FeSi Particles Research Articles

Improved magnetic and thermal conductivity performance of FeSi soft magnetic composites by adding h-BN

Low heat generation and high thermal conductivity are the basic guarantees for stable operation of magnetic devices. In this paper, h-BN nano-sheet were coated on FeSi particles to prepare FeSi/h-BN magnetic cores with a low loss and high thermal conductivity. The surface modified h-BN evenly coated on FeSi particles improved the insulation between magnetic particles. Appropriate amount of h-BN sheet addition effectively reduced the eddy current loss and improved thermal conductivity of FeSi soft magnetic composites (SMCs), which can be attributed to the high resistivity and high planar thermal conductivity of h-BN nano-sheet. The FeSi SMCs with 3 wt% h-BN has the optimum comprehensive properties, effective permeability of 57, saturation magnetization of 172.2 A.m2/kg, low core loss of 601.6 mW/cm3 at 60 mT and 100 kHz, and its thermal conductivity increased by 62 % to 11.03 W m-1K−1, which is useful for the stable operation of devices.

Significantly improved magnetic properties of FeSiAl soft-magnetic composites by adding FeSi fine particles and regulating annealing temperature

In this work, the effects of adding FeSi fine particles and regulating temperature on the magnetic properties of FeSiAl soft magnetic composites (SMCs) are studied. It shows that the addition of FeSi fine particles can effectively fill the pores among FeSiAl particles, reducing the content of non-magnetic substances and improving the density of the SMCs. Meanwhile, the saturation magnetization and DC-bias characteristics are enhanced. And the optimal particle mixture structure and best magnetic properties of SMCs are achieved when doping with 30 wt% FeSi fine particles. Additionally, increasing the annealing temperature to 700 °C is beneficial to eliminate the residual stress and structural defects, which further optimizes the magnetic properties of the SMCs. However, when the annealing temperature is increased to 800 °C, the insulation layer is severely destroyed, resulting in the deteriorated frequency stability and increased core loss.

Vortex-based soft magnetic composite with ultrastable permeability up to gigahertz frequencies

Soft magnetic materials with stable permeability up to hundreds of megahertz (MHz) are urgently needed for integrated transformers and inductors, which are crucial in the more-than-Moore era. However, traditional frequency-stable soft magnetic ferrites suffer from low saturation magnetization and temperature instability, making them unsuitable for integrated circuits. Herein, we fabricate a frequency-stable soft magnetic composite featuring a magnetic vortex structure via cold-sintering, where ultrafine FeSiAl particles are magnetically isolated and covalently bonded by Al2SiO5/SiO2/Fe2(MoO4)3 multilayered heterostructure. This construction results in an ultrastable permeability of 13 up to 1 gigahertz (GHz), relatively large saturation magnetization of 105 Am2/kg and low coercivity of 48 A/m, which we ascribe to the elimination of domain walls associated with almost uniform single-vortex structures, as observed by Lorentz transmission electron microscopy and reconstructed by micromagnetic simulation. Moreover, the ultimate compressive strength has been simultaneously increased up to 337.1 MPa attributed to the epitaxially grown interfaces between particles. This study deepens our understanding on the characteristics of magnetic vortices and provides alternative concept for designing integrated magnetic devices.

Evolution of the microstructure and electromagnetic properties of Fe–Si–Al particles during post ball-milling annealing

FeSiAl alloys with a composition of Fe-9.6Si-5.4Al, also known as Sendust alloys, present the unique potential to exhibit efficient electromagnetic wave absorption (EMA) in the P-band. However, the electromagnetic properties of this type of alloy are highly sensitive to the shape, microstructure, and microchemistry, which then inspire the current research. The evolution of the microstructure/microchemistry of FeSiAl particles was systematically revealed in a single particle scale for the first time, and the resulting influence on the electromagnetic properties was investigated. Recrystallization occurs in the annealing process on FeSiAl particles and the oxide films on the surface evolve evidently when annealed in 5%H2/Ar or air, which can conduce improved electromagnetic properties. The FeSiAl particles annealed in 5%H2/Ar present efficient EMA in the P-L band while those in air contribute to high reflection loss. This work indicates the feasibility of achieving a high and adjustable EMA efficiency in the P-L band through microstructure and microchemistry tailoring.

Efekat ojačanja kompozita glinice matriksom inkluzijama ZrB₂ i FeSiAl na dielektrična svojstva na mikrotalasnim frekvencijama

In this paper, two composites ZrB₂/Al₂O₃ and FeSiAl/Al₂O₃ were characterized using the Transmission/Reflection characterization technique. The volume contents of ZrB₂ and FeSiAl inclusions in these composites vary between 0 and 15%. The results obtained indicate that the percentage of the inclusions in the composites effectively improves the dielectric property. The comparison of the effect of ZrB₂ and FeSiAl inclusions on the dielectric properties of these composites confirms that reinforcing these composites with FeSiAl particles results in better dielectric properties. Furthermore, these results indicate that the dielectric property of the two composites studied decreases progressively with increasing frequency in the X band. This frequency dependence of the dielectric property of the composites studied is very important and shows that the composites studied are good candidates for microwave absorption applications in the X-band and for antenna design. Additionally, a comparison between the numerical results obtained in this work and the experimental results published in the literature reveals a close agreement, validating the reliability of the study's findings.

High-performance FeSiAl soft magnetic composites achieved by confined solid-state reaction

Soft magnetic composites (SMCs) consisting of insulated metallic magnetic particles are critical materials in modern electronics. However, the simultaneous optimization of power loss and permeability for SMCs remains challenging due to the vulnerable insulation layer inside. Here, we succeed in fabricating FeSiAl SMC by confined solid-state reaction between TiO2 and FeSiAl matrix, which leads to the formation of homogeneous and lattice-matched Al2O3 layer and brings about effective electrical insulation of FeSiAl particles. TiO2 can progressively release O atoms and confine the solid-state reaction strictly within the interfacial region. Meanwhile, itself becomes ferromagnetic with deficient oxygen, resulting in alleviated magnetic dilution. Fast domain wall displacement and small hysteresis loss are directly observed by in-situ Lorenz transmission electron microscopy. The obtained FeSiAl SMC exhibits low power loss of 130 mW·cm−3 (50 mT, 100 kHz) and high effective permeability of 143, which is desired in energy-saving and high-efficiency devices. This work relates the interfacial behavior with magnetic properties and highlights a new strategy for fabricating high-performance SMCs.

Interfacial Reaction Enhanced Liquid‐Phase Sintering of Metal/Oxide Soft Magnetic Composite

AbstractSoft magnetic composites (SMCs) are ungently demanded in high‐frequency power electronics for their large magnetization and high electrical resistivity. However, traditional cold‐pressed SMCs are faced with low mechanical strength and insulation instability, which severely restricts their applications. In this study, liquid‐phase sintering techniques to prepare FeSiAl/MoO3 SMCs are orginally employed, where consolidation and insulation of metallic magnetic particles are achieved in one step. The redox reaction between FeSiAl and MoO3 melt greatly reduces the interfacial energy, facilitates fully wetting of FeSiAl particles by MoO3 melt, and promotes the densification process during sintering. In the final FeSiAl/MoO3 SMC, FeSiAl particles are bonded covalently and insulated electrically/magnetically by the resultant Al2O3 transition layer, endowing the SMC with high crushing strength of 250 MPa, cut‐off frequency of 110 MHz, permeability of 35 (@1 MHz), and low power loss of 962 kW m−3 (5 MHz, 5 mT). This study provides alternative concept for designing new SMCs, and broadens the connotation and extension of liquid‐phase sintering.

A bilayer array metamaterial based on silicon carbon foam/FeSiAl for broadband electromagnetic absorption

In this paper, a bilayer array metamaterial (BAMM) based on silicon carbon (SiC) foam/FeSiAl composite was proposed and the electromagnetic (EM) absorption performance of the BAMM was enhanced by regulating the material composition and geometrical parameters. The introduction of magnetic FeSiAl particles contributed to the reinforced low-frequency absorption of the BAMM. The geometrical parameter design resulted in the broadened effective absorption bandwidth (EAB, reflection loss value≤−10 dB) by improving the impedance matching between the BAMM and the free space. At the same time, it was found that the tuning of the geometrical parameters has a more crucial effect on the absorption properties than the regulation of material composition. Moreover, the EM absorption mechanism was investigated by analyzing the distribution of the EM field and the power loss. In addition to the polarization and magnetic losses in the BAMM, the EM energy is mainly dissipated by the scattering effects concentrated at the outer edge of the unit cell and by the EM resonances between neighboring unit cells. The optimized SiC foam/FeSiAl-1based BAMM exhibits an effective absorption in the frequency range of 2–18 GHz by calculation, and then the corresponding experimental BAMM sample is prepared and measured. The experimental results are in good agreement with the simulations and demonstrate an EAB of 15.77 GHz, indicating that the geometrical parameters design based on high-loss materials is an attractive and efficient strategy to obtain broadband absorbers.

The effect of volume concentration on the properties of easy-plane FeSiAl composites working in high frequency band

In this study, to investigate the effect of volume concentration on core loss in the high frequency band (∼MHz), easy-plane soft magnetic composites (SMCs) of FeSiAl particles with different volume concentrations were prepared successfully by magnetic field orientation. The permeability of the SMCs was decomposed into the domain wall component and the spin component and was well simulated. The core loss was successfully decomposed into hysteresis loss, eddy current loss and anomalous loss. It was shown that the permeability of the SMCs was continuously improved as the volume concentration of FeSiAl in the SMCs increased, while the core loss decreased first and then increased due to the different performances of the hysteresis loss, eddy current loss, and anomalous loss. Samples with a permeability of 310 exhibited the lowest core loss of 399 kW m−3 (f = 3 MHz, 10 mT). The results indicated that there is an optimal volume concentration at which SMCs have a relatively high permeability and minimum core loss.

A Prominent Iron Silicides Strewn Field and Its Relation to the Bronze Age/Iron Age Chiemgau Meteorite Impact Event (Germany)

About 20 years ago, amateur archeologists and local history researchers discovered the iron silicide (FESI) strewn field measuring about 60 km x 30 km in the districts of the Chiemgau and the Inn-Salzach region in southeast Germany. They evidenced the connection between the FESi distribution and the pervasive rim wall craters and suggested a meteorite impact event, now widely recognized under the name of the Chiemgau impact. Widespread in the strewn field and in individual finds far beyond it they recovered and documented thousands of FESI particles of millimeter to centimeter size with a total mass of more than 2 kg, whereby a large lump of 8 kg stands out as a single find. The find layer is largely uniformly located at a depth of 30 - 40 cm in a glacial loose sediment soil. Microprobe, SEM-EDS, TEM and EBSD analyses determined as main minerals gupeiite and xifengite, subordinately hapkeite, naquite and linzhite. Besides the main elements Fe and Si of the matrix, more than 30 other chemical elements have been addressed so far, including uranium and various REE. Incorporated into the FESI matrix are the carbide minerals moissanite and titanium carbide as superpure crystals, and khamrabaevite, zirconium carbide, and uranium carbide, furthermore CAIs. SEM images indicate shock metamorphism. The present article describes the discovery history of this worldwide unique FESI occurrence with the exact find situations, as well as the very varied morphologies of the find particles with the macroscopically recognizable components and SEM EDS examples.

Change in Oxygen Reduction Reactivity of Intermetallics: A Mechanism of the Difference in Trenching around Al–Fe and Al–Fe–Si Particles on AA1050 in NaCl

Trenching around intermetallic particles on AA1050 aluminum in 0.1 M NaCl at pH 6.0 was analyzed by in situ observations. Deep trenches, which become the initiation site for pitting, were formed around the Al–Fe–Si particles but not around the Al–Fe particles. The open-circuit potentials of the bulk intermetallic compounds and Al-matrix of AA1050 without intermetallic particles were measured. It was determined that the Al–Fe–Si and Al–Fe particles were cathodically polarized by the Al-matrix of AA1050 under natural immersion conditions. This cathodic polarization was found to change the oxygen reduction reactivity of the intermetallic particles. The cathodic reactivity on bulk Al–Fe was higher than that on bulk Al–Fe–Si under as-polished condition. However, after potentiostatic cathodic polarization, the cathodic reactivity on bulk Al–Fe decreased, whereas that on bulk Al–Fe–Si increased. Micro-electrochemical measurements and surface analyses clarified that the change in the cathodic reactivity of the intermetallic particles plays a critical role in trenching on AA1050 aluminum.

Study on FeSiAl magnetic powder core coated with nano-Y2O3 and its influence on magnetic properties

The microstructure and magnetic properties of the FeSiAl /phosphoric acid/nano-Y2O3/kaolin soft magnetic composites were investigated in this article. The morphology and structure were characterized by SEM, EDS, XRD, DSC, and XPS. The surface of FeSiAl powder particles was densely and uniformly coated with a phosphoric acid/nano-Y2O3/kaolin insulating coating. It was discovered that nano-Y2O3 played a dominant role in the coating process. Using a precision magnetic analyzer and lossy power tester, the effective permeability, quality factor, DC bias performance, and the core loss of the FeSiAl/phosphoric acid/nano-Y2O3/kaolin SMCs after pressing and annealing were computed and examined. The results show that nano-Y2O3 can improve the quality factor and DC bias performance of the powder core, but leads to a reduction in magnetic permeability and the core loss is also a little high. This behavior may be caused by the competition mechanism: nano-Y2O3 lowers the magnetic coupling between FeSiAl particles, resulting in a decrease in permeability and an increase in the core loss. When the content of nano-Y2O3 is 5 wt%, the comprehensive magnetoelectric performance is good (ue=21.04, at f =100 kHz; Pcv = 1555.13 mW/cm3, at f = 50 kHz; Q = 150.25, at f = 70 kHz; at Bm = 1000 Gs). The effects of nano-Y2O3 coating on the permeability and the loss of FeSiAl SMCs will be a major focus of future research and development.

Fe-6.5 wt%Si soft magnetic composites with significant improvement of magnetic properties by compositing nano-MnZn ferrites

A novel soft magnetic composites (SMCs) was prepared by Fe-6.5 wt%Si/nano-MnZn ferrites composite powders in this work. The nano-MnZn ferrites (~ 20 nm) were synthesized by thermal decomposition method. The microstructure and electromagnetic characteristics of Fe-6.5 wt%Si/nano-MnZn ferrites SMCs were investigated in details. The results showed that the effective permeability increased firstly and then decreased with increasing nano-MnZn ferrites contents from 0 to 4 wt%. Moreover, appropriate added amounts of nano-MnZn ferrites can reduce the hysteresis losses of the SMCs. The SMCs with 2 wt% nano-MnZn ferrites and annealed at 400 ℃ have the optimum comprehensive performances with effective permeability of 142.2 (increased by 47%), total core losses of 816 mW/cm 3 (decreased by 12%) and acceptable electrical resistivity of 3.18 Ω·cm. • Fe-6.5 wt%Si/ nano-MnZn ferrites soft magnetic composites were prepared. • Nano-ferrites play a key role in ensuring adjacent Fe-Si particles connective. • Permeability and core losses were improved by compositing nano-ferrites.

Reduction of core loss for FeSi soft magnetic composites prepared using atomic layer deposition-based coating and high-temperature annealing

Using atomic layer deposition and high-temperature annealing to fabricate coatings for Fe-6.5 wt%Si powder reduce the hysteresis losses of the resultant composites drastically without sacrificing the permeability properties, and keep the eddy current losses at a relatively low value. The core loss of annealed FeSi SMCs is 39.67% lower than that of composites prepared using raw Fe-6.5 wt%Si powder, meanwhile the permeability remains at relatively high value (at B = 100 mT, f = 50 kHz). The decreasing of the core loss is mainly attributed to hysteresis loss reduction caused by grain growth. And the low eddy current loss is guaranteed by the uniform, complete, compact coating layer formed the surface of FeSi particles, which transforms to a protective and insulating layer containing silicate and metal oxide after annealing. On the premise of ensuring the integrity of the insulation layer, the annealing temperature of powder is significantly increased by surface modification, so as to reducing the hysteresis loss meanwhile controlling the eddy current loss. • Low core loss Fe-Si soft magnetic composites were prepared. • Nano-Al 2 O 3 was deposited on the surfaces of Fe-Si powders by ALD. • A protective and insulating layer formed at the interface after annealing. • Hysteresis loss reduced obviously due to the grain growth. • Decline of hysteresis loss dominates the dramatic reduction of total loss.

Influence of sintering temperature on heterogeneous-interface structural evolution and magnetic properties of Fe–Si soft magnetic powder cores

Ceramic oxides have attracted considerable research attention as ideal coating layers for novel Fe-based soft magnetic powder cores (SMPCs). However, maintenance of the integrity and uniformity of Fe-based/MOx core–shell heterostructures is challenging. The mechanism underlying the evolution of the core–shell heterostructure is a key determinant of the performance of Fe-based SMPCs. Herein, the laws governing the evolution of the core–shell structure of and heterogeneous interface in Fe–Si/SiO2 SMPCs with temperature and the influence of this evolution on SMPCs performance were investigated. The results revealed that at the sintering temperature of 1093–1183 K, the core–shell heterostructure gradually integrated, while SiO2 insulating coatings underwent amorphous-to-crystalline state transformation. When the sintering temperature was >1243 K, Fe–Si particles melted partially, and the core–shell heterostructure collapsed owing to the overheating induced by the gradient temperature field during the hot-pressing sintering process. When the sintering temperature was 1153 K, the core–shell heterostructure was intact, and the Fe–Si/SiO2 SMPCs had a saturation magnetisation of 245.5 emu/g, resistivity of 0.42 mΩ cm, and total loss of 923.2 kW/m3 at 10 mT and 100 kHz. When the core–shell heterostructure was destroyed, the resistivity dropped drastically, and the total loss increased by approximately 36.7% and 41.8%. Based on these results, the relationship among the core–shell heterostructure of Fe–Si/SiO2 SMPCs, sintering temperature, and magnetic properties was established, which is instrumental in achieving high power density, high efficiency, and miniaturisation in SMPCs.

Ultra-low core loss FeSiAl-based soft magnetic composites with ultra-thin MoO3 composite insulating layer

In this work, core/shell structured FeSiAl/MoO3 (spherical FeSiAl covered by ultra-thin MoO3 composite insulating layer) soft magnetic composites (SMCs) have been fabricated by a two-step heat treatment process. The influences of ammonium molybdate (AHM) content, first-step annealing temperature and second-step annealing temperature on magnetic, mechanical properties and electrical resistivity (ρ) have been comprehensively investigated. It is shown that the coating integrity and the thickness of MoO3 nanoparticles layer can be regulated by the content of AHM, leading to the improvement of ρ. Moreover, composite insulating layer with the thickness of 47 ± 8 nm is formed and completely coated on FeSiAl particles with 15 wt% AHM, resulting in the fact that the highest radial crushing strength (K = 62.3 MPa) and lowest core loss (Pcv = 128.8 mW/cm3) is obtained. In addition, Pcv is separated into two components: hysteresis loss component and eddy current loss component. Further studies display that eddy current loss is only half of hysteresis loss. As a result, the FeSiAl SMCs with 47 ± 8 nm MoO3 composite insulating layer possess the lowest core loss of 128.8 mW/cm3 at 50 mT/100 kHz. The low core loss of the FeSiAl/MoO3 SMCs with ultra-thin composite insulating layer has a great potential in the fields of conversion and power transmission.

Fe-Si and its nanocrystallization as soft magnetic phase in SmCo-based nanocomposites

Nanocomposite magnets have attracted much attention because of their ultra-high theoretical magnetic energy product and saving rare earth resources. In this study, the Fe93.5Si6.5 with higher hardness than the most common soft magnetic phase (α-Fe) was used to synthesize SmCo5/Fe-Si nanocomposite magnets, and its nanosized process was studied. The results showed that Fe-Si can be well dispersed into SmCo5 matrix through 12 hours of ball milling, and appeared in fine and evenly distributed grains in the SmCo5/Fe-Si nanocomposites, indicating it is suitable for soft magnetic phase. The nanosized process of Fe-Si phase can be summarized as from the irregular shape of agglomeration, to long chain, and finally too uniformly dispersed Fe-Si particles with increased milling time. As a result, the SmCo5/Fe-Si nanocomposite magnet with the optimal maximum magnetic energy product was 14.3 MGOe, accompanied by remanence of 9.5 kG and coercivity of 8.2 kOe. Our results show that by using Fe-Si with high hardness as the soft magnetic phase, the prepared nanocomposite magnet not only has good properties, but also can be expected that the two phases with closer mechanical properties can be deformed harmoniously.

Selective synthesis and magnetic properties of iron silicide (Fe3Si and FeSi) at low temperature

Iron silicide (Fe3Si and FeSi) particles have been selectively synthesized through a solid-state reaction route.

High performance of FeSiAl/hBN soft magnetic composites

FeSiAl/hBN soft magnetic composites were prepared by mixing gas atomized FeSiAl powder and hexagonal BN by ball milling at a certain mass ratio and then compacted and annealed. The microstructure of the composites was characterized by XRD, SEM and EDS. It was found that ball milling can destroy the weaker interlayer bond of hexagonal BN and turn it into nanoflakes attached to the surface of FeSiAl particles. The magnetic properties of the composites were measured by SQUID and B-H analyzer. It was found that the nanoflakes on the surface of FeSiAl particles effectively blocked the eddy current among different metallic particles and largely reduced eddy current loss. The permeability analysis showed that the composites had a relative lower magnetic loss at f = 30 MHz, which indicated that the FeSiAl/hBN composites can be used in a frequency higher than other FeSiAl composites. However, the saturation magnetization and permeability of the composites decreased with the increase of BN content. The experimental results show that the magnetic loss value of FeSiAl/1 wt% hBN soft magnetic composites is about 392 kW m−3 at f= 100 kHz and Bm= 100mT, which is just about 2/3 of commercial FeSiAl soft magnetic composites.

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.