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Cast tetrataenite rod behind ruler (left) surface features (right)
As tensions mount between China and the United States many automakers here are trying to reduce their reliance on a key component used in making electric vehicles – the rare earth permanent magnet.
As of this year China has the world’s largest reserves of magnet ores – enough to fulfill their projections of making 30 million electric vehicles annually by 2030. According to the US Geological Survey, the US imports about 78 percent of these rare earths from China.
Do we have to import these materials?
The metals in the magnets are actually abundant, but can be dirty and difficult to produce and because of this and volumes of government regulations, China has grown to dominate production. With states mandating the eventual phase-out of fossil fuel vehicle demand for magnets are on the rise and analysts say a genuine shortage may lie ahead.
Rare earth magnets, mostly made of neodymium, are widely seen as the most efficient way to power electric vehicles. Motors within an EV operate when a coil of wire, encircled by such powerful magnets, spins on an axis. The current in the wire causes a magnetic field of its own and this is either pulled or pushed by the stationary permanent magnets. All of this twisting motion is coupled to the four wheels of the car providing power and moving it forward.
The Tesla S and X models have two motors: one with rare earth magnets, one without. The induction motor provides more power, while the one with permanent magnets is more efficient and intended for highway use. Putting in the rare earth magnet motor boosts the models’ driving range by 10%—important if you are trying to beat competitors.
Just recently researchers from the University of Cambridge, working with colleagues from Austria, have discovered a replacement for the neodymium used in the rare earth magnets. Looking at tetrataenite – a mineral up until now only found in meteorites — they reasoned that since its magnetic properties are on par with rare earth devices, the mineral could potentially be used if only it could be created here, not just in outer space. In our solar system, tetrataenite takes millions of years to form.
In the 1960s, scientists were able to artificially create tetrataenite by bombarding iron-nickel alloys with neutrons, enabling the atoms to form the desired order, but this technique is not suitable for mass production. Likewise all recent attempts to make tetrataenite in the laboratory such as chemical vapor deposition are not easily scalable for making reasonably priced magnets.
In a paper published in the October 2022 issue of Advanced Science, “Direct Formation of Hard-Magnetic Tetrataenite in Bulk Alloy Castings”, a new method of tetraenite production may be just around the corner. According to Professor Lindsay Greer (one of the authors) from Cambridge’s Department of Materials Science & Metallurgy, “Scientists have been fascinated with getting that ordered structure, but it’s always felt like something that was very far away.”
Now, Greer and his team have documented a fabrication alternative that doesn’t require millions of years of cooling or neutron irradiation. It started when the researchers were studying the mechanical properties of iron-nickel alloys containing small amounts of phosphorus, an element that is also present in meteorites. The pattern of phases inside these materials showed the expected tree-like ordered growth structure called dendrites.
“For most people, it would have ended there: nothing interesting to see in the dendrites, but when I looked closer, I saw an interesting diffraction pattern indicating an ordered atomic structure,” said first author Dr Yurii Ivanov, who completed the work while at Cambridge and is now based at the Italian Institute of Technology in Genoa.
At first glance, the X-Ray diffraction pattern of tetrataenite looks like that of the structure expected for iron-nickel alloys, namely a disordered crystal not of interest as a high-performance magnet. It took Ivanov’s closer look to identify the tetrataenite, but even so Greer says it’s strange that no one noticed it before.
The researchers say that the phosphorus allows the iron and nickel atoms to move faster, enabling them to form the necessary ordered stacking almost instantly. By mixing iron, nickel and phosphorus in the right quantities, they were able to speed up tetrataenite formation such that it forms over a few seconds in simple casting.
“What was so astonishing was that no special treatment was needed: we just melted the alloy, poured it into a mould, and we had tetrataenite,” said Greer. “The previous view in the field was that you couldn’t get tetrataenite unless you did something extreme, because otherwise you’d have to wait millions of years for it to form. This result represents a total change in how we think about this material.”
While the researchers have found a promising method to produce tetrataenite, more work is needed to determine whether it will be suitable for high-performance magnets. The team is hoping to work on this with major magnet manufacturers.
Gary Hanington is Professor Emeritus of physical science at Great Basin College and Vice President of Engineering at AHV. He can be reached at garyh@ahv.com or gary.hanington@gbcnv.edu.
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Cast tetrataenite rod behind ruler (left) surface features (right)
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