Nomenclature
CAS number: 7440-47-3
Description and references
Cr; at. wt 51.9961; at. no. 24; valences 1-6.
Group VIB (6). Four naturally occurring isotopes: 50 (4.31%); 52
(83.76%); 53 (9.55%); 54 (2.38%). Artificial radioactive isotopes:
45-49; 51; 55-57; longest-lived isotope is 51Cr (T 1/2 27.704 days) prepd by (n,γ) reaction from 50Cr.
Abundance in earth's crust: 122 ppm. Isoln from crocoite (PbCrO4): L. N. Vauquelin, J.
Mines 6, ser. 1, 737 (1787); idem, Ann. 70, 70 (1809).
Commercial sources obtained from chrome ore, chromite (FeO.Cr2O3). Reviews of chromium,
its alloys and compds: ACS Monograph Series no. 132, entitled “Chromium,” M. J. Udy, Ed. (Reinhold,
New York, 1956) vol. 1, 433 pp; vol. 2, 402
pp; C. L. Rollinson, “Chromium, Molybdenum and Tungsten” in Comprehensive Inorganic Chemistry vol.
3, J. C. Bailar, Jr. et al., Eds. (Pergamon Press,
Oxford, 1973) pp 623-700; Chemistry of the
Elements, N. N. Greenwood, A. Earnshaw, Eds. (Pergamon
Press, New York, 1984) pp 1167-1210; J. H. Westbrook in Kirk-Othmer Encyclopedia of Chemical Technology vol. 6 (Wiley-Interscience, New York, 4th ed., 1993)
pp 228-263; B. J. Page, G. W. Loar, ibid. pp 263-311.
Review of biological function of the Cr(III) ion as essential trace
element: Mertz, Physiol. Rev. 49, 163-239 (1969). Review of carcinogenic risk: IARC Monographs 2, 100-125 (1973); ibid. 23, 205-323 (1980); of metabolism
and toxicity: M. D. Cohen et al., Crit. Rev. Toxicol. 23, 255-281 (1993); of
toxicology and human exposure: Toxicological
Profile for Chromium (PB2000-108022, 2000) 461 pp. Books:
Chromium: Metabolism and Toxicity, D. Burrows, Ed. (CRC Press, Boca Raton, 1983) 172 pp; Chromium in the Natural and Human Environments, J. O. Nriagu, E. Nieboer, Eds. (John Wiley & Sons, New York,
1988) 571 pp.
Properties
Steel-gray, lustrous metal; body-centered cubic
structure; hard as corundum and less fusible than platinum. Takes
a high polish. mp 1903 ±10°. bp 2642°. d20 7.14. Heat capacity (25°): 5.58 cal/mol/deg C. Heat of fusion: 3.5
kcal/mol; heat of vaporization: 81.7 kcal/mol (at bp); heat of sublimation
(25°): 94.8 kcal/mol (Rollinson). Also reported as mp 1875°. bp 2680°. d20 7.19. Specific heat (25° C): 23.9 J/mol/deg
K. Heat of fusion: 14.6 kJ/mol; heat of vaporization: 305 kJ/mol
(at bp) (Westbrook). Resistant to common corroding agents, highly
acid resistant. Reacts with dil HCl, H2SO4;
not with HNO3. Resists atmospheric attack at ambient temperatures.Caution
Potential symptom of overexposure
to chromium metal by inhalation is histologic fibrosis of the lungs.
See NIOSH Pocket Guide to Chemical
Hazards (DHHS/NIOSH 97-140, 1997) p 72. Chromic acid
and chromate salts are irritating to exposed tissues. Toxic effects
due to overexposure may include dermatitis, skin ulcers; nasal inflammation,
perforation of nasal septum; cancer of the lungs, nasal cavity and
paranasal sinus. See Patty's Industrial
Hygiene and Toxicology vol. 2C, G. D. Clayton,
F. E. Clayton, Eds. (John Wiley & Sons, New York, 4th ed., 1994)
p 1973-1985. Chromium hexavalent compounds are listed as known human
carcinogens: Report on Carcinogens, Eleventh
Edition (PB2005-104914, 2004) p III-63.Use
In manuf of chrome-steel or chrome-nickel-steel
alloys (stainless steel), nonferrous alloys, heat resistant bricks
for refractory furnaces. To greatly increase strength, hardness and
resistance of metals to abrasion, corrosion and oxidation. For chrome
plating of other metals; leather tanning; as pigment and mordant;
wood preservative. Use of
51Cr as diagnostic aid
see sodium chromate(VI).