5093. Iron

Nomenclature

CAS number: 7439-89-6

Description and references

Fe; at. no. 26; at. wt 55.845; valences 2, 3; seldom 1, 4, 6. Group VIII (8). Four naturally occurring isotopes: 54 (5.82%); 56 (91.66%); 57 (2.19%); 58 (0.33%); artificial, radioactive isotopes: 52; 53; 55; 59-61. Second most abundant metal in earth's crust after aluminum: about 5%. The earth's core is believed to consist mainly of iron. Important ores include hematite (Fe2O3), magnetite (Fe3O4), limonite [FeO(OH).nH2O] and siderite (FeCO3). Essential dietary nutrient. Study of iron and its compds by Mssbauer spectroscopy: Danon, “57Fe: Metal, Alloys and Inorganic Compounds” in Chemical Applications of Mssbauer Spectroscopy, V. I. Goldanskii, R. H. Herber, Eds. (Academic Press, New York, 1968) p 159-313. Ions involved in oxygen transport, electron transport, nitrogen fixation and a number of other biological processes: Nielands, “Evolution of Biological Iron Binding Centers” in Struct. Bonding 11, 145-170 (1972). Review of biology, pharmacology and toxicity of iron compounds: several authors, Clin. Toxicol. 4, 525-642 (1971); of metabolism and homeostasis: G. Papanikolaou, K. Pantopoulos, Toxicol. Appl. Pharmacol. 202, 199-211 (2005). Comprehensive reviews: Feldmann, Schenck in Ullmanns Encyklopdie der technischen Chemie vol. 6 (München-Berlin, 1955) pp 261-407; Nicholls in Comprehensive Inorganic Chemistry vol. 3, J. C. Bailar, Jr. et al., Eds. (Pergamon Press, Oxford, 1973) pp 979-1051; W. A. Knepper in Kirk-Othmer Encyclopedia of Chemical Technology vol. 13 (Wiley-Interscience, New York, 3rd ed., 1981) pp 735-753. Review of use in cereal flour fortification: R. Hurrell et al., Nutr. Rev. 60, 391-406 (2002).

Properties

Silvery-white or gray, soft, ductile, malleable, somewhat magnetic metal. Holds magnetism only after hardening (as alloy steel, e.g., Alnico). Supplied as ingots, powder, wire, sheets, etc. Takes a bright polish; can be rolled, hammered, bent, particularly when red hot. Stable in dry air but readily oxidizes in moist air, forming “rust” (chiefly oxide, hydrated). In powder form it is black to gray. Commercial iron usually contains some C, P, Si, S and Mn. d pure 7.86; cast 7.76; wrought 7.25-7.78; steel 7.6-7.78. mp pure 1535°; cast 1000-1300°; wrought 1500°; steel 1300°. bp 3000°. Electrical resistivity (20°): 9.71 microhm-cm. Readily attacked by dil mineral acids and attacked or dissolved by organic acids; not appreciably attacked by cold concd H2SO4 or HNO3, but is attacked by the hot acids.

Use

Alloyed with C, Mn, Cr, Ni, and other elements to form steels. Nutritional supplement in wheat flours, corn meal, grits and other cereal products. 55Fe and 59Fe used in tracer studies; the former in biological studies. Standard for elemental analysis.