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(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 and by Gay-Lussac and
The element is not found free in nature, but occurs as orthoboric acid usually found 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 ore rasorite (kernite) and tincal (borax ore). Both of
these ores are found in the Mojave Desert. Tincal is the most important source of boron
from the Mojave. 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 electrically 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.
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.
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.
Crystalline boron (99%) costs about $5/g. Amorphous boron costs about $2/g.
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.
Sources: CRC Handbook of Chemistry
and Physics and the American Chemical Society.