Hafnium and Hafnium Compounds

Abstract Hafnium, Hf, is in Group 4 (IVB) of the Periodic Table, as are the lighter elements zirconium and titanium. Hafnium is a heavy gray‐white metallic element never found free in nature. It is always found associated with the more plentiful zirconium. The two elements are almost identical in chemical behavior. Hafnium is obtained as a by‐product of the production of hafnium‐free nuclear‐grade zirconium. Hafnium's primary use is as a minor strengthening agent in high temperature nickel‐base superalloys. Additionally, hafnium is used as a neutron‐absorber material, primarily in the form of control rods in nuclear reactors. Hafnium is a hard, heavy, somewhat ductile metal having an appearance slightly darker than that of stainless steel. Hafnium's aqueous chemistry is characterized by a high degree of hydrolysis, the formation of polymeric species, a very slow approach to true equilibrium, and the multitude of complex ions that can be formed. Hafnium is a highly reactive metal. Most hafnium compounds have been of slight commercial interest aside from intermediates in the production of hafnium metal. However, hafnium oxide, hafnium carbide, and hafnium nitride are quite refractory and have received considerable study as the most refractory compounds of the Group 4 (IVB) elements.