Tantalum

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73 hafniumtantalumtungsten
Nb

Ta

Db
Ta-TableImage.png
General
Name, Symbol, Number tantalum, Ta, 73
Chemical series transition metals
Group, Period, Block 5, 6, d
Appearance gray blue
Ta,73.jpg
Atomic mass 180.94788(2) g/mol
Electron configuration [Xe] 4f14 5d3 6s2
Electrons per shell 2, 8, 18, 32, 11, 2
Physical properties
Phase solid
Density (near r.t.) 16.69 g/cm³
Liquid density at m.p. 15 g/cm³
Melting point 3290 K
(3017 °C, 5463 °F)
Boiling point 5731 K
(5458 °C, 9856 °F)
Heat of fusion 36.57 kJ/mol
Heat of vaporization 732.8 kJ/mol
Heat capacity (25 °C) 25.36 J/(mol·K)
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 3297 3597 3957 4395 4939 5634
Atomic properties
Crystal structure cubic body centered
Oxidation states 5 (mildly acidic oxide)
Electronegativity 1.5 (Pauling scale)
Ionization energies 1st: 761 kJ/mol
2nd: 1500 kJ/mol
Atomic radius 145 pm
Atomic radius (calc.) 200 pm
Covalent radius 138 pm
Miscellaneous
Magnetic ordering no data
Electrical resistivity (20 °C) 131 nΩ·m
Thermal conductivity (300 K) 57.5 W/(m·K)
Thermal expansion (25 °C) 6.3 µm/(m·K)
Speed of sound (thin rod) (20 °C) 3400 m/s
Speed of sound (thin rod) (r.t.) 186 m/s
Shear modulus 69 GPa
Bulk modulus 200 GPa
Poisson ratio 0.34
Mohs hardness 6.5
Vickers hardness 873 MPa
Brinell hardness 800 MPa
CAS registry number 7440-25-7
Notable isotopes
Main article: Isotopes of tantalum
iso NA half-life DM DE (MeV) DP
177Ta syn 56.56 h ε 1.166 177Hf
178Ta syn 2.36 h ε 1.910 178Hf
179Ta syn 1.82 a ε 0.110 179Hf
180Ta syn 8.125 h ε 0.854 180Hf
180Ta syn 8.125 h β- 0.708 180W
180mTa 0.012% >1.2×1015 y ε 0.929 180Hf
β- 0.783 180W
IT 0.075 180Ta
181Ta 99.988% Ta is stable with 108 neutrons
182Ta syn 114.43 d β- 1.814 182W
183Ta syn 5.1 d β- 1.070 183W

Tantalum, formerly tantalium (chemical symbol Ta, atomic number 73) is a rare, blue-gray, lustrous metal. It is very hard, has a high melting point, and is highly resistant to corrosion.

Capacitors made with tantalum and its oxide are widely used in portable telephones, pagers, personal computers, and automotive electronics. Tantalum is also used for making carbide tools for metalworking, and for the production of superalloys for jet engine components, chemical process equipment, nuclear reactors, and missile parts. Given its inertness, tantalum is often used in surgical instruments and implants. Tantalum pentoxide is used to make special glass for camera lenses. Tantalum carbide is useful for making extremely hard composites with metals and graphite, and these composites are then used in tool bits.

Contents

Occurrence and isolation

Tantalum occurs principally in the minerals tantalite [(Fe, Mn) Ta2O6] and euxenite [(Y,Ca,Ce,U,Th)(Nb,Ta,Ti)2O6]. Tantalite is usually found mixed with columbite in an ore called coltan. Other minerals containing tantalum include samarskite and fergusonite.

Tantalum ores are mined in Ethiopia, Australia, Brazil, Egypt, Canada, the Democratic Republic of the Congo, Mozambique, Nigeria, Portugal, Malaysia, and Thailand.[1] The exploitation of resources in the conflict regions of the Congo has raised ethical questions about human rights and endangered wildlife.

Several complicated steps are involved in the separation of tantalum from niobium. Commercially viable production of this element can follow one of several different methods, such as: (a) electrolysis of molten potassium fluorotantalate; (b) reduction of potassium fluorotantalate with sodium; or (c) reacting tantalum carbide with tantalum oxide. Tantalum is also a byproduct from tin smelting.

History and etymology

Tantalum was discovered in Sweden in 1802 by Anders Ekeberg and isolated in 1820 by Jöns Berzelius. Many contemporary chemists believed niobium and tantalum were the same element, until researchers showed (in 1844 and 1866) that niobic and tantalic acids are different compounds. Early investigators were able to isolate just the impure metal, and the first relatively pure, ductile metal was produced by Werner von Bolton in 1903. Wires made with tantalum metal were used for light bulbs until it was replaced by tungsten.

The name tantalum is derived from the Greek mythological character Tantalos, father of Niobe. Tantalus was punished after death by being condemned to stand knee-deep in water with perfect fruit growing above his head, both of which eternally "tantalized" him. If he bent to drink the water, it drained below the level he could reach, and if he reached for the fruit, the branches moved out of his grasp. This was considered similar to tantalum's general non-reactivity—it is unaffected by reagents and is therefore difficult to refine.

Notable characteristics

Tantalum is a transition metal that lies in period six of the periodic table, between hafnium and tungsten. In addition, it is located in group five (former group 5B), just below niobium, and its chemical properties are similar to those of niobium.

This element is dark, dense, ductile, very hard, and easily fabricated. It is highly conductive of heat and electricity. It is renowned for its resistance to corrosion by acids. At temperatures below 150 °C, it is almost completely immune to attack by the normally aggressive aqua regia. It can be dissolved with hydrofluoric acid or acidic solutions containing the fluoride ion and sulfur trioxide, as well as with a solution of potassium hydroxide. Tantalum's melting point of 3,017 °C (boiling point 5,458 °C) is exceeded only by the melting points of tungsten and rhenium.

Isotopes

Natural tantalum consists of two isotopes: Ta-181 is a stable isotope, and Ta-180m has a half life of over 1015 years (see scientific notation). In addition, numerous radioactive isotopes (atomic mass numbers ranging from 155 to 190) have been produced artificially, with very short half-lives.

Compounds

  • Tantalum carbide (TaC): This heavy, brown powder is an extremely hard, refractory, ceramic material. It is useful for making ceramic-metal composites and is commercially used in tool bits for cutting tools. It is sometimes used as a fine-crystalline additive to tungsten carbide alloys. When used as a mold coating, it produces a low friction surface. Scientists at the Los Alamos National Laboratory have developed a tantalum carbide-graphite composite material that is one of the hardest materials ever synthesized.
  • Tantalum pentachloride or tantalum(V) chloride (TaCl5): This white powder is the main starting material in tantalum chemistry. It hydrolyzes readily and releases HCl. It is prepared by heating tantalum metal in chlorine. Samples are often contaminated with tantalum(V) oxychloride (TaOCl3), formed by hydrolysis or from traces of oxygen during the preparation. TaCl5 is purified by sublimation to give white needles. It can form stable complexes with some compounds (such as ethers) and it can act as a catalyst for particular reactions.
  • Tantalum pentoxide or tantalum(V) oxide (Ta2O5): This oxide has a high refractive index and low absorption of light, and is useful for coatings in the near-UV to IR regions of the spectrum. It decomposes only above 1470 °C. It is used to make capacitors in automotive electronics, cell phones, and pagers. It is also used in thin-film components and high-speed tools. Given its high index of refraction, it has been utilized in the fabrication of the glass of many photographic lenses.

Applications

The major use for tantalum, as the metal powder, is in the production of electronic components, mainly capacitors and some high-end, audio-grade resistors. Tantalum electrolytic capacitors exploit the tendency of tantalum to form a protective oxide surface layer, using tantalum foil as one plate of the capacitor, the oxide as the dielectric (electrical insulator between plates), and an electrolytic solution as the other plate. Because the dielectric layer can be very thin (thinner than the similar layer in, for instance, an aluminum electrolytic capacitor), high capacitance can be achieved in a small volume. Given the size and weight advantages, tantalum capacitors are attractive for portable telephones, pagers, personal computers, and automotive electronics.

Tantalum is also used to produce a variety of strong, ductile alloys that have high melting points. Alloyed with other metals, it is also used in making carbide tools for metalworking equipment and in the production of superalloys for jet engine components, chemical process equipment, nuclear reactors, and missile parts. Tantalum wires and filaments are used for heating and evaporating metals such as aluminum.

Given that tantalum resists attack by body fluids and is nonirritating, it is widely used in making surgical instruments and implants. The oxide is used to make special glass (with high refractive index) for camera lenses. The metal is also used to make parts for vacuum furnaces.

Precautions

Compounds containing tantalum are rarely encountered, and the metal does not normally cause problems in the laboratory. Nonetheless, it should be handled with care, taking the usual laboratory precautions. There is some evidence that tantalum compounds can cause tumors, and its metal dust is a fire and explosion hazard.

See also

Notes

  1. International tantalum resources - a comprehensive picture, as of 2002. Retrieved December 5, 2007.

References

  • Chang, Raymond. 2006. Chemistry. 9th ed. New York: McGraw-Hill Science/Engineering/Math. ISBN 0073221031
  • Cotton, F. Albert, Geoffrey Wilkinson, Carlos A. Murillo, and Manfred Bochmann. 1999. Advanced Inorganic Chemistry. 6th ed. New York: Wiley. ISBN 0471199575
  • Fairbrother, F. 1967. The Chemistry of Niobium and Tantalum. New York: Elsevier. ASIN B0006BQA7U
  • Greenwood, N.N., and A. Earnshaw. 1998. Chemistry of the Elements. 2nd ed. Oxford, U.K.; Burlington, Massachusetts: Butterworth-Heinemann, Elsevier Science. ISBN 0750633654
  • Tantalum Los Alamos National Laboratory. Retrieved December 5, 2007.
  • Tantalum - raw materials and processing T.I.C. industry site. Retrieved December 5, 2007.
  • Tantalum SPECTRUM Chemical Fact Sheet. Retrieved December 5, 2007.
  • Tantalum WebElements.com. Retrieved December 5, 2007.

External links

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