(Kobald, from
the German, goblin or evil spirit, cobalos,
Greek, mine) Discovered by Brandt about 1735.
Cobalt occurs in the mineral 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. Cobalt is a brittle, hard
metal, closely 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.
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. The salts
have been used for centuries for the production
of 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. The cobalt amines are
of interest; the oxide and the nitrate are
important. 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. Cobalt-60, an artificial
isotope, is an important gamma ray source, and is
extensively used as a tracer and a
radiotherapeutic agent. Single compact sources of
Cobalt-60 vary from about $1 to $10/curie,
depending on quantity and specific activity.
Exposure to cobalt (metal fumes and dust) should
be limited to 0.05 mg/m^3 (8-hour time-weighted
average 40-hour week).
