Tantalum

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Tantalum,  73Ta
General properties
Name, symbol Tantalum, Ta
Tantalum in the periodic table
Nb

Ta

Db
HafniumTantalumTungsten
Atomic number 73
Standard atomic weight (Ar) 180.94788(2)
Group, block , d-block
Period period 6
Electron configuration [Xe] 4f14 5d3 6s2
per shell
2, 8, 18, 32, 11, 2
Physical properties
Gray
Phase Solid
Melting point 3290 K ​(3017 °C, ​5463 °F)
Boiling point 5731 K ​(5458 °C, ​9856 °F)
Density near r.t. 16.69 g/cm3
when liquid, at  15 g/cm3
Heat of fusion 36.57 kJ/mol
Heat of 753 kJ/mol
Molar heat capacity 25.36 J/(mol·K)
 pressure
Atomic properties
Oxidation states 5, 4, 3, 2, 1, −1, −3
Electronegativity Pauling scale: 1.5
energies 1st: 761 kJ/mol
2nd: 1500 kJ/mol
Atomic radius empirical: 146 pm
Covalent radius 170±8 pm
Miscellanea
Crystal structure

for α-Ta
Crystal structure

for β-Ta
Speed of sound thin rod 3400 m/s (at 20 °C)
Thermal expansion 6.3 µm/(m·K) (at 25 °C)
Thermal conductivity 57.5 W/(m·K)
Electrical resistivity 131 Ω·m (at 20 °C)
Magnetic ordering paramagnetic
Young's modulus 186 GPa
Shear modulus 69 GPa
Bulk modulus 200 GPa
Poisson ratio 0.34
Mohs hardness 6.5
Vickers hardness 870–1200 MPa
Brinell hardness 440–3430 MPa
CAS Registry Number 7440-25-7
History
Discovery Anders Gustaf Ekeberg (1802)
· references

Tantalum is a chemical element with symbol Ta and atomic number 73. Tantalum is a rare, hard, gray, lustrous transition metal that is highly corrosion-resistant, part of the refractory metals group, mostly used as alloys and in various electronics as capacitor material.

Properties

Chemical

Tantalum is extremely resistant to corrosion. Most acids acids will not attack tantalum at room temperature, except for hydrofluoric acid. Hot sulfuric acid will also corrode it. It is immune to aqua regia at temperatures below 150 °C. It can be dissolved with hydrofluoric acid or acidic solutions containing the fluoride ion as well as sulfur trioxide. Alkaline solutions, such as potassium hydroxide solutions will attack it.

Physical

Tantalum is a dark gray or blue-gray dense, ductile, very hard refractory metal, good electrical and heat conductor. Its melting point is 3017 °C, is fourth highest among all metals, after tungsten, rhenium and osmium. Its boiling point is 5458 °C. With a density of 16.69 g/cm3, tantalum is twice as dense as most stainless steels.

Tantalum exists in two crystalline phases, alpha and beta. The alpha phase is relatively ductile and soft. The beta phase is hard and brittle. The beta phase is metastable and converts to the alpha phase upon heating to 750–775 °C. Bulk tantalum is almost entirely alpha phase, and the beta phase usually exists as thin films obtained through various processes.

Availability

Bulk tantalum is sold by many chemical suppliers. Metallium sells short rods of tantalum at various prices. Tantalum rods can also be found on eBay.

Powdered tantalum is sold by chemical suppliers and can sometimes be found on eBay.

The most available source of tantalum comes from tantalum capacitors, found on many electronic boards, such as TVs, computers, etc. While there are many types of tantalum capacitors, the most common type is that of a raindrop with two little legs, Tatalum capacitors contain both tantalum metal as well as tantalum pentoxide.

International Space Station 500 Tenge Kazakhstan coins issued by the Bank of Kazakhstan in 2006 and 2013 have a core of tantalum and an outer disk made of silver.

Isolation

Tantalum can be isolated from tantalum capacitors, though the process is complex and requires dangerous chemicals, due to it's high chemical inertness.

First, the capacitors are roasted in a kiln to burn any plastic/ceramic covering. The roasted capacitors are cleaned of the resulting ash. The leftover capacitors are grounded and are dissolved in acid or aqua regia to remove any impurities. The insoluble precipitate is washed and dissolved in a potassium hydroxide solution. The resulting solution is reduced to tantalum pentoxide which is dried. Metallic tantalum is obtained by reducing tantalum pentoxide with aluminium or calcium powder.

This process is extremely messy and may not give a high yield.

The metal can also be obtained via the FFC Cambridge process.

Projects

  • Grow crystals (tantalum crucibles)
  • Tantalum electrodes
  • Element collecting

Handling

Safety

Bulk tantalum is highly bioinert and biocompatible and is used as implant material and coatings, though its use is limited due to its high density.

Tantalum halides will hydrolyze in the presence of water and may cause chemical burns on contact with bare skin.

Storage

Bulk tantalum does not require special storage and can be stored in any type of container. Powdered tantalum is more reactive, though it's stable in air.

Disposal

Tantalum does not require special disposal and can be dumped in the trash, though it's best to try to recycle it

References

Relevant Sciencemadness threads