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NEODYMIUM MAGNETS

Neodymium Magnets by Allstar Magnetics

 

Neodymium Magnets

Allstar Magnetics sells licensed neodymium magnets. A neodymium magnet (also known as NdFeB, NIB or Neo magnet), the most widely used type of rare-earth magnet, is a permanent magnet made from an alloy of neodymium, iron and boron to form the Nd2Fe14B tetragonal crystalline structure. Developed in 1982 by General Motors and Sumitomo Special Metals, neodymium magnets are the strongest type of permanent magnet commercially available. They have replaced other types of magnet in the many applications in modern products that require strong permanent magnets, such as motors in cordless tools, hard disk drives and magnetic fasteners. Not sure if Neodymium is the best material for your application? Click here for an attribute and application comparison for all of the magnetic materials we offer.

Neodymium Lineup


 

Description

The tetragonal Nd2Fe14B crystal structure has exceptionally high uniaxial magnetocrystalline anisotropy (HA~7 teslas - magnetic field strength H in A/m versus magnetic moment in A.m2). This gives the compound the potential to have high coercivity (i.e., resistance to being demagnetized). The compound also has a high saturation magnetization (Js ~1.6 T or 16 kG) and 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 ~ 512 kJ/m3 or 64 MG·Oe). This property is considerably 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.

 

History

In 1982, General Motors (GM) and Sumitomo Special Metals discovered the Nd2Fe14B compound. The research was initially driven by the high raw materials cost of SmCo permanent magnets, which had been developed earlier. GM focused on the development of melt-spun nanocrystalline Nd2Fe14B magnets, while Sumitomo developed full-density sintered Nd2Fe14B 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 facility became part of the Hitachi Corporation, and currently manufactures and licenses other companies to produce sintered Nd2Fe14B magnets. Hitachi holds 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 sources of rare earth ores.

The United States Department of Energy has identified a need to find substitutes for rare earth metals in permanent magnet technology, and has begun funding 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.

 

Production

There are two principal neodymium magnet manufacturing methods:

      ●  Classical powder metallurgy or sintered magnet process
      ●  Rapid solidification or bonded magnet process


Sintered Nd-magnets are prepared by the raw materials being melted in a furnace, cast into a mold and cooled to form ingots. The ingots are pulverized and milled; the powder is then sintered into dense blocks. The blocks are then heat-treated, cut to shape, surface treated and magnetized.

As of 2012, 50,000 tons of neodymium magnets are produced officially each year in China, and 80,000 tons 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.

Bonded Nd-magnets are prepared by melt spinning a thin ribbon of the NdFeB alloy. The ribbon contains randomly oriented Nd2Fe14B nano-scale grains. This ribbon is then pulverized into particles, mixed with a polymer, and either compression- or injection-molded into bonded magnets. Bonded magnets offer less flux intensity than sintered magnets, but can be net-shape formed into intricately shaped parts, as is typical with Halbach arrays or arcs, trapezoids and other shapes and assemblies (e.g. Pot Magnets, Separator Grids, etc.). There are approximately 5,500 tons of Neo bonded magnets produced each year. In addition, it is possible to hot-press the melt spun nanocrystalline particles into fully dense isotropic magnets, and then upset-forge or back-extrude these into high-energy anisotropic magnets.

 

Properties

Neodymium magnets are graded according to their maximum energy product, which relates to the magnetic flux output per unit volume. Higher values indicate stronger magnets and range from N35 up to N52. Letters following the grade indicate maximum operating temperatures (often the Curie temperature), which range from M (up to 100 degrees Celsius) to EH (200 degrees Celsius).

Grades of Neodymium magnets:

     ► N35-N52
     ► 33M-48M
     ► 30H-45H
     ► 30SH-42SH
     ► 30UH-35UH
     ► 28EH-35EH

Some important properties used to compare permanent magnets are: remanence (Br), which measures the strength of the magnetic field, coercivity (Hci); the material's resistance to becoming demagnetized, energy product (BHmax), the density of magnetic energy, and Curie temperature (TC), the temperature at which the material loses its magnetism. Neodymium magnets have higher remanence, much higher coercivity and energy product, but often lower Curie temperature than other types. Neodymium is alloyed with terbium and dysprosium in order to preserve its magnetic properties at high temperatures.[12] The table below compares the magnetic performance of neodymium magnets with other types of permanent magnets.

MagnetBr (T)Hci (kA/m)BHmax (kJ/m3)TC (°C)TC (°F)
Nd2Fe14B (sintered) 1.0–1.4 750–2000 200–440 310–400 590–752
Nd2Fe14B (bonded) 0.6–0.7 600–1200 60–100 310–400 590–752
SmCo5 (sintered) 0.8–1.1 600–2000 120–200 720 1328
Sm(Co, Fe, Cu, Zr)7 (sintered) 0.9–1.15 450–1300 150–240 800 1472
Alnico (sintered) 0.6–1.4 275 10–88 700–860 1292–1580
Sr-ferrite (sintered) 0.2–0.4 100–300 10–40 450 842

 

 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

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:

     ► Head actuators for computer hard disks
     ► Magnetic resonance imaging (MRI)
     ► Magnetic guitar pickups
     ► Mechanical e-cigarette firing switches
     ► Locks for doors
     ► Loudspeakers and headphones
     ► Magnetic bearings and couplings
     ► Benchtop NMR spectrometers
     ► Electric motors:
          ●  Cordless tools
          ●  Servomotors
          ●  Lifting and compressor motors
          ●  Synchronous motors
          ●  Spindle and stepper motors
          ●  Electrical power steering
          ●  Drive motors for hybrid and electric vehicles.
              (Toyota Prius require 1 kilogram (2.2 pounds) of neodymium.)
          ●  Actuators

     ►  Electric generators for wind turbines(only those with permanent magnet excitation)
          ●   direct-drive wind turbines require c. 600 kg of PM material per megawatt
          ●   turbines using gears require less PM material per megawatt
 
Neodymium content is estimated to be 31% of magnet weight.
 

New applications

In addition, the greater strength of neodymium magnets has inspired new applications in areas where magnets were not used before, such as magnetic jewelry clasps, children's magnetic building sets (and other neodymium magnet toys) and as part of the closing mechanism of modern sport parachute equipment. They also are the main metal in the formerly popular desk-toy magnets, "Buckyballs", though some retailers have chosen not to sell them due to child-safety concerns.

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 esophagael sphincter to treat gastroesophageal reflux disease (GERD).

 

GradeBr (KGs)Hc (KOe)Hci (KOe)BHmax (MGOe)Tmax (C)
N33 11.4-11.7 10.3-11.0 >12 31-33 80
N35 11.7-12.1 10.8-11.4 >12 33-35 80
N38 12.2-12.6 10.8-11.5 >12 36-38 80
N42 12.8-13.3 10.0-10.5 >12 40-42 80
N45 13.3-13.7 10.0-10.5 >12 43-45 80
N48 13.8-14.2 10.8-11.4 >12 45-48 80
N50 14.0-14.5 10.5-11.4 >12 47-51 80
N40M 12.6-12.9 10.8-11.5 >14 38-40 100
N42M 12.8-13.3 10.5-11.0 >14 40-42 100
N48M 13.7-14.3 12.9-13.6 >14 45-49 100
N35H 11.7-12.1 10.8-11.5 >17 33-35 120
N38H 12.2-12.6 11.5-12.0 >17 36-38 120
N40H 12.6-12.9 11.5-12.0 >17 38-40 120
N42H 12.8-13.2 12.0-12.5 >17 40-43 120
N45H 13.2-13.6 12.0-12.5 >17 43-47 120
N27SH 10.2-10.6 9.8-10.3 >20 25-27 150
N30SH 10.8-11.2 10.1-10.6 >20 28-30 150
N33SH 11.4-11.7 10.3-11.0 >20 31-33 150
N35SH 11.7-12.1 10.8-11.5 >20 33-35 150
N38SH 12.2-12.6 11.4-11.8 >20 36-39 150
N40SH 12.4-12.8 11.8-12.0 >20 38-41 150
N42SH 13.0-13.5 11.8-12.6 >20 39-43 150
N28UH 10.4-10.8 9.8-10.2 >25 26-28 180
N30UH 10.8-11.2 10.1-10.6 >25 28-30 180
N33UH 11.4-11.7 10.3-11.0 >25 31-33 180
N35UH 11.7-12.1 10.8-11.4 >25 33-35 180
N25EH 9.8-10.2 9.2-9.6 >30 23-25 200
N28EH 10.4-10.8 9.8-10.2 >30 26-28 200
N30EH 10.8-11.3 10.1-10.6 >30 28-30 200
N33EH 11.4-11.7 10.3-11.0 >30 31-33 200