1645. Calcium

Nomenclature

CAS number: 7440-70-2

Description and references

Ca; at. wt 40.078; at. no. 20; valence 2. Group IIA (2). Alkaline earth metal. Occurrence in the earth's crust 3.64% (fifth element in order of abundance). Sea water contains about 400 g/ton. Naturally occurring isotopes: 40 (96.941%), 44 (2.086%), 42 (0.647%), 48 (0.187%), 43 (0.135%), 46 (0.004%). Known radioactive isotopes: 35-39, 41, 45, 47-51. Found naturally only in the form of its compds, never uncombined, in minerals such as limestone, dolomite, marble, chalk, iceland spar, gypsum, anhydrite, fluorite, apatite. Principal commercial source is limestone, q.v. Major commercial production by high temperature vacuum reduction of calcium oxide in aluminothermal process; less commonly by electrolysis followed by redistillation. Essential constituent of bones, shells, teeth, coral, pearls. Essential nutrient for animal life. First isolated by Davy in 1808. Produced by electrolysis of calcium chloride: Rathenau, Suter, DE 155433 (1903); Z. Elektrochem. 10, 502 (1904); Goodwin, J. Am. Chem. Soc. 27, 1403 (1905); also by thermal reduction of lime with silicon, or with aluminum. Prepn of the pure metal for laboratory use: Whaley, Inorg. Synth. 6, 18 (1960). Purifn of commercial material: Marshall, Whaley, ibid. 24. Reviews: Schaufler in Ullmanns Encyklop"adie der technischen Chemie vol. 4 (Munich, 3rd ed., 1953) pp 830-836; Mantell in C. A. Hampel, Rare Metals Handbook (Reinhold, New York, 1954) p 17-29. Review of calcium and its compounds: Goodenough, Stenger, “Magnesium, Calcium, Strontium, Barium and Radium” in Comprehensive Inorganic Chemistry Vol. 1, J. C. Bailar Jr. et al., Eds. (Pergamon Press, Oxford, 1973) pp 591-664; Chemistry of the Elements, N. N. Greenwood, A. Earnshaw, Eds. (Pergamon Press, New York, 1984) pp 117-154; R. L. Petersen, M. B. Freilich in Kirk-Othmer Encyclopedia of Chemical Technology vol. 4 (Wiley-Interscience, New York, 4th ed., 1992) pp 777-796. Book: R. P. Rubin, Calcium and Cellular Secretion (Plenum, New York, 1982) 276 pp.

Properties

Lustrous, silver-white surface (when freshly cut); face-centered cubic structure, transforms to body-centered cubic form at 428 ±2°. Soft, ductile. Brinell hardness: 17. Much harder than sodium, but softer than aluminum or magnesium. Oxidizes and acquires bluish-gray tarnish on exposure to moist air. d420 1.54. mp 839°. bp 1484°. Dangerous when wet. Electrical resistivity at 20°: 3.5 μohm cm. Heat of combustion 151.9 cal/g. Specific heat (0-100°) 0.149 cal/g. Considerably less reactive than sodium. E° (aq) Ca2+/Ca -2.87 V. Reacts with water, alcohols, and dil acids with evolution of hydrogen, creating explosion hazard. Reacts with halogens. Dissolves in liquid ammonia to form a blue black soln. Ignites in air when finely divided. Emits characteristic orange-red color in flame. Insol in and inert towards benzene, kerosene.

Use

Reducing agent for production of less common metals; alloying agent to increase strength and corrosion resistance in lead, to improve mechanical and electrical properties in aluminum; refining agent to remove bismuth from lead. In metallurgy as scavenger to deoxidize, desulfurize and degas steel and cast iron; to control non-metallic inclusions in steel; to promote uniform microstructure in gray iron. As anode material in thermal batteries; as “getter” for oxygen and nitrogen.