Makale

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    Microstructural Investigation of Discarded NdFeB Magnets After Low‑Temperature Hydrogenation
    (Springer, 2024-06-16) Habibzadeh, Alireza; Kucuker, Mehmet Ali; Çakır, Öznur; Gökelma, Mertol
    With the imposition of some restrictions or the export of rare earth elements (REEs) by China, a dominant producer of these elements, the supply of REEs will soon be a challenge. To mitigate the supplv risk of REEs, a lot of attention has been paid to recycling recently. Despite the more commun recycling methods, including hydrometallurgical and pyrometalluraıcal processes, the hydrogen processing of magnetic serap (HPMS) is stili in the development stage. Magnet-to-magnet recycling via hydrogenation of end-of-life (EoL)NdFcB magnets provides a fine powder suitable for the produetion of new magnets from secondary sources, One of the crucial aspects of HPMS is the degree of recovery of the magnetic properties, as the yield effıciency can easily reach över 96%, The amount. morphology. and distribution of the Nd-rich phase are the key parameters to achieve the highest ma\imum energv produet (BH)max by isolatıng the matrix grain. Therefore, a better insight into the microstructure of the matrix grains and the Nd-rich phase before and alî er hydrogenation is an important aspect in terms of restoring the final magnetic properties. In this study, a low-temperature hydrogenation process in the range of roon. temperature to 400 °C was conducted to recycle NdFeB magnets fforn ııscarded hard disk drives (HDDs), and the hydroaenated powder was chaıacterized by eleetron microscopy and X-ray diffraction. fhe results show that there are three different morphologies of the Nd-rich phase, which undergo two different transformations through oxidation and hydride fbrmation. While at lower temperatures (below 250 °C) the degree of pulverization is higher and the experimental evidence of hydride formation is less clear, the opposite is true at higher temperatures. The formation of neodymium hydride at higher temperatures prevents fiırther oxidation of the Nd-rich phase due to its higb stability.