Fe-Co Powders Research Articles

Mössbauer and magnetic properties of graphene oxides coatings on Fe and FeCo powders for high frequency applications

Mössbauer and magnetic properties of graphene oxides coatings on Fe and FeCo powders for high frequency applications

Hierarchical core-shell FeCo@SiO2@NiFe2O4 nanocomposite for efficient microwave absorption

Narrow absorption band width is a common problem faced by current electromagnetic wave absorbing materials. It is urgent but challenging to explore new design solutions to solve this problem. Herein, a core-shell FeCo@SiO2 @NiFe2O4 composite was prepared by chemical co-precipitation method. The effects of calcination temperature on the structure of the cladding layer, magnetic properties and wave absorption properties of the composite powder were investigated. Results showed that the particles of NiFe2O4 @SiO2 cladding layer uniformly covered on the surface of FeCo powder gradually gathered and grew with the increase of calcination temperature from 500 to 800 ℃, resulting in the destruction of the local structure of the coating layer. The composite powder calcined at 700 ℃ has a uniform and dense coating layer structure, and has high saturation magnetization, high coercivity and excellent electromagnetic wave absorption performance. Consequently, the composite powder calcined at 700 °C has a maximum reflection loss of −52.38 dB with a frequency of 9.5 GHz when the matching thickness is 2.65 mm, and the EAB is up to 8.5 GHz with a matching thickness of 2.24 mm. The electromagnetic wave loss mechanism of the powder originates from the excellent impedance matching characteristics, high electromagnetic wave attenuation constant, multiple dielectric relaxation processes, multiple interface polarizations and high magnetic loss as well as high dielectric loss capability.

Structural and magnetic properties of Ni substituted FeCo alloy obtained through polyol process

Fe alloy powders with optimum magnetic properties are in demand for the fabrication of soft magnetic composites that find applications in power electronics and more electric vehicles. Fe-Co-Ni alloys with particles exhibiting spherical morphology and body-centered cubic structure are synthesized using a facile instant reduction polyol process. Curie temperatures from 840 to 760 °C are obtained with Ni substitution in the range of 7–14 at.%. The effective magnetic anisotropy realized using a modified law of approach to saturation and the Curie temperature studies suggests an additional amorphous phase that affects the magnetic behavior. The multidomain Fe-Co-Ni alloy particles have the potential for high-temperature applications as their effective magnetic anisotropies of 20–25 kJ/m3 are lower than Fe and FeCo powders.

Influence of Pr6O11 addition on structural and magnetic properties of mechanically alloyed Fe65Co35 nanoparticles

This work focuses on the synthesize of nanostructured (Fe65Co35)100-x (Pr6O11)x (x = 0, 5) powders using high energy ball milling. The influence of Pr6O11 on structural, morphological and magnetic properties of Fe65Co35 nanoparticles were carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM) with a dispersive energy analyzer (EDS), vibratory sample magnetometer (VSM) and differential scanning calorimetry (DSC). Results show that the praseodymium oxide addition increased the decrement rate of the crystallite size with milling time of about 27 % and decreased the increment rate of the internal micro-strain of 50 %. Moreover, because of its high grain fragmentation tendency, Pr6O11 increases the hardness and brittleness of Fe-Co powders. Moreover, it minimized the cold welding between Fe-Co ductile particles leading to a significant decrease in the average particle size (~1µm). The magnetic measurements conducted at room temperature show that the saturation magnetisation (Ms) and the coercivity (Hc) increased with milling time in both compositions. A low Ms and high Hc values were detected in (Fe65Co35)95 (Pr6O11)5 nanoparticles. The results demonstrated a soft ferromagnetic nature in all of the synthesized nanoparticles with Ms in the range 207 – 216 emu/g and Hc is found to be 113 Oe.

Chemically Synthesized FeCo Powder for Advanced Applications

Very weak stray magnetic fields, H ∼ 10− 4 Oe, of an assembly of FeCo particles of mesoscopic dimensions, d = 10–50 μm, are investigated using a sensitive scanning giant magneto-impedance magnetometer. Direct magnetic force microscopy measurement of individual FeCo particles reveals a complicated domain structure. It is proved, however, that the mean square value of the stray magnetic field of a dilute assembly of FeCo particles randomly distributed on the plane is a statistically well-defined quantity. It depends on the average particle diameter, average distance between the particles, and average particle magnetization per unit volume. It is shown that the average particle magnetization can be determined using a measured mean square value of the stray magnetic field and geometrical parameters of the assembly obtained from optical measurement.

Microstructure and Magnetic Properties of Bulk FeCo Alloys Fabricated from Mechanically Alloying and Chemically Synthesized Powders

Three different methods of fabrication of FeCo soft magnetic material using ferromagnetic powders are compared: (i) simple sintering of elemental powders of Fe and Co, (ii) sintering of mechanically alloying FeCo powder, and (iii) sintering of chemically synthesized FeCo powder. The microstructure of ferromagnetic powders and bulk sintered alloys is characterized using scanning electron microscopy and energy-dispersive X-ray spectroscopy analysis. The best magnetic properties with high saturation magnetization, Ms = 211.3 emu/g, are obtained for bulk FeCo alloy sintered from chemically synthesized powder. It consists of nearly spherical FeCo particles with diameters from 5 to 15 μ m. The mean particle size of chemically synthesized FeCo powder can be controlled by changing the melt composition, temperature, and process duration. The relatively large size of FeCo particles reduces the influence of surface oxidation on the particle magnetic properties. The low-cost chemical technology developed is promising for a large-scale production of small FeCo magnetic components of arbitrary shapes with high-dimensional precision.

Synthesis and properties of graphene and graphene/carbon nanotube-reinforced soft magnetic FeCo alloy composites by spark plasma sintering

The effect of the addition of graphene nanoplatelets (GNP) and graphene nanoplatelet/carbon nanotube (GNT) mixtures on the mechanical and magnetic properties of spark plasma sintered soft magnetic FeCo alloys was studied. Three different volume fractions (0.5, 1 and 2 vol%) of GNPs and GNTs were investigated. Ball milling was used to disperse the GNPs in monolithic FeCo powder, while magnetic stirring and ultrasonic agitation were used to prepare hybrid GNT prior to ball milling. The highest saturation induction (B sat) of 2.39 T was observed in the 1 vol% GNP composite. An increase in the volume fraction of the ordered nanocrystalline structure was found to reduce the coercivity (H c) of the composites. The addition of CNTs to the GNP composite prevented grain growth, leading to grain refinement. An 18 % increase in hardness was observed in the 1 vol% GNP composite as compared to the as-received FeCo alloy. A reduction in tensile strength was observed in all of the composite materials, except for the 0.5 vol% GNT composite, for which a value of 643 MPa was observed. Raman spectroscopy indicated a reduction in the defect density of the GNPs after adding CNTs.

Crystallization process and kinetics of SmCo/Fe and SmCo/FeCo partially crystallized amorphous alloys

Partially crystallized amorphous alloys SmCo/Fe and SmCo/FeCo with nanocrystalline α-Fe and α-(Fe,Co) grains distributed in the amorphous SmCo matrix were synthesized by mechanical alloying of a mixture of SmCo5 and α-Fe and FeCo powders. The crystallization process and kinetics of these amorphous alloys upon annealing have been investigated. For SmCo/Fe amorphous alloy, with the increase of the annealing temperature to 700°C, a SmCo5 phase and a SmCo7 phase precipitate in sequence then the SmCo5 transforms to SmCo7. The activation energies for the SmCo5 and SmCo7 crystallization are 2.5±0.1 and 2.8±0.1eV, respectively. Differently, the SmCo/FeCo amorphous alloy processes only one phase transformation to SmCo7 with an activation energy of 2.8±0.1eV after annealing to 700°C. The present study gives an insight into the phase transformation of the SmCo amorphous alloys with different soft phase and is of basic significance to the microstructure controlling of the SmCo based nanocomposite magnets.

Nanostructured Polymetallic Powders to Create New Functional Materials on its Base

In the paper, the particle morphology is considered and the slices of phase diagrams of nanosystems agreeable to the synthesis conditions are constructed according to the data obtained earlier by authors, as well as new results of the study of nanostructured Fe-Co, Fe-Ni, Co-Ni, Fe-Co-Ni, Fe-Pt, Cu-Ni and Ni-Cd powders. It is found that all considered polymetallic systems have common nature of the particle size spatial organization, i.e., 7-20 nm nanocrystals (for different systems) form highly compact aggregates (40-100 nm) which put together into loose porous agglomerates (up to 200-250 nm) and then into unconsolidated micron size formation of cloud type. It is classified uncovered features of nanostructured polymetallic phase diagrams in comparison with phase diagrams of bulk systems. Magnetic properties of nanosystems are studied.

Investigation of the structural and microwave dielectric properties of mechanically alloyed Fe40Co60 powders

Fe40Co60 powders were produced by mechanical Alloying (MA) route. Structural and microwave dielectric properties were investigated. Discussion of obtained results is conducted according to milling time. X-Ray powder Diffraction (XRD) shows that disordered α (Fe40Co60) solid solution of substitution with body centered cubic (bcc) lattice is formed after 2h milling. Halder Wagner analysis reveals that least grain size of 15.59 nm and residual strain up to 0.8% are reached after 60h milling. The evolution of the Voigtian mixing factors according to milling progression confirms that structural properties are governed by residual strain accumulated during high- energy mechanical alloying (Gaussian profiles). Scanning Electron Microscopy (SEM) indicates that obtained powders adopt flattened angular shapes with high surface area. Microwave measurements are undertaken on bulk samples. High values of the dielectric permittivity depicting the conductive behavior of Fe-Co powders are measured. Dielectric permittivity spectra according to milling time shift towards higher values. Enhancement of the dielectric properties is related to the developed structure after milling.

Effect of residual oxides in Co powder on properties and structure of sintered powder materials in Fe-Co system

Magnetic, electrical, and mechanical properties as well as the structure of Fe-Co powder materials are investigated. It is found that the structural rearrangement from the BCC solid solution of Co in α-Fe (α phase) to the HCP solid solution of Fe in α-Co (ɛ phase) takes place with the increase in Co content. There are nonequilibrium mixtures of these phases in areas of intermediate composition containing residual oxides present in the initial Co powder.

Influence of Milling and Compaction Processes οn Magnetic Properties of FeCo Powder

Magnetic and structural studies were performed on Fe50Co50 material. The samples (disk-shaped, diameter: 10 mm, thickness: 2.5 mm) were fabricated by compaction of powder under pressure of 800 MPa for 5 min at temperatures 300{600 ‐ C. The powder was obtained by milling of Fe50Co50 alloy swarfs in high-energy planetary mill. The milling time varied from 1 h to 40 h. In the course of milling process the mean size of alloy pieces was decreasing from about 0.5 mm to 0.05 mm (scanning electron microscopy), which provided more compact structure after compression. The annealing process during compaction strongly reduces a coercive fleld of the

Effect of the milling conditions on the formation of nanostructured Fe–Co powders

AbstractNanostructured Fe–12Co (wt%) powders were prepared by mechanical alloying in a planetary ball mill. The milling process was carried out at different milling conditions. The obtained powders were characterized by X‐ray diffraction, 57Fe Mössbauer spectrometry and magnetic measurements. The low and high speed ball‐milling conditions lead to the formation of a single and two‐bcc Fe(Co) structure, respectively, having different crystallite sizes, microstrains hyperfine parameters and magnetic properties. The average hyperfine magnetic field values: 〈B〉1 = 34.8 T and 〈B〉2 = 28.2 T of the two‐bcc Fe(Co) structure could be attributed to the nanocrystalline grains and to the grain boundaries, respectively. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Processing of FeCo Nanosized Soft-Magnetic Material by Powder Metallurgy Technique

A nanosized cobalt-based alloy containing 20 wt % Fe was synthesis by electroless chemical reduction method using alkaline tartarate bath and sodium hypophosphite as a reducing agent . The powder was investigated by optical microscope, SEM and XRD to identify the powder shape, size and the chemical composition. The prepared powder has a spherical shape with a particle size of about 200 nm. The investigated powder was cold compacted at 600 MPa and then sintered in hydrogen atmosphere at 1050 0C. Metallographic, physical, magnetic and electrical properties investigations were carried out for the prepared powder and its sintered compacts. The prepared powder has 2.5% phosphorus content which was liberated by heating the compacts to the sintering temperature in hydrogen atmosphere. From the results of the density measurements we can observe that the prepared sintered FeCo material had a relative density about 96% to the theoretical. But the results of the electrical properties measurements give an indication of the decreasing in the electrical resistivity than the materials produced by the traditional methods. On the other hand the magnetic measurements, of the FeCo powder has a lower specific saturation induction, Bs, than the sintered one which was due to the presence of the paramagnetic metal phosphides in the powder but after rising the temperature to sintering the, Bs, values is increased due to the conversion of the phosphides to the metallic state and the phosphorus was liberated, but the coercive force was decreased by sintering of the powder compacts by lowering the porosity of the materials with sintering and the formation of the soft magnetic materials Fe-Co solid solution which was investigated by XRD having the highest specific saturation induction value. Also the magnetic permeability of the prepared sintered material was increase with increasing the applied field until 50 Oe which has the highest value and decreased with increasing the field more than 50Oe. From the magneto-resistance measurements, it was shown that the sintered material has a positive magneto-resistance in the field direction but a negative one in the direction perpendicular to the current and the field.

Structural and magnetic properties of mechanically alloyed FeCo powders

The Fe 100 - x Co x ( x = 30 , 45, 50, 60 wt.%) alloys with average grain size of 10 nm were prepared by a mechanical alloying of the elemental Fe and Co powders using a high-energy ball mill. The prepared alloys were characterized by X-ray diffraction, Mössbauer spectrometry, TEM and magnetic (VSM) measurements. The lattice parameter, saturation magnetization and coercivity were analyzed as a dependence on the Co content. The average hyperfine magnetic field value of about 35 T suggests that the disordered BCC Fe–Co solid solution is formed after 30 h of milling. The ordering (transformation from α -BCC to B2 structure) below the temperature 720 ∘ C after cooling was confirmed by DSC in all compositions with the exception of Fe 70 Co 30 .

Fabrication of Nanostructured Fe-Co Alloy Powders by Hydrogen Reduction and Its Magnetic Properties

Magnetic properties of nanostructured materials are affected by the microstructures such as grain size (or particle size), internal strain and crystal structure. Thus, it is necessary to study the synthesis of nanostructured materials to make significant improvements in their magnetic properties. In this study, nanostructured Fe-20at.%Co and Fe-50at.%Co alloy powders were prepared by hydrogen reduction from the two oxide powder mixtures, Fe2O3 and Co3O4. Furthermore, the effect of microstructure on the magnetic properties of hydrogen reduced Fe-Co alloy powders was examined using XRD, SEM, TEM, and VSM.

Formation and Magnetic Properties of Nanocrystalline Fe<SUB>60</SUB>Co<SUB>40</SUB> Alloys Produced by Mechanical Alloying

The Fe60Co40 alloys were prepared by mechanical alloying of the Fe and Co powders using a high-energy ball mill. They were studied with respect to phase formation and magnetic properties using x-ray diffraction, scanning electron microscopy, and measurements of coercivity and remanence (Br). The evaluation of Fe lattice parameters during milling showed that formation of a body-centered cubic solid solution occurred by mechanical alloying after 12 h of milling. Intensive milling of Fe-Co powders results in a nonequilibrium microstructure characterized by grain refinement to a minimum of 10–13 nm and the introduction of internal strain up to 0.5%.

Magnetic nanoparticles produced by surfactant-assisted ball milling

Nanoparticles of Fe, Co, FeCo, SmCo, and NdFeB systems with sizes smaller than 30nm and narrow size distribution have been successfully prepared by ball milling in the presence of surfactants and organic carrier liquid. It has been observed that the nanoparticles prepared by milling Fe and FeCo powders were close to spherical in their shapes, whereas those of Co, SmCo, and Nd–Fe–B showed elongated rod shapes. The nanoparticles showed superparamagnetic behavior at room temperature, except for the SmCo nanoparticles that were ferromagnetic. Nanoparticles of all types showed ferromagnetic behavior at low temperatures. The compositions of nanoparticles prepared by milling the SmCo, NdFeB, and FeCo powders were found to be deviated from the starting powders.

Chemical Vapor Synthesis of Ultraflne Fe-Co Powder

Chemical Vapor Synthesis of Ultraflne Fe-Co Powder

Structural properties of Fe 50Co 50 nanostructured powder prepared by mechanical alloying

Mechanical alloying of high purity elemental powders in a planetary ball mill (Fritsch pulverisette 7) was used to prepare nanocrystalline Fe and equiatomic FeCo powders. Morphology changes, structural properties and local iron environment variations have been investigated by Scanning Electron Microscopy, X-ray diffraction and 57 Fe Mössbauer spectrometry. X-ray diffraction profile fitting, reveals the Co allotropic transformation from fcc to hcp form at the early stage of milling. The milling route implies diffusion of hcp-Co into α (Fe) leading to the formation, after 12 h, of the bcc-FeCo solid solution with a lattice parameter close to a = 0.2861 nm and a grain size of about 12 nm. The analysis of the evolution of the hyperfine magnetic field distribution, indicates that the disordered bcc-FeCo solid solution is formed after 12 h of milling, through the interdiffusion of Fe and Co elemental powders. The average hyperfine magnetic field of the bcc-FeCo solid solution ( B = 35 T) suggests that the disordered Fe 50Co 50 system is formed.