The cobalt of electronic structure [Ar] 4s2 3d7 is the second element of
the eighth secondary group, this transition metal is part of the iron group. The
simple cobalt body has physical properties quite similar to those of iron and
nickel. From a chemical point of view, it is less reactive than iron. Cobalt is
also an element of group 9, of which the first three Co, Rh and Ir constitute
the group of cobalt.
Natural cobalt minerals, in the form of paints, enamels or varnishes, have been
used since ancient times, in particular around 2600 BC. AD in Egypt or in the
civilizations of Mesopotamia which gave birth to Babylon. So the archaeologist
finds blue decorations on pottery or terracotta dishes. Glass beads tinted with
cobalt blue are common around 2200 BC. AD in present-day Iran. These techniques
for coloring the glass of an intense blue or obtaining enamels are common in the
Mediterranean world from the second century BC. They are generally silicates and
/ or aluminates of cobalt and potassium, formerly called safre or smalt
recognized in Western Europe in certain luxury Romanesque stained glass windows,
or later of cobalt oxides called "cobalt blue" .
Das Kobold or das Kobalt is the traditional name that the Saxon miners in search
of precious metals attribute to these deceptive derivatives. These generally
sulfur and / or arsenic ores too rich in cobalt give metallurgical treatment
smelly gases or toxic oxide fumes based on arsenic trioxide, poisonous fumes
and, if heated excessively, a flow of molten material , brittle when cold,
speiss or hard and brittle metals with high sulfur or arsenic contents that
metallurgists can neither process nor forge. The miners then believed the mining
district bewitched by evil and falsifying dwarfs, facetious and thieves, the
kobolds of bluish appearance and deadly which had stolen the precious metal,
very often copper, and replaced by this improper and confused material a.
These worthless minerals or their by-products are named in vernacular German by
a neutral noun Kobelet, Kobolt or Kobelt. Paracelsus mentions the cobolt in 1522
with a more Latin script. The Latin coboltum or cobaltum then established itself
in learned Europe. Note that the technical term cobolt also designated in French
the metallic arsenic reduced to powder b.
Until the eighteenth century and the following century, the term "cobalt" and
its cobolt variant, denotes the ore or its residue which was formerly mostly
unusable. However, from the seventeenth century with the Germanic fashion of
Blaufarbung, that is to say, coloring in blue, cobalt ore finds greater utility
because men of the chemical art and glassmaker manufacture with this waste of
'excellent blue pigments, in particular the smalt of glassmakers or ceramists,
the "blue of charron pencils" ... Georg Brandt, specialist in arsenic minerals,
strives to recognize the specific element underlying its ores or - mining
products between 1733 and 1738.
In Venice, the master glassmakers of Murano asked the Venice dwarfs to source
cobalt ore and produce their famous works tinted in Murano blue. The dwarves
brought this ore from mines north of the Alps, where they were decked out with
the term kobold (goblin, or goblin, supernatural creature) 8.
In 1735, the Swedish chemist Georg Brandt (1694-1768) claims to have extracted
from this mineral a reddish, hard and brittle white "semi-metal", in reality
samples of impure metal which he calls "cobalt" 9. In 1745, he demonstrated that
cobalt was the cause of the blue color that cobalt ore imparted to glasses10.
This clarification is not useless because the scholarly community most often
attributed the color blue either to bismuth, or to iron and arsenic11.
But most of this work goes almost unnoticed. It was not until 1780 that Torbern
Olof Bergman prepared pure metal and belatedly recognized the pioneering role of
Georg Brandt in the discovery of an element, then confirmed. In 1798, chemists
note that the ammoniacal solutions of cobalt chloride CoCl2 allow orange
crystals stable to heat to precipitate, up to 180 ¡ã C, a body which transforms
into another darker stable body beyond this temperature.
Its main minerals are in the form of arsenides, arseniosulphides, sulfides and
oxides, arsenates. Cobalt contents are generally low in these specific deposits,
but they are sometimes enriched by geochemical processes or concentrated by
natural erosion.
The main constituent minerals of these ores are cubic smaltite CoAs2, formerly
smaltine, orthorhombic cobaltite CoAsS, formerly cobaltine or "gray cobalt", or
oxidation products such as erythritis Co3 (AsO4) 2 ¡¤ 8H2O, formerly "flower
cobalt ". Let us also cite the orthorhombic CoAs modderite, the CoAs2
orthorhombic safflorite and the CoAs2 monoclinic clinosafflorite, the CoAs3-x
cubic skutterudite, the CoAsS monoclinic alloclasite .... Smaltines generically
designated arsenic cobalt ores, while cobaltins corresponded to sulfo-arsenic
ores.
Skutterudite crystals, Ouarzazate, Morocco
Its extraction is mainly done from copper or nickel ores, and even lead ores.
Carrolite CuS.Co2S3 is a mixed sulfide of copper and cobalt.
The most exploited or most promising minerals are in Africa, in particular in
the Democratic Republic of the Congo which produces 65% of world production14,
in Zambia and Morocco, in North America, for example in Canada and the United
States, but also in Russia, Australia and New Caledonia, formerly known in the
19th century for its cobalt-rich manganese deposits.
The concentrated ores from the old gray cobalt, smaltine and cobaltine
exploitations, or today the rare sulphide or arsenic ores, allow by air roasting
to obtain cobalt oxide, in a generally hydrated form called asbolane. This is
reduced either by hydrogen gas or by charcoal, made of cobalt metal.
During the 1990s, the cobalt-bearing sulphide ores were to provide a content of
0.1 to 0.03% by mass. But most of the cobalt is a byproduct of the copper mining
industry. Enrichment is carried out by flotation using detergents.
cobalt obtained by electrolysis
If the extraction of sulphides goes through pyrolysis, the extraction of oxides
uses the hydrometallurgy processes. The separation of copper and cobalt is
carried out during the electrolysis processes. 500 tonnes of minerals yield one
tonne of cobalt. Annual cobalt production in the early 1990s was around 40,000
tonnes.
Physical and chemical properties of the single metal body, preparation and
alloys
Cobalt pieces in test tube
The simple body is a bright white, steel gray or silver white metal with red
reflection, quite brittle, not very malleable, with a density between 8.8 and
8.9 at 25 ¡ã C and a Mohs hardness of around 5.5 g. It is harder and more brittle
than iron. But pure metal is sufficiently ductile and malleable to be able to be
forged, hot and cold rolled, drawn into wire.
There are two allotropic varieties of cobalt. Co¦Á is a metallic crystal with a
hexagonal mesh, with the parameters a = 2.507 Å and c = 4.069 Å, with a density
of 8.9 at 20 ¡ã C, the most stable at room temperature, and Co¦Â with a cubic
face-centered mesh, a = 3.544 Å, less compact and significantly less stable
below 400 ¡ã C. The phase transition between Co¦Á and Co¦Â with volume increase of
0.3% takes place at 417 ¡ã C ¡À 7 ¡ã C, it is sensitive to certain specific
impurities15. But this transition is slow, and there is quite commonly a mixture
of the two varieties over a wide range of temperatures, which explains the
slight variations in physical properties of the cobalt metal material. Co¦Â is a
metastable form at room temperature, however it can be obtained by quenching or
by certain electrolysis processes. It is likely that the delayed transition
plays a role in the bursting of certain cathodic deposits of cobalt by
electrolysis.
This body is ferromagnetic (capable of retaining a strong magnetization) at
ordinary temperature. The Curie point is around 1,121 ¡ã C. The permeability is
around 68, or two thirds of that of iron, with a maximum of 245. The coercive
field is around 707 A / m.
The electrical conductivity is 26% IACS, that is to say a little quarter that of
pure copper.
It is not as fusible as iron. It melts above 1490 ¡ã C, pure at 1495 ¡ã C. It
boils around 2,927 ¡ã C, in practice between 2,600 ¡ã C and 3,100 ¡ã C
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copper aluminum lead Zinc tin nickel iron
magnesium bismuth manganese chromium cobalt titanium
Tungsten vanadium niobium indium molybdenum antimony
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