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Jai Ganesh

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Terbium

Terbium

Gist

Terbium (Tb) is a rare-earth, silvery-white metal with atomic number 65, known for its softness, ductility, and unique fluorescent properties, making it valuable in electronic displays, solid-state devices, and alloys for high-stress environments like the aerospace and military industries. Discovered by Carl Mosander in 1843 and named after the village of Ytterby, Sweden, it is never found in nature as a free element but is found in minerals such as monazite and euxenite, with rich commercial sources in China's ion adsorption clays.

Terbium is used for its green luminescent properties in display screens and LED lights, in the magnetostrictive alloy Terfenol-D for sensors and actuators, as a crystal stabilizer in high-temperature fuel cells, and as a dopant in various solid-state devices and lasers. It is also found in the anti-counterfeiting features of some currencies.

Summary

Terbium is a chemical element; it has symbol Tb and atomic number 65. It is a silvery-white, rare earth metal that is malleable and ductile. The ninth member of the lanthanide series, terbium is a fairly electropositive metal that reacts with water, evolving hydrogen gas. Terbium is never found in nature as a free element, but it is contained in many minerals, including cerite, gadolinite, monazite, xenotime and euxenite.

Swedish chemist Carl Gustaf Mosander discovered terbium as a chemical element in 1843. He detected it as an impurity in yttrium oxide (Y2O3). Yttrium and terbium, as well as erbium and ytterbium, are named after the village of Ytterby in Sweden. Terbium was not isolated in pure form until the advent of ion exchange techniques.

Terbium is used to dope calcium fluoride, calcium tungstate and strontium molybdate in solid-state devices, and as a crystal stabilizer of fuel cells that operate at elevated temperatures. As a component of Terfenol-D (an alloy that expands and contracts when exposed to magnetic fields more than any other alloy), terbium is of use in actuators, in naval sonar systems and in sensors. Terbium is considered non-hazardous, though its biological role and toxicity have not been researched in depth.

Most of the world's terbium supply is used in green phosphors. Terbium oxide is used in fluorescent lamps and television and monitor cathode-ray tubes (CRTs). Terbium green phosphors are combined with divalent europium blue phosphors and trivalent europium red phosphors to provide trichromatic lighting technology, a high-efficiency white light used in indoor lighting.

Details

Terbium (Tb) is a chemical element, a rare-earth metal of the lanthanide series of the periodic table.

Terbium is a moderately hard, silvery white metal that is stable in air when in pure form. The metal is relatively stable in air even at high temperatures, because of formation of a tight, dark oxide layer that can be represented as a mixed oxide composed of Tb2O3 and TbO2. Terbium readily reacts with diluted acids, but it is insoluble in hydrofluoric acid (HF) because the presence of the fluoride ion protects the metal from further reaction by forming a protective layer of TbF3. The metal is a very strong paramagnet above 230 K (−43 °C, or −46 °F); it is antiferromagnetic between 220 K (−53 °C, or −64 °F) and 230 K, and it becomes ferromagnetic below 220 K.

The element was discovered in 1843 by Swedish chemist Carl Gustaf Mosander in a heavy rare-earth fraction called yttria, but its existence was not confirmed for at least 30 years, and pure compounds were not prepared until 1905. Terbium occurs in many rare-earth minerals but is almost exclusively obtained from bastnasite and from laterite ion-exchange clays. It is also found in the products of nuclear fission. Terbium is one of the least abundant of the rare earths; its abundance in Earth’s crust is about the same as thallium.

The only isotope occurring in ores is terbium-159. A total of 36 (excluding nuclear isomers) radioactive isotopes of terbium have been identified. Their mass ranges from 135 to 171 with half-life ranging from more than 200 nanoseconds (terbium-138) to 180 years (terbium-158).

Solvent-solvent extraction and ion-exchange techniques are utilized for commercial production of terbium. The metal is prepared in a highly pure form by metallothermic reduction of the anhydrous fluoride with calcium metal. Terbium exists in three allotropic (structural) forms. The α-phase is close-packed hexagonal with a = 3.6055 Å and c = 5.6966 Å at room temperature. The ferromagnetic ordering below 220 K is accompanied by an orthorhombic distortion of the hexagonal lattice to the β-phase with a = 3.605 Å, b = 6.244 Å, and c = 5.706 Å at 77 K (−196 °C, or −321 °F). The γ-phase is body-centred cubic with a = 4.07 Å at 1,289 °C (2,352 °F).

Terbium compounds are used as green phosphors in fluorescent lamps, computer monitors, and TV screens that use cathode-ray tubes. Another major use is with dysprosium and iron in the magnetostrictive alloy Terfenol-D (Tb0.3Dy0.7Fe2), which is a component of magnetically controlled actuators, sonar systems, and pressure sensors. Together with another lanthanide—gadolinium—terbium was used by Geoffrey Green and coworkers in 1990 to build a dual-stage room-temperature magnetic refrigerator prototype, with gadolinium as a high-temperature stage and terbium as a low-temperature stage.

Terbium is one of a few rare earths that have a +4 as well as a +3 oxidation state; the former is a result of stability of the half-filled 4f shell. The brown oxide prepared by air ignition has the approximate formula Tb4O7; the oxide TbO2 is obtained by using atomic oxygen. The tetrafluoride TbF4 is prepared by fluorinating the trifluoride; the Tb4+ ion is not known in solution. In other salts and in solution, terbium is present in the +3 oxidation state and behaves as a typical rare earth. Its solutions are pale pink to colourless.

Element Properties

atomic number  :  65
atomic weight  :  158.92534
melting point  :  1,356 °C (2,473 °F)
boiling point  :  3,230 °C (5,846 °F)
specific gravity  :  8.230 (24 °C, or 75 °F)
oxidation states  :  +4, +3.

Additional Information:

Appearance

A soft, silvery metal.

Uses

Terbium is used to dope calcium fluoride, calcium tungstate and strontium molybdate, all used in solid-state devices. It is also used in low-energy lightbulbs and mercury lamps. It has been used to improve the safety of medical x-rays by allowing the same quality image to be produced with a much shorter exposure time. Terbium salts are used in laser devices.

An alloy of terbium, dysprosium and iron lengthens and shortens in a magnetic field. This effect forms the basis of loudspeakers that sit on a flat surface, such as a window pane, which then acts as the speaker.

Biological role

Terbium has no known biological role. It has low toxicity.

Natural abundance

Terbium can be recovered from the minerals monazite and bastnaesite by ion exchange and solvent extraction. It is also obtained from euxenite, a complex oxide containing 1% or more of terbium.

The metal is usually produced commercially by reducing the anhydrous fluoride or chloride with calcium metal, under a vacuum. It is also possible to produce the metal by the electrolysis of terbium oxide in molten calcium chloride.

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