Mechanism and microstructure evolution of high temperature oxidation of end-of-life NdFeB rare earth permanent magnets

Nababan, Deddy C.; Mukhlis, Reiza; Durandet, Yvonne; Pownceby, Mark I.; Prentice, Leon H.; Rhamdhani, M. Akbar

doi:10.1016/j.corsci.2021.109290

Cited by 16 publications

(6 citation statements)

References 30 publications

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“…It was reported that during the oxidation of the Nd‐Fe‐B sintered magnets under high temperatures, there was an outward movement of Fe to the external oxidation surface. [ 20,32 ] The trends of the concentrations of Nd and Fe on the surface were in accordance with this phenomenon. Since the Fe 2 O 3 was prone to thermal sintering, it could be deduced that the severe sintering of the used Fe 2 O 3 −RE a O b OCs may be caused by the diffusion of the Fe 2 O 3 to the surface of the OC.…”

Section: Resultssupporting

confidence: 64%

“…It was reported that during the oxidation of the Nd-Fe-B sintered magnets under high temperatures, there was an outward movement of Fe to the external oxidation surface. [20,32] The trends of the concentrations of Nd and Fe on the surface were in accordance with this phenomenon. Since the Fe 2 O 3 was prone to thermal sintering, it could be deduced that the severe sintering of the used Fe 4, the BET surface area of the fresh OC (2.57 m 2 /g) and the pore structure were lower compared to other OCs reported, [15,33] which may be because the magnet scraps used as the raw material of the OC were dense metal alloys, and the surface sintering had already occurred during the roasting process of the waste scraps used for the preparation of Fe 2 O 3 ÀRE a O b OC.…”

Section: Date Analysissupporting

confidence: 68%

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Chemical looping gasification of biomass using rare earth oxides doped ferric oxide oxygen carrier for hydrogen‐rich syngas production

Lin,

Wang,

Huang

et al. 2023

Can J Chem Eng

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An efficient oxygen carrier (OC) is in great demand in the biomass chemical looping gasification (BCLG) process. In the present study, an innovative rare earth oxide doped ferric oxide OC (Fe2O3−REaOb) derived from the Nd‐Fe‐B sintered magnet waste scraps was employed for the BCLG process for hydrogen‐rich syngas production. The critical variables, including the temperature of gasification, the mass ratio of OC/biomass, the mass ratio of steam/biomass, and the cycle performance of the novel OC, were investigated regarding syngas yield and carbon conversion efficiency. Results found that the optimum conditions were achieved at 900°C, with a mass ratio of OC to biomass of 3:1 and a mass ratio of steam to biomass of 0.4, and a syngas yield of 1.19 Nm3/kg with an H2/CO mole ratio of 2.45, and a carbon conversion efficiency of 76.80% was reached. Additionally, a comparison between Fe2O3−REaOb OC, Fe2O3−Al2O3 OC, and Fe2O3−CeO2 OC was also conducted, with Fe2O3−REaOb OC demonstrating a superior performance. The synergistic effects between REaOb and Fe2O3, particularly the generation of perovskite oxide NdFeO3, contributed to the excellent performance of the Fe2O3−REaOb OC during the BCLG process. The outward diffusion of Fe and sintering of the OC reduced the syngas yield and carbon conversion efficiency by about 16.00% and 25.00% over the 20 redox cycles of the BCLG process. In summary, Fe2O3−REaOb can be an efficient and promising OC for hydrogen‐rich syngas production in the BCLG process.

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Section: Resultssupporting

confidence: 64%

Section: Date Analysissupporting

confidence: 68%

Chemical looping gasification of biomass using rare earth oxides doped ferric oxide oxygen carrier for hydrogen‐rich syngas production

Lin,

Wang,

Huang

et al. 2023

Can J Chem Eng

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“…It is known that when NdFeB magnets and/or powders were oxidized in air, an external oxidation zone (EOZ) consisting of mainly iron oxide (Fe 2 O 3 ) and internally oxidized zone (IOZ) which was the region where the Nd 2 Fe 14 B phase was dissociated were formed [12]. Once oxidized, the Nd 2 Fe 14 B phase was dissociated into the α-Fe and Nd 2 O 3 with the oxidation of the Nd rich one, where the α-Fe diffused toward the surface to form the iron oxide [32,33]. Oxygen diffusion into a magnet was known to occur through grain boundaries and/or high angle α-Fe in IOZ (columnar α-Fe grain) [34].…”

Section: Oxidation Mechanism During Selective Oxidation Heat Treatmentmentioning

confidence: 99%

Oxidation Behavior of Spent NdFeB Magnet Under Selective Oxidation Conditions

Seo,

Park,

et al. 2023

High Temperature Corrosion of mater.

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Oxidation behavior of the spent NdFeB magnet was investigated when exposed to the selective oxidation conditions to achieve effective separation of Nd element by forming an oxide form from metallic Fe one. XRD results con rmed that the selective oxidation heat treatment successfully leaded to the formation of Nd 2 O 3 and α-Fe phases, which was ascribed to the dissociation of the Nd 2 Fe 14 B phase as a consequence of only Nd's oxidation. The oxidation of the Nd element kept proceeding with time and temperature of the heat treatment, requiring 60 min when heat treated at 950 °C for the 100% oxidation degree based on the weight gain calculation. From the SEM analysis, it can be inferred that the oxygen diffusion for the oxidation mainly occurred through grain boundary at the initial stage and then, α-Fe lattice diffusion for inside grains. TEM analysis con rmed that the Nd 2 O 3 formed at the early oxidation had hcp structure and only coarsening with oxidation, maintaining its structure. As the no oxidation of the Fe element did not induced diffusion barriers such as the outmost Fe 2 O 3 layer and Fe 2 O 3 matrix, facile oxygen diffusion through the grain boundary and α-Fe lattice was possible, leading to the activation energy for oxygen diffusion as low as 28 kJ/mol. The speci c oxidation condition maintained the good microstructure for oxygen diffusion, α-Fe matrix containing submicron Nd 2 O 3 particles, which made it possible that the good diffusion paths such as grain boundary and α-Fe lattice kept working during the oxidation.

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“…Continuous eddy currents maintain the operating temperature close to the critical temperature of the magnets, which causes a time-dependent degradation through the magnetic viscosity [11]. Many studies have focused on investigating the effects of elevated temperature air exposure on the decay law of its magnetic decay law of the magnetics [12][13][14][15] and the evolution of their microstructures [16][17][18][19][20] during long-term aging. Li et al [16] found that two external-oxide layers composed of Fe 2 O 3 and Fe 3 O 4 and an internal oxidation zone (IOZ) were generated on the surface of the bare NdFeB magnet, but these had no protective effect for the internal oxidation.…”

Section: Introductionmentioning

confidence: 99%

“…Li et al [16] found that two external-oxide layers composed of Fe 2 O 3 and Fe 3 O 4 and an internal oxidation zone (IOZ) were generated on the surface of the bare NdFeB magnet, but these had no protective effect for the internal oxidation. The formation of IOZ is caused by the dissociation of the Nd 2 Fe 14 B phase to form oxides of neodymium and boron in a matrix of un-oxidized iron [16,19], and the columnar α-Fe grains oriented at right-angles to the specimen surface were believed to provide short-circuit diffusion paths for the inward transport of oxidation [16]. A logarithmic law can be well used to fit a time-dependent flux loss for the bare NdFeB magnet [20].…”

Section: Introductionmentioning

confidence: 99%

The Effect of Temperature Cycling on the Magnetic Degradation and Microstructure of a Zn-Coated NdFeB Magnet

Wu¹,

Long

Song³

et al. 2022

Coatings

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Temperature cycling tests in various temperature ranges were carried out to investigate the magnetic degradation of the Zn-coated NdFeB magnet. The losses of the surface magnetic field and magnetic flux were well fitted by using an index model. Compared with the lower limit temperature, the upper limit temperature had more obvious effect on the magnetic degradation. Once the upper limit temperature exceeded ≥160 °C, the magnetic degradation mainly occurred during the first cycle, which was different from the gradual decline with an increase in cycle number at a temperature of ≤140 °C. Moreover, the temperature cycling with a maximum upper limit temperature of 180 °C led to a loss of the remanence intensity, while the coercivity remained stable. Microstructure and element distribution analysis revealed that the oxidation of the Zn coating layer during the temperature cycling causes its cracking and an insertion of the oxygen element into the NdFeB substrate. The Nd-, Pr-rich phase at grain boundaries provided diffusion channels for oxygen elements, leading to a surface oxidation of NdFeB grains.

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Mechanism and microstructure evolution of high temperature oxidation of end-of-life NdFeB rare earth permanent magnets

Cited by 16 publications

References 30 publications

Chemical looping gasification of biomass using rare earth oxides doped ferric oxide oxygen carrier for hydrogen‐rich syngas production

Chemical looping gasification of biomass using rare earth oxides doped ferric oxide oxygen carrier for hydrogen‐rich syngas production

Oxidation Behavior of Spent NdFeB Magnet Under Selective Oxidation Conditions

The Effect of Temperature Cycling on the Magnetic Degradation and Microstructure of a Zn-Coated NdFeB Magnet

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