Magnetic Powder Cores Research Articles

High filling alumina/epoxy nanocomposite as coating layer for Fe-based amorphous powder cores with enhanced magnetic performance

A high-filling alumina/epoxy nanocomposite with improved thermal stability and insulation performance has been successfully designed as an organic–inorganic coating layer for the toroid-shaped FeSiBPNbCr amorphous magnetic powder cores (AMPCs). Unlike the organic coating, the organic–inorganic hybrid coating cores exhibited superior magnetic properties without compromising on saturation magnetization and permeability. The core loss declined by 40%, and the quality factor was 13% higher as half alumina was introduced into the epoxy resin matrix. A thin and uniform-coating layer of alumina/epoxy nanocomposite led to better high-frequency characteristics than those obtained with direct coating of the cores with alumina. Besides the outstanding magnetic properties, the Fe-based AMPCs with a convenient insulation-coating process cost lesser than Fe–Ni magnetic powder cores, thereby rendering the Fe-based AMPCs a potential candidate for a variety of industrial applications.

A Novel Fabrication of Spherical Fe50Ni50 Alloy Powders via in-Situ De-Wetting of Liquid Solid Interface

Spherical Fe50Ni50 alloy powders were fabricated via a novel route based on in-situ interface de-wetting between liquid Fe-Ni alloy and alumina. The obtained Fe50Ni50 alloy particles exhibit very good spherical shape according to SEM images. Furthermore, the cross-sectional SEM images show that there are no pores and bulk inclusions in the internal region of the spherical particles. The XRD results show a trace amount of the impurity alumina phase appearing in taenite phase. The size distribution agreed well with the SEM observation confirms that the alumina powders successfully segregated pre-alloy powders. As an incidental benefit, the surface alumina particles were treated as the electrical insulation coatings. The magnetic character shows that spherical Fe50Ni50 powders exhibit a good soft magnetic property even though with a slightly decreasing of saturation magnetization due to non-magnetic coatings. Our strategies provide a method to in-situ fabricate insulation coated Fe-Ni spherical alloy powders as magnetic powder core.

Heat Treatment Effects on Electrical Resistivity of Spinel Ferrite Layer for Powder Magnetic Core

Heat Treatment Effects on Electrical Resistivity of Spinel Ferrite Layer for Powder Magnetic Core

The core-shell structured Fe-based amorphous magnetic powder cores with excellent magnetic properties

The Fe-based soft magnetic amorphous powder cores (AMPCs) with excellent comprehensive magnetic properties were successfully designed and fabricated using the core-shell structured FeSiBCCr/TiO2 composite powders. The influence of the concentration of water (H2O) for the magnetic performance of the AMPCs has been systematically studied based on careful analysis of the process of nucleation and growth of TiO2 under different H2O concentration in the reaction system. The growth process for the TiO2 coating layer with the H2O concentration in the range of 0.01–0.02 ml/g corresponds to the heterogeneous nucleation phase, while the mixing phase of heterogeneous and homogeneous nucleation occurs when the concentration of H2O increases to 0.03 ml/g. Optimized soft magnetic properties have been achieved for the AMPCs with H2O concentration of 0.02 ml/g, including high permeability of 81.5 with a high frequency stability up to 10 MHz, high quality factor of 102 at 530 kHz, low core loss of 42 mW/cm3 at 500 kHz for Bm = 0.01 T, and better DC-bias property of 52% at a bias field of 100 Oe due to the uniform and proper thickness insulation coating layer, which can be used to produce miniature magnetic components for applications in medium and high-frequency fields.

Preparation and characterization of flaky FeSiAl composite magnetic powder core coated with MnZn ferrite

The flattening of FeSiAl soft magnetic powder was achieved by ball milling process, and MnZn/FeSiAl composite magnetic powder core was prepared by press molding. The effect of different coating amount of MnZn ferrite on the soft magnetic properties of FeSiAl was studied. At the same time, the optimal stress-relieving annealing temperature of the composite magnetic powder core is revealed. The results showed that the addition of MnZn ferrite affected the magnetic properties such as saturation magnetization (Ms), initial permeability (μi) and power loss (Pcm) of FeSiAl soft magnetic. With the increase of MnZn ferrite addition content, the saturation magnetization of composites decreased gradually, and the magnetic permeability increased first and then decreased, and the loss decreased first and then increased. When the addition content of MnZn ferrite was 5%, the permeability reached the maximum, which was 28.1% higher than that of the pure FeSiAl magnetic powder core under the same conditions. At the same time, the loss was the lowest, which was 13.3% lower than the pure FeSiAl powder core under the same conditions. When the annealing temperature is around 650 °C, the magnetic powder core has the largest magnetic permeability and the lowest loss.

Strategy to Enhance Magnetic Properties of Fe78Si9B13 Amorphous Powder Cores in the Industrial Condition

In this study, the soft magnetic properties of Fe78Si9B13 amorphous magnetic powder cores (AMPCs) were enhanced by coordinately adjusting the technological parameters, including the particle size distribution, molding pressure, and coating agent content, in the industrial condition. The results show that the optimized comprehensive soft magnetic properties of the Fe78Si9B13 AMPCs could be obtained under the following process conditions: (1) the distribution of particle size is 20 wt.% for 140–170 mesh, 70 wt.% for 170–270 mesh, and 10 wt.% for 270–400 mesh; (2) the molding pressure is in the range of 2.35–2.45 GPa; and (3) the additive amount of sodium silicate is 1.5 wt.%. After the collaborative optimization, the AMPCs’ compact density, ρ, the effective permeability, μe, and the residual effective permeability at the applied magnetizing field of 7.96 kA/m, μe@7.96 kA/m, increased from 5.61 g/cm3 to 5.86 g/cm3, from 58.13 to 77.01, and from 40.36 to 49.57, respectively. The attenuation ratio of the effective permeability, when in the frequency band of 20–100 kHz, was less than 0.85%. The core loss at the 50 kHz for the maximum magnetic flux density of 0.1 T reduced from 380.85 mW/cm3 to 335.23 mW/cm3. This work will encourage the further application of Fe-based AMPCs in the fields of electronics and telecommunication.

Improvement of soft magnetic properties of FeSiBPNb amorphous powder cores by addition of FeSi powder

The effect of FeSi powder with volume fraction of 0–40% on the soft magnetic properties of the FeSiBPNb amorphous powder cores has been systematically investigated in this study. The results shows that the amorphous magnetic powder core mixed with 10% FeSi powders in volume fraction exhibits superior DC-bias properties, constant permeability, low core loss up to a higher frequency range, and excellent soft magnetic properties after appropriate heating treatment. The DC-bias properties of the present amorphous magnetic cores decrease by only 20% as the external field increases to 100 Oe. Meanwhile, it also exhibits a high permeability of 60 at 10 MHz and a low core loss of 159 W/kg at Bm = 0.1 T and f = 50 kHz. The present Fe-based amorphous magnetic powder cores mixed FeSi powders with superior DC-bias properties are a potential candidate for a variety of industrial applications.

Direct Digital Control of Single-Phase Grid-Connected Inverters With <italic>LCL</italic> Filter Based on Inductance Estimation Model

Soft magnetic powder cores with their high saturation flux density and low core loss are excellent alternatives for filter inductors in inverter-based applications. However, their nonlinear current-dependent inductance characteristics pose a challenge for control of grid-connected inverter with LCL filter. In this paper, the variable inductance conundrum is discussed and a modified direct digital control method based on a variable-structure inductance estimation model that takes into consideration wide nonlinear variation in both inverter- and grid-side inductances is proposed. The proposed method is shown to have better grid-voltage harmonic rejection and improved stability margins. However, investigation of stability which is conventionally based on nominal values of filter inductors cannot predict instabilities over the entire range of inductance variation. Hence, a parametric approach to conventional stability methods with a parameter space defined by variation in actual and estimated inductance is explored in this paper. The effect of line impedance on stability is also investigated with impedance-based stability criterion by considering line inductance as an additional dimension in the parameter space. A pattern in stability margins is observed due to inductance variation, with inductance at its minimum being most vulnerable to instability. Experimental results measured from a 5 kW single-phase grid-connected inverter with various LCL filters have verified the feasibility of the proposed control method. The experimental results also match the analytical results with reasonable accuracy.

Enhanced soft magnetic properties of the Fe-based amorphous powder cores with novel TiO2 insulation coating layer

Abstract The core-shell structured FeSiBCCr@TiO2 amorphous magnetic powder cores (AMPCs) with excellent comprehensive magnetic properties were successfully prepared using spherical amorphous powders with high quality insulating layer. Scanning electron microscopy, Energy dispersive X-ray spectroscopy analysis, X-ray diffraction, and Fourier transform infrared spectroscopy revealed that the surface of the Fe-based amorphous powders was covered by a continuous amorphous TiO2 insulation layer. The performances of the AMPCs can be well tuned by changing the thickness of the insulation coating layer, which can be adjusted by controlling the concentration of tetrabutyl titanate (TBOT) in the hydrolysis and condensation reaction system. After annealing at 480 °C for 1 h, the AMPCs with TBOT concentrations of 0.15 ml/g exhibited excellent comprehensive soft magnetic properties, including the highest quality factor of 104.5 at 560 kHz and lowest core loss of 265 mW/cm3 at f = 100 kHz and Bm = 0.05 T. It also maintained a relatively high permeability of 67 up to 5 MHz and superior DC-bias permeability of 68% at a bias field of 100 Oe. This study demonstrated a modified method to develop a novel insulation coating layer to reduce the core loss and improve the magnetic properties of AMPCs.

Improved soft magnetic properties of Fe83.5Si7.5B5Cr4 amorphous nanocrystalline powder cores by adding Permalloy

In this paper, the effect of adding Permalloy (< 15 µm) on Fe83.5Si7.5B5Cr4 amorphous nanocrystalline magnetic powder (< 50 µm) was studied. The best stress relief annealing temperature were revealed at the same time. The results showed that the addition of Permalloy will significantly affect the soft magnetic properties of Fe-based amorphous nanocrystalline powders. Compared to the Fe83.5Si7.5B5Cr4 amorphous nanocrystalline powder, the saturation magnetization of composite powders obviously increased (by 9.8–17.1%). When Permalloy content was 15 wt%, the sample had the highest effective permeability, which increased by 21.6% (f = 200 kHz). At the same time, the core loss was also reduced by 5.3% (Bm = 40 mT, f = 200 kHz) when Permalloy content was 10 wt.%. In addition, the magnetic powder core had the highest effective permeability and the lowest core loss when the stress relief annealing temperature was set to 773 K.

Novel Fe-based nanocrystalline powder cores with high performance prepared by using industrial materials

The FeSiBPNbCu amorphous magnetic powder with partial crystallization is successfully synthesized using low purity industrial raw materials by gas atomization. The magnetic powder cores (MPCs) are then produced from the mixture of the FeSiBPNbCu powders with 2 wt % epoxy resin as insulation and bonding materials by cold pressing under a compact pressure of 1800 MPa. Evolution of the high-frequency properties for the MPCs with respect to the annealing temperature is systematically studied. The results show that upon annealing at the optimum temperature, the cores exhibit excellent magnetic properties, including high initial permeability of 86 with a high frequency stability up to 10 MHz, high quality factor of 110 at 1 MHz, and low core loss of 1290 mW/cm3 at 100 kHz for Bm = 0.1 T. It is emphasized that the MPCs prepared by partially crystallized magnetic powders can also achieve lower core losses and higher magnetic permeability, which is of great significance in industrial production.

Low core loss combined with high permeability for Fe-based amorphous powder cores produced by gas atomization powders

Toroid-shaped Fe-based soft magnetic amorphous powder cores were prepared from Fe76Si9B10P5 (at.%) amorphous powder by gas atomization and subsequent cold pressing with epoxy resin as a binder and insulation. The influence of epoxy resin content and annealing temperature on the magnetic properties of the amorphous soft magnetic powder cores were analyzed. The core loss at a frequency of 100 kHz for the samples with 2 wt% epoxy resin and annealed at 480 °C for 1 h is evaluated to be less than 800 mW/cm3 under a maximum induction of 100 mT. Meanwhile, the cores also exhibit high permeability of 86 at a frequency up to 20 MHz. These results suggest that Fe-based amorphous powder cores provide great potential for expanding the application of high frequency electronic elements used in rectifiers, inverters, transformers and inductance, which requires soft magnetic cores with high saturation magnetization, high permeability, and low core loss.

Effect of Heat Treatment on Electrical Resistivity of Spinel Ferrite Layer for Powder Magnetic Core

Effect of Heat Treatment on Electrical Resistivity of Spinel Ferrite Layer for Powder Magnetic Core

Properties of Fe-based nanocrystalline magnetic powder cores (MPC) and structure of particle size distribution (PSD)

Abstract This paper discusses the influence of the Particle Size Distribution (PSD) of the nanocrystalline Fe-based granular-soft-magnetic material on the final magnetic properties of a Magnetic Powder Core (MPC). Here we show how PSD impacts the final magnetic properties. Mixing fine and coarse particles, with a dominance of coarse particles, significantly influences the magnetic permeability increase of the core. Better magnetic features are noted for MPCs constructed with certain mass ratio of fine and coarse particles due to improvement in the magnetic path in the cores. This allows to offer new induction components to industry.

Fabrication and magnetic properties of novel Fe-based amorphous powder and corresponding powder cores

In this study, Fe77P6B10Si4Nb2Cr1 amorphous powder in the particle size range below 75 µm was synthesized using industrial raw materials by water atomization. Then the amorphous magnetic powder cores (AMPCs) were prepared from the mixture of the amorphous alloy powder with different contents of epoxy resin as insulation/bonding materials by cold pressing. After annealed at 673 K for 1 h, the evolution of the high-frequency properties for the FePBSiNbCr AMPCs with the epoxy resin contents was studied. The AMPCs showed excellent magnetic properties, including high effective permeability of 62–82 with a high frequency stability up to 10 MHz, low core loss of 308–500 mW/cm3 at 100 kHz under the maximum magnetic flux density of 0.05 T, and superior DC-bias permeability of 62–72% at a bias field of 100 Oe. The development of Fe-based AMPCs with excellent soft magnetic properties is encouraging for future applications as functional materials.

Fabrication of an Fe80.5Si7.5B6Nb5Cu Amorphous-Nanocrystalline Powder Core with Outstanding Soft Magnetic Properties

In this study, the melt spinning method was used to develop Fe80.5Si7.5B6Nb5Cu amorphous ribbons in the first step. Then, the Fe80.5Si7.5B6Nb5Cu amorphous-nanocrystalline core with a compact microstructure was obtained by multiple processes. The main properties of the magnetic powder core, such as micromorphology, thermal behavior, permeability, power loss and quality factor, have been analyzed. The obtained results show that an Fe80.5Si7.5B6Nb5Cu amorphous-nanocrystalline duplex core has high permeability (54.8–57), is relatively stable at different frequencies and magnetic fields, and the maximum power loss is only 313 W/kg; furthermore, it has a good quality factor.

Pure-iron/iron-based-alloy hybrid soft magnetic powder cores compacted at ultra-high pressure

We developed Fe/FeSiAl soft magnetic powder cores (SMCs) for realizing the miniaturization and high efficiency of an electromagnetic conversion coil in the high-frequency range (∼20 kHz). We found that Fe/FeSiAl SMCs can be formed with a higher density under higher compaction pressure than pure-iron SMCs. These SMCs delivered a saturation magnetic flux density of 1.7 T and iron loss (W1/20k) of 158 kW/m3. The proposed SMCs exhibited similar excellent characteristics even in block shapes, which are closer to the product shapes.

Effects of Annealing Temperature and Compaction Pressure on Magnetic Properties of Fe–Si Powder Cores Fabricated by an Improved Bluing Method

Fe-6.5wt%Si soft magnetic powder cores were prepared by using an improved bluing insulation method. A high-quality oxide insulation layer with good temperature stability was found to distribute continuously in the intervals between the Fe–Si particles. The effects of the annealing temperature and the compaction pressure on the core’s magnetic properties were investigated in detail. It was found that high temperature and low compaction pressure are beneficial to decrease the core’s inner stress and high compaction pressure is helpful to reduce the air gap. All the variations of the magnetic performance for the powder cores discussed in this paper were explained reasonably by considering these two factors. From the point of view of low loss, 760 °C and 2090 MPa were confirmed to be the relatively best annealing temperature and compaction pressure, respectively. The μ e , the % μ e at 100 Oe, and the loss at 50 kHz/1000 Gs for the core prepared under these two conditions are 63.57, 72.82%, and 547.66 mW/cm3, respectively.

Fe-Si/ZrO2 composites with core-shell structure and excellent magnetic properties prepared by mechanical milling and spark plasma sintering

Fe-Si alloy powders were coated with ZrO2 nanopowders via mechanical milling to fabricate Fe-Si (core)/ZrO2 (shell) composite powders. The resultant composite powders were consolidated to magnetic powder cores by spark plasma sintering (SPS). The effects of sintering temperature on microstructure, resistivity and magnetic properties were investigated along with the densification process of the composite compacts. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) revealed that the surfaces of the composite powders were coated with a layer of ZrO2 powders after mechanical milling. Moreover, the polished surface of the sintered composite compacts displayed a micro-morphology of core-shell structure with core of Fe-Si alloy particles and shell of ZrO2 layers indicating that the electric Fe-Si alloy particles were well insulated by the intergranular ZrO2 layers. The Fe-Si/ZrO2 magnetic powder cores with 7.5 wt.% ZrO2 sintered at 825 °C exhibited excellent magnetic properties: 1.43 T for saturation magnetic induction, 220 for maximum permeability and 25.48 Oe for coercivity. The core-shell structured powder cores possessed much higher resistivity and lower core loss (688 μΩ cm and 147 W/kg) than those of the raw Fe-Si powder cores (94 μΩ cm and 471 W/kg). Overall, the preparation process of magnetic powder cores by SPS provides a promising method to reduce core loss and improve magnetic properties of soft magnetic composite materials.

Improved permeability of Fe based amorphous magnetic powder cores by adding Permalloy

This paper focuses on improving the permeability of Fe-Si-B based amorphous magnetic powder cores by addition of micron-sized ferromagnetic crystalline metal particles (Permalloy). The effects of Permalloy content, size and the amount of insulation on magnetic properties and density were investigated. The results showed that the Fe based amorphous powder cores prepared with 15wt.% Permalloy (<15μm particle size) have higher permeability and relatively low core loss. Furthermore, compared with Fe-Si-B based amorphous powder, the saturation magnetization of mix powder increases by 60.7%, while the magnetic powder cores coated with 3wt.% coating agent (DC805) have low core loss of 57W/kg at 100kHz for Bm=500Oe.