Cobalt Co

Discovery

Cobalt compounds were used long before anyone knew the element existed. Egyptian glassmakers, Persian potters and, later, the makers of Chinese blue-and-white porcelain all used cobalt-bearing minerals to produce intense blue colours. Most people assumed the colour came from bismuth or other known substances.

In the 1730s the Swedish chemist Georg Brandt investigated the ores used to make blue glass and showed that the colour came from a previously unknown metal, not from bismuth as many believed. His discovery, usually dated to 1735, made cobalt the first metal to be discovered by a known person since antiquity. Brandt also showed that the poisonous, garlic-smelling fumes from these ores came from arsenic rather than from the new metal. Torbern Bergman confirmed in 1780 that cobalt was a distinct element.

Origin of the name

The name comes from the German Kobold, a mischievous goblin of mining folklore. Silver miners in the Harz and Erzgebirge mountains blamed goblins for ores that looked promising but yielded no useful metal when smelted and released toxic arsenic fumes. The symbol is Co.

Main uses

• Batteries: cobalt stabilises the layered cathodes of many lithium-ion batteries in phones, laptops and electric vehicles.
• Superalloys: cobalt-based and cobalt-containing alloys keep their strength in the hot sections of jet engines and gas turbines.
• Cutting tools: cobalt binds tungsten carbide grains together in hard-metal drill bits and saw blades.
• Magnets: samarium–cobalt and Alnico magnets work at high temperatures.
• Pigments and catalysts: cobalt blue colours ceramics and glass, and cobalt catalysts are used in oil refining and making synthetic fuels.

Isotopes

Cobalt has one stable isotope, cobalt-59. The radioactive cobalt-60, made by exposing cobalt-59 to neutrons, has a half-life of about 5.27 years and emits penetrating gamma rays. It is used in radiotherapy machines such as the Gamma Knife, to sterilise medical supplies, to irradiate food and to inspect welds. Cobalt-57 (about 272 days) serves as a calibration source and in Mössbauer spectroscopy.

In everyday life

Humans need cobalt only in the form of vitamin B12, which is essential for making red blood cells and maintaining nerves. Animal foods supply B12, so strict vegans are advised to take supplements. Grazing animals such as sheep can suffer from cobalt deficiency where soils are poor.

Inhaling cobalt-containing dust in hard-metal industries can harm the lungs. A large share of the world's cobalt is mined in the Democratic Republic of the Congo, where working conditions in informal mines have raised serious concerns.