In-situ X-ray diffraction reveals multi-stage hydrogenation and disproportionation phase transitions in (Nd,Pr)2Fe14B powder, highlighting structural mechanisms for magnet recycling.
The reaction of neodymium-iron-boron (Nd,Pr)2Fe14B powder with flowing hydrogen, which is relevant to the recycling of magnets, is investigated using in-situ X-ray diffraction (XRD). Hydrogenation via the formation of the (Nd,Pr)2Fe14BHx phase occurs at 245±5 °C. Disproportionation starts at 555±5 °C with α-Fe formation, followed by the formation of NdH2 and PrH2 at 645±5 °C, ending at 775±5 °C with the emergence of the Fe2B phase. These four phases (NdH2, PrH2, α/γ-Fe, and Fe2B) remain unchanged up to 950 °C. After cooling to 25 °C under hydrogen, powders exhibit a Fe-rich matrix containing micron-size Fe2B and Nd+Pr-rich particles. Based on XRD, these particles are a mixture of binary NdH2 and PrH2.
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Hsu et al. (2024) studied this question.
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