This section provides an overview for cobalt magnets as well as their applications and principles. Also, please take a look at the list of 15 cobalt magnet manufacturers and their company rankings.
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Cobalt magnet is a general term for magnets containing cobalt, and most often refers to samarium cobalt magnets. When cobalt, which has ferromagnetic properties, is alloyed with samarium, a rare earth, in a composition of 1:5 or 2:17, it has the properties of a powerful magnet. Next to neodymium magnets, samarium cobalt magnets have the strongest magnetic force and also have excellent temperature characteristics, making them important magnets for industrial applications.
Samarium cobalt magnets are mainly used in automobile motors, medical precision equipment parts, and sensors.
Samarium cobalt magnets are permanent magnets that combine magnetic force and temperature characteristics. Neodymium magnets are stronger than samarium cobalt magnets in terms of magnetic force, but samarium cobalt magnets are superior in terms of temperature characteristics. Since the magnetic force does not decrease even at high temperatures, samarium cobalt magnets are suitable for applications that require temperature stability. On the other hand, they are fragile and easily broken, so care must be taken when using them in applications where strength is required.
Specific applications include electrical motors, rotation sensors, and industrial motors.
Cobalt magnet is a general term for magnets with cobalt as the main component, and a typical example is the samarium cobalt magnet. Samarium cobalt magnets are one of the permanent magnets and have the second highest magnetic force after neodymium magnets.
Cobalt is a transition metal element with atomic number 27 and element symbol Co, and is ferromagnetic. It belongs to group 9 on the periodic table, the same group as iron. It is silvery-white in color and has properties similar to iron, but it is harder and less susceptible to oxidation. Samarium is a rare earth element with atomic number 62 and element symbol Sm. It is grayish-white in color and has soft properties. Samarium itself has no ferromagnetism.
When these metallic elements are combined to form SmCo5 (1-5 series) or Sm2CO17 (2-17 series) alloys, they exhibit high magnetic force. Samarium cobalt magnets have better thermal stability and corrosion resistance than neodymium magnets, so they are used in automotive products such as magnetic sensors, actuators for smartphone cameras, and medical devices. On the other hand, their mechanical strength is weak, which somewhat limits their applications.
While cobalt magnets are resistant to heat, there is a risk of ignition under certain conditions, so care must be taken when handling them. In particular, they are susceptible to ignition when the magnet surface is dry or cleanly polished, and may burn at low temperatures.
In addition, cobalt magnets are more brittle than other magnets and are easily chipped by impact, so depending on how they are used, a fine powder of cobalt alloy may be produced. This metallic powder is very dangerous because it can spontaneously combust or burn explosively. In general, metallic powders such as rare earths are highly flammable because of their large surface area and frequent contact with air. Because of their hazardous nature, they are designated as flammable solids in the category of hazardous materials. Since the metallic powder may ignite due to frictional heat, etc., it must be used safely by avoiding usage where heat is generated by rubbing against other objects or alloy powder is generated due to abrasion of the cobalt magnet.
As for magnets containing cobalt, when they were first developed, it was known that SmCo5, a magnet with a composition ratio of 5 cobalt to 1 samarium, exhibited high magnetic force. Later, Dr. Yoshio Tawara, a Japanese physicist, developed a cobalt magnet called Sm2(Co, Fe, Cu, Zr)17, which contains several transition metal elements such as iron, copper, and zirconium, in addition to samarium and cobalt. This magnet is made so that the composition ratio of cobalt, iron, copper, and zirconium combined is 17 to samarium-2. Research results have shown that this magnet has a very high performance among cobalt-based magnets.
An example of the composition of samarium cobalt magnets currently on the market is one that contains 51 wt% cobalt, 26 wt% samarium, 17 wt% iron, and 6 wt% copper. These magnets are superior to other magnets in terms of heat resistance, but tend to be more expensive because they contain more cobalt.
*Including some distributors, etc.
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