Trace Analysis Webinar
In this webinar we introduce Trace Analysis of Advanced Materials by Direct Solid-Sampling and Solution-Based Techniques
From Rock to Rare Series: Part 3 - Production
In Part 1 of this series, we dug into the mining of rare earth elements (REEs). In Part 2, we explored the refining and beneficiation processes that concentrate those materials into something usable. Now, in Part 3, we arrive at the stage where REEs truly show their power in the manufacturing of permanent magnets.
These magnets are the invisible force behind modern electronics such as electric vehicles drive motors, wind turbines, and aerospace guidance systems. Their strength is unmatched, but that power comes with exacting purity demands. When those aren’t met, the entire product can fail.
Why Rare Earth Magnets Matter
The strongest permanent magnets in use today are made from rare earth alloys, primarily neodymium-iron-baron (NdFeB) and samarium-cobalt (SmCo). Of the two, NdFeB magnets dominate in applications that require high magnetic strength at or near room temperature.
However, when temperatures rise, NdFeB magnets can lose both coercivity (resistance to demagnetization) and field strength. Engineers address these challenges through strategic alloy modifications, especially in critical environments like electric vehicle drivetrains or aerospace components.
Building a Better Magnet with Chemistry
To improve performance at elevated temperatures, small (but important) changes are made to the base composition of NdFeB magnets:
- Adding heavy rare earth elements (HREEs) such as dysprosium or terbium increases the magnet’s anisotropy. This results in greater coercivity at room temperature and slower degradation with heat.
- Substituting cobalt for some iron causes the Curie temperature (the point at which a magnet loses its magnetic properties) and stabilizes field strength across a wider temperature range.
- Combining cobalt with copper improves corrosion resistance and reduces irreversible magnetic losses over time.
SmCo magnets, while not quite as strong as NdFeB magnets, naturally perform better at high temperatures and resist corrosion without coatings. They can function at temperatures up to 350ºC, compared to about 230ºC for modified NdFeB magnets. The tradeoff is that SmCo tends to be more brittle and more expensive than NdFeB magnets due to their higher rare earth content.
Sintered NdFeB Manufacturing Journey
Most high-strength NdFeB magnets are produced through sintering, a complex process that transforms raw elements into dense, high-performance components. This is how it’s done for NdFeB magnets:
- Raw Material Preparation: Neodymium, iron, and boron (along with additives) are melted in a vacuum induction furnace to form an alloy ingot.
- Jet Milling to Powder: The solidified ingot is crushed into chips and then pulverized into fine powder using a jet mill under inert gas to prevent oxidization and ignition.
- Magnetic Alignment: The powder placed into a mild and exposed to a magnetic field that aligns the particles along a specific axis.
- Compaction: The powder is compacted into a “green body” using either axial or isostatic pressing techniques.
- Sintering: The compact is sintered at around 1000-1100ºC in a vacuum or inert atmosphere, resulting in a dense, solid magnet with up to 98% of theoretical density.
- Heat Treatment: A controlled heating cycle is used to fine-tune both magnetic and mechanical properties.
- Machine and Shaping: Diamond-coated tools are used to shape the magnets into precise dimensions because they are brittle.
- Surface Coating: NdFeB magnets are coated with options like nickel, epoxy, zinc, or vapor deposited aluminum to prevent corrosion and mechanical damage.
- Magnetization: The finished magnet is pulsed with a strong magnetic field to permanently magnetize it along the aligned axis.
Bonded vs. Sintered: Two Paths to Magnet Production
While sintered magnets are the norm for high-performance applications, bonded magnets offer an alternative. Instead of sintering, powdered alloy is mixed with a bonding resin like epoxy, die-pressed, and cured (sometimes in a magnetic field for orientation). Bonded magnets are easier to mold into complex shapes but offer lower magnetic strength and temperature tolerance.
Purity’s Impact on Performance
The purity of raw materials in magnet production is critical. Even small amounts of unwanted elements can degrade performance, increase failure rates, or create costly inefficiencies.
Common problem impurities include:
- Oxygen, carbon, and hydrogen – these gases can form brittle compounds, disrupt grain boundaries, and reduce sintered density.
- Sulfur and chlorine – known to accelerate corrosion and introduce microcracks.
- Silicon, aluminum, and calcium – often picked up from tooling or feedstock, these elements can create non-magnetic inclusions that reduce overall field strength.
How Purity is Verified at EAG Laboratories
EAG Laboratories’ Purity Survey service uses multiple techniques to evaluate both gaseous and solid-state impurities:
- Inert Gas Fusion (LECO analysis) measures gas-forming elements like oxygen, carbon, hydrogen, and sulfur with high sensitivity.
- ICP-MS, LA-ICP-MS, and GDMS, can all be used to identify and quantify trace contaminants such as silicon, calcium, and aluminum.
- ICP-OES or XRF confirms the major element composition to ensure alloy specifications are met.
Together, these techniques help magnet manufacturers maintain consistency, especially when scaling production or switching suppliers.
The Role of EAG Laboratories in Supporting Magnet Manufacturers
As demand grows for powerful permanent magnets across the clean energy and advanced electronics sectors, so does the need for tight quality control. Whether supporting new alloy development, verifying batch consistency, or troubleshooting performance issues, EAG Laboratories is equipped with the instrumentation and expertise to help manufacturers ensure that purity standards are upheld.
A comprehensive purity survey can help identify problems before they turn into production failures, reduce warranty risks, and build trust across the supply chain. Talk to an EAG Laboratories expert today!
Further Reading:
- SmCo vs Neodymium. Stanford Magnets (2024) https://www.stanfordmagnets.com/smco-magnets-vs-neodymium-magnets.html
- Magnetic materials and devices for the 21st century: stronger, lighter, and more energy efficient. Gutfleisch, O., Willard, M. A., Brück, E., Chen, C. H., Sankar, S. G., & Liu, J. P. (2011). Advanced Materials, 23(7), 821-842. https://doi.org/10.1002/adma.201002180
- Magnet Manufacturing Process. Arnold Magnetic Technologies. https://www.arnoldmagnetics.com/resources/magnet-manufacturing-process/
- How Are Magnets Manufactured? ALB Materials. https://www.albmagnets.com/content/6-how-are-magnets-manufactured
- Rare earth permanent magnets supply chain deep dive assessment. DoE, U. S. (2022). Department of Energy Response to Executive Order, 14017, 2022-02. https://www.osti.gov/biblio/1871577
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