Structural Formula Vector Image
Title: Hafnium
CAS Registry Number: 7440-58-6
Literature References: Hf; at. wt 178.49; at. no. 72; valences 4; also 2, 3. Group IVB (4). Six naturally occurring isotopes: 180 (35.22%); 178 (27.1%); 177 (18.56%); 179 (13.75%); 176 (5.21%); 174 (0.163%; a-emitter, T½ 2 ´ 1015 years); artificial isotopes: 157; 158; 168-173; 175; 181-183. Abundance in earth's crust: 5 ppm. Found in all zirconium-contg minerals. Discovered in 1923 by Coster and Hevesy: Nature 111, 79 (1923). Extraction from the mineral cyrtolite: Larsen et al., Inorg. Synth. 3, 67 (1950). Prepd by thermal decompn of its iodide; by reduction of the tetrachloride or of the hydrofluohafniate with metallic sodium; by reduction of the oxide with a mixture of calcium and sodium: van Arkel, de Boer, Z. Anorg. Chem. 148, 345 (1925); de Boer, Fast, ibid. 187, 193 (1930); US 2741628. Spectra: Coster et al., cited by Mellor, A Comprehensive Treatise on Inorganic and Theoretical Chemistry 7, 170 (1930). A dibromide and tribromide have been prepd: Schumb, Morehouse, J. Am. Chem. Soc. 69, 2696 (1947). Reviews of hafnium and its compds: Larsen, "Zirconium and Hafnium Chemistry" in Adv. Inorg. Chem. Radiochem. 13, 1-133 (1970); Bradley, Thornton, "Zirconium and Hafnium" in Comprehensive Inorganic Chemistry vol. 3, J. C. Bailar, Jr. et al., Eds. (Pergamon Press, Oxford, 1973) pp 419-490; R. H. Nielson in Kirk-Othmer Encyclopedia of Chemical Technology vol. 12 (Wiley-Interscience, New York, 3rd ed., 1980) pp 67-80.
Properties: Highly lustrous, ductile metal of hexagonal cryst structure. mp 2227°; d 13.3. Resembles zirconium and thorium.
Melting point: mp 2227°
Density: d 13.3
Derivative Type: Dioxide
Molecular Formula: HfO2
Molecular Weight: 210.49
Percent Composition: Hf 84.80%, O 15.20%
Properties: Obtained by igniting the hydroxide, the oxalate, or the sulfate. d20 9.68. mp 2774°.
Melting point: mp 2774°
Density: d20 9.68
Derivative Type: Tetrachloride
Molecular Formula: HfCl4
Molecular Weight: 320.30
Percent Composition: Hf 55.73%, Cl 44.27%
Properties: White cryst mass, obtained by heating the oxide in the presence of chlorine and a reducing agent. Hydrolyzed to hafnyl chloride, HfOCl2, by water. Volatilizes appreciably at 250°.
Derivative Type: Sulfate
Molecular Formula: Hf(SO4)2
Molecular Weight: 370.62
Percent Composition: Hf 48.16%, S 17.30%, O 34.54%
Properties: Prepd by the action of fuming sulfuric acid on the tetrachloride, dec above 500°.
CAUTION: Potential symptoms of overexposure to hafnium in exptl animals are irritation of eyes, skin, mucous membranes; liver damage. See NIOSH Pocket Guide to Chemical Hazards (DHHS/NIOSH 97-140, 1997) p 156.

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