Amorphous Core Research Articles

Microstructure evolution and soft magnetic property optimization of core-shell FeSiBCCr@SiO2&ZrO2 amorphous magnetic powder cores

In this study, core-shell structured FeSiBCCr@SiO2&ZrO2 amorphous magnetic powder cores (AMPCs) were successfully prepared by the sol-gel method using tetraethyl orthosilicate (TEOS) and zirconium oxychloride hydrate (ZrOCl2·8H2O) as raw materials. The growth mechanism and potential chemical reactions of the SiO2&ZrO2 mixed insulation layer were analyzed by XRD, XPS and SEM‒EDS. In addition, the effect of the insulation layer content on the soft magnetic properties of FeSiBCCr@SiO2&ZrO2 AMPCs was systematically investigated. The SiO2&ZrO2 insulation layer can significantly increase the resistivity, effectively improve the DC bias performance and reduce the core loss of AMPCs. S2* (1.2 mL TEOS and 1.4 g ZrOCl2·8H2O) had a minimum core loss of 2290 mW/cm3 at high frequency (50 mT, 1 MHz). It had a high effective permeability of 48.2 and a superior direct current (DC) bias performance of 77.9% at 8 kA/m. This study provides a valid method to practically produce SMPCs with high resistivity, low core loss at high frequency and excellent DC bias performance through a novel insulation coating process.

In-situ investigation of tension-compression asymmetry of Ni-SiOC nanocomposites

Ni-SiOC nanocomposites are synthesized through co-sputtering Ni and Si-O-C and then annealed at high temperature up to 800 °C to obtain two characteristic microstructures, core (crystalline Ni)-shell (amorphous ceramic SiOC) nanostructures and submicron-grained Ni containing amorphous ceramic SiOC particles. In-situ scanning electron microscope (SEM) compression tests show that both types of Ni-SiOC nanocomposites exhibit high strength and good plastic flow stability due to microstructure-promoted plastic co-deformation between amorphous ceramics and Ni grains. However, in-situ tension tests reveal that the core-shell nanostructures exhibit brittle fracture behaviour at a low strength due to cracking along amorphous cores, while the submicron-grained Ni can reach the similar strength to that of compression but a limited plasticity due to interface decohesion facilitated by deformation incompatibility between Ni and amorphous ceramic SiOC.

Industrial stress annealed wound cores compared to other solutions

Stress annealed nanocrystalline wound FeCuNbSiB cores, now available on the market, provide NO localized air gap, a range of low permeability (µr = 200 to 3000), low magnetic losses (386 W/kg at 0,8T-50 kHz), a high B-H linearity and a constant temperature drift of the magnetic properties (uncoated core) that makes it easy to correct. This paper aims to support engineers in passive magnetic component design by comparing this new industrial product with competing solutions at µr ∼ 1000, the nanocrystalline cut core and the iron-based amorphous wound core. On the one hand, the amorphous solution appears to be more dissipative than nanocrystalline solutions. On the other hand, the latter have a high frequency stability (cut off frequency: 5–7 MHz) and better temperature stability of losses (−90 mW/kg.°C) compared to the amorphous solution (−135 mW/kg.°C). The magnetic losses of the cut core are equal or slightly superior to the stress annealed product they are compared at high induction and medium frequency.

Effect of external DC field on current transformers with amorphous and nanocrystalline cores

Nanocrystalline and amorphous stress-annealed and field annealed tapes are used for cores of DC-tolerant current transformers. We analyze the influence of external DC field of arbitrary direction on the performance of these transformers. For the realistic core shapes the demagnetization is high, which leads to effective external field suppression. However, DC tolerant transformers are tolerant to the DC component of the current and not to the external field - they can be saturated by 30 mT field from permanent magnet. This means that for the practical applications in domestic energy meters some external shielding is required.

Sensitivity and noise of parallel fluxgate sensor with amorphous wire cores

Fluxgate sensors are vectorial magnetic field sensors suitable for the measurement of fields up to mT with maximum pT resolution. Due to their low weight, low power, and low cost, fluxgates are ideal sensors to monitor the Earth’s field and measure its spatial deviations. The sensitivity of the sensor directly depends on the material and geometry of the core, and on the geometric parameters of the coils. Fluxgate is still the most sensitive room-temperature vectorial magnetic field sensor [1]. This work is devoted to the study of parallel fluxgate with multiple wire cores. The achieved sensitivity for a 35 mm long sensor is 12 mV/µT and the minimum noise was 25 pT/√Hz at 1 Hz for as-cast amorphous wires.

Effects of heat treatment in air on soft magnetic properties of FeCoSiBPC amorphous core

The oxidation behavior and soft magnetic properties of industrially prepared Fe80Co3Si3B10P1C3 amorphous cores were investigated under heat treatment in air. Results indicate that the FeCoSiBPC amorphous core heat-treated in air can obtain higher permeability (μi) and maximum saturation magnetic induction (Bm) than that annealed in vacuum. The improvement of soft magnetic properties originates from the formation of a Co-rich layer between the oxide layer and the amorphous substrate after the selective oxidation of Fe. The core loss (Pcm) of the amorphous cores decreases after annealing at 280 ℃ in air for 30 min, and increases with the annealing time extend to 60 min. The Pcm of the samples treated in air is inferior to that of the ones annealed in vacuum for 30 min. The variation of Pcm can be explained by the thinning of the amorphous substrate based on the Gyorgy's model and simple models of domain wall pinning.

Construction of amorphous carbon-coated alpha-Fe2O3 core–shell nanostructure for efficient photocatalytic performance

Construction of amorphous carbon-coated alpha-Fe2O3 core–shell nanostructure for efficient photocatalytic performance

Fe-Based Amorphous Magnetic Powder Cores with Low Core Loss Fabricated by Novel Gas-Water Combined Atomization Powders.

FeSiBCCr amorphous powders were produced by a novel gas–water combined atomization process, and the corresponding MPCs (magnetic powder cores) were subsequently fabricated by phosphating treatment (0.4~1.6 wt.%), cold pressing (550~2350 MPa), and annealing (423~773 K), respectively. The results showed that the powders had high circularity, excellent thermal stability (ΔT = 59 K), and high saturation magnetization (0.83 T), which could provide raw powders for high-performance MPCs. With increasing phosphoric acid concentrations, despite the increase in DC-bias%, the uniformity of the insulation layers deteriorated, which led to a decrease in permeability and an increase in core loss. With increasing compaction pressures, the core loss increased continuously, and the permeability and DC-bias% first increased and then decreased. When annealing below the crystallization temperature, with increasing annealing temperatures, the permeability increased, and the core loss and DC-bias% decreased continuously. Under the optimized process of 0.4 wt.% phosphating concentration, 550 MPa pressure, and 773 K annealing temperature, the MPCs had a permeability of 21.54 ± 1.21, DC-bias% of 90.3 ± 0.2, and a core loss (Bm = 50 mT, f = 100 kHz) of 103.0 ± 26.3 mW cm−3. The MPCs had excellent high-frequency low-loss characteristics and showed great application potential under the development trends of high current, high power, and high frequency of electronic components.

Concentric core-shell tracks and spectroscopic properties of SrTiO3 under intense electronic excitation

A deeper understanding of the intrinsic link between the irradiation-induced microstructures and the corresponding spectroscopic properties is becoming increasingly attractive for the research fields of materials science, physics, and information technology. In this work, the structural damage response, spectroscopic features, and associated physical mechanisms of SrTiO3 single crystals under swift heavy ion irradiation were comparatively analyzed using a combination of experimental and theoretical approaches. Corresponding to 0.11–5.00 MeV/u ion irradiation with electronic energy loss ranging from 4.0 to 29.3 keV/nm, the inelastic thermal spike calculations combined with molecular dynamics simulations are compared with the experimental observations, revealing the track fine structures (individual spherical defects with a disordered region, and discontinuous and continuous tracks consisting of an amorphous core and a disordered outer shell) and demonstrating the dominant effects of the deposition energy and lattice temperature on track damage formation and evolution; thus, two essential thresholds for defect formation of ∼0.60 eV/atom and amorphous region formation of ∼1.81 eV/atom were identified to better describe the concentric core-shell track structure. The enhanced nanohillock formation in the surface region is attributed to the combined action of kinetic and potential energy depositions, and the fluence dependence in regulating the hillock dimensions is also presented. The measured refractive index profiles along different crystal axes further indicate the anisotropy of irradiation-induced lattice expansion. With increasing ion fluence and damage level, the intrinsic bandgap gradually decreased, and the concentration of additional radiative recombination centers (1.81 eV, 2.31 eV, and 2.42 eV) accordingly increased in the SrTiO3 crystal, providing the possibility of regulating related defects to achieve tunable/selective photon emission for more critical technological applications.

Investigation on Vibration Characteristics of Amorphous Metal Alloy Core Dry-type Distribution Transformer

Large power transformers have severe vibration and noise problems. Thus, as the source of noise, it is vitally important to have accurate core vibration calculations. The calculation of the vibration is incredibly difficult to consider the complex propagation pathway of the vibration in the clamp and the Amorphous Metal Alloy Core Distribution Transformer (AMACDT). To understand the vibration characteristics of AMACDT, this manuscript provides a different approach on investigation of the vibration characteristics of an SCBH15-200/10 type. Based on the vibration characteristics calculation and displacement of an Amorphous Metal Alloy Core Distribution Transformer (AMACDT), they are obtained and solved using Finite Element Analysis software (FEA). Conferring to the outcomes of the vibration analysis, the method by adding bar-reinforcements on the upper clamp of transformer is proposed to lessen the vibration amplitude. To verify the usefulness and application of the suggested approach, the analytical results are obtained. The suggested approach is analyzed with those of experimental.

Distributed Winding IPM Motor with an Amorphous Metal Stator Core

Distributed Winding IPM Motor with an Amorphous Metal Stator Core

Effects of Nanoscale Morphology on Optical Properties of Photoluminescent Polymer Optical Fibers.

Bicomponent photoluminescent polymer optical fibers (PL-POFs) have been melt-spun and in-situ drawn to different extents. The results suggest that scattering in the sheath can effectively increase the photoluminescent dye excitation probability in the fiber core. The core/sheath PL-POFs are made of a semi-crystalline fluoropolymer sheath of low refractive index (RI) and an amorphous cycloolefin polymeric core of high RI, which is doped with a luminescent dye. The axial light emission, as well as the guiding attenuation coefficients of the core/sheath PL-POFs, have been measured using a side-illumination set-up. The incident blue laser is down-converted to red light, which is re-emitted and partially guided by the core. The axial light emission is measured at the fiber tip as a function of the distance from the illumination position to the integrating sphere. It is demonstrated that the presence of a semi-crystalline sheath significantly enhances the axial light emission and that it also lowers the attenuation coefficient, compared to the emission and guiding properties of PL core-only fibers. Additionally, the attenuation coefficient has been found to be lower in more strongly drawn PL-POFs. Wide-angle X-ray diffraction and small-angle X-ray scattering experiments reveal structural differences in differently drawn PL-POFs that can be linked to the observed differences in the optical properties.

Hybrid Microfluxgate and Current Transformer Sensor

In this work, we develop the hybrid current sensor comprising a microfluxgate and a current transformer (CT) for wide-bandwidth current measurement. The microfluxgate consists of two microcoil chips 3.5 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times1.75$ </tex-math></inline-formula> mm in dimension made by using the standard Complementary Metal-Oxide Semiconductor MicroElectroMechanical Systems (CMOS-MEMS) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.35 ~\mu \text{m}$ </tex-math></inline-formula> process. The aluminum wire-bonding technique is used to construct the top excitation coil surrounding the amorphous soft magnetic core patterned by photolithography and wet etching techniques. Under the optimal excitation condition, the response of the microfluxgate current sensor becomes linear with a maximized sensitivity. The in-house made CT is combined with the microfluxgate driving system to form the hybrid current sensor by using a summing amplifier. The hybrid current sensor has a spectral current noise of 0.4 mA/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\surd $ </tex-math></inline-formula> Hz at 1 Hz. The maximum sensing range is ±10 A, and the non-linearity is less than 2% within the ±4.6 A range, corresponding to a linear dynamic range of 60 dB in a 10 Hz bandwidth. The hybrid microfluxgate-and-CT sensor has a flat bandwidth from dc to 100 kHz. It has the potential to become a practical miniature device featuring a high-dynamic range, wide bandwidth, and low-temperature drift.

Ultralight broadband microwave-absorbing materials based on the short fibers of glass-coated amorphous magnetic microwires

Glass-coated amorphous magnetic microwires (GAWs) typically have a glass skin and amorphous metal alloy inner core, giving them special electromagnetic (EM) properties. GAWs not only exhibit multiple EM losses and suitable impedance matching but also have a conductive core with magnetic properties. In this study, GAW filament fibers (LFs) and short fibers (SFs) were prepared, and they exhibited completely different EM performance. LFs with filaments closely arrayed reflected EM waves and could thus act as an EM shielding material, whereas SFs with randomly distributed fibers demonstrated excellent microwave-absorbing (MA) properties. Single-layer SFs of just 3 g/m2 and a length of 5 mm had a minimum reflectivity (RL) of −20.4 dB at 12.3 GHz, and the effective absorption bandwidth (EAB) of RL< −10 dB was 5.36 GHz with a thickness of just 1 mm. Moreover, the MA properties of the SFs were obtained and controlled by adjusting the length, content, and lamination of the SFs in accordance with their multiple MA mechanisms. Double-layer SFs with a thickness of 2 mm could also achieve an EAB (RL< −10 dB) above 10 GHz. The novel and effective strategy proposed in this study can thus produce SFs GAWs from ultralight MA fabric that exhibit excellent MA properties and broadband.

(INVITED)Tm:YAG crystal-derived double-clad fibers – A hybrid approach towards high gain and high efficiency Tm lasers

The hybrid approach of combining a Tm:YAG laser crystal with an amorphous fused silica tube is investigated to evaluate the suitability of the resulting crystal-derived fibers for efficient double-clad fiber lasers. The fabrication process and fiber properties of these Tm fibers are investigated, focusing on the dependence of the active fiber properties on the incorporated Tm3+ concentration. Crystal rods with different doping concentrations (TmxY1-x)3Al5O12 (x = 0.02, 0.05 and 0.08) were used as starting core material for fiber drawing. The investigated fibers are mechanically stable and result in a fairly homogenous and amorphous core glass with optical absorption and emission spectra that are similar to conventional Tm:Al doped silica fibers. Regarding laser properties with 790 nm cladding pumping, we could achieve a maximum slope efficiency of 47% with an output power of 4 W. The fiber laser results are compared to a conventionally fabricated double-clad Tm fiber prepared by Modified Chemical Vapor Deposition and solution doping. To the best of our knowledge, we demonstrate the highest laser output and the highest efficiency obtained from a Tm:YAG crystal-derived fiber.

Design of High-Power Solid-State Transformers with Grain-Oriented Electrical Steel Cores

The paper proposes a simple structure of high-power solid-state transformers (SSTs) able to control the energy flow in critical lines of the medium-voltage (20 kV) distribution grid. With an increasing number of renewable intermittent sources connected at the nodes of the meshed distribution grid and a reduced number of nodes connected to large power plants, the distribution grid stability is more and more difficult to achieve. Control of the energy flow in critical lines can improve the stability of the distribution grid. This control can be provided by the proposed high-power SSTs operating a 20 kV with powers over 10 MW. This function is difficult to achieve with standard SST technologies that operate at high frequencies. These devices are made with expensive magnetic materials (amorphous or nanocrystalline cores) and a limited power by SST cells. The required total power is reached by assembling many SST cells. On the other hand, existing SST designs are mainly aimed at reducing the equipment’s size and it is difficult to design small objects able to operate at high voltages. The authors propose to use cores made with grain-oriented electrical steel (GOES) thin strips assembled in wound cores. Experimental results obtained, with GOES wound cores, show that the core losses are lower for a square voltage than for a sine one. This counterintuitive result is explained with an analytical calculus of eddy currents and confirmed by a non-linear time-stepping simulation. Therefore, simple converter structures, operating with rectangular voltages and low switching losses, are the best solutions. Experimental results also show that the core losses decrease with temperature. Consequently, high-power SST cells can be made with transformers whose GOES cores are hotter than coils for reducing core losses and keeping copper losses at low levels. The paper proposes an appropriate transformer mechanical structure that avoids any contact between the hot GOES wound core and the winding, with a specific cooling system and thermal insulation of the hot GOES wound core. The proposed design makes it possible to build SST cells over 1MW and full SSTs over 10 MW at moderate costs.

Vibration reduction method of switched reluctance motors with amorphous alloy cores based on inverse-magnetostriction effect

Vibration reduction method of switched reluctance motors with amorphous alloy cores based on inverse-magnetostriction effect

Inhalable microparticle platform based on a novel shell-forming lipid excipient and its feasibility for respirable delivery of biologics

Administration of biologics such as proteins, vaccines, and phages via the respiratory route is becoming increasingly popular. Inhalable powder formulations for the successful delivery of biologics must first ensure both powder dispersibility and physicochemical stability. A lipid-based inhalable microparticle platform combining the stability advantages offered by dry powder formulations and high dispersibility afforded by a rugose morphology was spray dried and tested. A new simplified spray drying method requiring no organic solvents or complicated feedstock preparation processes was introduced for the manufacture of the microparticles. Trehalose was selected to form the amorphous particle core, because of its well-known ability to stabilize biologics, and also because of its ability to serve as a surrogate for small molecule actives. Phospholipid distearoyl phosphatidylcholine (DSPC), the lipid component in this formulation, was used as a shell former to improve powder dispersibility. Effectiveness of the lipid excipient in modifying trehalose particle morphology and enhancing powder dispersibility was evaluated at different lipid mass fractions (5%, 10%, 25%, 50%) and compared with that of several previously published shell-forming excipients at their effective mass fractions, i.e., 5% trileucine, 20% leucine, and 40% pullulan. A strong dependence of particle morphology on the lipid mass fraction was observed. Particles transitioned from typical smooth spherical trehalose particles without lipid to highly rugose microparticles at higher lipid mass fractions (>5%). In vitro aerosol performance testing demonstrated a significant improvement of powder dispersibility even at lipid mass fractions as low as 5%. Powder formulations with excellent aerosol performance comparable to those modified with leucine and trileucine were achieved at higher lipid mass fractions (>25%). A model biologic-containing formulation with 35% myoglobin, 35% glass stabilizer (trehalose), and 30% lipid shell former was shown to produce highly rugose particle structure as designed and excellent aerosol performance for efficient pulmonary delivery. A short-term stability at 40 °C proved that this protein-containing formulation had good thermal stability as designed. The results demonstrated great potential for the new lipid microparticle as a platform for the delivery of both small-molecule APIs and large-molecule biologics to the lung.

Photostable carbon dots with intense green emission in an open reactor synthesis

Carbon dots (CDs) are novel fluorescent nanoparticles that combine intense emission of visible light with eco-friendly and inexpensive carbon-based composition. In this work, CDs are synthesized trough a glycothermal treatment of resorcinol (1,3-hydroxybenzene) in air atmosphere. The presence of catalysts (NaOH and H2SO4) increases the reaction rate, promoting a faster and massive production of nanoparticles. The spectroscopic monitoring of fluorescence during CD synthesis, supported by a DFT study, allows to depict the formation and structural evolution of OH terminated polycyclic aromatic hydrocarbons (PAHs) from resorcinol polycondensation. In purified CDs, PAHs embedded in the amorphous carbogenic core are responsible for an intense green fluorescence emission with a quantum yield up to ∼40%. Such band exhibits high resistance to UV photobleaching, attributed to the physical protection of the carbogenic matrix. Finally, adding a strong acid/base to the CD solution, the CD fluorescence can be cyclically quenched/restored (due to reversible aggregation), suggesting the convenient use of such CDs in on/off sensors or stimulus-responding devices.

Novel Epoxy-Free Imaging of the Proton Exchange Membrane Fuel Cell Components and Microstructure Degradation By Transmission Electron Microscopy

Performance, durability, and efficiency limitations of proton exchange membrane fuel cells (PEMFCs), as one of the alternative clean energy resources, has been hindering the widespread adoption of these devices. Improving those parameters is closely entangled with identifying the degradation mechanism of each component in the electrodes i.e., catalyst – commonly platinum nanoparticles, catalyst support – carbon, and the ion conductive polymer – ionomer, as well as the effects that degradation can have on the porous network of the electrodes[1]. Degradation during typical automotive operation protocols like startup/shut down (SUSD)[2,3] is of a special interest. Therefore, it is essential to observe the changes of the microstructure, as whole, and each individual component’s response to the working condition, in order to understand degradation mechanisms and devise degradation mitigation strategies. Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) in conjunction with energy dispersive spectroscopy (EDS) have proven to be valuable tools in unravelling the complex changes of the microstructure and understanding of the degradation mechanisms[4]. Moreover, correlating the numerical microstructural descriptors, extracted by quantification of the TEM and EDS results, with the visual observations helped the research community to draw a connection between the degradation and microstructural changes[5]. However, the conventionally prepared TEM samples by slicing (microtomy) an epoxy-embedded piece of a catalyst coated membrane (CCM) have limitations in observing carbon and ionomer, and distinguishing them from each other and from the epoxy. Partial epoxy-embedding showed very promising results regarding distinguishing carbon from ionomer in selected regions of the CCM[6]. However, not a full CCM was observed. Therefore, we report for the first time, an epoxy-free microtomy approach for a whole CCM, successfully implemented on a fresh and degraded cathode layer of beginning-of-life (BOL) and SUSD samples, respectively. Electrochemical characterization of the samples presented here are discussed in previous publication[2]. The Pt catalyst, carbon, ionomer and porous network of the cathodes were clearly observable and distinguishable in both BOL and SUSD samples using high-resolution TEM and 3D electron tomography-TEM (ET-TEM) imaging. The microstructural comparison revealed the changes in Pt particles distribution – moving into the ionomer network rather than sitting on and inside the carbon support, disintegration of corroded carbon and dispersion of broken-off graphitic carbon pieces in the ionomer, and alteration of the ionomer network – formation of more ionomer filaments. In addition, ET-TEM of the BOL and SUSD samples confirmed the presence of Pt particles inside the amorphous core of the carbon particle and their migration during SUSD operation, respectively. Finally, the visual results were correlated with the microstructural descriptors quantified using our proprietary quantification technique. The numerical microstructure properties corroborated the observations that was made based on the TEM images observations. Therefore, implementation of whole-CCM-epoxy-free microtomy technique can be considered as a novel method in aiding the research community in understanding the degradation mechanism and microstructural properties alteration.