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Tantalum

From Academic Kids

Hafnium - Tantalum - Tungsten
Nb
Ta
Db  
 
 
image:Ta-TableImage.png
General
Name, Symbol, Number Tantalum, Ta, 73
Chemical series Transition metals
Group, Period, Block 5 (VB), 6, d
Density, Hardness 16650 kg/m3, 6.5
Appearance gray blue
Atomic Properties
Atomic weight (not SI) 180.9479 amu
Atomic radius (calc.) 145 (200) pm
Covalent radius 138 pm
van der Waals radius no data
Electron configuration [Xe]4f14 5d3 6s2
e- 's per energy level 2, 8, 18, 32, 11, 2
Oxidation state (Oxide) 5 (mildly acidic)
Crystal structure Cubic body centered
Physical Properties
State of matter solid
Melting point 3290 K (5463 ?F)
Boiling point 5731 K (9856 ?F)
Molar volume 10.85 cm3/mol
Heat of vaporization 743 kJ/mol
Heat of fusion 31.6 kJ/mol
Vapor pressure 0.776 Pa at 3269 K
Speed of sound 3400 m/s at 20 ?C
Miscellaneous
Electronegativity 1.5 (Pauling scale)
Specific heat capacity 140 J/(kg?K)
Electrical conductivity 7.61 MS/m
Thermal conductivity 57.5 W/(m?K)
1st ionization potential 761 kJ/mol
2nd ionization potential 1500 kJ/mol
Most Stable/Notable Isotopes
iso NA half-life
(not SI)
DM DE MeV
(not SI)
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
β-
0,854
0,708
180Hf
180W
180mTa 0,012 % >1,2 ? 1015 a ε
β-
IT
0,929
0,783
0,075
180Hf
180W
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
SI units & STP are used except where noted.

Tantalum (formerly tantalium) is a chemical element in the periodic table that has the symbol Ta and atomic number 73. A rare, hard, blue-gray, lustrous, transition metal, tantalum is highly corrosion-resistant and occurs in the mineral tantalite. Tantalum is used in surgical instruments and implants because it does not react with body fluids.

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Contents

Notable characteristics

Tantalum is gray, heavy, ductile, very hard, easily fabricated, highly resistant to corrosion by acids, and is a good conductor of heat and electricity. In fact, at temperatures below 150 °C tantalum is almost completely immune to chemical attack, even by the very aggressive aqua regia, and can only be attacked by hydrofluoric acid, acidic solutions containing the fluoride ion, and free sulfur trioxide. The element has a melting point exceeded only by tungsten and rhenium (melting point 3290 K, boiling point 5731 K).

Applications

The major use for tantalum, as tantalum metal powder, is in the production of electronic components, mainly tantalum capacitors. Tantalum electrolytic capacitors exploit the natural tendency of tantalum to form a protective oxide surface layer, using tantalum foil as one plate of the capacitor, the oxide as the dielectric, 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), a high capacitance can be achieved in a small space. This size and weight advantage makes tantalum capacitors attractive for portable telephones, pagers, personal computers, and automotive electronics.

Tantalum is also used to produce a variety of alloys that have high melting points, are strong and have good ductility. 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. It is ductile and can be drawn into fine wire, which is used as a filament for evaporating metals such as aluminium.

Because it is totally immune to the action of body liquids and is nonirritating it is widely used in making surgical appliances. Tantalum oxide is used to make special high refractive index glass for camera lenses. The metal is also used to make vacuum furnace parts.

History

Tantalum (Greek Tantalos, mythological character) was discovered in Sweden in 1802 by Anders Ekeberg and isolated in 1820 by J?Berzelius. Many contemporary chemists believed niobium and tantalum were the same elements until 1844 and later 1866 when researchers showed that niobic and tantalic acids were different compounds. Early investigators were only able to isolate 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 tungsten replaced it.

Its name is derived from the character Tantalus, father of Niobe in Greek mythology, who 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 sits among reagents and is unaffected by them.

Occurrence

Tantalum occurs principally in the mineral tantalite [(Fe, Mn) Ta2O6] and euxenite (other minerals: samarskite, and fergusonite).

Tantalum ores are mined in Australia, Brazil, Egypt, Canada, the Democratic Republic of the Congo, Mozambique, Nigeria, Portugal, and Thailand. A comprehensive, 2002 picture (http://www.doir.wa.gov.au/documents/gswa/gsdMRB_22_chap10.pdf) of non-Australian mines is reasonably current.

Tantalite is largely found mixed with columbite in an ore called coltan. Ethical questions have been raised about human rights and endangered wildlife, due to the exploitation of resources in the conflict regions of the Congo (see coltan).

Several complicated steps are involved in the separation of tantalum from niobium. Commercially production of this element can follow one of several different methods which includes; electrolysis of molten potassium fluorotantalate, reduction of potassium fluorotantalate with sodium, or by reacting tantalum carbide with tantalum oxide. Tantalum is also a byproduct from tin extraction.

Compounds

Los Alamos National Laboratory scientists have developed a tantalum carbide-graphite composite material that is one of the hardest materials ever synthesized. Korean researchers have developed a tantalum-tungsten-copper (http://english.chosun.com/w21data/html/news/200505/200505060005.html) alloy which is two to three times stronger and more flexible than steel alloys.

Isotopes

Natural tantalum consists of two isotopes. Ta-181 is a stable isotope, and Ta-180m, which has a half life of over 1015 years (see scientific notation) and is a nuclear isomer of Ta-180. Ta-180 has a ground state half life of only 8 hours.

Precautions

Compounds containing Tantalum are rarely encountered, and the metal does not normally cause problems in the laboratory, but it should still be regarded as highly toxic. There is some evidence that tantalum compounds can cause tumors, and its metal dust is a fire and explosion hazard. However, refined tantalum is used in surgical instruments and implants because it does not react with body fluids.

References

External links

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