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History

In 1761, Johann Gottlob Lehmann found an ore orange red in the mountains of the the Ural, which it named the red lead of Siberia . This ore though badly identified like a lead compound with Selenium and Iron, was in fact a Chromate of lead (PbCrO₄).

In 1770, Peter Simon Pallas visited the same site that Lehmann and found a red “lead” ore, which was very quickly used as pigment in paintings. The use of Siberian red lead as pigment developed quickly and the yellow shining obtained starting from Crocoïte became a color with the mode very.

In 1797, Nicolas Louis Vauquelin accepted some ore samples of crocoïte. It was then able to produce oxide chromium (CrO₃) in addition of the Hydrochloric acid with chromite. In 1798, Vauquelin discovered that it could isolate metal chromium by heating oxide in a furnace with coal. It was also able to detect chromium traces in certain invaluable stones like the rubies or emeralds. It as showed with his Laugier colleague as one found some in almost all the meteorites.

During the 18th century, chromium was mainly used like pigment in painting. Nowadays, one mainly uses it (to 85%) in metal alloys, the remainder being it in industrial chemistry.

Properties

Chromium belongs to the series of the Métaux of transition. It is a hard metal, of a color steel-silver plated gray. It resists corrosion and tarnishing.

The most common states of oxidation of chromium are +2, +3, and +6; +3 being most stable. +4 and +5 are relatively rare. The compounds of the chromium of state of oxidation +6 (hexavalent Chromium) as the Chlorochromate of pyridinium are powerful Oxydant S. chromium in its state of oxidation +2 is a reducer.

Composed

The potassium dichromate is oxidizing powerful and used for the cleaning of the glassmaking of laboratory so eliminating any organic trace.

Green chromium is composed of chromium oxide Cr₂O₃, it is used in painting on enamel.

Yellow chromium, PbCrO₄, are a yellow pigment shining used in painting.

Use

Uses of chromium:

In Metallurgy, to improve the corrosion resistance, and to add one finished shining:

Like alloy component (e.g. in the stainless steel)
in the plating with chromium (Chromage)
in anodic aluminum

Like catalyst in certain reactions of hydrogenation, but also in the form tricarbonylée like grouping activator of a benzene, which allows many chemical conversions to give rise to natural compounds.
chromium salts are used to give a green color to glass
the chromates and the oxides are used in the dyes and paintings. At the beginning of the 19th century the lead chromate, of a sharp yellow, quite opaque and resistant to the light, is used like Pigment, its colors goes from the green yellow to the orange yellow but has the disadvantage of being toxic.
In Medicine, chromium can be used against the Diabète, but its use is discussed.

Biological role

Trivalent chromium is a essential Oligo-élément for the metabolism of sugar at the human being. A chromium deficiency can affect the potential of the Insuline to control the sugar level in the organization.

Chromium does not have, like other trace elements, summer found in a protein with a biological activity, and thus its mechanism of action in the regulation of sugar remains unexplained.

Layers

Chromium is extracted from the mines in the form of ore of Chromite FeCr₂O₄. Chromium is obtained commercially by heating the ore in the presence of Aluminum or of Silicium.

About half of the chromite ore is produced in South Africa. The Kazakhstan, the India and the Turkey are also important producers. One finds chromite deposits important, but geographically concentrated in Kazakhstan and in South Africa.

Roughly 15 million tons of chromite was produced in 2000, and was converted into about 4 million tons of ferro-chromium for a commercial value of 2,5 billion dollars.

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