| Atomic Number: | 5 | Atomic Symbol: | B |
| Atomic Weight: | 10.81 | Electron Configuration: | 2-3 |
| Shells: | 2,3 | Filling Orbital: | 2p1 |
| Melting Point: | 2300oC | Boiling Point: | 2550oC |
| Uses: | with Ti & W in heat resistant alloys for jets & rockets,
in Tennis rackets |
History
(Ar. Buraq, Pers. Burah) Boron compounds have been known for
thousands of years, but the element was not discovered until 1808 by Sir Humphry
Davy of England and by Gay-Lussac and Thenard of France.
Sources
The element is not found free in nature, but occurs as
orthoboric acid usually in certain volcanic spring waters and as borates in
boron and colemantie. Ulexite, another boron mineral, is interesting as it is
nature's own version of "fiber optics."
Important sources of boron are the ore rasorite (kernite) and tincal (borax
ore). Both of these ores are found in the Mohave Desert. Tincal is the most
important source of boron from the Mohave. Extensive borax deposits are also
found in Turkey.
Boron exists naturally as 19.78% 10B isotope and 80.22% 11B isotope.
High-purity crystalline boron may be prepared by the vapor phase reduction of
boron trichloride or tribromide with hydrogen on electically heated filaments.
The impure or amorphous, boron, a brownish-black powder, can be obtained by
heating the trioxide with magnesium powder.
Boron of 99.9999% purity has been produced and is available commercially.
Elemental boron has an energy band gap of 1.50 to 1.56 eV, which is higher than
that of either silicon or germanium.
Properties
Optical characteristics include transmitting portions of the
infrared. Boron is a poor conductor of electricity at room temperature but a
good conductor at high temperature.
Uses
Amorphous boron is used in pyrotechnic flares to provide a
distinctive green color, and in rockets as an igniter.
By far the most commercially important boron compound in terms of dollar
sales is Na2B4O7.5H2O. This
pentahydrate is used in very large quantities in the manufacture of insulation
fiberglass and sodium perborate bleach.
Boric acid is also an important boron compound with major markets in textile
products. Use of borax as a mild antiseptic is minor in terms of dollars and
tons. Boron compounds are also extensively used in the manufacture of
borosilicate glasses. Other boron compounds show promise in treating arthritis.
The isotope boron-10 is used as a control for nuclear reactors, as a shield
for nuclear radiation, and in instruments used for detecting neutrons. Boron
nitride has remarkable properties and can be used to make a material as hard as
diamond. The nitride also behaves like an electrical insulator but conducts heat
like a metal.
It also has lubricating properties similar to graphite. The hydrides are
easily oxidized with considerable energy liberation, and have been studied for
use as rocket fuels. Demand is increasing for boron filaments, a high-strength,
lightweight material chiefly employed for advanced aerospace structures.
Boron is similar to carbon in that it has a capacity to form stable
covalently bonded molecular networks. Carbonates, metalloboranes,
phosphacarboranes, and other families comprise thousands of compounds.
Costs
Crystalline boron (99%) costs about $5/g. Amorphous boron costs
about $2/g.
Handling
Elemental boron and the borates are not considered to be toxic,
and they do not require special care in handling. However, some of the more
exotic boron hydrogen compounds are definitely toxic and do require care.