Nomenclature
CAS number: 7440-25-7
Description and 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%), T >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 μohm-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.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”).