|
|
Atomic Number: |
27 |
Melting Point: | 1495 ºC | |
| Atomic Symbol: | Co | Boiling Point: | 2927 ºC | ||
| Atomic Weight: | 58.9332 amu | Density: | 8900
kg/m 3 |
||
| Atomic Radius: |
124.3 pm |
Oxidation States: | 3, 2 | ||
| Covalent Radius: | 126 pm | Electron Configuration: | [Ar]4s23d7 | ||
| van der Waals Radius: |
-- |
State of Matter: | solid (ferromagnetic) |
(Ger. Kobald: goblin or evil spirit; Gr. cobalos: mine) Brandt discovered cobalt in about 1735. He was able to show that cobalt was the source of the blue color in glasses, which previously had been attributed to the bismuth found with cobalt.
Cobalt is a brittle, hard metal, resembling iron and nickel in appearance. It has a metallic permeability of about two thirds that of iron. Cobalt tends to exist as a mixture of two allotropes over a wide temperature range. The transformation is sluggish and accounts in part for the wide variation in reported data on physical properties of cobalt.
Due to the various oxidation states, there is an abundant number of compounds. Oxides are antiferromagnetic at low temperature.
Cobalt occurs in the minerals cobaltite, smaltite, and erythrite, and is often associated with nickel , silver , lead , copper , and iron ores, from which it is most frequently obtained as a by-product. It is also present in meteorites.
Important ore deposits are found in Zaire, Morocco, and Canada. The U.S. Geological Survey has announced that the bottom of the north central Pacific Ocean may have cobalt-rich deposits at relatively shallow depths in water close to the the Hawaiian Islands and other U.S. Pacific territories.
It is alloyed with iron, nickel and other metals to make Alnico, an alloy of unusual magnetic strength with many important uses. Stellite alloys, containing cobalt, chromium , and tungsten , are used for high-speed, heavy-duty, high temperature cutting tools, and for dies.
Cobalt is also used in other magnetic steels and stainless steels, and in alloys used in jet turbines and gas turbine generators. The metal is used in electroplating because of its appearance, hardness, and resistance to oxidation.
Cobalt salts have been used for centuries to produce brilliant and permanent blue colors in porcelain, glass, pottery, tiles, and enamels. It is the principal ingredient in Sevre's and Thenard's blue. A solution of the chloride is used as a sympathetic ink. Cobalt carefully used in the form of the chloride, sulfate, acetate, or nitrate has been found effective in correcting a certain mineral deficiency disease in animals.
Soils should contain 0.13 to 0.30 ppm of cobalt for proper animal nutrition.
Naturally occurring cobalt is composed of 1 stable isotope, 59-Co. 22 radioisotopes have been characterized with the most stable being 60Co. Cobalt-60, an artificial isotope, is an important gamma ray source, and is extensively used as a tracer and a radiotherapeutic agent.
Powdered cobalt in metal form is a fire hazard. Cobalt compounds should be handled with care due to cobalt's slight toxicity. Exposure to cobalt (metal fumes and dust) should be limited to 0.05 mg/m3 (8-hour time-weighted average 40-hour week).
Cobalt-60 is a powerful gamma ray emitter and exposure to 60Co is therefore a cancer risk. Ingestion of 60Co will lead to incorporation of some cobalt into tissues, which is released very slowly. Cobalt-60 is a risk factor in a nuclear confrontation because neutron emissions will convert iron into this isotope.
