Samarium-Cobalt - General Information

Samarium Cobalt alloys are typically machined in the unmagnetized state. Samarium–cobalt are ground using a water based coolants grinding process and a diamond grinding wheel. The same type of process is required if holes drilling are needed. The grinding waste produced must not be allowed to completely dried as samarium–cobalt has a low ignition point. A small spark, such as that produced with static electricity, can easily commence combustion. The fire produced will be extremely hot and difficult to control.

The reduction/melt method and reduction/diffusion method are used to manufacture samarium–cobalt magnets. The reduction/melt method is used for both SmCo5 and Sm2Co17 production. The raw materials are melted in an induction furnace filled with argon gas. The mixture is cast into a mold and cooled with water to form an ingot. The ingot is pulverized and the particles are further milled to further reduce the particle size. The resulting powder is pressed in a die of desired shape, in a magnetic field to orient the magnetic field of the particles.

Sintering is applied at a temperature of 1100˚C–1250˚C, followed by solution treatment at 1100˚C–1200˚C and tempering is finally performed on the magnet at about 700˚C–900˚C. It then is ground and further magnetized to increase its magnetic properties. The finished product is tested, inspected and packed.

Characteristics of Samarium-cobalt include:

  • Samarium–cobalt magnets can easily chip; eye protection must be worn when handling them.
  • Allowing magnets to snap together can cause the magnets to shatter, which can cause a potential hazard.
  • Samarium–cobalt is manufactured by a process called sintering and inherent cracks are possible.
  • The magnets do not provide mechanical integrity; instead the magnet must be utilized for its magnetic functions and other mechanical systems must be designed to provide the mechanical reliability of the system.
  • Very brittle, and hard to machine
  • Samarium-cobalt is extremely resistant to demagnetization
  • Good temperature stability (maximum use temperatures between 250 and 550 °C; Curie temperatures from 700 to 800 °C)
  • Does not need to be protected against oxidation
  • High magnetic strength - up to about 32MGOe
  • Expensive and subject to price fluctuations (cobalt is market price sensitive)

Some of the properties of samarium–cobalt magnets include:

  • Density: 8.4 g/cm³
  • Electrical resistivity 0.8×10−4 Ω·cm
  • Coefficient of thermal expansion (perpendicular to axis): 12.5 µm/(m·K)
  • Flux density variation under 5% per 100°C change in temperature (in the range of 25–250°C)

Uses include:

  • High-end electric motors
  • Turbo machinery
  • Traveling-wave tube field magnets
  • Applications that will require the system to function at cryogenic temperatures or very hot temperatures (over 180°C)
  • Applications in which performance is required to be consistent with temperature change
  • The cost of SmCo magnets is about 25 to 50 times that of Ferrite magnets.

Quick Facts

Density - 0.300 lbs per cubic inch
Saturation magnetizing field required - about 50kOe
Manufacturing methods - sintering (most common), with some injection molding and compression bonding.
Shapes available - blocks, bars, discs, rings, arc segments, etc.
Grades available - from about 1410 to 3214. (First 2 digits represent BHmax, and second two digits represent Intrinsic Coercivity, Hci.)
Sizes - off tool the largest die pressed blocks are about 3" cube, while isostatically pressed blocks can be much longer in the orientation direction (up to 9 feet).

Surface Treatments

In general, no surface treatment is required for SmCo magnets since they are not subject to oxidation.

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