Metal Profile: Dysprosium

What is dysprosium?

Dy-Metal-2.jpg
Pure dysprosium metal ingots. Image © Copyright Strategic Metal Investments Ltd.

Dysprosium metal is a soft, lustrous-silver rare earth element (REE) that is used in permanent magnets due to its paramagnetic strength and high-temperature durability.

Properties:

  • Atomic Symbol: Dy
  • Atomic Number: 66
  • Element Category: Lanthanide metal
  • Atomic Weight: 162.50
  • Melting Point: 1412°C
  • Boiling Point: 2567°C
  • Density: 8.551g/cm3
  • Vickers Hardness: 540 MPa

Characteristics:

While relatively stable in air at ambient temperatures, dysprosium metal will react with cold water and rapidly dissolves in contact with acids.

In hydrofluoric acid, however, the heavy rare earth metal will form a protective layer of dysprosium fluoride (DyF3).

The soft, silver-colored metal's main application is in permanent magnets. This is due to the fact that pure dysprosium is strongly paramagnetic above -93°C (-136°F), meaning it is attracted to magnetic fields within a wide range of temperatures.

Along with holmium, dysprosium also has the highest magnetic moment (the strength and direction of pull resulting affected by a magnetic field) of any element.

Dysprosium's high melting temperature and neutron absorption cross section also allow it to be used in nuclear control rods.

While dysprosium will machine without sparking, it is not commercially used as a pure metal or in structural alloys.

Like other lanthanide (or rare earth) elements, dysprosium is most often naturally associated in ore bodies with other rare earth elements.

History:

The French chemist Paul-Emile Lecoq de Boisbadran first recognized dysprosium as an independent element in 1886 while he was analyzing erbium oxide.

Reflecting the intimate nature of REEs, de Boisbaudran was initially investigating impure yttrium oxide, from which he drew erbium and terbium using acid and ammonia.

Erbium oxide, itself, was found to be harboring two other elements, holmium, and thulium.

As de Boisbaudran worked on away at his home, the elements began to reveal themselves like Russian dolls, and after 32 acid sequences and 26 ammonia precipitations, de Boisbaudran was able to identify dysprosium as a unique element. He named the new element after the Greek word dysprositos, meaning 'hard to get'.

More pure forms of the element were prepared in 1906 by Georges Urbain, while a pure form (by today's standards) of the element was not produced until 1950, after the development of io- exchange separation and metallographic reduction techniques by Frank Harold Spedding, a pioneer of rare earth research, and his team at Ames Laboratory.

The Ames Laboratory, along with the Naval Ordnance Laboratory, was also central in developing one of the first major uses for dysprosium, Terfenol-D. The magnetostrictive material was researched during the 1970s and commercialized in the 1980s for use in naval sonars, magnetomechanical sensors, actuators and transducers.

Dysprosium's use in permanent magnets also grew with the creation of neodymium-iron-boron (NdFeB) magnets in the 1980s. Research by General Motors and Sumitomo Special Metals led to the creation of these stronger, cheaper versions of the first permanent (samarium-cobalt) magnets, which had been developed 20 years earlier.

The addition of between 3 to 6 percent dysprosium (by weight) to the NdFeB magnetic alloy increases the magnet's Curie point and coercivity, thereby, improving stability and performance at high temperatures while also reducing demagnetization.

NdFeB magnets are now the standard in electronic applications and hybrid electric vehicles.

The REEs, including dysprosium, were thrust into the global media spotlight in 2009 after limits on Chinese exports of the elements led to supply shortfalls and investor interest in the metals. This, in turn, led to rapidly increasing prices and significant investment in the development of alternative sources.

Production:

Recent media attention examining global dependence on Chinese REE production often highlights the fact that the country accounts for roughly 90% of global REE production.

While a number of ore types, including monazite and bastnasite, may contain dysprosium, the sources with the highest percentage of contained dysprosium are the ion adsorption clays of Jiangxi Province, China and xenotime ores in South China and Malaysia.

Depending upon the type of ore, a variety of hydrometallurgical techniques must be employed in order to extract individual REEs. Froth flotation and roasting of concentrates is most the most common method of extracting rare earth sulphate, a precursor compound that can consequently be processed via ion exchange displacement. The resulting dysprosium ions are then stabilized with fluorine to form dysprosium fluoride.

Dysprosium fluoride can be reduced into metal ingots by heating with calcium at high temperatures in tantalum crucibles.

Global production of dysprosium is limited to about 1800 metric tonnes (contained dysprosium) annually. This accounts for only about 1 percent of all rare earth refined each year.

The largest rare earth producers include Baotou Steel Rare Earth Hi-Tech Co., China Minmetals Corp., and Aluminum Corp. of China (CHALCO).

Applications:

By far, the largest consumer of dysprosium is the permanent magnet industry. Such magnets dominate the market for high-efficiency traction motors that are used in hybrid and electric vehicles, wind turbine generators and hard disc drives.

Click here to read more about dysprosium applications. 

Sources:

Emsley, John. Nature's Building Blocks: An A-Z Guide to the Elements.
Oxford University Press; New Edition edition (Sept. 14 2011)
Arnold Magnetic Technologies. The Important Role of Dysprosium in Modern Permanent Magnets. January 17, 2012.
British Geological Survey. Rare Earth Elements. November 2011.
URL: www.mineralsuk.com
Kingsnorth, Prof. Dudley. "Can China's Rare Earths Dynasty Survive". China's Industrial Minerals & Markets Conference. Presentation: September 24, 2013.

Follow Terence on Google+