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COBALT
by Jonathan Buhalis

History

cobalt blue glass, A. Jonathan BuhalisCobalt is a hard gray metal related to iron and nickel. Compounds containing cobalt have been used for centuries to color glass (hence "cobalt blue"). Such compounds are found in ceramic and glass from ancient Egypt, Persia, and China.

In mining, cobalt occurs with copper and nickel ores. German miners in medieval times would find that nickel from such ores was brittle and useless. Worse, cobalt minerals in Europe also contain arsenic. Consequently, other apparently valuable ores would give off poisonous vapors when smelted. These misfortunes were attributed to the evil mining spirits called kobolds.

The new metal was finally isolated in 1735 by Swedish chemist George Brandt. The name adopted, "cobalt", was derived from "kobold". Cobalt was still used primarily as a coloring agent until the 20th century. Since the 1930s, it is a key ingredient of tough metals including steel superalloys.

Mining and Production

Cobalt is found as a minor component in copper, nickel, and sometimes silver ore. The greatest concentration of cobalt is in central Africa, in a formation that straddles Democratic Congo (former Zaire) and Zambia. Cobalt is also mined in Canada, Australia, and other places.

Cobalt from copper ore is obtained by roasting and leeching with sulphuric acid. When nickel ore is smelted, the cobalt remains with the chemically similar nickel. It is then leeched out using acid. In either case, cobalt can be precipitated from the acid relatively easily.

Outside of Africa, cobalt is only 1% or less of the metal content of ores (up to 4% in DR Congo). Therefore, the production rate tends to follow the market demand for copper and nickel, allowing for the several-year lag built into mining.

Refining of cobalt is an energy-intensive process that doesn’t necessarily take place near the mine. Norway, Finland, and China are all noteworthy as big refining centers. Only recently has capacity for some ore processing started to expand in DR Congo, funded primarily by China.

Properties and Uses

The traditional role of cobalt in blue coloring remains. Cobalt compounds ranging from light blue to deep purple are used to color glass, pottery, and ceramic. Other chemical uses include cobalt salts that accelerate drying of paint, cobalt metal oxides as a catalyst to remove sulphur from oil and gas, and cobalt in various strong plastics.

One such strong plastic is the backing material for video tape. Because cobalt has magnetic properties, it is also introduced into the iron oxide on the front side of the tape. The first non-steel permanent magnet, alnico (aluminum-nickel-cobalt), was invented about 70 years ago and used for decades in superior industrial magnets. Alnico was replaced by various samarium-cobalt alloys in the 1970s. Since then, technology has moved on to other supermagnet designs. Where strength or high temperature is an issue, such as in rotating generators, however, cobalt steel is still a favorite choice. Cobalt remains magnetic to a higher temperature than any other material.

Cobalt can be found in most rechargeable batteries. In NiCad (nickel-cadmium batteries), about 1% cobalt is added to one electrode. Nickel-metal-hydride batteries incorporate cobalt into both electrodes (in different forms, they have different chemistries). The more recent lithium ion batteries contain one lithium carbide electrode (LiC6) and one that is a lithium cobalt compound (LiCoO2). By weight, cobalt is a significant fraction of the battery.

Finally, the cutting edge of technology often demands cobalt for use in superalloy steels. These applications include turbine blades and jet engines. Nickel has been a component of the strongest steel alloys for over a hundred years, but cobalt made an appearance after World War II. Now, various recipes for high-temperature high-performance steel exist with different amounts of cobalt, nickel, chromium, and trace elements.
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Content by Jonathan Buhalis
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