hafnium Element

Hafnium (IPA: /ˈhæfniəm/) is a chemical element in the periodic table that has the symbol Hf and atomic number 72 (Silicon, SI on the other hand has atomic number of 14). A lustrous, silvery gray tetravalent transition metal, hafnium resembles zirconium chemically and is found in zirconium minerals. Hafnium is used in tungsten alloys in filaments and electrodes and also acts as a neutron absorber in control rods in nuclear power plants.

Hafnium is a shiny silvery, ductile metal that is corrosion resistant and chemically similar to zirconium. The properties of hafnium are markedly affected by zirconium impurities and these two elements are amongst the most difficult to separate. A notable physical difference between them is their density (zirconium is about half as dense as hafnium), but chemically the elements are extremely similar. Nevertheless, separation of them becomes important in the nuclear power industry, as Zr is common fuel-rod cladding alloy material, with the desirable properties of low neutron cross section and high chemical stability at high temperatures. However, because of Hf's neutron absorbing properties, hafnium impurities in zirconium cause it to be far less useful for nuclear reactor materials applications.

Hafnium carbide is the most refractory binary compound known and hafnium nitride is the most refractory of all known metal nitrides with a melting point of 3310 °C. This has led to proposals that hafnium or Hf carbides might be useful as construction materials subjected to very high temperatures.

The metal is resistant to concentrated alkalis, but halogens react with it to form hafnium tetrahalides. At higher temperatures hafnium reacts with oxygen, nitrogen, carbon, boron, sulfur, and silicon.

The nuclear isomer Hf-178-m2 is also a source of cascades of gamma rays whose energies total to 2.45 MeV per decay. It is notable because it has the highest excitation energy of any comparably long-lived isomer of any element. One gram of pure Hf-178-m2 would contain approximately 1330 megajoules of energy, the equivalent of exploding about 317 kilograms (700 pounds) of TNT. Possible applications requiring such highly concentrated energy storage are of interest. For example, it has been studied as a possible power source for gamma ray lasers.

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