Title: Tantalum
CAS Registry Number: 7440-25-7
Literature References: Ta; at. wt 180.94788; at. no. 73; valence 5, also 4, 3, 2. Group VB (5). Two naturally occurring isotopes: 181 (99.9877%); 180 (0.0123%), T½ >1012 years; artificial radioactive isotopes: 172-179; 182-186. Occurs almost invariably with niobium; less abundant than niobium. Found in the minerals columbite [(Fe,Mn)(Nb,Ta)2O6], tantalite [(Fe,Mn)(Ta, Nb)2O6] and microlite [(Na,Ca)2Ta2O6(O,OH,F)]. Discovered by Ekeberg in 1802; first obtained pure by Bolton: Z. Elektrochem. 11, 45 (1905). Prepn: Schoeller, Powell, J. Chem. Soc. 119, 1927 (1921). Reviews of tantalum and its compounds: G. L. Miller, Tantalum and Niobium (Academic Press, New York, 1959) 767 pp; Brown, "The Chemistry of Niobium and Tantalum" in Comprehensive Inorganic Chemistry vol. 3, J. C. Bailar, Jr. et al., Eds. (Pergamon Press, Oxford, 1973) pp 553-622.
Properties: Gray, very hard, malleable, ductile metal; can readily be drawn in fine wires. mp 2996°. bp 5429°. d 16.69. Spec heat (0°): 0.036 cal/g/°C. Electrical resistivity (18°): 12.4 mohm-cm. Insol in water. Very resistant to chemical attack; not attacked by acids other than hydrofluoric; not attacked by aq alkalies; slowly attacked by fused alkalies. Reacts with fluorine, chlorine, and oxygen only on heating. At high temps absorbs several hundred times its volume of hydrogen; combines with nitrogen, with carbon.
Melting point: mp 2996°
Boiling point: bp 5429°
Density: d 16.69
CAUTION: Potential symptoms of overexposure to metal and oxide dust are irritation of eyes and skin. See NIOSH Pocket Guide to Chemical Hazards (DHHS/NIOSH 97-140, 1997) p 294.
Use: In pen points; analytical weights; apparatus and instruments for chemical, surgical, and dental use instead of platinum, in tantalum capacitors (a type of electrolytic condenser, trademarked "Tantalytic"). |