Surfactant-assisted High-energy Ball Milling Research Articles

Novel Ni-V-Y Electrocatalysts for Hydrogen Evolution Reaction

Generation of renewable energy is improving globally, the ability to store generated energy remains an issue. A new class of water electrolysers that utilize anion exchange membranes (AEMs) are effective at converting water to hydrogen gas which can be used as fuel. Novel electrocatalysts are required for AEMs to be active, stable, and cost effective when used in AEM water electrolysers. Previously, S. Ghobrial investigated the Ni-Nb-Y alloy system as an electrocatalyst for the hydrogen evolution reaction, with Ni and Y components contributed to electrocatalytic activity [1]. Nb phase did not contribute to electrochemical activity and behaved only as a glass former. For the second-generation alloy, V replaced Nb to create a Ni-V-Y alloy. Thermodynamic modelling via FactSage was used to develop the amorphous alloy system. To create the amorphous alloys, a two-step ball milling process was used. Elemental powders were mechanically alloyed and amorphized under cryogenic conditions. The micron sized alloyed powder was size reduced to nanoparticles suitable for use as electrocatalysts via surfactant assisted high energy ball milling (SA-HEBM). Both micron powders and nanoparticles were structurally characterized using X-ray diffraction and SEM. The catalytic activity of the electrocatalysts were electrochemically characterized using steady state polarization to determine Tafel slopes and exchange current densities. A Ni-V-Y alloy was successfully produced via cryomilling and SA-HEBM. The combination of the NiVY amorphous phase + Ni3V + Ni5Y phases in the micron and nanopowders improved activity relative to the intermetallics alone via the spillover effect. The surfactant used in SA-HEBM is not completely removed by the current centrifugation process leading to lower-than-expected activity and marginal spillover enhancement in nanoparticles. With an improved cleaning process, it is predicted the nanoparticles will have higher activities than their micron powder counterparts.[1] - S. Ghobrial, Amorphous Ni-Nb-Y Alloys as Hydrogen Evolution Electrocatalysts, Toronto: University of Toronto, 2019.

Magnetization performance of hard/soft Nd9.6Fe80.3Zr3.7B6.4/α-Fe magnetic nanocomposites produced by surfactant-assisted high-energy ball milling

Neodymium iron boron (NdFeB) magnets are sintered anisotropic materials. They were commercially introduced in the early 1980s, and since have been used in different applications owing to their superior properties. Herein, we investigated the influence of 0.5 to 8 h of milling time on the morphological, structural, and magnetic performance of Nd9.6Fe80.3Zr3.7B6.4 powders produced using surfactant-assisted high-energy ball milling (SA-HEBM). The results revealed that the relationship between coercivity (H ci ) and milling time had a non-monotonous character reaching a maximum value of H ci = 8.92 kOe after 1 h of milling. The effect of the volume ratio of various magnetic phases (Nd2Fe14B and α-Fe) on microstructure and magnetic properties was also reported. The highest specific saturation magnetization (σ s = 120 emu g−1) was attained after 8 h of milling for powders with volume fraction: Nd2Fe14B–81 ± 2% and α-Fe–12 ± 2%. The expected value of Nd2Fe14B specific saturation magnetization was estimated (σ N = 108 ± 2.5 emu g−1) using the experimental value of σ s and magnetic phase volume fractions. The ratio of remanence to saturation magnetization of the Nd2Fe14B with milling time was also determined and analyzed.

Incorporating Co and Y into Amorphous Ni-Based Alloys to Stabilize Hydrous β-NiOOH for Efficient Electrocatalytic Water Oxidation

The use of novel anion exchange membranes (AEM) are of interest in a wide variety of electrochemical systems. On particular interest is in alkaline water electrolysers since it eliminates the aqueous KOH electrolyte and can provide improved form factors and much higher current densities that rival proton exchange membrane (PEM) electrolysers.1 The use of AEM water electrolysis also enables the use of less expensive earth-abundant non-platinum group metals (PGM) materials, such as nickel-based alloys as electrocatalysts.1 Conventional Ni electrocatalysts for the oxygen evolution reaction (OER) still display large overpotentials and slower reaction kinetics. The addition of secondary metals, such as Fe and Co, are commonly added to enhance the OER performance but suffer from stability issues. 2–4 The leaching of Co is noted to be much less severe which allows for more long-term electrocatalytic benefits to Ni by way of stabilizing the β-NiOOH phase over γ-NiOOH.4–6 As a result, Co is a very desired alloying element but a reduction in the amount used is required as Co is quickly becoming limited in supply due to it being essential for many renewable energy applications.7 Recent studies have shown that Y has catalytic synergy with Co by accepting excess electrons to facilitate OH- absorption and improve the formation of active intermediates.8,9 These findings indicate Y can enhance the OER activity of Co and reduce the Co concentration required.In this work, amorphous Ni79.2-xCoxNb12.5Y8.3 (x = 0 and 5 at.% Co) nanoparticles were synthesized using cryogenic mechanical alloying followed by surfactant-assisted high energy ball milling (SA-HEBM).10 This two-stage ball milling process provided a novel processing route for the production of nanostructured / amorphous materials with a wide range of possible compositions not achievable through rapid solidification, electrodeposition, or chemical reduction techniques. The resulting structures were characterized through x-ray diffraction and electron microscopy.The electrocatalytic activity and stability of amorphous nanoparticles on the alkaline oxygen evolution reaction were investigated through prolonged cyclic voltammetry and Tafel measurements. Cyclic voltammagrams demonstrated stable and reproducible curves for amorphous alloys up to 10000 cycles while crystalline Ni and Ni95Co5 showed signs of deactivation with cycling. Initially the addition of Co to crystalline Ni resulted in enhanced OER catalytic performance, but the performance drastically reduced beyond 500 cycles. A similar increase in performance was observed when adding Co to amorphous Ni79.2Nb12.5Y8.3, except the activity and stability was maintained throughout the 10000 cycles. The pairing of X-ray photoelectron spectroscopy (XPS) revealed no signs of overcharging in amorphous Ni74.2Co5Nb12.5Y8.3 and that the Y and Co were integrated into the Ni oxy-hydroxide structure. In contrast, XPS analysis of amorphous Ni79.2Nb12.5Y8.3 showed signs of overcharging which resulted in Y segregating from the surface to form Y2O3. From these results it is found that the presence of Co in amorphous Ni-based alloys stabilizes β-NiOOH and allows Y to remain incorporated for providing synergistic benefits. The presence of Co and Y in amorphous Ni-based materials is shown to enhance the OER activity and provide excellent long-term cycling stability. These features, along with the high surface area achieved through SA-HEBM, provide a cost-effective and simple method for producing stable and active amorphous electrocatalysts for the oxygen evolution reaction in AEM water electrolysis. V. R. Stamenkovic, D. Strmcnik, P. P. Lopes, and N. M. Markovic, Nat. Mater., 16, 57–69 (2016).F. Lyu, Q. Wang, S. M. Choi, and Y. Yin, Small, 15, 1804201 (2019).I. Roger, M. A. Shipman, and M. D. Symes, Nat. Rev. Chem., 1, 1–13 (2017).D. Y. Chung et al., Nat. Energy, 5, 222–230 (2020).T. N. Lambert et al., Chem. Commun., 51, 9511–9514 (2015).K. M. Cole, D. W. Kirk, and S. J. Thorpe, J. Electrochem. Soc., 165, J3122–J3129 (2018).X. Sun, H. Hao, Z. Liu, F. Zhao, and J. Song, Resour. Conserv. Recycl., 149, 45–55 (2019).M. Kim, B. Lee, H. Ju, S. W. Lee, and J. Kim, Adv. Mater., 31, 1901977 (2019).G. Zhang, B. Wang, L. Li, and S. Yang, Small, 15, 1904105 (2019).S. Ghobrial, K. M. Cole, D. W. Kirk, and S. J. Thorpe, Electrocatalysis, 10, 680–689 (2019). Figure 1

Structural and magnetic properties of rare-earth-free MnAl(MCNT)/Fe nanocomposite magnets processed by resin-bonding technique

In this study, the potential of multi-walled carbon nanotubes (MCNT) in processing rare-earth-free MnAl(MCNT)/Fe nanocomposite magnets was exploited through adopting a combination of surfactant-assisted milling and resin-bonding techniques. The required hard and soft magnetic phases such as MnAl(MCNT) and α-Fe, respectively, were individually subjected to surfactant-assisted high-energy ball milling. The surfactant-coated MnAl(MCNT) and Fe nanopowders, thus, obtained were characterized with respect to their structural and magnetic properties. Relatively, a very high coercivity, Hc (4.48 kOe), was obtained for the surfactant-coated MnAl(MCNT) powders after 6 h of milling, while in the case of Fe powders with high saturation magnetization, Ms (218.6 emu/g) was achieved at 3 h of surfactant-assisted milling. The MnAl(MCNT) powders with high Hc were mixed with the Fe powders of high Ms with different weight percentages: 0, 5 and 10. The nanocomposite powder mixtures were further milled for 1 h and then processed in the form of resin bonded magnets under aligning magnetic field of 20 kOe. The obtained bonded nanocomposite magnet, i.e. MnAl(MCNT) with 5 wt% of Fe addition demonstrated a good combination of high Ms (63.7 emu/g) and high Hc (4.46 kOe).

Chemical synthesis and coercivity enhancement of Nd2Fe14B nanostructures mediated by non-magnetic layer

High-performance Nd2Fe14B magnets have been widely required in various fields recently due to the lightweight and miniaturization of devices. In this work, we synthesize Nd2Fe14B nanostructures with tunable magnetic properties through surfactant-assisted high energy ball milling (SAHEBM) process, achieving prominently enhanced coercivity by forming non-magnetic layers as grain boundary phase. When the reduction annealing process was carried out as pellet with Ca, the coercivity increased from 0.8 kOe to ver 3 kOe as Nd2Fe14B powder, which is proved to be the contribution of the chemical diffusion of Nd elements and the formation f Nd-rich layer as magnetic insulating medium. In addition, two-dimensional graphene oxide (GO) was employed to build extra grain boundary, by which the coercivity of the core@dual-shell structure can achieve up to 8 kOe, tenfold of the original sample. The intrinsic mechanism indicated that the Nd-diffusion induced Nd-rich phase along with the reduced GO in the system could form non-magnetic layer as grain boundary and magnetically isolate the adjacent grains, significantly enhancing the exchange coupling effect. This work markedly opens up an effective approach for the chemical preparation of high-performance Nd2Fe14B nanostructured magnets, especially after post treatment, and gives an insight on the interactions at nanoscale.

Characterization of Amorphous Ni-Nb-Y Nanoparticles for the Hydrogen Evolution Reaction Produced Through Surfactant-Assisted Ball Milling

Amorphous Ni79.2Nb12.5Y8.3 and Ni81.3Nb6.3Y12.5 nanoparticles were synthesized using cryogenic mechanical alloying followed by surfactant-assisted high energy ball milling (SA-HEBM). These alloys were tested towards the hydrogen evolution reaction (HER) along with pure crystalline Ni and Ni5Y nanoparticles also produced through SA-HEBM. This two-stage ball milling process provided a novel processing route for the production of nanostructured/amorphous materials with a wide range of possible compositions not achievable through rapid solidification, electrodeposition, or chemical reduction techniques. The investigation of different surfactant and solvent concentrations resulted in improved nanoparticle yields whereby average particle sizes between 41 and 89 nm were obtained for crystalline and amorphous materials. Electrochemical testing showed that Ni81.3Nb6.3Y12.5 exhibited the lowest Tafel values and the fastest HER kinetics on both an electrochemically active surface area and on a mass loading basis. This investigation demonstrates their potential for use in anion exchange membrane water electrolysis.

A novel strategy for approaching high performance SmCo5/Co nanocomposites

Anisotropic SmCo5/Co magnetic nanocomposites have been fabricated by chemical deposition of Co nanowires based on SmCo5 nanoflakes. The SmCo5 nanoflakes with an average thickness of 200 nm and diameter of 4 μm were first prepared by surfactant-assisted high-energy ball-milling. The Co nanowires with mean diameter of 20 nm and length of 200 nm were then deposited via a solvothermal chemical process. This strategy can effectively control the content of SmCo5 nanoflakes and Co nanowires, and the hard magnetic nanoflakes can be coated with a uniform distribution of Co nanowires. Both of the SmCo5 nanoflakes and Co nanowires are anisotropic, and could be magnetically aligned simultaneously in the nanocomposites, which is confirmed by XRD patterns. Magnetic measurements of the “bi-anisotropic” SmCo5/Co composites show an enhanced remanent magnetization with increasing the content of Co nanowires. The exchange-coupled SmCo5/Co nanocomposites with up to 40 wt % Co content exhibits the highest (BH)max value of 23.8 MGOe, larger than the single phase SmCo5 nanoflakes.

Preparation and magnetic properties of Nd(FeMo) and its nitrides

Abstract In this study, a Nd(FeMo)12 alloy was prepared using a magnetic levitation melting furnace and subsequent heat treatment. The nitrides of this alloy, which exhibit uniaxial anisotropy, were then synthesized by gas-solid reaction. The melting process of the Nd(FeMo)12 alloy, as well as the microstructure and magnetic properties of the nitrides, was investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and magnetometer measurements. A homogeneous Nd(FeMo)12 phase was obtained by magnetic levitation melting using a MoFe alloy as a raw material, followed by heat treatment for 72 h. The nitrogenation of the Nd(FeMo)12 alloy was investigated. The magnetic properties of Nd(FeMo)12N1.52 powders obtained at a nitriding temperature of 550 °C were enhanced after grinding. No phase decomposition occurred during grinding. The nitriding powders exhibited a fine polycrystalline structure after grinding, as determined by transmission electron microscopy. The coercivity of the powders increased with a decrease in particle size, and Nd(FeMo)12N1.52 nano-powders with a coercivity of 3800 Oe was prepared by 70 h of surfactant-assisted high energy ball milling. Nd(FeMo)12N1.52 powders obtained exhibit an HA of 11 T and TC of 598 K.

Magnetic anisotropy and enhanced remanence in textured polycrystalline MnAlCuC-based flakes

Anisotropic MnAlCuC and MnAlCuC/Fe polycrystalline flakes have been produced by surfactant-assisted ball milling. The [001] textured MnAlCuC flakes were formed via continuous basal cleavage along the (110) planes of the microparticles during the surfactant-assisted high-energy ball milling. The c-axes of most the grains are parallel to the flake surface. The remanent magnetization (Mr) of annealed MnAlCuC/Fe has an enhancement of around 62.4% compared with uncoated powders. A high coercivity up to 207.4 kA/m of as-milled MnAlCuC flakes was obtained due to the domain wall pinning effect of the defects and the associated strained areas.

Crystal structure and magnetic properties of (Nd,Tb)2Fe14B nanoflakes prepared by surfactant-assisted ball milling

The microstructure, crystal structure, and magnetic properties were studied for (Nd,Tb)2Fe14B nanoflakes prepared by surfactant-assisted high-energy ball milling (HEBM). Effects of ball-milling time on the c-axis crystallographic alignment, morphology, and magnetic properties of (Nd,Tb)2Fe14B nanoflakes were systematically investigated. X-ray diffraction (XRD) results indicate that the average crystal grain size of the nanoflakes decreases from 60 nm of 1 hour milling to 33 nm of 7 hours milling. The nanoflakes milled for 3 hours bear an average thickness of 100 nm and an average diameter of 2 μm leading to a high aspect ratio of 20. In addition, the intensity ratio of I(006)/I(105) indicates that the degree of c-axis crystal texture increases first, peaks for 3 hours, then drops with increasing the milling time. Meanwhile, the coercivity (Hc) of the nanoflakes drops monotonically. The remanence (Mr) of nanoflakes milled for 3 hours in the easy axis direction is 11 kG, while the Mr in the hard axis direction is 1.8 kG, indicating a strong magnetic anisotropy. The optimal magnetic properties of Mr of 11 kG, and Hc of 7 kOe, (BH)max of 24.7 MGOe have been achieved.

Magnetization reversal behavior of SmCo6.6Nb0.4 nanoflakes prepared by surfactant-assisted ball milling

In this paper, the recoil loops of SmCo6.6Nb0.4 nanoflakes prepared by the surfactant-assisted high energy ball milling (SA-HEBM) were systematically studied. The recoil loop openness was observed in both the aligned and non-aligned samples. Reversible and irreversible portions of the demagnetization process derived from the recoil loop were also investigated. For both the aligned and non-aligned samples, reversible portion (▵mrev) is too small to determine the coercivity. Irreversible portion (▵mirrev) shows similar tendency, i.e. increasing slowly at low reverse field and then growing up rapidly after a critical field (nucleation field Hno). The demagnetization process can be described as following: the reversible demagnetization is dominant when the applied reverse field is lower than 8 kOe, under which the irreversible nucleation also occurs. The reverse domain walls are pinned by the grain boundaries until the reverse field is larger than 8 kOe. With increasing field, the pinning effects are weakened and the rapid reversible demagnetization starts. Finally, the demagnetization process is accomplished. The values of ΔM in the Henkel plots are totally opposite for the aligned and non-aligned SmCo6.6Nb0.4 nanoflakes.

Magnetic properties and coercivity mechanism of Sm1-xPrxCo5 (x=0-0.6) nanoflakes prepared by surfactant-assisted ball milling

Sm1-xPrxCo5 (x=0-0.6) nanoflakes with CaCu5 structure were successfully prepared by surfactant-assisted high-energy ball milling (SAHEBM). The crystal structure and magnetic properties of Sm1-xPrxCo5 (x=0-0.6) nanoflakes were studied by X-ray diffraction and vibrating sample magnetometer. Effects of Pr addition on the structure, magnetic properties and coercivity mechanism of Sm1-xPrxCo5 nanoflakes were systematically investigated. XRD results show that all the nanoflakes have a hexagonal CaCu5-type (Sm, Pr)1Co5 main phase and the (Sm, Pr)2Co7 impurity phase, and all of the samples exhibit a strong (00l) texture after magnetic alignment. As the Pr content increases, remanence firstly increases, then slightly reduced, while anisotropy field (HA) and Hci of decrease monotonically. Maximum energy product [(BH)max] of the flakes increases first, peaks at 24.4 MGOe with Pr content of x = 0.4, then drops again. Magnetization behavior analysis indicate that the coercivity mechanism is mainly controlled by inhomogeneous domain wall pinning, and the pinning strength weakens with the increased Pr content, suggesting the great influence of HA on the coercivity of flakes.

High-frequency electromagnetic properties of soft magnetic Nd2Co17 micron flakes fractured along c crystal plane with natural resonance frequency exceeding 10 GHz

Planar anisotropy Nd2Co17 flakes fractured along c crystal plane were fabricated by surfactant-assisted high-energy ball milling technique. The magnetic flakes have a diameter range of 5–20 μm and a typical thickness of approximately 120 nm. The frequency dependence of complex permeability of Nd2Co17 epoxy resin composite has been investigated in the frequency range of 0.1–18 GHz. The measurement results show that the natural resonance frequency reaches 12.5 GHz while the initial permeability survives up to 2.26. The superior high frequency properties come from the large out-of-plane anisotropy field and the flake structure fractured along the c crystal plane of Nd2Co17. The planar anisotropic Nd2Co17 flakes have significant potential applications in the high-frequency devices working in the frequency beyond 10 GHz.

Effect of flake thickness on coercivity of nanocrystalline SmCo5 bulk prepared from anisotropic nanoflake powder

In this study, nanocrystalline SmCo5 bulk magnets were prepared by hot-pressing of nanoflake powders fabricated via surfactant-assisted high energy ball milling. Effect of the flake thickness on magnetic coercivity of the SmCo5 bulk was investigated. Anisotropic SmCo5 nanoflakes with thickness between 100 and 1000 nm were prepared by varying the milling parameter of ball-to-powder weight ratio. XRD analysis revealed that as-milled flake powders possessed nanocrystalline grains with no observable oxide peaks. The coercivity of the flake powders varied between 19.9 and 21.3 kOe for 1000 nm to 100 nm thick flakes, which indicated that the flake thickness in this range had no obvious effect on the coercivity of the powders. However, the coercivity of the bulks showed a strong dependence on the flake thickness. The bulk coercivity value of 10.97 kOe corresponding to the flake thickness of 100 nm, was 80% higher compared to the bulk prepared with the flakes of 1000 nm. XRD results on compacted samples did not show any grain growth, however, Sm2O3 and free Co were detected in SmCo5 bulks and their content increased with reduced flake thickness. Interestingly enough the bulk coercivity was not deteriorated with the presence of Sm oxide and Co.

Microstructure and Improved Coercivity of Mn<sub>1.33</sub>Ga Nanoflakes by Surfactant-Assisted Ball Milling

In recent years, Mn x Ga alloys with tetragonal structure have attracted much attention because of the erratic fluctuation of rare earth supply and especially the tunable magnetic properties from fer-rimagnetic to ferromagnetic by varying Mn content. It is theoretically estimated that MnGa compound in L1 0 structure owes high anisotropy constant K u of 26 Mergs/cm3 and magnetization Ms of 845 emu/cm3, and thus can be regarded as a potential candidate for rare-earth-free permanent magnets [1-2]. At present, surfactant-assisted high-energy ball milling (HEBM) method has been regarded as one of the effective ways to realize high coercivity for magnetic materials with large anisotropy. It was reported [3-4] that high-aspect-ratio single-crystal or textured polynanocrystalline flakes of Sm-Co-based permanent magnetic materials with a submicron or nanosize thickness and high coercivity can be achieved. In this study, textured rare-earth-free Mn 1.33 Ga polycrystalline nanoflakes were prepared by surfactant-assisted HEBM in heptane with 15wt. % oleic acid (OA), and the effects of milling time on structure and magnetic properties were also investigated.

FeCo Coating on SmCo<sub>5</sub> Nanochips by a Sonochemical Method

To study the influence of soft magnetic phase coating on magnetic properties of hard/soft phase nanocomposite materials, the coating of soft magnetic FeCo on hard magnetic SmCo <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> nanochips was performed via a sonochemical process. First, anisotropic hard magnetic SmCo <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> nanochips were prepared by surfactant-assisted high-energy ball milling in the presence of oleic acid as a surfactant and heptane as a solvent. Then, the soft magnetic FeCo was coated on SmCo <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> nanochips by the reduction of FeCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and CoCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> with hydrazine using ultrasonic waves in the presence of NaOH. The amount of the soft phase coating on the hard magnetic nanochips was controlled by varying the initial ratio of soft-phase precursors to hard magnetic particles during the reaction. The soft-phase coating on the hard phase chips has lead to an enhanced remanence due to an exchange coupling between the soft and the hard magnetic phases at optimal hard/soft phase ratios. The composite chips also show a strong magnetic anisotropy when aligned in a magnetic field. The anisotropic SmCo <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> /FeCo core/shell nanocomposite chips are promising candidates as building blocks for high-performance anisotropic nanocomposite bonded or fully dense magnets via a bottom-up fabrication approach.

Polycrystalline Nd2Fe14B/α-Fe nanocomposite flakes with a sub-micro/nanometre thickness prepared by surfactant-assisted high-energy ball milling

A surfactant-assisted high-energy ball milling technique was employed to synthesize Nd2Fe14B/α-Fe nanoparticles and nanoflakes from melt-spun nanocrystalline powders. The microstructure evolution in ball milling process was investigated. In the beginning stage (0–4h) of ball milling, raw powders were crushed into micrometre-sized particles. While flakes were mainly formed by reducing thickness of particles via peeling layer by layer along preferential planes in the late stage (8–16h). The selected area electron diffraction and high-resolution transmission electron microscopy images show that preferential cleavage planes are basal planes. With ball milling proceeding, more and more defects were induced by ball milling. As a result, the coercivity and remanence decreased to 1.6kOe and 3.2kGs, respectively. After 16h ball milling, the exchange decoupling occurred due to severe amorphorization. A weakly-textured nanocomposite magnet was fabricated after 12h ball milling and the anisotropy in magnetic properties can be further improved by employing settling down process to select particle size and aligning particles in external field.

Crystallographic alignment evolution and magnetic properties of anisotropic Sm0.6Pr0.4Co5 nanoflakes prepared by surfactant-assisted ball milling

The microstructure, crystal structure and magnetic properties were studied for Sm0.6Pr0.4Co5 nanoflakes prepared by surfactant-assisted high-energy ball milling (SAHEBM). Effect of ball-milling time on the c-axis crystallographic alignment, morphology and magnetic properties of Sm0.6Pr0.4Co5 nanoflakes was systematically investigated. With increasing milling time from 1h to 7h, the intensity ratio between (002) and (111) reflection peaks indicating degree of c-axis crystal texture of the (Sm, Pr)Co5 phase increases first, peaks at 3h, then drops again, revealing that the strongest c-axis crystal texture was obtained in the nanoflakes milled for 3h. On the other hand, the coercivity (Hci) of the flakes increases gradually from 1.71 to 14.65kOe with the increase of ball milling time. As a result, an optimal magnetic properties of Mr of 10.23kGs, Hci of 11.45kOe and (BH)max of 24.40MGOe was obtained in Sm0.6Pr0.4Co5 nanoflakes milled for 3h, which also displayed a high aspect ratio, small in-plane size, pronounced (001) out-of-plane texture.

Structural characterization and microwave properties of chemically functionalized iron particles obtained by high-energy ball milling in paraffin-containing organic environment

Magnetodielectric composites comprising dispersed metal particles as magnetic filler and organic dielectrics as a host matrix are of great importance because of both technological and fundamental interests. Surfactant-assisted high-energy ball milling in organic media is successfully used for the dispersion and surface modification of metal particles. In this paper, we have carried out structural and chemical characterization of iron particles (bulk/surface) prepared in paraffin-containing environment. The study was performed with high-resolution X-ray spectroscopic techniques using synchrotron radiation from BESSY II/HZB Berlin and DORIS/DESY Hamburg. It has been shown that high-energy ball milling leads to nanofragmentation of iron grains and formation of bare metal surface which is very active in dehydrogenation of organic molecules. The paraffin molecules are destructed with the accumulation of polycondensed aromatic structures containing covalently-bound paraffin residues on the iron surface. Under dry milling (without solvent), the organic environment molecules decompose almost completely, while under wet milling, the destruction of paraffin and perfluorononanoic acid molecules slows down significantly. An addition of perfluorononanoic acid along with n-heptane into the milling liquid results in sharp change in microwave characteristics, which may be attributed to formation of platelet-shaped particles with the surface covered with long-chain residues of paraffin and surfactant molecules.

Effects of Milling Conditions on Nano-scale MnFe(P,Si) Particles by Surfactant-assisted High-energy Ball Milling

The influence of the milling conditions on the nano-scale MnFe(P,Si) particles obtained by surfactant-assisted high-energy ball milling has been investigated by X-ray diffraction (XRD) and magnetic measurements. The presence of surfactant oleic acid prevents the re-welding of crushed particles and enhances the dispersion of nanoparticles in the solvent during the ball milling. The XRD peak intensities decrease and the peaks broaden with increasing milling time, indicating a decrease in grain size. For increasing milling time, the spontaneous magnetization becomes lower and the thermal hysteresis becomes smaller. The surfactant concentration does not have a strong impact on the magnetic properties of the obtained nanoparticles, which is consistent with the X-ray diffraction data showing the same patterns at different surfactant concentrations.