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 tetrahalides.
Uses
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.
Handling
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 - 40-hour
week).
Costs
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.
Last Updated: 12/19/97, CST Information Services Team
Hafnium