior to other current therapies. Hence, BNCT has not entered routine clinical use.

Recent applications

On 19 December 2001, BNCT has been successfully used for the first time in Pavia (Italy) on a 42 years old man to treat liver cancer. His liver has been explanted, has been subjected to the treatment, and has been reimplanted.Sony VAIO VGN-NS90HS Battery

The first clinical trial of BNCT in Argentina were performed on 9 October 2003. BNCT has been used in Japan for head and neck cancers in 2009.[3] Taiwan BNCT group also started treating head and neck cancers at the Tsing Hua Open-pool Reactor (THOR) of National Tsing Hua University on 11 August 2010.Sony VAIO VGN-NS92JS Battery

Early history of neutron capture therapy

After the initial discovery of the neutron in 1932 by Sir James Chadwick, a study by H. J. Taylor in 1935 showed the ability of the boron-10 nuclei to capture thermal neutrons. The neutron capture initiated the fission of the boron-10 nuclei into helium-4 alpha particles as well as lithium-7 particles. Sony VAIO VGN-NS92XS Battery

In 1936, Locher realised the potential of this discovery in the field of medicine and subsequently suggested that neutron capture could be used to treat tumours. A binary system uses two separate components for the therapy of cancer. Each component in itself is relatively harmless to the cells, but when combined together for treatment they produce a highly cytocidal effect which is lethal.Sony VAIO VGN-NW11S/S Battery

As development on neutron capture therapy continued, other radioactive isotopes such as uranium-235 were researched. However, studies in the late 1950s by Lussenhop et al. showed that the amounts of uranium needed for successful neutron capture therapy was too toxic for human use.Sony VAIO VGN-NW11S/T Battery

A boronic acid is an alkyl or aryl substituted boric acid containing a carbon–boron bond belonging to the larger class of organoboranes. Boronic acids act as Lewis acids. Their unique feature is that they are capable of forming reversible covalent complexes with sugars, amino acids, Sony VAIO VGN-NW11Z/S Battery

hydroxamic acids, etc. (molecules with vicinal, (1,2) or occasionally (1,3) substituted Lewis base donors (alcohol, amine, carboxylate)). The pKa of a boronic acid is ~9, but they can form tetrahedral boronate complexes with pKa ~7. They are occasionally used in the area of molecular recognition to bind to saccharides for fluorescent detection or selective transport of saccharides across membranes.Sony VAIO VGN-NW11Z/T Battery

Boronic acids are used extensively in organic chemistry as chemical building blocks and intermediates predominantly in the Suzuki coupling. A key concept in its chemistry is transmetallation of its organic residue to a transition metal.

The compound bortezomib with a boronic acid group is a drug used in chemotherapy. The boron atom in this molecule is a key substructure because through it certain proteasomes are blocked that would otherwise degrade proteins.Sony VAIO VGN-NW21EF/S Battery

Synthesis

Boronic acids can be obtained via several methods. The most common way is reaction of organometallic compounds based on lithium or magnesium (Grignards) with borate esters. For example phenylboronic acid is produced from phenylmagnesium bromide and trimethyl borate followed by hydrolysis .Sony VAIO VGN-NW21JF Battery

Another method is reaction of an arylsilane (RSiR3) with boron tribromide (BBr3) in a transmetallation to RBBr2 followed by acidic hydrolysis.

A third method is by palladium catalysed reaction of aryl halides and triflates with diboronyl esters in a coupling reaction. An alternative to esters in this method is the use of diboronic acid or tetrahydroxydiboron ([B(OH2)]2).Sony VAIO VGN-NW21MF Battery

Saccharide recognition

The covalent pair-wise interaction between boronic acids and 1,2- or 1,3-diols in aqueous systems is rapid and reversible. As such the equilibrium established between boronic acids and the hydroxyl groups present on saccharides has been successfully employed to develop a range of sensors for saccharides.Sony VAIO VGN-NW21MF/W Battery

One of the key advantages with this dynamic covalent strategy[24] lies in the ability of boronic acids to overcome the challenge of binding neutral species in aqueous media. If arranged correctly, the introduction of a tertiary amine within these supramolecular systems will permit binding to occur at physiological pH and allow signalling mechanisms such as photoinduced electron transfer mediated fluorescence emission to report the binding event.Sony VAIO VGN-NW21ZF Battery

Potential applications for this research include systems to monitor diabetic blood glucose levels. As the sensors employ an optical response, monitoring could be achieved using minimally invasive methods, one such example is the investigation of a contact lens doped with boronic acid based sensors to monitor glucose levels within ocular fluid.Sony VAIO VGN-NW31EF/W Battery

In organic chemistry, the hydroboration–oxidation reaction is a two-step organic reaction that converts an alkene into a neutral alcohol by the net addition of water across the double bond. The hydrogen and hydroxyl group are added in a syn addition leading to cis stereochemistry.Sony VAIO VGN-NW31JF Battery

Hydroboration–oxidation is an anti-Markovnikov reaction, with the hydroxyl group attaching to the less-substituted carbon. The reaction was first reported by Herbert C. Brown in the late 1950s[2] and it was recognized in his receiving the Nobel Prize in Chemistry in 1979.Sony VAIO VGN-NW320F/B Battery

where THF is tetrahydrofuran, the archetypal solvent used for this reaction. In the first step, borane (BH3) adds to the double bond, transferring one hydrogen from itself to the adjacent carbon. The second step substitutes the boron group BH2 with the hydroxyl group, creating the final product.Sony VAIO VGN-NW320F/TC Battery

The reaction described in the original 1957 Brown publication 1-hexene is converted to 1-hexanol.

Hydroboration mechanism

Borane exists as a toxic, colorless gas called diborane (B2H6). In diborane, two hydrogen atoms are each bonded to both boron atoms by single pairs of electrons ("three-center two-electron bonds"). Sony VAIO VGN-NW35E Battery

This delocalization satisfies the octet around each boron and reduces the electrophilicity. That said, even diborane is intensely Lewis acidic, because of its vacant p orbitals. Because dimerization happens instantaneously, it is not possible to isolate pure borane.Sony VAIO VGN-NW380F/S Battery

However, when diborane is treated with an ether or amine, a stable complex is formed, as the lone pair from the Lewis basic oxygen or nitrogen atom is donated to the borane. These complexes act chemically like borane. Solutions of BH3 complexes in THF or diethyl ether are commercially available and more easily handled than diborane gas, and so are the more common form found in laboratories. Sony VAIO VGN-NW380F/T Battery

For simplicity in illustration, borane will be used instead of the borane–ether complex in this article.

The addition of BH3 to the alkene is a concerted reaction, with multiple bond formation and breaking occurring simultaneously. The intermediate step can be visualized more clearly by a theoretical transition state.Sony VAIO VGN-NW50JB Battery

Knowing that the group containing the boron will be replaced by a hydroxyl group, it can be seen that the first step determines the regioselectivity. The hydroborane will add to the alkene so that the boron always ends up on the lesser substituted carbon. In the transition state, the more substituted carbon bears a partial positive charge (a partial carbocation). Sony VAIO VGN-NW51FB/N Battery

As a general rule, carbocations that are more substituted tolerate positive charge better than those that aren't. Had the hydroborane attacked with the opposite orientation, the lesser substituted carbon would bear the (partial) positive charge, which is electronically unfavorable. Hydroborane also tends to add to the lesser substituted carbon because it is less sterically hindered.Sony VAIO VGN-NW51FB/W Battery

Hydroborations are also stereoselective, with the new constituents adding in syn (on the same face of the alkene). Thus 1-methylcyclopentene reacts with diborane predominantly to the trans-alkane.

Until all hydrogens attached to boron have been transferred away, the boron group BH2 will continue adding to more alkenes.Sony VAIO VGN-NW70JB Battery

This means that one equivalent of hydroborane will conduct the reaction with three equivalents of alkene. Furthermore, it is not necessary for the hydroborane to have more than one hydrogen. Therefore, BH3 can be better represented as R-BH, where R can represents the remainder of the molecule. Sony VAIO VGN-NW71FB/N Battery

A widely used hydroboration reagent is 9-BBN which has just one hydrogen at boron and the same applies for catecholborane.

Hydroboration–oxidation

In the second hydroboration–oxidation step, the nucleophilic hydroperoxide anion attacks the boron atom.Sony VAIO VGN-NW71FB/W Battery

Alkyl migration to oxygen gives the alkyl borane withretention of stereochemistry (in reality, the reaction occurs via the trialkyl borate B(OR)3, rather than the monoalkyl borinic ester BH2OR).

Oxymercuration–reduction is another reaction that converts an alkene into an alcohol. Unlike hydroboration–oxidation, oxymercuration-reduction is not stereospecific. Sony VAIO VGN-NW91FS Battery

Further, oxymercuration–reduction is a Markovnikov reaction. Therefore, oxymercuration–reduction and hydroboration–oxidation are complementary because they add with opposite regiochemistry.

Alkyne hydroboration

A hydroboration reaction also takes place on alkynes. Sony VAIO VGN-NW91GS Battery

Again the mode of action is syn and secondary reaction products are aldehydes from terminal alkynes and ketonesfrom internal alkynes. In order to prevent hydroboration across both the pi-bonds, a bulky borane like disiamyl (di-sec-iso-amyl) borane is used.Sony VAIO VGN-NW91VS Battery

Organoborane reactions

Amines can be obtained from the intermediate organoborane by action of chloramine. Reaction with iodine or bromine afford the corresponding alkyl halides. Acarboxylic acid simply replaces the borane group by a proton.Sony VAIO VGN-SR11M Battery,Sony VAIO VGN-SR11MR Battery,Sony VAIO VGN-SR140D Battery,Sony VAIO VGN-SR140D/B Battery,Sony VAIO VGN-SR140D/P Battery