hafnium

A brilliant, silvery, metallic element separated from ores of zirconium and used in nuclear reactor control rods, as a getter for oxygen and nitrogen, and in the manufacture of tungsten filaments. Atomic number 72; atomic weight 178.49; melting point 2,220°C; boiling point 5,400°C; specific gravity 13.3; valence 4. See Table at element.