Jan 15 2002
Background
The element zirconium was not identified until 1789 when Klaproth analysed a sample of jargon from Ceylon. It was not until 1824 when it was first isolated by Berzelius, who heated a potassium and potassium zirconium fluoride in an iron tube. However, it took another 90 years for a relatively pure sample to be prepared.
Occurrence
Zirconium has been identified in S-type stars, the sun and meteorites. Samples taken from the surface of the moon have also been found to contain high levels of zirconium compared to terrestrial rocks.
Zirconium is principally found in zircon, (ZrSiO4, zirconium silicate), with most notable commercial deposits in Florida, South Carolina, Australia and Brazil. It has also been identified in over 30 other minerals.
Zirconia (ZrO2) appears naturally as Baddeleyite in deposits in Brazil. Baddeleyite contains approximately 1% Hafnium, which is difficult to separate due to its chemical similarity.
Production
Zirconium is produced by the reduction of the chloride using the Kroll and other processes.
Key Properties
Zirconium is a grey to white lustrous metal. It can spontaneously ignite in air in a fine powder form, especially at high temperatures. Larger samples do not suffer from this problem.
As mentioned earlier, zirconium deposits are generally contaminated with hafnium, which cannot easily be separated. Consequently, commercial zirconium samples typically contain 1 to 3% hafniuim.
Zirconium has a low neutron absorption cross section and is resistant to the corrosive environment with nuclear reactors.
Zirconium has excellent resistance to most common acids, alkalis, sea water and other agents.
Applications
Zirconium is used in nuclear reactors due to its low neutron absorption cross section and resistance to the corrosive environment encountered within nuclear reactors. It is useful in this application as it neutrons can pass through a zirconium internal wall without loss of appreciable concentration. Thus, typical applications include cladding for fuel cells. For these reasons, nuclear power generation applications account for more than 90% of commercial zirconium production, with reactor grade zirconium being essentially hafnium free.
Due to its chemical resistance, it is used in chemical plants.
Other applications inlcude:
• A getter in vacuum tubes
• In surgical appliances
• An alloying element for steels and other alloys such as magnesium
• Photoflash bulbs
• Explosive primers
• Rayon spinnerets
• Lamp filaments
Zirconium compounds also have a number of applications such as:
• Nb-Zr compounds are used in low temperature superconducting magnets
• Zn-Zr compounds are magnetic below 35K
• Zr-O compounds (ZrO2) are used as gemstones, laboratory crucibles, furnace linings for metallurgical, ceramics and glass. Refractory applications consume a large proportion of all zirconium produced.
Source: AzoM.com