Hafnium Information
Scroll Down To Download
Hafnium Element
Hafnium is a chemical element
with the symbol Hf and atomic number 72. A lustrous, silvery gray, tetravalent
transition metal, hafnium chemically resembles zirconium and is found in many
zirconium minerals. Its existence was predicted by Dmitri Mendeleev in 1869,
though it was not identified until 1923, by Coster and Hevesy, making it the
last stable element to be discovered. Hafnium is named after Hafnia, the Latin
name for Copenhagen, where it was discovered.[4][5]
Hafnium is used in filaments
and electrodes. Some semiconductor fabrication processes use its oxide for
integrated circuits at 45 nm and smaller feature lengths. Some superalloys used
for special applications contain hafnium in combination with niobium, titanium,
or tungsten.
Ion-exchange and
solvent-extraction techniques have supplanted fractional crystallization and
distillation as the preferred methods of separating hafnium from zirconium. In
the procedure, crude zirconium tetrachloride is dissolved in an aqueous
solution of ammonium thiocyanate, and methyl isobutyl ketone is passed
countercurrent to the aqueous mixture, with the result that the hafnium tetrachloride
is preferentially extracted. The metal itself is prepared by magnesium
reduction of hafnium tetrachloride (Kroll process, which is also used for
titanium) and by the thermal decomposition of tetraiodide (de Boer–van Arkel
process).
For some purposes separation of
the two elements is not important; zirconium containing about 1 percent of
hafnium is as acceptable as pure zirconium. In the case of the largest single
use of zirconium, however, namely, as a structural and cladding material in
nuclear reactors, it is essential that the zirconium be essentially free of
hafnium, because the usefulness of zirconium in reactors is based on its
extremely low absorption cross section for neutrons. Hafnium, on the other
hand, has an exceptionally high cross section, and accordingly even slight
hafnium contamination nullifies the intrinsic advantage of the zirconium.
Because of its high neutron-capture cross section and its excellent mechanical
properties, hafnium is used for fabricating nuclear-control rods.
Hafnium's large neutron capture
cross section makes it a good material for neutron absorption in control rods
in nuclear power plants, but at the same time requires that it be removed from
the neutron-transparent corrosion-resistant zirconium alloys used in nuclear
reactors.
Movies ColdStar is The Best
Website/Platform For Hollywood HD Movies. We Provide Direct Download Links For
Fast And Secure Downloading. Just Click On Download Button.
Comments
Post a Comment