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FeSiCr/epoxy resin soft magnetic composites with powder modification by silane coupling agent were fabricated for injection molding. The flowability, wettability, and magnetic properties of the composites were studied by a melting index detector, contact angle tester, vibrating sample magnetometer, inductance/capacitance/resistance (LCR) meter, and an alternating current magnetic measurement system. The cross-section morphologies of the composite rings were observed by scanning electron microscopy (SEM). The results showed that the silane coupling agent obviously improved the flowability of the composites due to the increase of compatibility and combination between epoxy resin and the FeSiCr particles. At the same powder content, the permeability and density decreased slightly in the coupled samples compared with those without modification. The core losses of both coupled and uncoupled samples with 90–93 wt.% contents followed Steinmetz's law with the frequency exponent equivalent to 1.128–1.179 in the broad frequency range of 100–2000 kHz. By curve fitting and loss separation, the excess loss and its frequency exponent (α) of the composite samples with 93 wt.% powder content were determined. The influence of the coupling agent on the flowability and magnetic properties is also discussed. [ABSTRACT FROM AUTHOR]

The major method used to reduce the magnetic loss of soft magnetic composites (SMCs) is to coat the magnetic powder with an insulating layer, but the permeability is usually sacrificed in the process. In order to achieve a better balance between low losses and high permeability, a novel photodecomposition method was used in this study to create a ZnO insulating layer. The effect of the concentration of diethyl zinc on the formation of a ZnO insulating film by photodecomposition was studied. The ZnO film was best formed with a diethyl zinc n-hexane solution at a concentration of around 0.40 mol/L. Combined with conventional coupling treatment processes, a thin and dense insulating layer was coated on the surface of iron powder in situ. Treating the iron powder before coating by photodecomposition led to a synergistic effect, significantly reduced core loss, and the effective permeability only decreased slightly. An iron-based soft magnetic composite with a loss value of 124 kW/m3 and an effective permeability of 107 was obtained at the frequency of 100 kHz and a magnetic field intensity of 20 mT. [ABSTRACT FROM AUTHOR]

The SiO2 coated sphere and flaky carbonyl iron powders (CIPs) heterogeneous nanocomposites have been prepared through the Stöber method and subsequently, through an annealing process for eliminating the crystal defect and enhancing the insulation and oxidation resistance of SiO2 shell. The CIP@SiO2 heterogeneous nanocomposites were characterized by X-ray diffraction (XRD), Fourier Transform infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM), Thermogravimetric (TG) analysis and Vector Network Analyzer (VNA). The CIP surface had been successfully assembly-coated with nano SiO2 layer, obtained by the SEM, XRD, and FTIR. Both the annealing treatment and the SiO2 shell can synergetically improve the oxidation resistance property due to the reduction of defects and residual stress, and isolation of oxygen, respectively. Changed everywhere permittivity (magnetic permeability) by effective permittivity (magnetic permeability). The real part of the permittivity of the nanocomposite decreased significantly, while the imaginary part of permittivity remained the same indicating the increase of dielectric loss. The permeability decreased slightly for the SiO2 insulated shell blocking the magnetic path. Hence, the electromagnetic match property was greatly improved by coating SiO2 insulated shell, and this composite showed a broad absorption band. [ABSTRACT FROM AUTHOR]

Fe@Composite-Ferrite soft magnetic composites (SMCs) were successfully fabricated by ions doping on the surface of Fe@Fe 3 O 4 powders which can improve the thermal stability and insulation. Compared with the traditional SMCs which were constructed by soft magnetic particle and non-magnetic boundary, this new material maintains high B m of 1.3214 T at 5000 A/m, 50 Hz, high μ max of 625.14 and low P cm of 10.02 W/kg at 50 Hz, 1.3 T. A three-dimensional simulation loss model and correlation theory of magnetic domain walls were used to analyze the relative loss mechanism and the effect of the new ferrite coating on the domain walls during magnetization. The novel composite-ferrite boundary greatly reduces the pinning, promoting domain wall motion and increasing the number of active magnetic objects. • Composite ferrite coating can be formed on the surface of iron powders by a simple and controllable method. • Comparing with the traditional SMCs, the Fe@Composite-Ferrite SMCs maintains higher magnetic induction, better magnetic permeability and lower total core loss. • The effects of heat treatment temperature and the particle size of iron powder on magnetic properties have been studied. • A three-dimensional simulation loss model and correlation theory of magnetic domain walls were used to analyze the relative loss mechanism. [ABSTRACT FROM AUTHOR]

In this paper, we present a design, simulation and experimental measurement of a cross array metamaterial absorber (MMA) based on the flaked Carbonyl iron powder (CIP) filled rubber plate in the microwave regime. The metamaterial absorber is a layered structure consisting of multilayer periodic cross electric resonators, magnetic rubber plate and the ground metal plate. The MMA exhibits dual band absorbing property and the absorption can be tuned from 1∼8GHz in the same thickness depending on the dimension and position of the cross arrays. The obviously broadened absorbing band of the designed structure is a result of the synergistic effects of the electrical resonance of the cross arrays and intrinsic absorption of the magnetic layer. The polarization and oblique incident angle in TE and TM model are also investigated in detail to explore the absorbing mechanisms. The resonance current of the cross array can excite the enhanced local magnetic field and dielectric field which can promote the absorption. The measurement results are basically consistent with the simulations but the absorbing peaks move a little bit to higher frequency for the reason that the surface oxidation of the flaked CIP in the preparation process. [ABSTRACT FROM AUTHOR]

• Co-Ba composite ferrites (CBCF) insulation layer was successfully cladded on the surface of Fe powder by a simple method. • Clausius-Maxwell formula model was used to simulate permeability in Fe@Co-Ba composite ferrites theoretically. • The SMCs coated with CBCF maintains high permeability (up to 121) and low core loss (129 kW/m3 at 20 mT, 100kHz). • Evolution of the Co-Ba composite ferrites coating with the annealing temperature is observed by BSEM images. To balance the core loss and permeability of soft magnetic composites (SMCs), a Co-Ba composite ferrite insulation layer was employed to clad the surface of reduced iron powder by sol-gel method. The successful preparation of the honeycomb-like Co-Ba composite ferrite coating layer was verified by scanning electron microscopy (SEM), the composition of the coating was determined by X-ray diffraction (XRD), and the magnetic properties were tested with a B-H curve analyzer. BSEM images of the polished cross-section and core loss separation results confirmed that an excessively high annealing temperature causes the composite ferrite insulation layer to fail. A high effective permeability of up to 121 at 300 kHz and low core loss (P cv) of 129 kW/m3 at 100 kHz and 0.02 T were obtained in prepared samples at the optimized annealing temperature of 500 °C. Subsequently, simulation analysis based on the Clausius-Maxwell formula model was used to confirm the feasibility of the enhancement on effective permeability in Fe@Co-Ba composite ferrite theoretically. The agreement between simulation and experimental results further indicated that a good balance between the core loss and permeability of Fe-based SMCs was achieved by Co-Ba composite ferrite cladding. [ABSTRACT FROM AUTHOR]

The schematic of the preparation of the coated iron powder in the reactor by a one-pot synthesis method. The above schematic diagram can be clearly stated: The surface of iron powder is covered by a lot of hydroxyl groups. After placing the reactor under isothermal treatment, the aluminum ions begin to hydrolyze. The hydroxyl groups of hydrolysates form chemical bond with the hydroxyl groups of iron powder surface. Therefore, the precursor of alumina is formed on the surface of iron powder. Besides, the surfactant suppressed the formation of the alumina insulating coating to form a denser and smoother insulating coating on the surface of the iron powder. • Al 2 O 3 can be formed on the surface of iron powder by one-pot synthesis method. • The thickness of alumina insulating coating can be controlled by aluminum nitrate concentration. • The formation model of the alumina insulation layer was established. • Using the surfactant can help form the denser and smoother insulating coating. In this work, the effects of the Al 2 O 3 insulating coating and surfactant on magnetic properties of the iron powders coated with Al 2 O 3 by one-pot synthesis method were investigated. The morphology, phase composition and magnetoelectric properties of iron powders coated with Al 2 O 3 were tested respectively. Compared with uncoated iron powder, the composite powder of Al 2 O 3 insulating layer not only has better permeability stability in the frequency range of 5–300 kHz, but also has lower core loss, especially eddy current loss in the frequency range of 5–100 kHz. The surface of iron powder modified by surfactant will change crystallization process of aluminum hydroxide. After the addition of dodecyl trimethyl ammonium bromide (DTAB) as the surfactant, the Al 2 O 3 insulating coating becomes denser and smoother, and the core loss of coated powders is further reduced. [ABSTRACT FROM AUTHOR]

In this paper, Fe-based soft magnetic composites (SMCs) hydrothermally coated with lithium aluminum oxide (Li–Al–O) with better magnetic properties and lower core losses than Al 2 O 3 coated layers have be investigated. The microstructure and composition of the coating and magnetic properties of the composites were determined by scanning electron microscopy (SEM), X-ray diffraction (XRD) and B–H curve analyzer. Those results revealed that when Li 2 CO 3 was added to the aluminum nitrate solution, the originally formed Al 2 O 3 coating layer converted to a layer with a mixture of several lithium aluminum oxides. Fe-based SMCs coated with lithium aluminum oxide showed lower core losses, higher and stable effective permeability as compared with iron rings coated with Al 2 O 3 , especially in high frequency range of 100–300 kHz. The above schematic diagram can be clearly stated: In this work, iron powders, aluminum nitrate, lithium carbonate, and deionized water were simultaneously added to the poly tetra fluoroethylene liner. As the reaction proceeds, The Al3+ and Li+ which adsorbed on the surface of the iron powders combined with the OH− in water form the precursor of the Li–Al–O. The iron powders coated with the precursor were calcined at a high temperature to obtain the lithium aluminum oxide-coated iron powders. And then, the calcined iron powders were subjected to compression molding and annealing to obtain the Fe-based SMCs. Image 1 • Li-Al-O can be formed on the surface of iron powders by hydrothermal synthesis method. • The thickness of Li-Al-O insulation layer can be controlled by concentrations of Al(NO 3) 3 and Li 2 CO 3. • Comparing with Al 2 O 3 , the Fe-based SMCs coated with Li-Al-O coating have higher, more stable effective permeability and lower total core losses. [ABSTRACT FROM AUTHOR]