Optimizing FeSiCr-Based Soft Magnetic Composites Using the Deionized Water as the Phosphating Solvent.

To prepare a soft magnetic powder core, the magnetic powder surface has to be insulated by phosphating treatment. Organic chemicals such as ethanol and acetone are generally used as solvents for phosphoric acid, which may cause serious environmental problems. This work proposed deionized water as the environmentally friendly phosphating solvent for FeSiCr powder. The soft magnetic composites (SMCs) were prepared using phosphoric acid for inorganic coating and modified silicon polymer for organic coating. The effect of different phosphating solvents, including deionized water, ethanol, and acetone, on the structure and magnetic properties of SMCs were investigated. It is found that the solvent affects the phosphating solution's stability and the phosphoric acid's ionization. The phosphoric acid is more stable in deionized water than in ethanol and acetone. The phosphating reaction in deionized water is also more stable in deionized water, resulting in a dense phosphate coating on the particle surface. The effects of phosphoric acid concentration and temperature on the magnetic properties of FeSiCr-based SMCs were further studied. With the increase in phosphoric acid concentration and temperature, the magnetic permeability and saturation magnetization of the powder core decrease, and the core loss decreases, followed by an increase. The optimized combination of properties was obtained for the SMCs phosphated with 0.2 wt.% phosphoric acid in deionized water at 35 °C, including a high effective permeability µe of 25.7, high quality factor Q of 80.2, low core loss Pcv of 709.5 mW/cm3 measured at 0.05 T @ 100 kHz, and high withstanding voltage of 276 V, due to the formation of uniform and dense insulating coating layers. In addition, the SMCs prepared with phosphated powder show good corrosion resistance. The anti-corrosion properties of the SMCs using deionized water as a phosphating solvent are better than those using ethanol and acetone.

Advanced Magnetic Actuation: Harnessing the Dynamics of Sm2Fe17-xCuxN3 Composites.

Recently, there has been an escalating demand for advanced materials with superior magnetic properties, especially in the actuator domain. High coercivity (Hci), an essential magnetic property, is pivotal for programmable shape changes in magnetic actuators and profoundly affects their performance. In this study, a new Sm2Fe17-xCuxN3 magnet with a high Hci was achieved by modifying the temperature of the reduction-diffusion process─lowering it from 900 to 700 °C through the introduction of Cu and finer control over the structure and morphology of the Sm2Fe17-xCuxN3 magnetic component within the actuator composite. Consequently, the Sm2Fe17-xCuxN3 magnet demonstrated a remarkable Hci of 11.5 kOe, eclipsing the value of 6.9 kOe attained by unalloyed Sm2Fe17N3 at reduced temperatures. By capitalizing on the enhanced magnetic properties of the Sm2Fe17-xCuxN3 composite and incorporating poly(ethylene glycol) into the elastomer matrix, we successfully fabricated a robust actuator. This innovative approach harnesses the strengths of hard magnets as actuators, offering stability under high-temperature conditions, precision control, longevity, wireless functionality, and energy efficiency, highlighting the vast potential of hard magnets for a range of applications.

Preparation of Fe@Fe3O4/ZnFe2O4 Powders and Their Consolidation via Hybrid Cold-Sintering/Spark Plasma-Sintering.

Our study is focused on optimizing the synthesis conditions for the in situ oxidation of Fe particles to produce Fe@Fe3O4 core-shell powder and preparation via co-precipitation of ZnFe2O4 nanoparticles to produce Fe@Fe3O4/ZnFe2O4 soft magnetic composites (SMC) through a hybrid cold-sintering/spark plasma-sintering technique. XRD and FTIR measurements confirmed the formation of a nanocrystalline oxide layer on the surface of Fe powder and the nanosized nature of ZnFe2O4 nanoparticles. SEM-EDX investigations revealed that the oxidic phase of our composite was distributed on the surface of the Fe particles, forming a quasi-continuous matrix. The DC magnetic characteristics of the composite compact revealed a saturation induction of 0.8 T, coercivity of 590 A/m, and maximum relative permeability of 156. AC magnetic characterization indicated that for frequencies higher than 1 kHz and induction of 0.1 T, interparticle eddy current losses dominated due to ineffective electrical insulation between neighboring particles in the composite compact. Nevertheless, the magnetic characteristics obtained in both DC and AC magnetization regimes were comparable to those reported for cold-sintered Fe-based SMCs.

Highly Compressible 3D-Printed Soft Magnetoelastic Sensors for Human-Machine Interfaces.

Incorporating perception into robots or objects holds great potential to revolutionize daily human life. To achieve this, critical factors include the design of an integrable three-dimensional (3D) soft sensor with self-powering capability, a wide working range, and tuneable functionalities. Here, we introduce a highly compressible 3D-printed soft magnetoelastic sensor with a wide strain sensing range. Inspired by the lattice metamaterial, which offers a highly porous structure with tuneable mechanical properties, we realized a remarkably compliant 3D self-powering sensor. Using magnetoelastic composite materials and 3D printing combined with sacrificial molding, a broad design space for constituent materials and structures is investigated, allowing for tuneable mechanical properties and sensor performances. These sensors are successfully integrated with two robotic systems as the robot operation and perception units, enabling robot control and recognition of diverse physical interactions with a user. Overall, we believe that this work represents a cornerstone for compliant 3D self-powered soft sensors, giving impetus to the development of advanced human-machine interfaces.

3D Printing Soft Magnet: Binder Study for Vat Photopolymerization of Ferrosilicon Magnetic Composites.

Liquid Crystal Display (LCD) masking is a 3D printing technique that can produce soft magnetic composite parts to high resolution and complexity for robotics and energy electronics applications. This additive manufacturing technique has the potential to produce larger, lighter-weight, more efficient, and more durable parts for automotive and mechanical applications. This study conducted a binder study to create a low-viscosity and stiff binder capable of loading at least 60 v/v% Fe-6.5 wt%Si particles. Percolation Theory was applied to anticipate the magnetic interaction of suspended particles. A series of binders were formulated, with adjustments to diluent ratios. The behavior of the binders was assessed by studying their rheological properties, conversion rates, and mechanical properties. A post-cure study was conducted across various energy settings using UV, thermal, and a combination of both energy sources to find the combination that provided the best mechanical properties. As a result, 64 v/v% Fe-6.5 wt%Si loading was achieved and cured using UV light of 405 nm wavelength. Vibrating Sample Spectroscopy (VSM) was used to characterize the composite's magnetic behavior, and a significant increase in saturation magnetization and negligible change in coercivity was observed when the added load exceeded the percolation threshold.

Low Core Losses of Fe-Based Soft Magnetic Composites with an Zn-O-Si Insulating Layer Obtained by Coupling Synergistic Photodecomposition.

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.

Spark Plasma Sintered Soft Magnetic Composite Based on Fe-Si-Al Surface Oxidized Powders.

Soft magnetic composites (SMCs) need a stable matrix to apply heat treatments for enhancing their magnetic characteristics. A stable matrix can be offered by alumina, but the densification of the ferromagnetic particles covered by this oxide (by sintering) can be very difficult. This paper proposes a feasible synthesis route for obtaining alumina matrix SMCs. An Fe-Si-Al alloy with nominal composition Fe85Si9Al6 was obtained by mechanical alloying of elemental Fe, Si, and Al powders, and further, the as-milled powders were superficially oxidized by immersion in HCl solution. The oxide layer was composed of iron, silicon, and aluminum oxides, as the Fourier-transform infrared spectroscopy technique revealed. The Fe-Si-Al@oxide powder was densified by the spark plasma sintering technique-SPS. Upon sintering, a continuous matrix of oxide (mainly alumina) was formed by the reaction of the Fe-Si-Al powder coreswith their oxide layer. The main part of the composite compacts after sintering consisted of an Fe3Si-ordered phase dispersed in an oxide matrix. The DC and AC tests of magnetic composite compacts showed that upon increasing the sintering temperature, the density, magnetic induction, and magnetic permeability increased. The initial magnetic permeability was constant in the entire range of testing frequencies and the magnetic losses increased linearly. The stability of the magnetic characteristics in frequency is promising for developing further such types of magnetic composite.

Recent Advances in Multi-Functional Coatings for Soft Magnetic Composites.

During the past 50 years, the aim to reduce the eddy current losses in magnetic cores to a minimum led to the formulation of new materials starting from electrically insulated iron powders, today called Soft Magnetic Composites (SMC). Nowadays, this promising branch of materials is still held back by the mandatory tradeoff between energetic, electrical, magnetic, and mechanical performances. In most cases, the research activity focuses on the deposition of an insulating/binding layer, being one of the critical points in optimizing the final composite. This insulation usually is achieved by either inorganic or organic layer constituents. The main difference is the temperature limit since most inorganic materials typically withstand higher treatment temperatures. As a result, the literature shows many materials and process approaches, each one designed to meet a specific application. The present work summarizes the recent advances in state of the art, analyzing the relationship among material compositions and magnetic and mechanical properties. Each coating shows its own processing sets, which vary from simple mechanical mixing to advanced chemical methods to metallurgical treatments. From state of the art, Aluminum coatings are characterized by higher current losses and low mechanical properties. In contrast, higher mechanical properties are obtained by adopting Silicon coatings. The phosphates coatings show the best-balanced overall properties. Each coating type was thoroughly investigated and then compared with the literature background highlighting. The present paper thus represents a critical overview of the topic that could serve as a starting point for the design and development of new and high-performing coating solutions for SMCs. However, global research activity continuously refines the recipes, introducing new layer materials. The following steps and advances will determine whetherthese materials breakthrough in the market.

Ironsand (Titanomagnetite-Titanohematite): Chemistry, Magnetic Properties and Direct Applications for Wireless Power Transfer.

Ironsand is an abundant and inexpensive magnetic mineral resource. However, the magnetic properties of unprocessed ironsand are often inadequate for any practical applications. In this work, the applicability of ironsand for use as a component in a soft magnetic composite for large-scale inductive power transfer applications was investigated. After magnetic separation, the chemical, structural and magnetic properties of ironsand sourced from different locations were compared. Differences observed in the DC magnetic properties were consistent with changes in the chemical compositions obtained from X-ray Absorption Near-Edge Spectroscopy (XANES), which suggests varying the titanohematite to titanomagnetite content. Increased content in titanomagnetite and magnetic permeability correlated well with the total Fe content in the materials. The best-performing ironsand with the highest permeability and lowest core losses was used alongside Mn,Zn-Ferrite particles (ranging from ∼100 µm to 2 mm) to fabricate toroid cores with varying magnetic material loading. It was shown that ironsand can be used to replace up to 15 wt.% of the magnetic materials with minimal impact on the composite magnetic performance, thus reducing the cost. Ironsand was also used as a supporting material in a single-rail wireless power transfer system, effectively increasing the power transfer, demonstrating potential applications to reduce flux leakage.

Reprogrammable Ferromagnetic Domains for Reconfigurable Soft Magnetic Actuators.

Soft magnetic materials have shown promise in diverse applications due to their fast response, remote actuation, and large penetration range for various conditions. Herein, a new soft magnetic composite material capable of reprogramming its magnetization profile without changing intrinsic magnetic properties of embedded magnetic particles or the molecular property of base material is reported. This composite contains magnetic microspheres in an elastomeric matrix, and the magnetic microspheres are composed of ferromagnetic microparticles encapsulated with oligomeric-PEG. By controlling the encapsulating polymer phase transition, the magnetization profiles of the magnetic composite can be rewritten by physically realigning the ferromagnetic particles. Diverse magnetic actuators with reprogrammable magnetization profiles are developed to demonstrate the complete reprogramming of complex magnetization profile.

Synthesis and Spark Plasma Sintering of Soft Magnetic Composite in a Fe2O3­Al System by Mechanical Alloying.

We have applied mechanical alloying (MA) to produce soft magnetic composite material using a mixture of elemental Fe2O3­Al powders. An optimal milling and sintering conditions to obtain soft magnetic α-Fe/Al2O3 composite with fine microstructure were investigated by X-ray diffraction, differential scanning calorimeter and vibrating sample magnetometer measurements. It is found that the average grain sizes of α-Fe in α-Fe/Al2O3 composite ball-milled for 5 hours is estimated to be in the range of 50 nm. The saturation magnetization of ball-milled powders showed a maximum value of 88 emu/g after 30 min. of MA and reaches to 77 emu/g after 5 h of MA. The magnetic hardening due to the reduction of the α-Fe grain size with ball milling was also observed. Densification of the ball-milled powders was performed in the spark plasma sintering (SPS) machine at 1000 °C and 1100 °C. FE-SEM observation shows that the average grain size of α-Fe in α-Fe/Al2O3 composite sintered at 1000 °C is in the range of 100 nm, which is nearly same value estimated from the so-called Hall plot. It can be also seen that the coercivity of SPS sample sintered at 1000 °C is still high value of 92 Oe, suggesting that the grain growth of magnetic α-Fe phase during SPS process tends to be suppressed.