Wednesday, January 12, 2011

Dysprosium: The Hard to Get At Rare Earth Element?

Even though this rare earth element and its myriad of uses has yet to become a household name, does dysprosium truly deserve its reputation as the hard to get at rare earth element?

By: Ringo Bones

Given that this rare earth element is never found free in nature, the derivation of its name – dysprositos, Greek for hard to get at – is probably an apt name of its chemical properties that eludes dysprosium’s purification to six-nines level (99.9999% purity) until the advent of modern ion-exchange and solvent-extraction procedures of the mid to late 1950s. Dysprosium, atomic number 66, chemical symbol Dy, is a member of the lanthanide – or rare earth series of elements – which also includes such rare earth metals as cerium, lanthanum and yttrium. Dysprosium has a melting point of about 1,500 degree Celsius and a boiling point of 2,300 degree Celsius.

The discovery of dysprosium was credited to the French chemist Paul Émil Lecoq de Boisbaudran back in 1886. Although Georges Urbain later obtained a reasonably pure sample of the metal in 1906, the free element has never been chemically isolated until the advent of modern ion-exchange and solvent-extraction techniques of the mid to late 1950s.

Dysprosium occurs naturally in minerals usually found in granite or pegmatite veins, such as euxenite, gadolinite, samarskite and xenotime. Dysprosium is also found among the products of nuclear-fission reactions. Dysprosium is separated from other rare earth metals which it occurs via ion-exchange and solvent-extraction methods.

Dysprosium is used primarily in nuclear reactor control rods and its other chief practical use is in nuclear reactors, where it serves as a nuclear “poison” – that is, it is employed as a neutron-eating material to keep the neutron-spawning atomic chain reaction from getting out of hand and also in magnetic alloys.

Dysprosium has a valence of +3 and forms yellow-green colored compounds. Dysprosium is ferromagnetic below – 123 degrees Celsius. Just like pure gallium when chilled with liquid nitrogen, dysprosium will stick to an ordinary bar magnet. And at liquid helium temperatures, dysprosium becomes a superconductor.

Dysprosium’s high magnetic susceptibility makes it useful for data storage devices and as a component of Terfenol-D – a powerful rare earth magnet first used in US Navy sonar systems. Soluble dysprosium salts are mildly toxic while the insoluble salts are considered non-toxic.

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