Chromium ( Cr )

Material Information

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General Description:

Discovered in 1780 by N.L. Vanquelin in Paris, France.

Chromium is a bright, blue/white metal with excellent corrosion resistance. It is obtained by the aluminum reduction of Cr₂O₃, the source of which is chromite, a double oxide of chromium and iron which generally also contains magnesium. It has an abundance within the earth's crust of approximately 100 ppm. Chromium is soluble in HCl and H₂SO₄, but not in H₃PO₄, HNO₃ or HClO₄ due to the formation of a stable and insoluble oxide layer on its surface; this, along with its hardness, has been used to advantage in the chromium plating of steel which has good corrosion resistance. Chromium is alloyed with nickel in the manufacture of heat resisting alloys, and with iron, or nickel and iron, to produce stainless and heat resistant steels.

Chromium is an important trace element for humans as it assists in the manufacture of glucose.

Atomic Properties

Atomic number	24
Atomic radius - Goldschmidt ( nm )	0.128
Atomic weight ( amu )	51.996
Crystal structure	Body centred cubic
Electronic structure	Ar 3d⁵ 4s¹
Ionization potential	No.	eV
	1	6.77
	2	16.5
	3	31.0
	4	49.1
	5	69.3
	6	90.6
Natural isotope distribution	Mass No.	%
	50	4.35
	52	83.79
	53	9.50
	54	2.36
Photo-electric work function ( eV )	4.4
Thermal neutron absorption cross-section ( Barns )	3.1
Valences shown	2, 3, 6

Electrical Properties

Electrical resistivity @20C ( µOhmcm )	13.2
Temperature coefficient @0-100C ( K^-¹ )	0.00214

Mechanical Properties

Material condition	Soft	Hard	Polycrystalline
Bulk modulus ( GPa )			160.2
Hardness - Vickers	130	220
Poisson's ratio			0.21
Tensile modulus ( GPa )			279
Tensile strength ( MPa )	103	689

Physical Properties

Boiling point ( C )	2672
Density @20C ( g cm^-³ )	7.1
Melting point ( C )	1857

Thermal Properties

Coefficient of thermal expansion @0-100C ( x10^-⁶ K^-¹ )	6.5
Latent heat of evaporation ( J g^-¹ )	6580
Latent heat of fusion ( J g^-¹ )	260
Specific heat @25C ( J K^-¹ kg^-¹ )	518
Thermal conductivity @0-100C ( W m^-¹ K^-¹ )	94

All information and technical data are given as a guide only. Although every effort has been made to ensure that the information is correct, no warranty is given as to its completeness or accuracy.

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