Terbium was discovered in 1843. It is stable in the air but very reactive in nature. It is used as a component of Terfenol –D which is used in actuators and in sensors.
History and Discovery
Terbium was discovered in 1843 by Carl Gustaf Mosander. He found it as impurity in yttrium oxide Y2O3. It was not isolated until the discovery of ion exchange method. Yttrium and terbium are named after the name of village Ytterby (Sweden) .
|Periodic Table Classification
|State at 20C
|[Xe] 4f9 6s2
|2, 8, 18, 27, 8, 2
|8.23 g.cm-3 at 20°C
|158.93 g.mol -1
|Electronegativity according to Pauling
Terbium is present in the Earth crust is approximately 1.2 mg/kg. It is present along with many rare earth element in minerals like monazite (reddish brown phosphate) about 0.03%, xenotime (phosphate mineral) and euxenite (brownish black mineral). No mineral has yet been discovered in which high amount of terbium is present. The commercial sources are ion-adsorption clays of Southern China. Small amount of terbium is also present in bastnasite (three carbonate fluoride mineral).
Terbium is rare earth metal which is silvery white in color. It is a soft metal that can be cut with a knife and can easily be deformed. It is stable in the air as compared to other lanthanides. It is also very reactive. It exist in two crystal allotropes and transformation temperature in between is about 1289OC. Terbium has ferromagnetic order at temperature below 219 K. Above this temperature it becomes antiferromagnetic. This unusual change create disordered paramagnetic state at 230 K. Terbium has chemical symbol Tb. Its atomic number is 65 and atomic weight is 158.925. Its melting point is 1356OC and boiling point of terbium is about 3123OC. Terbium density at room temperature is about 8.23 g/cm3 .
Terbium is a reactive metal and is electropositive in nature. It reacts slowly with cold water and quickly with hot water to forms terbium hydroxide. It burns and forms a mixed terbium (lll, IV) oxide. Terbium mostly exist in +3 oxidation state in the form of Tb2O3 and +4 state as TbO2 and TbF4. It reacts with all halogens to form white trihalides. It is also dissolves in dilute sulfuric acid and form solution that contain pale pink terbium (lll) ions. It combines with nitrogen, carbon, sulfur, phosphorus, boron, selenium, silicon and arsenic at high temperature and form binary compounds .
Significance and Uses
- Terbium is doped in calcium fluoride, calcium tungsten and strontium molybdate which are used in solid state devices like crystal stabilizer of fuel cells, they are operated at high temperature with ZrO2.
- Terbium is used in the production of electronic devices.
- Terbium is widely used in the formation of various alloys.
- Terbium is used in naval sonar systems, sensors, SoundBug (small speaker) and in magnetomechanical devices as Terfenol-D.
- Its oxides are used in green phosphors fluorescent lamp and color TV tubes.
- Sodium terbium borate also used in solid state devices.
- It is also used to detect endospores, which is the non- reproductive structure of microorganisms.
- It also gives green color on Blackberry and other high definition screen.
- Terbium is also used in lasers and semiconductor devices.
Terbium and its compounds when in powder form can cause irritation when contact with the skin and eyes. It has no biological role. It is slightly toxic when ingested.
Isotopes of Terbium
Terbium is composed of one stable isotope Terbium-159. Thirty six radioisotopes in which the heaviest one is terbium-171 and lightest one is terbium-135. The most stable synthetic radioisotope are terbium-158 with half-life is 180 years, terbium-157 with half- life of 71 years. All remaining have half- lives less than quarter a year and majority have just half a minute long. Terbium also has twenty seven nuclear isomers having mass 141-154, 156 and 158. The most stable of them is terbium- 156m have half-life of 24.4 hours and terbium-156m2 is 22.7 hours.
. “Chemical reactions of Terbium”. Web elements. Retrieved 2009-06-06