Terbium
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 TV tubes. 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.
Occurrence
Terbium is never found in nature by itself, but is contained along with other rare earth elements in many minerals, including monazite ((Ce,La,Th,Nd,Y)PO4 with up to 0.03% terbium), xenotime (YPO4) and euxenite ((Y,Ca,Er,La,Ce,U,Th)(Nb,Ta,Ti)2O6 with 1% or more terbium). The crust abundance of terbium is estimated as 1.2 mg/kg.
Currently, the richest commercial sources of terbium are the ion-adsorption clays of southern China; the concentrates with about two-thirds yttrium oxide by weight have about 1% terbia. Small amounts of terbium occur in bastnäsite and monazite; when these are processed by solvent extraction to recover the valuable heavy lanthanides as samarium-europium-gadolinium concentrate, terbium is recovered therein. Due to the large volumes of bastnäsite processed relative to the ion-adsorption clays, a significant proportion of the world's terbium supply comes from bastnäsite.
| Symbol | Tb | |
| Atomic Number | 65 | |
| Atomic Weight | 158.92534 | |
| Oxidation States | +3 | |
| Electronegativity, Pauling | 1.22 | |
| State at RT | Solid, Metal | |
| Melting Point, K | 1629 | |
| Boiling Point, K | 3296 |
Appearance and Characteristics
Harmful effects:
Terbium is considered to be moderately toxic.
Characteristics:
- 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.
- Euro banknotes use rare earth chemistry to defeat counterfeiters. Shining UV light on a euro results in green fluorescence from terbium Tb3+, red from europium Eu3+, and blue from thulium Tm3+.
- 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.
