FeSi Particles Research Articles

Microwave absorption properties of FeSi flaky particles prepared via a ball-milling process

Flaky FeSi alloy particles with different aspect ratio were produced via ball-milling and a subsequent annealing. The microstructure and the morphology of the particles were examined by XRD and SEM. The dc resistivity, the static magnetization properties and electromagnetic properties were measured. Particles with high aspect ratio were found possess high permittivity and permeability. On the other hand, the variation of grain size and defects density was found influence the permittivity and permeability. High specific area was believed contribute to the intense dielectric loss and the high shape magnetic anisotropy lead to high permeability in the target band. Increased electromagnetic parameters compel the absorption peak’s shift to lower frequency. Coating using flaky FeSi particles milled for 12h as fillers presented a reflection loss of −10dB at 2GHz and a matching thickness of 1.88mm. The flaky FeSi alloy particles prepared through ball-milling and annealing can be promising candidates for EMA application at 1–4GHz band.

Fe-Si particles on the surface of blast furnace coke

This study investigates the surface of unpolished samples of blast furnace (BF) coke drilled from the tuyere zone, which hosts Fe-Si particles (mostly Fe3Si) that vary in size, shape, depth of submersion (penetration) into the coke matrix, and contact features with the surface. Based on the shape of the particles and the extent of their contact with the coke matrix, they have been grouped into three major types: (I) sphere-like droplets with limited contact area, (II) semi-spheres with a larger contact area, and (III) irregular segregations with a spherical surface, which exhibit the largest contact area among the three types of particles. Considering the ratio between the height (h) of the particles and half of their length at the surface level (l) along the cross-section, these three types can be characterized as follows: (I) h > l, (II) h ≈ l, and (III) h < l. All the three types of particles can be found near each other. The shape and the extent of the contact depend on the degree of penetration of the material into the matrix, which is a function of the composition of the particles. Type (I) particles were initially saturated with Si at an earlier stage and, for that reason, they can react less with carbon in the coke matrix than type (II) and (III), thereby moving faster through the coke cone. Thermodynamic calculations have shown that the temperature interval of 1250–1300°C can be considered the starting point for Si entering into molten iron under quartz-dominated coke ash. Accordingly, the initial pick-up of Si by molten iron can be assumed to be mineral-related. In terms of BF practice, better conditions for sliding Fe-Si droplets through the coke cone are available when they come into contact with free SiO2 concentrated into small grains, and when the SiO2/ΣMe x O y mass ratio in the coke ash is high.

A Novel Composite Material Designed from FeSi Powder and Mn0.8Zn0.2Fe2O4Ferrite

A design of the novel microcomposite material composed of spherical FeSi particles and Mn0.8Zn0.2Fe2O4ferrite is reported together with a characterization of basic mechanical and electrical properties. The sol-gel autocombustion method was used for a preparation of Mn0.8Zn0.2Fe2O4ferrite, which has a spinel-type crystal structure as verified by XRD and TEM analysis. The final microcomposite samples were prepared by a combination of the traditional PM compaction technique supplemented with unconventional microwave sintering process of the prepared green compacts. The composition and distribution of the secondary phase formed by the spinel ferrite were examined by SEM. It is demonstrated that the prepared composite material has a tight arrangement without any significant porosity, which manifests itself through superior mechanical properties (high mechanical hardness, Young modulus, and transverse rupture strength) and specific electric resistivity compared to the related composite materials including resin as the organic binder.

A comparison of soft magnetic composites designed from different ferromagnetic powders and phenolic resins

Soft magnetic composites (SMCs) were prepared from three different ferromagnetic powder particles: iron powder ASC 100.29, spherical FeSi particles and vitroperm (Fe73Cu1Nb3Si16B7) flakes. Two types of hybrid organic–inorganic phenolic resins modified with either silica nanoparticles or boron were used to design a thin insulating layer perfectly covering the ferromagnetic particles. Fourier transform infrared (FTIR) spectrometry confirmed an incorporation of silica or boron into the polymer matrix, which manifested itself through an improved thermal stability of the hybrid resins verified by thermogravimetric-differential scanning calorimetry (TG-DSC) analysis. The core-shell particles prepared from the ferromagnetic powder particles and the modified hybrid resins were further compacted to the cylindrical and toroidal shapes for the mechanical, electrical and magnetic testing. A uniform distribution of the resin between the ferromagnetic particles was evidenced by scanning electron microscope (SEM) analysis, which was also reflected in a rather high value of the electrical resistivity. A low porosity and extraordinary high values of mechanical hardness and flexural strength were found in SMC consisting of the iron powder and phenolic resin modified with boron. The coercive fields of the prepared samples were comparable with the commercial SMCs.

Effects of magnetic fields on Fe-Si composite electrodeposition

Abstract Coatings containing Fe-Si particles were electrodeposited on 3.0wt% Si steel sheets under magnetic fields. The effects of magnetic flux density (MFD), electrode arrangement and current density on the surface morphology, the silicon content in the coatings and the cathode current efficiency were investigated. When a magnetic field was applied parallel to the current and when the MFD was less than 0.5 T, numerous needle-like structures appeared on the coating surface. With increasing MFD, the needle-like structures weakened and were transformed into dome-shaped structures. Meanwhile, compared to results obtained in the absence of a magnetic field, the silicon content in the coatings significantly increased as the MFD was increased for all of the samples obtained using a vertical electrode system. However, in the case of an aclinic electrode system, the silicon content decreased. Furthermore, the cathode current efficiency was considerably diminished when a magnetic field was applied. A possible mechanism for these phenomena was discussed.

Effect of particle conductivity on Fe-Si composite electrodeposition

Coatings containing Fe-Si or Si particles were electrodeposited on 3.0%(mass fraction) Si steel sheets. The surface morphology, the cross-section and the silicon content of coating have been investigated, respectively. It was found that the number of particles on the coating surface and cross-section significantly decreased with increasing silicon content in the applied particles, leading to a decrease of the silicon content of coatings. About 10.2% silicon content of coatings deposited with Fe-30%Si particles can be obtained, whereas that for Si particles was only 2.9% at a particle concentration of 100 g/L and current density of 2 A/dm2. This is mainly attributed to the conductivity of applied particles. High conductivity can promote the co-deposition of the particles. With increasing silicon content in the particles, their conductivity decreased sharply, resulting in the decrease of silicon content of coatings. Present work may initiate a new method to modify the particle content of the composite coatings via changing the conductivity of the particles during the composite electrodeposition. In this paper, a possible mechanism was proposed to explain the phenomena.

Magnetic Properties of Soft Magnetic FeSi Composite Powder Cores

Soft magnetic composites (SMCs), which are used in electromagnetic applications, can be described as ferromagnetic powder particles surrounded by an electrical insulating lm. These composite materials o er several advantages over traditional laminated steel cores such as reduction in weight and size. They have some unique properties, including three-dimensional isotropic ferromagnetic behaviour, very low eddy current loss, relatively low total core loss at medium and high frequencies, high electrical resistivity and good relative magnetic permeability. FeSi powder was used as a base ferromagnetic material for preparation of soft magnetic composites. The commercial FeSi particles of a precise spherical shape were prepared in two granulometric fractions (up to 150 μm or up to 356 μm). The phenol-formaldehyde resin modi ed by SiO2 nanoparticles was used as an electroinsulating layer. The FeSi particles covered by the synthesized resin were compacted at 800 MPa into the ring samples for magnetic measurements. The nal samples were treated thermally under the curing schedule, which was suggested according to thermal degradation of the modi ed resin.

Imaging of Magnetic Domains and Domain Walls in Spherical Fe-Si Powder Using Magnetic Force Microscopy

The commercial Fe-Si powder, produced by Hoganes Corporation, represents promising soft magnetic material for technological applications. The powder consists of spherical particles with diameter up to 150 μm. Internal microstructure of the powder is formed by grains of diameter of about 30 μm. Each separate grain has a random orientation of the easy magnetization axis and is su ciently large to split into several magnetic domains. A comparative study of the atomic force microscopy (AFM) topography and the corresponding magnetic force microscopy (MFM) images was employed in order to examine the correlation between the grain size, boundaries of grains and characterization of the magnetic domains, which gives us an important knowledge about possible behavior of particles under the in uence of the external magnetic eld and further utilization of the spherical Fe-Si particles in electrotechnical industry. The grain size and the crystallographic orientation of grains were analyzed by the electron backscattering di raction (EBSD) technique.

A comprehensive study of soft magnetic materials based on FeSi spheres and polymeric resin modified by silica nanorods

A novel soft magnetic composite (SMC) based on spherical FeSi particles precisely covered by hybrid phenolic resin was designed. The hybrid resin including silica nano-rods chemically incorporated into the phenolic polymer matrix was prepared by the modified sol–gel method. A chemical bridge connecting silica nano-rods with the base polymeric net was verified by FTIR, 13C and 29Si NMR spectroscopy, whereas the shape and size of silica nano-rods were determined by TEM. It is shown that the modification of polymeric resin by silica nano-rods generally leads to the improved thermal and mechanical properties of the final samples. The hybrid resin serves as a perfect insulating coating deposited on FeSi particles and the core–shell particles can be further compacted by standard powder metallurgy methods in order to prepare final samples for mechanical, electric and magnetic testing. SEM images evidence negligible porosity, uniform distribution of the hybrid resin around FeSi particles, as well as, dimensional shape stability of the final samples after thermal treatment. The hardness, flexural strength and density of the final samples are comparable to the sintered SMCs, but they simultaneously exhibit much higher specific resistivity along with only slightly lower coercivity and permeability.

Electromagnetic properties of flake-shaped Fe–Si alloy particles prepared by ball milling

Flake-shaped Fe–Si alloy particles with high aspect ratios were fabricated by ball milling commercially available Fe–Si powder, aiming to fabricate high-performance microwave absorbing fillers for coatings applied in 1–4GHz range. To compare with spherical particles, higher permittivity and permeability was observed by using flaky particles as fillers. High aspect ratios contributed to an enhanced dielectric relaxation in the 1–4GHz band, resulting in an increased permittivity. The thin thickness together with the high resistivity of Fe–Si flakes was believed to be helpful for suppressing the effect of eddy current and thus lead to an increase in the permeability. The electromagnetic wave absorbing (EMA) performances were observed to be enhanced. With a thin thickness of 2mm, a wide absorption band with a minimum reflection loss of −12dB was achieved in 1–4GHz range, when using 75wt% of flaky Fe–Si particles as fillers. The study indicated that flake-shaped Fe–Si particles were a promising candidate for EMA materials in L and S bands.

Viscosity of Magnetorheological Fluids Using Iron–Silicon Nanoparticles

Fe-6.5Si fine particles were mechanically fabricated by a milling method for use in magnetorheological fluids. Oleic acid was used as a surfactant for the dispersed substance for preparing the hydrophobic fluid with silicon oil as a dispersing medium. Further, oleic acid and sodium dodecyl benzene sulfonate were used as surfactants, forming a bilayer structure, for preparing the hydrophilic fluid with polyethylene glycol as a dispersing medium. The adsorption of oleic acid onto the Fe-Si particles was achieved by oxidizing the particle surface with trimethylamine N-oxide dihydrate. In order to make a comparative examination of the fluid properties, ferromagnetic nanoparticles were synthesized by chemical precipitation and the subsequent process was accompanied under the same conditions as applied for the magnetorheological fluid. The fluid particles were characterized by magnetization measurements. The viscosity of the fluids was obtained at various concentrations under an external field. The viscosity values of the magnetorheological fluid were higher than those of the ferromagnetic fluid. Moreover, they increased considerably by using silicon oil as the dispersing medium as well as under an applied magnetic field and at higher fluid concentrations. The magnetorheological fluids may be effectively resistant to a strong impact from outside when the appropriate fluid concentration is used and a magnetic field is applied for increasing the shear strength of the fluids.

Effects of particle sizes on the electromagnetic property of flaky FeSi composites

Flaky FeSi absorbents with different size ranges were fabricated by sintering after mechanical milling process. X-ray diffraction (XRD) was used to analyze the particle crystal grain structure. The complex permittivity and permeability of FeSi/paraffin composites were measured in frequency of 2–12 GHz using a vector network analyzer, and the DC electric conductivity was measured by the standard four-point contact method, then microwave reflection loss (RL) and shielding effectiveness (SE) were calculated. It was obtained that α-Fe appeared in the super-lattice diffraction peaks in XRD pattern. As the particles size decreased, the permittivity decreased due to the inferior microwave electrical conductivity and dielectric loss tangent, while the permeability increased due to the decrease of diameter-thickness ratio, which could be demonstrated in the comparison between the experiment and calculation results. When thickness is 1 mm, the composites with the smallest FeSi particles addition had a better absorbing property for the better impedance matching characteristic, and the minimum RL was −7.9 dB at 4.6 GHz. While the composites with larger FeSi particles addition had an excellent shielding property due to the higher permittivity, the SE value ranged from 15 dB to 30 dB at the frequency band.

Fluidization of high-density particles: The influence of fines on reactor performance

Abstract The effect of fines on the hydrodynamics of a gas–solid fluidized bed and ozone decomposition reaction was investigated using high-density iron-silicon (FeSi) particles with a particle density of 6690 kg/m3. The addition of fines decreased the bubble size, dense phase voidage and reactor performance. The bubble size decrease is in accordance with reported literature; while, increase in dense phase voidage and reactor performance was found in the literature on less dense catalyst. The reactor performance was quantified using an apparent overall mass transfer parameter derived from fitting a two-phase model to the experimental data. The method allowed for reactor performance comparison despite the fluctuation in FeSi particle activity. Model fitting results suggest that smaller bubbles should improve mass transfer in addition to reactor performance. However, the decreased dense phase voidage with addition of fines counteracted the effects of smaller bubbles. Higher entrainment rate of the bed with fines was noted.

Understanding the enhanced microwave permeability of Fe–Si–Al particles by Mössbauer spectroscopy

The microwave permeability of milled Fe–Si–Al flaky particles has been found to be much larger than those of unmilled particles with irregular shape. Transmission Mössbauer spectra are found significantly different for particles with different shapes. More than 8 absorption peaks have been found for the unmilled particles while there are only 6 absorption peaks for the flaky particles. The unmilled particles are found with the ordered D03 type superlattice structure. Therefore the Mössbauer spectra can be fitted with 5 sextets representing 5 different Fe-site environments. However, the flaky particles are with the disorder α-Fe(Si,Al) structure, and their Mössbauer spectra can be fitted with a model with the distribution of hyperfine magnetic field and isomer shift. It also has been revealed by Mössbauer spectroscopy that the flaky particles have stronger tendency to possess the planar magnetic anisotropy, and their average magnetic moment is found to be about 1.63μB.

Microwave Permeability and Mössbauer Spectra of Flaky Fe–Si–Al Particles

Fe84.94Si9.68Al5.38 flaky particles have been obtained by ball attrition method. The volume fraction dependence of microwave permeability has been measured for composites filled with these particles. Effective medium theories have been employed to extract the apparent microwave permeability. It is found that the flaky Fe-Si-Al particles have large apparent microwave permeability and large microwave magnetic loss. For example, at 0.5 GHz, the real and imaginary parts of apparent permeability are 10 and 5, respectively. The extracted microwave permeability is found to be consistent with generalized Snoek's limit. Due to high microwave magnetic loss, the flaky Fe-Si-Al particles can be useful for technical applications in the field of electromagnetic compatibility. Mossbauer spectroscopy measurements show that the hyperfine magnetic field and isomer shift have wide distribution, indicating that Fe atoms in the flaky Fe-Si-Al alloys have complicated environments.

Thermal diffusivity and mechanical properties of polymer matrix composites

Polypropylene–iron-silicon (FeSi) composites with spherical particles and filler content from 0 vol. % to 70 vol. % are prepared by kneading and injection molding. Modulus, crystallinity, and thermal diffusivity of samples are characterized with dynamic mechanical analyzer, differential scanning calorimeter, and laser flash method. Modulus as well as thermal diffusivity of the composites increase with filler fraction while crystallinity is not significantly affected. Measurement values of thermal diffusivity are close to the lower bound of the theoretical Hashin-Shtrikman model. A model interconnectivity shows a poor conductive network of particles. From measurement values of thermal diffusivity, the mean free path length of phonons in the amorphous and crystalline structure of the polymer and in the FeSi particles is estimated to be 0.155 nm, 0.450 nm, and 0.120 nm, respectively. Additionally, the free mean path length of the temperature conduction connected with the electrons in the FeSi particles together with the mean free path in the particle-polymer interface was estimated. The free mean path is approximately 5.5 nm and decreases to 2.5 nm with increasing filler fraction, which is a result of the increasing area of polymer-particle interfaces. A linear dependence of thermal diffusivity with the square root of the modulus independent on the measurement temperature in the range from 300 K to 415 K was found.

Theoretical consideration of experimental data of thermal and magnetic properties of polymer-bonded soft magnetic composites

Spherical iron silicon (FeSi) particles and irregular shaped magnetite (Fe3O4) particles with particle sizes ≤146 μm and varying volume filler fractions up to x = 0.7 (70 vol%) were mixed with polypropylene (PP) matrix. The samples were prepared by kneading and injection moulding and show particle–particle interaction at elevated filler fraction of x ≥ 0.5. Thermal and magnetic properties of the composites were characterized and show a significant increase at filler fractions of x ≥ 0.3. The thermal conductivity of PP (0.176 W/(m K)) was increased up to seven times to 1.239 W/(m K) at x = 0.7. FeSi-filled composites show slightly higher values of thermal conductivity than Fe3O4-filled composites. The magnetic permeability of the composites rise from 1 for PP to a maximum value of 23.1 for PP/FeSi composites at x = 0.7. The nonlinear increase in the thermal conductivity corresponds with the lower boundary of the Hashin–Shtrikman model. The Bruggeman model can be applied to describe the nonlinear increase in the magnetic permeability. Magnetic permeability increases with mean particle diameter as well as magnetic coercivity and loss dissipation increases with inverse mean particle diameter.

Surface modification of 5083 Al alloy by electrical discharge alloying processing with a 75 mass% Si–Fe alloy electrode

This study experimentally investigates the surface modification of 5083 Al alloy by the electrical discharge alloying (EDA) process with a Si–Fe alloy as an electrode. Samples were analyzed by transmission electron microscopy (TEM), scanning electron microscopy (SEM), micro-hardness and corrosion resistance tests. The micro-hardness of EDA alloyed layer was evidently higher than that of the base metal (5083 Al alloy). The TEM results show that the matrix of the alloyed layer has an amorphous-like structure; the matrix contains fine needle-like Si particles, block-like Si particles and nano-size Al4.5FeSi and Al13Fe4 particles. The TEM results support experimental results for the high hardness of the alloyed layer. Moreover, the EDA alloyed layer with composite microstructures has good corrosion resistance in NaCl aqueous solution.

Comparative study on effects of microstructures of hot rolled and twin roll casting 1235 aluminium alloy on surface quality of aluminium foils produced

Twin roll casting is an attractive technology for producing aluminium sheets for foils. But, surface defects, such as matte defects, may occur on aluminium foils produced in this way. However, it is not the case on aluminium foils produced by traditional hot rolled process. Optical microscopy, scanning electronic microscopy, energy spectrum and transmission electronic microscopy were used to investigate the effects of the microstructures of the twin roll cast and hot rolled aluminium alloy sheet for foils on the surface defects of the foils produced. It is discovered that central segregation band and surface microsegregation band in twin roll casting aluminium sheet may result in a non-uniformly distributed secondary Al–Fe and Al–Fe–Si particles in workpieces in a lower reduction pass. These non-uniformly distributed Al–Fe and Al–Fe–Si particles and microporosities in a size of several microns generated in solidification process of twin roll casting are the main cause for the surface matte defects of the aluminium foils produced.

Microstructure characteristics of FeMo–Sialon ceramic composite

A new metal–Sialon based ceramic composite of FeMo–Sialon has been processed using Si 3N 4, α-Al 2O 3 and FeMo70 alloy powders as the main raw materials. To explain why this composite has excellent mechanical properties, microstructure characterizations are carried out using the transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The results show that FeMo, FeSi 2 and Mo have formed an alloy mixture of Mo–Fe–Si in the FeMo–Sialon ceramic composite. Elongated β-Sialon crystals, interlacing with each other, vary in size. The Y-SiAlON glass, as an inter-granular phase, surrounds the grain boundaries of β-Sialon crystals. Some of β-Sialon crystals are semi-surrounded by dumbbell-like Mo–Fe–Si particles. The good mechanical properties of FeMo–Sialon composite are greatly dependent on the elongated Sialon grains and Mo–Fe–Si particles with interlocking structures.