The metal hafnium, atomic number 72, is a silver-gray transition metal with unique physical and chemical properties. Hafnium plays an important role in metallurgy and refining, and is often used to improve the formability and corrosion resistance of metal materials. Its alloys have high melting point, high hardness and excellent heat resistance, and are widely used in high-tech fields such as rocket nozzles, nuclear reactor control rods and aircraft front protection layers. In addition, hafnium acts as an getter, effectively removing impurity gases such as oxygen and nitrogen from the system.