Tantalum

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Tantalum, 73Ta
Tantalum
Pronunciation/ˈtæntələm/ ​(TAN-təl-əm)
Appearancegray blue
Standard atomic weight Ar°(Ta)
Tantalum in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
Nb
↑
Ta
↓
Db
hafnium ← tantalum → tungsten
kJ/mol
Heat of vaporization753 kJ/mol
Molar heat capacity25.36 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
Discovery
Anders Gustaf Ekeberg (1802)
Recognized as a distinct element byHeinrich Rose (1844)
Isotopes of tantalum
Main isotopes[6] Decay
abun­dance half-life (t1/2) mode pro­duct
177Ta synth 56.56 h
β+
177Hf
178Ta synth 2.36 h β+
178Hf
179Ta synth 1.82 y ε
179Hf
180Ta synth 8.125 h ε
180Hf
β−
180W
180mTa 0.0120%
stable
181Ta 99.988% stable
182Ta synth 114.43 d β−
182W
183Ta synth 5.1 d β−
183W
 Category: Tantalum
| references

Tantalum is a

symbol Ta and atomic number 73. Previously known as tantalium, it is named after Tantalus, a figure in Greek mythology.[7] Tantalum is a very hard, ductile, 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 high-melting-point alloys. 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 reaction vessels and vacuum furnaces. 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.[8][9] Tantalum is considered a technology-critical element by the European Commission.[10]

History

Tantalum was discovered in Sweden in 1802 by

columbium (now niobium).[13] 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/cm3 and 7.935 g/cm3, he concluded that they were identical and kept the name tantalum.[14] 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, the goddess of tears), and pelopium (from Pelops).[15][16]
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

light bulb filaments until tungsten replaced it in widespread use.[22]

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.)[23] Anders Ekeberg wrote "This metal I call tantalum ... partly in allusion to its incapacity, when immersed in acid, to absorb any and be saturated."[24]

For decades, the commercial technology for separating tantalum from niobium involved the

solvent extraction from fluoride-containing solutions of tantalum.[18]

Characteristics

Physical properties

Tantalum is dark (blue-gray),[25] dense, ductile, very hard, easily fabricated, and highly conductive of heat and electricity. The metal is highly resistant to corrosion by acids: at temperatures below 150 °C 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

tetragonal (space group P42/mnm, a = 1.0194 nm, c = 0.5313 nm), Knoop hardness is 1000–1300 HN and electrical resistivity is relatively high at 170–210 µΩ⋅cm. 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[26]
obtained by magnetron sputtering, chemical vapor deposition or electrochemical deposition from a eutectic molten salt solution.[27]

Isotopes

Main article: Isotopes of tantalum

Natural tantalum consists of two stable

cosmogenic short-lived nuclides). It is also the rarest primordial isotope in the Universe, taking into account the elemental abundance of tantalum and isotopic abundance of 180mTa in the natural mixture of isotopes (and again excluding radiogenic and cosmogenic short-lived nuclides).[29]

Tantalum has been examined theoretically as a "salting" material for nuclear weapons (cobalt is the better-known hypothetical salting material). An external shell of 181Ta would be irradiated by the intensive high-energy neutron flux from a hypothetical exploding nuclear weapon. This would transmute the tantalum into the radioactive isotope 182Ta, which has a half-life of 114.4 days and produces gamma rays with approximately 1.12 million electron-volts (MeV) of energy apiece, which would significantly increase the radioactivity of the nuclear fallout from the explosion for several months. Such "salted" weapons have never been built or tested, as far as is publicly known, and certainly never used as weapons.[30]

Tantalum can be used as a target material for accelerated proton beams for the production of various short-lived isotopes including 8Li, 80Rb, and 160Yb.[31]

Chemical compounds

Tantalum forms compounds in oxidation states −III to +V. 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 exhibit the +V oxidation state. Like niobium, tantalum is barely soluble in dilute solutions of hydrochloric, sulfuric, nitric and phosphoric acids due to the precipitation of hydrous Ta(V) oxide.[32] In basic media, Ta can be solubilized due to the formation of polyoxotantalate species.[33]

Oxides, nitrides, carbides, sulfides

defect structures, and are lightly studied or poorly characterized.[34]

Tantalates, compounds containing [TaO4]3− or [TaO3]− are numerous. Lithium tantalate (LiTaO3) adopts a perovskite structure. Lanthanum tantalate (LaTaO4) contains isolated TaO3−
4 tetrahedra.[35]

As in the cases of other

refractory metals, 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.[36]

The best studied chalcogenide is TaS2, a layered

transition metal dichalcogenides. A tantalum-tellurium alloy forms quasicrystals.[35]

Halides

Tantalum halides span the oxidation states of +5, +4, and +3.

oxychloride. The lower halides TaX
4 and TaX
3, feature Ta-Ta bonds.[35][32]

Organotantalum compounds

Organotantalum compounds include pentamethyltantalum, mixed alkyltantalum chlorides, alkyltantalum hydrides, alkylidene complexes as well as cyclopentadienyl derivatives of the same.[38][39] Diverse salts and substituted derivatives are known for the hexacarbonyl [Ta(CO)6]− and related isocyanides.

Ta(CH3)5.

Occurrence

Tantalite, Pilbara district, Australia

Tantalum is estimated to make up about 1 

samarskite and fergusonite
.

Grey and white world map with China, Australia, Brazil and Kongo colored blue representing less than 10% of the tantalum world production each and Rwanda colored in green representing 60% of tantalum world production
Tantalum producers in 2015 with Rwanda being the main producer

global financial crisis.[42] Less than a year after it reopened, Global Advanced Metals announced that due to again "... softening tantalum demand ...", and other factors, tantalum mining operations were to cease at the end of February 2012.[43] Wodgina produces a primary tantalum concentrate which is further upgraded at the Greenbushes operation before being sold to customers.[44] Whereas the large-scale producers of niobium are in Brazil and Canada, the ore there also yields a small percentage of tantalum. Some other countries such as China, Ethiopia, and Mozambique mine ores with a higher percentage of tantalum, and they produce a significant percentage of the world's output of it. Tantalum is also produced in Thailand and Malaysia as a by-product of the tin mining there. During gravitational separation of the ores from placer deposits, not only is cassiterite (SnO2) found, but a small percentage of tantalite also included. The slag from the tin smelters then contains economically useful amounts of tantalum, which is leached from the slag.[18][45]

Grey and white world map with Canada, Brazil and Mozambique colored blue representing less than 20% of the tantalum world production each and Australia colored in green representing 60% of tantalum world production
Tantalum producers in 2006 with Australia being the main producer

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.[46] Future sources of supply of tantalum, in order of estimated size, are being explored in Saudi Arabia, Egypt, Greenland, China, Mozambique, Canada, Australia, the United States, Finland, and Brazil.[47][48]

Status as a conflict resource

See also: Coltan mining and ethics and Coltan § Ethics of mining in the Democratic Republic of Congo

Tantalum is considered a

conflict resource. Coltan, the industrial name for a columbite–tantalite mineral from which niobium and tantalum are extracted,[49] 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,[50] 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[51] – 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.[52][53][54][55] 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.[45] 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.[56]

Production and fabrication

Time trend of tantalum production until 2012[57]

Several steps are involved in the extraction of tantalum from tantalite. First, the mineral is crushed and concentrated by gravity separation. This is generally carried out near the mine 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.[58] Extraction begins with leaching the ore with hydrofluoric acid together with sulfuric acid or hydrochloric acid. This step allows the tantalum and niobium to be separated from the various non-metallic impurities in the rock. Although Ta occurs as various minerals, it is conveniently represented as the pentoxide, since most oxides of tantalum(V) behave similarly under these conditions. A simplified equation for its extraction is thus:

Ta2O5 + 14 HF → 2 H2[TaF7] + 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 H[NbF6] + 5 H2O

These equations are simplified: it is suspected that bisulfate (HSO4−) and chloride compete as ligands for the Nb(V) and Ta(V) ions, when sulfuric and hydrochloric acids are used, respectively.

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 fluorides
and other complexes.

Separation of the tantalum from niobium is then achieved by lowering the

oxyfluoride H2[NbOF5] is formed under these conditions. Subsequent to removal of the niobium, the solution of purified H2[TaF7] is neutralised with aqueous ammonia to precipitate hydrated tantalum oxide as a solid, which can be calcined to tantalum pentoxide (Ta2O5).[59]

Instead of hydrolysis, the H2[TaF7] can be treated with potassium fluoride to produce potassium heptafluorotantalate:

H2[TaF7] + 2 KF → K2[TaF7] + 2 HF

Unlike H2[TaF7], the potassium salt is readily crystallized and handled as a solid.

K2[TaF7] can be converted to metallic tantalum by

reduction with sodium, at approximately 800 °C in molten salt.[60]

K2[TaF7] + 5 Na → Ta + 5 NaF + 2 KF

In an older method, called the Marignac process, the mixture of H2[TaF7] and H2[NbOF5] was converted to a mixture of K2[TaF7] and K2[NbOF5], which was then separated by fractional crystallization, exploiting their different water solubilities.

Electrolysis

See also: FFC Cambridge process

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 1,000 °C (1,830 °F) is the electrolyte. The first refinery has enough capacity to supply 3–4% of annual global demand.[61]

Fabrication and metalworking

All

ductile and can be readily formed as metal sheets.[62]

Applications

Electronics

Tantalum electrolytic capacitor

The major use for tantalum, as the metal powder, is in the production of electronic components, mainly

cameras.[63]

Alloys

Tantalum is also used to produce a variety of alloys 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 superalloys for jet engine components, chemical process equipment, nuclear reactors, missile parts, heat exchangers, tanks, and vessels.[64][63][65] Because of its ductility, tantalum can be drawn into fine wires or filaments, which are used for evaporating metals such as aluminium. Since it resists attack by body fluids and is nonirritating, tantalum is widely used in making surgical instruments and implants. For example, porous tantalum coatings are used in the construction of orthopedic implants due to tantalum's ability to form a direct bond to hard tissue.[66]

Tantalum is inert against most acids except

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.[67] Tantalum was extensively used in the production of ultra high frequency electron tubes for radio transmitters. Tantalum is capable of capturing oxygen and nitrogen by forming nitrides and oxides and therefore helped to sustain the high vacuum needed for the tubes when used for internal parts such as grids and plates.[37][67]

Other uses

Bimetallic coins minted by the Bank of Kazakhstan with silver ring and tantalum center. These two feature the Apollo–Soyuz and the International Space Station

Tantalum was used by NASA to shield components of spacecraft, such as Voyager 1 and Voyager 2, from radiation.[68] 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 thermowells, valve bodies, and tantalum fasteners. Due to its high density, shaped charge and explosively formed penetrator liners have been constructed from tantalum.[69] Tantalum greatly increases the armor penetration capabilities of a shaped charge due to its high density and high melting point.[70][71]

It is also occasionally used in precious

Omega, and Panerai. Medical researcher Gerald L. Burke first observed in 1940 that tantalum is also highly bio-inert and could be used safely as an orthopedic implant material.[72] The high stiffness of tantalum makes it necessary to use it as highly porous foam or scaffold with lower stiffness for hip replacement implants to avoid stress shielding.[73] Because tantalum is a non-ferrous, non-magnetic metal, these implants are considered to be acceptable for patients undergoing MRI procedures.[74] The oxide is used to make special high refractive index glass for camera lenses.[75]

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.[76] The latest value for upper crust concentration is 0.92 ppm, and the Nb/Ta(w/w) ratio stands at 12.7.[77]

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.[78] Some values on dissolved concentrations in oceans have been published, but they are contradictory. Values in freshwaters fare little better, but, in all cases, they are probably below 1 ng L−1, since ‘dissolved’ concentrations in natural waters are well below most current analytical capabilities.[79] Analysis requires pre-concentration procedures that, for the moment, do not give consistent results. And in any case, tantalum appears to be present in natural waters mostly as particulate matter rather than dissolved.[78]

Values for concentrations in soils, bed sediments and atmospheric aerosols are easier to come by.[78] Values in soils are close to 1 ppm and thus to UCC values. This indicates detrital origin. For atmospheric aerosols the values available are scattered and limited. When tantalum enrichment is observed, it is probably due to loss of more water-soluble elements in aerosols in the clouds.[80]

Pollution linked to human use of the element has not been detected.[81] Tantalum appears to be a very conservative element in biogeochemical terms, but its cycling and reactivity are still not fully understood.

Precautions

Compounds containing tantalum are rarely encountered in the laboratory. The metal is highly

biocompatible[72] and is used for body implants and coatings, therefore attention may be focused on other elements or the physical nature of the chemical compound.[82]

People can be exposed to tantalum in the workplace by breathing it in, skin contact, or eye contact. The

immediately dangerous to life and health.[83]

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External links

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