The chemical element terbium is classed as a lanthanide and rare earth metal. It was discovered in 1843 by Carl Gustaf Mosander.
|Classification:||Terbium is a lanthanide and rare earth metal|
|Melting point:||1360 oC, 1633 K|
|Boiling point:||3220 oC, 3493 K|
|Neutrons in most abundant isotope:||94|
|Electron configuration:||[Xe] 4f9 6s2|
|Density @ 20oC:||8.27 g/cm3|
|Atomic volume:||19.20 cm3/mol|
|Structure:||hexagonal close packed|
|Specific heat capacity||0.18 J g-1 K-1|
|Heat of fusion||10.15 kJ mol-1|
|Heat of atomization||389 kJ mol-1|
|Heat of vaporization||330.90 kJ mol-1|
|1st ionization energy||565.80 kJ mol-1|
|2nd ionization energy||1110 kJ mol-1|
|3rd ionization energy||2114 kJ mol-1|
|Minimum oxidation number||0|
|Min. common oxidation no.||0|
|Maximum oxidation number||4|
|Max. common oxidation no.||3|
|Electronegativity (Pauling Scale)||1.21|
|Polarizability volume||25.5 Å3|
|Reaction with air||mild, ⇒ Tb4O7|
|Reaction with 15 M HNO3||mild, ⇒ Tb(NO3)3|
|Reaction with 6 M HCl||mild, ⇒ H2, TbCl3|
|Reaction with 6 M NaOH||–|
|Oxide(s)||Tb2O3 (terbia), Tb4O7|
|Atomic radius||175 pm|
|Ionic radius (1+ ion)||–|
|Ionic radius (2+ ion)||–|
|Ionic radius (3+ ion)||106.3 pm|
|Ionic radius (1- ion)||–|
|Ionic radius (2- ion)||–|
|Ionic radius (3- ion)||–|
|Thermal conductivity||11.1 W m-1 K-1|
|Electrical conductivity||0.9 x 106 S m-1|
|Freezing/Melting point:||1360 oC, 1633 K|
Discovery of Terbium
Terbium was discovered in 1843 by the Swedish chemist Carl Gustaf Mosander. It was not the first element he had discovered.
Four years earlier, in 1839, Mosander had discovered lanthanum in the mineral cerite. His mentor, Jöns Berzelius, had previously discovered the new element cerium in cerite. Mosander had continued to study cerite and his persistence was rewarded. Lanthanum had been present in the cerite all along, but Berzelius had not found it. (1)
In 1843, Mosander decided to study the mineral gadolinite. Gadolinite contained yttria (yttrium oxide) in which the element yttrium had been discovered by Johan Gadolin in 1794.Mosander wondered if he might repeat his earlier triumph and find another new element hiding with a known element.
Using ammonium hydroxide he precipitated fractions of different basicity from yttria. In these fractions he found two differently colored, previously unknown substances. These he called erbia and terbia; they contained the new rare earth metals erbium and terbium. Again Mosander had found new elements where others had already looked. (2), (3), (4)
Mosander named terbium and erbium after the Ytterby Mine in Sweden, the source of gadolinite mineral they were discovered in. (The elements yttrium and ytterbium were also named after the same mine.)
A modern analysis of gadolinite from this historically important mine gives extremely high concentrations for a number of rare earths: yttrium = 16%; thulium = 5%; ytterbium = 3%; terbium = 2% and dysprosium = 2%. (5)
The confusion over the identities (and even the existence) of a number of rare earth elements was settled finally by George Urbain in Paris, who carried out tens of thousands of fractional crystallizations of rare earth salts.
Crystallizations could take years to produce small samples of pure salts.
Urbain finally put to rest uncertainty about the identities of pure earths, including terbium, whose salts had never before been completely free of other rare earth salts.
Urbain obtained terbium’s spectrum, and this was verified by Gustav Eberhard in Potsdam, Brandenburg.
Urbain found there were fifteen rare earth metals (we now recognize seventeen), one of which was terbium. In the process, he discovered the rare earth lutetium, adding his own name to the list of scientists who have discovered elements. (6), (7), (8), (9), (10)
Appearance and Characteristics
Terbium is considered to be moderately toxic.
Terbium is a silver gray rare earth metal that is both malleable and ductile. Like other rare earth metals, it forms 3+ ions. Unlike most, it also forms 4+ ions relatively easily.
Terbium does not tarnish rapidly in air and it is soft enough to be cut with a knife.
Its oxide terbia (Tb2O3) is a white powder and the heptaoxide (Tb4O7) is a dark maroon color. The heptaoxide contains terbium in both its +3 and +4 oxidation states.
Terbium exists in two crystal allotropes with transformation at a temperature of 1289 oC.
Tb3+ ions emit a strong green luminescence when excited.
Uses of Terbium
The luminescence of Tb3+ is important in a significant number of applications. Terbium is used in color phosphors in lighting applications such as trichromatic lighting and in color TV tubes. It also makes the green color on your Blackberry or other high definition screen.
Tb3+ ions can be used to check for the presence of microbes. Terbium chloride is applied to the test area, which is then illuminated with UV light. Within minutes, any live endospores present will glow green. (11)
A terbium-iron alloy is used to provide metallic films for magneto-optic recording of data.
Hybrid car engines have electric motors and all electric motors are based on magnets. These magnets need to retain their magnetism at high temperatures. Alloying neodymium with terbium and dysprosium produces such magnets. These magnets are also used in the electric motors of wind-turbines, where high temperatures are also generated.
Terfenol-D (a terbium, iron and dysprosium alloy) expands or contracts in the presence of a magnetic field (magnetostriction). It is used in a speaker called the ‘SoundBug’, which turns any flat surface into a speaker. The ‘SoundBug’ vibrates any material it is placed on, such as a table or desk, making it into a speaker.
Terbium is also used as a dopant for materials in solid-state devices and optical fibers.
Abundance and Isotopes
Abundance earth’s crust: 0.9 parts per million by weight, 0.1 parts per million by moles
Abundance solar system: 100 parts per trillion by weight, 1 part per trillion by moles
Cost, pure: $5,040 per 100g
Cost, bulk: $ per 100g
Source: Terbium is not found free in nature but is found in a number of minerals: mainly monazite, zenotime and euxenite. Commercially it is produced from monazite using a complex ion-exchange process. The metal may be obtained by reducing its anhydrous fluoride or chloride with calcium metal in an argon atmosphere.
Isotopes: Terbium has 26 isotopes whose half-lives are known, with mass numbers 140 to 165. Naturally occurring terbium consists of its one stable isotope, 159Tb.
1. Latanium, a New Metal., The London and Edinburgh Philosophical Magazine and Journal of Science, 1839, 14, p3901.
2. Mary Elvira Weeks, The discovery of the elements. XVI. The rare earth elements., J. Chem. Educ., 1932, p1751.
3. Per Enghag, Encyclopedia of the elements: technical data, history, processing, applications., John Wiley and Sons, 2004, p447.
4. Paul Caro, Rare earths., Editorial Complutense., 1998, p35.
5. James L. Marshall and Virginia R. Marshall, Rediscovery of the Elements: Ytterby Gruva (Ytterby Mine)., 2001, J. Chem. Educ., p1343.
6. Georges Champetier and Charlotte H. Boatner, Georges Urbain., 1940, J. Chem. Educ., p103.
7. G. Eberhard, A Spectroscopic Investigation of Dr. Urbain’s Preparations of Terbium., Astrophysical Journal., 1906 vol. 24, p309.
8. Ralph P. Oesper, Georges Urbain., 1938, J. Chem. Educ., p201.
9. G. Urbain, On a yttria earth neighboring gadolinium. Comptes Rendus, 1904, 139, p736.
10. G. Urbain, On the isolation of terbium., Comptes Rendus, 1905, 141, p521.
11. JPL Develops High-Speed Test to Improve Pathogen Decontamination
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