Chrom (Cr)

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Chrom 24Cr51.996

1780 von Nicholas Louis Vauquelin in Paris, Frankreich, entdeckt und dargestellt.

[Griechich: chroma = Farbe]
  French: chrome
  English: chromium
  Italian: cromo
  Spanish: cromo

Beschreibung: Hartes, blauweißes Metall. Löslich in HCl und H2SO4, aber nicht in HNO3, H3PO4 oder HClO4, da Passivierung erfolgt. Hauptsächlich verwendet für Legierungen, Verchromungen und Pulvermetallurgie.

Chrom single crystal properties

 

State: Single crystal
Crystal structure: bcc
Production method: Floating zone
Standard size: diameter 6-10mm
thickness 1-2mm
Orientation: (100), (110) and (111)
Orientation accuracy: <2°, <1°, <0.4° or <0.1d°
Polishing: as cut, one or two sides polished
Roughness of surface: <0.03 µm
Purity: 99.999%

 

Typical analysis (ppm): Ag < 0.10
C 10.0
Ca 0.01
Cd < 0.10
Cl 1.60
Co < 0.10
Cu < 0.10
Fe 18.0
H < 2.00
Mg < 0.10
Mn < 0.10
Mo < 0.20
N < 5.00
Na < 0.10
Ni 3.00
O < 5.00
Si 4.80

Cr balance

 

 

Further Materials properties

 

Crystal structure: (cell dimensions/pm), space group, b.c.c. (a=288.46), Im3m
X-ray diffractions mass absorption coefficients: CuKa 260 (µ/r) / cm2g-1
MoKa 31.1 (µ/r) / cm2g-1
Neutron scattering length: 0.3635 b/10-12 cm
Thermal neutron capture cross-section: 3.1 sa / barns
Density: 7.19 kg/m-3
Melting point: 1856.85 ±20 °C / 2130 ±20 °K
Boiling point: 2671.85 °C / 2945 °K
Molar volume: 7.23 cm3
Thermal conductivity: 93.7 [300 K] Wm-1K-1
Coefficient of linear thermal expansion: 6.2 x 10-6 K-1
Electrical resistivity: 12.7 x 10-8 [293 K] Wm
Mass magnetic susceptibility: +4.45 x 10-9(s) kg-1m3
Young's modulus: 279 GPa
Rigidity modulus: 115.3 GPa
Bulk modulus: 160.2 GPa
Poisson's ratio: 0.21 GPa
Radi: Cr4+ 56; Cr3+ 64; Cr2+ 84; atomic 1253
Electronegativity: 1.66 (Pauling); 1.56 (Allred); 3.72 eV (absolute)
Effective nuclear charge: 3.45 (Slater); 5.13 (Clementi); 6.92 (Froese-Fischer)
Number of Isotopes (incl. nuclear isomers): 13
Isotope mass range: 45 -> 57

 

 

Biological data

 

Biological role: Essential to some species, including humans; it is also stimulatory.
Toxicity  
Toxic intake: 200 g
Lethal intake: metal, oral, human = 70 mg kg-1. LD50 (acetate, oral, rat) = 11000 mg kg-1
Hazards: Chromium is a human poison by ingestion, it is also a suspected carcinogen. Chromates have a corrosive action on skin an tissue
Level in humans  
Blood: 0.006 - 0.11 mg dm-3
Bone: 0.1 - 0.33 ppm
Liver: 0.02 - 3.3 ppm
Muscle: 0.024 - 0.84 ppm
Daily dietary intake: 0.01 - 1.2 mg
Total mass of element in average
[70 kg] person:		 14 mg

 

Geological data

 

Minerals:Many minerals are known, and aluminium is present in many other minerals
MineralFormulaDensityHardnessCrystal apperance
Chromite  FeCr2O4  4.7  5.5  cub., compacted, met. black
Chrocoite  PbCrO4  6.0  2.5 - 3  mon., adam./vit. red-orange

 

Chief ore: chromite
World production: 20000 tonnes/year (chromium metal); 9.6 x 106 (chromite ore)
Main mining areas: Turkey, South Africa, Zimbabwe, Rusia, Philippines.
Reserves: 1 x 109 tonnes
Specimen: available as chips, chunks, crystallites or powder. Safe.

 

Abundances  
Sun: 5.13 x 105 (relative to H = 1 x 1023)
Earth's crust: c. 100 ppm
Seawater:  
Atlantic surface: 1.8 x 10-4 ppm
Atlantic deep: 2.3 x 10-4 ppm
Pacific surface: 1.5 x 10-4 ppm
Pacific deep: 2.5 x 10-4 ppm
Residence time: 10000 years
Classification: recycled
Oxidation state: VI

 

Other sizes and specifications on request


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