Microstructural investigation of oxidized NdFeB powders: Influence of particle size on the oxidation behaviour

Steyaert, S.; Breton, J.M. Le; Harris, I.R.

doi:10.1016/s0304-8853(97)00211-4

Cited by 11 publications

(5 citation statements)

References 7 publications

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“…The remaining Nd 2 Fe 14 B phase remains unchanged during the oxidation treatment, in agreement with Mössbauer investigation of the oxidation of the Nd 2 Fe 14 B phase [3]. This is consistent with a picture of the formation of α-Fe at the surface of the Nd 2 Fe 14 B grains, as shown by electron microscopy observations of oxidized magnets and powders with the same composition [10,11]. At 400 • C for long treatment times or at higher temperature, the α-Fe phase is oxidized and almost completely disappeared at 500 • C. These results are in complete agreement with x-ray diffraction and Mössbauer investigations of the oxidation of the Nd 2 Fe 14 B phase [1].…”

Section: Discussion and Concluding Remarkssupporting

confidence: 88%

NMR investigation of the oxidation of the Nd₂Fe₁₄B phase

Breton

Tomka

Riedi

2001

J. Phys. D: Appl. Phys.

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The oxidation behaviour of the Nd2Fe14B phase is followed by nuclear magnetic resonance of Nd16Fe76B8 powders oxidized in ambient air at temperatures between 200 and 650 °C. It is shown that upon oxidation in the 200-400 °C temperature range, the destruction of the Nd2Fe14B phase leads to the formation of inhomogeneous or very small size α-Fe grains at the surface of the Nd2Fe14B grains, in agreement with previous investigations of the same powders. At 400 °C for long treatment times or at higher temperature, the α-Fe phase is oxidized and almost completely disappears at 500 °C. This validates the results of previous qualitative and quantitative Mössbauer studies of the oxidation of the Nd2Fe14B phase.

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Section: Discussion and Concluding Remarkssupporting

confidence: 88%

NMR investigation of the oxidation of the Nd₂Fe₁₄B phase

Breton

Tomka

Riedi

2001

J. Phys. D: Appl. Phys.

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“…The mean grain size being about 10 to 15 µm, the powders are composed mainly of fractions of hard grains. However, even if some hard grain particles are crossed by an Nd-rich intergranular region, it was shown previously that, in this temperature range and with this particle size, the intergranular diffusion does not affect the oxidation kinetics [38].…”

Section: Fitted Curves Of Oxidationmentioning

confidence: 77%

“…These models assume that the oxidation process is governed by oxygen diffusion through the corrosion product layer which continues to adhere to the non-oxidized part of the particle. These assumptions were checked in the case of an Nd 16 Fe 76 B 8 magnet [38].…”

Section: 22mentioning

confidence: 99%

Microstructure and corrosion resistance of Nd-Fe-B magnets containing additives

Steyaert¹,

Breton²,

Teillet³

1998

J. Phys. D: Appl. Phys.

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The oxidation behaviour of the phase in Nd-Fe-B sintered magnets containing additional elements (Al, Co, V, Nb, Mo) was investigated by Mössbauer spectrometry. The microstructure of the different samples was first characterized. Added elements were detected in both intergranular and intragranular precipitates. The presence of X-Fe-B (, V, Mo) precipitates was evidenced by high-resolution scanning electron microscopy, x-ray diffraction and Mössbauer spectrometry. The presence of Al and Co substituted to Fe in the phase was evidenced, and quantified using Mössbauer spectrometry and Curie temperature measurements. Powdered magnets sieved to a particle size less than m were oxidized in an ambient air furnace in the 200-C temperature range. These conditions are known to allow the oxidation process of the hard matrix (namely the intragranular diffusion process) to be followed accurately. The experimental oxidation kinetics were determined using Mössbauer spectrometry and fitted according to a single-particle analysis model. The results show a decrease of the dissociation rate of the hard matrix compared with the rate obtained for a sintered magnet containing no additives. As the activation energy was found to be comparable for each sample (106-112 kJ ), the pre-exponential factor of the diffusivity has a greater influence on the dissociation rate ( for the magnets containing V or Mo and for the magnet containing Nb, compared with for a magnet without additives). The slowing down of the dissociation rate is attributed to the presence of corrosion-resistant X-Fe-B (, V, Mo) intragranular precipitates in the oxidized layer and appears to be strongly dependent on the density of the intragranular precipitates.

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“…Changes to the basic Nd 16 Fe 76 B 8 composition might also change the microstructure of the IOZ and have a corresponding effect on the oxidation kinetics. Steyaert et al [66] concluded that, based on their microstructural study, both particle size and temperature range play important parts in the determination of the kinetic parameters of Nd-Fe-B powder's oxidation. Parida et al [67] studied the oxygen potential diagram for the system Nd-Fe-O at 1350 K, and the oxygen potentials corresponding to the equilibria between alloys/intermetallics and Nd 2 O 3 (s) are shown in Fig.…”

Section: Ndfeb's Oxidation Thermodynamics Kinetics and Mechanismmentioning

confidence: 99%

Review of High-Temperature Recovery of Rare Earth (Nd/Dy) from Magnet Waste

Firdaus

Rhamdhani

Durandet

et al. 2016

J. Sustain. Metall.

104

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Rare-earth metals, particularly neodymium, dysprosium, and praseodymium are becoming increasingly important in the transition to a green economy due to their essential role in permanent magnet applications such as in electric motors and generators. With the increasingly limited rare-earth supply and complexity of processing Nd, Dy, and Pr from primary ores, recycling of rare-earth based magnets has become a necessary option to manage supply and demand. Depending on the form of the starting material (sludge or scrap), there are different routes that can be used to recover neodymium from secondary sources, ranging from hydrometallurgical (based on its primary production process), electrochemical to pyrometallurgical. Pyrometallurgical routes provide solution in cases where water is scarce and generation of waste is to be limited. This paper presents a systematic review of previous studies on the high-temperature (pyrometallurgical) recovery of rare earths from magnets. The features and conditions at which the recycling processes had been studied are mapped and evaluated technically. The review also highlights the reaction mechanisms, behaviors of the rare-earth elements, and the formation of intermediate compounds in high-temperature recycling processes. Recommendations for further scientific research to enable the development of recovery of the rare-earth and magnet recycling are also presented.

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Microstructural investigation of oxidized NdFeB powders: Influence of particle size on the oxidation behaviour

Cited by 11 publications

References 7 publications

NMR investigation of the oxidation of the Nd₂Fe₁₄B phase

NMR investigation of the oxidation of the Nd₂Fe₁₄B phase

Microstructure and corrosion resistance of Nd-Fe-B magnets containing additives

Review of High-Temperature Recovery of Rare Earth (Nd/Dy) from Magnet Waste

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Microstructural investigation of oxidized NdFeB powders: Influence of particle size on the oxidation behaviour

Cited by 11 publications

References 7 publications

NMR investigation of the oxidation of the Nd2Fe14B phase

NMR investigation of the oxidation of the Nd2Fe14B phase

Microstructure and corrosion resistance of Nd-Fe-B magnets containing additives

Review of High-Temperature Recovery of Rare Earth (Nd/Dy) from Magnet Waste

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Product

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NMR investigation of the oxidation of the Nd₂Fe₁₄B phase

NMR investigation of the oxidation of the Nd₂Fe₁₄B phase