52 Chromium


Natural rubies are corundum (aluminum oxide) due to chromium (III) ions A red-colored artificial ruby may also be achieved by doping chromium(III) into artificial corundum crystals, thus making chromium a requirement for making synthetic rubies. Such a synthetic ruby crystal was the basis for the first laser, produced in 1960, which relied on stimulated emission of light from the chromium atoms in such a crystal. Primer paint containing hexavalent chromium is still widely used for aerospace and automobile refinishing applications.

Chromium deficiency, involving a lack of Cr(III) in the body. Some studies suggest that the biologically active form of chromium (III) in an oligopeptide called low-molecular-weight chromium-binding substance (LMWC), which might play a role in the insulin signaling pathway.
The acute toxicity of chromium(VI) is due to its strong oxidative properties. After it reaches the bloodstream, it damages the kidneys, the liver and blood cells through oxidation reactions. Hemolysis, renal, and liver failure result. The carcinogenicity of chromate dust has been known for a long time, and in 1890 the first publication described the elevated cancer risk of workers in a chromate dye company.Three mechanisms have been proposed to describe the genotoxicity of chromium(VI). The first mechanism includes highly reactive hydroxyl radicals and other reactive radicals which are by products of the reduction of chromium(VI) to chromium(III). The second process includes the direct binding of chromium(V), produced by reduction in the cell, and chromium(IV) compounds to the DNA. The last mechanism attributed the genotoxicity to the binding to the DNA of the end product of the chromium(III) reduction.
Production use of Chromium

4 FeCr2O4 + 8 Na2CO3 + 7 O2 → 8 Na2CrO4 + 2 Fe2O3 + 8 CO2
2 Na2CrO4 + H2SO4 → Na2Cr2O7 + Na2SO4 + H2O
Na2Cr2O7 + 2 C → Cr2O3 + Na2CO3 + CO
Cr2O3 + 2 Al → Al2O3 + 2 Cr

Physical properties
Phase (at STP) solid
Melting point 2180 K ​(1907 °C, ​3465 °F)
Boiling point 2944 K ​(2671 °C, ​4840 °F)
Density (near r.t.) 7.19 g/cm3
when liquid (at m.p.) 6.3 g/cm3
Heat of fusion 21.0 kJ/mol
Heat of vaporization 347 kJ/mol
Atomic number (Z) 24
Group, period group 6, period 4
Block d-block
Transition metal
Electron configuration [Ar] 3d5 4s1
Electrons per shell
2, 8, 13, 1
Piece of chromium produced with aluminothermic reaction
Chromium, remelted in a horizontal arc zone-refiner, showing large visible crystal grains

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