Tantalum

Chemical properties

Tantalum is a refractory metal in Group V-B of the periodic table. The pure metal is ductile, steel-blue to gray solid or black, odorless powder.

Physical properties

Tantalum has properties similar to niobium and vanadium above it in group 5. It is a veryhard and heavy metal with a bluish color when in its rough state, but if polished, it has a silveryshine. It is ductile, meaning it can be drawn into fine wires, and also malleable, meaningit can be hammered and worked into shapes. Thin strips and wires of tantalum will ignite inair if exposed to a flame.
Tantalum’s melting point is 2,996°C, which is almost as high as tungsten and rhenium. Itboiling point is 5,425°C, and its density is 19.3 g/cm³.

Isotopes

There are 49 isotopes of tantalum. Only the isotope Ta-181 is stable andaccounts for 99.988% of the total mass of the element on Earth. Just 0.012% of the element’s mass is contributed by Ta-180, which has a half-life of 1.2×10⁺¹⁵ years and isthus considered naturally stable. The remaining 47 isotopes are all artificially producedin nuclear reactions or particle accelerators and have half-lives ranging from a few microsecondsto few days to about two years.

Origin of Name

Tantalum was named after Tantalus, who was the father of Niobe, the queen of Thebes, a city in Greek mythology. (Note: The element tantalum was originally confused with the element nobelium.)

Occurrence

Tantalum is the 51st most abundant element found on Earth. Although it is found in afree state, it is usually mixed with other minerals and is obtained by heating tantalum potassiumfluoride or by the electrolysis of melted salts of tantalum. Tantalum is mainly obtainedfrom the following ores and minerals: columbite [(Fe, Mn, Mg)(Nb, Ta)₂O₆]; tantalite [(Fe,Mn)(Ta, Nb)₂O₆]; and euxenite [(Y, Ca, Er, La, Ce, U, Th)(Nb, Ta, Ti)₂O₆]. Tantalum’s oresare mined in South America, Thailand, Malaysia, Africa, Spain, and Canada. The UnitedStates has a few small native deposits but imports most of the tantalum it uses.
Since tantalum and niobium are so similar chemically, a solvent process must be employedto separate them from the common ores. They are dissolved in a solvent, resulting in 98% pure niobium oxide being extracted during this part of the process. This is followed by 99.5%pure tantalum oxide being extracted in a second solvent process.

History

Discovered in 1802 by Ekeberg, but many chemists thought niobium and tantalum were identical elements until Rose, in 1844, and Marignac, in 1866, showed that niobic and tantalic acids were two different acids. The early investigators only isolated the impure metal. The first relatively pure ductile tantalum was produced by von Bolton in 1903. Tantalum occurs principally in the mineral columbite-tantalite (Fe, Mn)(Nb, Ta)2O6. Tantalum ores are found in Australia, Brazil, Rwanda, Zimbabwe, Congo- Kinshasa, Nigeria, and Canada. Separation of tantalum from niobium requires several complicated steps. Several methods are used to commercially produce the element, including electrolysis of molten potassium fluorotantalate, reduction of potassium fluorotantalate with sodium, or reacting tantalum carbide with tantalum oxide. Thirty-four isotopes and isomers of tantalum are known to exist. Natural tantalum contains two isotopes, one of which is radioactive with a very long half-life. Tantalum is a gray, heavy, and very hard metal. When pure, it is ductile and can be drawn into fine wire, which is used as a filament for evaporating metals such as aluminum. Tantalum is almost completely immune to chemical attack at temperatures below 150°C, and is attacked only by hydrofluoric acid, acidic solutions containing the fluoride ion, and free sulfur trioxide. Alkalis attack it only slowly. At high temperatures, tantalum becomes much more reactive. The element has a melting point exceeded only by tungsten and rhenium. Tantalum is used to make a variety of alloys with desirable properties such as high melting point, high strength, good ductility, etc. Scientists at Los Alamos have produced a tantalum carbide graphite composite material that is said to be one of the hardest materials ever made. The compound has a melting point of 3738°C. Tantalum has good “gettering” ability at high temperatures, and tantalum oxide films are stable and have good rectifying and dielectric properties. Tantalum is used to make electrolytic capacitors and vacuum furnace parts, which account for about 60% of its use. The metal is also widely used to fabricate chemical process equipment, nuclear reactors, and aircraft and missile parts. Tantalum is completely immune to body liquids and is a nonirritating metal. It has, therefore, found wide use in making surgical appliances. Tantalum oxide is used to make special glass with a high index of refraction for camera lenses. The metal has many other uses. The price of (99.9%) tantalum is about $2/g.

Characteristics

Tantalum is almost as chemically inert at room temperatures (it has the ability to resistchemical attacks, including hydrofluoric acid) as are platinum and gold. It is often substitutedfor the more expensive metal platinum, and its inertness makes it suitable for constructingdental and surgical instruments and artificial joints in the human body.

The Uses of Tantalum

In pen points; analytical weights; apparatus and instruments for chemical, surgical, and dental use instead of platinum, in tantalum capacitors (a type of electrolytic condenser, trademarked "Tantalytic").

The Uses of Tantalum

A mixture of tantalum carbide (TaC) and graphite is a very hard material and is used toform the cutting edge of machine tools. Tantalum pentoxide (Ta₂O₅) is dielectric, making ituseful to make capacitors in the electronics industry. When mixed with high-quality glass, itimparts a high index of refraction, making it ideal for camera and other types of lenses.Because of its hardness and noncorrosiveness, tantalum is used to make dental and surgicaltools and implants and artificial joints, pins, and screws. The metal does not interactwith human tissues and fluids. Since tantalum can be drawn into thin wires, it is used inthe electronics industry, to make smoke detectors, as a getter in vacuum tubes to absorbresidual gases, and as filaments in incandescent lamps. It has many other uses in the electronicsindustry.
The use of tantalum to make miniaturized electrolytic capacitors that store electric chargesin devices such as cell phones and computers is becoming increasingly popular. Powderedtantalum is used in the process of sintering to form malleable bars and plates as well as specialelectrodes for the electronics industry.
As a result of their hardness, noncorrosiveness, and ductility, tantalum alloys are used tofabricate parts for nuclear reactors, missiles, and airplanes, and in industries where metal withthese qualities is required.

The Uses of Tantalum

Manufacture of capacitors and other electronic components; chemical equipment and corrosion-resistant tools.

Definition

Element of atomic number 73 in group VB of the periodic table, aw 180.9479, valences of 2, 3, 5; no stable isotopes.

Definition

A silvery transition element. It is strong, highly resistant to corrosion, and is easily worked. Tantalum is used in turbine blades and cutting tools and in surgical and dental work. Symbol: Ta; m.p. 2996°C; b.p. 5425 ± 100°C; r.d. 16.654 (20°C); p.n. 73; r.a.m. 180.9479.

Definition

tantalum: Symbol Ta. A heavy bluegrey metallic transition element; a.n. 73; r.a.m. 180.948; r.d. 16.63; m.p. 2996°C; b.p. 5427°C. It is found with niobium in the ore columbite– tantalite (Fe,Mn)(Ta,Nb)₂O₆. It is extracted by dissolving in hydrofluoric acid, separating the tantalum and niobium fluorides to give K₂TaF₇, and reduction of this with sodium. The element contains the stable isotope tantalum–181 and the long-lived radioactive isotope tantalum–180 (0.012%; half-life >10⁷ years). There are several other short-lived isotopes. The element is used in certain alloys and in electronic components. Tantalum parts are also used in surgery because of the unreactive nature of the metal (e.g. in pins to join bones). Chemically, the metal forms a passive oxide layer in air. It forms complexes in the +2, +3, +4, and +5 oxidation states. Tantalum was identified in 1802 by Anders Ekeberg (1767–1813) and Ürst isolated in 1820 by Berzelius.

Production Methods

It was identi?ed that tantalum minerals exists in over 70 differentchemicalcompositions.Thoseofgreatesteconomic importance are tantalite, microlite, and wodginite; however, it is common practice to name any tantalum-containing mineral concentrate as “tantalite”. Tantalum resources are widespread, with the most important known resources being found in Brazil and Australia. In mid-2008, the main mining operations were in Australia, Brazil,Canada,Mozambique,andEthiopiaandinmid-2009, in Brazil, Ethiopia, and China, with additional quantities originating in central Africa, Russia, and Southeast Asia. There is continued interest in exploration of this element in other countries, primarily in Egypt, Canada, Mozambique, and Saudi Arabia.
The major world mine producers of tantalum in 2010 were Brazil (180 tons), Mozambique (110 tons), Rwanda (100 tons), and Australia (80 tons). Other countries produced around 170 tons, so the total world production of tantalum was approximately 670 tons. The major producers of tantalum mineral concentrates are Australia, Brazil, and Canada.

Production Methods

The first successful industrial process used to extract tantalum and niobium from the tantalite-columbite-containing minerals employed alkali fusion to decompose the ore, acid treatment to remove most of the impurities, and the historic Marignac fractional-crystallization method to separate the tantalum from the niobium and to purify the resulting K2TaF7. Most tantalum production now employs recovery of the tantalum and niobium values by dissolution of the ore or ore concentrate in hydrofluoric acid. Then the dissolved tantalum and niobium values are selectively stripped from the appropriately acidified aqueous solution and separated from each other in a liquid-liquid extraction process using methyl isobutyl ketone (MIBK) or other suitable organic solvent. The resulting purified tantalum-bearing solution is generally treated with potassium fluoride or hydroxide to recover the tantalum in the form of potassium tantalum fluoride, K2TaF7, or with ammonium hydroxide to precipitate tantalum hydroxide, which is subsequently calcined to obtain tantalum pentoxide, Ta2O5. Tantalum metal is generally obtained by sodium reduction of K2TaF7, although electrolysis of K2TaF7 and carbon reduction of Ta2O5 in an electric furnace have also been used. Tantalum metal can absorb large volumes of hydrogen during heating in a hydrogenbearing atmosphere at an intermediate temperature range (450–700 °C (842-1,292 °F)). The hydrogen is readily removed by heating in vacuum at higher temperatures.

General Description

Tantalum dust is a black odorless powder. Mp: 2996°C; bp: approx. 5250°C. Density: 16.65 g cm-3. Insoluble in water. Tantalum oxide dust is a white, microcrystalline powder Mp: 1800°C. Density: 7.6 g cm-3. Insoluble in water. The mixture is listed as a toxic inhalation hazard by OHSA.

Hazard

Dust or powder may be flammable. Toxic by inhalation.

Hazard

The dust and powder of tantalum are explosive. Several tantalum compounds are toxic ifinhaled or ingested, but the metal itself is nonpoisonous.

Health Hazard

Tantalum has a low order of toxicity but has produced transient inflammatory lesions in the lungs of animals. Surgical implantation of tantalum metal products such as plates and screws has not shown any adverse tissue reaction, thus demonstrating its physiological inertness.

Flammability and Explosibility

Flammable

Safety Profile

An inhalation hazard. Some industrial skin injuries from tantalum have been reported. Systemic industrial poisoning, however, is apparently unknown. Questionable carcinogen with experimental tumorigenic data. The dry powder iptes spontaneously in air. Incompatible with bromine trifluoride, fluorine, lead chromate. See also specific tantalum compounds.

Carcinogenicity

Although Oppenheimer et al., using embedded metal foil technique, have elicited two malignant ?brosarcomas in 50 embeddings of tantalum metal in 25Wistar rats aftera latent period of714days, these results remain a controversial issue. Miller et al. have studied tumorigenic transforming potential of tungsten, iron, nickel, and cobalt with tantalum as a comparison on an immortalized nontumorigenic human osteoblast-like cell line. No tumorigenic activity of Ta was reported, but data are not shown.
In the recent study, intramuscularly pellets (1mm 2mm cylinders) of weapons-grade WA were implantedtosimulateshrapnelwounds.Ratswereimplanted with 4 (low dose) or 20 pellets (high dose) of WA. Tantalum (20 pellets) and nickel (20 pellets) served as negative and positive controls, respectively. Rats implanted with tantalum (n=46) did not develop tumors.

Shipping

UN3089 Metal powders, flammable, n.o.s., Hazard Class: 4.1; Labels: 4.1-Flammable solid.

Incompatibilities

A flammable solid; the dry powder can ignite spontaneously in air. Incompatible with lead chromate. A strong reducing agent; incompatible with oxidizers (chlorates, nitrates, peroxides, permanganates, perchlorates, chlorine, bromine, bromine trifluoride, fluorine, etc.); contact may cause fires or explosions. Keep away from alkaline materials, strong bases, strong acids, oxoacids, epoxides. Tantalum metal is attacked by hydrogen fluoride, fused alkalis, fuming sulfuric acid.

Waste Disposal

Sanitary landfill if necessary; recover if possible because of economic value. Technology exists for tantalum recovery from spent catalysts, for example.