73
  Ta  
180.947900
Tantalum

Name: Tantalum
Symbol: Ta
Atomic Number: 73
AtomicWeight: 180.947900
Family: transition metals
CAS RN: 7440-25-7
Description: A greyish silver, heavy, ductile and very hard metal.
State (25 C): Solid
Oxidation states: +5

Molar Volume: 10.9 cm3/mole
Valence Electrons: 5d36s2

Boiling Point:  5698K, 5425C, 9797F
Melting Point:
3269K, 2996C, 5425F
Electrons Energy Level: 2, 8, 18, 32, 11, 2
Isotopes: 35 + 1 Stable
Heat of Vaporization: 743 kJ/mol
Heat of Fusion: 31.6 kJ/mol
Density: 16.65 g/cm3 @ 300K
Specific Heat: 0.14 J/gK
Atomic Radius: 2.09
Ionic Radius: 0.64
Electronegativity: 1.5 (Pauling); 1.33 (Allrod Rochow)
Vapor Pressure: 0.776 Pa @ 2996C

1s2 2s2p6 3s2p6d10 4s2p6d10f14 5s2p6d3 6s2

History

Tantalum was discovered in Swedin in 1802 by Anders Ekeberg and isolated in 1802 by Jons Jacob 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. The English word tantalize was named after Tantalus, and tantalum was named after the tantalizing problems posed by the inertness of the element and its compounds.

For many years, the commercial technology for separating tantalum from niobium involved the fractional crystallization of potassium heptafluorotantalate away from potassium oxypentafluoroniobate monohydrate, that had been discovered by Marignac in the 1860's. The method has been supplanted by solvent extraction from fluoride-containing solutions.

Characteristics

Tantalum is rare, blue-gray, dense, ductile, hard, lustrous, easily fabricated, and highly conductive of heat and electricity.  The metal is renowned for its resistance to corrosion by acids; in fact, at temperatures below 150C tantalum is almost completely immune to attack by the normally aggressive agqua 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 high melting point of 3017C (boiling point 5458C) is exceeded only by tungsten and rhenium for metals, and carbon.

1s2
2s2 2p6
3s2 3p6 3d10
4s2 4p6 4d10 4f14
5s2 5p6 5d3
6s2

Occurrence

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

Tantalum oresare mined in Ethiopia, Austrailia, Brazil, Egypt, Canada, the Democratic Republic of the Congo, Mozambique, Nigeria, Portugal, Malaysia and Thailand.  A comprehensive, 2002 picture 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.

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 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 smelting.

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 powder, pressed into a pellet shape, as one "plate" of the capacitor, the oxide as the dielectric, and an electrolytic solution or conductive solid 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 volume. Because of 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 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.   Because of its ductility, Ta can be drawn into fine wires or filaments, which are used for evaporating metals such as aluminum.

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

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 an amorphous tantalum-tungsten-copper alloy which is more flexible and two to three times stronger than traditional steel alloys.

Tantalum Ore
Columbite, (Fe, Mn, Mg)(Nb, Ta)2O6
Tantalite, (Fe, Mn)(Ta, Nb)2O6
Euxenite, (Y, Ca, Er, La, Ce, U, Th)(Nb, Ta, Ti)2O6
Tantalum Pentoxide, Ta2O5 Tantalum Carbide, TaC

Isotopes

Natural tantalum consists of two isotopes.  Ta-181 is a stable isotope, and Ta-180m has a half-life of over 1.2E 15 years and is a nuclear isomer of Ta-180.  Ta-180 has a ground state half-life of only 8 hours.

Tantalum has been proposed as a "salting" material for nuclear weapons (cobalt is another, better-known salting material).  A jacket of 181Ta, irradiated by the intense high-energy neutron flux from an exploding thermonuclear weapon, would transmute into the radioactive isotope 182Ta with a half-life of 114.43 days and produce approximately 1.12 MeV of gamma radiation, significantly increasing the radioactivity of the weapon's fallout for several months.  Such a weapon is not known to have ever been built, tested, or used.

atom.gif (700 bytes)

Isotopes  
Atomic Mass
 
Half-Life
155Ta 154.97459 12 ms
156Ta 155.97230 144 ms
157Ta 156.96819 10.1 ms
158Ta 157.96670 49 ms
159Ta 158.963018 1.04 seconds
160Ta 159.96149 1.70 seconds
161Ta 160.95842 ~3 seconds
162Ta 161.95729 3.57 seconds
163Ta 162.95433 10.6 seconds
164Ta 163.95353 14.2 seconds
165Ta 164.950773 31.0 seconds
166Ta 165.95051 34.4 seconds
167Ta 166.94809 1.33 minutes
168Ta 167.94805 2.0 minutes
169Ta 168.94601 4.9 minutes
170Ta 169.94618 6.76 minutes
171Ta 170.94448 23.3 minutes
172Ta 171.94490 36.8 minutes
173Ta 172.94375 3.14 hours
174Ta 173.94445 1.14 hours
175Ta 174.94374 10.5 hours
176Ta 175.94486 8.09 hours
177Ta 176.944472 56.56 hours
178Ta 177.945778 9.31 minutes
179Ta 178.9459295 1.82 years
180Ta 179.9474648 8.152 hours
180mTa   >1.2E 15 years
181Ta 180.9479958 Stable
182Ta 181.9501518 114.43 days
183Ta 182.9513726 5.1 days
184Ta 183.954008 8.7 hours
185Ta 184.955559 49.4 minutes
186Ta 185.95855 10.5 minutes
187Ta 186.96053 ~2 minutes
188Ta 187.96370 ~20 seconds
189Ta 188.96583 ~3 seconds
190Ta 189.96923 ~0.3 seconds

Precautions

80px-Flammable.jpg (2186 bytes) Compounds containing tantalum are rarely encountered, and the metal does not normally cause problems in the laboratory, but it should still 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.

atom.gif (700 bytes)

Tantalum Data
 

Atomic Structure

  • Atomic Radius: 2.09
  • Atomic Volume: 10.9cm3/mol
  • Covalent Radius: 1.34
  • Cross Section (Thermal Neutron Capture) Barns: 20.6
  • Crystal Structure: Cubic body centered
  • Electron Configuration:
    1s2 2s2p6 3s2p6d10 4s2p6d10f14 5s2p6d3 6s2
  • Electrons per Energy Level: 2, 8, 18, 32, 11, 2
  • Ionic Radius: 0.64
  • Filling Orbital: 5d3
  • Number of Electrons (with no charge): 73
  • Number of Neutrons (most common/stable nuclide): 108
  • Number of Protons: 73
  • Oxidation States: 5
  • Valence Electrons: 5d3 6s2

Chemical Properties

  • Electrochemical Equivalent: 1.3502 g/amp-hr
  • Electron Work Function: 4.25eV
  • Electronegativity: 1.5 (Pauling); 1.33 (Allrod Rochow)
  • Heat of Fusion: 31.6 kJ/mol
  • Incompatibilities:
    Strong oxidizers, bromine trifluoride, fluorine
  • Ionization Potential
    • First: 7.89
  • Valence Electron Potential (-eV): 110

Physical Properties

  • Atomic Mass Average: 180.9479
  • Boiling Point: 5698K, 5425C, 9797F
  • Coefficient of Lineal Thermal Expansion/K-1: 6.6E-6
  • Conductivity
    Electrical: 0.0761 106/cm
    Thermal: 0.575 W/cmK
  • Density: 16.65 g/cm3 @ 300K
  • Description:
    Rare gray metal with a high melting point, which resists corrosion due to an oxide film that forms on its surface.
  • Elastic Modulus:
    • Bulk: 196.3/GPa
    • Rigidity: 69.2/GPa
    • Youngs: 185.7/GPa
  • Enthalpy of Atomization: 782 kJ/mole @ 25C
  • Enthalpy of Fusion: 31.4 kJ/mole
  • Enthalpy of Vaporization: 753.1 kJ/mole
  • Flammablity Class: Combustible Solid, fine dust is easily ignited
  • Freezing Point: see melting point
  • Hardness Scale
    • Brinell: 800 MN m-2
    • Mohs: 6.5
    • Vickers: 873 MN m-2
  • Heat of Vaporization: 743 kJ/mol
  • Melting Point: 3269K, 2996C, 5425F
  • Molar Volume: 10.9 cm3/mole
  • Optical Reflectivity: 78%
  • Physical State (at 20C & 1atm): Solid
  • Specific Heat: 0.14 J/gK
  • Vapor Pressure: 0.776 Pa @ 2996C

Regulatory / Health

  • CAS Number
    • 7440-25-7
  • RTECS: WW5505000
  • OSHA Permissible Exposure Limit (PEL)
    • TWA: 5 mg/m3
  • OSHA PEL Vacated 1989
    • TWA: 5 mg/m3
  • NIOSH Recommended Exposure Limit (REL)
    • TWA: 5 mg/m3
    • STEL: 10 mg/m3
    • IDLH: 2500 mg/m3
  • Routes of Exposure: Inhalation; Skin and/or eye contact
  • Target Organs: Eyes, skin, respiratory system
  • Levels In Humans:
    Note: this data represents naturally occuring levels of elements in the typical human, it DOES NOT represent recommended daily allowances.
    • Blood/mg dm-3: n/a
    • Bone/p.p.m: 0.03
    • Liver/p.p.m: n/a
    • Muscle/p.p.m: n/a
    • Daily Dietary Intake: 0.001 mg
    • Total Mass In Avg. 70kg human: 0.2 mg

Who / Where / When / How

  • Discoverer: Anders G. Ekeberg
  • Discovery Location: Uppsala Sweden
  • Discovery Year: 1802
  • Name Origin:
    From king Tantalus of Greek mythology.
  • Abundance:
    • Earth's Crust/p.p.m.: 2
    • Seawater/p.p.m.: 0.000002
    • Atmosphere/p.p.m.: N/A
    • Sun (Relative to H=1E12): N/A
  • Sources:
    Chiefly occurs in the mineral tantalite. Always found with niobium. Annual world production is around 840 tons. Primary mining areas are Australia, Zaire, Brazil, Russia, Norway, Canada and Madagascar.
  • Uses:
    Used in metal alloys. Tantalum pentoxide is used in capacitors, condensers, cutting tools, vacuum tube filaments and in camera lenses to increase refracting power.

Ionization Energy (eV): 7.89 eV
Estimated Crustal Abundance: 2.0 milligrams per kilogram
Estimated Oceanic Abundance:
210-6 milligrams per liter

Transition Metals
Group 3
(IIIB)
4
(IVB)
5
(VB)
6
(VIB)
7
(VIIB)
8
(VIIIB)
9
(VIIIB)
10 (VIIIB) 11
(IB)
12
(IIB)
Period 4 21
Sc
44.95
22
Ti
47.86
23
V
50.94
24
Cr
51.99
25
Mn
54.93
26
Fe
55.84
27
Co
58.93
28
Ni
58.69
29
Cu
63.54
30
Zn
65.39
Period 5 39
Y
88.90
40
Zr
91.22
41
Nb
92.90
42
Mo
95.94
43
Tc
98.00
44
Ru
101.0
45
Rh
102.9
46
Pd
106.4
47
Ag
107.8
48
Cd
112.4
Period 6 57
La
138.9
72
Hf
178.4
73
Ta
180.9
74
W
183.8
75
Re
186.2
76
Os
190.2
77
Ir
192.2
78
Pt
195.0
79
Au
196.9
80
Hg
200.5
Period 7 89
Ac
227.0
104
Rf
261.0
105
Db
262.0
106
Sg
266.0
107
Bh
264.0
108
Hs
269.0
109
Mt
268.0
110
Ds
269.0
111
Rg
272.0
112
Uub
277.0