Product Code Database
A neodymium magnet (also known as NdFeB, NIB or Neo magnet) is a permanent magnet made from an alloy of neodymium, iron, and boron that forms the Nd2Fe14B tetragonal crystalline structure. They are the most widely used type of rare-earth magnet.
Developed independently in 1984 by General Motors and Sumitomo Special Metals, neodymium magnets are the strongest type of permanent magnet available commercially. They have replaced other types of magnets in many applications in modern products that require strong permanent magnets, such as Electric motor in cordless tools, hard disk drives and magnetic fasteners.
NdFeB magnets can be classified as sintered or bonded, depending on the manufacturing process used. Sintered NdFeB Magnets, What are Sintered NdFeB Magnets? Bonded NdFeB Magnets, What are Bonded NdFeB Magnets?
GM commercialized its inventions of isotropic Neo powder, bonded neo magnets, and the related production processes by founding Magnequench in 1986 (Magnequench has since become part of Neo Materials Technology, Inc., which later merged into Molycorp). The company supplied melt-spun Nd2Fe14B powder to bonded magnet manufacturers. The Sumitomo Group facility became part of Hitachi, and has manufactured but also licensed other companies to produce sintered Nd2Fe14B magnets. Hitachi has held more than 600 patents covering neodymium magnets.
Chinese manufacturers have become a dominant force in neodymium magnet production, based on their control of much of the world's rare-earth mines.
The United States Department of Energy has identified a need to find substitutes for rare-earth metals in permanent magnet technology and has funded such research. The Advanced Research Projects Agency-Energy has sponsored a Rare Earth Alternatives in Critical Technologies (REACT) program, to develop alternative materials. In 2011, ARPA-E awarded 31.6 million dollars to fund rare-earth substitute projects. Because of its role in permanent magnets used for Wind turbine, it has been argued that neodymium will be one of the main objects of geopolitical competition in a world running on renewable energy. This perspective has been criticized for failing to recognize that most wind turbines do not use permanent magnets and for underestimating the power of economic incentives for expanded production.
The strength of neodymium magnets is the result of several factors. The most important is that the tetragonal Nd2Fe14B crystal structure has exceptionally high uniaxial magnetocrystalline anisotropy ( HA ≈ 7T – magnetic field strength H in units of A/m versus magnetic moment in A·m2). This means a crystal of the material preferentially magnetizes along a specific crystal axis but is very difficult to magnetize in other directions. Like other magnets, the neodymium magnet alloy is composed of microcrystalline grains which are aligned in a powerful magnetic field during manufacture so their magnetic axes all point in the same direction. The resistance of the crystal lattice to turning its direction of magnetization gives the compound a very high coercivity, or resistance to being demagnetized.
The neodymium atom can have a large magnetic dipole moment because it has 4 unpaired electrons in its electron structure as opposed to (on average) 3 in iron. In a magnet it is the unpaired electrons, aligned so that their spin is in the same direction, which generate the magnetic field. This gives the Nd2Fe14B compound a high saturation magnetization ( Js ≈ 1.6T or 16kG) and a remanent magnetization of typically 1.3 teslas. Therefore, as the maximum energy density is proportional to Js2, this magnetic phase has the potential for storing large amounts of magnetic energy ( BHmax ≈ 512kJ/m3 or 64MG·Oe).
This magnetic energy value is about 18 times greater than "ordinary" ferrite magnets by volume and 12 times by mass. This magnetic energy property is higher in NdFeB alloys than in samarium cobalt (SmCo) magnets, which were the first type of rare-earth magnet to be commercialized. In practice, the magnetic properties of neodymium magnets depend on the alloy composition, microstructure, and manufacturing technique employed.
The Nd2Fe14B crystal structure can be described as alternating layers of iron atoms and a neodymium-boron compound. The diamagnetic boron atoms do not contribute directly to the magnetism but improve cohesion by strong covalent bonding. The relatively low rare earth content (12% by volume, 26.7% by mass) and the relative abundance of neodymium and iron compared with samarium and cobalt makes neodymium magnets lower in price than the other major rare-earth magnet family, samarium–cobalt magnets.
Although they have higher remanence and much higher coercivity and energy product, neodymium magnets have lower Curie temperature than many other types of magnets. That Nd2Fe14B maintains magnetic order up to beyond room temperature has been attributed to the Fe present in the material stabilising magnetic order on the Nd sub-lattice. Special neodymium magnet alloys that include terbium and dysprosium have been developed that have higher Curie temperature, allowing them to tolerate higher temperatures than those alloys containing only Nd.
| + Magnetic properties of various permanent magnets |
| 590–752 |
| 590–752 |
| 1328 |
| 1472 |
| 1292–1580 |
| 842 |
| + Comparison of physical properties of sintered neodymium and Sm-Co magnets Typical Physical and Chemical Properties of Some Magnetic Materials, Permanent Magnets Comparison and Selection. ! Property !! Neodymium !! Sm-Co |
| 0.8–1.16 |
| 0.493–2.79 |
| 1.05–1.1 |
| −(0.05–0.03) |
| −(0.30–0.15) |
| 700–850 |
| 8.2–8.5 |
| (5–9)×10−6 |
| (10–13)×10−6 |
| 150–180 |
| 800–1000 |
| 35–40 |
| 400–650 |
| (50–90)×10−6 |
This vulnerability is addressed in many commercial products by adding a protective coating to prevent exposure to the atmosphere. Nickel, nickel-copper-nickel and zinc platings are the standard methods, although plating with other metals, or polymer and lacquer protective coatings, are also in use.
Grades of sintered NdFeB magnets: "Grades of Neodymium magnets" (PDF). Everbeen Magnet. Retrieved December 6, 2015.
Bonded neo Nd-Fe-B powder is bound in a matrix of a thermoplastic polymer to form the magnets. The magnetic alloy material is formed by splat quenching onto a water-cooled drum. This metal ribbon is crushed to a powder and then heat-treated to improve its coercivity. The powder is mixed with a polymer to form a mouldable putty, similar to a glass-filled polymer. This is pelletised for storage and can later be shaped by injection moulding. An external magnetic field is applied during the moulding process, orienting the field of the completed magnet. Bonded neo powder
In 2015, Nitto Denko of Japan announced their development of a new method of sintering neodymium magnet material. The method exploits an "organic/inorganic hybrid technology" to form a clay-like mixture that can be fashioned into various shapes for sintering. It is said to be possible to control a non-uniform orientation of the magnetic field in the sintered material to locally concentrate the field, for instance to improve the performance of electric motors. Mass production is planned for 2017.
As of 2012, 50,000short ton of neodymium magnets are produced officially each year in China, and 80,000tons in a "company-by-company" build-up done in 2013. China produces more than 95% of rare earth elements and produces about 76% of the world's total rare-earth magnets, as well as most of the world's neodymium.
The strength and magnetic field homogeneity on neodymium magnets has also opened new applications in the medical field with the introduction of open magnetic resonance imaging (MRI) scanners used to image the body in radiology departments as an alternative to superconducting magnets that use a coil of superconducting wire to produce the magnetic field.
Neodymium magnets are used as a surgically placed anti-reflux system which is a band of magnets surgically implanted around the lower esophageal sphincter to treat gastroesophageal reflux disease (GERD). They have also been Magnetic implant in order to provide Perception of magnetic fields, though this is an experimental procedure only popular among biohackers and grinders.
Neodymium is used as a magnetic crane which is a lifting device that lifts objects by magnetic force. These cranes lift ferrous materials like steel plates, pipes, and scrap metal using the persistent magnetic field of the permanent magnets without requiring a continuous power supply. Magnetic cranes are used in scrap yards, shipyards, warehouses, and manufacturing plants.
Magnets that get too near each other can strike each other with enough force to chip and shatter the brittle magnets, and the flying chips can cause various injuries, especially Eye injury. There have even been cases where young children who have swallowed several magnets have had sections of the digestive tract pinched between two magnets, causing injury or death. Also this could be a serious health risk if working with machines that have magnets in or attached to them.
The stronger magnetic fields can be hazardous to mechanical and electronic devices, as they can erase magnetic media such as and , and magnetize watches and the of Cathode-ray tube-type monitors at a greater distance than other types of magnet. In some cases, chipped magnets can act as a fire hazard as they come together, sending sparks flying as if they were a lighter flint, because some neodymium magnets contain ferrocerium.
Applications
Existing magnet applications
Neodymium magnets have replaced alnico and ferrite magnets in many of the myriad applications in modern technology where strong permanent magnets are required, because their greater strength allows the use of smaller, lighter magnets for a given application. Some examples are:
New applications
The greater strength of neodymium magnets has inspired new applications in areas where magnets were not used before, such as magnetic jewelry clasps, keeping up foil insulation, children's magnetic building sets (and other neodymium magnet toys) and as part of the closing mechanism of modern sport parachute equipment. They are the main metal in the formerly popular desk-toy magnets, "Buckyballs" and "Buckycubes", though some U.S. retailers have chosen not to sell them because of child-safety concerns, and they have been banned in Canada for the same reason. While a similar ban has been lifted in the United States in 2016, the minimum age requirement advised by the CPSC is now 14, and there are now new warning label requirements.
Hazards
The greater forces exerted by rare-earth magnets create hazards that may not occur with other types of magnet. Neodymium magnets larger than a few cubic centimeters are strong enough to cause injuries to body parts pinched between two magnets, or a magnet and a ferrous metal surface, even causing broken bones.
See also
Further reading
External links
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