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Rare-Earth MAGNETS

Magnets

INTORDUCTION

Contrary to their name, rare-earth magnets are not made from rare materials; they are nevertheless the most powerful permanent magnets currently available.

The term "rare-earth" originates from the 17 chemical elements in the periodic table used in making the magnets: the 15 lanthanides, scandium, and yttrium.

Rare-earth magnets are available in two types: samarium-cobalt or neodymium, and are excessively brittle and susceptible to corrosion. For this reason, the magnets must be plated or coated.

Compared to traditional ferrite and ceramic magnets, the magnetic field produced by rare-earth magnets is considerably stronger, measuring 1.4 Tesla, the unit of measuring magnetic flux density, versus the 0.5 Tesla (ferrite) to 1.0 Tesla (ceramic).

Type 1: Samarium-cobalt

Samarium-cobalt magnets were the first class of rare-earth magnets invented.

Higher cost and weaker magnetic field than neodymium magnets, makes samarium-cobalt less popular than the latter; however, this type of magnet has a higher Curie temperature, making it ideal for use in applications where high field strength is needed at high operating temperatures.

Note that while Samarium-cobalt magnets may resist oxidation, they are prone to chipping and cracking because they are very brittle.

Type 2: Neodymium

Neodymium is both the strongest and cheapest type of rare-earth magnet.

Neodymium magnets are created from a combination of the alloy of neodymium, iron, and boron.

This type of magnet is primarily used in jewelry clasps, magnetic hold downs, hard drives, and electric motors for cordless tools, as they strong and compact permanent magnets.

Compared to samarium-cobalt magnets, neodymium magnets exhibit a higher magnetic field strength at the cost of a lower Curie temperature and higher vulnerability to oxidation.

Nevertheless, the magnets may be coated in a protective layer made from gold, nickel, zinc, or tin plating and epoxy resin coating to protect against corrosion and mechanical damage.

The price of neodymium magnets was significantly higher prior to the 1990's, but expiring patents opened up commerce to more manufacturers, thus creating the competition necessary to lower prices.

Applications

Rare-earth magnets are being increasingly used in applications requiring powerful magnets such as audio speakers, headphones, bicycle dynamos, high-performance servo motors, hard drives, linear motors, electrodynamic bearings, launched roller coasters and even in toys.

SynLube Incorporated is a distributor for FILTERMAG™ and UNIMAG™ Filter Magnets that both utilize rare-earth magnets to remove ferromagnetic particles of any size from fluid flow, if they are attached to the outside perimeter of conventional iron cased "spin-on" filters, be they for Motor Oil, ATF, Fuel, or Coolant.

The high magnetic field strength allows the rare-earth magnets to be smelted into a smaller and lighter size, allowing for some novel miniature applications.

Manufacture

Once the raw material is grounded, it is combined in various mixtures to create materials of varying grades of magnetism, durability, and Curie temperature.

The resulting mixture is then pressed together into a form.

Afterwards, a large electromagnetic field is used to arrange the atomic particles and their electron spin in a specific direction.

Next everything is sintered to form a solid object by heating the powder right below its melting temperature thereby forcing the atoms to fuse together into a solid piece.

Now that a solid shape has been established, it can be milled to the desired dimensions.

After the desired shape is finalized the soon-to-be magnet must be plated to protect against corrosion.

Nickel, copper + nickel, epoxy coating, gold, zinc, or ABS plastic, are all adequate plating materials.

After this production stage the material is ready to be magnetized.

Do note that neodymium magnets can only be magnetized in the direction that their electrons were aligned in during the preparation stage.

Finished magnets are then packaged and shipped to their users.

Sometimes it is necessary to place non magnetic spacers, such as plastic or paper between the individual magnets so they can be easily separated from each other.

Source

There is only one mine in USA that specializes in production of rare-earths.

Over 90% of World's supply of raw materials for rare-earth magnet production is from China.

Japan used to produce almost all the rare-earth magnets for about last 20 years, but current Chinese restrictions on raw materials exports are quickly moving all the rare-earth magnet production to China.


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Last modified: 2013-07-11

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