Boron B

Discovery

Borax, a sodium borate mineral, was traded for centuries as a flux for soldering and for glazes; it reached Europe from Tibet and Central Asia via trade routes. Nobody knew it contained an undiscovered element until the chemical revolution of the early nineteenth century.

In 1808 two teams isolated impure boron almost simultaneously. In Paris, Joseph Louis Gay-Lussac and Louis Jacques Thénard reduced boric acid with potassium, and in London Humphry Davy did similar work, first by electrolysis and then by reduction with potassium. None of them obtained pure material. Relatively pure boron was not produced until the early twentieth century, notably by the American chemist Ezekiel Weintraub in 1909.

Origin of the name

The name is derived from borax, which in turn comes from the Arabic buraq and ultimately from Persian, combined with the ending of carbon, because boron resembles carbon in some respects. The symbol is B.

Main uses

• Glass: borosilicate glass resists thermal shock, which is why it is used for laboratory ware, oven dishes and telescope mirrors.
• Fibreglass and insulation: boron compounds are added to glass fibres for textiles and building insulation.
• Magnets: neodymium–iron–boron magnets are the strongest permanent magnets in common use, found in motors, headphones and hard drives.
• Hard materials: boron carbide is used in body armour and abrasives, and cubic boron nitride cuts hardened steel.
• Nuclear safety: boron-rich control rods and dissolved boric acid absorb neutrons in reactors.
• Agriculture and cleaning: borates serve as fertiliser additives, detergents and wood preservatives.

Isotopes

Natural boron is a mixture of two stable isotopes: about 20 percent boron-10 and 80 percent boron-11. Boron-10 has a very large appetite for slow neutrons, which is the basis of its use in reactor control, radiation shielding and neutron detectors. The same property is exploited in boron neutron capture therapy, an experimental cancer treatment in which a boron-10 drug accumulates in tumour cells and is then irradiated with neutrons. Radioactive isotopes of boron are all very short-lived, with half-lives under a second.

In everyday life

Plants need small amounts of boron for cell walls and reproduction, and deficiency can cause problems in crops such as beets and apples. In people boron occurs in fruit, nuts and vegetables, though no essential role has been firmly established.

Boric acid and borax are mildly toxic if swallowed in quantity and are kept away from children and pets. Boron compounds also give fireworks a green colour.