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For nuclear submarines
(Hafinia, Latin name for Copenhagen) Many years before its discovery in 1932 (credited
to D. Coster and G. von Hevesey), Hafnium was thought to be present in various minerals
and concentrations. On the basis of the Bohr theory, the new element was expected to be
associated with zirconium.
It was finally identified in zircon from Norway, by means of X-ray spectroscope
analysis. It was named in honor of the city in which the discovery was made. Most
zirconium minerals contain 1 to 5 percent hafnium.
It was originally separated from zirconium by repeated recrystallization of the double
ammonium or potassium fluorides by von Hevesey and Jantzen. Metallic hafnium was first
prepared by van Arkel and deBoer by passing the vapor of the tetraiodide over a heated
tungsten filament. Almost all hafnium metal now produced is made by reducing the
tetrachloride with magnesium or with sodium (Kroll Process).
Hafnium is a ductile metal with a brilliant silver luster. Its properties are
considerably influenced by presence of zirconium impurities. Of all the elements,
zirconium and hafnium are two of the most difficult to separate. Although their chemistry
is almost identical, the density of zirconium is about half of hafnium. Very pure hafnium
has been produced, with zirconium being the major impurity.
Hafnium has been successfully alloyed with iron
, titanium , niobium
, tantalum , and other metals. Hafnium carbide is
the most refractory binary composition known, and the nitride is the most refractory of
all known metal nitrides (m.p. 3310C). At 700 degrees C 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
Because the element not only has a good absorption cross section for thermal neutrons
(almost 600 times that of zirconium), but also excellent mechanical properties and is
extremely corrosion-resistant, hafnium is used for reactor control rods. Such rods are
used in nuclear submarines.
Hafnium is used in gas-filled and incandescent lamps, and is an efficient getter for
scavenging oxygen and nitrogen.
Finely divided hafnium is pyrophoric and can ignite spontaneously in air. Care should
be taken when machining the metal or when handling hot sponge hafnium.
Exposure to hafnium should not exceed 0.5 mg/hr. (8 hour time-weighted average -
The price of the metal is in the broad range between $100/lb and $500/lb, depending on
purity and quantity. The yearly demand for hafnium in the U.S. now exceeds 100,000 lb.
Sources: CRC Handbook of Chemistry
and Physics and the American Chemical Society.