What is Terbium?

Terbium 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 hydrogengas. Terbium is never found in nature as a free element, but it is contained in many minerals, including cerite, gadolinite, monazite, xenotime, and euxenite.

Properties

  • Atomic Symbol: Tb
  • Atomic Number: 65
  • Element Category: Lanthanide metal
  • Atomic Weight: 158.925

Applications

It is used in the following applications:

  • Used as a dopant in 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, together with ZrO2.
  • Used in alloys and in the production of electronic devices. As a component of Terfenol-D, terbium is used in actuators, in naval sonar systems, sensors, in the SoundBug device (its first commercial application), and other magnetomechanical devices. Terfenol-D is a terbium alloy that expands or contracts in the presence of a magnetic field. It has the highest magnetostriction of any alloy.
  • Used in green phosphors in fluorescent lamps and color TV tubes. Sodium terbium borate is used in solid state devices. The brilliant fluorescence allows terbium to be used as a probe in biochemistry, where it somewhat resembles calcium in its behavior. Terbium “green” phosphors (which fluoresce a brilliant lemon-yellow) are combined with divalent europium blue phosphors and trivalent europium red phosphors to provide the trichromatic lighting technology which is by far the largest consumer of the world’s terbium supply. Trichromatic lighting provides much higher light output for a given amount of electrical energy than does incandescent lighting.
  • Used to detect endospores, as it acts as an assay of dipicolinic acid based on photoluminescence

Discovery

Terbium was first isolated in 1843 by the Swedish chemist Carl Mosander at Stockholm. He had already investigated cerium oxide and separated a new element from it, lanthanum, and now he focussed his attention on yttrium, discovered in 1794, because he thought this too might harbour another element. In fact Mosander was able to obtain two other metal oxides from it: terbium oxide (yellow) and erbium oxide (rose pink) and these he announced in 1843. This was not the end of the story, however, because later that century these too yielded other rare earth elements (aka lanthanoids). Today these elements are easily separated by a process known as liquid-liquid extraction.

Source

Along with other rare earth elements, terbium can be found in minerals, including cerite and gadolinite. The element can be extracted from monazite, in which it is present to the extent of 0.03 percent; from euxenite, a complex oxide containing 1 percent or more of terbia; and xenotime.

Recent advances ion-exchange techniques for separating the rare earth elements have enabled the isolation of terbium. One method for producing the rare earth metal is by reducing the anhydrous chloride or fluoride with calcium, although other methods of isolation are available. Vacuum remelting can remove calcium and tantalum impurities.

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