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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
Atomic number (Z)73
Groupgroup 5
Periodperiod 6
Block  d-block
Electron configuration[Xe] 4f14 5d3 6s2
Electrons per shell2, 8, 18, 32, 11, 2
Physical properties
Phase at STPsolid
Melting point3290 K ​(3017 °C, ​5463 °F)
Boiling point5731 K ​(5458 °C, ​9856 °F)
Density (at 20° C)16.678 g/cm3 [3]
when liquid (at m.p.)15 g/cm3
Heat of fusion36.57 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
Oxidation statescommon: +5
−3,[4] −1,[5] 0,[6] +1,[7] +2,[5] +3,[5] +4[5]
ElectronegativityPauling scale: 1.5
Ionization energies
  • 1st: 761 kJ/mol
  • 2nd: 1500 kJ/mol
Atomic radiusempirical: 146 pm
Covalent radius170±8 pm
Color lines in a spectral range
Spectral lines of tantalum
Other properties
Natural occurrenceprimordial
Crystal structure ​body-centered cubic (bcc)[3] (cI2)
Lattice constant
Body-centered cubic crystal structure for tantalum
a = 330.29 pm (at 20 °C)[3]
Thermal expansion6.3 µm/(m⋅K) (at 25 °C)
Thermal conductivity57.5 W/(m⋅K)
Electrical resistivity131 nΩ⋅m (at 20 °C)
Magnetic orderingparamagnetic[8]
Molar magnetic susceptibility+154.0×10−6 cm3/mol (293 K)[9]
Young's modulus186 GPa
Shear modulus69 GPa
Bulk modulus200 GPa
Speed of sound thin rod3400 m/s (at 20 °C)
Poisson ratio0.34
Mohs hardness6.5
Vickers hardness870–1200 MPa
Brinell hardness440–3430 MPa
CAS Number7440-25-7
History
Namingafter Tantalus, Greek mythological figure
DiscoveryAnders Gustaf Ekeberg (1802)
Recognized as a distinct element byHeinrich Rose (1844)
Isotopes of tantalum
Main isotopes[10] Decay
Isotope abun­dance half-life (t1/2) mode pro­duct
177Ta synth 56.36 h β+ 177Hf
178Ta synth 2.36 h β+ 178Hf
179Ta synth 1.82 y ε 179Hf
180Ta synth 8.154 h ε 180Hf
β− 180W
180mTa 0.0120% observ. stable
181Ta 99.988% stable
182Ta synth 114.74 d β− 182W
183Ta synth 5.1 d β− 183W
 Category: Tantalum
| references

Tantalum is a chemical element; it has symbol Ta and atomic number 73. It is named after Tantalus, a figure in Greek mythology.[11] 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.

History

[edit]

Tantalum was discovered in Sweden in 1802 by Anders Ekeberg, in two mineral samples – one from Sweden and the other from Finland.[12][13] One year earlier, Charles Hatchett had discovered columbium (now niobium).[14] 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.[15] 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).[16][17] 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.[18]

The differences between tantalum and niobium were demonstrated unequivocally in 1864 by Christian Wilhelm Blomstrand,[19] and Henri Etienne Sainte-Claire Deville, as well as by Louis J. Troost, who determined the empirical formulas of some of their compounds in 1865.[19][20] Further confirmation came from the Swiss chemist Jean Charles Galissard de Marignac,[21] in 1866, who proved that there were only two elements. These discoveries did not stop scientists from publishing articles about the so-called ilmenium until 1871.[22] De Marignac was the first to produce the metallic form of tantalum in 1864, when he reduced tantalum chloride by heating it in an atmosphere of hydrogen.[23] 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.[24]

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.)[25] Anders Ekeberg wrote "This metal I call tantalum ... partly in allusion to its incapacity, when immersed in acid, to absorb any and be saturated."[26]

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.[20]

Characteristics

[edit]

Physical properties

[edit]

Tantalum is dark (blue-gray),[27] 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.[28]

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.[3] It is relatively ductile, has Knoop hardness 200–400 HN and electrical resistivity 15–60 μΩ⋅cm. The beta phase is hard and brittle; its crystal symmetry is 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[29] obtained by magnetron sputtering, chemical vapor deposition or electrochemical deposition from a eutectic molten salt solution.[30]

Isotopes

[edit]
Main article: Isotopes of tantalum

Natural tantalum consists of two stable isotopes: 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 180W, or electron capture to 180Hf. However, radioactivity of this nuclear isomer has never been observed, and only a lower limit on its half-life of 2.9×1017 years has been set.[31] The ground state of 180Ta has a half-life of only 8 hours. Among primordial nuclides (half-life > 108 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).[32]

Tantalum has been examined theoretically as a "salting" material for nuclear weapons (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 fallout for months. Such "salted" weapons are not known to have been built, tested, or used.[33]

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.[34]

Chemical compounds

[edit]

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, nitric and phosphoric acids due to the precipitation of hydrous Ta(V) oxide.[35] In basic media, Ta can be solubilized due to the formation of polyoxotantalate species.[36]

Oxides, nitrides, carbides, sulfides

[edit]

Tantalum pentoxide (Ta2O5) is the most important compound from the perspective of applications. Oxides of tantalum in lower oxidation states are numerous, including many defect structures, and are lightly studied or poorly characterized.[37]

Tantalates, compounds containing [TaO4]3− or [TaO3]− are numerous. Lithium tantalate (LiTaO3) adopts a perovskite structure. Lanthanum tantalate (LaTaO4) contains isolated TaO3−
4 tetrahedra.[38]

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.[39]

The best studied chalcogenide is Tantalum sulfide (TaS2), a layered semiconductor, as seen for other transition metal dichalcogenides. A tantalum-tellurium alloy forms quasicrystals.[38]

Halides

[edit]

Tantalum halides span the oxidation states of +5, +4, and +3. Tantalum pentafluoride (TaF5) is a white solid with a melting point of 97.0 °C. The anion [TaF7]2- is used for its separation from niobium.[40] The chloride TaCl
5, which exists as a dimer, is the main reagent in synthesis of new Ta compounds. It hydrolyzes readily to an oxychloride. The lower halides TaX
4 and TaX
3, feature Ta-Ta bonds.[38][35]

Organotantalum compounds

[edit]

Organotantalum compounds include pentamethyltantalum, mixed alkyltantalum chlorides, alkyltantalum hydrides, alkylidene complexes, as well as cyclopentadienyl derivatives of the same.[41][42] Diverse salts and substituted derivatives are known for the hexacarbonyl [Ta(CO)6]− and related isocyanides.

Ta(CH3)5.

Occurrence

[edit]
Tantalite, Pilbara district, Australia

Tantalum is estimated to make up about 1 ppm[43] or 2 ppm[35] 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)).[44] Tantalite (Fe, Mn)Ta2O6 is the most important mineral for tantalum extraction. Tantalite has the same mineral structure as columbite (Fe, Mn) (Ta, Nb)2O6; 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.

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

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 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.[45] 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.[46] Wodgina produces a primary tantalum concentrate which is further upgraded at the Greenbushes operation before being sold to customers.[47] 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.[20][48]

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.[49] 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.[50][51]

Status as a conflict resource

[edit]
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,[52] 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,[53] 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[54] – 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.[55][56][57][58] 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.[48] 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.[59]

Production and fabrication

[edit]
Time trend of tantalum production until 2012[60]

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

[edit]

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.[61] 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.[61] 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 fluorides 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 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).[62]

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.[63]

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

[edit]
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.[64]

Fabrication and metalworking

[edit]

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.[65]

Applications

[edit]

Electronics

[edit]
Tantalum electrolytic capacitor

The major use for tantalum, as the metal powder, is in the production of electronic components, mainly capacitors and some high-power 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 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.[66]

Alloys

[edit]

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.[67][66][68] 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.[69] 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.[40][69]

Surgical uses

[edit]

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.[70] 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.[71] 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.[72]

Other uses

[edit]
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.[73] 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.[74] Tantalum greatly increases the armor penetration capabilities of a shaped charge due to its high density and high melting point.[75][76] It is also occasionally used in precious watches e.g. from Audemars Piguet, F. P. Journe, Hublot, Montblanc, Omega, and Panerai. Tantalum oxide is used to make special high refractive index glass for camera lenses.[77] 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.[78][79]

Environmental issues

[edit]

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.[80] The latest value for upper crust concentration is 0.92 ppm, and the Nb/Ta(w/w) ratio stands at 12.7.[81]

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.[82] 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.[83] 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.[82]

Values for concentrations in soils, bed sediments and atmospheric aerosols are easier to come by.[82] 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.[84]

Pollution linked to human use of the element has not been detected.[85] Tantalum appears to be a very conservative element in biogeochemical terms, but its cycling and reactivity are still not fully understood.

Precautions

[edit]

Compounds containing tantalum are rarely encountered in the laboratory. The metal is highly biocompatible[70] and is used for body implants and coatings, therefore attention may be focused on other elements or the physical nature of the chemical compound.[86]

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 immediately dangerous to life and health if tantalum dust accidentally bonds with the wrong tissue.[87]

References

[edit]
[edit]
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Tantalum

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from Grokipedia
Tantalum is a with the symbol Ta and 73. It is a rare, hard, blue-gray lustrous valued for its exceptional resistance, high melting point, and ductility. Discovered in 1802 by Swedish Anders Gustaf Ekeberg from samples in , the element was named after from due to its resistance to acids, akin to the mythological figure's eternal frustration. Tantalum primarily occurs in the mineral , often collinear with in pegmatites and carbonatites, with major production from ores imported mainly from , the , and . Its ability to form a thin, stable layer enables tantalum's dominant use in electrolytic capacitors, which provide high in compact volumes critical for portable electronics, while its supports applications in surgical implants and its high-temperature strength aids superalloys in components.

History

Discovery and etymology

Tantalum was discovered in 1802 by Swedish chemist Anders Gustaf Ekeberg, who isolated its oxide from mineral samples including yttrotantalite from , , and from Kimito, Finland. Ekeberg identified the substance as a new element, distinct from columbium (later named ), which had been reported by Charles Hatchett in , based on its chemical behavior and resistance to acids. Ekeberg derived the name tantalum from , a figure in punished by standing in water beneath fruit-laden branches that receded when he attempted to drink or eat, symbolizing the element's oxide, which tantalized chemists by remaining insoluble despite immersion in acids. Early analyses led to confusion with , with some chemists like proposing they were identical. This was resolved in 1846 when German chemist Heinrich Rose demonstrated their distinction through differences in atomic weights and compound properties, naming the earths tantalic acid and niobic acid. Swiss chemist Jean Charles Galissard de Marignac provided further confirmation in 1866 by separating the elements more effectively and verifying only two distinct substances existed.

Early isolation and industrial development

The first relatively pure and ductile metallic tantalum was isolated in by German chemist Werner von Bolton, who achieved this by reducing tantalum oxides in a and subsequently melting impure tantalum to refine it into a workable form suitable for . Prior efforts had yielded only impure tantalum, hampered by its chemical similarity to —particularly their near-identical ionic radii (tantalum 64 pm, niobium 64.6 pm) and reactivity patterns—which complicated selective extraction from co-occurring minerals like columbite-tantalite. This similarity necessitated laborious separation techniques, such as fractional crystallization of double fluorides or early solvent methods, often resulting in contamination levels exceeding 1-2% niobium. Following Bolton's breakthrough, initiated commercial production of tantalum wire in around 1905-1910 for use as incandescent lamp filaments, capitalizing on its high (3017°C) and resistance to oxidation, though it was soon displaced by due to cost and advantages. In the 1920s and 1930s, emerged as a key method for tantalum fabrication, involving chemical reduction of tantalum halides (e.g., TaF₅ with sodium or magnesium) to produce fine powders that were then compacted and sintered under or inert atmospheres to form anodes for electrolytic capacitors. These early capacitors, developed by firms like Fansteel and Tansitor, employed tantalum foil or powder with electrolytes, offering superior density over aluminum alternatives for military radios and early . World War II accelerated industrial scaling, with U.S. and Allied demand for tantalum in vacuum tubes, equipment, and superalloys spiking amid electronics proliferation; annual consumption rose from negligible pre-war levels to thousands of pounds by 1945, sourced primarily from columbite-tantalite concentrates. Supply chains faced severe disruptions from Axis submarine campaigns targeting ore shipments from and , prompting domestic refining advancements like improved acid digestion and to yield 99%+ purity tantalum from ores averaging 20-60% Ta₂O₅. Post-war, these processes laid groundwork for mid-century expansion, though yields remained low (often <50%) due to persistent niobium interference without advanced ion-exchange separations.

Properties

Physical properties

Tantalum is a dense transition metal with a body-centered cubic crystal structure, characterized by a lattice parameter of 330.29 pm at 20 °C. Its density measures 16.65 g/cm³ at room temperature, contributing to its use in high-mass applications. The metal exhibits exceptional ductility, allowing it to be drawn into wires as thin as needed for electronic components without fracturing. The melting point of tantalum is 3017 °C, ranking it among the highest-melting pure metals, which enables its application in refractory environments. It demonstrates good electrical conductivity, with a resistivity of 13.1 μΩ·cm at 20 °C, corresponding to about 7.6 × 10⁶ S/m. Tantalum becomes superconducting at a critical temperature of approximately 4.48 K in high-purity samples. Mechanically, annealed tantalum possesses a tensile strength typically ranging from 170 to 300 MPa, with yield strengths of 100 to 200 MPa, and elongation exceeding 25% in gauge lengths. Its coefficient of linear thermal expansion is 6.5 × 10⁻⁶ K⁻¹ between 20 and 100 °C, indicating low dimensional change under heating. These properties, derived from empirical measurements, underscore tantalum's suitability for demanding structural and conductive roles in engineering.

Chemical properties

Tantalum, a group 5 d-block transition metal with the electron configuration [Xe] 4f¹⁴ 5d³ 6s², displays reactivity patterns influenced by its valence electrons, favoring high coordination numbers and stable pentavalent bonding. The element predominantly adopts the +5 oxidation state in compounds, reflecting the stability of d⁰ configurations, while lower oxidation states such as +3 or +4 are less common and typically unstable in aqueous media due to facile oxidation to +5. Tantalum exhibits a strong affinity for oxygen, rapidly forming a dense, adherent layer of Ta₂O₅ upon exposure to air or oxygen-containing environments; this passive oxide film, akin to those on other reactive , provides robust protection against further oxidation and chemical attack. This passivation confers exceptional corrosion resistance, rendering tantalum inert to most mineral acids (e.g., HCl up to 30% concentration below 190 °C, H₂SO₄ up to 98% below 190 °C, HNO₃ up to 65% below 190 °C) and unaffected by dilute bases such as KOH (<5% at <100 °C); it also resists halogens like Cl₂, Br₂, and I₂ below 150 °C, though fluorine and hydrofluoric acid penetrate the oxide layer. Tantalum dissolves only in hydrofluoric acid or mixtures of HF with oxidizing agents like HNO₃, where fluoride complexes disrupt the passive film; the standard reduction potential for Ta₂O₅(s) + 10H⁺ + 10e⁻ → 2Ta(s) + 5H₂O is -0.752 V versus the standard hydrogen electrode, indicating the thermodynamic favorability of the oxidized state in acidic conditions.

Isotopes

Natural tantalum is composed predominantly of the stable isotope ^{181}Ta, which accounts for 99.988% of its abundance, alongside a trace amount of the radioactive metastable isomer ^{180m}Ta at 0.012%. The ground state ^{180}Ta decays rapidly with a half-life of approximately 8.15 hours primarily via beta minus emission to ^{180}Hf, but the natural occurrence is almost exclusively the higher-energy isomer ^{180m}Ta, which persists due to hindered electromagnetic transitions. Experimental measurements have established a lower limit for the half-life of ^{180m}Ta exceeding 2 \times 10^{16} years, with theoretical predictions ranging from 10^{17} to 10^{19} years, rendering it effectively stable over cosmic timescales despite its radioactivity. Tantalum possesses over 30 known synthetic radioisotopes, typically produced via neutron capture on stable tantalum or proton spallation reactions for nuclear research. Notable examples include ^{179}Ta, generated through neutron irradiation pathways with a half-life of 1.82 years, and ^{182}Ta, with a half-life of 114 days, which emits beta particles and gamma rays suitable for tracer studies but lacks practical fissionability due to insufficient neutron cross-sections for chain reactions. None of tantalum's isotopes exhibit significant fissionable properties akin to uranium or plutonium isotopes, limiting their role in nuclear energy applications. Isotopic variations in tantalum, particularly ratios involving ^{180m}Ta and ^{181}Ta, serve as tracers in geochemical and cosmochemical analyses to infer nucleosynthetic processes and early solar system differentiation, as the anomalously low abundance of ^{180m}Ta reflects p-process origins rather than cosmogenic production in terrestrial environments. These signatures enable distinctions between primordial and secondary contributions in meteorites and planetary materials, though cosmogenic activation in surface samples primarily yields short-lived isotopes without altering bulk natural abundances.

Occurrence and geology

Mineral forms and deposits

Tantalum primarily occurs in oxide minerals, with the chief ore being tantalite-(Fe) and tantalite-(Mn), which are the iron- and manganese-dominant end-members of the columbite-tantalite solid solution series, often collectively termed coltan. Other significant tantalum-bearing minerals include microlite (a calcium-sodium tantalate), wodginite ((Mn,Fe,Sn)Ta2O8), and pyrochlore-group minerals such as microlite and betafite. These minerals are predominantly hosted in rare-element class granitic pegmatites, particularly lithium-cesium-tantalum (LCT)-type pegmatites formed through fractional crystallization of granitic magmas. Tantalum mineralization is associated with highly fractionated zones enriched in incompatible elements, often alongside lithium-bearing spodumene, beryl, and tin minerals like cassiterite. Alluvial and placer deposits form through the weathering and erosion of primary pegmatites, concentrating heavy tantalum minerals in sedimentary environments. Economic occurrences in carbonatites are rare, typically limited to accessory pyrochlore. Tantalum is commonly extracted as a byproduct from lithium and tin mining operations, where pegmatite ores are processed for primary commodities, allowing recovery of tantalum concentrates from tailings or co-mineralized zones.

Global distribution and reserves

Identified reserves of tantalum, defined as economically extractable portions under current conditions, total several hundred thousand metric tons globally, with the largest concentrations in (240,000 metric tons), (110,000 metric tons), and (40,000 metric tons). Additional significant resources exist in and the (approximately 55,000 metric tons, largely subeconomic at 2024 prices), though formal reserves for many African producers remain unquantified due to predominant artisanal and small-scale operations lacking detailed geological assessments. In , the Greenbushes deposit in Western Australia represents a major hard-rock resource, contributing substantially to the country's reserve base as a co-product of lithium mining. Current mine production, reported as tantalum content in ore and concentrates, reached an estimated 2,100 metric tons worldwide in 2024, dominated by the Democratic Republic of Congo (880 metric tons), Nigeria (390 metric tons), and Rwanda (350 metric tons). Australia and Brazil contributed smaller shares at 52 and 210 metric tons, respectively, reflecting a geographic mismatch between reserves and output, where African nations leverage alluvial and artisanal deposits despite lacking formalized reserve estimates. Emerging production in regions like Ethiopia remains limited and unquantified in official statistics, while Canadian exploration focuses on pegmatite-hosted resources to bolster supply security. Exploration trends emphasize diversification into geologically stable jurisdictions such as and to mitigate risks from supply disruptions in conflict-prone areas, though resource nationalism—evident in export controls or fiscal policy shifts in countries like —poses challenges to long-term reserve development. Overall, world resources are deemed adequate for foreseeable demand, but accurate reserve delineation in high-production African regions is hindered by informal mining practices and geopolitical instability.

Production

Mining methods

Tantalum is extracted primarily through surface mining techniques targeting pegmatite-hosted deposits, which contain key minerals such as tantalite ((Fe,Mn)Ta₂O₆) and columbite-tantalite (coltan). Open-pit methods predominate for near-surface, low-grade ore bodies amenable to bulk extraction, involving overburden stripping, drilling, blasting, and mechanical excavation to access disseminated tantalum-bearing phases. These operations are efficient for massive or steeply dipping deposits, with ore grades typically ranging from 0.01% to 0.1% Ta₂O₅, though artisanal targeting of high-grade zones can exceed 0.2%. In central Africa, alluvial placer deposits formed by the reworking of weathered are mined via manual or semi-mechanized washing and panning to concentrate dense grains from sediments. This method exploits the high specific gravity of coltan (5.2–7.2 g/cm³) relative to surrounding materials, often in riverbeds or eluvial zones, yielding concentrates through simple gravity separation without extensive crushing. Artisanal and small-scale mining (ASM) dominates in the Democratic Republic of Congo (DRC) and Rwanda, regions that produced about 60% of global tantalum mine output in 2024, primarily from such alluvial and semi-pegmatite sources. These low-capital operations rely on hand tools for digging and rudimentary sluicing, achieving variable recovery rates of 13%–78%, with lower efficiencies common due to incomplete separation of fine-grained tantalum minerals locked in gangue. Over the past decade, ASM has contributed approximately 60% to worldwide primary tantalum supply, underscoring its scale despite inefficiencies. Mechanized mining in Australia, exemplified by the Greenbushes operation, processes weathered pegmatite-derived alluvial clays using dual ore-washing systems and advanced gravity concentration, attaining recovery rates of 70%–95% for sand-sized or coarser particles. This approach, enhanced by screening and hydrocycloning, contrasts with ASM by enabling higher throughput and selectivity, with yields up to 85% in soft, unconsolidated deposits.

Refining and processing

Tantalum concentrates, typically derived from minerals like , undergo acid digestion in a mixture of hydrofluoric and sulfuric acids to dissolve and as complex fluorides, forming a liquor from which impurities such as , , and are removed via precipitation or solvent extraction steps. The critical separation of tantalum from chemically similar niobium occurs primarily through solvent extraction in hydrofluoric acid media, utilizing selective organic extractants like methyl isobutyl ketone (MIBK) or trioctylamine (TOA) to preferentially transfer tantalum into the organic phase, achieving purities exceeding 98% after stripping and precipitation as potassium heptafluorotantalate (K₂TaF₇); fractional crystallization of double fluoride salts with potassium offers an alternative but less efficient method due to solubility differences in their complexes. Conversion to metal proceeds via reduction of K₂TaF₇ with sodium metal in a sealed bomb reactor at temperatures around 800–900°C, yielding crude tantalum sponge contaminated with alkali metals, which requires leaching and vacuum arc remelting for purification; alternatively, calcined tantalum pentoxide (Ta₂O₅) is reduced with carbon under high vacuum at 1,600–1,800°C to produce sponge via the reaction 2Ta₂O₅ + 14C → 4Ta + 14CO, minimizing oxygen contamination. For applications demanding ultra-high purity, such as electronics, capacitor-grade tantalum powder is generated through energy-intensive molten salt electrolysis of TaF₅ or related salts, depositing fine particles via electrochemical reduction, or by hydrogen-assisted reduction of Ta₂O₅ in fluidized beds, with processes consuming significant electricity to achieve sub-ppm impurity levels. U.S. apparent consumption of tantalum, reflecting downstream refining demand, totaled an estimated 370 metric tons (tantalum content) in 2023, a decline attributed to inventory drawdowns and market fluctuations.

Fabrication techniques

Tantalum's fabrication is complicated by its high melting point of 3017°C, strong affinity for oxygen, and susceptibility to hydrogen embrittlement, which can cause brittleness during processing if not controlled through vacuum or inert atmospheres. Primary techniques include powder metallurgy and electron-beam melting to produce usable forms like powders, ingots, and sintered parts, often requiring subsequent annealing to restore ductility. Powder metallurgy dominates for high-purity components, starting with tantalum powder produced via sodium reduction or potassium heptafluorotantalate decomposition, which is then compacted under high pressure and sintered in vacuum at temperatures around 2000–2500°C to achieve densities exceeding 95% of theoretical without melting. This method minimizes interstitial contamination but demands precise control to avoid oxidation, which forms a tenacious Ta₂O₅ layer that embrittles the material. Electron-beam melting refines crude powder or scrap into high-purity ingots (up to 5N grade) through multiple vacuum cycles, where an electron beam selectively melts the charge, volatilizing impurities like carbon and oxygen. This produces homogeneous billets for further forging or rolling, with typical ingot diameters of 100–300 mm. Forming processes such as hot forging, rolling, and extrusion are conducted above 1000°C in protective environments to prevent surface oxidation and cracking, yielding sheets as thin as 0.1 mm or wire. Annealing follows deformation, heating in high vacuum (>10⁻⁵ ) to 2000°F or higher for 1–2 hours to recrystallize the microstructure and eliminate hydrogen-induced , restoring elongation to over 20%. employs electron-beam or gas-tungsten arc methods in vacuum to fuse tantalum, avoiding filler metals that introduce impurities; suits thin alloys, providing joints with tensile strengths matching when surfaces are etched to remove oxides. Alloying during fabrication enhances fabricability and properties; for instance, adding 2.5–10 wt% via powder blending and consolidation increases yield strength to 500–800 MPa while maintaining corrosion resistance, processed similarly to pure tantalum but with adjusted parameters. Titanium additions (up to 40 wt%) in binary alloys are achieved through in-situ mixing in powder bed fusion or melting, improving but requiring dealloying steps like processing to refine ligament structures. These alloys demand specialized annealing to mitigate phase segregation and embrittlement risks.

Supply chain controversies

Role in African conflicts

Coltan mining in the eastern (DRC) has provided revenue to armed militias through control of artisanal sites, imposition of taxes on miners, and organization of smuggling networks, particularly during periods of elevated global prices. investigations in the early 2000s documented that Rwandan forces and allied militias controlled 60–70% of production in occupied DRC territories, using proceeds to finance military operations amid the Second Congo War (1998–2003). Export volumes from the DRC and neighboring surged in the late 1990s and early 2000s, with DRC output rising from negligible levels pre-1998 to approximately 1,400 metric tons of ore (yielding over 200 tons of tantalum content) by 2000, driven by a global price spike from $50 per kilogram in 1999 to $400 per kilogram in 2001 due to demand for capacitors. This boom correlated with intensified economies, as groups like the (RCD) and other rebels leveraged mining to sustain combat, though empirical analyses indicate 's role in overall rebel financing was episodic and secondary to , contributing an estimated 10–20% of income for specific groups in eastern provinces during peak years before 2010. Artisanal and small-scale mining (ASM) sites, which dominate coltan extraction in the DRC, frequently involve child labor, with reports documenting thousands of children under 18 engaged in hazardous tasks such as digging pits up to 30 meters deep and carrying heavy loads, often in militia-controlled areas where families displaced by violence rely on mining for survival. The DRC's share of global tantalum production peaked at around 30% (410 metric tons) in 2008 before declining sharply, falling to less than 10% of certified supply by the mid-2010s as international buyers shifted to alternative sources and smuggling routes contracted amid volatile prices and site closures. Despite persistent violence, post-2010 data from supply chain mapping show reduced flows from conflict zones funding militias at prior scales, with overtaking minerals (tin, tantalum, tungsten) as the primary conflict commodity in eastern DRC.

International regulations and traceability

Section 1502 of the Dodd–Frank Wall Street Reform and Consumer Protection Act, signed into law on July 21, 2010, requires U.S. Securities and Exchange Commission-registered companies to annually disclose whether their products contain tantalum, tin, , or (3TG minerals) sourced from the (DRC) or adjoining countries, including conducting reasonable country-of-origin inquiries and, if necessary, to determine if such minerals directly or indirectly finance armed conflict. This provision aims to pressure companies to avoid conflict-sourced minerals without banning them outright, with the first disclosures required in 2014. Complementing this, the European Union's Regulation (EU) 2017/821, adopted on May 17, 2017, and applicable from January 1, 2021, imposes supply chain obligations on EU importers of 3TG minerals exceeding specified volumes (e.g., 5 tons for tantalum ores annually), mandating risk assessments, mitigation plans, and third-party audits aligned with guidelines. Traceability initiatives have emerged to operationalize these regulations, particularly in , where most tantalum originates. The International Tin Supply Chain Initiative (ITSCI), established in 2009 and implemented via the iTSCi programme from 2011, deploys on-site monitoring, bagging with tags, and digital tracking at over 1,000 artisanal sites across the DRC, , , and , covering approximately 50% of African tantalum production as of 2023 through validated and designations (, yellow, red). Participating companies, including those under the Responsible Minerals Initiative, integrate iTSCi into compliance reporting. Additionally, blockchain-based pilots have tested enhanced verification; for instance, 's 2021 trial with Boston Metal and Traxys used technology to trace (tantalum-bearing ore) from mine to , logging transactions on a permissioned network to prevent fraud, though scalability remains limited. United Nations Group of Experts reports on the DRC have documented partial successes from these frameworks, noting that enhanced since 2014 has reduced direct mineral revenues to certain armed groups by marginalizing them from monitored sites and formal trade channels, with validated exports from and eastern DRC showing lower conflict linkages compared to pre-regulation baselines. For example, the 2023 report highlighted iTSCi compliance in —accounting for 60% of global output—correlating with decreased armed group involvement in certified mines, though and upstream laundering persist, limiting overall impact to incremental rather than transformative. These outcomes reflect empirical progress in mapping but underscore reliance on voluntary participation and regional enforcement.

Critiques of conflict minerals framework

Critics argue that the conflict minerals framework, exemplified by the U.S. Dodd-Frank Act Section 1502, misattributes causation by portraying minerals like tantalum as the primary driver of violence in the (DRC), when empirical evidence indicates they exacerbate rather than originate longstanding ethnic tensions and governance failures. Conflicts in eastern DRC, rooted in ethnic divisions and regional power struggles predating the 1990s boom, persisted with or without mineral revenues, which constitute a minor share of armed group financing compared to taxation, , and illicit in other commodities. This causal inversion, per analysts, fosters moralistic interventions that overlook how weak state institutions and foreign meddling sustain instability independently of resource extraction. Implementation of traceability requirements has produced verifiable unintended economic harms, including sharp declines in legitimate and heightened . Following Dodd-Frank's 2010 enactment and 2012 SEC rule, validated mineral exports from eastern DRC fell by over 50% between 2013 and 2014, displacing hundreds of thousands of small-scale miners into poverty and informal labor. A 2019 econometric analysis linked these disruptions to a more than doubling of rates in mining-adjacent villages, as reduced incomes curtailed access to food and healthcare without diminishing armed group revenues, which shifted to undocumented channels. networks, entrenched for decades, adapted by rerouting tantalum via —where over 90% of reported originates from DRC sources—bypassing certification while formal trade collapsed. The framework's top-down approach neglects market-driven sourcing from stable producers, where tantalum supply exceeds DRC contributions through diversified, low-risk channels. Australia and Brazil historically accounted for over 40% of global output in peak years, with Australia supplying 54% of U.S. tantalum ore imports in 2023, enabling ethical alternatives unhindered by regional stigma. Regulations have accelerated this shift, stigmatizing all Central African tantalum and undermining local development, yet U.S. Government Accountability Office assessments confirm no net reduction in violence or armed group activity post-2010. Proponents of reform advocate voluntary industry standards over mandatory disclosures, citing evidence that consumer-driven certification in non-conflict zones fosters accountability without the perverse incentives of embargoes.

Applications

Electronics and capacitors

Tantalum capacitors are electrolytic devices that utilize as the material, forming a thin layer as the , which enables exceptionally high per unit volume compared to alternatives like aluminum electrolytic capacitors. This volumetric efficiency can be up to three times greater than that of aluminum types for equivalent ratings, allowing for compact designs in space-constrained applications. Over 50% of global tantalum consumption is directed toward capacitor production, primarily for in consumer devices, automotive systems, and equipment. In smartphones, tantalum capacitors support and decoupling in high-density circuits, while in electric vehicles (EVs), they are integral to battery monitoring and for efficient and discharge. Aerospace applications leverage their stability under extreme conditions, including temperatures exceeding 175°C and high , where failure rates remain low even in military-grade systems rated for 1% failure per 1,000 hours. Demand for tantalum in these capacitors has grown with the expansion of infrastructure and EV adoption, contributing to overall market expansion from approximately $387 million in 2023 to a projected $550 million by 2030. This growth reflects tantalum's role in enabling reliable performance in miniaturized, high-reliability , where alternatives fall short in or durability under stress.

Alloys and aerospace

Tantalum is alloyed with nickel-based superalloys to enhance high-temperature strength and creep resistance in components, particularly blades exposed to extreme heat exceeding 1000°C. These superalloys, incorporating up to several percent tantalum, maintain structural integrity under oxidative and corrosive conditions in jet engines, where tantalum contributes to solid-solution strengthening and . The Ta-10W alloy, containing 9-11% , exemplifies tantalum's utility in high-temperature fabrication, with a of 3038°C (5495°F) enabling its use in parts requiring and resistance to thermal . This alloy's chemical stability against liquid metals like mercury and sodium-potassium mixtures supports applications in systems, though its of approximately 16.6 g/cm³ necessitates design trade-offs against lighter alternatives such as (around 4.5 g/cm³), balancing performance gains in resistance and tolerance against weight penalties in . In nuclear contexts relevant to aerospace-derived technologies, tantalum alloys serve in radiation-shielding components and fuel cladding, retaining mechanical properties under ; for instance, cold-sprayed tantalum coatings on substrates have demonstrated viability for fusion walls by withstanding plasma at temperatures up to °C. Advancements in tantalum welding to nickel superalloys, reported in studies up to 2023, address challenges in joining for and assemblies, improving joint integrity without embrittlement.

Medical implants and devices

Tantalum exhibits exceptional , resistance, and mechanical properties that render it suitable for long-term implantation in orthopedic, dental, and cardiovascular applications. Its inert nature minimizes inflammatory responses, enabling stable integration with human tissues without eliciting adverse reactions over extended periods. Porous tantalum, marketed as trabecular metal, features a highly interconnected pore structure with 75-80% , mimicking the architecture of cancellous to facilitate and vascular ingrowth. This material enhances implant stability through high frictional coefficients (up to 0.8) and an (approximately 2.5-3.9 GPa) closely matching that of (0.1-30 GPa), reducing stress shielding compared to traditional or alloys. Clinical applications include acetabular cups, spinal cages, and dental implants, where it promotes bone apposition rates exceeding 50% within 4-6 weeks post-implantation in animal models and human trials. In cardiovascular devices, tantalum serves as radiopaque markers in self-expanding stents, such as those with eight markers per end for precise fluoroscopic visualization during deployment, and contributes to overall device durability due to its non-thrombogenic surface. These stents demonstrate endothelialization within 6-8 weeks, supporting patency rates above 90% in long-term follow-up studies. Tantalum's diamagnetic ensure MRI compatibility, with no significant artifact distortion or device migration at field strengths up to 3 Tesla, unlike ferromagnetic alternatives. Recent advancements in surface modifications, including nanostructured coatings via or nanotube formation, have improved cellular adhesion and antibacterial efficacy; for instance, zinc oxide-modified tantalum nanotubes reduced bacterial adhesion by over 90% while accelerating proliferation studies from 2022 onward. These techniques address limitations in pristine tantalum's bioactivity, enhancing surgical outcomes in load-bearing implants.

Chemical processing and other uses

Tantalum exhibits superior resistance to most acids, including hydrochloric, sulfuric, and nitric acids, even at elevated temperatures up to 150–200°C, rendering it ideal for chemical processing equipment exposed to aggressive environments. This property stems from the formation of a layer that passivates the surface, preventing further degradation. Consequently, tantalum is fabricated into linings for reactors, columns, and storage tanks handling hot, concentrated acids; heat exchangers for corrosive fluids; and components such as , valves, heaters, and generators in industries like and pharmaceuticals. Tantalum carbide (TaC), a compound with approaching that of (Vickers hardness ~1800–2000 HV) and high (~3880°C), is incorporated into cermets and coatings for cutting tools. These applications include metalcutting inserts, milling cutters, drill bits, and wear-resistant parts for ferrous alloys, stainless steels, and superalloys, where TaC enhances abrasion resistance and stability when alloyed with or binders. In jewelry, pure tantalum is utilized for rings and bands due to its lustrous, gray-blue metallic sheen, nature (lacking or common allergens), and durability against scratching and tarnishing under normal wear. Its (16.65 g/cm³) provides a substantial feel comparable to , while resistance to body acids and salts ensures longevity without polishing. Minor applications include tantalum(V) oxide (Ta₂O₅) films for optical coatings, leveraging its high (n ≈ 2.1–2.2) in anti-reflective layers on lenses and sensors to minimize reflection and improve transmission .

Emerging technologies

Tantalum nanoparticles have shown promise in electrocatalysis for applications. In 2024, /tantalum core-shell nanoparticles were developed as electrocatalysts for direct methanol fuel cells, demonstrating sub-nanometer shell thicknesses that enhance stability and activity under operational conditions. Similarly, tantalum-stabilized oxide electrocatalysts, introduced in early 2025, mitigate dissolution during the oxygen evolution reaction in , enabling higher durability in acidic electrolytes compared to pure ruthenium oxide. Tantalum oxide nanoparticles integrated with have also advanced photocatalytic hydrogen production from ethanol/water solutions under white LED illumination, achieving improved charge separation and quantum efficiency. In quantum computing, tantalum has emerged as a superior material for superconducting components, surpassing in coherence times. Researchers in 2023 decoded tantalum surface profiles to reduce qubit loss mechanisms, yielding T1 coherence times exceeding 0.3 milliseconds. By 2025, tantalum airbridges were fabricated via lift-off methods for scalable superconducting quantum processors, serving as jumpers, crossovers, and coupling elements with low loss and high reliability. These advancements stem from tantalum's reduced two-level system defects and improved layer control, facilitating longer-lived qubits essential for fault-tolerant systems. Recent welding techniques for tantalum alloys address challenges in high-temperature applications. In 2024, of pure tantalum using interlayers improved joint strength by preventing oxidation and enhancing interfacial bonding, achieving shear strengths comparable to . Laser welding of additively manufactured Ta-10W alloys, also reported in 2024, mitigated internal cracking through optimized parameters, resulting in defect-free welds with maintained and tensile properties. For fusion reactors, tantalum coatings applied via cold spray in 2023 have demonstrated resilience in plasma-facing environments. These coatings on substrates withstood temperatures up to 1,200°C and fluxes while absorbing isotopes, reducing activation and enabling more compact reactor designs. Tungsten-tantalum alloys with 1-5% tantalum, developed around 2022 but tested post-2020, exhibit enhanced recrystallization resistance and low activation under fusion . In hypersonic materials, hafnium-tantalum carbides have been optimized via field-assisted for leading-edge components. A 2024 study on HfC-TaC alloys revealed solid solution strengthening that balances hardness and toughness, with compositions achieving up to 4.5 MPa·m^{1/2} at ultra-high temperatures exceeding 2,000°C. These carbides' high melting points and oxidation resistance position them as candidates for thermal protection systems in hypersonic vehicles.

Chemical compounds

Inorganic compounds

Tantalum predominantly forms inorganic compounds in the +5 , with lower states less stable and requiring specific reducing conditions. These compounds exhibit high chemical stability, particularly resistance to most acids except and fused alkalies. Oxides
Tantalum(V) oxide (Ta₂O₅), a white crystalline solid with a of 1872 °C, is the primary oxide and occurs naturally in minerals such as . It is synthesized industrially by calcining ammonium tantalate or tantalum hydroxide derived from ore processing, or by direct of tantalum foil in atmospheric oxygen at 600 °C for 6 hours, producing irregular microparticles. Lower oxides like TaO₂ form under reducing conditions but disproportionate readily to Ta and Ta₂O₅. Halides
Tantalum(V) chloride (TaCl₅), a hygroscopic pale yellow solid, is prepared by chlorination of tantalum oxide with carbon and gas at elevated temperatures (typically 400–600 °C), following the reaction Ta₂O₅ + 5C + 5Cl₂ → 2TaCl₅ + 5CO, or by direct reaction of tantalum metal chips with at 550 °C. Tantalum pentafluoride (TaF₅), a white sublimate, is obtained similarly via fluorination of tantalum or its chloride with or gas, and it hydrolyzes stepwise in water to form tantalum oxyfluorides. Other halides, such as TaBr₅ and TaI₅, are synthesized analogously but are less common due to thermal instability. Carbides and nitrides
(TaC), a compound with a rock-salt structure, is produced by carbothermal reduction of Ta₂O₅ with carbon at temperatures above 1800 °C (Ta₂O₅ + 5C → 2TaC + 5CO) or via reaction of tantalum precursors with nitrogen-doped carbon sources like mesoporous graphitic C₃N₄ under inert atmospheres. (TaN), often in cubic or hexagonal forms, is synthesized by of TaCl₅ with gas at 800–1000 °C or through solid-state metathesis reactions involving tantalum halides and at ambient pressures. These binary phases exhibit high and stability. Sulfides
Tantalum(IV) and (V) sulfides, such as TaS₂ in layered 2H or 1T polytypes, are prepared by direct combination of tantalum powder with at 900–1000 °C in sealed ampoules or by chemical vapor transport methods. Ta₂S₅ decomposes above 500 °C but can be stabilized in cluster forms via of tantalum-sulfur mixtures. These compounds are sparingly soluble in water and acids.

Organometallic and specialized compounds

Tantalum organometallic compounds primarily involve Ta-C σ-bonds in alkyl or aryl derivatives, frequently stabilized by multidentate ligands such as imido, amido, or groups to accommodate the metal's preference for high coordination numbers and oxidation states like Ta(V). These complexes exhibit reactivity patterns including migratory insertions and hydrogenolysis, as demonstrated in trialkyl tantalum imido species that undergo stepwise alkyl group removal under hydrogen to form lower-coordinate derivatives. or coordination in such compounds further enables π-backbonding and potential activation of unsaturated substrates. In catalytic applications, tantalum alkyl complexes, often bearing chelating ligands like ureates or diamidophosphines, facilitate processes such as photocatalytic hydroaminoalkylation of unactivated alkenes with primary amines at , proceeding via radical mechanisms initiated by visible light. Cationic alkyl tantalum , including tetramethyl derivatives, have been explored for stoichiometric activations that mimic early catalysis in C-H bond functionalization, though their high reactivity limits broader adoption compared to or analogs. Alkylidene tantalum complexes, generated via α-hydrogen abstraction from alkyl precursors, show promise in metathesis-like transformations but require bulky ligands to prevent decomposition. Tantalum's tendency toward dinuclear and oligomeric clusters arises from its ability to form metal-metal bonds or bridging ligands, as seen in structural analyses of nearly 50 crystallographically characterized organotantalum species, where bulky substituents inhibit higher nuclearity. These clusters exhibit unique electronic properties suitable for advanced synthesis, such as in the formation of heterobimetallic units with coinage metals via salt metathesis, enabling π-bonding interactions that stabilize alkylidyne-alkyl intermediates. Specialized organotantalum precursors, including amido and imido derivatives like tert-butylimido tris(tert-butylimido)tantalum (TBTEMT), are employed in metal-organic (MOCVD) and (ALD) to produce (TaN) thin films for microelectronic diffusion barriers and gate electrodes. These processes yield conformal films with controlled at temperatures around 200–400°C, leveraging the precursors' volatility and thermal stability, though scalability is constrained by tantalum's rarity and precursor synthesis costs exceeding those of alternatives like . Commercial deployment remains niche, primarily in high-performance semiconductors where TaN's high thermal stability and conductivity justify the expense.

Health, safety, and environmental aspects

Toxicity and handling precautions

Tantalum exhibits low , with oral LD50 values exceeding 2,000 mg/kg in rats, indicating minimal risk from ingestion under normal conditions. Inhalation of tantalum dust or fumes primarily poses risks through mechanical irritation and potential pulmonary effects, including or inflammatory lesions observed in following severe exposure; prolonged occupational exposure has been associated with chronic rhinitis and pneumoconiosis-like conditions in workers handling tantalum alloys or powders. Handling precautions emphasize dust control to prevent respiratory hazards, with the OSHA permissible exposure limit (PEL) set at 5 mg/m³ as an 8-hour time-weighted average for tantalum metal and oxide dust. The (NFPA) rates tantalum dust with a health of 1 (slight) and flammability of 1-2 for powders, necessitating non-sparking tools, ventilation, and such as respirators when concentrations exceed limits. Tantalum powders are pyrophoric and require storage under inert atmospheres to mitigate fire risks. Tantalum demonstrates high , owing to its chemical inertness in physiological environments, enabling safe use in medical implants without significant tissue reaction or systemic effects. reactions or allergies to tantalum are rare, with no evidence of widespread in human tissues, as the metal's biological inertness limits absorption and retention.

Environmental effects of extraction and use

Tantalum extraction, primarily from coltan ore through open-pit and artisanal mining, generates significant localized ecological disruptions, including land clearance, soil erosion, and waste rock disposal that can exceed ore volumes by factors of 10 to 100 depending on deposit grade. In artisanal and small-scale mining (ASM) operations, which dominate production in the Democratic Republic of Congo (DRC)—accounting for a substantial share of global supply—these activities contribute to deforestation and habitat fragmentation, with studies documenting elevated forest loss radiating at least 5 km from mine sites and an average additional 4.5% of initial forest cover depleted within 10 years of mining onset. Water contamination risks arise from sediment runoff and, in processing stages involving hydrofluoric acid leaching, potential acidic effluents, though rigorous tailings management in formal operations mitigates broader dispersal. Ore processing, typically entailing separation followed by chemical dissolution, demands energy-intensive steps and that, if unregulated, exacerbate in ASM areas lacking containment infrastructure. However, tantalum's geochemical inertness—forming stable oxides resistant to —limits its mobility in the environment post-extraction, with natural concentrations in soils and sediments rarely exceeding 1-2 ppm and primarily particulate-bound in waters, reducing long-term dispersion risks. In end-use applications such as capacitors, tantalum's exceptional resistance and durability minimize material degradation and emissions during product lifecycles, often spanning decades in with negligible release under operational stresses. Recycling from scrap remains inefficient, with post-consumer recovery rates below 1% globally as of 2023, constrained by disassembly challenges in e-waste despite tantalum's economic for targeted recovery due to prices averaging $170-190 per kg Ta₂O₅ equivalent. Given tantalum's crustal abundance below 2 ppm and annual production under 2,000 metric tons, these localized impacts contrast with a modest global footprint, where extraction-related disturbances affect far less area than for high-volume metals like iron or .

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