Hafnium is a chemical element with the symbol Hf and atomic number 72. It is a shiny, silvery-gray transition metal commonly used in nuclear reactors and as an alloy with titanium in Aerospace applications. Hafnium is highly resistant to corrosion and has a very high melting point, making it a great material for high-temperature applications such as in jet engines and gas turbines. Hafnium is also used as a neutron absorber in nuclear power plants, and in semiconductor manufacturing where it is used as a gate insulator in metal-oxide-semiconductor (MOS) devices due to its high dielectric constant.