Ames Laboratory beefing up magnets for electric-drive cars
Posted on Wednesday, January 09, 2008 @ 20:45:36 UTC by vlad
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 Ask Iver Anderson at the U.S. Department of Energy’s Ames Laboratory
about consumer interest in and desire for “ultragreen” electric-drive
vehicles, and he’ll reply without a moment’s hesitation that the trend
is unstoppable and growing fast.
The Ames Lab senior metallurgist and Iowa State
University adjunct professor of materials science and engineering is
playing a major role in advancing electric drive motor technology to
meet the enormous swell in consumer demand expected over the next five
years.
He and his Ames Lab colleagues, Bill McCallum
and Matthew Kramer, have designed a high- performance permanent magnet
alloy that operates with good magnetic strength at 200 degrees Celsius,
or 392 degrees Fahrenheit, to help make electric drive motors more
efficient and cost-effective. The work is part of the DOE’s Vehicle
Technologies Program to develop more energy-efficient and
environmentally friendly highway transportation technologies that will
enable America to use less petroleum.
Anderson explained that future ultragreen vehicles include fully
electric cars, fuel-cell automobiles and plug-in hybrids. “They all
have electric drive motors, so that’s a common theme,” he said. “It’s
important that those motors be made economically with an operating
envelope that fits how they will be driven. The automotive companies in
this country have set out a series of parameters that they would like
electric motors to meet.”
One of those constraints being addressed by Anderson and his
colleagues is the need for permanent-magnet electric motors to operate
well at temperatures up to 200 degrees Celsius. “That raised a lot of
eyebrows for people who know anything about magnets,” said Anderson. He
explained that the most desirable permanent-magnet materials are
neodymium-iron-boron magnet materials based on a 2-14-1 crystal
structure – Nd2Fe14B. “Most of those types of
magnets tend to lose a lot of their magnetic energy at fairly modest
temperatures and are operating at much less than half of their power by
the time they reach 100 C to 125 C,” he said. “So our challenge was to
design a high-performance 2-14-1 permanent magnet alloy that would
operate with good magnetic strength at 200 C.”
Meeting that challenge, Anderson, McCallum and Kramer designed an
alloy that replaces pure neodymium with a mixed rare earth. “We used a
combination of neodymium, yttrium and dysprosium because they all form
2-14-1 crystal structures,” said Anderson. “Together they have much
less degradation of their magnetic properties with temperature due to
the influence of the yttrium and dysprosium. Our concept, put forth in
our patent application, is that the mixed rare earth 2-14-1 phase would
have a lower temperature coefficient.” (The relative change of a
physical property, e.g., coercivity, when the temperature is changed by
1 kelvin.)
Once they had tweaked the new alloy to
perfection, the next thing the researchers did was process it in a
fine, spherical powder form using gas atomization, a technique in which
kinetic energy from supersonic jets of gas is transferred to a stream
of liquid metal, causing it to break up into droplets. “This method
best fits the needs of the automobile industry because they want to
make their motors by a very high-volume manufacturing process, and that
method is injection molding,” explained Anderson. (Injection molding is
a process for forming objects from a blended mixture of plastic and
metal powder by heating this molding compound to a fluid state and
injecting it into a mold.)
Stressing the importance of being able to use the injection-molding
manufacturing process, Anderson said, “Currently, each magnet making up
the magnet array in an electric motor is glued in by hand. “That’s fine
for small runs of 50,000 automobiles, but try doing that for the
millions of cars with electric drive motors – one for the front and one
for the back – that consumers will want to buy in the next 10 years,”
he said. “It’s not going to work.”
Anderson and his colleagues have been refining and pushing the
2-14-1 alloy composition to be more suitable for the rapid
solidification that happens in the atomized powder droplets and
ultimately for the injection-molding process. “We’ve succeeded in
getting very nice properties for these fine spherical powders,” he
said. He noted that in comparing their powders to spherical commercial
powders of larger size, he and his colleagues look at the “crossover in
temperature” at which the properties of their magnet powders become
better than the commercial powders for higher temperature uses. “It
used to be 175 C,” he said, “but now we’ve moved that crossover
temperature down to the neighborhood of 75 C, which is a tremendous
accomplishment – we’re very happy about that.”
Anderson said they now have what they think is a really good alloy,
and also have switched from helium gas to argon gas in the atomization
process, which makes the powder-making process a lot cheaper. “That’s a
move in the right direction for the purposes of commercialization,” he
said, “and that’s what we’ve been driving for.” (No pun intended.)
Reflecting on the goals of the Vehicle Technologies Program,
Anderson said, “We need to support our auto companies and help them
develop better products. We can do that by getting things worked out at
the basic science end – that’s our job.” Summing up the effort he and
his colleagues have made in that regard, he added, “You can think of
this alloy design work as the fundamental end of extending the
temperature range of 2-14-1 magnet alloys. Then, we’re also working on
the process end, which is a fundamental rapid solidification effort to
develop the solidified microstructure that will carry the best magnetic
properties over in a form that can be mass-produced. You can call this
‘use-inspired’ research, for sure. And there’s an urgent need for this
in our society.”
Source: Ames Laboratory
Via: http://www.physorg.com/news119117780.html
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