Hafnium << HAF nee uhm >> a chemical element, is a silver-colored metal. It absorbs neutrons better than most metals and is resistant to corrosion. For these reasons, rods made of hafnium are used to control the rate of reactions in nuclear reactors of nuclear submarines. When the reaction rate is too high, the rods are pushed into the reactor to absorb some of the neutrons. When the rate is low, the rods are withdrawn. Hafnium is also used in some gas-filled and incandescent lamps.
The highest concentrations of hafnium occur in the minerals zircon and baddeleyite. Hafnium is always found in combination with the more common element zirconium, which it resembles in its chemical and physical properties. Hafnium is a common by-product of the production of this element.
Hafnium has the chemical symbol Hf. Its atomic number (number of protons in its nucleus) is 72. Its relative atomic mass is 178.49. An element’s relative atomic mass equals its mass (amount of matter) divided by 1/12 of the mass of carbon 12, the most abundant form of carbon. Hafnium melts at about 2227 °C and boils at 4602 °C. Its specific gravity is 13.31 grams per cubic centimeter.
Chemists classify hafnium as a transtion metal . For information on the position of hafnium on the periodic table, see the article Periodic table .
Dirk Coster, a Dutch physicist, and Georg von Hevesy, a Hungarian chemist, discovered hafnium in 1923 in Copenhagen, Denmark. The word hafnium comes from Hafnia, the Latin name for Copenhagen.
