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Magnetic materials for future engines

McHenry and his team make metal amorphous nanocomposites in his lab. Credit: Engineering College, Carnegie Mellon UniversityAccording to a University…



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

According to a University of Chicago statistic, 50 percent of US power goes through an engine. Vehicles such as cars and aircraft are dependent on engines for converting power, as well as household appliances such as vacuum cleaners and refrigerators. As this space is so large, more efficient engines could make a significant difference in energy use.

When a motor is working to convert electrical energy into mechanical energy, an alternating current provides a magnetic field to the magnetic materials inside the engine. The magnetic dipoles then change from north to south and cause the engine to spin. This switch of the magnetic material makes it heat up, losing energy.

But what happens if the magnetic material does not heat up when it’s spinning at high speed? Michael McHenry, a professor of Materials Science and Technology at Carnegie Mellon University and his group addresses this problem by synthesizing metal amorphous nanocomposite material (MANC), a class of soft magnetic materials that are effective in converting energy at high frequencies, less motors for to deliver comparable power.

“The power of the engine depends on its speed,” said McHenry. “When you rotate a motor at high speeds, the magnetic material changes at higher frequency. Most magnetic steel, most engines are off, lose power at higher frequencies because they heat up.”

Currently, motors are typically made of silicone steel. MANCs provide an alternative to silicon steel and, due to their high resistivity (how strong they resist an electric current), they do not heat up so much and can therefore spin at much higher speeds.

“As a result, you can either reduce the size of the engine at a given power density or make a higher power engine of the same size,” said McHenry.

McHenry’s team, in collaboration with the National Energy Technology Laboratory (NETL), NASA Glenn Research Center, and North Carolina State University, design a two and a half kilowatt engine weighing less than two and a half kilo. Lastly, they benchmark it at 6000 revolutions per minute and are looking to build bigger ones that will spin even faster. The design, financed by the Department of Energy (DOE) Advance Manufacturing Office, combines permanent magnets with MANC.

To synthesize MANC materials, McHenry and his team quickly solidify liquid metals at about one million degrees per second. Because they work on the lab scale they look at 1

0 grams of samples and screen them for their magnetic properties. Through different partnerships with partners’ research institutions and industry, they can take these MANCs and scale up the manufacturing process for use in real-world applications.

During the power conversion process of a conventional engine, the magnetization of the motor material changes, which often results in power loss. But with MANC, the losses associated with switching of magnetization are greatly reduced because they are a glassy metal instead of a crystalline metal. The structural difference is at atomic level: when the material is melted, rapidly cools, atoms do not have time to find positions in a crystal grid.

McHenry’s team and partners are some of the few that show the use of MANC in engines. Their design also uses their own patented materials – a combination of iron and cobalt, and iron and nickel, mixed with glass shapes. The efficient MANCs also enable the use of lower-priced lower magnets, which do not require critical rare earth materials in engine design.

While scientists test in smaller proportions at laboratory scale, collaborate with companies in industry and other research laboratories can bring these metals to the scale for use in industry.

“Finally, we can go to higher speeds and higher forces with these patterns,” said McHenry. “At the moment we are benchmarking a smaller engine, and then we will try to build larger. The engines have airplanes, vehicles and even vacuum cleaner applications. The engines are important in a number of applications. In total, the engines represent a large use of electricity so they are one area where efficiency can make a big difference. “


Explore further:
Magnetic materials increase energy density in power conversion

More information:
Satoru Simizu et al. Metal Amorphous Nanocomposite Soft Magnetic Material-Enabled High Power Density, Rare Earth Free Rotational Machines, IEEE Transactions on Magnetics (2018). DOI: 10.1109 / TMAG.2018.2794390

Journal Reference:
IEEE Transactions on Magnetics

Provided by:
Carnegie Mellon University Materials Science and Engineering

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