The New “Hot-Roll Nano Neo Magnet” Method To Produce NdFeB Magnets

Neodymium iron boron (Neo) permanent magnets have registered heightened demand due to their rapidly increasing applications in the clean energy (wind energy and automotive) and consumer electronics sectors. 

Neodymium magnets operate best at lower temperatures; they even get stronger as the temperature gets colder. But in many applications, permanent magnets need to function in high temperatures. And even moderate temperatures around 150°C degrade the performance of the permanent magnets.

Now, researchers from the Critical Materials Institute, a U.S. Department of Energy Innovation Hub led by Ames National Laboratory, have developed a new method for manufacturing high-performance permanent magnets. The new “Hot-roll Nano Neo Magnet” method produces a nanograin neodymium permanent magnet encased in stainless steel in a simple, commercially scalable process.

The biggest challenge of creating permanent magnets is increasing their resistance to demagnetization at high temperatures. Researchers explained two ways to address this challenge. The first is to add dysprosium to the Neo magnet. However, the U.S. Department of Energy (DOE) and many other countries have listed dysprosium as a critical material, which means it is available in very limited supply. Another way is to manufacture magnets that have small grain sizes by beginning the manufacturing process with much smaller particles of the magnetic material.

“There are two traditional ways of making magnets. One is you make a lot of powder of a particular size, three microns to five microns, that’s typically the size,” said Jun Cui, a scientist at Ames Lab. “And those powders are terribly air sensitive. It is so sensitive that it can light itself on fire, so you have to handle everything with care.” 

The second involves beginning with smaller powders; rather than being measured in microns, they are measured in nanometers – a human hair is usually 70 microns in diameter, and one micron equals 1,000 nanometers.

The micron-sized powders are exposed to a magnetic field to make the magnetic poles of each of the particles point in the same direction and then compress. They are then fused together into a single solid, fully dense material. 

For a Neo magnet containing dysprosium, the sintering process involves heating the material to extremely high temperatures to densify the magnet. For the nanoparticle approach, the powder does not contain dysprosium but must first be packed extremely tightly and then subjected to two phases of hot deformation to densify the magnet. When formed, these magnets are still air sensitive, so they go through a final coating process where they are coated with nickel.

The new method simplifies the process. “We end up just starting out as powders, and then we pack them into a stainless-steel tube. We pack them really dense, and then we just hot roll them,” Cui explained. “We heat it up and then send it to the rolling mill, and then the whole thing just goes.”

Cui highlighted the many advantages of the new system:

Because the stainless-steel tube is completely sealed, it does not require a vacuum furnace to protect the magnet materials from the air.
They can also make thinner magnets that maintain their structural integrity and magnetic properties.
It eliminates the coating process, as the materials remain in the stainless steel casing throughout the process.
Finally, instead of a batch process, “We can make very long magnets continuously, which can be sliced into numerous smaller magnets,” Cui said. “So now you are suddenly looking at a completely new way of making magnets that is cost-effective.”
In addition, the new process is semi-continuous, making it more cost and energy efficient compared to the batch processes currently used in the industry.