An image reflecting the importance of boron as an essential mineral for plants. The tree and its strange metallic foliage ‘grow’ from a ‘pure’ dark powdered cone of the element.

Fact Box

Uses

Amorphous boron is used as a rocket fuel igniter and in pyrotechnic flares. It gives the flares a distinctive green colour.

The most important compounds of boron are boric (or boracic) acid, borax (sodium borate) and boric oxide. These can be found in eye drops, mild antiseptics, washing powders and tile glazes. Borax used to be used to make bleach and as a food preservative.

Boric oxide is also commonly used in the manufacture of borosilicate glass (Pyrex). It makes the glass tough and heat resistant. Fibreglass textiles and insulation are made from borosilcate glass.

Sodium octaborate is a flame retardant.

The isotope boron-10 is good at absorbing neutrons. This means it can be used to regulate nuclear reactors. It also has a role in instruments used to detect neutrons.

History

For centuries the only source of borax, Na2B2O5(OH)4, was the crystallized deposits of Lake Yamdok Cho, in Tibet. It was used as a flux used by goldsmiths.

In 1808, Louis-Josef Gay-Lussac and Louis-Jacques Thénard working in Paris, and Sir Humphry Davy in London, independently extracted boron by heating borax with potassium metal. In fact, neither had produced the pure element which is almost impossible to obtain. A purer type of boron was isolated in 1892 by Henri Moissan. Eventually, E. Weintraub in the USA produced totally pure boron by sparking a mixture of boron chloride, BCl3 vapour, and hydrogen. The material so obtained boron was found to have very different properties to those previously reported.