Hafnium

Hafnium is a hard, silvery-gray metal that is almost always found mixed with zirconium in the mineral zircon. The two are chemical near-twins, which is why hafnium went unnoticed until 1923, when Dirk Coster and George de Hevesy found it in Copenhagen (Latin Hafnia). Today it is a by-product of refining zirconium.

Its main role here is hafnium dioxide (HfO₂). As chip transistors shrank, the silicon dioxide layer insulating each gate grew so thin that current leaked straight through. Since 2007, chipmakers have used hafnium dioxide instead: it controls the switch just as well while being physically thicker, so far less current escapes. Hafnium also soaks up neutrons, so it is used in control rods for nuclear reactors.