Terbium

Terbium is a chemical element in the periodic table that has the symbol Tb and atomic number 65.

Notable characteristics

Terbium is a silvery-gray rare earth metal that is malleable, ductile and soft enough to be cut with a knife. It is reasonably stable in air, and two crystal modifications exist, with a transformation temperature of 1289 °C.

Applications

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, together with ZrO₂. Terbium is also used in alloys and in the production of electronic devices, its oxide is used in green phosphors in fluorescent lamps and color TV tubes. Sodium terbium borate is used as a laser material that emits coherent light at 546 nm.

History

Terbium was discovered by Swedish chemist Carl Gustaf Mosander in 1843 and named after the village Ytterby in Sweden, who detected it as an impurity in Yttrium-oxide, Y₂O₃. It was not isolated in pure form until the recent advent of ion exchange techniques.

Occurrence

Terbium is never found in nature as the free element, but it is contained in many minerals, including cerite, gadolinite, monazite ((Ce,LaTh,Nd,Y)PO₄, which contains up to 0.03% of Terbium), xenotime (YPO₄) and euxenite ((Y,Ca,Er,La,Ce,U,Th)(Nb,Ta,Ti)₂O₆, which contains 1% or more of Terbium).

Compounds

Terbium compounds include:

Fluorides
* TbF₃
* TbF₄
Chlorides
* TbCl₃
Bromides
* TbBr₃
Iodides
* TbI₃
Oxides
* Tb₂O₃
* Tb₄O₇
Sulfides
* Tb₂S₃
Nitrides
* TbN
Isotopes

Naturally occurring Terbium is composed of 1 stable isotope, 159-Tb. 33 radioisotopes have been characterized, with the most stable being 158-Tb with a half-life of 180 years, 157-Tb with a half-life of 71 years, and 160-Tb with a half-life of 72.3 days. All of the remaining radioactive isotopes have half-lifes that are less than 6.907 days, and the majority of these have half lifes that are less than 24 seconds. This element also has 18 meta states, with the most stable being 156m1-Tb (t_½ 24.4 hours), 154m2-Tb (t_½ 22.7 hours) and 154m1-Tb (t_½ 9.4 hours).

The primary decay mode before the most abundant stable isotope, 159-Tb, is electron capture, and the primary mode after is beta minus decay. The primary decay products before 159-Tb are element Gd (Gadolinium) isotopes, and the primary products after are element Dy (Dysprosium) isotopes.

Precautions

As with the other lanthanides, terbium compounds are of low to moderate toxicity, although their toxicity has not been investigated in detail. Terbium has no known biological role.