Magnetic materials for the engines of the future

McHenry and his team make amorphous metal nanocomposites in his laboratory. Credit: College of Engineering, Carnegie Mellon University

According to a University of Chicago statistic, 50% of American energy goes through an engine. Vehicles such as cars and planes use motors to transform the current, as do household appliances such as vacuum cleaners and refrigerators. Because of the size of this space, the use of more efficient engines could have a significant impact on energy consumption.

When a motor operates to transform electrical energy into mechanical energy, an alternating current provides a magnetic field to the magnetic materials inside the motor. The magnetic dipoles then rock from north to south and turn the engine. This switching of magnetic materials causes its heating, loss of energy.

But what would happen if the magnetic material did not heat up when it was spun at high speed? Michael McHenry, professor of materials science and engineering (MSE) at Carnegie Mellon University, and his group are tackling this problem by synthesizing amorphous metal nanocomposite materials (MANC), a class of soft magnetic materials capable of transform the energy at high frequencies. smaller engines for comparable power.

"The power of an engine depends on its speed," said McHenry. "When you run a motor at a high speed, the magnetic material switches to a higher frequency.Most of the magnetic steels, which make up most engines, lose power at higher frequencies because they heat up."

Currently, engines are usually made from silicon steels. MANCs offer an alternative to silicon steels and, due to their high resistivity (resistance to electric current), they heat less and can run at much higher speeds.

"As a result, you can reduce the size of the engine to a given power density or create a larger power engine at the same size," said McHenry.

McHenry's group, in collaboration with the National Laboratory for Energy Technology (NETL), NASA's Glenn Research Center, and North Carolina State University, is designing a two-kilowatt-and-a-half-weight motor weighing less two and a half pounds. In recent times, they have estimated at 6,000 rotations per minute and are looking to create larger ones that rotate even faster. The design, which is funded by the Department of Energy's (DOE) Advanced Manufacturing Office, combines permanent magnets with MANC.

To synthesize MANC materials, McHenry and his team rapidly solidify liquid metals at about a million degrees per second. Since they work at the laboratory scale, they examine samples of 10 grams and analyze them to determine their magnetic properties. Through various partnerships with partner research institutes and industry, they can utilize these MANCs and intensify the manufacturing process for use in real-world applications.

During the power transformation process in a conventional engine, the magnetization of the engine materials switches, often leading to a loss of power. But with the MANCs, the losses associated with switching the magnetization are greatly reduced because it is a vitreous metal rather than a crystalline metal. The structural difference is at the atomic level: when the material is melted and then rapidly cooled, the atoms do not have time to find positions in a crystal lattice.

The McHenry Group and its collaborators are among the few people who demonstrate the use of MANC in engines. Their design also uniquely uses their own patented materials – a combination of iron and cobalt, and iron and nickel, mixed with glass jigs. Effective MANCs also allow the use of permanent magnets at lower cost, not requiring critical rare earth materials, in engine design.

While researchers are testing in smaller scale at the laboratory scale, collaborations with industry companies and other research labs can bring these metals up to scale for a use in the industry.

"Ultimately, we can achieve higher speeds and powers with these designs," said McHenry. "Right now, we're looking at a smaller engine, and then we're trying to build bigger ones. Engines have applications in aerospace, vehicles and even vacuum cleaners – engines are important in many applications. Overall, engines represent a huge use of electrical energy, making it an area in which efficiency can make all the difference. "

Explore further:
Magnetic materials increase energy density in power transformation

More information:
Satoru Simizu et al. High Power Density Activated by a Soft Magnetic Material Amorphous Metal Nanocomposite, Rare Earthless Rotary Machines, IEEE Transactions on Magnetics (2018). DOI: 10.1109 / TMAG.2018.2794390

Journal reference:
IEEE Transactions on Magnetics

Provided by:
Carnegie Mellon University Science and Materials Engineering

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