The pressure effect on particle size distribution of recycling NdFeB magnets

Date

2024-12-5

Author

Özaltun, Gizem

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Rare earth permanent magnets (REPMs), specifically NdFeB magnets, play a crucial role in industries due to their improved magnetic performance. However, sustainable alternatives, such as recycling, are needed, as there are significant geopolitical supply concerns regarding the dependence on rare earth elements (REEs), which are also included in the list of critical raw materials identified by the European Commission. The objective of this thesis is to investigate the impact of hydrogen pressure on scrap NdFeB magnets using different characterization techniques to obtain ideal particle size distribution for further manufacturing steps. In this study, scrap NdFeB permanent magnets from hard disk drives were subjected to the hydrogen decrepitation (HD) process at different pressures (2, 4, and 6 bar) followed by a ball-milling process. Magnetic measurements showed the demagnetization of HD powders, a consequence of hydrogen entering the structure. Unexpectedly, M/H tests revealed that ball-milled powders had increased coercivity. The X-ray diffraction analysis showed the formation of Nd2Fe14B3.31 and Nd2O3 phases, confirming that there is no NdH2 phase formation at room temperature. The research additionally demonstrated differences in the expected hydrogen concentration associated with pressure. The 4 bar HD powders, which showed the highest Nd2Fe14B3.31 phase content and the least amount of oxide phase, were found to have the best conditions for further processing. Characterization of the particle size distribution showed that when hydrogen pressure got higher, the particle size dramatically reduced. However, the excessive particle size reduction after ball-milling showed that it was a consequence of the prolonged milling time.

Subject Keywords

Recycling, Permanent Magnet, Hydrogen Decrepitation

URI

https://hdl.handle.net/11511/113000

Collections

Graduate School of Natural and Applied Sciences, Thesis