Rare earth element
Atomic number: 66
Used in: High-temperature magnets
Criticality rating: critical
Like neodymium, dysprosium is prized for its magnetic properties – not least, when mixed with terbium and iron to form the alloy Terfenol D. It has the peerless ability to change shape in response to a magnetic field.
This “magnetostrictive” property has led to some far-out uses. The US navy has used Terfenol-D to develop an advanced active sonar transducer, producing and then picking up high-powered “pings” underwater.
Dysprosium's greatest selling point, however, is how it handles the heat. Magnets made from a pure neodymium-iron-boron alloy lose their magnetisation at temperatures above 300 °C. Adding in a small amount of dysprosium, at about 5 per cent by weight, solves that problem, making the element a vital component in high-performance magnets found in countless technologies from turbines to hard discs.
According to the US DoE, the wide range of its current and projected uses, together with the lack of any immediately suitable replacement, makes dysprosium the single most critical element for emerging clean energy technologies. China is the only country with significant known deposits, with the new mines opening in Australia and Canada only containing small quantities of the element in their rare earth ores. Even the US DoE's most conservative projections predict a shortfall of dysprosium before 2015.