Highlights

• University of Birmingham researchers demonstrate hydrogen decrepitation successfully embrittles Sm₂Co₁₇ magnets in rotor assemblies, absorbing approximately 0.2 wt% hydrogen regardless of constraint—but liberation requires additional mechanical agitation and demagnetization steps.
• Scalable SmCo magnet recycling could reduce Western dependence on China-dominated samarium and cobalt supply chains by converting aerospace and defense scrap into reusable powder feedstock.
• The study reveals HD is not a one-step solution: constrained magnets don't automatically fall out as powder, and high Curie temperatures make demagnetization energy-intensive, requiring integrated processing systems for commercial viability.

---

A new open-access study led by James Griffiths, PhD, (opens in a new tab) University of Birmingham, with collaborators O.P. Brooks, V. Kozak, H. Kitaguchi, D. Brown, A. Campbell, A. Lambourne, and R.S. Sheridan reports that hydrogen decrepitation (HD) can meaningfully embrittle and enable powder recovery from samarium–cobalt 2:17 (Sm₂TM₁₇) sintered magnets extracted from scrap rotor assemblies.

These high-performance magnets—used in aerospace, defense, and industrial machines operating at elevated temperatures—are built on critical materials (samarium and cobalt) that sit inside geopolitically fragile supply chains. In controlled experiments, the team exposed both loose magnets and magnets still constrained inside rotors to hydrogen at 2–10 bar, 100 °C for 72 hours, then measured hydrogen uptake, lattice expansion, and magnetic property changes.

The headline result is both encouraging and sobering: constrained magnets absorb hydrogen just as effectively as loose magnets, but they do not reliably fall out of rotor housings as powder without additional mechanical agitation and a demagnetization step. Hydrogen decrepitation helps—but it is not a one-step “magic recycling” solution.

Why This Matters for Rare Earth Exchanges™ Readers

Samarium (a rare earth) and cobalt (a critical metal) underpin some of the most demanding magnet applications in the world. While this study is about recycling, not geopolitics, the strategic implication is clear: every viable recycling route that converts end-of-life magnets into usable feedstock reduces dependence on virgin supply chains, where China dominates processing, metals, and magnet manufacturing. Recycling alone will not dismantle China’s midstream leverage, but it can chip away at the “separation wall” by turning scrap into strategic inventory.

Study Methods — In Plain English

The researchers examined Sm₂TM₁₇ magnets (TM = Co, Fe, Cu, Zr) in two realistic conditions:

• Loose magnets (removed arc segments)
• Constrained magnets (still compressed inside rotor assemblies)

They subjected samples to hydrogen under controlled pressure and temperature, then used advanced materials and magnetic characterization tools—SEM/TEM microscopy, X-ray diffraction with Rietveld refinement, residual gas analysis, particle-size measurements, and vibrating sample magnetometry—to answer three practical questions:

1. Do constrained magnets still absorb hydrogen?
2. Does HD alone free powder from rotor assemblies?
3. Does HD destroy the magnet’s coercivity mechanism?

Key Findings

• Hydrogen uptake is similar whether magnets are loose or constrained (~0.195–0.233 wt%), with unit-cell volume expansion of ~1.35–1.87%.
• Physical constraint blocks crack propagation: magnets become highly embrittled but are not liberated as powder from rotors without mechanical agitation.
• Magnetized rotors do not demagnetize during HD, though magnetic properties decline—likely due to hydrogen-induced lattice strain affecting exchange coupling, not destruction of the domain-wall pinning coercivity mechanism.
• Best recovery requires a combined process: hydrogen exposure plus mechanical agitation and a demagnetization step (likely reverse-field demagnetization and/or thermal methods).

Implications: A Recycling Wedge Against Midstream Dominance

This study reinforces a core REEx theme: the West’s vulnerability is not just mining—it’s usable materials. SmCo magnets are “high-performance, high-consequence” components. A scalable recycling pathway could mean:

• Lower virgin samarium and cobalt demand per unit of output
• Greater feedstock certainty for allied magnet and motor manufacturers
• Improved lifecycle economics if recovery scales and contamination is controlled

This does not replace separated rare-earth supply, but it meaningfully reduces pressure on it—an incremental but important step in a system where China’s processing leverage can be exercised through licensing and export signaling.

Limitations and Controversial Considerations

• HD does not automatically free magnets from rotor housings, limiting throughput unless disassembly and agitation systems are engineered.
• Demagnetization is a real hurdle: Sm₂TM₁₇ magnets have very high Curie temperatures, making thermal demagnetization energy-intensive; reverse-field approaches may be more practical but add complexity.
• Coatings and adhesives in real-world rotors can contaminate powder streams and require preprocessing.
• Data availability is confidential, limiting full independent reproduction.
• Competing interest disclosure matters: the lead author reports Rolls-Royce funding and a pending patent related to SmCo magnet recycling—legitimate, and relevant for investors.

Conclusion

This study represents a credible technical advance toward converting end-of-life SmCo rotor magnets into reusable powder feedstock—an outcome that, if scaled, could modestly but meaningfully reduce Western exposure to China-dominated magnet materials. It also makes the industrial reality plain: constraint and magnetization are not edge cases; they are the real recycling challenge. Hydrogen decrepitation helps, but efficient recovery will require integrated mechanical and demagnetization solutions, not chemistry alone.

The IP

James Griffiths has a patent #Samarium Cobalt Magnet Recycling GB202408808D0 pending to Rolls-Royce Plc. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Citation:

Griffiths, J. et al. “Hydrogen decrepitation of Sm₂TM₁₇ sintered magnets from scrap rotor assemblies.” Journal of Magnetism and Magnetic Materials 639 (1 Feb 2026) 173755. https://doi.org/10.1016/j.jmmm.2025.173755 (opens in a new tab)

©!-- /wp:paragraph -->