PTL:Hafnium
From ChemEd Collaborative
Hafnium is a transition metal in Group IVB and the 6th period. It has oxidation numbers ranging from 0 to +4, with +4 being common. Other elements of the group are titanium (Ti) and zirconium (Zr).
Contents |
Discovered
In their book on inorganic chemistry (Pergamon, 1984) Greenwood and Earnshaw stated that "The discovery of hafnium was one of chemistry's more controversial episodes." There were several, dubious reports of its discovery in 1911 and 1922. However, D. Coster and G. von Hevesy, working in Niels Bohr's lab in Copenhagen in 1922, used Moseley's x-ray spectroscopic method to show that element 72 was present in zircons (ZrSiO4).
Name
They named the element after the Latin name for Copenhagen (Hafnia). Thus, the element was the first to be discovered by x-ray methods. One reason it had escaped discovery earlier is that, of all the elements, zirconium and hafnium are the most difficult to separate.
Characteristics
The chief mineral of hafnium is zircon, zirconium orthosilicate, ZrSiO4, which usually contains about 1.2% hafnium oxide.
Hafnium has an abundance in the earth's crust of about 4.5 ppm, roughly comparable to that of uranium, boron, tantalum, and bromine.
The metal is hard, shiny, and ductile, although the color of Hf sponge or powder is dull gray. In the solid state, the metal has a hexagonal closest packed structure.
Prepared
It is produced by reducing HfCl4 with sodium or magnesium (the Kroll process).
HfCl4 + 4 Na 
4 NaCl + Hf
Uses
The most important use of hafnium is in the [control rods] that regulate neutron flux in [nuclear reactors]. Not only is the element resistant to corrosion in hot water, but it has a large cross section for neutron capture. The element is also used in vacuum tubes and incandescent lamps, since it is a good "getter", an agent used to remove traces of air (by formation of the metal oxide, HfO2, and nitride, HfN).
Emission Spectra
This is the emission spectra for Hafnium.
