SAMARIUM COBALT
Samarium cobalt (SmCo) is a magnetic material made of an alloy of the rare earth element samarium and hard metal cobalt as well as traces of iron, copper, hafnium, zirconium and praseodymium. Like neodymium, samarium cobalt magnets are known as rare earth magnets as samarium is part of the same rare earth group of elements as neodymium. Samarium cobalt magnets were developed in the early 1970s by the U.S. Air Force Materials Laboratory and were then the strongest magnets available until the introduction of neodymium magnets approximately ten years later. At the time of their introduction they were revolutionary, tripling the strength of the strongest available magnetic material.
Samarium cobalt magnets are typically manufactured by a method of reduction and melting followed by a process of bonding or sintering the raw material to form the magnet. Sintering is the most common manufacturing method as described here.
Similarly to the process for manufacturing neodymium magnets the raw materials for producing samarium cobalt magnets are heated in an induction furnace and melted. The liquid alloy is then poured into moulds and cooled to form ingots. Once the ingots are cooled they are broken down and milled to produce tiny micron-sized particles of samarium cobalt powder. The powder is then pressed using one of two methods; die pressing, where the powder is placed in a hard die and pressed or isostatic pressing where the powder is placed into a rubber die and pressed with equal pressure in all directions. Isostatic pressed magnets generally have better magnetic characteristics while die pressed magnets can be created to smaller dimensions.
Once the powder is pressed it is sintered at a temperature up to 1250?C, fusing the powder into a solid. The sintered material is then given a solution treatment at similar temperatures before being tempered between 700?C and 900?C, and then cooled in the presence of an externally applied magnetic field.
Finally, the magnetic material is machined, grinded and finished using water-cooled diamond-coated grinding machinery before being coated and magnetised.
Samarium cobalt magnets are available in two types or grades, commonly referred to as series 1:5 and series 2:17. Both series’ have high magnetic strength and have maximum energy products up to 35MGOe. Although they are not as strong as neodymium magnets their major strength is that they can maintain their performance in temperatures up to 350?. They are also extremely resistant to corrosion, even without coating. However, because they contain cobalt, they are relatively expensive to produce.
