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August 06, 2008

Cheap, recyclable ultrastrong magnets that will enable smaller, more powerful engines


Ultra-strong, high-temperature, high-performance permanent magnet compounds, such as Samarium Cobalt, are the mainstay materials for several industries that rely on high-performance motor and power generation applications, including the Department of Defense (DOD) and the automotive industry. Until now, producing Samarium Cobalt has been a difficult and expensive multi-step process. Northeastern University researchers have broken new ground with an innovative invention of a rapid, high-volume and cost-effective one-step method for producing pure Samarium Cobalt rare earth permanent magnet materials.

To create a field
with the strength of 100 mT (1,000 G) at a 1 mm distance from the pole, a barium ferrite magnet must be around 25 times larger than a samarium-cobalt magnet.


Smaller and more powerful motors will make wheel motors more practical. Wheel motors can reduce losses in a car by 30-40% by have no transmission to wheel power losses.

Samarium-cobalt (SmCo) magnets are produced by pressing powdered alloys to shape and then sintering them in a furnace. This powder can also be mixed with polymer binders to form bonded magnets.

SmCo exhibit excellent thermal qualities with several grades designed specifically for use up to 570°F. For high-energy material, SmCo offers the best resistance to temperature. Until this development sintered samarium-cobalt has commonly beenused in stepper motors for robotics and aerospace as well as motors for magnetic pumps and couplings. But high costs confined it to small or thermally demanding situations. This low cost breakthrough will enable widespread use. Engines and generators can be made smaller, lighter, more efficient and reliable. Compact, high-power motors without field coils will be made common.

Electron Energy Corporation already makes and sells existing Samarium Cobalt magnets with some over 1 Tesla and 30 megagauss of energy. Samarium-Cobalt (SmCo) can achieve a maximum of 225 kJ/m**3. Samarium Cobalt batteries were used for Nasa's Deep space one space probe which used an ion engine.

The 2006 Progress Report for Automotive Propulsion Materials Program for the Freedomcar project explained the benefits of a strong permanent magnet


The Freedomcar project looked at superconducting magnets, which are stronger then Samarium Cobalt magnets but need cooling.

Permanent magnets are used in the traction motors of hybrid electric vehicles because of their superior magnetic properties (energy product) compared with other permanent magnets. Higher-strength magnets are desired because they would enable manufacturers to reduce the size, weight, and volume of the traction motor and thus increase the fuel efficiency of the vehicle.

A major component of the HEV is the electrical machine (traction motor) used to drive the wheels. The traction motor employs a number of permanent magnets (PMs). Energy product is directly proportional to the energy stored per unit volume of the magnet; the torque produced by a PM electric motor is approximately proportional to the energy product of the PM. Increasing the energy product of the PM will proportionally increase the torque. Therefore, increasing the energy product will reduce the weight and size of the PM required to generate the same torque. Furthermore, reducing the weight and size of the PM may reduce the size of the entire motor required to generate the same torque. This will further reduce the overall weight of the motor and increase the mileage of the HEV.

Typical performance requirements for linear drive motors are (BH)max = 40 MGOe (320 kJ/m3) and Hc = 2 Tesla (1.6 MA/m). It is the objective of this study to increase the energy product by using stronger magnetic alignment Figure 2. Energy product vs coercive field for various fields generated by the SCM while maintaining the same coercive field (by raising the operating applications. point vertically in Figure 2). So far, NdFeB magnets show the highest value of remanence Br and energy product (BH)max, and samarium-cobalt magnets exhibit the highest coercive fields, Hc.


The direct chemical synthesis process is able to produce Samarium Cobalt rapidly and in large amounts, at a small fraction of the cost of the current industry method.

Samarium Cobalt magnets are superior to other classes of permanent magnetic materials for advanced high-temperature applications and the Northeastern invention goes beyond the currently known fabrication process of these nanostructured magnets. Unlike the traditional multi-step metallurgical techniques that provide limited control of the size and shape of the final magnetic particles, the Northeastern scientists’ one-step method produces air-stable “nanoblades” (elongated nanoparticles shaped like blades) that allow for a more efficient assembly that may ultimately result in smaller and lighter magnets without sacrificing performance.

This revolutionary invention is anticipated to not only revitalize the permanent magnet industry, it has the potential to bring major changes to several federal and commercial industries, including its potential to impact the size, weight, and performance of aircraft, ships, and land-based vehicles, as well as contribute to more efficient computer technologies and emerging biomedical applications.

“This work represents the most promising advance in rare earth permanent magnet processing in many years,” said Laura Henderson Lewis, Professor of Chemical Engineering and Chair of the Department of Chemical Engineering at Northeastern University and a collaborator on this project. “I expect it to revitalize international interest in the development of this important class of engineering materials.”


FURTHER READING
A turbogenerator study which used permanent magnets to make parts of a generator smaller and more efficient.

Cheap, strong permanent magnet can help make more powerful in wheel motors.

Different kinds of permanent magnet engines are analyzed and compared in this 123 page Oak Ridge National Lab study for the Freedomcar project

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