Cobalt material

COBALT AND COBALT ALLOYS. A white metal, Co, resembling nickel
but with a bluish tinge instead of the yellow of nickel. It is rarer and
costlier than nickel, and its price has varied widely in recent years.
Although allied to nickel, it has distinctive differences. It is more
active chemically than nickel. It is dissolved by dilute sulfuric, nitric,
or hydrochloric acid and is attacked slowly by alkalies. The oxidation
rate of pure cobalt is 25 times that of nickel. Its power of whitening
copper alloys is inferior to that of nickel, but small amounts in nickelcopper
alloys will neutralize the yellowish tinge of the nickel and
make them whiter. The metal is diamagnetic like nickel, but has

nearly 3 times the maximum permeability. Like tungsten, it imparts
red-hardness to tool steels. It also hardens alloys to a greater extent
than nickel, especially in the presence of carbon, and can form more
chemical compounds in alloys than nickel.
Cobalt has a specific gravity of 8.756, a melting point of 2723°F
(1495°C), Brinell hardness 85, and an electrical conductivity about
16% that of copper. The ultimate tensile strength of pure cast cobalt
is 34,000 lb/in2 (234 MPa), but with 0.25% carbon it is increased to
62,000 lb/in2 (427 MPa). Strength can be increased slightly by annealing
and appreciably by swaging or zone refining. The metal is used in
tool-steel cutters, in magnet alloys, in high-permeability alloys, and as
a catalyst; and its compounds are used as pigments and for producing
many chemicals. The metal has two forms: a close-packed hexagonal
COBOLT AND COBALT ALLOYS 243
crystal form, which is stable below 782°F (417°C), and a cubic form
stable at higher temperatures to the melting point. Cobalt has
valences of 2 and 3, while nickel has only a valence of 2.
The natural cobalt is cobalt 59, which is stable and nonradioactive,
but the other isotopes from 54 to 64 are all radioactive, emitting beta
and gamma rays. Most have very short life, except cobalt 57 which
has a half-life of 270 days, cobalt 56 with a half-life of 80 days, and
cobalt 58 with a half-life of 72 days. Cobalt 60, with a half-life of 5.3
years, is used for radiographic inspection. It is also used for irradiating
plastics and as a catalyst for the sulfonation of paraffin oils, since
gamma rays cause the reaction of sulfur dioxide and liquid paraffin.
Cobalt 60 emits gamma rays of 1.1- to 1.3-MeV energy, which gives
high penetration for irradiation. The decay loss in a year is about
12%, the cobalt changing to nickel.

From the cobalt materials handbook which you should buy, if your are in materials engineering.