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Samarium Cobalt Magnets

 

SmCo Overstock Allstar Magnetics

A samarium–cobalt (SmCo) magnet, a type of rare earth magnet, is a strong permanent magnet made of an alloy of samarium and cobalt. They were developed in the early 1970s, by Albert Gale and Dr. Daas, of Raytheon Corporation. They are generally ranked similarly in strength to neodymium magnets, but have higher temperature ratings and higher coercivity. They are brittle, and prone to cracking and chipping. Samarium–cobalt magnets have maximum energy products (BHmax) that range from 16 megagauss-oersteds (MGOe) to 33 MGOe, that is approx. 128 kJ/m3 to 264 kJ/m3; their theoretical limit is 34 MGOe, about 272 kJ/m3.

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samarium cobalt magnet

Attributes

-Extremely resistant to demagnetization
- Good temperature stability (maximum use temperatures between 250 °C (523 K) and 550 °C (823 K); Curie temperatures from 700 °C (973 K) to 800 °C (1,070 K)
- Expensive and subject to price fluctuations (cobalt is market price sensitive)

Physical and mechanical properties
Comparison of physical properties of sintered neodymium and Sm-Co magnets
PropertyNeodymiumSm-Co
Remanence (T) 1–1.3 0.82–1.16
Coercivity (MA/m) 0.875–1.99 0.493–1.59
Relative permeability 1.05 1.05
Temperature coefficient of remanence (%/K) −0.12 −0.03
Temperature coefficient of coercivity (%/K) −0.55..–0.65 −0.15..–0.30
Curie temperature (°C) 320 800
Density (g/cm3) 7.3–7.5 8.2–8.4
CTE, magnetizing direction (1/K) 5.2×10−6 5.2×10−6
CTE, normal to magnetizing direction (1/K) −0.8×10−6 11×10−6
Flexural strength (N/mm2) 250 150
Compressive strength (N/mm2) 1100 800
Tensile strength (N/mm2) 75 35
Vickers hardness (HV) 550–650 500–650
Electrical resistivity (Ω·cm) (110–170)×10−6 86×10−6

Uses

Fender is using one of legendary designer Bill Lawrence's latest designs named the Samarium Cobalt Noiseless series of electric guitar pickups in Fender's Vintage Hot Rod '57 Stratocaster.[5] The Samarium Cobalt Noiseless Pickups were used in American Deluxe Series Guitars and Basses from 2004 until Early 2010. In the mid 1980s some expensive headphones such as the Ross RE-278 utilised Samarium Cobalt "Super Magnet" transducers. Other uses include: High-end electric motors used in the more competitive classes in slotcar racing Turbomachinery 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 Benchtop NMR spectrometers

Hazards

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 as with all sintered materials, inherent cracks are very 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.

Production

The reduction/melt method and reduction/diffusion method are used to manufacture samarium–cobalt magnets. The reduction/melt method will be described since it 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.[citation needed] It then is ground and further magnetized to increase its magnetic properties. The finished product is tested, inspected and packed

Machining

The alloys are typically machined in the unmagnetized state. Samarium–cobalt should be ground using a wet grinding process (water based coolants) and a diamond grinding wheel. The same type of process is required if drilling holes or other features that are confined. The grinding waste produced must not be allowed to completely dry 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.