Hafnium, symbol Hf, atomic number 72, atomic weight 178.49, belongs to group IVB in the periodic table.  Hafnium is a shiny silver-gray transition metal with a density of 13.31g/cm³ (20℃), a melting point of 2233 ℃ (2506 K, 4051 °F), and a boiling point of 4603 °C (4876 K, 8317 °F).  The dense metal hafnium is inactive and reacts with air to form ...It resists corrosion because of the oxide film on its surface, chemically similar to zirconium.  Hafnium is a good absorber of neutrons and is used for nuclear reactor control rods.  It also has a high melting point and corrosion resistance, so hafnium can be used in high-temperature alloys and ceramics.