Samarium cobalt

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Samarium-cobalt (abbreviated as SmCo ) is an alloy of the rare earth metal samarium (Sm) with the metal cobalt (Co). Two crystal structures are suitable for use as permanent magnets: SmCo 5 , without additional alloying elements, and Sm 2 Co 17 with iron, copper and zirconium as additional alloying elements.

SmCo 5 was developed as a rare earth magnet alloy in 1966 and Sm 2 Co 17 in 1972 by Karl J. Strnat at the US Air Force Materials Laboratory at Wright-Patterson Air Force Base . Sm 2 Co 17 has improved magnetic properties compared to SmCo 5 , but is more difficult to manufacture. In the 1970s, until the discovery of neodymium-iron-boron, samarium cobalt was the material with the highest magnetic energy density.

General

The alloy SmCo 5 has a maximum magnetic energy density of up to (BH) max = 200 kJ / m 3 , the alloy Sm 2 Co 17 up to 260 kJ / m 3 . By replacing the Sm with other rare earths, such as Pr or Gd, the remanence, and thus the energy product, can be changed. The Curie temperature of the SmCo magnets is between 700 and 850 ° C. SmCo 5 magnets can be used up to around 250 ° C. Special Sm 2 Co 17 alloys up to 550 ° C. The specific electrical resistance is between 50 and 100 × 10 −6  Ω · cm.

Usually, SmCo magnets are manufactured using powder metallurgy . The alloying elements are first melted in a vacuum induction furnace, quickly cooled and then ground to a particle size of less than 10 µm, where only single-crystalline powder is present. The metal powder is then aligned in a magnetic field and, depending on the process, pressed simultaneously or afterwards to form a green compact. This is then densely sintered in a vacuum or under protective gas. The magnets receive their coercive field strength through a heat treatment .

In addition to these sintered magnets, there is also a plastic-bonded variant. Compared to NdFeB, however, their importance is much less.

SmCo magnets are very brittle and are therefore usually only machined with diamond-coated grinding wheels or by wire EDM . Whenever possible, the magnets are only magnetized after machining.

From around 150 to 180 ° C, SmCo has a higher energy product than neodymium-iron-boron , which is why it is mainly used at higher application temperatures. But the better corrosion resistance, the lower reversible temperature coefficient or the better resistance to ionizing radiation can also make the use of SmCo useful. By adding the antiferromagnetic behavior of gadolinium , the reversible temperature coefficient of remanence can be reduced to zero or even reversed to positive values.

Due to the higher production costs of SmCo, the economic importance is less than that of NdFeB. Applications for the material include rotating electrical machines with permanent excitation, sensors in automotive engineering and chemical pumps.

Individual evidence

  1. ↑ History of Rare-Earth Magnets. Retrieved May 29, 2013 .
  2. ^ Arnold Magnetic Technologies: RECOMA Samarium Cobalt Magnet Catalogs. (No longer available online.) Formerly in the original ; accessed on September 21, 2014 .  ( Page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.@1@ 2Template: Dead Link / www.arnoldmagnetics.com  
  3. ^ Electron Energy Corporation: Samarium Cobalt Magnets. (No longer available online.) Archived from the original on September 21, 2014 ; accessed on September 21, 2014 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.electronenergy.com
  4. ↑ Vacuum melt: permanent magnets made from samarium-cobalt alloys. Retrieved September 21, 2014 .
  5. ↑ MS Schramberg: Magnetic Characteristics. (No longer available online.) Archived from the original on June 3, 2013 ; accessed on September 21, 2014 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.magnete.de
  6. ↑ Standard Specifications for Permanent Magnet Materials (PDF; 1.4 MB), MMPA Standard No. 0100-00, 2000

literature

  • Peter Campbell: Permanent Magnet Materials and their Application . Cambridge University Press, 1996, ISBN 978-0-521-56688-9 .
  • Juha Pyrhonen, Tapani Jokinen, Valeria Hrabovcova: Design of Rotating Electrical Machines . Wiley, 2009, ISBN 978-0-470-69516-6 .