For release: July 6, 1998
Contacts:
Bill McCallum, 515-294-4736
Alan Russell, 515-294-0973
Susan Dieterle, 515-294-1405
AMES, Iowa - A unique attempt to alter the tiny particles of a magnetic material is underway at the U.S. Department of Energy's (DOE) Ames Laboratory that, if successful, would result in efficient power sources for deep-space probes as well as cars, electronics, computers and power tools.
Bill McCallum, a senior scientist at Ames Lab, and Alan Russell, associate scientist, received a one-year, $165,000 contract from DOE in March to study a method of developing neodymium-iron-boron magnets that retain their magnetic properties at higher operating temperatures. The magnets would be part of the internal power source for probes launched into space to study other planets.
Neodymium-iron-boron is a powerful magnetic material discovered in the 1980s. It works best at room temperature, but begins losing its magnetic properties at higher temperatures. At 312 degrees Celsius (about 590 Farenheit), it loses its power completely.
NASA is investigating possible use of magnets in a Stirling engine to power deep-space probes. Stirling engines have a sealed cylinder in which hot gases move two pistons back and forth. By placing magnets on the ends of the pistons and surrounding the cylinder with wire coils, the magnets would induce a current flow in the wires as they moved back and forth. However, the magnets now available aren't effective at high temperatures.
McCallum and Russell say many attempts have been made to raise the operating temperature of the neodymium-iron-boron magnets by adding different elements to the overall composition. However, the resulting materials often have low resistance to the forces of demagnetization, which would make them ineffective in a Stirling engine because the magnets would be exposed to reverse magnetic fields as they moved back and forth on the pistons.
So, rather than have a material in which the composition is uniform, McCallum and Russell are attempting to produce particles that each have two different compositions - one at the outer edge to resist demagnetization and another at the core to retain magnetic power at higher temperatures.
"We believe this to be the first in-depth study and attempt at controlling the composition of a magnetic material in this way," McCallum says, adding that all other permanent magnets have a uniform composition within the individual grains.
He illustrates their approach by comparing the hoped-for particle structure to an M&M candy. Instead of having a hard shell, the candy would have a dark-chocolate core that would gradually become milk chocolate at the surface - turning it into what scientists call a "functionally graded" material whose composition gradually changes between the core and the outer edge.
"The properties of the material on the outside would, in a way, be protecting the material on the inside," McCallum says.
But to do this, scientists will have to control the structure of particles that are only 1 micron wide. By comparison, a human hair is about 60 microns wide. "Each of these particles has to have this gradient structure, so we have to learn how to control the composition on a very fine scale," McCallum says.
Russell notes that, although the project's roots are in the space program, the development of magnets with higher operating temperatures would affect everyday life. "It would probably have a much bigger benefit for planet Earth than it would for a spacecraft orbiting Jupiter," he says.
Neodymium-iron-boron magnets are already used in computers, high-end power tools and electronics, but the low operating temperature limits their use in cars and other high-temperature applications. In addition to having a higher operating temperature, McCallum says, the new magnets would be smaller and more powerful than current magnets, making them attractive for a variety of uses.
McCallum adds that Ames Laboratory is one of the nation's premier institutions in working with permanent magnets. "In order to control this material at the required level, we have to understand how the structure itself evolves," he says. "This is a particularly strong area for Ames Lab."
Next March, McCallum and Russell will present the results of their research. If their findings are favorable, NASA will consider moving to a second phase of the project, which would involve attempts to produce the new magnets in sizes large enough for use in a Stirling engine.
Although the work is tricky, both men are optimistic that they'll be able to lay the groundwork for the new type of magnet. "I think that there is a high probability that we will be able to produce this particle structure," McCallum says.
Adds Russell, "The Ames Lab team working with us on this contract - Bruce Cook, Kevin Dennis, Joel Harringa, Fran Laabs, Tammie Bloomer and Les Reed - has a wealth of experience with rare-earth and magnetic materials. They will be the keys to success for this project."
Ames Laboratory is operated for the DOE by Iowa State University. The Lab conducts research into various areas of national concern, including energy resources, high-speed computer design, environmental cleanup and restoration, and the synthesis and study of new materials.
Last revision: 7/2/98 sd