Cobalt nanowires with high aspect ratio have been synthesized via a solvothermal chemical process. Based on the shape anisotropy and orientation of the nanowire assemblies, a record high ...room-temperature coercivity of 10.6 kOe has been measured in Co nanowires with a diameter of about 15 nm and a mean length of 200 nm. As a result, energy product of the wires reaches 44 MGOe. It is discovered that the morphology uniformity of the nanowires is the key to achieving the high coercivity and high energy density. Nanowires of this type are ideal building blocks for future bonded, consolidated and thin film magnets with high energy density and high thermal stability.
A straightforward and environment-friendly process for acid-free leaching of rare-earth elements and cobalt, which are critical materials, from waste magnet materials has been developed. The process ...also allows for selective leaching of rare-earth elements from magnet-containing electronic wastes, such as end-of-life hard disk drives and electric motors. The use of copper salts eliminates the use of volatile toxic acids in the dissolution and separation processes, which allows for a more eco-friendly approach to recovering critical elements and a safer work environment. Recovered critical materials were shown to be suitable for reinsertion into the materials supply chain.
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•New bonded magnets made with wastes from additive manufacturing (AM).•Environmentally benign process for recycling waste AM polymer bonded NdFeB magnets.•Process is simple and can be ...easily integrated into existing or new startup plants.•Process enables closed-loop sustainability in critical rare earth elements supply.•Properties of recycled magnets are on par with original end-of-life materials.
In this work, we describe an efficient and environmentally benign method of recycling of additive printed Nd-Fe-B polymer bonded magnets. Rapid pulverization of bonded magnets into composite powder containing Nd-Fe-B particles and polymer binder was achieved by milling at cryogenic temperatures. The recycled bonded magnets fabricated by warm compaction of ground cryomilled coarse composite powders and nylon particles showed improved magnetic properties and density. Remanent magnetization and saturation magnetization increased by 4% and 6.5% respectively, due to enhanced density while coercivity and energy product were retained from the original additive printed bonded magnets. This study presents a facile method that enables the direct reuse of end-of-life bonded magnets for remaking new bonded magnets. In addition to magnetic properties, mechanical properties comparable to commercial products have been achieved. This research advances efforts to ensure sustainability in critical materials by forming close loop supply chain.
We report magnetic properties and microstructure of high energy-product MnBi bulk magnets fabricated by low-temperature ball-milling and warm compaction technique. A maximum energy product (BH)max of ...8.4 MGOe and a coercivity of 6.2 kOe were obtained in the bulk MnBi magnet at room temperature. Magnetic characterization at elevated temperatures showed an increase in coercivity to 16.2 kOe while (BH)max value decreased to 6.8 MGOe at 400 K. Microstructure characterization revealed that the bulk magnets consist of oriented uniform nanoscale grains with average size about 50 nm.
A surfactant- and template-free approach is described for the synthesis of mesoporous α-Fe 2 O 3 , Fe 3 O 4 and α-Fe nanowires (NWs). In this approach, α-FeOOH NWs (length 550 nm and diameter 30 nm) ...were first prepared by hydrolysis of FeCl 3 . On subsequent thermal treatment in a fluidized bed reactor in the presence of a forming gas (Ar 93% + H 2 7%), α-FeOOH transformed to mesoporous NWs of ɑ-Fe 2 O 3 , Fe 3 O 4 and ɑ-Fe by controlling the process parameters such as reaction time and temperature. The obtained NWs of α-Fe 2 O 3 , Fe 3 O 4 and α-Fe were ferromagnetic at room temperature with a coercive field ( H c ) of 412, 583 and 628 Oe respectively. The aligned NWs showed 1.6 to 2 times-enhanced remanence in the parallel direction relative to the perpendicular direction due to magnetic anisotropy. These mesoporous magnetic NWs with a high specific surface area (82 m 2 g −1 for α-Fe 2 O 3 NWs) were used in photocatalysis due to the high adsorptivity of three probe dye molecules. The as-prepared α-Fe 2 O 3 NWs exhibited only modest photocatalytic activity; however, the catalytic activity could be further enhanced by decorating the mesoporous ɑ-Fe 2 O 3 NWs with 10 nm sized ZnO nanoparticles. The developed ɑ-Fe 2 O 3 /ZnO nanowire nanohybrids could eliminate 100% of the probe dyes: methylene blue, Rhodamine B and methyl orange within 90 min irradiation with solar light, underlining the high photocatalytic degradation efficiency of the nanohybrid. The nanowire nanohybrids could be easily recovered by applying an external magnetic field and reused for at least 4 times without significant loss of their photocatalytic activity.
Extrusion based additive manufacturing of polymer composite magnets can increase the solid loading volume fraction with greater mechanical force through the printing nozzle as compared to traditional ...injection molding process. About 63 vol% of isotropic NdFeB magnet powders were compounded with 37 vol% of polyphenylene sulfide and bonded permanent magnets were fabricated while using Big Area Additive Manufacturing without any degradation in magnetic properties. The polyphenylene sulfide bonded magnets have a tensile stress of 20 MPa, almost double than that of nylon bonded permanent magnets. Additively manufactured and surface-protective-resin coated bonded magnets meet the industrial stability criterion of up to 175 °C with a flux-loss of 2.35% over 1000 h. They also exhibit better corrosion resistance behavior when exposed to acidic (pH = 1.35) solution for 24 h and also annealed at 80 °C over 100 h (at 95% relative humidity) over without coated magnets. Thus, polyphenylene sulfide bonded, additively manufactured, protective resin coated bonded permanent magnets provide better thermal, mechanical, and magnetic properties.
Recycling of rare earth elements, such as Sm and Nd, is one technique towards mitigating long-term supply and cost concerns for materials and devices that depend on these elements. In this work ...recycled Sm-Co powder recovered from industrial grinding swarfs, or waste material from magnet processing, was investigated for use in preparation of filament for 3D printing of bonded magnets. Recycled Sm-Co powder recovered from swarfs was blended into polylactic acid (PLA). Up to 20 vol.% of the recycled Sm-Co in PLA was extruded at 160°C to produce a filament. It was demonstrated that no degradation of magnetic properties occurred due to the preparation or extrusion of the bonded magnet material. Good uniformity of the magnetic properties is exhibited throughout the filament, with the material first extruded being the exception. The material does exhibit some magnetic anisotropy, allowing for the possibility of the development of anisotropic filaments. This work provides a path forward for producing recycled magnetic filament for 3D printing of permanent magnets.
Additive manufacturing synthesis using laser engineered net shaping (LENS) is utilized to rapidly print libraries of mischmetal (MM = La, Ce, Nd, and Pr) containing R2TM14B alloys (R = MM + separated ...Nd and TM = Fe and Co) enabling robust evaluation of physical properties over a wide composition range. High-throughput characterization of the magnetic and thermal properties are used to identify compositions for potential high-temperature, high-performance permanent magnets with reduced critical rare-earth elements. Improved Curie temperature (T c ∼ 450 °C) is obtained with substitution of Fe by Co in pseudoternary R2TM14B alloys. Furthermore, a 4-fold decrease in the Nd content can be achieved through substitution with less critical Ce- and La-rich MM, while retaining high T c. Guided by the properties of the LENS printed samples, selected compositions with and without TiC additions are synthesized via melt-spinning techniques to produce nanostructured ribbons. The maximum room temperature coercivity (H c) and energy product ((BH)max) without TiC are found to be 5.8 kOe, 8.5 MGOe, respectively, while TiC additions as a grain refiner gave Hc and (BH)max of 4.9 kOe, 9.8 MGOe, respectively. Structural characterization of the melt-spun ribbons shows homogeneous grain refinement with TiC additions, which leads to an increase in the energy product.
In the recent past, heterostructures of magnetic oxide thin films have attracted a great deal of research excitement due to very interesting physical properties such as antiferromagnetic interlayer ...coupling, tunable exchange-bias, interfacial driven magnetic properties and high mobility electron gas across the interfaces. In this work, we report on the comprehensive magnetic properties observed from the heterostructures of (2 unit cells) La0.7Sr0.3CrO3/(8 unit cells) La0.7Sr0.3MnO3/(2 unit cells) La0.7Sr0.3CrO3, which are epitaxially deposited on SrTiO3 substrate by plasma-assisted oxide molecular beam epitaxy. Using SQUID magnetometer, the magnetic properties are studied when the magnetic field was applied both in plane and out of plane. The Curie temperature of this structure is found to be at 290 K. Most significantly, at 2 K, we observed a complete up/down shift (along magnetization axis) of hysteresis loop when the sample was cooled under a magnetic field of ± 5000 Oe in the in-plane configuration. We believe that the strong antiferromagnetic (super) exchange coupling of Mn-Cr across the two interfaces is responsible for the observed exchange bias. We will present and discuss our in-detailed experimental findings collected on this heterostructure as a function of temperature and magnetic field.
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