Terbium Information
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Terbium Element
Terbium is a chemical element
with the symbol Tb and atomic number 65. It is a silvery-white, rare earth
metal that is malleable, ductile, and soft enough to be cut with a knife. 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 are named after the
village of Ytterby in Sweden. Terbium was not isolated in pure form until the
advent of ion exchange techniques.
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 is used to dope calcium
fluoride, calcium tungstate and strontium molybdate, materials that are used in
solid-state devices, and as a crystal stabilizer of fuel cells which 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.
Most of the world's terbium
supply is used in green phosphors. Terbium oxide is 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 for standard illumination in indoor lighting.
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