The mineral gadolinite was discovered in a quarry near the town of Ytterby, Sweden in 1784. In 1843, Carl Gustaf Mosander, a Swedish chemist, was able to separate gadolinite into three compounds; one of which was named terbium after the city where it was found.
Terbium is a silvery white rare earth metal that is malleable, ductile and soft enough to be cut with a knife. It is reasonably stable in air and very slow to oxidize or tarnish. Terbium occurs in a number of minerals, usually in association with other heavy rare earth elements. It is mainly produced by solvent extraction of rare earth elements from clay deposits in China.
Applications of Terbium:
- Energy and Electronics: Terbium oxide (or ´terbia´) is used in green phosphors in fluorescent lamps and colour TV tubes. When the terbium phosphors are combined with divalent europium blue phosphors and trivalent europium red phosphors, they provide trichromatic, or 3 wave length, fluorescent lighting. Trichromatic fluorescent lighting is a harsh white light with a much higher light output for a given amount of electrical energy than conventional fluorescent lighting. This application is by far the largest use of the world's terbium supply.
- Science and Materials: Terbium is a component of Terfenol-D (Terbium Dysprosium and Iron): an alloy that expands or contracts to a high degree in the presence of a magnetic field. This material is used in actuators and sensors. Terbium, along with zirconium dioxide, is also a crystal stabilizer in fuel cells that operate at high temperatures. Sodium terbium borate is used to make special lasers.