Listing description
Boron (
Detailed description
Elemental boron
is not found naturally. Industrially, very pure isolated boron is produced with
difficulty, as boron tends to form refractory materials containing small
amounts of carbon or other elements. Several allotropes of boron exist: amorphous boron is a brown powder and
crystalline boron is black, extremely hard (about 9.5 on Mohs' scale), and a poor conductor at room
temperature. Elemental boron is used as a dopant in the semiconductor
industry.
The major uses of
boron compounds are in sodium perborate bleaches, and the borax component of
fiberglass insulation. Boron compounds play specialized roles as high-strength
lightweight structural and refractory materials. They are used in glasses and
ceramics to give them resistance to thermal shock. Boron-containing reagents are used for the synthesis of organic compounds, and as an intermediate in the
synthesis of pharmaceuticals that do not contain boron.
In biology,
borates have low toxicity in mammals (similar to table salt), but much more so
to many arthropods. A boron-containing natural
antibiotic is known. Small amounts of boron compounds play a strengthening role
in the cell walls of all plants, making boron a necessary element in soils.
Experiments indicate a role for boron as an ultratrace
element in animals, but
the nature of its role in animal physiology is unknown.
History and etymology
The name boron
originates from the Arabic word بورق buraq or the Persian word بوره burah;[7] which are names for the mineral borax.[8]
Boron compounds
were known thousands of years ago. Borax was known from the deserts of western
Tibet, where it received the name of tincal, derived from the Sanskrit. Borax glazes were used in China from
AD300, and some tincal even reached the West, where the Arabic alchemist Jābir
ibn Hayyān
seems to mention it in 700. Marco Polo brought some glazes back to Italy in
the 13th century. Agricola, around 1600, reports the use of borax as a flux in metallurgy. In 1777, boric acid was recognized in the hot springs (soffioni) near Florence, Italy, and became known as sal
sedativum, with mainly medical uses. The rare mineral is called sassolite, which is found at Sasso, Italy.
Sasso was the main source of European borax from 1827 to 1872, at which date
American sources replaced it.[9][10]
Boron was not
recognized as an element until it was isolated by Sir Humphry Davy[11] and by Joseph
Louis Gay-Lussac
and Louis
Jacques Thénard[12] in 1808 through the reaction of boric
acid and potassium. Davy called the element boracium.[13] Jöns
Jakob Berzelius
identified boron as an element in 1824. The first pure boron was arguably
produced by the American chemist W. Weintraub in 1909.[14][15]
Market trend
Estimated global
consumption of boron rose to a record 1.8 million tonnes of B2O3
in 2005, following a period of strong growth in demand from Asia, Europe and
North America. Boron mining and refining capacities are considered to be
adequate to meet expected levels of growth through the next decade.
The form in which
boron is consumed has changed in recent years. The use of ores like colemanite has declined following concerns over arsenic content. Consumers have moved towards
the use of refined borates and boric acid that have a lower pollutant content.
The average cost of crystalline boron is $5/g.[53]
Increasing demand
for boric acid has led a number of producers to invest in additional capacity.
Eti Mine Company of Turkey opened a new boric acid plant with the production
capacity of 100,000 tonnes per year at Emet in 2003. Rio Tinto Group increased the capacity of its boron
plant from 260,000 tonnes per year in 2003 to 310,000 tonnes per year by May
2005, with plans to grow this to 366,000 tonnes per year in 2006. Chinese boron
producers have been unable to meet rapidly growing demand for high quality
borates. This has led to imports of sodium tetraborate (borax) growing by a hundredfold between 2000 and
2005 and boric acid imports increasing by 28% per year over the same period.[54][55]
The rise in
global demand has been driven by high growth rates in fiberglass and borosilicate production. A rapid increase in the
manufacture of reinforcement-grade fiberglass in Asia with a consequent
increase in demand for borates has offset the development of boron-free
reinforcement-grade fiberglass in Europe and the USA. 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.[54][56]
Applications
Insulation
The main use of
boron compounds is in the form of sodium
tetraborate
pentahydrate (Na2B4O7) for making insulating
fiberglass and sodium perborate bleach.[57]
Detergents formulations and bleaching agents
Borax is used in
laundry products, mainly as a precursor to bleaches. Specifically, sodium perborate serves as a source of active oxygen in many detergents, laundry detergents, cleaning products, and laundry bleaches. It is also present in some tooth bleaching formulas.[57]
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.[58] Borosilicate glass, which is typically 12–15% B2O3,
80% SiO2, and 2% Al2O3, has a low coefficient of thermal expansion giving it a good resistance to
thermal shock. Duran and Pyrex are two major brand names for this
glass.[59]
Boron filaments
are high-strength, lightweight materials that are used chiefly for advanced aerospace structures as a component of composite
materials, as well as
limited production consumer and sporting goods such as golf
clubs and fishing rods.[60][61] The fibers can be produced by chemical
vapor deposition
of boron on a tungsten filament.[43][62]
Boron fibers and
sub-millimeter sized crystalline boron springs are produced by laser-assisted chemical
vapor deposition.
Translation of the focused laser beam allows to produce even complex helical
structures. Such structures show good mechanical properties (elastic modulus 450 GPa, fracture strain
3.7 %, fracture stress 17 GPa) and can be applied as reinforcement of
ceramics or in micromechanical systems.[63]
Shielding in nuclear reactors
Boron shielding
is used as a control for nuclear reactors, taking advantage of its high
cross-section for neutron capture.
Semiconductor industry
Boron is a useful
dopant for such semiconductors as silicon, germanium, and silicon carbide. Having one fewer valence electron
than the host atom, it donates a hole resulting in p-type conductivity. Traditional method of
introducing boron into semiconductors is via its atomic diffusion at high temperatures. This process
uses either solid (B2O3), liquid (BBr3), or
gaseous boron sources (B2H6 or BF3). However,
after 1970s, it was mostly replaced by ion implantation, which relies mostly on BF3
as a boron source. Boron trichloride gas is also an
important chemical in semiconductor industry, however not for doping but rather
for plasma
etching of metals and
their oxides. Triethylborane is also injected into vapor
deposition
reactors as a boron source. Examples are the plasma deposition of
boron-containing hard carbon films, silicon nitride-boron nitride films, and
for doping of diamond film with boron.
PRICE
$2758.79/KG
OR $1253.99
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