Samarium–cobalt magnet

Samarium- cobalt ( SmCo abbreviated ) is an alloy of the rare earth metal samarium (Sm ) and the metal cobalt ( Co). Samarium- cobalt is produced in two alloy structures, SmCo5 without iron content and Sm2Co17 with 20-25 % iron content. Both alloys are used in permanent magnets.

SmCo5 has been developed as a rare-earth magnet in 1966 and Sm2Co17 in 1972 by Karl J. Strnat the U.S. Air Force Materials Laboratory at Wright - Patterson Air Force Base. Sm2Co17 has over SmCo5 improved magnetic properties, but can be difficult to produce. Samarium- cobalt was in the 1970s until the discovery of neodymium-iron- boron, the material with the highest known magnetic energy density.

General

The alloy has a SmCo5 maximum magnetic energy density (BH) max = 130 to 200 kJ/m3, the alloy of a Sm2Co17 160-260 kJ/m3. The Curie temperature of the SmCo magnet is 450 ° C. Both alloys can be used up to about 300 ° C for temperatures, and are extremely difficult to demagnetize. The specific electrical resistance is 86 × 10-6 Ω · cm.

For the preparation of the two starting materials are melted alloy in a protective argon gas atmosphere and cast into ingot form. To improve the thermal properties of the melt are mixed various alloying additives. For solidification of the melt in the form of ingots to large crystal structures that can be easily demagnetize and are not directly usable as a magnetic material form. Therefore, these bars, the powder thus formed is crushed and pulverized by appropriate grinding processes under protective gas, and converted by sintering at temperatures of about 1100-1250 C ˚ or pressing with plastics into the desired initial shape. In combination with the sintering or Verpressungsprozess and after that, the magnetization of the material takes place.

Subsequent processing of sintered magnets designed to be difficult, since the material is magnetized ferromagnetic tools and Chips also not easily separated by the magnetization from the body. Furthermore, the finely divided material is liable to spontaneous combustion, so that water-cooled diamond-coated tools have to be used. The sintered material is prone to sharp chipping, even if two magnets snap together, no brakes, so wear appropriate protective clothing and safety goggles should be worn when working with samarium- cobalt. In plastics verpresstes samarium -cobalt powder can subsequently edit lighter and also has the disadvantage of not sharp-edged splinters, but has inferior magnetic properties than sintered magnets.

The sintered magnets are not particularly stable in itself and should be used in applications only because of their magnetic properties. Other objects, such as the mechanical loads on train or pressure, should be taken over by other suitable materials.

SmCo today is used mainly for its compared to the neodymium-iron- boron high -temperature and corrosion resistance, as well as the lower reversible temperature coefficient of magnetization. Due to the high cost of SmCo the economic significance is lower. Applications of the material are among others the case of rotating electric machines with permanent excitation.