Boron is the
chemical elementA chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons.Common examples of elements...
with
atomic numberIn chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...
5 and the chemical symbol
B. Boron is a trivalent
metalloidMetalloid, or semi metal is a term used in chemistry when classifying the chemical elements. On the basis of their general physical and chemical properties, nearly every element in the periodic table can be termed either a metal or a nonmetal...
element which occurs abundantly in the
evaporiteEvaporites are water-soluble mineral sediments that result from the evaporation of bodies of surficial water. Evaporites are considered sedimentary rocks.- Formation of evaporite rocks :...
oreAn ore is a type of rock that contains minerals such as gemstones or metals that can be extracted through mining and refined for use. Samples of ore in the form of exceptionally beautiful crystals, exotic layering visible when sectioned or polished or metallic presentations such as large nuggets or...
s
boraxBorax, also known as sodium borate, sodium tetraborate, or disodium tetraborate, is an important boron compound, a mineral, and a salt of boric acid. It is usually a white powder consisting of soft colorless crystals that dissolve easily in water.Borax has a wide variety of uses...
and
ulexiteUlexite is a mineral occurring in silky white rounded crystalline masses or in parallel fibers...
.
Several
allotropesAllotropy or allotropism is a behavior exhibited by certain chemical elements: these elements can exist in two or more different forms, known as allotropes of that element. In each allotrope, the element's atoms are bonded together in a different manner...
of boron exist: amorphous boron is a brown powder; whereas 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
dopantA dopant, also called doping agent and dope, is an impurity element added to a crystal lattice in low concentrations in order to alter the optical/electrical properties of the crystal....
in the semiconductor industry, while boron compounds play important roles as light structural materials, insecticides and preservatives, and reagents for chemical synthesis.
Boron is an essential plant
nutrientA nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. Nutrients are the substances that enrich the body. They build and repair tissues, give heat and energy, and regulate body processes...
. Whereas lack of boron results in
boron deficiency disorderBoron deficiency is an uncommon disorder affecting plants growing in deficient soils and is often associated with areas of high rainfall and leached soils. Boron may be present but locked up in soils with a high pH, and the deficiency may be worse in wet seasons.Symptoms include dying growing tips...
, high soil concentrations of boron may also be toxic to plants. As an
ultratrace elementIn biochemistry, an ultratrace element is a chemical element that normally comprises less than one microgram per gram of a given organism....
, boron is necessary for the optimal health of rats and presumably other mammals, though its physiological role in animals is not yet fully understood.
Allotropes
Boron is similar to
carbonCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
in its capability to form stable
covalently bondedA covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms, or between atoms and other covalent bonds...
molecular networks. Even nominally disordered (amorphous) boron contains regular boron icosahedra which are, however, bonded randomly to each other without
long-range orderIn physics, long-range order characterizes physical systems in which remote portions of the same sample exhibit correlated behavior.This can be seen with a correlation function, namely the spin-spin correlation function:...
. Crystalline boron is a very hard, black material with a high melting point of above 2000 °C. It exists in four major
polymorphsPolymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals, and is related to allotropy, which refers to elemental solids...
: α, ß, γ and T. Whereas α, ß and T phases are based on B
12 icosahedra, the γ-phase can be described as a
rocksaltSodium chloride, also known as salt, common salt, table salt, or halite, is an ionic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...
-type arrangement of the icosahedra and B
2 atomic pairs. It can be produced by compressing other boron phases to 12-20 GPa and heating to 1500-1800 °C; it remains stable after releasing the temperature and pressure. The T phase is produced at similar pressures, but higher temperatures of 1800-2200 °C. As to the α and ß phases, they might both coexist at
ambient conditionsIn physical sciences, standard conditions for temperature and pressure are standard sets of conditions for experimental measurements, to allow comparisons to be made between different sets of data...
with the ß phase being more stable. Compressing boron above 160 GPa produces a boron phase with an as yet unknown structure, and this phase is a superconductor at temperatures 6-12 K.
| Boron phase |
α |
ß |
γ |
T |
| Symmetry |
Rhombohedral |
Rhombohedral |
Orthorhombic |
Tetragonal |
| Atoms/unit cell |
12 |
~105 |
28 |
| Density (g/cm3) |
2.46 |
2.35 |
2.52 |
2.36 |
| Vickers hardness (GPa) |
42 |
45 |
50-58 |
|
Bulk modulusThe bulk modulus of a substance measures the substance's resistance to uniform compression. It is defined as the pressure increase needed to cause a given relative decrease in volume. Its base unit is Pascal....
(GPa) |
185 |
224 |
227 |
|
| Bandgap (eV) |
2 |
1.6 |
2.1 |
|
Chemical
Chemically, boron is closer to
siliconSilicon is the most common metalloid. It is a chemical element, which has the symbol Si and atomic number 14. A tetravalent metalloid, silicon is less reactive than its chemical analog carbon...
than to
aluminiumAluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13. It is not soluble in water under normal circumstances....
. Crystalline boron is chemically inert and resistant to attack by boiling
hydrofluoricHydrofluoric acid is a solution of hydrogen fluoride in water. While it is extremely corrosive and difficult to handle, it is technically a weak acid...
or
hydrochloric acidHydrochloric acid is the solution of hydrogen chloride in water. It is a highly corrosive, strong mineral acid and has major industrial uses. It is found naturally in gastric acid....
. When finely divided, it is attacked slowly by hot concentrated
hydrogen peroxideHydrogen peroxide is a very pale blue liquid, slightly more viscous than water, that appears colorless in dilute solution. It is a weak acid, has strong oxidizing properties, and is a powerful bleaching agent. It is used as a disinfectant, antiseptic, oxidizer, and in rocketry as a propellant...
, hot concentrated
nitric acidNitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure older samples tend to acquire a stronger yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as...
, hot
sulfuric acidSulfuric acid, , is a strong mineral acid. It is soluble in water at all concentrations. Sulfuric acid has many applications, and is one of the top products of the chemical industry. World production in 2001 was 165 million tonnes, with an approximate value of US$8 billion...
or hot mixture of sulfuric and
chromic acidChromic acid generally refers to a collection of compounds generated by the acidification of solutions containing chromate and dichromate anions or the dissolving of chromium trioxide in sulfuric acid. Often the species are assigned the formulas H2CrO4 and...
s.
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 trioxideBoron oxide is one of the oxides of boron. It is white, glassy, and solid, also known as diboron trioxide, formula B2O3. It is almost always found as the vitreous form; however, it can be crystallized after extensive annealing...
:
- 4 B + 3 O2 (g) → 2 B2O3 (s)
Boron reacts with
sulfurSulfur or sulphur is the chemical element that has the atomic number 16. It is denoted with the symbol S. It is an abundant, multivalent non-metal. Sulfur, in its native form, is a yellow crystalline solid. In nature, it can be found as the pure element and as sulfide and sulfate minerals...
to produce
boron sulfideBoron sulfide is the chemical compound with the formula B2S3. This polymeric material that has been of interest as a component of “high-tech” glasses and as a reagent for preparing organosulfur compounds. Like the sulfides of silicon and phosphorus,...
:
- 2 B + 3 S (g) → B2S3 (s)
The first synthesis was performed by
Jöns Jakob BerzeliusFriherre Jöns Jacob Berzelius was a Swedish chemist. He worked out the modern technique of chemical formula notation, and is together with John Dalton, Antoine Lavoisier, and Robert Boyle considered a father of modern chemistry.-Career:Berzelius was born at Väversunda in Östergötland in Sweden. He...
in 1824. Another reaction, starting from boron and
hydrogen sulfideHydrogen sulfide is the chemical compound with the formula H
2S. This colorless, toxic and flammable gas is partially responsible for the foul odor of rotten eggs and flatulence....
, was conducted by
Friedrich WöhlerFriedrich Wöhler was a German chemist, best-known for his synthesis of urea, but also the first to isolate several chemical elements.-Biography:He was born in Eschersheim, nowadays a district of Frankfurt am Main...
and
Henri Etienne Sainte-Claire DevilleHenri Etienne Sainte-Claire Deville was a French chemist.He was born in the island of St Thomas, West Indies, where his father was French consul. Together with his elder brother Charles he was educated in Paris at the College Rollin...
and published in 1858.
- 2 B + 3 H2S → B2S3 (s) + 3 H2
Wöhler and Deville also documented vigorous reactions between boron and the
halogenThe halogens or halogen elements are a series of nonmetal elements from Group 17 IUPAC Style of the periodic table, comprising fluorine, ; chlorine, ; bromine, ; iodine, ; and astatine,...
s resulting in
boron trichlorideBoron trichloride is a chemical compound with the formula BCl3. This colorless gas is a valuable reagent in organic synthesis. It is also dangerously reactive.-Production and properties:...
,
boron trifluorideBoron trifluoride is the chemical compound with the formula BF
3. This pungent colourless toxic gas forms white fumes in moist air. It is a useful Lewis acid and a versatile building block for other boron compounds.-Structure and bonding:...
and
boron tribromideBoron tribromide, BBr3, is a colorless, fuming liquid compound containing boron and bromine. It is usually made by heating boron trioxide with carbon in the presence of bromine: this generates free boron which reacts vigorously with the bromine...
. For example:
- 2 B + 3 Br2 → 2 BBr3
Boron can form compounds whose formal oxidation state is not three, such as B(IV) in boron carbide BC, B(II) in B
2F
4, and B(I) in boron fluoride BF. Boron compounds such as BCl
3 behave as
electrophileIn chemistry, an electrophile is a reagent attracted to electrons that participates in a chemical reaction by accepting an electron pair in order to bond to a nucleophile. Because electrophiles accept electrons, they are Lewis acids...
s or
Lewis acidA Lewis acid, A, is a chemical compound that can accept a pair of electrons from a Lewis base, B, that acts as an electron-pair donor, forming an adduct, AB:
A + :B → A—B...
s in their reactions. Boron is the least
electronegativeElectronegativity, symbol χ, is a chemical property that describes the ability of an atom to attract electrons towards itself in a covalent bond. An atom's electronegativity is affected by both its atomic weight and the distance that its valence electrons reside from the charged nucleus...
non-metal.
Isotopes
Boron has two naturally occurring and stable
isotopeIsotopes are different types of atoms of the same chemical element, each having a different number of neutrons. Correspondingly, isotopes differ in mass number but not in atomic number. The difference in the number of nucleons comes from a difference how many neutrons are in the atomic nucleus...
s, (80.1%) and (19.9%). The mass difference results in a wide range of δ values, which are defined as a fractional difference between the and 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 which decays through
proton emissionProton emission is a type of radioactive decay in which a proton is ejected from a nucleus. Proton emission can occur from high-lying excited states in a nucleus following a beta decay, in which case the process is known as beta-delayed proton emission, or can occur from the ground state of very...
and
alpha decayAlpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle, and thereby transforms into an atom with a mass number 4 less and atomic number 2 less...
. It has a
half-lifeHalf-life is the period of time, for a substance undergoing decay, to decrease by half. The name originally was used to describe a characteristic of unstable atoms , but may apply to any quantity which follows a set-rate decay....
of 3.5×10
−22 sThe second , sometimes abbreviated sec., is the name of a unit of time, and is the International System of Units base unit of time...
. Isotopic fractionation of boron is controlled by the exchange reactions of the boron species B(
OOxygen Oxygen Oxygen (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O...
HHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H
2...
)
3 and B(OH)
4. Boron isotopes are also fractionated during mineral crystallization, during H
2O phase changes in hydrothermal systems, and during hydrothermal alteration of
rockIn geology, rock is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...
. The latter effect results in preferential removal of the (OH)
4 ionAn ion is an atom or molecule where the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge...
onto clays. It results in solutions enriched in (OH)
3 and therefore may be responsible for the large enrichment in seawater relative to both
oceanAn ocean is a large body of saline water, and a principal component of the hydrosphere. Approximately 75% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
ic crust and
continentA continent is one of several large landmasses on Earth. They are generally identified by convention rather than any strict criterion, with seven regions commonly regarded as continents – they are : Asia, Africa, North America, South America, Antarctica, Europe, and Australia.Plate tectonics is...
al crust; this difference may act as an
isotopic signatureAn isotopic signature is a ratio of stable or unstable isotopes of particular elements found in an investigated material...
. The exotic exhibits a
nuclear haloIn nuclear physics, an atomic nucleus is called a halo nucleus or is said to have a nuclear halo if its radius is appreciably larger than that predicted by the liquid drop model, wherein the nucleus is assumed to be a sphere of constant density....
, i.e. its radius is appreciably larger than that predicted by the
liquid drop modelIn nuclear physics, the semi-empirical mass formula , sometimes also called Weizsäcker's formula, is a formula used to approximate the mass and various other properties of an atomic nucleus...
.
Enriched boron (boron-10)
The isotope is good at capturing thermal neutrons. Natural boron is about 20% and 80%. The
nuclear industryNuclear power is power produced from controlled nuclear reactions. Commercial plants in use to date use nuclear fission reactions....
enriches natural boron to nearly pure . The waste product, or depleted boron, is nearly pure . is a candidate as a fuel for
aneutronic fusionAneutronic fusion is any form of fusion power where no more than 1% of the total energy released is carried by neutrons. Since the most-studied fusion reactions release up to 80% of their energy in neutrons, successful aneutronic fusion would greatly reduce problems associated with neutron...
and is used in the semiconductor industry. Enriched boron or is used in both radiation shielding and in
boron neutron capture therapyBoron neutron capture therapy is an experimental form of radiotherapy that uses a neutron beam that interacts with boron injected to a patient...
. In the latter, a compound containing is attached to a
muscleMuscle is the contractile tissue of the body and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
near a
tumorA tumor or tumour is the name for a swelling or lesion formed by an abnormal growth of cells . Tumor is not synonymous with cancer. A tumor can be benign, pre-malignant or malignant, whereas cancer is by definition malignant....
. 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.
In nuclear reactors, is used for reactivity control and in
emergency shutdown systemsA scram or SCRAM is an emergency shutdown of a nuclear reactor – though the term has been extended to cover shutdowns of other complex operations, such as server farms and even large model railroads...
. It can serve either function in the form of borosilicate control rods or as
boric acidBoric acid, also called boracic acid or orthoboric acid or Acidum Boricum, is a weak acid often used as an antiseptic, insecticide, flame retardant, in nuclear power plants to control the fission rate of uranium, and as a precursor of other chemical compounds. It exists in the form of colorless...
. In
pressurized water reactorPressurized water reactors comprise a majority of all western nuclear power plants and are one of two types of light water reactor , the other type being boiling water reactors . In a PWR the primary coolant is pumped under high pressure to the reactor core, then the heated water transfers...
s, 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, has a theoretical role as structural material (as boron fibers or BN
nanotubeAn inorganic nanotube is a cylindrical molecule often composed of metal oxides, and morphologically similar to a carbon nanotube. Inorganic nanotubes have been observed to occur naturally in some mineral deposits....
material) which would also serve a special role in the radiation shield. One of the difficulties in dealing with cosmic rays, which are mostly high energy protons, is that some secondary radiation from interaction of cosmic rays and spacecraft materials is high energy
spallationIn general, spallation is a process in which fragments of material are ejected from a body due to impact or stress. In nuclear physics, it is the process in which a heavy nucleus emits a large number of nucleons as a result of being hit by a high-energy particle, thus greatly reducing its atomic...
neutrons. Such neutrons can be moderated by materials high in light elements such as
polyethylenePolyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons. Its primary use is within packaging .- Description :Polyethylene is a thermoplastic polymer consisting of long chains of the monomer ethylene...
, but the moderated neutrons continue to be a radiation hazard unless actively absorbed in the shielding. Among light elements that absorb thermal neutrons, and 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; and neutrons cause
fissionIn nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts, often producing free neutrons and lighter nuclei, which may eventually produce photons...
in if it is present in the spacecraft's semiconductors, producing a
gamma rayGamma rays are electromagnetic radiation of high frequency . They are produced by sub-atomic particle interactions, such as electron-positron annihilation, neutral pion decay, radioactive decay, fusion, fission or inverse Compton scattering in astrophysical processes...
, an
alpha particleAlpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus; hence, it can be written as or . They have a net spin of zero, and normally a total energy of about 5 MeV...
, and a
lithiumLithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number three. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...
ion. The resultant fission products may then dump charge into nearby semiconductor 'chip' structures, causing data loss (bit flipping, or
single event upsetA single event upset is a change of state caused by ions or electro-magnetic radiation striking a sensitive node in a micro-electronic device, such as in a microprocessor, semiconductor memory, or power transistors. The state change is a result of the free charge created by ionization in or close...
). In radiation hardened semiconductor designs, one countermeasure is to use
depleted boron which is greatly enriched in and contains almost no . is largely immune to radiation damage. Depleted boron is a by-product of the
nuclear industryNuclear power is power produced from controlled nuclear reactions. Commercial plants in use to date use nuclear fission reactions....
.
is also a candidate as a fuel for
aneutronic fusionAneutronic fusion is any form of fusion power where no more than 1% of the total energy released is carried by neutrons. Since the most-studied fusion reactions release up to 80% of their energy in neutrons, successful aneutronic fusion would greatly reduce problems associated with neutron...
. When struck by a proton with energy of about 500 k
eVIn physics, the electron volt is a unit of energy. By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electrostatic potential difference of one volt...
, 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. Whereas, the alpha particles from fusion can be turned directly into electric power, and all radiation stops as soon as the reactor is turned off.
NMR spectroscopy
Both and possess nuclear spin. The nuclear spin of is 3 and that of is 3/2. These isotopes are, therefore, of use in
nuclear magnetic resonanceNuclear magnetic resonance is a property that magnetic nuclei have in a magnetic field and applied electromagnetic pulse, which cause the nuclei to absorb energy from the EM pulse and radiate this energy back out...
spectroscopy; and spectrometers specially adapted to detecting the boron-11 nuclei are available commercially. The and 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%. The worldwide commercial borate deposits are estimated as 10 million tonnes.
TurkeyTurkey , known officially as the Republic of Turkey
, is a Eurasian country that stretches across the Anatolian peninsula in Western Asia and Thrace in the Balkan region of southeastern Europe...
and the
United StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
are the world's largest producers of boron. Turkey has almost 72% of the world’s boron reserves. Boron does not appear on Earth in elemental form but is found combined in
boraxBorax, also known as sodium borate, sodium tetraborate, or disodium tetraborate, is an important boron compound, a mineral, and a salt of boric acid. It is usually a white powder consisting of soft colorless crystals that dissolve easily in water.Borax has a wide variety of uses...
, boric acid,
colemaniteColemanite is a borate mineral found in evaporite deposits of alkaline lacustrine environments...
,
kerniteKernite, also known as rasorite is a hydrated sodium borate hydroxide mineral with formula Na2B4O62·3H2O. It is a colorless to white mineral crystallizing in the monoclinic crystal system typically occurring as prismatic to acicular crystals or...
,
ulexiteUlexite is a mineral occurring in silky white rounded crystalline masses or in parallel fibers...
and
borateBorates in chemistry are chemical compounds containing boron oxoanions, with boron in oxidation state +3. The simplest borate ion is the trigonal planar, BO33−, although many others are known. BO33− forms salts with metallic elements. Boron found in...
s. Boric acid is sometimes found in
volcanic3. Conduit
4. Base
5. Sill
6. Dike
7. Layers of ash emitted by the volcano
8. Flank| 9. Layers of lava emitted by the volcano
10. Throat
11. Parasitic cone
12. Lava flow
13. Vent
14. Crater
15...
spring waters. Ulexite is a borate
mineralA mineral is a naturally occurring solid formed through geological processes that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties. A rock, by comparison, is an aggregate of minerals and/or mineraloids, and need not have a specific...
; 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). They are both found in the
Mojave DesertThe Mojave Desert , , locally referred to as the High Desert, occupies a significant portion of southeastern California and smaller parts of central California, southern Nevada, southwestern Utah and northwestern Arizona, in the United States...
of
CaliforniaCalifornia is the most populous state in the United States, and the third largest by area. California is the second most populous sub-national entity in the Americas, behind only São Paulo, Brazil...
, but the largest borax deposits are in Central and Western
TurkeyTurkey , known officially as the Republic of Turkey
, is a Eurasian country that stretches across the Anatolian peninsula in Western Asia and Thrace in the Balkan region of southeastern Europe...
including the provinces of
EskişehirEskişehir is a city in northwestern Turkey and the capital of the Eskişehir Province. According to the 2008 census, the population of the district was 614,247; of which 599,796 live in the city of Eskişehir. The city is located on the banks of the Porsuk River, 792 m above sea level, where it...
,
KütahyaKütahya is a city in western Turkey with 213,000 inhabitants , lying on the Porsuk river, at 969 metres above sea level. It is the capital of Kütahya Province, inhabited by some 684,082 people...
and
BalıkesirBalıkesir is the capital city of Balıkesir Province. Balıkesir is in the Marmara region of Turkey and has a population of 247.072 inhabitants. Old name is Karesi.- History :...
History and etymology
The name boron originates from the
ArabicArabic is a Central Semitic language, thus related to and classified alongside other Semitic languages such as Hebrew and the Neo-Aramaic languages. In terms of speakers, the Arabic macrolanguage is the largest member of the Semitic language family. It is spoken by more than 280 million people as...
word
buraq or the
PersianPersian is an Iranian language within the Indo-Iranian branch of the Indo-European languages. It is widely spoken in Iran, Afghanistan, Tajikistan, Uzbekistan and to some extent in Iraq and Bahrain, and has a status of official language in the first three countries under different names...
word
burah; 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
SanskritSanskrit is a historical Indo-Aryan language, one of the liturgical languages of Hinduism and Buddhism, and one of the 22 official languages of India. It is also declared as a classical language by the government of India....
. Borax glazes were used in China from AD300, and some tincal even reached the West, where the Arabic alchemist
GeberGeber is the Latinized form of "Jabir", with the full name of Abu Musa Jābir ibn Hayyān al azdi , a prominent polymath: a chemist and alchemist, astronomer and astrologer, engineer, geologist, philosopher, physicist, and pharmacist and physician...
seems to mention it in 700.
Marco PoloMarco Polo was a merchant from the Venetian Republic who wrote Il Milione, which introduced Europeans to Central Asia and China. He learned about trading whilst his father and uncle, Niccolò and Maffeo, voyaged through Asia and met Kublai Khan. In 1269, they returned to Venice to meet Marco for...
brought some glazes back to Italy in the 13th century. Agricola, around 1600, reports its use as a flux in
metallurgyMetallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their mixtures, which are called alloys. It is also the technology of metals: the way in which science is applied to their practical use...
. In 1777,
boric acidBoric acid, also called boracic acid or orthoboric acid or Acidum Boricum, is a weak acid often used as an antiseptic, insecticide, flame retardant, in nuclear power plants to control the fission rate of uranium, and as a precursor of other chemical compounds. It exists in the form of colorless...
was recognized in the hot springs (
soffioniSoffioni , a name applied in Italy to certain volcanic vents which emit jets of steam, generally associated with hydrogen sulfide and carbon dioxide, sometimes also with a little ammonia and marsh gas....
) near
FlorenceFlorence is the capital city of the Italian region of Tuscany and of the province of Florence...
, Italy, and became known as
sal sedativum, with mainly medical uses. The rare mineral is called
sassoliteSassolite is a borate mineral, and is the mineral form of boric acid. It occurs in volcanic fumaroles and hot springs, as well as in bedded sedimentary borate deposits. Its mineral form was first noted in the early 19th century, and was named after Sasso, Italy, where it was found. According to...
, which is found at Sasso, Italy. This was the main source of European borax from 1827 to 1872, at which date American sources replaced it.
Boron was not recognized as an element until it was isolated by Sir
Humphry DavySir Humphry Davy, 1st Baronet FRS MRIA was a British chemist and inventor. He is probably best remembered today for his discoveries of several alkali and alkaline earth metals, as well as contributions to the discoveries of the elemental nature of chlorine and iodine. He invented the Davy lamp,...
,
Joseph Louis Gay-LussacJoseph Louis Gay-Lussac was a French chemist and physicist. He is known mostly for two laws related to gases, and for his work on alcohol-water mixtures, which led to the degrees Gay-Lussac used to measure alcoholic beverages in many countries.- Biography :Gay-Lussac was born at...
and
Louis Jacques ThénardLouis Jacques Thénard , was a French chemist.His father, a poor peasant, managed to have him educated at the academy of Sens, and sent him at the age of sixteen to study pharmacy in Paris. There he attended the lectures of Antoine François Fourcroy and Louis Nicolas Vauquelin...
in 1808 through the reaction of boric acid and
potassiumPotassium is the chemical element with the symbol K , atomic number 19, and atomic mass 39.0983. Potassium was first isolated from potash...
. Davy called the element
boracium.
Jöns Jakob BerzeliusFriherre Jöns Jacob Berzelius was a Swedish chemist. He worked out the modern technique of chemical formula notation, and is together with John Dalton, Antoine Lavoisier, and Robert Boyle considered a father of modern chemistry.-Career:Berzelius was born at Väversunda in Östergötland in Sweden. He...
identified boron as an element in 1824. The first pure boron was arguably produced by the American chemist W. Weintraub in 1909.
Production
Pure elemental boron is difficult to extract. The earliest methods involved reduction of boric oxide with metals such as
magnesiumMagnesium is a chemical element with the symbol Mg, atomic number 12 and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the earth's crust by mass, although ninth in the Universe as a whole...
or
aluminiumAluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13. It is not soluble in water under normal circumstances....
. However the product is almost always contaminated with metal
borideIn chemistry a boride is a chemical compound between boron and a less electronegative element. This is a very large group of compounds that are generally high melting and are not ionic in nature. Some borides exhibit very useful physical properties. The term boride is also loosely applied to...
s. Pure boron can be prepared by reducing volatile boron halides with
hydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H
2...
at high temperatures. Ultrapure boron, for the use in semiconductor industry, is produced by the decomposition of
diboraneDiborane is the chemical compound consisting of boron and hydrogen with the formula B2H6. It is a colorless gas at room temperature with a repulsively sweet odor. Diborane mixes well with air, easily forming explosive mixtures. Diborane will ignite spontaneously in moist air...
at high temperatures and then further purified with the
zone meltingZone melting is a group of similar methods of purifying crystals, in which a narrow region of a crystal is molten, and this molten zone is moved along the crystal...
or
Czochralski processThe Czochralski process is a method of crystal growth used to obtain single crystals of semiconductors , metals , salts, and synthetic gemstones...
es.
Isotope enrichment
Because of its high neutron cross-section, boron-10 is often used to control fission in nuclear reactors as neutron-capturing substance. Several industrial-scale enrichment processes have been developed, however only the fractionated vacuum distillation of the
dimethyl etherDimethyl ether is the organic compound with the formula CH
3OCH
3. The simplest ether, it is a colourless gas that is a useful precursor to other organic compounds and an aerosol propellant...
adduct of
boron trifluorideBoron trifluoride is the chemical compound with the formula BF
3. This pungent colourless toxic gas forms white fumes in moist air. It is a useful Lewis acid and a versatile building block for other boron compounds.-Structure and bonding:...
(DME-BF
3) and column chromatography of borates are being used.
Market trend
Estimated global consumption of boron rose to a record 1.8 million tonnes of B
2O
3 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
colemaniteColemanite is a borate mineral found in evaporite deposits of alkaline lacustrine environments...
has declined following concerns over
arsenicArsenic is the chemical element that has the symbol As, atomic number 33 and atomic mass 74.92. Arsenic was first documented by Albertus Magnus in 1250. Arsenic is a notoriously poisonous metalloid with many allotropic forms, including a yellow and several black and grey forms...
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.
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
EmetEmet is a town and a district of Kütahya Province in the Aegean region of Turkey.It is also a Hebrew word meaning truth,often used in the legend of the Golem.-Emet boron mine:...
in 2003.
Rio Tinto GroupThe Rio Tinto Group is a diversified, multinational mining and resources group with headquarters in London, England and Melbourne, Australia. The company was founded in 1873, when a multinational consortium of investors purchased a mine complex on the Rio Tinto river, in Huelva, Spain from the...
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 growth rates in
fiberglassFiberglass, , is material made from extremely fine fibers of glass. It is used as a reinforcing agent for many polymer products; the resulting composite material, properly known as fiber-reinforced polymer or glass-reinforced plastic , is called "fiberglass" in popular usage...
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 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.
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. Borosilicate glass, which is typically 12%-15% B
2O
3, 80% SiO
2, and 2% Al
2O
3, has a low
coefficient of thermal expansionWhen the temperature of a substance changes, the energy that is stored in the intermolecular bonds between atoms changes. When the stored energy increases, so does the length of the molecular bonds...
giving it a good resistance to thermal shock. Duran and
PyrexPyrex is a brand name for glassware, introduced by Corning Incorporated in 1915. According to Carroll Gantz, Dr. Jesse Littleton of Corning discovered its cooking potential by presenting his wife with a makeshift casserole made from a cut down Nonex battery jar...
are two major brand names for this glass.
Boron filaments are high-strength, lightweight materials that are chiefly used for advanced
aerospaceAerospace comprises the atmosphere of Earth and surrounding space. Typically the term is used to refer to the industry that researches, designs, manufactures, operates, and maintains vehicles moving through air and space...
structures as a component of
composite materialComposite materials are engineered materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct on a macroscopic level within the finished structure.- History :The most primitive composite materials were straw...
s, as well as limited production consumer and sporting goods such as
golf clubGolf clubs are used in the sport of golf to hit a golf ball. Each club is composed of a shaft with a lance and a clubhead. Woods are used for long-distance fairway shots; irons, the most versatile class, are used for a variety of shots; putters are used mainly on the green to roll the ball into...
s and
fishing rodA fishing rod or a fishing pole is a tool used to catch fish, usually in conjunction with the sport of angling, can also be used in competition casting . . A length of fishing line is attached to a long, flexible rod or pole: one end terminates in a hook for catching the fish...
s. The fibers can be produced by
chemical vapor depositionChemical vapor deposition is a chemical process used to produce high-purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films. In a typical CVD process, the wafer is exposed to one or more volatile precursors, which react and/or...
of boron on a
tungstenTungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A steel-gray metal, tungsten is found in several ores, including wolframite and scheelite...
filament.
Boron fibers and sub-millimeter sized crystalline boron springs are produced by
laserA laser is a device that emits light through a process called stimulated emission. Laser light is usually spatially coherent, which means that the light either is emitted in a narrow, low-divergence beam, or can be converted into one with the help of optical components such as lenses...
-assisted
chemical vapor depositionChemical vapor deposition is a chemical process used to produce high-purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films. In a typical CVD process, the wafer is exposed to one or more volatile precursors, which react and/or...
. Translation of the focused laser beam allows to produce even complex helical structures. Such structures show good mechanical properties (
elastic modulusAn elastic modulus, or modulus of elasticity, is the mathematical description of an object or substance's tendency to be deformed elastically when a force is applied to it...
450 GPa, fracture strain 3.7 %, fracture stress 17 GPa) and can be applied as reinforcement of ceramics or in micromechanical systems.
Semiconductor industry
Boron is an important technological
dopantA dopant, also called doping agent and dope, is an impurity element added to a crystal lattice in low concentrations in order to alter the optical/electrical properties of the crystal....
for such important semiconductors as
siliconSilicon is the most common metalloid. It is a chemical element, which has the symbol Si and atomic number 14. A tetravalent metalloid, silicon is less reactive than its chemical analog carbon...
,
germaniumGermanium is a chemical element with the symbol Ge and atomic number 32. It is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbors tin and silicon. Germanium has five naturally occurring isotopes ranging in atomic mass number from 70 to 76...
and
silicon carbideSilicon carbide , also known as carborundum, is a compound of silicon and carbon with a chemical formula SiC. It occurs in nature as the extremely rare mineral moissanite. Silicon carbide powder has been mass-produced since 1893 for use as an abrasive...
. Having one less valence electron than the host atom, it donates a
holeAn electron hole is the conceptual and mathematical opposite of an electron, useful in the study of physics, chemistry, and electrical engineering. The concept describes the lack of an electron at a position where one could exist in an atom or atomic lattice. It is different from the positron,...
resulting in p-type conductivity. Traditional method of introducing boron into semiconductors is via its atomic
diffusionMolecular diffusion, often called simply diffusion, is a net transport of molecules from a region of higher concentration to one of lower concentration by random molecular motion. The result of diffusion is a gradual mixing of material...
at high temperatures. This process uses either solid (B
2O
3), liquid (BBr
3) or gaseous boron sources (B
2H
6 or BF
3). However, after 1970s, it was mostly replaced by
ion implantationIon implantation is a materials engineering process by which ions of a material can be implanted into another solid, thereby changing the physical properties of the solid. Ion implantation is used in semiconductor device fabrication and in metal finishing, as well as various applications in...
, which relies mostly on BF
3 as a boron source. Boron trichloride gas is also an important chemical in semiconductor industry, however not for doping but rather for
plasma etchingPlasma etching is a form of plasma processing used to fabricate integrated circuits. It involves a high-speed stream of glow discharge of an appropriate gas mixture being shot at a sample. The plasma source, known as etch species, can be either charged or neutral...
of metals and their oxides.
Engineering materials
Boron carbideBoron carbide is an extremely hard ceramic material used in tank armor, bulletproof vests, and numerous industrial applications...
, a ceramic material which is obtained by decomposing B
2O
3 with carbon in the electric furnace:
- 2 B2O3 + 7 C → B4C + 6 CO
It is used in
tank armorMilitary vehicles are commonly armoured to withstand the impact of shrapnel, bullets, missiles, or shells, protecting the personnel inside from enemy fire. Such vehicles include tanks, aircraft, and ships.Civilian vehicles may also be armoured...
,
bulletproof vestA ballistic vest, bulletproof vest or bullet-resistant vest is an item of protective clothing that helps absorb the impact from firearm-fired projectiles and shrapnel from explosions, and is worn on the torso...
s, and numerous other structural applications. Its ability to absorb neutrons without forming long lived
radionuclideA radionuclide is an atom with an unstable nucleus, which is a nucleus characterized by excess energy which is available to be imparted either to a newly-created radiation particle within the nucleus, or else to an atomic electron . The radionuclide, in this process, undergoes radioactive decay,...
s makes the material attractive as an absorbent for neutron radiation arising in nuclear power plants. Nuclear applications of boron carbide include shielding, control rod and shut down pellets. Within control rods, boron carbide is often powdered, to increase its surface area.
Magnesium diborideMagnesium diboride is a simple ionic binary compound that has proven to be an inexpensive and useful superconducting material....
is an important
superconducting materialSuperconductivity is a phenomenon occurring in certain materials generally at very low temperatures, characterized by exactly zero electrical resistance and the exclusion of the interior magnetic field . It was discovered by Heike Kamerlingh Onnes in 1911. Like ferromagnetism and atomic spectral...
with the transition temperature of 39 K. MgB
2 wires are produced with the
powder-in-tubePowder-in-tube is a process used for making electrical conductors from brittle superconducting materials such as Niobium-tin,BSCCO, or magnesium diboride.PIT is sometimes called oxide powder in tube ....
process and applied in superconducting magnets.
Boron is a part of
neodymium magnetA neodymium magnet , a type of rare-earth magnet, is a permanent magnet made from an alloy of neodymium, iron, and boron to form the Nd2Fe14B tetragonal crystalline structure...
(Nd
2Fe
14B), which is the strongest type of permanent magnet. It is found in all kinds of domestic and professional electromechanical and electronic devices, such as
magnetic resonance imagingMagnetic Resonance Imaging , or nuclear magnetic resonance imaging , is primarily a medical imaging technique most commonly used in radiology to visualize the internal structure and function of the body...
(MRI), various motors and
actuatorAn actuator is a mechanical device for moving or controlling a mechanism or system. An actuator typically is a mechanical device that takes energy, usually created by air, electricity, or liquid, and converts that into some kind of motion....
s, computer HDDs, CD and DVD players, mobile phones, timer switches, speakers, etc.
High-hardness compounds
Mechanical properties of BCN solids and ReB2
| Material |
Diamond |
cubic-BC2N |
cubic-BC5 |
cubic-BN |
B4C |
ReB2 |
| Vickers hardness (GPa) |
115 |
76 |
71 |
62 |
38 |
22 |
| Fracture toughness In materials science, fracture toughness is a property which describes the ability of a material containing a crack to resist fracture, and is one of the most important properties of any material for virtually all design applications....
(MPa m1/2) |
5.3 |
4.5 |
9.5 |
6.8 |
3.5 |
|
Several boron compounds are known for their extreme hardness and toughness, including
- Heterodiamond
Heterodiamond is a superhard material containing boron, carbon, and nitrogen . It is formed at high temperatures and high pressures, e.g., by application of an explosive shock wave to a mixture of diamond and cubic boron nitride. The heterodiamond is a polycrystalline material coagulated with...
(also called BCN);
- Boron nitride
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 exist in various crystalline forms...
. This material is isoelectronic to carbonCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
. 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 borazonBorazon is a brand name of a cubic form of boron nitride . It is one of the hardest known materials, along with various forms of diamond and boron nitride. Borazon is a crystal created by heating equal quantities of boron and nitrogen at temperatures greater than 1800 °C at 7 GPa...
, is a superior abrasive. Its hardness is only slightly smaller, but chemical stability is superior to that of diamond.
- Rhenium diboride
Rhenium diboride is a synthetic superhard material. It was first synthesized in 1962 and re-emerged recently due to hopes of achieving high hardness comparable to that of diamond...
can be produced at ambient pressures, but is rather expensive because of rhenium. The hardness of ReB2 exhibits considerable anisotropyAnisotropy is the property of being directionally dependent, as opposed to isotropy, which implies homogeneity in all directions. It can be defined as a difference, when measured along different axes, in a material's physical property An example of anisotropy is the light coming through a...
because of its hexagonal layered structure. Its value is comparable to that of tungsten carbideTungsten carbide, WC is an inorganic chemical compound containing equal parts of tungsten and carbon atoms. Colloquially, tungsten carbide is often simply called carbide. In its most basic form, it is a fine gray powder, but it can be pressed and formed into shapes for use in industrial machinery,...
, silicon carbideSilicon carbide , also known as carborundum, is a compound of silicon and carbon with a chemical formula SiC. It occurs in nature as the extremely rare mineral moissanite. Silicon carbide powder has been mass-produced since 1893 for use as an abrasive...
, titanium diboride or zirconium diborideZirconium diboride is a highly covalent refractory ceramic material with a hexagonal crystal structure. ZrB
2 is an Ultra High Temperature Ceramic with a melting point of 3246 °C...
.
- 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.
Boron carbide and cubic boron nitride powders are widely used as abrasives. Metal
borideIn chemistry a boride is a chemical compound between boron and a less electronegative element. This is a very large group of compounds that are generally high melting and are not ionic in nature. Some borides exhibit very useful physical properties. The term boride is also loosely applied to...
s are used for coating tools through
chemical vapor depositionChemical vapor deposition is a chemical process used to produce high-purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films. In a typical CVD process, the wafer is exposed to one or more volatile precursors, which react and/or...
or
physical vapor depositionPhysical vapor deposition is a variety of vacuum deposition and is a general term used to describe any of a variety of methods to deposit thin films by the condensation of a vaporized form of the material onto various surfaces...
. Implantation of boron ions into metals and alloys, through
ion implantationIon implantation is a materials engineering process by which ions of a material can be implanted into another solid, thereby changing the physical properties of the solid. Ion implantation is used in semiconductor device fabrication and in metal finishing, as well as various applications in...
or
ion beam depositionIon Beam Deposition is a process of applying materials to a target through the application of an ion beam.thumb|Ion beam deposition setup with mass separator...
, 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.
In chemistry
Sodium tetraborate pentahydrate (Na
2B
4O
7 • 5H
2O) is used in large amounts in making insulating fiberglass and sodium perborate bleach. Sodium tetraborate decahydrate (Na
2B
4O
7 • 10 H
2O) can be found in adhesives and in anti-corrosion systems. Sodium borates are used as a
fluxIn metallurgy, a flux is a chemical cleaning agent which facilitates soldering, brazing, and welding by removing oxidation from the metals to be joined. Common fluxes are: ammonium chloride or rosin for soldering tin; hydrochloric acid and zinc chloride for soldering galvanized iron ; and borax for...
for soldering silver and gold and with
ammonium chlorideAmmonium chloride is, in its pure form, a clear white water-soluble crystalline salt of ammonia. The aqueous ammonium chloride solution is mildly acidic. Sal ammoniac is a name of natural, mineralogical form of ammonium chloride...
for welding ferrous metals. They are also fire retarding additives to plastics and rubber articles. Sodium perborate serves as a source of active oxygen in many
detergentA detergent is a material intended to assist cleaning. The term is sometimes used to differentiate between soap and other surfactants used for cleaning...
s,
laundry detergentLaundry detergent, or washing powder, is a substance which is a type of detergent that is added when one is washing laundry to aid in getting the laundry cleaner.-Format:...
s, cleaning products, and laundry
bleachA bleach is a chemical that removes colors or whitens, often via oxidation. Common chemical bleaches include household "chlorine bleach", a solution of approximately 3–6% sodium hypochlorite , and "oxygen bleach", which contains hydrogen peroxide or a peroxide-releasing compound such as sodium...
es. It is also present in some
tooth bleachingDental bleaching, also known as tooth whitening, is a common procedure in general dentistry but most especially in the field of cosmetic dentistry. A child's deciduous teeth are generally whiter than the adult teeth that follow. As a person ages the adult teeth often become darker due to changes in...
formulas.
Boric acid (also known as orthoboric acid) H
3BO
3 is used in the production of textile
fiberglassFiberglass, , is material made from extremely fine fibers of glass. It is used as a reinforcing agent for many polymer products; the resulting composite material, properly known as fiber-reinforced polymer or glass-reinforced plastic , is called "fiberglass" in popular usage...
and
flat panel displayFlat panel displays encompass a growing number of technologies enabling video displays that are lighter and much thinner than traditional television and video displays that use cathode ray tubes, and are usually less than 4 inches thick...
s. It also has antiseptic, antifungal, and antiviral properties and for this reasons is applied as a water clarifier in swimming pool water treatment. Boric acid is also traditionally used as an insecticide, notably against ants, fleas, and cockroaches.
TriethylboraneTriethylborane , also called triethylborine and triethylboron, is an organoborane , a near-colorless to yellowish transparent liquid with pungent ether-like odor...
is a substance which ignites the
JP-7JP-7 is a jet fuel developed by the U.S. Air Force for use in supersonic aircraft because of its high flashpoint and thermal stability. It is the fuel used in the Pratt & Whitney J58 engines, used in the Lockheed SR-71 Blackbird. The air compression of Mach 3+ cruising flight generates very high...
fuel of the
Pratt & Whitney J58The Pratt & Whitney J58 was a variable cycle turbojet aircraft engine used on the Lockheed A-12, and subsequently on the YF-12 and SR-71 Blackbird aircraft. It was essentially a hybrid turbojet/ramjet engine....
turbojetTurbojets are the oldest kind of general purpose jet engines. Two engineers, Frank Whittle in the United Kingdom and Hans von Ohain in Germany, developed the concept independently into practical engines during the late 1930s, although credit for the first turbojet is given to Whittle who submitted...
/
ramjetA ramjet, sometimes referred to as a stovepipe jet, or an athodyd, is a form of jet engine using the engine's forward motion to compress incoming air, without a rotary compressor...
engines powering the Lockheed
SR-71 BlackbirdThe Lockheed SR-71 is an advanced, long-range, Mach 3 strategic reconnaissance aircraft developed from the Lockheed A-12 and YF-12A aircraft by the Lockheed Skunk Works as a Black project. The SR-71 was unofficially named the Blackbird, and called the Habu by its crews, referring to an Okinawan...
. It was also used to ignite the
F-1 EnginesThe F-1 is a rocket engine developed by Rocketdyne and used in the Saturn V. Five F-1 engines were used in the S-IC first stage of each Saturn V, which served as the main launch vehicle in the Apollo program...
on the
Saturn VThe Saturn V was a multistage liquid-fuel expendable rocket used by NASA's Apollo and Skylab programs from 1967 until 1973. In total NASA launched thirteen Saturn V rockets with no loss of payload. It remains the largest and most powerful launch vehicle ever brought to operational status from a...
Rocket utilized by
NASAThe National Aeronautics and Space Administration is an agency of the United States government, responsible for the nation's public space program. NASA was established by the National Aeronautics and Space Act on July 29, 1958, replacing its predecessor, the National Advisory Committee for...
's Apollo and
SkylabSkylab was the United States' first space station, and the second space station visited by a human crew. It was also the only space station NASA launched alone...
programs from 1967 until 1973. Triethylborane is suitable for this because of its pyrophoric properties, especially the fact that it burns with very high temperature. Triethylborane is an industrial
initiatorIn chemistry, radical initiators are substances that can produce radical species under mild conditions and promote radical polymerization reactions. These substances generally possess weak bonds—bonds that have small bond dissociation energies. Radical initiators are utilized in industrial...
in
radicalIn chemistry, radicals are atoms, molecules, or ions with unpaired electrons on an otherwise open shell configuration. These unpaired electrons are usually highly reactive, so radicals are likely to take part in chemical reactions...
reactions, where it is effective even at low temperatures. It is also injected into
vapor depositionChemical vapor deposition is a chemical process used to produce high-purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films. In a typical CVD process, the wafer is exposed to one or more volatile precursors, which react and/or...
reactors as a boron source. Examples are the plasma deposition of boron-containing hard carbon films, silicon nitride-boron nitride films, and for
dopingIn semiconductor production, doping is the process of intentionally introducing impurities into an extremely pure semiconductor to change its electrical properties. The impurities are dependent upon the type of semiconductor. Lightly- and moderately-doped semiconductors are referred to as extrinsic...
of
diamondIn mineralogy, diamond is an allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is the second most stable form of carbon, after graphite; however, the conversion rate from diamond to graphite is...
film with boron.
Boron compounds show promise in treating
arthritisArthritis is a group of conditions involving damage to the joints of the body....
. Because of its distinctive green flame, amorphous boron is used in
pyrotechnic flaresA flare, also sometimes called a fusee, is a type of pyrotechnic that produces a brilliant light or intense heat without an explosion. Flares are used for signaling, illumination, or defensive countermeasures in civilian and military applications...
. It is also used as a melting point depressant in nickel-chromium braze alloys.
Biological role
There is a boron-containing natural
antibioticIn common usage, an antibiotic is a substance or compound that kills or inhibits the growth of bacteria...
,
boromycinBoromycin is a bacteriocidal polyether-macrolide antibiotic. It was initially isolated from the Streptomyces strain Streptomyces antibioticus, and is notable for being the first natural product found to contain the element boron. It is effective against most Gram-positive bacteria, but is...
, isolated from
streptomycesStreptomyces is the largest genus of Actinobacteria and the type genus of the family Streptomycetaceae. Over 500 species of Streptomyces bacteria have been described. As with the other Actinobacteria, streptomycetes are gram-positive, and have genomes with high GC-content...
. Boron is an essential plant
nutrientA nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. Nutrients are the substances that enrich the body. They build and repair tissues, give heat and energy, and regulate body processes...
, required primarily for maintaining the integrity of cell walls. Conversely, high soil concentrations of > 1.0
ppmParts-per notation is used, especially in science and engineering, to denote relative proportions in measured quantities; particularly in low-value proportions at the parts-per-million , parts-per-billion , and parts-per-trillion level...
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 content in the soil is greater than 1.8 ppm. 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.
As an
ultratrace elementIn biochemistry, an ultratrace element is a chemical element that normally comprises less than one microgram per gram of a given organism....
, 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.
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. The results showed that supplemental boron reduced excretion of calcium by 44%, and activated
estrogenEstrogens are a group of steroid compounds, named for their importance in the estrous cycle, and functioning as the primary female sex hormone, their name comes from estrus/oistros + gen/gonos = to generate.Estrogens are used as part of some oral contraceptives, in estrogen replacement...
and
vitamin DVitamin D is a group of fat-soluble prohormones, the two major forms of which are vitamin D2 and vitamin D3 . Vitamin D obtained from sun exposure, food, and supplements, is biologically inert and must undergo two hydroxylation reactions to be activated in the body...
. However, whether these effects were conventionally nutritional, or medicinal, could not be determined. The US
National Institutes of HealthThe National Institutes of Health is an agency of the United States Department of Health and Human Services and is the primary agency of the United States government responsible for biomedical and health-related research. It consists of 27 separate institutes and centers which includes the Office...
quotes this source:
- Total daily boron intake in normal human diet
In nutrition, the diet is the sum of food consumed by a person or other organism. Dietary habits are the habitual decisions an individual or culture makes when choosing what foods to eat. Although humans are omnivores, each culture holds some food preferences and some food taboos. Individual...
s ranges from 2.1–4.3 mg boron/kg body weight (bw)/day.
Analytical quantification
For determination of boron content in food or materials the
colorimetricColorimetry or Colourimetry is "the science and technology used to quantify and describe physically the human color perception."It is similar to spectrophotometry, but is distinguished by its interest in reducing spectra to the physical correlates of color perception, most often the CIE XYZ...
curcumin method is used. Boron has to be transferred to boric acid or
borateBorates in chemistry are chemical compounds containing boron oxoanions, with boron in oxidation state +3. The simplest borate ion is the trigonal planar, BO33−, although many others are known. BO33− forms salts with metallic elements. Boron found in...
s and on reaction with
curcuminCurcumin is the principal curcuminoid of the popular Indian spice turmeric, which is a member of the ginger family . The other two curcuminoids are desmethoxycurcumin and bis-desmethoxycurcumin. The curcuminoids are polyphenols and are responsible for the yellow color of turmeric. Curcumin can...
in acidic solution, a red colored boron-chelate complex,
rosocyanineRosocyanine and Rubrocurcumin are two red colored materials, which are formed by the reaction between curcumin and borates.-Application:The color reaction between borates and curcumin is used within the spectrophotometrical determination and quantification of boron present in food or materials...
, is formed.
Health issues
Elemental boron and borates are non-toxic to humans and animals (approximately similar to table salt). The LD
50 (dose at which there is 50% mortality) for animals is about 6 g per kg of body weight. Substances with LD
50 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. Fish have survived for 30 min in a saturated boric acid solution and can survive longer in strong borax solutions. Borates are more toxic to insects than to mammals. 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.
The
boraneIn chemistry, a borane is a chemical compound of boron and hydrogen. The boranes comprise a large group of compounds with the generic formulae of BxHy. These compounds do not occur in nature. Many of the boranes readily oxidise on contact with air, some violently...
s (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.
Congenital endothelial dystrophy type 2Congenital endothelial dystrophy type 2 is a rare form of human corneal dystrophy. It is associated with mutations in SLC4A11 gene....
, a rare form of
corneal dystrophyHuman corneal dystrophies is a group of disorders, characterised by a noninflammatory, inherited, bilateral opacity of the transparent front part of the human eye called the cornea...
, is linked to mutations in
SLC4A11Sodium bicarbonate transporter-like protein 11 is a protein that in humans is encoded by the SLC4A11 gene.-Further reading:...
gene that encodes a transporter reportedly regulating the intracellular concentration of boron.
See also
- Allotropes of boron
Elemental boron can exist in several allotropes, the most common of which are crystalline boron and brown amorphous boron. Crystalline boron has four major polymorphs: α, β, γ and T...
- :Category:Boron compounds
- Boron deficiency
- Boron oxide
- Boron nitride
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 exist in various crystalline forms...
- Boron neutron capture therapy
Boron neutron capture therapy is an experimental form of radiotherapy that uses a neutron beam that interacts with boron injected to a patient...
- Boronic acid
A boronic acid is an alkyl or aryl substituted boric acid containing a carbon to boron chemical bond belonging to the larger class of organoboranes. Boronic acids act as Lewis acids. Their unique feature are that they are capable of forming reversible covalent complexes with sugars, amino acids,...
- Hydroboration-oxidation reaction
In organic chemistry, the hydroboration-oxidation reaction is a two-step organic chemical 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...
- Suzuki coupling
External links