Terbium (Tb, atomic number 65) was discovered by Mosander in 1843. Terbium is found in cerite, gadolinite and other minerals along with other rare earths. It is also recovered from monazite in which it is present to the extent of 0.03%, from xenotime and from euxnite (a complex oxide containing 1% more of terbia). Terbium has been isolated only in recent years with the development of ion exchange techniques for separating the rare earth elements. As with other rare earth metals; terbium can be produced by reducing the anhydrous chloride or fluoride with calcium metal in a tatalum crucible. Calcium and tantalum impurities can be removed by vacuum re-melting. Other methods of isolation are also possible. Terbium is reasonably stable in air. It is a silver grey metal which is malleable, ductile and soft enough to be cut with a knife. Two crystal modifications exist with a transformation temperature of 1289 degrees Celsius. The oxide is a chocolate or dark maroon color.
Some known uses of Terbium are as follows:
- Solid state devices use sodium terbium borate.
- The oxide has potential application as an activator for green phosphors used in color television tubes.
- In combination with Zr02 as a crystal stabilizer of fuel cells which operate at elevated temperatures.