Coercivity enhancement of recycled Nd–Fe–B sintered magnets by grain boundary diffusion with DyH3 nano-particles

Ji, Wei-xiao; Liu, Weiqiang; Yue, Ming; Zhang, Dongtao; Zhang, Jiuxing

doi:10.1016/j.physb.2015.03.013

Cited by 24 publications

(10 citation statements)

References 9 publications

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“…Otherwise, a higher initial pressure of hydrogen is required to start the hydrogenation process . The common nickel coating with a thickness of about 13 μm can be easily removed or damaged manually or by electrochemical technology. ,,, Damaging the coating by bending and breaking the magnets is preferable to complete decoating, as this provides sufficient free surface area for hydrogen diffusion and prevents a higher degree of oxidation . Piotrowicz et al reported that the optimal pressure of hydrogenation decreases from 2–4 bar to 1–2 bar by removing the coating layer before hydrogenation.…”

Section: Hydrogen Processing Parametersmentioning

confidence: 99%

“…To prevent oxidation and increase the corrosion resistance of NdFeB magnets, they are commonly coated with nickel or Ni-Cu-Ni. Also, there are various other alternatives for coating such as a Ni-Ni(S)-Ni(P) multilayer coating, alumina ceramic coatings, a multilayer titanium nitride ceramic coating, etc. − The presence of the coating layer harms the efficiency of the hydrogenation in the recycling process due to protecting the grain boundaries from diffusion and preserving the magnetic properties of NdFeB magnets . Therefore, the coating layer should be removed partially or completely to allow the hydrogen gas to enter the magnet.…”

Section: Hydrogen Processing Parametersmentioning

confidence: 99%

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Review on the Parameters of Recycling NdFeB Magnets via a Hydrogenation Process

2023

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Regarding the restrictions recently imposed by China on the export of rare-earth elements (REEs), the world may face a serious challenge in supplying some REEs such as neodymium and dysprosium soon. Recycling secondary sources is strongly recommended to mitigate the supply risk of REEs. Hydrogen processing of magnetic scrap (HPMS) as one of the best approaches for magnet-to-magnet recycling is thoroughly reviewed in this study in terms of parameters and properties. The processes of hydrogen decrepitation (HD) and hydrogenation–disproportionation–desorption–recombination (HDDR) are two common methods for HPMS. Employing a hydrogenation process can shorten the production route of new magnets from the discarded magnets compared to other recycling routes such as the hydrometallurgical route. However, determining the optimal pressure and temperature for the process is challenging due to the sensitivity to the initial chemical composition and the interaction of temperature and pressure. Pressure, temperature, initial chemical composition, gas flow rate, particle size distribution, grain size, and oxygen content are the effective parameters for the final magnetic properties. All these influencing parameters are discussed in detail in this review. The recovery rate of magnetic properties has been the concern of most research in this field and can be achieved up to 90% by employing a low hydrogenation temperature and pressure and using additives such as REE hydrides after hydrogenation and before sintering.

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Section: Hydrogen Processing Parametersmentioning

confidence: 99%

Section: Hydrogen Processing Parametersmentioning

confidence: 99%

Review on the Parameters of Recycling NdFeB Magnets via a Hydrogenation Process

2023

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“…The reported HRE-based diffusion sources can enhance the H cj by > 900 kA/m for the magnets with a thickness of <5 mm. The effective HRE containing GBD sources mainly include fluorides, hydrides, and metals/alloys [20][21][22][23][24][25][26][27][28][29].…”

Section: Development Of Diffusion Sources and Their Fabricationmentioning

confidence: 99%

Grain Boundary Diffusion Sources and Their Coating Methods for Nd-Fe-B Permanent Magnets

Cao

et al. 2021

Metals

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Nd-Fe-B magnets containing no heavy rare earth (HRE) elements exhibit insufficient coercivity to withstand the demagnetization field at elevated temperatures. The grain boundary diffusion (GBD) process provides the best route to fabricate high-coercive Nd-Fe-B magnets with low consumption of expensive HRE resources. Here we give a special review on the grain boundary diffusion sources and their coating methods. Up to now, various types of grain boundary sources have been developed, starting from the earliest Tb or Dy metal. The HRE-M eutectic alloys were firstly proposed for reducing the cost of the diffusion source. After that, the diffusion sources based on light rare earth and even non rare earth elements have also been proposed, leading to new understanding of GBD. Now, the diffusion sources including inorganic compounds, metals, and alloys have been employed in the industry. At the same time, to coat the diffusion source on the magnets before diffusion treatment, various methods have been developed. Different from the previous review articles for GBD, this review gives an introduction of typical types of diffusion sources and their fabrication approaches. The effects of diffusion source on the microstructure and magnetic properties are summarized briefly. In particular, the principles and applicability of different coating approaches were discussed in detail. It is believed that this review can provide a technical guidance for the industry for designing the diffusion process and products meeting specific requirements.

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“…Compared with the above-mentioned regular way, this new approach is simpler and more energy-saving. Ji et al [31] recycled waste VCM magnets disassembled from hard disk drives in computer via GBD method by using DyH 3 nanoparticles. They disassembled the Nd-Fe-B sintered magnet with coatings from the waste hard disk drive.…”

Section: Magnet-magnet Technology Based On Grain Boundary Diffusion T...mentioning

confidence: 99%

“…The dissembling process of VCM magnets: (a) the cap of the hard disk drive, (b) the de-capped hard disk drive with the voice coil motor labeled in red square, (c) the dismounted magnet. [31] 2. Main recycling techniques for bulk Nd-Fe-B sintered magnet wastes…”

Section: Introductionmentioning

confidence: 99%

Progress in recycling of Nd–Fe–B sintered magnet wastes*

et al. 2019

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Significant efforts have been put into the recycling of bulk Nd–Fe–B sintered magnet wastes around the world in the past decade because bulk Nd–Fe–B sintered magnet wastes are valuable secondary rare-earth resources. There are two major facts behind the efforts. First, the waste magnets contain total rare-earth content as high as more than 30 wt.%, which is higher than most natural rare-earth mines. Second, the waste magnets maintain the physical and chemical properties of the original magnets even with deterioration of the properties on surfaces due to corrosion and contamination. In this review, various techniques for recycling bulk Nd–Fe–B sintered magnet wastes, the overall properties of the recycled Nd–Fe–B sintered magnets, and the mass production of recycled magnets from the wastes are reviewed.

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Coercivity enhancement of recycled Nd–Fe–B sintered magnets by grain boundary diffusion with DyH3 nano-particles

Cited by 24 publications

References 9 publications

Review on the Parameters of Recycling NdFeB Magnets via a Hydrogenation Process

Review on the Parameters of Recycling NdFeB Magnets via a Hydrogenation Process

Grain Boundary Diffusion Sources and Their Coating Methods for Nd-Fe-B Permanent Magnets

Progress in recycling of Nd–Fe–B sintered magnet wastes*

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