A new method for manufacturing high-performance permanent magnets has been developed by researchers from the Critical Materials Institute, a U.S. Department of Energy Innovation Hub led by Ames National Laboratory.
A simple, commercially scalable process known as the “Hot-roll Nano Neo Magnet” produces a nanograin neodymium permanent magnet encased in stainless steel. In contrast to the batch processes that are currently utilized in industry, this semi-continuous process is more energy-efficient and cost-effective.
Neodymium iron boron (Neo) permanent magnets are becoming more and more important for a number of different technologies, such as wind turbines, electric cars, and mobile phones. Permanent magnets must operate at high temperatures in many applications. Sadly, even moderate temperatures around 150°C (302°F) affect the permanent magnets’ performance.
“There are two classic methods for producing magnets. One is that you make a lot of powder of a specific size, often three to five microns. And those granules are extremely sensitive to air. It is so sensitive that it can set itself on fire, so you must touch it with caution.”
Jun Cui, a scientist at Ames Lab,
Ames Lab scientist Jun Cui says that making permanent magnets more resistant to demagnetization at high temperatures is the biggest challenge. He provided two approaches to this problem. The first is to give the Neo magnet dysprosium. However, due to the DOE’s and many other nations’ designation of dysprosium as a critical material, its availability is extremely limited. The second method involves starting the manufacturing process with much smaller magnetic material particles to produce magnets with smaller grain sizes.
“There are two traditional methods of making magnets,” Cui explained. One is when you produce a large quantity of powder with a particular size—typically three to five microns. Additionally, these powders are extremely sensitive to air. Because it is so sensitive that it can set itself on fire, you need to be careful with everything.” The second approach involves starting with powders that are smaller and are measured in nanometers rather than microns. A human hair typically has a diameter of 70 microns, and one micron is equivalent to 1,000 nanometers.
After being exposed to a magnetic field, the powders of micron size are compacted so that their magnetic poles point in the same direction. They are then fused together to form a single, extremely dense material. In order to densify a Neo magnet that contains dysprosium, the sintering procedure involves heating the material to extremely high temperatures.
For the nanoparticle method, the powders don’t have any dysprosium in them, but they do have to be packed very tightly at first. After that, they go through two phases of hot deformation to make the magnet more dense. These magnets undergo a final coating process in which they are coated with nickel because they are still air-sensitive after being formed.
The new method that Cui and his team came up with makes the process easier. We end up packing them into a stainless-steel tube after starting as powders. Cui explained, “We just hot roll them after we pack them really densely.” After we heat it up and send it to the rolling mill, everything just works.”
Cui mentioned a few advantages of this new method. First, the stainless-steel tube is completely sealed, so it doesn’t need a vacuum furnace to keep the magnet materials out of the air. Second, they are able to produce thinner magnets that retain their magnetic properties and structural integrity. Third, it dispenses with the covering step since the materials stay in the treated steel packaging in the meantime. Finally, Cui stated, “We can make very long magnets continuously, which can be sliced into numerous smaller magnets.” This is in place of a batch process. Therefore, you are suddenly considering a brand-new, less expensive method of producing magnets.”
Provided by Ames National Laboratory
