FeCo Alloy Particles Research Articles

Characterization of magnetic FeCo particles with controlled bimetallic composition

In this study, six bimetallic FeCo particles were synthesized via the hydrothermal method, employing hydrazine hydrate as a reducing agent. These particles were synthesized at specific Fe:Co ratios of 1:0, 3:1, 1:1, 1:3, 1:9 and 0:1. The synthetic feeding of Fe:Co is of fundamental importance as it not only modulates the composition of the particles but also exerts control over their structural, morphological, and performance attributes. X-ray diffraction (XRD) analysis revealed that for particles synthesized from pure ferrous salt and pure cobalt salt, the former exhibited a Fe3O4 spinel structure, while the latter presented an hcp-type metallic Co structure. Conversely, for the remaining four Fe:Co synthetic feedings, the structure of FeCo bimetallic alloys exhibited a gradual transformation from an Fe-based bcc structure to a Co-based bcc structure, eventually culminating in a Co-based hcp structure as the Co content increased. Scanning electron microscopy (SEM) images indicated that particles prepared with a Fe:Co feeding ratio of 1:0 and 3:1 manifested as cube-shaped particles with approximate sizes of 200 nm and 100 nm, respectively. Particles synthesized with a 1:1 Fe:Co ratio exhibited pyramid-like shapes accompanied by small spinel structures. In contrast, those prepared with a 3:1 and 9:1 Fe:Co feeding ratio displayed a flower-like morphology with particle sizes around 10 µm, while particles synthesized using pure cobalt salts assumed a palm frond-like appearance. Moreover, the investigation into thermal stability established that FeCo alloy particles exhibited superior resistance to air oxidation when compared to pure Co particles. The magnetic studies indicated that all the particles were paramagnetic materials, with their magnetic properties being contingent on the composition. Notably, the particles synthesized with synthetic feedings of 1:1 and 3:1 exhibited the highest saturation magnetization of 151.80 emu·g−1 and the lowest saturation magnetization of 62.79 emu·g−1, respectively. These findings hold significant promise for the development of stable and finely-tailored magnetic particles with diverse potential applications in technology.

PANI/FeCo@C composite microspheres with broadband microwave absorption performance

Composite microwave absorbers with multiple loss mechanism have attracted more and more attention. Herein, we report a strategy of step-by-step synthesis of polyaniline (PANI)/FeCo@C composite microspheres by hydrothermal, calcination and in-situ polymerization. The multilayer heterogeneous interfaces of microspheres and the multi dipole center of polyaniline molecular chain significantly improve the polarization relaxation loss. Polyaniline on the surface connects the microspheres to form a conductive network, which effectively enhances the conduction loss. FeCo alloy particles also provide a certain magnetic loss. Their synergistic effect makes the composite microspheres exhibit good microwave absorption performance. When the thickness of P2 is only 1.7 mm, it could exhibit an effective absorption bandwidth (EAB) of 5.31 GHz and maximum reflection loss (RL) of −33.86 dB. Moreover, we optimized the macro structure of the absorber through gradient design, and successfully extended the effective absorption bandwidth to 11.81 GHz by introducing multiple interference. This work provides a useful reference for the comprehensive optimization of micro regulation and macro design of composite microwave absorbers.

Facile synthesis of carbon quantum dot ‑carbon nanotube composites on an eggshell-derived catalyst by one-step chemical vapor deposition

Carbon nanotubes (CNTs) based composites such as carbon quantum dot-CNT (CQD-CNT) demonstrate excellent performance in the fields of bioimaging and biomedicine. Nevertheless, CQD-CNT composites were mostly prepared by multiple and cumbersome steps, including the synthesis of CQDs, functionalization of CNTs and subsequent assembly of CQDs on CNTs. Here, a facile one-step synthesis of CQD-CNT was successfully conducted on an active CaO supported FeCo (Fe-Co/CaO) catalyst derived from waste eggshells via chemical vapor deposition, and other CNT-based composites such as carbon fiber-graphene sheet-CNT (CNF-GNS-CNT) and CNF-CNT as well as CNTs were also synthesized by modulating the catalyst support, growth temperature and growth time. The catalysts and produced CNTs and CNT-based composites were analyzed by multiple characterization tools. The results showed that nano CaO supported FeCo catalyst only synthesized MWCNTs, whereas Fe-Co/CaO was favorable for the synthesis of CNT-based composites. Cobalt oxides and iron oxides were well dispersed in the fresh Fe-Co/CaO catalyst, and FeCo alloy particles of different sizes were formed after catalyst reduction and heating to different growth temperatures. At a low growth temperature of 750 °C, CNF-GNS-CNT was synthesized on Fe-Co/CaO, in which CNTs and CNFs were grown on small (~10 nm) and larger (~30 nm) metal particles, respectively, whereas GNSs were mainly produced on CaO. At a high growth temperature of 850 °C, surface area and pore volume of catalysts decreased greatly, and higher solubility of carbon atoms in metal particles resulted in less desorbed CHx, which is not favorable for the growth of GNSs. Instead, CQD-CNT composites were selectively synthesized at 850 °C, which was ascribed to the oxidation corrosion of CNFs by OH radicals, but with the extension of growth time, only CNTs were produced due to the complete oxidation of CQDs. Further, larger metal particles were produced at a higher temperature of 950 °C, which were wrapped by graphite, and the partial deactivation of metal particles led to a few small particles remained active for CNT growth with a low carbon yield.

The influence of highly dispersed preparations on metabolism and productivity of young cattle

Preparations of highly dispersed particles of trace elements are increasingly used in animal husbandry. This is determined by their extraordinary biological properties such as the ability to penetrate into tissues and organs, a high surface area, and so on. One of the promising directions for using highly dispersed particles both in the post-embryonic and embryonic periods of animal development is the use of trace elements as sources. This is determined by the relatively lower toxicity, higher bioavailability of elements from preparations of highly dispersed particles, which reduces the load on the environment and allows you to produce products enriched with minerals. The purpose of the research was to study the effect of highly dispersed drugs on rumen digestion, the composition of the rumen microbiome, metabolism and productivity of young cattle. A comprehensive assessment of the use of highly dispersed SiO2 and FeCo preparations in cattle nutrition has been provided in the paper. The digestibility of feed, metabolism, and productivity of young cattle when feeding highly dispersed particles have been studied. An unusual fact of increasing bacterial biomass when using highly dispersed particles of silicon dioxide in animal feeding has been described. A method for increasing the digestibility of feed components by ruminants through the use of highly dispersed FeCo alloy particles has been proposed. As follows from the data obtained the use of highly dispersed particles allowed to increase the live weight of experimental young animals to 413 kg in the 1st experimental group and 416 kg in the 2nd experimental group, which was by 11 (P ≤ 0,01) and 14 kg (P ≤ 0,01) higher than the control indicator. As follows from the analysis of the data obtained, the profitability of rearing young animals in the 1st and 2nd experimental groups was by 2,4 and 2,2 % higher than the same indicator calculated for the control group.

Tailoring complex permittivity and permeability to enhance microwave absorption properties of FeCo alloy particles through adjusting hydrazine reduction process parameters

Owing to their high permeability, metallic soft magnetic materials exhibit high potential as microwave absorbers. The great challenge in designing desirable absorption properties from these materials is their large electrical permittivity at microwave frequencies. So, decreasing their permittivity within acceptable limits while keeping permeability at sufficiently high or improved levels is considered an important requirement for matching impedance and obtaining excellent electromagnetic (EM) absorption properties. In the present research, FeCo alloy particles produced employing by a simple wet chemical reduction process with the intention of investigating dependence of their EM properties on synthesis parameters. The characterizations were done with the help of x-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The intrinsic EM properties (εr, μr) in a frequency range of 2–18 GHz were measured by a vector network analyzer (VNA) for the paraffin composites containing obtained products. The results indicated that the concentration of NaOH and metallic salts as the synthesis precursors can tune the permittivity and permeability. Under optimum conditions, bandwidths of 7.3 and 5.5 GHz with thicknesses of only 1.2 and 1.5 mm were obtained respectively. Also, Reflection loss (RL) of −45 dB was attained. The excellent EM absorption properties demonstrated that the synthesized FeCo alloy may be an ideal absorber having both a wide absorption bandwidth and a low thickness.

Hydrothermal synthesis of polyhedral FeCo alloys with enhanced electromagnetic absorption performances

Polyhedral FeCo alloys with grain sizes of 1–2 μm were synthesized by using a low-temperature hydrothermal method. The effects of heating time and molar ratio on microstructure and electromagnetic absorption performances of the alloys were studied. Their growth follows the Ostwald ripening mechanism. At the given reaction time of 10 h, as the molar ratio of Fe:Co was varied from 3:7 to 4:6, morphology of the alloy particles was changed from flower-like to polyhedral shape. Specifically, the Fe6Co4 sample had superior impedance matching, while a strong dielectric resonance at about 10 GHz was observed in the complex dielectric constant imaginary part, thus resulting in significantly enhanced electromagnetic absorption performance. It exhibited an optimum reflection loss (RL) value of −52.20 dB at 10.48 GHz, with a sample thickness of 1.7 mm. Meanwhile, the RL of −10 dB was over the frequency range of 7.6–13.6 GHz, covering the Ku-band and the entire X-band. Most importantly, the matching thickness of all the samples was less than 2 mm. These results indicate that the FeCo alloy particles are suitable for electromagnetic absorbing materials at the C, X and Ku bands.

Morphology and magnetic properties of FeCo particles synthesized with different compositions of Co and Fe through co-precipitation, flux treatment, and reduction

Abstract FeCo alloy particles with Co to Fe compositions ranging from molar ratios of 0:1–1:1 in a precursor were synthesized through co-precipitation, flux treatment, and reduction. By adding Co2+ to Fe ions, particle size was remarkably reduced to 10–50 nm from 50 to 250 nm of Fe particles. The lattice parameter calculated from the (1 1 0) peak of the (bcc) structure decreased from 0.2870 nm in Fe particles to 0.2854 nm in FeCo particles. The coercive force increased with increasing Co/Fe composition ratio, showing a value of approximately 80 kA/m at the Co/Fe composition ratio of 1.0, at which the lattice parameter corresponded to a composition of approximately Fe62Co38. A maximum saturation magnetization of approximately 160 Am2/kg was obtained at a Co/Fe composition ratio of around 0.2–0.5.

Prussian blue analogues derived magnetic FeCo alloy/carbon composites with tunable chemical composition and enhanced microwave absorption

A series of magnetic FeCo alloy/carbon composites have been successfully prepared through in situ pyrolysis of Prussian blue analogues (PBAs) with different Fe/Co ratios. The Fe/Co ratio can affect the crystalline phase, particle size, and magnetic property of the FeCo alloy particles, as well as the relative graphitization degree of the carbon frameworks. As a result, the electromagnetic functions of these composites will be highly associated with the Fe/Co ratio, where high Co content is beneficial to the formation of strong dielectric loss and moderate Co content can facilitate the magnetic loss. When Fe/Co ratio reaches 1:1, the as-obtained composite (sample S4) displays excellent reflection loss characteristics with powerful absorption in a very broad frequency range (over −10 dB in 3.2–18.0 GHz), which is superior to those of single magnetic metal (Fe or Co)/carbon composite derived from PBAs, as well as many previously reported FeCo alloy/carbon composites. Electromagnetic analysis reveals that the excellent microwave absorption of sample S4 benefits from its preferable matching of characteristic impedance and good attenuation ability toward incident electromagnetic waves. These results provide new insight into the fabrication of carbon-based magnetic composites with enhanced microwave absorption by rationally manipulating the chemical composition of magnetic components.

Tuning microwave permittivity coefficients for enhancing electromagnetic wave absorption properties of FeCo alloy particles by means of sodium stearate surfactant

FeCo is well known as one of the most important Fe base alloys due to its unique properties. In this research FeCo were prepared by a wet chemical reduction method. Sodium stearate (SS) surfactant was used in different amounts as a modifier. XRD and FE-SEM were used to study phase and morphology characteristics of the products. Paraffin matrix composite samples containing 80%wt FeCo were prepared to measure the frequency dependence of the permeability and the permittivity utilizing Vector Network Analyzer (VNA). The results showed that by an increase in SS amounts, the permittivity was decreased. Reflection loss (RL) plots in the frequency range of 1–18 GHz demonstrated that the most wideband RL plots were for the sample with 0.004 mol SS because of its good impedance matching characteristics. For this sample, the RL bandwidth (−10 dB) by a thickness of 2.7 mm occurred 2.2 GHz in C band. Also, it covered the whole range of X and Ku bands having thicknesses of 1.5 mm and 1.1 mm, respectively. The maximum RL of −44 dB was obtained in the frequency of 5 GHz. The results of the research indicate that the composites containing FeCo particles are suitable candidates applicable as thin and wideband microwave absorbers.

Heterogeneous nucleation in the polyol process for the synthesis of FeCo alloy powders

Here, we report a polyol method to prepare monodispersed FeCo alloy particles with Pt seeds added in the production of nanoparticles. The prepared samples were characterized by using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and magnetic measurements. Structural studies revealed that the FeCo nanoparticles had a body-centered cubic (BCC) structure. FE-SEM analysis demonstrated a sphere morphology for the FeCo alloy particles. The size of the FeCo nanoparticles could be well tuned by changing the number of Pt-seed partices in the FeCo alloy. The magnetic properties of the FeCo alloys were investigated as a function of the Pt-seed concentration and temperature. The saturation magnetization and coercivity of the FeCo nanoparticles were found to depend on the molar ratio of Fe/Co, as well as the number of Pt-seeds, and increased with increasing FeCo concentration. A higher value of the saturation magnetization, 218 emu/g, was obtained for the 0.07-M concentration of FeCo alloy. In the process of producing an FeCo alloy powder by heterogeneous nucleation, a powder having minute sizes could be produced under the experimental conditions of a Pt-seed-added temperature of 90 °C and a Pt/FeCo mole ratio of 8 × 10−5, and showed far superior properties.

Particle size dependence in thermal disorder/order transformation of FeCo alloy

FeCo alloy particles synthesized by liquid phase reduction are disorder distribution of the alloying elements in bcc crystalline lattice. The particle size dependence of thermally ordering behavior during heating was investigated. Superlattice lines such indices as 100, 111 etc., which appear in the x-ray diffraction pattern when the atomic arrangement is ordered, are difficult to detect due to quite small difference between Fe and Co in the atomic x-ray scattering factor. In this study, the energy near to Fe K absorption edge for incident x-ray was used in order to apply the anomalous x-ray dispersion effect. From results of the in situ heated x-ray diffraction experiments using the Synchrotron radiation source, different ordering-onset temperature was observed for the two samples with different particle size. This is considered due to a difference on the lattice distortion and its elimination during heating.

Characteristics of a Fe-Co Alloy-Dispersed Al2O3 Nanocomposite Powder Synthesized by a Solution Chemistry Route

An optimum route to synthesize a Fe-Co alloy-dispersed Al2O3 nanocomposite powders and their magnetic properties were investigated. Nanocomposite powders of Al2O3 and Fe-Co alloys were prepared by the solution chemistry method using Al2O3 and metal nitrates powders. Al2O3/Fe-Co alloy powders were sythesized by calcination at 350℃ and hydrogen reduction at 700℃ of Al2O3, Fe- and Ni-nitrate powders. Microstructural analysis for the nanocomposite powders synthesized by ball milling and a hydrogen reduction process showed that the Fe-Co alloy particles with an average size of 20 nm were well distributed on the surface of the Al2O3 powders. The ferromagnetism of the nano-sized Fe-Co alloy contributed to the magnetic properties of the nanocomposite powders. The increase in coercive force was explained as being due to nano-sized particles of the Fe-Co alloy.

Synthesis and microwave absorbing properties of FeCo alloy particles/graphite nanoflake composites

Exfoliated graphite was processed into nano-sized flakes by jet milling, ultrasonication and acid treatments, and then FeCo alloy particles were uniformly deposited onto the surface of the prepared graphite nanoflakes (GNFs) by a co-deposition and subsequent annealing process in reducing atmosphere. The FeCo-GNFs composites demonstrate good soft magnetic performance and effective microwave absorption, especially in the lower frequency range. The strongest absorption reaches −30.6 dB at 7.4 GHz with a coating thickness of 2 mm. Furthermore, effective microwave absorption at different frequency bands can be acquired by adjusting the coating thicknesses and filling ratios of FeCo-GNFs absorber. Considering the low cost and high efficiency, the FeCo-GNFs composites have great potential as microwave absorber for practical applications.

Magnetic, electric and dielectric properties of FeCo alloy nanoparticles dispersed in amorphous matrix

AbstractNanocrystalline Fe53Co47 alloy was synthesized by a single‐step transmetallation chemical method at room temperature. The Fe53Co47 alloy nanoparticles of 77 and 47 wt% were dispersed in silica matrix by the sol–gel process using tetraethyl orthosilcate. Structural studies reveal that the as‐prepared alloy powders are in bcc phase and silica is in an amorphous state. The phase‐transition temperature and Mössbauer spectra analysis of the Fe–Co alloy establishes the homogeneous alloy formation. A saturation magnetization of 218 emu/g was obtained for pure FeCo alloy at room temperature. Scanning electron microscopic analysis demonstrates the hollow‐sphere morphology for FeCo alloy particles. Magnetic nanocomposite consisting of 47 wt% FeCo–silica shows enhanced thermal stability over the native FeCo alloy. Electrical and dielectric properties of 47 wt% FeCo–silica nanocomposites were investigated as a function of frequency and temperature. It was found that the dielectric constants and dielectric loss were stable throughout the measured temperature (310–373 K). Our results indicate that FeCo–silica nanocomposite is a promising candidate for high‐frequency applications.

Alloy Compositional Gradation in Surface Layer and Oxidation Resistance on Chemical Synthesized FeCo Nanoparticles

X-ray photoelectron spectroscopy (XPS) has been used for analyzing the surface composition of polyol process-derived Fe30Co70, Fe50Co50, and Fe70Co30 alloy nanoparticles with diameters 50, 100 and 150 nm, respectively. These Fe-Co alloy particles have high oxidation resistance in the atmospheric environment even though their particle size is so small. The XPS results revealed that the concentration of iron at the surface of the as-synthesized Fe-Co alloy nanoparticles was lower than that in bulk and increased with increasing bulk cobalt composition, although the surface of nanoparticles was covered with native oxide layer formed during their exposure to atmosphere. This low concentration of iron and very thin oxide layer at the surface are considered to protect the particle from oxidation. The concentration of iron at the surface of Fe70Co30 nanoparticles increased when they were annealed at 573 K in N2 and H2 atmosphere. The results indicate that nonuniformity of the chemical composition between particle surface and core occurs during the formation of the same in polyol, and atomic diffusion at the surface of particle can occur even at relatively low temperature. The above is considered to arise from the difference in the chemical characteristics of iron and cobalt during co-precipitation in the polyol.

Effect of Cu seed on the synthesis and characterization of FeCo alloy nano-particles by using polyol method

Fine metal particles with uniform shape, narrow size distribution and high purity are increasingly needed for specific uses in high tech industrial application. We report the direct chemical synthesis of FeCo alloy particles using the mixture of FeCl2·4H2O, Co (Ac)2·4H2O (Ac: acetate) and NaOH in ethylene glycol, and then obtained FeCo alloy particles better dispersed by adding the polyvinylpyrrolidone (PVP) and also the size could be controlled by adding copper. The prepared nano-particles were characterized using FESEM, XRD and VSM. The mean diameter of these particles was varied in the range of sub-micrometer to nanometer with metal-ion concentration. FeCo particles showed the typical soft magnetic properties.

Structure and magnetic moments of mass-filtered deposited nanoparticles

Mass-filtered 3d transition metal nanoparticles have been produced by means of an ultrahigh vacuum compatible arc cluster ion source. High resolution transmission electron microscopy images of individual Fe, Co, and FeCo alloy particles with diameters of about 12 nm reveal the crystalline structure of the nanoparticles. X-ray absorption spectroscopy confirms the purity of the particles after in situ deposition. Analysis of the x-ray magnetic circular dichroism reveals bulklike total magnetic moments in all cases and strongly enhanced orbital moments for the iron nanoparticles. Furthermore, the data hint at a chemically ordered alloy in the case of FeCo particles.

Synthesis of Fe-Co Alloy Particles by Modified Polyol Process

The successful synthesis of Fe-Co nanoparticles by using a modified polyol process is reported. The formation of the alloy nanoparticles was confirmed by X-ray diffraction and X-ray extended absorption fine structure analyses. The concentration of iron in these particles could be varied between 40% and 90% by controlling the reaction conditions such as initial Fe/Co ratio, reaction temperature and hydroxyl ion concentration. The shape of the particles changed from spherical to cubic when the concentration of Fe was increased from 40 to above 60 at. %. The highest magnetization of 225 emu/g was recorded for Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">70</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">30</sub> nanoparticles. The magnetization of these particles decreased by about 20% when exposed to severe oxidizing atmosphere for seven days

Polyol Process for Fe-Based Hard(fct-FePt) and Soft(FeCo) Magnetic Nanoparticles

The polyol process and the parameters influencing the synthesis of metal and alloy nanoparticle are discussed. Then, the synthesis strategies to obtain hard (Fe-Pt) and soft (Fe-Co) nanoparticles by using polyol process is presented. Under optimum synthesis conditions, partially ordered Fe-Pt nanoparticles with an average grain diameter of 8 nm exhibited a coercivity of 460 kA/m in the as-synthesized state. In the case of Fe-Co alloy particles, synthesis technique to prepare particles with varying Fe concentration in the size ranging between 300 and 50 nm is reported

錯体重合法を応用した炭素／Ｆｅ‐Ｃｏ合金複合材料の調製と磁気特性

We have successfully prepared Carbon/Fe-Co alloy composites starting from metal organic precursors synthesized by polymerized complex method. The carbon/Fe-Co alloy composites were obtained after the carbonization of the precursors heat-treated at ambient pressure and lower temperatures ranging from 500 to 700°C in N2 gas flow. Crystalline sizes of both carbon matrix and Fe-Co alloy particles were determined by X-ray diffraction measurements as a function of the Co concentration and the carbonized temperature. The alloy particles were widely dispersed in the carbon matrix and the particle size carbonized at 600°C was about 20∼50 nm observed by scanning electron microscopy. The composite carbonized at 600°C had very small coercivity of 14 Oe and exhibited relatively large permeability spectra at frequency of GHz range.