Hafnium

Hafnium is a metallic element with the symbol Hf and the atomic number 72. A lustrous, silvery gray tetravalent transition metal, hafnium resembles zirconium chemically and is found in zirconium minerals from which it is difficult to separate. Hafnium is used in tungsten alloys in filaments and electrodes, in integrated circuits as a gate insulator for transistors, and as a neutron absorber in control rods in water-cooled nuclear reactors in power plants. It is considered toxic as are its compounds.