Boron

Boron (pronEng|ˈbɔərɒn) is a chemical element with atomic number 5 and the chemical symbol B. Boron is a trivalent nonmetallic element which occurs abundantly in the evaporite ores borax and ulexite. Boron is never found as a free element on Earth.

Several allotropes of boron exist; amorphous boron is a brown powder, though crystalline boron is black, hard (9.3 on Mohs' scale), and a weak conductor at room temperature (22-28 °C, 72-82 °F). Elemental boron is used as a dopant in the semiconductor industry, while boron compounds play important roles as light structural materials, nontoxic insecticides and preservatives, and reagents for chemical synthesis.

Boron is an essential plant nutrient, although higher soil concentrations of boron may also be toxic to plants. As an ultratrace element, boron is necessary for the optimal health of rats and presumably other mammals, though its physiological role in animals is poorly understood.

Characteristics

Brown amorphous boron is a product of certain chemical reactions. It contains boron atoms randomly bonded to each other without long range order.

Crystalline boron, a very hard, black material with a high melting point, exists in many polymorphs. Two rhombohedral forms, α-boron and β-boron containing 12 and 106.7 atoms in the rhombohedral unit cell respectively, and 50-atom tetragonal boron are the three most characterised crystalline forms.

Optical characteristics of crystalline/elemental boron include the transmittance of infrared light. At standard temperatures, elemental boron is a poor electrical conductor, but is a good electrical conductor at high temperatures.

Chemically boron is electron-deficient, possessing a vacant p-orbital. It is an electrophile. Compounds of boron often behave as Lewis acids, readily bonding with electron-rich substances to compensate for boron's electron deficiency. The reactions of boron are dominated by such requirement for electrons. Also, boron is the least electronegative non-metal, meaning that it is usually oxidized (loses electrons) in reactions.

Boron is also similar to carbon with its capability to form stable covalently bonded molecular networks. Boron is also used for heat resistant alloys. Boron can form compounds whose formal oxidation state is not three, such as B(II) in B₂F₄. [cite web|url=http://lb.chemie.uni-hamburg.de/search/index.php?content=166/dGp23678|title=Compound Descriptions: B₂F₄|accessdate=2007-12-10|publisher=Landol Börnstein Substance/Property Index]

History

Compounds of boron (Arabic "Buraq" from Persian "Burah" from Turkish "Bor") have been known of for thousands of years. In early Egypt, mummification depended upon an ore known as natron, which contained borates as well as some other common salts. Borax glazes were used in China from CE 300, and boron compounds were used in glassmaking in ancient Rome.

The sources for borax and boric acid were at first dry lakes in Tibet and from 1818 on the geysers in the tuscan village Larderello Italy. During the 19th century the deposits in south America, California and Turkey were discovered. cite journal | journal = Environmental Health Perspectives | volume = 102, Supplement 7| year =1994 | title = An Introduction to Boron: History, Sources, Uses, and Chemistry | first = William G. | last = Woods | url = http://www.ehponline.org/realfiles/members/1994/Suppl-7/woods-full.html| accessdate = 2008-09-20]

The element was not isolated until 1808 by Sir Humphry Davy [cite journal | title = The Bakerian Lecture: An Account of Some New Analytical Researches on the Nature of Certain Bodies, Particularly the Alkalies, Phosphorus, Sulphur, Carbonaceous Matter, and the Acids Hitherto Undecompounded; With Some General Observations on Chemical Theory | journal = Philosophical Transactions of the Royal Society of London (1776-1886) | volume = 99 | year = 1809 | pages = 39–104 Humphry Davy | author link = Humphry Davy | doi = 10.1098/rstl.1809.0005] , Joseph Louis Gay-Lussac, and Louis Jacques Thénard, to about 50 percent purity, by the reduction of boric acid with sodium or magnesium. [cite journal | title =The Metals Boron and Aluminium: "Classics of Science" | journal = The Science News-Letter | volume = 19 | issue = 518 | year = 1931 | pages = 171–173 | url = http://www.jstor.org/stable/3907433 | accessdate 2008-09-22] These men did not recognize the substance as an element. It was Jöns Jakob Berzelius in 1824 who identified boron as an element. The first pure boron was produced by the American chemist W. Weintraub in 1909, although this is disputed by some researchers. [cite journal| author= | title=| journal= Z. Angew. Phys.| year=1970| pages=277| volume=29] [cite journal | title=Boron. I. Preparation and Properties of Pure Crystalline Boron | author = A. W. Laubengayer, D. T. Hurd, A. E. Newkirk, J. L. Hoard
journal=J. Am. Chem. Soc.year=1943| volume= 65 | issue = 10| pages=1924-1931 | doi = 10.1021/ja01250a036]

Applications

The only major use of metallic boron is as boron fiber. The fibers are used to reinforce the fuselage of fighter aircraft, for example the B-1 bomber. The fibers are produced by vapor deposition of boron on a tungsten filament. [cite journal | title = Inorganic Fibers—A Literature Review | first = Theodore F. | last 0 Cooke | journal = Journal of the American Ceramic Society | volume = 74 | issue = 12 | pages = 2959–2978 | doi = 10.1111/j.1151-2916.1991.tb04289.x]

Glass and ceramics

Nearly all boron ore extracted from the Earth is destined for refinement into boric acid and sodium tetraborate. In the United States 70% of the boron is used for the production of glass and ceramics. For scientific glassware, for example, borosilicate glass is used because of its capabilities to withstand chemical reactions and sudden changes in temperature. Duran and Pyrex are two major brand names under which this glass is available.

oaps and detergents

Sodium perborate serves as a source of active oxygen in many detergents, laundry detergents, cleaning products, and laundry bleaches. It is also present in some tooth bleaching formulas.

Fire retardants

Zinc borate is used as fire retardant for plastics and rubber articles and also for cellulose insulation and in cotton mattresses.

Other uses

* After the discovery that magnesium diboride becomes superconductive at temperatures below 39 K in 2001 it took some time before the first MgB₂ wires could be produced with the powder-in-tube (PIT) process. By 2008 the metallic superconductors based on niobium alloys dominated the market. [cite journal | title = Magnesium Diboride: Better Late than Never.Preview By: | last = Canfield, | first = Paul C.; | coauthors =Crabtree, George W. | journal = Physics Today | volume = 56 | issue = 3 | pages = 34–41 | year = 2003 | url = http://www.cmp.ameslab.gov/personnel/canfield/pub/pt0303.pdf] [cite journal | journal = Physica C: Superconductivity | volume = 456 | issues = 1–2 |year = 2007 | pages 209–217 | doi = 10.1016/j.physc.2007.01.030 | title = Development of ex situ processed MgB₂ wires and their applications to magnets | first = Valeria | last = Braccini | coauthor = Nardelli, Davide; Penco, Roberto; Grasso Giovanni]
* Sodium tetraborate pentahydrate (Na₂B₄O₇ • 5H₂O), which is used in large amounts in making insulating fiberglass and sodium perborate bleach,
* Boron carbide, a ceramic material, is used to make armor materials, especially in bulletproof vests for soldiers and police officers.
* Orthoboric acid (H₃BO₃) or boric acid is used in the production of textile fiberglass, flat panel displays and eye drops.
* Sodium tetraborate decahydrate (Na₂B₄O₇ • 10H₂O) or borax is used in the production of adhesives and in anti-corrosion systems.
* Boron nitride is a material in which the extra electron of nitrogen (with respect to carbon) enables it to form structures that are isoelectronic with carbon allotropes.
*Boron reacts with ammonia at high temperatures to give a compound called borazole (B₃N₃H₆), also known as inorganic benzene.
*Triethylborane was used to ignite the JP-7 fuel of the Pratt / Whitney J-58 ramjet engines powering the Lockheed SR-71 Blackbird.
* Boron is an essential plant micronutrient. [cite web
title = Functions of Boron in Plant Nutrition
first =
last =
coauthors =
url = http://www.borax.com/agriculture/files/an203.pdf
publisher = U.S. Borax Inc.
pages =
year =
doi = ] [cite journal
title = Functions of Boron in Plant Nutrition
first = Dale G.
last = Blevins
coauthors = Lukaszewski, Krystyna M.
journal = Annual Review of Plant Physiology and Plant Molecular Biology
volume = 49
issue =
pages = 481–500
year = 1998
url =
doi = 10.1146/annurev.arplant.49.1.481 ]
* Because of its distinctive green flame, amorphous boron is used in pyrotechnic flares. [cite journal
title = Pyrotechnic Chemistry
author = B. J. Kosanke, B. Sturman, T. Shimizu, I. von Maltitz, R. J. Hancox, M. A. Wilson, N. Kubota, D. R. Dillehay, C. Jennings-White, T. Smith, D. Chapman, M. PodlesakMitwirkende Personen B. J. Kosanke
publisher = Journal of Pyrotechnics,
pages = 419
year = 2004
ISBN = 9781889526157
doi = ]
* Boric acid is an important compound used in textile products.
* Boric acid is traditionally used as an insecticide, notably against ants, fleas, and cockroaches. [cite journal
title = Oral toxicity of boric acid and other boron compounds to immature cat fleas (Siphonaptera: Pulicidae)
first = J. H.
last = Klotz
coauthors = Moss, J. I.; Zhao, R.; Davis, L. R.; Patterson, R. S.
journal = J. Econ. Entomol.
volume = 87
issue = 6
pages = 1534-6
year = 1994
url = http://grande.nal.usda.gov/ibids/index.php?mode2=detail&origin=ibids_references&therow=51171
doi = ]
* Borax is sometimes found in laundry detergent.
* Boron filaments are high-strength, lightweight materials that are chiefly used 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. [cite web | title = Selected Mechanical and Physical Properties of Boron Filaments | year = 1966 | first = H. W. | last = Herring | publisher = NASA | accessdate = 2008-09-20| url = http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19660005941_1966005941.pdf ]
* Boron is used as a melting point depressant in nickel-chromium braze alloys. [cite journal
title = Evaluation of transient liquid phase bonding between nickel-based superalloys
first = Xiaowei
last = Wu
coauthors = Chandel R. S.; Li, Hang
journal = Journal of Materials Science
volume = 36
issue = 6
pages = 1539–1546
year = 2001
url =
doi = 10.1023/A:1017513200502 ]
* Boron slurry is used as an energetic material with very high energy density like rocket fuels and jet engines.
* Boron compounds show promise in treating arthritis. [cite journal
title = Boron and Arthritis: The Results of a Double-blind Pilot Study
first = Richard L. a; b; c
last = Travers
coauthors = Rennie, George C.; Newnham, Rex E.
journal = Journal of Nutritional & Environmental Medicine
volume = 1
issue = 2
pages = 127 - 132
year = 1990
url =
doi = 10.3109/13590849009003147 ]
* Due to its high neutron cross-section, boron is often used to control fission in nuclear reactors.
* Sodium tetraborate pentahydrate is used as a water clarifier in swimming pool water treatment.

Hardest boron compounds

The hardest boron compounds are created synthetically. Rhenium diboride (ReB₂) and cubic (or beta)-boron nitride can actually scratch diamond, but are still not as hard as diamond although rhenium diboride surpasses diamond in certain directions. Rhenium diboride is nearly as hard as cubic boron nitride and boron suboxide, and much harder than osmium diboride (which was the first step towards rhenium diboride synthesis).

It is still a matter of research as to which boron compound is the hardest:
* Heterodiamond (called also BCN,it is supposed to be an improvement of boron nitride, although it contains carbon).
* Cubic boron nitride (CBN or borazon, the latter being the commercial name. Discovered in 1957).
* Rhenium diboride (as ReB₂ synthesis requires considerably less pressure compared to cubic boron nitride. It is seen as an interesting economical alternative to CBN for the industry).

Like all superhard materials with properties similar to diamond, these boron-based materials do not possess a unique hardness value but rather a hardness "range". This is because hardness tests (e.g. Knoop, Vickers, Rockwell) depend on many conditions (direction, load...) according to whether the diamond used in the test will indent more or less deeply the given material. As a result, they all scratch each other as well as diamond under certain conditions.Fact|date=May 2008

These borides have been primarily developed as a substitute for diamond in coated tools (CVD or PVD diamond-like coated), as well as diamond powder coated blades, since diamond becomes soluble in iron and unstable at high temperatures, thus reducing tool life.

Interestingly enough, boron nitride in its hexagonal form (h-BN), is a very soft material (only 2 in Mohs hardness scale) compared to the cubic form, h-BN being slightly more inert chemically than c-BN at very high temperatures, a feature extremely useful in advanced foundry and casting refractory applications (high end crucibles).

At a lesser degree, certain boronized (or borided) metals and alloys, through means of ion implantation or only ion beam deposition of boron ions, show a spectacular increase in surface resistance and microhardness, thus having superficial characteristics similar to the corresponding borides. Laser alloying has also been successfully used for the same purpose. Atomic penetration of materials (aforementioned laser and implantation methods) are preferred over deposition methods (CVD deposition and PVD deposition) since the borides are formed "within" the metallic substrate (the ions literally penetrate the metal), relatively deep from the surface.

Ultrahard fullerite, aggregated diamond nanorods and synthetic flawless diamond are still being considered as the undisputed hardest materials. None of these contain boron.

Boron compounds

The boron oxygen compounds sodium tetraborate, boric acid and sodium perborate are the compound with the largest production capacities. For some special applications the carbide and nitride boron carbide and boron nitride are produced. Sodium borohydride is one of the few hydrides produced on industrial scale as reduction reagent in chemical synthesis.

Occurrence

The world wide commercial borate deposits are estimated to be 10¹⁰ kg of boron.cite journal | title = Distribution of boron in the environment | journal = Biological Trace Element Research | volume =66 | issue =1-3 | year = 1998 | doi = 10.1007/BF02783133 | pages = 131–143| first = Peter | last = Argust] cite journal | journal = Environmental Health Perspectives | volume = 102, Supplement 7| year =1994 | title = An Introduction to Boron: History, Sources, Uses, and Chemistry | first = William G. | last = Woods | url = http://www.ehponline.org/realfiles/members/1994/Suppl-7/woods-full.html| accessdate = 2008-09-20]
Turkey and the United States are the world's largest producers of boron.cite web | publisher = United States Geological Survey | title = Mineral Commodity Summaries: Boron | year =2008 | url = http://minerals.usgs.gov/minerals/pubs/commodity/boron/mcs-2008-boron.pdf | accessdate = 2008-09-20] cite web | publisher = United States Geological Survey | url = http://minerals.usgs.gov/minerals/pubs/commodity/boron/myb1-2006-boron.pdf
first = Dennis S. | last = Kostick | year = 2006 | title = Mineral Yearbook: Boron | accessdate = 2008-09-20] Turkey has almost 72% of the world’s boron potential and boron reserves. [cite web|url= http://www.byegm.gov.tr/YAYINLARIMIZ/kitaplar/turkiye2006/english/302-303.htm|title=Developments in the Ecomomic Sector (of Turkey)|publisher=Turkish government|accessdate=2007-12-21] Boron does not appear in nature in elemental form but is found combined in borax, boric acid, colemanite, kernite, ulexite and borates. Boric acid is sometimes found in volcanic spring waters. Ulexite is a borate mineral that naturally has properties of fiber optics.

Economically important sources are from the ore rasorite (kernite) and tincal (borax ore) which are both found in the Mojave Desert of California, with borax being the most important source there. The largest borax deposits are found in Central and Western Turkey including the provinces of Eskişehir, Kütahya and Balıkesir.

"See also: ."

Production

Pure elemental boron is not easy to prepare. The earliest methods used involve reduction of boric oxide with metals such as magnesium or aluminium. However the product is almost always contaminated with metal borides. (The reaction is quite spectacular though.) Pure boron can be prepared by reducing volatile boron halogenides with hydrogen at high temperatures. The highly pure boron, for the use in semiconductor industry, is produced by the decomposition of diborane at high temperatures and then further purified with the Czochralski process.

Isotope enrichment

Due to the use of boron-10 in nuclear reactors as neutron-capturing substance, several industrial-scale enrichment process have been developed. Although nearly all possible enrichment methods are adaptable to boron enrichment, only the fractionated vacuum distillation of the dimethyl ether adduct of boron trifluoride (DME-BF₃) and column chromatography of borates are used. [cite web | url = http://library.igcar.gov.in/html/Contents/IGCNewsletter/nl48/A2.htm | title = Commissioning of Boron Enrichment Plant | publisher = Indira Gandhi Centre for Atomic Research | accessdate = 2008-09-21]

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. 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 or boric acid that have a lower pollutant content. The average cost of crystalline boron is $5/g. [cite web | url = http://www.rareearth.org/boron_properties.htm | publisher = Rare-Earth Magnets | title = Boron Properties | accessdate = 2008-09-18 Source: Los Alamos National Laboratory]

Increasing demand for boric acid has led a number of producers to invest in additional capacity. Eti Mine Company of Turkey opened a new 100,000 tonnes per year capacity boric acid plant at Emet in 2003. Rio Tinto 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 disodium tetraborate 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 rates of growth 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. The recent rises in energy prices can be expected to lead to greater use of insulation-grade fiberglass, with consequent growth in the use of boron.

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. [cite web | url = http://www.roskill.com/reports/prePublication/prepubboron| title =. Dead link 2008-08-19]

Boron in biology

A boron-containing natural antibiotic, boromycin, isolated from streptomyces, is known. [cite journal| author=R. Hütter, W. Keller-Schien, F. Knüsel, V. Prelog , G. C. Rodgers jr., P. Suter, G. Vogel, W. Voser, H. Zähner | title=Stoffwechselprodukte von Mikroorganismen. 57. Mitteilung. Boromycin| journal= Helvetica Chimica Acta | year= 1967| pages=1533–1539| volume=50 | doi = 10.1002/hlca.19670500612] [cite journal| author=J. D. Dunitz, D. M. Hawley, D. Miklo, D. N. J. White, Yu. Berlin, R. Marui, V. Prelog | title=Structure of boromycin | journal= Helvetica Chimica Acta| year= 1971| pages=1709–1713| volume=54| doi = 10.1002/hlca.19710540624]

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. 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 in the soil is greater than 1.8 ppm. When boron in the soil exceeds 2.0 ppm, few plants will perform well. Plants sensitive to boron in the soil may not survive. When boron levels in plant tissue exceed 200 ppm symptoms of boron toxicity are likely to appear.

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 show the effects of boron deficiency, which manifest as poor coat/hair quality. 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.cite journal|title = Ultratrace elements in nutrition: Current knowledge and speculation| first = Forrest H. | last = Nielsen| The Journal of Trace Elements in Experimental Medicine| journal =The Journal of Trace Elements in Experimental Medicine | volume = 11| issue = 2&ndash;3 |pages =251&ndash;274| doi = 10.1002/(SICI)1520-670X(1998)11:2/3<251::AID-JTRA15>3.0.CO;2-Q]

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. [ cite web | url = http://www.pdrhealth.com/drug_info/nmdrugprofiles/nutsupdrugs/bor_0040.shtml
title = Boron | accessdate = 2008-09-18 | publisher = PDRhealth] The U.S. Department of agriculture conducted an experiment in which postmenopausal women took 3 mg of boron a day. The results showed that supplemental boron reduced excretion of calcium by 44%, and activated estrogen and vitamin D. However, whether these effects were conventionally nutritional, or medicinal, could not be determined.

The US National Institute of Health quotes this source::Total daily boron intake in normal human diets ranges from 2.1–4.3 mg boron/kg body weight (bw)/day. [cite journal | title = Total boron | author = Zook EG and Lehman J. | journal = J. Assoc. Off Agric. Chem | volume = 48 | title = 850-5 | year = 1965]

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. This is quite remarkable.

Isotopes

Boron has two naturally-occurring and stable isotopes, SimpleNuclide|Boron|11 (80.1%) and SimpleNuclide|Boron|10 (19.9%). The mass difference results in a wide range of δSimpleNuclide|Boron|11 values in natural waters, ranging from -16 to +59.Fact|date=September 2008 There are 13 known isotopes of boron, the shortest-lived isotope is SimpleNuclide|Boron|7 which decays through proton emission and alpha decay. It has a half-life of 3.26500x10^-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. The latter effect species preferential removal of the SimpleNuclide|Boron|10(OH)₄ ion onto clays results in solutions enriched in SimpleNuclide|Boron|11(OH)₃ may be responsible for the large SimpleNuclide|Boron|11 enrichment in seawater relative to both oceanic crust and continental crust; this difference may act as an isotopic signature.

The exotic SimpleNuclide|Boron|17 exhibits a nuclear halo. Fact|date=March 2008

Enriched boron (boron-10)

The SimpleNuclide|Boron|10 isotope is good at capturing thermal neutrons. Natural boron is about 20% SimpleNuclide|Boron|10 and 80%SimpleNuclide|Boron|11. The nuclear industry enriches natural boron to nearly pure SimpleNuclide|Boron|10. The waste product, or depleted boron, is nearly pure SimpleNuclide|Boron|11. SimpleNuclide|Boron|11 is a candidate as a fuel for aneutronic fusion and is used in the semiconductor industry. Enriched boron or SimpleNuclide|Boron|10 is used in both radiation shielding and in boron neutron capture therapy. In the latter, a compound containing SimpleNuclide|Boron|10 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. [cite journal | title =A Critical Assessment of Boron Neutron Capture Therapy: An Overview | journal = Journal of Neuro-Oncology | volume = 62 | issue = 1 | year = 2003 | doi = 10.1023/A:1023262817500 | pages = 1&ndash;5 | first = Rolf F. | last = Barth] [cite journal | journal = Radiation Research | pages = 1&ndash;18 | volume =151| issue =1 | year = 1999 | title =The Radiation Biology of Boron Neutron Capture Therapy
first = Jeffrey A. | last = Coderre1 | coauthors = Morris, Gerard M.] [cite journal | title = Boron Neutron Capture Therapy of Cancer
first =Rolf F. | last =Barth | coauthors = Soloway, Albert H.; Fairchild, Ralph G.
url = http://cancerres.aacrjournals.org/cgi/content/citation/50/4/1061
journal = Cancer Research | volume = 50 | pages = 1061&ndash;1070 | year =1990]

In nuclear reactors, SimpleNuclide|Boron|10 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. 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, SimpleNuclide|Boron|10 has a theoretical role as structural material (as boron fibers or BN nanotube material) which also would 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 structural materials, is in the form of high energy spallation neutrons. Such neutrons can be moderated by materials high in light elements such as structural polyethylene, but the moderated neutrons continue to be a radiation hazard unless actively absorbed in a way which dumps the absorption energy in the shielding, far away from biological systems. Among light elements that absorb thermal neutrons, SimpleNuclide|Lithium|6 and SimpleNuclide|Boron|10 appear as potential spacecraft structural materials able to do double duty in this regard.

Depleted boron (boron-11)

Cosmic radiation produces secondary neutrons when it hits spacecraft structures. Neutrons cause fission in SimpleNuclide|Boron|10 if it is present in the spacecraft's semiconductors. This produces a gamma ray, an alpha particle, and a lithium ion. The resultant fission products may then dump charge into nearby chip structures, causing data loss (bit flipping, or single event upset). In radiation hardened semiconductor designs, one measure is to use depleted boron which is greatly enriched in SimpleNuclide|Boron|11 and contains almost no SimpleNuclide|Boron|10. SimpleNuclide|Boron|11 is largely immune to radiation damage. Depleted boron is a by-product of the nuclear industry.

SimpleNuclide|Boron|11 is also a candidate as a fuel for aneutronic fusion. When struck by a proton 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. This induces long term radioactivity in reactor structures and weakens them, as well as endangering operating personnel. The alpha particles from SimpleNuclide|Boron|11 fusion can be turned directly into electric power and all radiation stops as soon as the reactor is turned off. [cite journal | first = W. M. | last = Nevins | title = A Review of Confinement Requirements for Advanced Fuels | journal = Journal of Fusion Energy | volume = 17 | issue = 1 | year = 1998 | doi = 10.1023/A:1022513215080 | pages = 25&ndash;32]

Boron in NMR spectroscopy

Both SimpleNuclide|Boron|10 and SimpleNuclide|Boron|11 possess nuclear spin. The nuclear spin of boron-10 is 3 and that of boron-11 is 3/2. These isotopes are, therefore, of use in nuclear magnetic resonance spectroscopy; and spectrometers specially adapted to detecting the boron-11 nucleus are available commercially. The boron-10 and boron-11 nuclei also cause splitting in the resonances of attached nuclei.

Precautions

Elemental boron is nontoxic and common boron compounds such as borates and boric acid have low toxicity (approximately similar to table salt with the lethal dose being 2 to 3 grams per kg) and therefore do not require special precautions while handling. Some of the more exotic boron hydrogen compounds, however, "are" toxic as well as highly flammable and do require special care when handling.

ee also

*Boron deficiency
*Boronic acid
*Suzuki coupling
*Hydroboration-oxidation reaction

References

* [http://periodic.lanl.gov/elements/5.html Los Alamos National Laboratory &ndash; Boron]

External links

* [http://www.du.edu/~jcalvert/phys/boron.htm Boron]
* [http://www.webelements.com/boron/ WebElements.com &ndash; Boron]
* [http://www.compchemwiki.org/index.php?title=Boron Computational Chemistry Wiki]
* [http://www.inchem.org/documents/ehc/ehc/ehc204.htm Environmental Health Criteria 204: Boron (1998)] by the IPCS.
* [http://education.jlab.org/itselemental/ele005.html It's Elemental &ndash; Boron]
* [http://www.npi.gov.au/database/substance-info/profiles/15.html National Pollutant Inventory - Boron and compounds]

boron