Hafnium
Hafnium, a chemical element. It is a silvery metal, usually found in minerals in combination with the element zirconium. Hafnium is used for control rods in nuclear reactors, in alloys, and in incandescent bulbs. The element was discovered in 1923 by Dirk Coster, a Danish physicist, and Georg von Hevesy, a Hungarian chemist. The discovery was made in Copenhagen, Denmark, and the name comes from Hafn, an old name for Copenhagen.
Symbol: Hf. Atomic number: 72. Atomic weight: 178.49. Melting point: 4,041 F. (2,227 C.). Boiling point: 8,316 F. (4,602 C.). Specific gravity: 13.31. Hafnium belongs in Group IVB of the Periodic Table and has a valence of +4. Sixteen isotopes of hafnium are known.