Tantalum is a chemical element; it has symbol Ta and atomic number 73. It is named after Tantalus, a figure in Greek mythology.[Euripides, Orestes] Tantalum is a very hard, ductility, lustrous, blue-gray transition metal that is highly corrosion-resistant. It is part of the refractory metals group, which are widely used as components of strong superalloy. It is a group 5 element, along with vanadium and niobium, and it always occurs in geologic sources together with the chemically similar niobium, mainly in the mineral groups tantalite, columbite, and coltan.
The chemical inertness and very high melting point of tantalum make it valuable for laboratory and industrial equipment such as Chemical reactor and . It is used in tantalum capacitors for electronic equipment such as computers. It is being investigated for use as a material for high-quality superconducting resonators in quantum processors.
History
Tantalum was discovered in Sweden in 1802 by
Anders Ekeberg, in two mineral samples – one from Sweden and the other from Finland.
One year earlier,
Charles Hatchett had discovered
columbium (now niobium).
In 1809, the English chemist William Hyde Wollaston compared the oxides of columbium and tantalum,
columbite and
tantalite. Although the two oxides had different measured densities of 5.918 g/cm
3 and 7.935 g/cm
3, he concluded that they were identical and kept the name tantalum.
After Friedrich Wöhler confirmed these results, it was thought that columbium and tantalum were the same element. This conclusion was disputed in 1846 by the German chemist
Heinrich Rose, who argued that there were two additional elements in the tantalite sample, and he named them after the children of
Tantalus: niobium (from
Niobe), and pelopium (from
Pelops).
The supposed element "pelopium" was later identified as a mixture of tantalum and niobium, and it was found that the niobium was identical to the columbium already discovered in 1801 by Hatchett.
The differences between tantalum and niobium were demonstrated unequivocally in 1864 by Christian Wilhelm Blomstrand,[Marietjie Ungerer. Separation of Tantalum and Niobium by Solvent Extraction. page 22. ] Early investigators had only been able to produce impure tantalum, and the first relatively pure ductile metal was produced by Werner von Bolton in Charlottenburg in 1903. Wires made with metallic tantalum were used for light bulb filaments until tungsten replaced it in widespread use.
The name tantalum was derived from the name of the mythological Tantalus, the father of Niobe in Greek mythology. In the story, he had been 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.)
For decades, the commercial technology for separating tantalum from niobium involved the fractional crystallization of potassium heptafluorotantalate away from potassium oxypentafluoroniobate monohydrate, a process that was discovered by Jean Charles Galissard de Marignac in 1866. This method has been supplanted by solvent extraction from fluoride-containing solutions of tantalum.
Characteristics
Physical properties
Tantalum is dark (blue-gray),
dense, ductile, very hard, easily fabricated, and highly conductive of heat and electricity. The metal is highly resistant to
corrosion by
: at temperatures below 150 °
Celsius tantalum 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 molten potassium hydroxide. Tantalum's high melting point of 3017 °C (boiling point 5458 °C) is exceeded among the elements only by
tungsten,
rhenium, and
osmium for metals, and
carbon.
Tantalum exists in two crystalline phases, alpha and beta. The alpha phase is stable at all temperatures up to the melting point and has body-centered cubic structure with lattice constant a = 0.33029 nm at 20 °C.
Isotopes
Natural tantalum consists of two stable
:
180mTa (0.012%) and
181Ta (99.988%).
180mTa (
m denotes a metastable state) is predicted to decay in three ways: isomeric transition to the
ground state of
180Ta,
beta decay to
180Tungsten, or electron capture to
180Hafnium. However, radioactivity of this
nuclear isomer has never been observed, and only a lower limit on its
half-life of 2.9 years has been set.
The ground state of
180Ta has a half-life of only 8 hours. Among primordial nuclides (half-life > 10
8 years)
180mTa is the only
nuclear isomer and the rarest of all (calculated from the elemental abundance of tantalum and the isotopic abundance of
180mTa within it).
Tantalum has been examined theoretically as a "Salted bomb" material for (cobalt is the better-known hypothetical salting material). An external shell of tantalum would be irradiated by the intense neutron flux from the weapon, transmuting it into the radioactive isotope 182Ta, whose gamma rays would significantly increase the radioactivity of the nuclear fallout for months. Such "salted" weapons are not known to have been built, tested, or used.
Tantalum is used as a target material for spallation by high-energy proton beams for the production of a large number of isotopes including 8Li, 80Rb, and 160Yb.
Chemical compounds
Tantalum forms compounds in oxidation states −3 to +5. Most commonly encountered are oxides of Ta(V), which includes all minerals. The chemical properties of Ta and Nb are very similar. In aqueous media, Ta only exhibits the +5 oxidation state. Like niobium, tantalum is barely soluble in dilute solutions of hydrochloric,
Sulfuric acid,
Nitric acid and
due to the precipitation of hydrous Ta(V) oxide.
In basic media, Ta can be solubilized due to the formation of polyoxotantalate species.
Oxides, nitrides, carbides, sulfides
Tantalum pentoxide (Ta
2O
5) is the most important compound from the perspective of applications. Oxides of tantalum in lower oxidation states are numerous, including many
, and are lightly studied or poorly characterized.
Tantalates, compounds containing TaO43− or TaO3− are numerous. Lithium tantalate (LiTaO3) adopts a perovskite structure. Lanthanum tantalate (LaTaO4) contains isolated tetrahedra.
As in the cases of other , the hardest known compounds of tantalum are nitrides and carbides. Tantalum carbide, TaC, like the more commonly used tungsten carbide, is a hard ceramic that is used in cutting tools. Tantalum(III) nitride is used as a thin film insulator in some microelectronic fabrication processes.
The best studied chalcogenide is Tantalum sulfide (TaS2), a layered semiconductor, as seen for other transition metal dichalcogenides. A tantalum-tellurium alloy forms .
Halides
Tantalum halides span the oxidation states of +5, +4, and +3. Tantalum pentafluoride (TaF
5) is a white solid with a melting point of 97.0 °C. The anion TaF
72- is used for its separation from niobium.
The chloride , which exists as a dimer, is the main reagent in synthesis of new Ta compounds. It hydrolyzes readily to an
oxychloride. The lower halides and , feature Ta-Ta bonds.
Organotantalum compounds
Organotantalum compounds include pentamethyltantalum, mixed alkyltantalum chlorides, alkyltantalum hydrides, alkylidene complexes, as well as cyclopentadienyl derivatives of the same.
Diverse salts and substituted derivatives are known for the hexacarbonyl Ta(CO)
6− and related
.
Occurrence
Tantalum is estimated to make up about 1 ppm
or 2 ppm
of the Earth's crust by weight. There are many species of tantalum minerals, only some of which are so far being used by industry as raw materials:
tantalite (a series consisting of tantalite-(Fe), tantalite-(Mn), and tantalite-(Mg)),
microlite (now a group name),
wodginite,
euxenite (actually euxenite-(Y)), and
polycrase (actually polycrase-(Y)).
Tantalite (
iron,
manganese)Ta
2oxygen6 is the most important mineral for tantalum extraction. Tantalite has the same mineral structure as
columbite (
iron,
manganese) (Ta,
niobium)
2oxygen6; when there is more tantalum than niobium it is called tantalite and when there is more niobium than tantalum is it called columbite (or
niobite). The high density of tantalite and other tantalum containing minerals makes the use of gravitational separation the best method. Other minerals include
samarskite and
fergusonite.
Australia was the main producer of tantalum prior to the 2010s, with Global Advanced Metals (formerly known as Talison Minerals) being the largest tantalum mining company in that country. They operate two mines in Western Australia, Greenbushes in the southwest and Wodgina mine in the Pilbara region. The Wodgina mine was reopened in January 2011 after mining at the site was suspended in late 2008 due to the 2008 financial crisis.[
] Wodgina produces a primary tantalum concentrate which is further upgraded at the Greenbushes operation before being sold to customers.
World tantalum mine production has undergone an important geographic shift since the start of the 21st century when production was predominantly from Australia and Brazil. Beginning in 2007 and through 2014, the major sources of tantalum production from mines dramatically shifted to the Democratic Republic of the Congo, Rwanda, and some other African countries.
Status as a conflict resource
Tantalum is considered a conflict resource.
Coltan, the industrial name for a
columbite–
tantalite mineral from which niobium and tantalum are extracted,
[ Tantalum-Niobium International Study Center: Coltan Retrieved 2008-01-27] can also be found in
Central Africa, which is why tantalum is being linked to warfare in the Democratic Republic of the Congo (formerly
Zaire). According to an October 23, 2003
United Nations report,
the smuggling and exportation of coltan has helped fuel the war in the Congo, a crisis that has resulted in approximately 5.4 million deaths since 1998
– making it the world's deadliest documented conflict since World War II. Ethical questions have been raised about responsible corporate behavior, human rights, and endangering wildlife, due to the exploitation of resources such as coltan in the armed conflict regions of the
Congo Basin.
The United States Geological Survey reports in its yearbook that this region produced a little less than 1% of the world's tantalum output in 2002–2006, peaking at 10% in 2000 and 2008.
USGS data published in January 2021 indicated that close to 40% of the world's tantalum mine production came from the Democratic Republic of the Congo, with another 18% coming from neighboring
Rwanda and
Burundi.
Production and fabrication
Several steps are involved in the extraction of tantalum from tantalite. First, the mineral is
crusher and concentrated by gravity separation. This is generally carried out near the
mining site.
Refining
The refining of tantalum from its ores is one of the more demanding separation processes in industrial metallurgy. The chief problem is that tantalum ores contain significant amounts of
niobium, which has chemical properties almost identical to those of Ta. A large number of procedures have been developed to address this challenge.
In modern times, the separation is achieved by hydrometallurgy.
- Ta2O5 + 14 HF → 2 H2TaF7 + 5 H2O
Completely analogous reactions occur for the niobium component, but the hexafluoride is typically predominant under the conditions of the extraction.
- Nb2O5 + 12 HF → 2 HNbF6 + 5 H2O
These equations are simplified: it is suspected that bisulfate (HSO
4−) and chloride compete as ligands for the Nb(V) and Ta(V) ions, when sulfuric and hydrochloric acids are used, respectively.
The tantalum and niobium fluoride complexes are then removed from the
aqueous solution by liquid-liquid extraction into
organic solvents, such as
cyclohexanone,
octanol, and methyl isobutyl ketone. This simple procedure allows the removal of most metal-containing impurities (e.g. iron, manganese, titanium, zirconium), which remain in the aqueous phase in the form of their
and other complexes.
Separation of the tantalum from niobium is then achieved by lowering the ionic strength of the acid mixture, which causes the niobium to dissolve in the aqueous phase. It is proposed that oxyfluoride H2NbOF5 is formed under these conditions. Subsequent to removal of the niobium, the solution of purified H2TaF7 is neutralised with aqueous ammonia to precipitate hydrated tantalum oxide as a solid, which can be calcination to tantalum pentoxide (Ta2O5).
Instead of hydrolysis, the H2TaF7 can be treated with potassium fluoride to produce potassium heptafluorotantalate:
- H2TaF7 + 2 KF → K2TaF7 + 2 HF
Unlike H
2TaF
7, the potassium salt is readily crystallized and handled as a solid.
K2TaF7 can be converted to metallic tantalum by reduction with sodium, at approximately 800 °C in molten salt.
- K2TaF7 + 5 Na → Ta + 5 NaF + 2 KF
In an older method, called the Marignac process, the mixture of H2TaF7 and H2NbOF5 was converted to a mixture of K2TaF7 and K2NbOF5, which was then separated by fractional crystallization, exploiting their different water solubilities.
Electrolysis
Tantalum can also be refined by electrolysis, using a modified version of the Hall–Héroult process. Instead of requiring the input oxide and output metal to be in liquid form, tantalum electrolysis operates on non-liquid powdered oxides. The initial discovery came in 1997 when Cambridge University researchers immersed small samples of certain oxides in baths of molten salt and reduced the oxide with electric current. The cathode uses powdered metal oxide. The anode is made of carbon. The molten salt at is the electrolyte. The first refinery has enough capacity to supply 3–4% of annual global demand.
Fabrication and metalworking
All
welding of tantalum must be done in an inert atmosphere of
argon or
helium in order to shield it from contamination with atmospheric gases. Tantalum is not
solderable. Grinding tantalum is difficult, especially so for annealed tantalum. In the annealed condition, tantalum is extremely
ductile and can be readily formed as metal sheets.
Applications
Electronics
The major use for tantalum, as the metal powder, is in the production of electronic components, mainly
and some high-power
. 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 aluminium 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, personal computers, automotive electronics and
cameras.
Alloys
Tantalum is also used to produce a variety of
that have high melting points, strength, and ductility. Alloyed with other metals, it is also used in making carbide tools for metalworking equipment and in the production of
for jet engine components, chemical process equipment,
, missile parts, heat exchangers, tanks, and vessels.
Because of its ductility, tantalum can be drawn into fine wires or filaments, which are used for evaporating metals such as
aluminium.
Tantalum is inert against most acids except hydrofluoric acid and hot sulfuric acid, and hot alkaline solutions also cause tantalum to corrode. This property makes it a useful metal for chemical reaction vessels and pipes for corrosive liquids. Heat exchanging coils for the steam heating of hydrochloric acid are made from tantalum.
Surgical uses
Tantalum is widely used in surgery because of two unique characteristics of tantalum. Tantalum's hardness and ductility is useful in making sharp, durable surgical instruments and also for monofilament sutures. However, a completely unrelated use for tantalum in surgery arises from its unique ability to form a lasting and durable structural bond with human hard tissue, making it uniquely useful for bone and dental implants.
Tantalum coatings are increasingly used in the construction of complex tantalum-coated titanium surgical implants due to the tantalum plating's ability to form a strong and biologically stable bond to hard tissue.
An incidental consequence of its use for durable surgical implants is that tantalum implants are considered to be acceptable for patients undergoing MRI procedures because tantalum is a non-ferrous, non-magnetic metal.
Other uses
Tantalum was used by
NASA to shield components of spacecraft, such as
Voyager 1 and
Voyager 2, from radiation.
The high melting point and oxidation resistance led to the use of the metal in the production of
vacuum furnace parts. Tantalum is extremely inert and is therefore formed into a variety of corrosion resistant parts, such as
, valve bodies, and tantalum fasteners. Due to its high density,
shaped charge and explosively formed penetrator liners have been constructed from tantalum.
Tantalum greatly increases the armor penetration capabilities of a shaped charge due to its high density and high melting point.
It is also occasionally used in precious
e.g. from
Audemars Piguet, F. P. Journe,
Hublot, Montblanc,
Omega SA, and
Panerai. Tantalum oxide is used to make special high
refractive index glass for
camera lenses.
Spherical tantalum powder, produced by atomizing molten tantalum using gas or liquid, is commonly used in additive manufacturing due to its uniform shape, excellent
flowability, and high melting point.
Environmental issues
Tantalum receives far less attention in the environmental field than it does in other geosciences. Upper Crust Concentration (UCC) and the Nb/Ta ratio in the upper crust and in minerals are available because these measurements are useful as a geochemical tool.
The latest value for upper crust concentration is 0.92 ppm, and the Nb/Ta(w/w) ratio stands at 12.7.
Little data is available on tantalum concentrations in the different environmental compartments, especially in natural waters where reliable estimates of 'dissolved' tantalum concentrations in seawater and freshwaters have not even been produced.
Values for concentrations in soils, bed sediments and atmospheric aerosols are easier to come by.
Pollution linked to human use of the element has not been detected.
Precautions
Compounds containing tantalum are rarely encountered in the laboratory. The metal is highly
biocompatible and is used for body implants and
, therefore attention may be focused on other elements or the physical nature of the chemical compound.
People can be exposed to tantalum in the workplace by breathing it in, skin contact, or eye contact. The Occupational Safety and Health Administration (OSHA) has set the legal limit (permissible exposure limit) for tantalum exposure in the workplace as 5 mg/m3 over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 5 mg/m3 over an 8-hour workday and a short-term limit of 10 mg/m3. There is a paradox arising because of tantalum's ability to form a strong and permanent bond with bone tissue: at levels of 2500 mg/m3, tantalum dust becomes IDLH if tantalum dust accidentally bonds with the wrong tissue.
External links
