SmCo5 Particles Research Articles

Hydrogen‐Induced Disproportionation of Samarium‐Cobalt Intermetallics Enabling Promoted Hydrogen Evolution Reaction Activity and Durability in Alkaline Media

AbstractTransition‐metal nanoparticles hold great promise as electrocatalysts for alkaline hydrogen evolution reaction (HER), however, addressing the simultaneous challenges of ensuring sufficient active sites, promoting favorable water dissociation, and optimizing binding energy toward hydrogen intermediates remains a formidable task. To overcome these hurdles, a novel gaseous hydrogen engineering strategy is proposed by in situ embedding cobalt nanoparticles within a samarium hydride matrix (Co/SmH2) via hydrogen‐induced disproportionation of SmCo5 particles for efficient alkaline HER. The as‐designed Co/SmH2 delivered an overpotential as low as 252 mV at 100 mA cm−2, surpassing the performance of pristine Co by 100 mV. Notably, this catalyst lasts remarkably long maintaining a durability at ≈500 mA cm−2 for 120 h. A combination of in situ Raman spectroscopy, in situ X‐ray absorption spectroscopy, density functional theory calculation and post‐HER characterizations unambiguously unveiled that the surface SmH2 transforms into samarium (hydr)oxide during electrocatalysis. This transformation not only inhibits the aggregation of the ultrafine cobalt nanoparticles but also significantly enhances the water dissociation and optimizes the binding energy of active cobalt species toward hydrogen intermediate, resulting in concurrent improvement of kinetics, thermodynamics, and stability of the HER process.

Microwave-assisted chemical synthesis of SmCo5 magnetic particles with high coercivity

The hard-magnetic SmCo5-based materials with high coercivity have an enormous range of high-value-added technological applications. We reported the novel synthesis of SmCo5 particles with desired particle size by a microwave-assisted combustion process. The process consists of a combination of Sm-Co oxide precursor preparation by microwave-assisted combustion, and the following calcium hydride reduction-diffusion. The microwave-assisted combustion offers a time and energy-saving, and environmentally-friendly methodology to form the homogenous Sm-Co oxide precursor nanoparticles. This high-quality Sm-Co oxide precursor paves the way for achieving high coercivity in SmCo5 magnetic materials. A high coercivity up to 39.2 kOe was achieved in the aligned SmCo5 particles. These SmCo5 magnetic particles show promising prospects for high-performance permanent magnet applications and can be utilized for the development of exchange-coupled nanocomposite magnets with high energy density. This work also provides instructive information for designing and synthesizing rare-earth-based magnetic materials.

Hard magnetic SmCo5-Cu nanocomposites produced by severe plastic deformation

Textured nanocrystalline SmCo5-Cu magnets are produced by high-pressure torsion (HPT) of powder blends consisting of SmCo5 and Cu powder. The process enables a free selection of the magnetic phase and the grain boundary phase and overcomes limitations imposed by the phase diagram as in conventional sintering routes. Different numbers of rotations and thus strains, and the effect of the amount of Cu as the binder phase are investigated systematically with regard to the microstructure, and magnetic properties after HPT. With increasing number of rotations, a structural refinement, and an increasing coercivity are observed. TEM and EBSD analyses reveal fragmentation via particle fracture and plastic deformation as microstructural refinement processes. TEM analyses showed an amorphous structure of strongly deformed SmCo5 particles after 20 rotations during the HPT process. The magnetic hardening is ascribed to the microstructural refinement and the magnetic decoupling of the hard magnetic SmCo5 grains by Cu. XRD and microstructural analyses as well as magnetic hysteresis measurements indicate the formation of a texture during the HPT process. Consequently, the work demonstrates a new approach for the generation of textured nanostructured hard magnets.

Enhancing the coercivity of SmCo5 magnet through particle size control

The bottom-up synthesis of SmCo5 particles with stable single-domain size exhibit a maximum coercivity of 2.6 MA m−1 (33.1 kOe).

A Flame-Reaction Method for the Large-Scale Synthesis of High-Performance Smx Coy Nanomagnets.

We report a flame-reaction method to synthesize high-performance Smx Coy (x=1, y=5; x=2, y=17) particles on a multigram scale. This flame reaction allows the controlled decomposition of Sm(NO3 )3 and Co(NO3 )2 to 320 nm SmCo-O (SmCoO3 + Co3 O4 ) particles. A 5.8 g sample of SmCo3.8 -O particles was coated with CaO and then reduced at 900 °C by Ca to give 4.2 g of 260 nm SmCo5 particles. The SmCo5 particles are strongly ferromagnetic and the aligned particles in epoxy resin exhibit a large room-temperature coercivity (Hc ) of 41.8 kOe and giant (BH)max (maximum magnetic energy product) of 19.6 MGOe, the highest value ever reported for SmCo5 made by chemical methods. This synthesis can be extended to synthesize Sm2 Co17 particles, providing a general approach to scaling up the synthesis of high-performance Smx Coy nanomagnets for permanent magnet applications.

Chemically synthesized anisotropic SmCo5 nanomagnets with a large energy product.

In this communication, we report a facile strategy to chemically synthesize anisotropic SmCo5 nanomagnets with a large magnetic energy product (BH). First, we designed a Co3O4@Sm2O3-CaO precursor by a one-pot method, which could be further reduced into uniform single-crystal SmCo5 particles under the stabilization of CaO coating. Following that, CaO was removed under an oxygen-free environment to impede oxidation. Finally, 130 ± 10 nm SmCo5 particles were aligned to be nanomagnet, exhibiting a large (BH)max value of 18.1 MGOe, which is the highest value reported by chemical methods.

A new synthesis of SmCo5 particles with high magnetic performance through spray pyrolysis

SmCo5 particles were synthesized by a spray pyrolysis process with in situ hydrogen (H2) reduction. The as-synthesized particles showed homogenous elemental distribution and low crystallization. The crystallization of the as-synthesized SmCo5 particles was further increased by annealing at 700 °C in Ar environment. After the annealing, the SEM images showed that surface roughness of the particles was increased due to the reordering of the atoms, the XRD patterns showed that the crystallization of the particles was increased, and VSM characterization showed that the magnetic properties were improved. Finally, the magnetic properties of SmCo5 particles synthesized in this report were compared with those in other reports. It was concluded that this paper proposed an easy way to synthesize high purity SmCo5 particles with high magnetic performance.

A facile synthesis of anisotropic SmCo5 nanochips with high magnetic performance

Highly anisotropic SmCo5 single crystal particles are promising candidates for high-density data storage and building nanocomposite permanent magnets with large maximum energy product. Previously, nanocrystalline SmCo5 particles obtained by calciothermic reduction exhibit low magnetic energy product due to magnetic isotropy caused by severely agglomerated equiaxial particles. In this study, we report a new strategy to fabricate highly anisotropic SmCo5 nanochips by reductive annealing of precursors with a special designed morphology. The precursors containing single crystal Co(OH)2 nanoflakes and crystalline Sm(OH)3 nanorods were synthesized by a hydrothermal process, and converted into SmCo5 nanochips by subsequent thermal reduction, during which the Co(OH)2 nanoflakes facilitate the formation of SmCo5 nanochips as a template and Sm(OH)3 nanorods help to maintain the hexagonal morphology and single crystal nature. The SmCo5 nanochips exhibit strong magnetic anisotropy and excellent room temperature magnetic properties with a remanence of 7.7 kG, coercivity of 19.3 kOe, and maximum energy product of 14.4 MGOe, which is the highest recorded value for chemical synthesized nanostructured SmCo5 particles.

Designing shape anisotropic SmCo5 particles by chemical synthesis to reveal the morphological evolution mechanism.

In this work, we describe a new protocol to synthesize SmCo5 single crystal particles with remarkable shape anisotropy (hexagonal and rodlike), which exhibit a giant coercivity of 36.6 kOe and a high Mr/Ms value of 0.95 after an alignment. On this basis, the morphological evolution mechanism is illustrated by employing the template effect.

Synthesis of SmCo5 nanoparticles with small size and high performance by hydrogenation technique

SmCo5 nanoparticles (NPs) have promising applications in high-density magnetic storage and magnetic nanocomposites. In this work, A novel method to yield SmCo5 particles with small size and high coercivity was reported. Firstly, Sm2O3–Co NPs with size of 6–15 nm were fabricated by a solvothermal route. Then the agglomerated SmCo5 particles were obtained by thermal reduction of the precursor, which show high coercivity of 2.0 T at room temperature. At last, the as-synthesized SmCo5 particles were further hydrogenated under high hydrogen pressure of 4 MPa at room temperature, where hydrogen absorption process could form small-sized SmCo5Hx particles due to their lattice expansion and hydrogen desorption process could convert SmCo5Hx NPs into SmCo5 NPs. The prepared SmCo5 NPs after hydrogenation, showing well distribution, have a small size of 5–20 nm and room temperature coercivity of 1.22 T.

Chemical synthesis of SmCo5/Co magnetic nanocomposites

A three-step chemical synthesis of SmCo5/Co nanocomposites was developed. Firstly, the Co–Sm(OH)3–Ca(OH)2 precursors were prepared by co-precipitation. Secondly, SmCo5 particles were obtained by reductive annealing of the precursors. At last, the SmCo5/Co nanocomposites were achieved by chemical deposition based on SmCo5 particles. The SmCo5/Co nanocomposites contain hard magnetic phase of SmCo5 with about 100 nm in size and soft magnetic phase of Co with about 8 nm in size, exhibiting independent two-phase structure without alloying. Compared to that of single-phase SmCo5 particles, the saturation magnetization of SmCo5/Co nanocomposites is increased by 27.5%. The synthesis provides a new route to fabricate SmCo-based nanocomposites.

Microstructure and magnetic properties of Cu90−xCo10Nix–7.5% SmCo5 composite alloys prepared by mechanical alloying and hot pressing

ABSTRACTNanocrystalline composites of Cu90−xCo10Nix (x = 0, 10, 20 wt-%) alloys reinforced with 7.5 wt-% of intermetallic SmCo5 particles were prepared by several processing steps. The production of these alloys started with the synthesis of Cu90−xCo10Nix powder alloys by mechanical alloying of pure Cu, Co and Ni in a planetary mill for 30 h at 250 rev min−1. As a second step, intermetallic SmCo5 particles were added, and additional milling was performed for 10 h. The resulting powders of both milling processes were characterised by means of an X-ray diffraction method, a scanning electron microscopy and an electron probe microanalysis. As a final fabrication step, Cu90−xCo10Nix–7.5% SmCo5 alloy powders were consolidated by hot pressing under 88 MPa for 75 min at 750°C in an argon atmosphere. The resulting compacts are reinforced by the precipitation of Co(Ni) during consolidation, and the presence of second-phase particles of oxides and intermetallic SmCo5.

The chemical synthesis of SmCo5 single-crystal particles with small size and high performance

SmCo5 nanoparticles have promising applications in high-density magnetic storage and magnetic nanocomposites. However, conventional calciothermic reduction process yields agglomerated SmCo5 magnets for high temperature annealing, limiting the application and development of SmCo5 nanoparticles. In this work, we exploited a novel strategy to fabricate SmCo5 single-crystal nanoparticles by an assistance of graphite oxide sheets. Sm2O3-Co particles coated with graphite oxide sheets were synthesized by solvothermal route, and the following reductive annealing generated SmCo5 particles. The size and magnetic performance of SmCo5 particles can be tuned by manipulating surfactants. The high coercivity of 24.4kOe and ideal size of 20–100nm can be achieved in SmCo5 single-crystal nanoparticles. In this technology, graphite oxide sheets can prevent the particles from sintering effectively and sustain the generation of single crystal.

Structure and magnetism of SmCo5 nanoflakes prepared by surfactant-assisted ball milling with different ball sizes

Anisotropic magnetic SmCo5 nanoflakes have been fabricated by surfactant-assisted ball milling (SABM) using hardened steel balls of one of the following sizes: 4, 6.5, 9.5 and 12.7mm in diameters. The magnetic properties of SmCo5 particles prepared by SABM with different milling ball sizes in diameters were investigated systematically. It was showed that the nanoflakes milled by amount of small size balls had a higher coercivity and lower anisotropy, i.e., worse grain orientation although in a short milling time while the nanoflakes prepared with same weight of big balls tend to have a lower coercivity, better grain orientation. The coercivity mechanism of the nanoflake was studied and it was mainly dominated with the domain-wall pinning. The SEM analysis shows that the morphology of nanoflakes prepared with different ball sizes are almost the same when the balls to powder weight ratio is fixed. The different magnetic properties caused by different ball sizes are mainly due to the different microstructure changes, i.e, grain refinement and c-axis orientation, which are demonstrated by X-ray diffraction (XRD) analysis and transmission electron microscope (TEM). Based on the experiments above, a combined milling process was suggested and done to improve magnetic properties as your need.

Magnetic and structural properties of hot pressed Cu–SmCo5 composites obtained by mechanical alloying

Cu–8 wt-%SmCo5 alloys were obtained through mechanical milling for novel industrial applications. Copper and SmCo5 powder mixtures were mechanically alloyed in a planetary ball mill to disperse SmCo5 fine particles in the copper matrix with the aim to modify the structural, mechanical, electrical and magnetic properties. The resulting alloyed powders were characterised as a function of milling time. Under the magnetic field, SmCo5 particles achieved Ms to improve the soft magnetic properties of copper–8 wt-%SmCo5 to be used in dielectromagnetic components. The magnetic properties of Cu–8 wt-%SmCo5 powders reached their optimum values after milling time ranging from 10 to 15 h. The consolidation of milled alloy powders was performed by uniaxial hot pressing at 923 K for 2 h under argon atmosphere to obtain dense compacts. The consolidation process resulted in good dense metal matrix composite materials with adequate properties of compression strength >900 MPa, 95 HRB in hardness, electrical conductivity up to 43% of that of the International Annealed Copper Standard (IACS) and magnetic properties such as coercive field, saturation and remanent magnetisation obtained at 218 Oe, 70·23 emu g−1 and 6·09 emu g−1 respectively at 300 K. The existence of a coercive field and a little magnetic memory of the consolidated system is a typical behaviour of magnetically soft materials. The variation of electric and magnetic properties and its dependence on structure strength change with milling time were discussed.

Eddy-current-resistant SmCo5/CaF2 magnets produced via high-energy milling in polar and non-polar liquids

Processes of high-energy ball milling of SmCo5 alloys were compared for three single-liquid environments without using additional surfactants. Both coarsely grained as-cast and nanocrystalline pre-milled SmCo5 precursors showed tendency toward formation of thin flakes if milled in polar liquids (acetone and ethanol) in a marked contrast to milling in non-polar heptane. CaF2 dielectric powder added prior to milling in the polar liquids tends to become attached on the flake surfaces. Milling in heptane in the presence of CaF2 produces flake-like SmCo5 particles which with increasing the milling time are found to incorporate an increasing amount of CaF2. The SmCo5—5wt% CaF2 mixtures milled for the optimum time in both the polar and non-polar liquids were successfully hot-pressed into laminated composite magnets having intrinsic coercivity of 25–30kOe, maximum energy product of approximately 6.5MGOe and electrical resistivity of 500–600μΩcm, which is more than 7 times the resistivity of conventional Sm–Co magnets.

Manipulation of the magnetic exchange interaction in SmCo films with high thermal stability by controlling phase transformation

High thermal stability and tunable magnetic exchange interaction (MEI) in SmCo materials have been the critical problem in applications to magnetic recording media and nanocomposite permanent magnets. We constructed SmCo films with a high thermal stability and tunable MEI by controlling the phase transformation through properly increasing the Sm concentration (20.5–37.7 at.%) and controlling the annealing process. Microstructure studies show that the SmCo5 phases ensure that the film has a high thermal stability. Moreover, we manipulated the MEI in the film with non-magnetic precipitated SmCo2 particles in the vicinity of SmCo5 particles. These results provide a novel way to tune the MEI in SmCo materials while maintaining a high thermal stability.

Anisotropic SmCo5 flakes and nanocrystalline particles by high energy ball milling

This work is focused on the evolution of structure, texture and magnetic properties in SmCo5 powders during high energy ball milling (HEBM) in heptane with and without oleic acid (OA). Single-crystal micron SmCo5 flakes were formed in the early stage of HEBM (0–0.5 h). However, HEBM of 1–2 h without OA led to the formation of a mixture of single-crystal microflakes and loosely agglomerated polycrystalline microparticles with the highest coercivity of 15.7 kOe. HEBM of 3–5 h without OA led to the formation of isotropic, more or less equiaxed SmCo5 particles with a size of 2–30 μm and a polycrystalline nanostructure due to the coalescence of flakes and particles. In the case of HEBM in heptane with 15 wt. % OA, prolonged milling (from 1 to 5 h) led first to the formation of SmCo5 single-crystal submicron flakes and later to submicron- and nanosize-nanocrystalline flakes with a [001]-out-of-plane texture. OA plays an essential role in the formation of anisotropic SmCo5 flakes via the impediment of cold welding and agglomeration of flakes. The highest coercivity of 17.7 kOe was obtained in a flake sample milled for 5 h with a thickness of 8–80 nm, an average grain size of 8 nm and an aspect ratio of 102–103.

Anisotropic SmCo5 nanoflakes by surfactant-assisted high energy ball milling

Crystallographically anisotropic SmCo5 nanoflakes were fabricated directly by one-step surfactant-assisted high energy ball milling (HEBM) of Sm17Co83 ingot powders for 5 h in heptane and oleic acid (OA) without preprocessing or further annealing. The SmCo5 nanoflakes have a strong [001] out-of-plane texture. The thickness of nanoflakes is in the range of 8–80 nm while their length is 0.5–8 μm. The surfactant OA plays an important role in the formation of SmCo5 nanoflakes. HEBM of SmCo5 ingots in heptane without OA resulted in the formation of magnetically isotropic more or less equiaxed SmCo5 particles with a size of 2–30 μm. Closely packed “kebablike” SmCo5 nanoflakes were formed by HEBM in heptane with 15 wt % OA. HEBM in 150 wt % OA led to well-separated nanoflakes instead of the closely packed kebablike nanostructure. This resulted in the enhanced [001] out-of-plane texture. In-plane transmission electron microscope examination showed that the SmCo5 nanoflakes were composed of grains with sizes in the range of 4–8 nm. Coercivities of about 18.0 kOe were obtained for the anisotropic SmCo5 nanoflakes.

Anisotropic nanostructured magnets by magnetic-field-assisted processing

It has been a great challenge to produce anisotropic nanocrystalline bulk magnets. In this paper, we report our recent work in preparing anisotropic bonded magnets consisting of SmCo5 nanocrystalline particles. The work involved synthesis of nanocrystalline hard magnetic SmCo5 particles by ball milling in the presence of a magnetic field. Structural and magnetic characterizations show the alignment of the c-axis of the SmCo5 grains upon the magnetic-field-assisted ball milling, while the grain size was controlled under 15 nm. The formation of the texture may be attributed to the effect of magnetic fields on the grain orientation during the cold welding process during ball milling. The as-milled particles were then compacted under a magnetic field with a binder to form bonded bulk SmCo5 nanostructured magnets. X-ray diffraction patterns show c-axis alignment in the bulk magnets, which was consistent with the magnetic measurements.