Hafnium, element symbol Hf, atomic number 72, atomic weight 178.49, belongs to group IV B of the periodic table. Hafnium is a lustrous silver-gray transition metal with a density of 13.31g/cm³(20 °C), a melting point of 2233 °C (2506 K, 4051 °F) and a boiling point of 4603 °C (4876 K, 8317 °F). The compact hafnium metal is inactive and reacts with air to form an oxide coating, which is stable at room temperature, while the powdered hafnium is prone to spontaneous combustion in air. Hafnium does not react with dilute hydrochloric acid, dilute sulfuric acid, and strong alkali solutions, but is soluble in hydrofluoric acid and aqua regia. Hafnium is rarely found in the Earth’s crust and often coexists with zirconium. Hafnium has high temperature resistance, corrosion resistance, oxidation resistance, easy processing, rapid heat absorption and heat release properties, and is used as atomic energy materials, alloy materials, high temperature resistant materials, electronic materials and so on.