Difference between revisions of "Boron" - New World Encyclopedia

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== Boron nitride ==
 
== Boron nitride ==
[[Boron nitride]] is a material in which the extra electron of nitrogen (with respect to carbon) in some ways compensates for boron's deficiency of an electron. Boron nitride can be used to make crystals that are extremely hard, second in hardness only to [[diamond]], and the similarity of this compound to diamond extends to other applications. Like diamond, boron nitride acts as an electrical [[insulator]] but is an excellent conductor of heat.
 
  
Like carbon, boron nitride exists in a second form that has structural and [[lubrication|lubricating]] qualities similar to [[graphite]].
+
Boron nitride is a material in which the extra electron of the nitrogen atom (compared to a carbon atom) in some ways compensates for the boron atom's deficiency of an electron (compared to carbon). Boron nitride can be used to make crystals that are extremely hard, second in hardness only to [[diamond]]. Also, like diamond, boron nitride acts as an electrical [[insulator]]*, but it is an excellent conductor of heat.
This form of boron nitride is composed of layers of fused hexagonal sheets (analogous to graphite). These sheets (unlike those in graphite) are '''in registry'''. This means that layers are placed directly upon one another such that a viewer looking down onto the structure would view only the top layer. The polar B-N bonds interfere with electron transfer so that boron nitride in this form is not an electrical conductor (in contrast to graphite which is a [[semimetal]] that conducts electricity through a network of pi bonds in the plane of its hexagonal sheets).
 
  
Boron nitride nanotubes can be constructed analogously to carbon nanotubes.
+
Like carbon, boron nitride exists in a second form that has structural and [[lubrication|lubricating]]* qualities similar to those of [[graphite]]. Like graphite, this form of boron nitride is composed of layers of fused hexagonal sheets. Yet, unlike graphite, these sheets are "in registry." This means that the layers are placed directly above one another, such that a viewer looking down onto the structure would view only the top layer. The polar B-N bonds interfere with electron transfer, so that boron nitride in this form is not an electrical conductor. (By contrast, graphite conducts electricity through a network of pi bonds in the plane of its hexagonal sheets.)
 +
 
 +
Boron nitride nanotubes can be constructed in a form analogous to carbon nanotubes.
  
 
==Applications==
 
==Applications==
The most economically important compounds of boron are:
 
  
* [[Sodium tetraborate]] pentahydrate ([[sodium|Na]]<sub>2</sub>B<sub>4</sub>[[oxygen|O]]<sub>7</sub> · 5[[water (molecule)|H<sub>2</sub>O]]), which is used in large amounts in making insulating [[fiberglass]] and [[sodium perborate]] [[Bleach (chemical)|bleach]],
 
* Orthoboric acid ([[hydrogen|H]]<sub>3</sub>B[[oxygen|O]]<sub>3</sub>) or [[boric acid]], used in the production of textile [[fiberglass]] and [[flat panel display]]s or [[eye drop]]s, among many uses, and
 
* [[Sodium tetraborate]] decahydrate ([[sodium|Na]]<sub>2</sub>B<sub>4</sub>[[oxygen|O]]<sub>7</sub> · 10[[water (molecule)|H<sub>2</sub>O]]) or [[borax]], used in the production of adhesives, in anti-corrosion systems and many other uses.
 
 
==Uses==
 
 
Of the several hundred uses of boron compounds, especially notable uses include:
 
Of the several hundred uses of boron compounds, especially notable uses include:
  
* Boron is an essential plant [[micronutrient]], notably playing a role in plant [[fertilizer|fertilisation]] and in the building of [[cell wall]] structures; as such, [[borates]] are used in [[agriculture]].
+
* As boron is an essential plant [[micronutrient]], [[borates]]* are used in [[agriculture]].
* Because of its distinctive green flame, amorphous boron is used in [[Flare (pyrotechnic)|pyrotechnic flares]].
+
* Because it produces a distinctive green flame, amorphous boron is used in [[Flare (pyrotechnic)|pyrotechnic flares]]*.
* [[Boric acid]] is an important compound used in [[textile]] products. For example, boron compounds are used as nontoxic flame retardants used to treat cotton fiber. [http://www.natbat.com/docs/boron.htm]
+
* [[Boric acid]]* is an important compound used in [[textile]] products. For example, boron compounds are used as nontoxic flame retardants to treat cotton fiber. [http://www.natbat.com/docs/boron.htm]
* [[Boric acid]] is also traditionally used as an [[insecticide]], notably against [[ant]]s or [[cockroach]]es.
+
* [[Boric acid]]* is also traditionally used as an [[insecticide]], notably against [[ant]]s and [[cockroach]]es.
* Compounds of boron are used extensively in organic synthesis and in the manufacture of [[borosilicate glass|borosilicate]] and [[borophophosilicate glass|borophosphosilicate]] [[glass]]es.
+
* Compounds of boron are used extensively in organic synthesis and in the manufacture of [[borosilicate glass|borosilicate]]* and [[borophophosilicate glass|borophosphosilicate]]* [[glass]]es.
* Other compounds are used as [[wood]] preservatives, and are particularly attractive in this regard because they possess low [[toxicity]].
+
* Other compounds are used as [[wood]] preservatives, and are particularly attractive in this regard because they have low [[toxicity]]*.
* <sup>10</sup>B is used to assist control of [[nuclear reactor]]s, a [[radiation protection|shield]] against [[Radioactive decay|radiation]] and in [[neutron]] detection.
+
* <sup>10</sup>B is used to control reactions in [[nuclear reactor]]s, as a [[radiation protection|shield]]* against [[Radioactive decay|radiation]]*, and in [[neutron]] detection.
 
* Purified <sup>11</sup>B ([[#Depleted boron|depleted boron]]) is used for [[borosilicate glass]]es in [[radiation hardening|rad-hard]] electronics.
 
* Purified <sup>11</sup>B ([[#Depleted boron|depleted boron]]) is used for [[borosilicate glass]]es in [[radiation hardening|rad-hard]] electronics.
 
* Research is being conducted into the production of hydrogen fuel through the interaction of water and a borohydride (such as NaBH<sub>4</sub>).  The engine would work by mixing borohydride with water to produce hydrogen as needed, thus solving some present issues of safely transporting hydrogen gas.  The research is being conducted at the University of Minessota, United States by Abu-Hamed and at the Weizmann Institute of Science in Rehovot, Israel. To succeed, the rate of hydrogen production by the small engine needs only to meet the energy demands of the engine. Five kilograms of hydrogen (corresponding to 40 kg of NaBH<sub>4</sub>) has the same amount of energy as twenty gallons (60 kg) of fuel. <ref> (David Adam, Environmental Correspondent, London/ in New Scientist 29/07/06) </ref>
 
* Research is being conducted into the production of hydrogen fuel through the interaction of water and a borohydride (such as NaBH<sub>4</sub>).  The engine would work by mixing borohydride with water to produce hydrogen as needed, thus solving some present issues of safely transporting hydrogen gas.  The research is being conducted at the University of Minessota, United States by Abu-Hamed and at the Weizmann Institute of Science in Rehovot, Israel. To succeed, the rate of hydrogen production by the small engine needs only to meet the energy demands of the engine. Five kilograms of hydrogen (corresponding to 40 kg of NaBH<sub>4</sub>) has the same amount of energy as twenty gallons (60 kg) of fuel. <ref> (David Adam, Environmental Correspondent, London/ in New Scientist 29/07/06) </ref>
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[[borane|Hydrides of boron]] are [[oxidation|oxidized]] easily and liberate a considerable amount of [[energy]]. They have therefore been studied for use as possible [[rocket fuel]]s, along with elemental boron.  However, issues of cost, incomplete combustion, and [[boric oxide]] deposits have so far made this use infeasible.
 
[[borane|Hydrides of boron]] are [[oxidation|oxidized]] easily and liberate a considerable amount of [[energy]]. They have therefore been studied for use as possible [[rocket fuel]]s, along with elemental boron.  However, issues of cost, incomplete combustion, and [[boric oxide]] deposits have so far made this use infeasible.
 +
 +
The most economically important compounds of boron are:
 +
 +
* [[Sodium tetraborate]] pentahydrate ([[sodium|Na]]<sub>2</sub>B<sub>4</sub>[[oxygen|O]]<sub>7</sub> · 5[[water (molecule)|H<sub>2</sub>O]]), which is used in large amounts in making insulating [[fiberglass]] and [[sodium perborate]] [[Bleach (chemical)|bleach]],
 +
* Orthoboric acid ([[hydrogen|H]]<sub>3</sub>B[[oxygen|O]]<sub>3</sub>) or [[boric acid]], used in the production of textile [[fiberglass]] and [[flat panel display]]s or [[eye drop]]s, among many uses, and
 +
* [[Sodium tetraborate]] decahydrate ([[sodium|Na]]<sub>2</sub>B<sub>4</sub>[[oxygen|O]]<sub>7</sub> · 10[[water (molecule)|H<sub>2</sub>O]]) or [[borax]], used in the production of adhesives, in anti-corrosion systems and many other uses.
  
 
===Food===
 
===Food===
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For determination of boron content in food or materials the [[colorimetry|colorimetric]] curcumin method is used. Boron has to be transferred to [[boric acid]] or [[borate]]s and on reaction with [[curcumin]] in acidic solution a red colored boron-[[chelate]] complex -  [[rosocyanine]] - is formed.
 
For determination of boron content in food or materials the [[colorimetry|colorimetric]] curcumin method is used. Boron has to be transferred to [[boric acid]] or [[borate]]s and on reaction with [[curcumin]] in acidic solution a red colored boron-[[chelate]] complex -  [[rosocyanine]] - is formed.
  
==Market trend==
 
Estimated global consumption of boron rose to a record 1.8 million tonnes of B<sub>2</sub>O<sub>3</sub> 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 beneficiated 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.
 
 
Increasing demand for boric acid has led a number of producers to invest in additional capacity. Eti Mine 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 [[fibreglass]] and borosilicate production. A rapid increase in the manufacture of reinforcement-grade fibreglass in Asia with a consequent increase in demand for borates has offset the development of boron-free reinforcement-grade fibreglass in Europe and the USA. The recent rises in energy prices can be expected to lead to greater use of insulation-grade fibreglass, 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.<ref>http://www.roskill.com/reports/prePublication/prepubboron</ref>
 
  
 
==Precautions==
 
==Precautions==
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==See also==
 
==See also==
* [[Boron deficiency]]
+
 
* [[:Category:Boron compounds|Boron compounds]]
+
* [[Chemical element]]
 +
* [[Periodic table]]
  
 
==References==
 
==References==

Revision as of 18:33, 17 October 2006

5 berylliumboroncarbon
-

B

Al
B-TableImage.png
periodic table
General
Name, Symbol, Number boron, B, 5
Chemical series metalloids
Group, Period, Block 13, 2, p
Appearance black/brown
B,5.jpg
Atomic mass 10.811(7) g/mol
Electron configuration 1s2 2s2 2p1
Electrons per shell 2, 3
Physical properties
Phase solid
Density (near r.t.) 2.34 g/cm³
Liquid density at m.p. 2.08 g/cm³
Melting point 2349 K
(2076 °C, 3769 °F)
Boiling point 4200 K
(3927 °C, 7101 °F)
Heat of fusion 50.2 kJ/mol
Heat of vaporization 480 kJ/mol
Heat capacity (25 °C) 11.087 J/(mol·K)
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 2348 2562 2822 3141 3545 4072
Atomic properties
Crystal structure rhombohedral
Oxidation states 3
(mildly acidic oxide)
Electronegativity 2.04 (Pauling scale)
Ionization energies
(more)
1st: 800.6 kJ/mol
2nd: 2427.1 kJ/mol
3rd: 3659.7 kJ/mol
Atomic radius 85 pm
Atomic radius (calc.) 87 pm
Covalent radius 82 pm
Miscellaneous
Magnetic ordering nonmagnetic
Electrical resistivity (20 °C) 1.5×104 Ω·m
Thermal conductivity (300 K) 27.4 W/(m·K)
Thermal expansion (25 °C) 5–7 µm/(m·K)
Speed of sound (thin rod) (20 °C) 16200 m/s
Bulk modulus (β form) 185 GPa
Mohs hardness 9.3
Vickers hardness 49000 MPa
CAS registry number 7440-42-8
Notable isotopes
Main article: Isotopes of boron
iso NA half-life DM DE (MeV) DP
10B 19.9%* B is stable with 5 neutrons
11B 80.1%* B is stable with 6 neutrons
*Boron-10 content may be as low as 19.1% and as
high as 20.3% in natural samples. Boron-11 is
the remainder in such cases.

Boron (chemical symbol B, atomic number 5)

It is classified as a metalloid—some of its properties resemble those of metals, and others resemble those of nonmetals. . A trivalent element, Boron is not found free in nature but occurs abundantly in the ore borax.

Several allotropes of boron exist; amorphous boron is a brown powder, though metallic (crystalline) boron is black, hard (9.3 on Mohs' scale), and a weak conductor at room temperature.

Elemental boron is used as a dopant in the semiconductor industry, while boron compounds play important roles as light structural materals, nontoxic insecticides and preservatives, and reagents for chemical synthesis.

Boron is an essential plant nutrient, and as an ultratrace mineral is necessary for the optimal health of animals, though its physiological role in animals is poorly understood.

Occurrence

In nature, boron does not appear in elemental form but is found combined in borax, boric acid, colemanite, kernite (rasorite), ulexite, and borates. Boric acid is sometimes found in volcanic spring waters. Also, a boron-containing natural antibiotic named boromycin has been isolated from Streptomyces.[1][2]

Borax crystals.

Economically important sources are from kernite and borax ores, both of which are found in the Mojave Desert of California, with borax being the main source there. Extensive borax deposits are also found in Turkey. The United States and Turkey are the world's largest producers of boron.

Pure elemental boron is not easy to prepare. The earliest methods involved reduction of boric oxide with metals such as magnesium or aluminum. The product, however, is almost always contaminated with metal borides. Pure boron can be prepared by reducing volatile boron halogenides with hydrogen at high temperatures. Highly pure boron, for use in the semiconductor industry, is produced by the high-temperature decomposition of diborane, followed by what is called the Czochralski process.

  • Ulexite is a borate mineral that has fiber optic properties.

History

Compounds of boron (Arabic Buraq, from Persian Burah, from Turkish Bor) have been known of for thousands of years. In early Egypt, the process of mummification depended on 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 element was first isolated in 1808 by Sir Humphry Davy, Joseph Louis Gay-Lussac, and Louis Jacques Thénard. By reducing boric acid with sodium or magnesium, they obtained boron at about 50 percent purity. These men, however, did not recognize the substance as an element. In 1824, Jöns Jakob Berzelius identified boron as an element. It is generally thought that the first pure boron was produced by American chemist W. Weintraub in 1909, but some researchers have cast doubt on the accuracy of that view.[3]

  • Boron was not believed to be useful to the human body until 1989 research suggested its signficance.[citation needed]

Notable characteristics

In the periodic table, boron is situated at the top of group 13 (former group 3A), just above aluminum, and in period 2, between beryllium and carbon. It is classified as a metalloid.

Boron exists in different allotropic forms. Amorphous boron is a brown powder and is produced by certain chemical reactions. It contains boron atoms randomly bonded to one another, without long-range order. By contrast, crystalline (metallic) boron is black in color and extremely hard (9.3 on Mohs' scale). It has a high melting point and exists in many polymorphs—forms of boron that differ in their crystal lattice structure.

The best characterized crystalline forms are: two rhombohedral forms, α-boron and β-boron, containing 12 and 106.7 atoms in each rhombohedral unit cell, respectively; and a tetragonal, 50-atom form. These forms are somewhat analogous to diamond crystals, but unlike diamond, boron has various possible structures because each boron atom can form three bonds, forcing the atoms to be asymmetrically bonded in three-dimensional space.

Crystalline boron can transmit infrared light. At standard temperatures, it is a poor conductor of electricity, but it becomes is a good conductor at high temperatures.

Boron is similar to carbon in terms of being able to form stable, covalently bonded molecular networks. On the other hand, each boron atom has one less electron than a carbon atom, and boron behaves as an electrophile—it seeks to form a covalent bond with an element that can provide a pair of electrons to form the bond. The reactions of boron are dominated by this requirement for electrons. Based on this property, boron is called a Lewis acid.

Isotopes

There are 13 known isotopes of boron. Two stable isotopes occur in nature: 11B (about 80%) and 10B (about 20%). Also, 11B is a by-product of the nuclear industry. The shortest-lived isotope is 7B which has a half-life of 3.26500x10-22 seconds and decays through proton emission and alpha decay.

The 10B isotope is good at capturing thermal neutrons, such as from cosmic rays. It then undergoes nuclear fission, producing a gamma ray, an alpha particle, and a lithium ion. When this happens within an integrated circuit, the fission products may dump charge into nearby chip structures, resulting in data loss. To avoid this effect in critical semiconductor designs, "depleted boron" (consisting almost entirely of 11B) is used.

The ability of 10B to capture thermal neutrons has been used in radiation shielding and medical therapy. In nuclear reactors, 10B is used for reactivity control and in emergency shutdown systems. It can serve either function in the form of borosilicate rods or as boric acid.

In medical treatment for a tumor, a compound containing 10B may be attached to the tumor tissue, and the patient is treated with a relatively low dose of thermal neutrons. The 10B absorbs neutrons and releases short-range alpha radiation. This radiation kills the tumor cells.

Boron nitride

Boron nitride is a material in which the extra electron of the nitrogen atom (compared to a carbon atom) in some ways compensates for the boron atom's deficiency of an electron (compared to carbon). Boron nitride can be used to make crystals that are extremely hard, second in hardness only to diamond. Also, like diamond, boron nitride acts as an electrical insulator, but it is an excellent conductor of heat.

Like carbon, boron nitride exists in a second form that has structural and lubricating qualities similar to those of graphite. Like graphite, this form of boron nitride is composed of layers of fused hexagonal sheets. Yet, unlike graphite, these sheets are "in registry." This means that the layers are placed directly above one another, such that a viewer looking down onto the structure would view only the top layer. The polar B-N bonds interfere with electron transfer, so that boron nitride in this form is not an electrical conductor. (By contrast, graphite conducts electricity through a network of pi bonds in the plane of its hexagonal sheets.)

Boron nitride nanotubes can be constructed in a form analogous to carbon nanotubes.

Applications

Of the several hundred uses of boron compounds, especially notable uses include:

  • As boron is an essential plant micronutrient, borates are used in agriculture.
  • Because it produces a distinctive green flame, amorphous boron is used in pyrotechnic flares.
  • Boric acid is an important compound used in textile products. For example, boron compounds are used as nontoxic flame retardants to treat cotton fiber. [1]
  • Boric acid is also traditionally used as an insecticide, notably against ants and cockroaches.
  • Compounds of boron are used extensively in organic synthesis and in the manufacture of borosilicate and borophosphosilicate glasses.
  • Other compounds are used as wood preservatives, and are particularly attractive in this regard because they have low toxicity.
  • 10B is used to control reactions in nuclear reactors, as a shield against radiation, and in neutron detection.
  • Purified 11B (depleted boron) is used for borosilicate glasses in rad-hard electronics.
  • Research is being conducted into the production of hydrogen fuel through the interaction of water and a borohydride (such as NaBH4). The engine would work by mixing borohydride with water to produce hydrogen as needed, thus solving some present issues of safely transporting hydrogen gas. The research is being conducted at the University of Minessota, United States by Abu-Hamed and at the Weizmann Institute of Science in Rehovot, Israel. To succeed, the rate of hydrogen production by the small engine needs only to meet the energy demands of the engine. Five kilograms of hydrogen (corresponding to 40 kg of NaBH4) has the same amount of energy as twenty gallons (60 kg) of fuel. [4]
  • Sodium borohydride (NaBH4), the same chemical as used in the experimental car, is a popular chemical reducing agent, used (for example) for reducing aldehydes and ketones to alcohols.
  • 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.
  • Boron in trace amounts is used as dopant for P-type semiconductors.

Boron compounds are being investigated for use in a broad range of applications, including as components in sugar-permeable membranes, carbohydrate sensors and bioconjugates.

Medicinal applications being investigated include boron neutron capture therapy and drug delivery. Other boron compounds show promise in treating arthritis.

Hydrides of boron are oxidized easily and liberate a considerable amount of energy. They have therefore been studied for use as possible rocket fuels, along with elemental boron. However, issues of cost, incomplete combustion, and boric oxide deposits have so far made this use infeasible.

The most economically important compounds of boron are:

  • Sodium tetraborate pentahydrate (Na2B4O7 · 5H2O), which is used in large amounts in making insulating fiberglass and sodium perborate bleach,
  • Orthoboric acid (H3BO3) or boric acid, used in the production of textile fiberglass and flat panel displays or eye drops, among many uses, and
  • Sodium tetraborate decahydrate (Na2B4O7 · 10H2O) or borax, used in the production of adhesives, in anti-corrosion systems and many other uses.

Food

Boron occurs in all foods produced by plants. Since 1989 its nutritional value has been argued. The U.S. Department of agriculture conducted an experiment in which postmenopausal women took 3 mg of boron a day. The results showed that boron can drop excretion of calcium by 44%, and activate estrogen and vitamin D.

See also Borate minerals.

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.


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 handling care.

See also

References
ISBN links support NWE through referral fees

  1. Hütter (1967). . Helv. Chim. Acta. 50: 1533-1539.
  2. Dunitz (1971). . Helv. Chim. Acta. 54: 1709-1713.
  3. (1970) . Z. Angew. Phys. 29: 277.
  4. (David Adam, Environmental Correspondent, London/ in New Scientist 29/07/06)

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