Scientific findings may optimize magnets powering hybrid cars | Science| In-depth reporting on science and technology | DW | 06.04.2011
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Scientific findings may optimize magnets powering hybrid cars

As rare earths become more expensive and harder to mine, research teams are focusing their efforts on reducing the use of these metals that lie at the core of many high-technology goods.

A rare earth magnet

Rare earths add to magnets' attractive proprieties

A team of scientists in Austria showed that the use of dysprosium - a strategic rare-earth metal widely used in the motors of hybrid cars and other green technologies - can be optimized and perhaps eventually eliminated. Thomas Schrefl, head of the lab, presented the findings to the Minerals, Metals & Materials Society in March.

The findings are a notch in green-tech manufacturers' efforts to minimize dependence on certain rare earths, the supply of which is largely controlled by China. Schrefl's group, one of several research initiatives spread across continents, has arrived at its findings using a mix of the Schrödinger equation, super computers and some unexpected algorithms.

The magnet at the heart of the hybrid

Thomas Schrefl

Schrefl's research could reduce the need for expensive rare earths

The group of elements known as rare earths is at the core of many high tech goods, ranging from mobile phones to military missiles. Dysprosium, the focus of Schrefl's research, belongs to this group of metals. An ingredient in the permanent magnet that powers the motors of electric cars or wind turbines, it is especially vital to the clean-energy industry.

"Rare-earth magnets are the only ones which offer such compact drives with such high efficiency at the same time," said Manfred Schrödl, head of the Institute of Power Systems and Energy Economics at the Technical University Vienna. "So we combine the advantages to make the optimum motor."

Walking by rows of electric motors in the cavernous workshop, Schrödl pulled out a rotor disc the size of a paperweight. Its surface was stippled with slender rare-earth magnetic strips made of a neodymium-iron-boron alloy and some dysprosium, which is added to preserve magnetic properties at high temperatures.

As slight as this magnet rotor seemed in relation to the rest of the engine, it was surprisingly heavy; the motor of every hybrid car uses about two kilos (4.4 pounds) of rare-earth magnetic materials, which adds up quickly considering the hundreds of thousands of hybrid cars entering the market every year. In a single wind-turbine motor, the amount of rare earths can weigh tons.

A cure for the magnet medicine

To explain his findings on rare-earth magnets, Schrefl first offered a primer on the making of one.

Aesculapian staff

Rare earths serve as medicine for magnets

Grains of the neodymium-iron-boron alloy are pressed into a mold. Because this metal compound is intrinsically magnetic, each of these particles is a tiny magnet with two opposing poles. To get all the north poles at one end and the south poles at the other, the molded grains are exposed to a strong magnetic field - one powerful enough to flip the magnetic particles into alignment - and voila, a magnet is made.

For reasons previously unclear, however, the resulting rare-earth magnet is weaker than expected. Dysprosium is added to perk up its strength.

"It is like medicine for the magnet," Schrefl said. "But it doesn’t change the atom arrangement, it just improves the magnetic properties."

The lab's goal is to do away with "magnet medicine" by tweaking the actual atom arrangement. But first, the scientists had to identify the culprit particles - not a simple matter since they would need to see what was happening on a scale of a few nanometers, a scale too tiny for the most powerful microscope.

To create a simulation that would show the crystal structure on an atomic scale, the team took a fundamental equation of quantum mechanics - the Schrödinger equation, which shows the probability of finding an atom in a certain region of space - and solved it with the help of super computers and algorithms like those used in online image-compression.

The scientists simplified the Schrödinger's equation so that its complexity grew linearly instead of exponentially with the number of particles in the system, Schrefl said.

"We basically compress the equations, the way you compress an image before sending it out on the Internet," he said. These algorithms allowed them to create material simulations that had previously been too complex to compute.

Earlier this year, while studying the simulations, Schrefl isolated misaligned atoms at the crystal grain boundaries that were weakening the magnetic strength. It is this shift in atom position, he said, that deteriorates the magnetic properties and causes the need for dysprosium.

The hard-to-get metal

A map showing the countries with rare earth deposits

A bright silver metal soft enough to cut with a knife, dysprosium derives its name from a Greek word that means "hard to get." It seems that the French chemist who isolated it back in 1886 had a moment of clairvoyance.

China, which controls almost all of the global rare-earth supplies slashed its export quotas as much as 40 percent in the last year, and analysts suspect the numbers will continue to fall. In 2010, the United States Department of Energy identified dysprosium as one of the most critical elements that is at risk of supply disruption.

The price of rare earths has spiked in recent years, but the problem with dysprosium is not just its cost.

"In the south of China, the reserves of iron-absorption clays containing dysprosium are running down," said Judith Chegwidden of Roskill Information Services, a UK-based metals and minerals consultancy. "They will be exhausted maybe within 15 or 20 years."

Production of both hybrids cars and wind turbines, on the other hand, is expected to grow at a healthy clip amid calls for cleaner transportation and energy sources.

An optimization worth the change

Anxious to find alternatives, some manufacturers have funded research teams in Japan, America and Europe, including the one led by Schrefl at the St. Pölten University of Applied Sciences in Austria. His project is a somewhat secretive one, funded by a Japanese car manufacturer that the scientists are not allowed to name.

A person's hand sorting the rare earth coltan

The difficulty of getting to rare earths gives them their name

The team is now testing heat treatments and additives that re-align these atoms, thereby reducing the amount of dysprosium the magnet needs.

So will their new and improved magnets be fitted into hybrid-car hoods anytime soon?

"It's probably very soon I guess, but I can't tell you," Schrefl said, laughing.

The one thing we do know is that in Japan, where Schrefl's sponsor is based, motors account for about half the total domestic power consumption, according to the country's National Institute of Science and Technology Policy. It is estimated that a one percent improvement in the efficiency of electric motors, perhaps with the use of optimized magnets, would save the power equivalent to that produced by a 500MW thermal power station.

In a nation dealing with a stricken nuclear plant, those numbers could add up to mean something worth the change.

Author: Sruthi Pinnamaneni

Editor: Sean Sinico

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