FeSi Particles Research Articles

Data mining and design of electromagnetic properties of Co/FeSi filled coatings based on genetic algorithms optimized artificial neural networks (GA-ANN)

It is difficult to establish analytical relationships between coating parameters (type and filling ratios of absorbent) and electromagnetic (EM) properties based on traditional trial-and-error methods. Data mining is expected to predict the EM properties of coatings filled with arbitrary set type/content of absorbent based on the measured parameters within a few samples, to solve this problem. In this study, a method for predicting EM properties of coatings was established based on GA-ANN algorithm. The proposed model was found be capable of predicting EM properties of coatings, not only in wide range of filling ratio but also in case of mixed absorbents. The GA-ANN model presented lower error and higher accuracy to compare with the conventional ANN methods. Additionally, GA was used to optimize the design of coatings via using of mixed absorbent aiming to obtain broadband electromagnetic absorption (EMA) characteristics. The optimized mixture coating with the thickness of 2.06 mm contained 13.5 wt% of Co and 55.6 wt% of FeSi particles, whose effective absorption bandwidth with reflection loss less than −10 dB ( ERL 10 ) could reach 9.3 GHz. • A predictive model for electromagnetic properties of coating was established. • The model was built based on genetic algorithm optimized artificial neural network. • Electromagnetic property for arbitrarily C02/F25 content were accurately predicted. • A broadband absorbing coating was designed based on the predictive model.

Effects of Fe/Si Stoichiometry on Formation of Fe3Si/FeSi-Al2O3 Composites by Aluminothermic Combustion Synthesis

Aluminothermic combustion synthesis was conducted with Fe2O3–Al–Fe–Si reaction systems under Fe/Si stoichiometry from Fe-20 to Fe-50 at. % Si to investigate the formation Fe3Si/FeSi–Al2O3 composites. The solid-state combustion was sufficiently exothermic to sustain the overall reaction in the mode of self-propagating high-temperature synthesis (SHS). Dependence of iron silicide phases formed from SHS on Fe/Si stoichiometry was examined. Experimental evidence indicated that combustion exothermicity and flame-front velocity were affected by the Si percentage. According to the X-ray diffraction (XRD) analysis, Fe3Si–Al2O3 composites were synthesized from the reaction systems with Fe-20 and Fe-25 at.% Si. The increase of Si content led to the formation of both Fe3Si and FeSi in the final products of Fe-33.3 and Fe-40 at.% Si reaction systems, and the content of FeSi increased with Si percentage. Further increase of Si to Fe-50 at.% Si produced the FeSi–Al2O3 composite. Scanning electron microscopy (SEM) images revealed that the fracture surface morphology of the products featured micron-sized and nearly spherical Fe3Si and FeSi particles distributing over the dense and connecting substrate formed by Al2O3.

Formation mechanism and magnetic performance of Fe-Si soft magnetic composites coated with MnO-SiO2 composite coatings

Fe-Si soft magnetic composites (SMCs) coated with MnO-SiO2 composite coatings were fabricated via sintering the ball milled Fe-Si/MnO2 composite powders. The transformation mechanism from MnO2 coating to MnO-SiO2 composite coatings was studied. The effect of MnO2 content on the microstructure and magnetic properties of Fe-Si soft magnetic composites has also been investigated systematically. The analysis results indicated that MnO2 would be reduced to MnO by Si in the Fe-Si particles at 780.1 ℃. When the temperature reached 985.8 ℃, the generated MnO and SiO2 would further combine to form 2MnO·SiO2, finally forming the MnO-SiO2 composite coatings. With the increase of the MnO2 content from 0.0 wt% to 10.0 wt%, the MnO-SiO2 composite coatings became thicker, thus the saturation magnetization and permeability decreased gradually. However, exorbitant MnO2 content above 5.0 wt% would result in excessive in-situ Fe existed in the composite coatings and obvious reduction of Si content in the Fe-Si particles due to the above solid-state reactions. Therefore, the increasing trend of the resistivity was weakened. And the 5.0 wt% MnO2 coated Fe-Si SMCs exhibited superior comprehensive performance such as high saturation magnetization (186.5 A·m2/kg), good permeability (71), low total core loss (362.6 mW/cm3 at 50 kHz).

Soft magnetic properties of FeSiAl/carbonyl iron composites with high magnetic permeability and low magnetic loss

FeSiAl/carbonyl iron composites with high magnetic permeability and low magnetic loss was prepared. The microstructure and magnetic properties of the sample were studied by using XRD, SEM, EDS, XPS and superconducting quantum interference device (SQUID Quantum Design MPMS-3) magnetic property measurement system. It is found that with increase of carbonyl iron content, magnetic permeability of the composites increased, and magnetic loss first decreased and then increased. This manifestation may be produced by a competitive mechanism: the presence of carbonyl iron particles strengthens the magnetic coupling among FeSiAl particles, which leads to an increase in magnetic permeability and reduces hysteresis loss; on the other hand, the hysteresis loss of carbonyl iron itself is greater than that of FeSiAl. The composite has the lowest magnetic loss and highest magnetic permeability when the carbonyl iron content is 4%, which may have commercial application value in high-power electrical systems.

Novel High-Entropy Aluminide-Silicide Alloy.

Novel high-entropy (multi-principal elements) alloy based on Fe-Al-Si-Ni-Ti in equimolar proportions has been developed. The alloy powder obtained by mechanical alloying is composed of orthorhombic FeTiSi phase with the admixture of B2 FeAl. During spark plasma sintering of this powder, the FeSi phase is formed and the amount of FeAl phase increases at the expense of the FeTiSi phase. The material is characterized by a high compressive strength (approx. 1500 MPa) at room temperature, being brittle. At 800 °C, the alloy is plastically deformable, having a yield strength of 459 MPa. The wear resistance of the material is very good, comparable to the tool steel. During the wear test, the spallation of the FeSi particles from the wear track was observed locally.

Iron Based Soft Magnetic Composite Material Prepared By Injection Molding

Abstract Soft magnetic composite materials consisting of FeSi powder and polypropylene were prepared by the injection molding method, with different polypropylene contents of 25, 30 and 35 vol. %. The magnetic and electrical properties as well as the structure of the composites were investigated. The samples exhibited very low porosity, high electrical resistivity, relatively low coercivity, sufficient saturation magnetic flux density and permeability, and high resonant frequency. FeSi particles were found to be well insulated from each other and homogeneously dispersed in the polymer matrix of the composite. The observed isotropic structure was confirmed by the fitting of the experimental dependence with the analytical expression of the reversible relative permeability vs. magnetic flux density.

Study on the electromagnetic properties and microwave absorbing mechanism of flaky FeSiAl alloy based on annealing and phosphate coating

A low-frequency composite absorbing material with high permeability and low permittivity in low frequency was prepared after the flaky FeSiAl alloy powder was annealed in N2 atmosphere and modified with zinc-based phosphate solution. The effects of annealing temperature and phosphating time on the phase composition, morphology and static magnetic properties of the flaky FeSiAl alloy were investigated with x-ray diffraction (XRD), scanning electron microscope (SEM) and vibrating sample magnetometer (VSM). With the aid of vector network analyzer (VNA), the electromagnetic properties and absorbing performance of the powder treated in two ways were studied. The results showed that after annealing in N2 atmosphere, the crystallization degree of FeSiAl powder increased, the crystal type underwent a phase transition of A2-A2/B2-A2/B2/D03, the permittivity decreased, and the permeability was greatly improved. After phosphating, the phosphating reaction products were deposited on the surface of FeSiAl particles, the permittivity was significantly reduced, the low-frequency impedance matching and low-frequency absorption performance were improved. The causes and frequency changes of electromagnetic wave absorption peaks were analyzed with the λ/4 interference cancellation theory, the interface reflection model and the impedance matching principle.

Microstructure and magnetic properties of FeSiAl soft magnetic composites prepared by chemical in-situ coprecipitation with NaOH

The FeSiAl powder was dispersed into NaOH solution with 10 wt% concentration, after a certain time then NaHCO3 with 2 wt% concentration was added. After calcination at 1250 °C, the coating changed into the oxide insulation on the surface of FeSiAl particles. The microstructure, formation mechanism, and magnetic properties of the coated powder prepared by the chemistry in-situ generation method has been investigated. The electrical insulation layer oxide was confirmed that there existence of Al2O3 phase. The thickenss of coating layer was about 20 nm measured by the TEM. The saturation magnetization (Ms) of FeSiAl powder slightly increased after coated, but obviously increased after calcined. Then the FeSiAl resistivity obviously increased after coated, and further increased after calcination. The FeSiAl soft magnetic composite has the magnetic properties of effective permeability μe = 56.03 and total magnetic loss Pcv = 1042.86 mW/cm3 that measured under the condition of frequency 1000 kHz and 20 mT. This is an effective method to prepare high performance FeSiAl@Al2O3 soft magnetic composite applied at higher frequency.

Preparation and magnetic properties of core–shell structured Fe-Si/Fe3O4 composites via in-situ reaction method

The Fe-Si/Fe3O4 soft magnetic composites (SMCs) have been fabricated via in-situ reaction method. A layer of Fe3O4 was formed on the Fe-Si particles in the KNO3 solution, and the growth mechanism of the Fe3O4 coating layer has been studied, and its formation and thickness can be controlled by adjusting the concentration of KNO3 solution to obtain the microstructure of the composites and then adjust the magnetic performance of SMCs. The formation of Fe3O4 shell on Fe-Si particles can effectively reduce the core loss of the composites. The samples in-situ reacted in 0.1 mol/L KNO3 solution exhibit excellent comprehensive properties with high saturation magnetization, relatively high permeability (34), great frequency stability of permeability, and very low core loss of 13.6 w/kg (measured at 20 mT and 150 kHz).

Morphological Change and Open-circuit Potential of Single Metastable Pit on AA1050 Aluminum in NaCl Solution

The relationship between the change in the open-circuit potential (OCP) and the morphology of metastable pitting at Al–Fe–Si particles of AA1050 aluminum in 0.1 M NaCl was clarified. First, a metastable pit grew in the depth direction as the OCP decreased suddenly. Second, the pit started to grow on the Al surface, and the OCP remained low. Finally, the pit was repassivated with the reincrease of the OCP. In the early stage of OCP measurements of the electrode area of 1 cm 2 , the potential oscillations and values were found to be associated with the growth of many metastable pits rather than the initiation and repassivation of each metastable pit. The amplitude of the OCP oscillation decreased with time and disappeared. Then, the OCP decreased slowly and became constant. The transition from metastable to stable pitting was determined to occur gradually.

Flaky FeSi particles with tunable size, morphology and microstructure developing for high-efficiency and broadband absorbing materials

Compared with spherical ferromagnetic particles, flaky particles due to the higher permeability present great potentials as high-efficiency electromagnetic absorbing materials, especially in S band (2–4 GHz). FeSi flakes with different diameters were synthesized by ball-milling and subsequent screened processes, and hydrogen annealing and SiO2 coating were then utilized to further optimize the electromagnetic parameters for high-efficiency absorption. FeSi flakes with high diameter possess higher permittivity for the larger specific areas and higher permeability for the increased shape anisotropy. The decreased defects after annealing induce the reducing permittivity. The eddy current effect can be effectively suppressed after the SiO2 is coated on the surface of FeSi flakes. As for the coating containing 70 wt% FeSi@SiO2 flakes, the maximum reflection loss (RLmax) of –73 dB can be observed at 2.5 GHz with the coating thickness of 3 mm. Effective absorption band (ERL5, RL < –5 dB) can reach 13 GHz at a very thin thickness of 1 mm, and ERL5 covers the whole S-C band when the thickness of 2.5 mm is utilized. The coatings containing FeSi and FeSi@SiO2 flakes as fillers present adjustable electromagnetic absorbing (EMA) performances and can be promising candidates for EMA application, especially in S band.

Dielectric and microwave absorption properties of FeSiAl/Al2O3 composites containing FeSiAl particles of different sizes

Here in, the effects of FeSiAl particle size on the dielectric and microwave absorption properties of FeSiAl/Al2O3 composites were studied. FeSiAl/Al2O3 composites containing 18–25 μm, 25–48 μm, and 48–75 μm FeSiAl particles were prepared by hot-pressed sintering based on uniformly mixed FeSiAl and Al2O3 powders. Results show that the real permittivity and the imaginary permittivity are significantly promoted with increasing FeSiAl particle size, which is ascribed to the enhanced interfacial polarization and conductance loss. In addition, the favorable matching impedance and suitable attenuation coefficient enabled the composite containing 25–48 μm FeSiAl powder to show a minimum reflection loss of −34.4 dB at 11.7 GHz and an effective absorption bandwidth (<-10 dB) of 1.4 GHz in 11.0–12.4 GHz, when the thickness is 1.1 mm. By adjusting the thickness to 1.4 mm, the effective absorption bandwidth of the composite reaches a maximum value of 2.0 GHz in the 8.3–10.3 GHz range, indicating tunable, strong, and highly efficient microwave absorption performance.

Synthesis of well-insulated Fe–Si–Al soft magnetic composites via a silane-assisted organic/inorganic composite coating route

In this study, an organic/inorganic composite coating method based on silane, silicon oil, and tetraethyl orthosilicate was developed to prepare Fe–Si–Al soft magnetic composites (SMCs). The insulation reaction processes may have involved the hydroxylation of magnetic powder and condensation of silanol groups. Analyses of the microstructure and high frequency stability of the effective permeability of the SMCs demonstrated the formation of a high-quality silicon oxide coating layer on the surfaces of the Fe–Si–Al particles. The effects of the insulation content on the density, resistivity, and magnetic properties were studied for the well-insulated Fe–Si–Al SMCs, and the underlying physical mechanisms were clarified. The results showed that increasing the insulation content reduced the effective permeability and the eddy current loss, but increased the DC-bias performance and hysteresis loss. The enhancement of the effective demagnetizing field indicated by the decrease in the density of the SMCs may have been responsible for the enhanced hysteresis. In addition, the increase in the resistivity of the SMCs may have contributed to the decrease in the eddy current.

Fabrication and Characterization of Carbon-Fiber-Reinforced Polymer-FeSi Composites with Enhanced Magnetic Properties.

In this work, we aimed to manufacture and characterize carbon-fiber–polymer–metal-particles magnetic composites with a sandwichlike structure. The composites were manufactured by stacking the plain woven carbon fiber prepregs (or carbon-fiber-reinforced polymers (CFRP)) and layers of the FeSi particles. The layer of FeSi particles were formed by evenly distributing the FeSi powder on the surface of carbon fiber prepreg sheet. The composites were found to have better magnetic properties when the magnetic field were applied in in-plane (0°) rather than in through-thickness (90°), and the highest saturation magnetization of 149.71 A.m2/kg was achieved. The best inductance and permeability of 12.2 μH and 13.08 were achieved. The composites obviously exhibited mechanical strength that was good but lower than that of CFRP composite. The lowest tensile strength and lowest flexural strength were 306.98 MPa and 855.53 MPa, which correspond to 39.58% and 59.83% of the tensile strength and flexural strength of CFRP (four layers), respectively.

Effect of Si Content on the Formation of {100} &lt;uvw&gt; Orientation in 0.27% Al Non-oriented Electrical Steel during Cell-to-Dendrite Transition Process

The effects of Si content (0.73%, 2.23%, 4.57%) and solidification rate (10 µm/s, 35 µm/s, 80 µm/s) on the as-cast microstructure and crystal orientation of 0.27% Al non-oriented electrical steel have been studied by directional solidification technology. Si atoms were inclined to segregate on the trunks and stems of cells and dendrites, and precipitate in the form of quadrilateral Fe-Si particles with size less than 4 μm. Increasing Si content would lead to a decrease in thermal conductivity of steel and directly cause an increase in temperature gradient of liquid steel, and as a result, make solid–liquid interface more stable and easier to grow as cell crystal. Moreover, decreasing solidification rate could further aggravate Si segregation at solid–liquid interface. Higher Si content (4.57%) together with lower solidification rate (10 µm/s) was more beneficial to the grain nucleation with {100} orientation, whereas higher solidification rate (80 µm/s) played a major role in the grain nucleation with {110} orientation.

Effects of Cu addition on the microstructure and properties of the Al–Mn–Fe–Si alloy

Abstract Heat exchanger materials with high strength and thin thickness are highly required due to the increasing demands of weight reduction and fuel economy of the automobile. In this work, 0.5 wt% Cu was added to an Al-1.5Mn-0.3Fe-0.6Si (wt.%) alloy to improve the strength. The microstructure, mechanical properties, and electrochemical properties of the tested alloys were systematically investigated. The results suggest that part of Cu is dissolved into the Al matrix, and the balance is incorporated into the Al(Mn,Fe)Si particles. Cu addition improves the strength at the expense of deteriorating the pitting corrosion resistance. On the one hand, the improved strength derives from enhanced solid solution hardening and increased nanoparticle strengthening. On the other hand, the incorporation of Cu in the Al(Mn,Fe)Si intermetallic particles increases the potential difference between the particles and the Al matrix, resulting in the deteriorated pitting corrosion resistance.

Magnetic behavior of soft magnetic composites constructed by rapidly quenched flake-like FeSiAl alloy

Herein, flake-like FeSiAl particles are prepared by rapid quenching and subsequent ball milling processes. Then, soft magnetic composites are fabricated by orderly aligned flake-like FeSiAl particles, resulting in the formation of nacre-like structure. The influence of processing parameters on columnar microstructure of the thin strips has been studied in detail. Furthermore, the magnetic permeability and loss of the soft magnetic composites, with different compositions, are explored. The results reveal that the soft magnetic composite, with flake-like Fe85Si9.6Al5.4, renders the magnetic permeability of 200 at 1 MHz, which is much higher than the spherical FeSiAl particles. Moreover, the negative temperature-dependent loss and a valley temperature of 65 °C are observed at the Sendust composition of Fe85Si8.8Al6.2, which maintained the magnetic permeability of 172 at 1 MHz and a loss of 380 kW/m3 at 50 kHz (stimulated at 100 mT). It is worth emphasizing that the nacre-like SMC exhibits outstanding properties and renders promise for next-generation magnetic devices.

Temperature-controlled conversion from Fe–Si particles to integrated Fe–Si/SiO2 core–shell structure particles during fluidised bed chemical vapour deposition

In the synthesis of ferromagnetic/SiO2 core–shell structures, the minimum formation conditions and evolution mechanism are worth investigating. In the present study, to determine the minimum formation temperature of an integrated Fe–Si/SiO2 core–shell structure during chemical vapour deposition in a fluidised bed, the effects of deposition temperature on the structural and magnetic performances of SiO2 insulation coatings on Fe–Si particles were investigated. Thermodynamic calculations and differential scanning calorimetry were used to understand the thermal decomposition of C8H20O4Si. The results of the theoretical and structural studies showed that the minimum deposition temperature of the amorphous SiO2 insulation coating on the Fe–Si particle surface was ~880 K and that the Fe–Si/SiO2 composite structure started to convert into an integrated Fe–Si/SiO2 core–shell structure after the deposition temperature was raised above 920 K. The increase in the thickness of the SiO2 insulation layer due to the increased deposition temperature was studied using X-ray diffraction and scanning electron microscope analyses. The results of X-ray photoelectron spectroscopy showed that four and five types of electronic structures existed in the SiO2 insulation shell for silicon and oxygen, respectively, and that only 32.74 at.% of the oxygen from the Si(OSi)3(OH) group interacted with the Fe–Si alloy surface. The results of the performance test indicated that the integrated Fe–Si/SiO2 core–shell structure led to a substantial enhancement in the electrical resistivity of the particles and reduction in their saturation magnetisation, but hardly affected the coercive force.

Influence of annealing treatment on microstructure and magnetic properties of cold sprayed Ni-coated FeSiAl soft magnetic composite coating

Fully dense and thick Ni/FeSiAl soft magnetic composite deposits were successfully fabricated by cold spraying (CS) using the Ni-coated FeSiAl composite powder. To improve magnetic properties, the post-annealing treatments were conducted on CS deposits to eliminate the undesired internal defects, like strain stress and dislocations, and fine grains. Characterization of the composite coating was carried out in terms of X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD) analyses. XRD patterns displayed that no newly formed phases were observed at different annealing temperatures, even though EDS analysis showed obvious element diffusion between Ni matrix and FeSiAl particles at the temperature of 800 °C for 2 h. Grain growth and stress relief after annealing treatment were proved by both XRD and EBSD analyses. The magnetic property measurements showed that the coercivity was decreased by around two times (from 62 to 30 Oe) and the magnetization saturation was increased by 15% (from 68 to 80 emu/g). The relevant mechanisms were discussed in terms of microstructural evolution. This work shows that the post heat treatment can be a potential method to improve the soft magnetic properties of CS coating.

Ultra-low inter-particle eddy current loss of Fe3Si/Al2O3 soft magnetic composites evolved from FeSiAl/Fe3O4 core-shell particles

Abstract FeSiAl/Fe3O4 core-shell composite particles and transformed Fe3Si/Al2O3 composite compacts have been prepared via ball milling coating combined with subsequent spark plasma sintering (SPS) process. The formation mechanism of the Al2O3 insulating layer and the magnetic properties of the Fe3Si/Al2O3 composite compacts have been investigated systematically. The FeSiAl particles are coated with uniform Fe3O4 nanoparticles by ball milling method. And during SPS process, the new phase Fe3Si/Al2O3 composite compacts are formed due to the high temperature solid phase reaction between FeSiAl alloy core and Fe3O4 coatings. The Fe3Si phase possesses excellent soft magnetic properties and the uniform Al2O3 layer shows good insulativity. Therefore, the Fe3Si/Al2O3 composite compacts exhibit superior soft magnetic performance such as enhanced saturation magnetization, reduced coercivity, good permeability stability, high resistivity and thus low core loss at high frequency compared with the original FeSiAl compacts. The investigated results in this work indicate that FeSiAl alloy particles coated with iron oxides can be transformed into soft magnetic composite materials with new insulating layer via high temperature solid phase reaction, which provides a promising approach to develop new-style soft magnetic composites with excellent electro-magnetic properties.