Atomic Number: 72
Atomic Symbol: Hf
Atomic Weight: 178.49
Melting Point: 4,051 F (2,233 C)
Boiling Point: 8,317 F (4,603 C)
Word origin: Hafnium was derived from Hafinia, the Latin name for Copenhagen, the city where it was discovered.
Discovery: Dutch physicist Dirk Coster and Hungarian radiochemist George von Hevesy are credited with the discovery of hafnium in 1932, although it was thought to be present in various minerals and concentrations before then. It was named in honor of the city in which the discovery was made.
Properties of hafnium
The properties of hafnium, which has a bright silver sheen, are greatly influenced by presence of zirconium impurities. Zirconium and hafnium are two of the most difficult elements to separate.
Hafnium has been successfully alloyed with a number of elements, including iron, niobium, tantalum and iron.
Hafnium carbide (HfC) is the most refractory binary composition known, and the nitride is the most refractory of all known metal nitrides (with a melting point of 5,990 F / 3,310 C). At 700 C (1,292 F), hafnium rapidly absorbs hydrogen to form the composition HfH1.86.
Hafnium is resistant to concentrated alkalis, but at elevated temperatures reacts with oxygen, nitrogen, carbon, boron, sulfur, and silicon. Halogens react directly to form tetrahalides.
Sources of hafnium
Most zirconium minerals contain 1 percent to 5 percent hafnium.
It was originally separated from zirconium by repeated recrystallization of the double ammonium or potassium fluorides. Metallic hafnium was first prepared by passing the vapor of the tetraiodide over heat. Almost all hafnium metal now produced is made through the Kroll process of reducing the tetrachloride with magnesium or with sodium.
Uses of hafnium
The element has superior absorption cross section for thermal neutrons (almost 600 times that of zirconium), has excellent mechanical properties and is extremely corrosion-resistant, making hafnium conducive to producing reactor control rods in nuclear submarines.
Hafnium is used in gas-filled and incandescent lamps.