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Communication

Effect of Various Metal Oxide Insulating Layers on the Magnetic Properties of Fe-Si-Cr Systems

by
Zhenyi Huang
1,
Huaqin Huang
2,
Hao He
2,
Zhaoyang Wu
1,
Xuesong Wang
1,* and
Rui Wang
2,*
1
School of Metallurgical Engineering, Anhui University of Technology, Maanshan 243002, China
2
Key Laboratory of Green Fabrication and Surface Technology of Advanced Metal Materials, Anhui University of Technology, Ministry of Education, Maanshan 243002, China
*
Authors to whom correspondence should be addressed.
Coatings 2023, 13(4), 804; https://doi.org/10.3390/coatings13040804
Submission received: 24 March 2023 / Revised: 11 April 2023 / Accepted: 12 April 2023 / Published: 20 April 2023
(This article belongs to the Section Ceramic Coatings and Engineering Technology)
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Abstract

:
Iron-based soft magnetic composites (SMCs) are the key components of high-frequency electromagnetic systems. Selecting a suitable insulating oxide layer and ensuring the integrity and homogeneity of the heterogeneous core–shell structure of SMCs are essential for optimizing their magnetic properties. In this study, four types of SMCs—Fe-Si-Cr/ZrO2, Fe-Si-Cr/TiO2, Fe-Si-Cr/MgO, and Fe-Si-Cr/CaO—were prepared via ball milling, followed by hot-press sintering. The differences between the microscopic morphologies and magnetic fproperties of the Fe-Si-Cr/AOx SMCs prepared using four different metal oxides were investigated. ZrO2, TiO2, MgO, and CaO were successfully coated on the surface of the Fe-Si-Cr alloy powders through ball milling, forming a heterogeneous Fe-Si-Cr/AOx core–shell structure with the Fe-Si-Cr alloy powder as the core and the metal oxide as the shell. ZrO2 is relatively hard and less prone to breakage and refinement during ball milling, resulting in a lower degree of agglomeration on the surface of the composites and prevention of peeling and collapse during hot-press sintering. When ZrO2 was used as the insulation layer, the magnetic dilution effect was minimized, resulting in the highest resistivity (4.2 mΩ·cm), lowest total loss (580.8 kW/m3 for P10mt/100kHz), and lowest eddy current loss (470.0 kW/m3 for Pec 10mt/100kHz), while the permeability stabilized earlier at lower frequencies.

Graphical Abstract

1. Introduction

Iron-based soft magnetic composites (SMCs), which are characterized by high saturation magnetization, high permeability, and low core losses, are the key components of high-frequency electromagnetic systems [1,2]. With the development of frequency control technology, the further reduction in losses in the energy conversion of iron-based SMCs is the key to achieving the miniaturization and efficient application of high-frequency devices [3]. The preparation of iron-based SMCs involves the formation of a heterogeneous core–shell structure by coating the surface of iron-based alloy powders with an insulating layer, either physically or chemically, followed by hot-press sintering and heat treatment. Although optimizing the composition of iron-based alloy powders leads to improved magnetic conductivity of iron-based SMCs, a high-quality insulation layer is essential for ameliorating high-frequency energy losses [4]. Therefore, the selection of a suitable insulating layer is among the most important considerations in the design and development of iron-based SMCs.
In recent years, organic insulators such as polyimide [5], silicone resin [6], and epoxy resin [7] have been widely utilized in industrial production owing to their favorable adhesion and extensibility properties; however, their poor thermal stability limits their practical applicability. To overcome the shortcomings of organic insulating layers when utilized in iron-based SMCs, researchers have used metal oxides (AOx) such as MgO [8], ZrO2 [9], MnO2 [10], and Al2O3 [11] as insulating layers given their high thermal stability and resistivity, which are strongly dependent on point defects [12,13,14]. For example, Wei et al. [15] deposited MgO cladding on an Fe-Si-Al alloy powder, which resulted in a permeability of 74.49 and a loss of 414.76 mW/cm3 at 50 kHz. Dong et al. [16] coated TiO2 onto the surface of amorphous FeSiBCCr powders via hydrolysis and condensation reactions, and the resultant composite displayed a permeability of 67 and a loss of 265 mW/cm3 at 5 mT and 100 kHz. Yan et al. [9] employed mechanical ball milling to uniformly coat ZrO2 particles on the surface of iron powder, which led to enhanced resistivity (225.76 μΩ/cm) and a significant reduction in the eddy current loss; however, the ball milling process increased the occurrence of defects and stresses. Choi et al. [17] prepared Al2O3 insulating layers of varying thicknesses on the surface of Fe-Si-Cr alloy powders using the sol-gel method, thereby fabricating a composite with an effective permeability of 33.9 and a loss of 252 mW/cm3 at 50 mT and 100 kHz. Although previous studies [18,19,20,21] have demonstrated that metal oxides are promising candidates for use as insulating layers in the production of Fe-based SMCs, recent studies have predominantly focused on developing new metal oxide insulating layers and improving the properties of Fe-based SMCs [22,23].
The effects of specific metal oxide insulating layers on the magnetic properties of homogeneous iron-based SMCs have not yet been investigated. In this study, various metal oxides were used as insulation layers (AOx) to coat Fe-Si-Cr alloy powder by simple mechanical ball milling, followed by the preparation of Fe-Si-Cr/AOx SMCs via hot-press sintering and heat treatment. The results of our study provide valuable insights for the development of efficient iron-based SMCs that possess high power densities and are amenable to miniaturization.

2. Materials and Methods

2.1. Materials and Reagents

Fe-Si-Cr alloy powder (Si = 5.51 wt.%, Cr = 4.98 wt.%, average particle size of 23.78 μm with a standard deviation of 6.140), produced via gas atomization, was sourced from Changsha Tijo Metal Material Co., Ltd. (Changsha, China) CaO, MgO, TiO2, and ZrO2 powders (purity ≥ 99.9%, average particle size: 100–300 nm) were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). High-purity argon (purity ≥ 99.99%, Nanjing Special Gas Factory Co., Ltd. (Nanjing, China)) was used as the protective gas during the heat treatment process.

2.2. Experimental Process

2.2.1. Material Preparation

First, the Fe-Si-Cr alloy and metal oxide (CaO, MgO, TiO2, or ZrO2) powders were placed in stainless-steel ball mill jars at a mass ratio of 10:1, ball-to-material ratio of 8:1, and ball-milled at a rate of 300 rpm for 1 h to prepare the Fe-Si-Cr/AOx composite powders. The Fe-Si-Cr/AOx composite powder was then placed in a graphite mold and sintered in an SM-100E electrically pressurized sintering machine (Hubei Precision Materials Technology Co., Ltd. Huangshi, China). The sintering temperature was increased from 25 °C to 900 °C within 10 min and maintained at this level for 10 min at a pressure of 14 MPa. After sintering, the SMCs were annealed at 650 °C for 120 min [22]. The final dimensions of the prepared Fe-Si-Cr/AOx SMCs were 5 mm in height with outer and inner diameters of 30 and 20 mm, respectively.

2.2.2. Material Characterization

The physical phases of the Fe-Si-Cr alloy powder and Fe-Si-Cr/AOx composite powders were analyzed on a Bruker D8 Advance X-ray diffractometer (XRD, Bruker, Berlin, Germany) within the 2θ range of 10–90° at a scan rate of 1 (°)/min. The surface and sectional morphologies and compositional distributions of the Fe-Si-Cr/AOx composite powders and SMCs were characterized by scanning electron microscopy (SEM, Tescan Mira3 Xmu, TESCAN, Prague, Czech Republic) combined with energy-dispersive X-ray spectroscopy (EDS). The electronic structures of the oxide elements in the Fe-Si-Cr/AOx soft magnetic composite cores were investigated by XPS (ULVAC-PHI, Tokyo, Japan) and with a PHI-5000 Versaprobe instrument. The hysteresis loops of the Fe-Si-Cr/AOx SMCs were analyzed at 25 °C using an MPMS-3 vibrating sample magnetometer (VSM, Quantum Design, San Diego, CA, USA) with an external field range of ±20,000 Oe and a step size of 50 Oe. A four-point probe system (RTS-8, Suzhou Jingge Electronics Co., Ltd., Suzhou, China) and an AC magnetic analyzer (SY-8219, IWATSU, Tokyo, Japan) were used to characterize the resistivity and loss of the Fe-Si-Cr/AOx SMCs. The hardness was measured using a hardness tester (HRS-150, Shanghai Optical Instrument Factory, Shanghai, China).

3. Results and Discussion

3.1. Microstructure of Fe-Si-Cr/AOx Composite Powders and SMCs

Figure 1 shows the XRD patterns of raw Fe-Si-Cr and Fe-Si-Cr/AOx composite powders coated with various metal oxides. The diffraction peaks at 2θ = 44.73°, 65.12°, and 82.48° in the profile of the raw Fe-Si-Cr alloy powder correspond to the (110), (200), and (211) crystal planes of the α-Fe (Si, Cr) phase in the body-centered cubic structure, respectively, according to the JPCDS standard card 06-0696 [24]. In contrast, new diffraction peaks were observed in the XRD patterns of the Fe-Si-Cr/AOx composite powders in addition to the three diffraction peaks of the-Fe (Si, Cr) phase. For example, the new diffraction peaks at 2θ = 28.18 and 31.44° for the ZrO2-coated composite powder correspond to the (−111) and (111) crystal planes of monoclinic ZrO2 (JCPDS Standard Card 27-0997) [25]. The peak at 2θ = 25.41° corresponds to the (101) crystal plane diffraction of anatase TiO2, while that at 2θ = 42.94°, 62.34° corresponds to the (200) and (220) crystal plane diffraction of the cubic magnesite structure MgO at 2θ = 32.18°. The diffraction peaks at 37.39° and 53.82° correspond to the (111), (200), and (220) crystal planes of the face-centered cubic structure of CaO, respectively. The peaks attributed to the metal oxides are unambiguous, and no other spurious peaks are observed. Furthermore, the position (44.71°, 65.10°, 82.44°) and half-height width (0.29, 0.49, 0.58) of the characteristic peaks of the α-Fe (Si, Cr) phase were minimally altered after coating with the metal oxides, while the crystallite sizes were almost same (31.03–31.77 nm), indicating that the Fe-Si-Cr/AOx composite powder prepared by ball milling did not affect the crystal structure of the Fe-Si-Cr alloy powder substrate.
To further investigate the effect of each metal oxide layer on the morphological characteristics of the Fe-Si-Cr/AOx composite powders, their surface morphologies and elemental distributions were analyzed by SEM and EDS, and the results are shown in Figure 2. The surfaces of the raw Fe-Si-Cr alloy powders (Figure 2a) were generally smooth, showing some defects such as pits produced during gas atomization. In comparison, the dimensions of the Fe-Si-Cr/AOx composite powders changed negligibly but were slightly deformed after depositing the metal oxide insulating layers by ball milling, owing to the plastic deformation of the Fe-Si-Cr substrate resulting from collisions during the ball milling process. The surface of the Fe-Si-Cr/AOx composite powder was rough and covered with numerous agglomerated small particles. The pit defects visible on the surface of the pristine powder substrate were filled with oxide particles. The EDS analysis indicated that Zr, Ti, Mg, Ca, and O were distributed over the entire surface of the Fe-Si-Cr/AOx composite powders. This suggests that each of the corresponding metal oxides, CaO, MgO, TiO2, and ZrO2, formed an insulation layer on the surface of the Fe-Si-Cr alloy powders, constituting a heterogeneous core–shell structure comprising the Fe-Si-Cr alloy powder as the core and AOx as the shell. This powdered raw material was used for the preparation of Fe-Si-Cr/AOx SMCs. The combined SEM and EDS results further indicated that the uniformity and integrity of the insulation layer were the most and least favorable when ZrO2 and CaO were utilized, respectively. This is because the metal oxide powder gradually broke down and was refined during ball milling. Therefore, the lower the hardness, the easier it is to form an ultrafine powder, resulting in increased surface energy of the powder. Consequently, a more unstable energy state is attained, leading to an increase in the agglomeration coefficient. The hardness of the four metal oxides decreased in the following order: ZrO2 (7.5 Mohs) > TiO2 (6.0 Mohs) > MgO (5.5 Mohs) > CaO (1.6 Mohs) [26,27,28,29]. Lower hardness can result in agglomeration, which occurs more easily during the pressing process, resulting in an uneven coating. Consequently, the degree of agglomeration on the surface of the Fe-Si-Cr/CaO substrate after ball milling increased and the quality of the insulation layer deteriorated.
Backscattered SEM images of the Fe-Si-Cr/AOx SMCs with polished sections obtained after sintering and annealing are shown in Figure 3. Backscattered electrons are sensitive to the atomic number of the material; the higher the atomic number, the brighter the corresponding backscattered electron image. The elemental distribution signals showed that Fe was mainly concentrated in the internal Fe-Si-Cr substrate region, whereas O as well as Zr, Ti, Mg, and Ca derived from ZrO2, TiO2, MgO, and CaO were predominantly distributed at the interface. This indicated that the heterogeneous Fe-Si-Cr/AOx core–shell structure was successfully assembled to form SMCs. A comparison of the Fe-Si-Cr/AOx SMCs comprising four different metal oxide coatings revealed that the insulating layers of Fe-Si-Cr/ZrO2 (Figure 3a) and Fe-Si-Cr/TiO2 (Figure 3b) were complete and relatively uniform in thickness. However, the insulating layers of Fe-Si-Cr/MgO (Figure 3c) and Fe-Si-Cr/CaO (Figure 3d) were non-uniformly distributed, with some porosity and agglomeration due to the frictional force between the Fe-Si-Cr/AOx core–shell heterostructure composite powders [30]. During sintering, the composite powders collided and were compressed, thus reducing the gaps between the powder particles. The hardness values of MgO and CaO are lower than those of ZrO2 and TiO2. Due to the low hardness, CaO and MgO agglomerate during the pressing process, and the insulating layer that originally covered the powder is detached, resulting in the formation of pores between the spherical powder powders.
Figure 4 shows the XPS data for the Fe-Si-Cr/AOx SMCs’ polished section, which comprised four different types of metal oxides as insulating layers. The corrected positions of Zr3d (Figure 4a), Ti2p (Figure 4b), Mg1s (Figure 4c), and Ca2p (Figure 4d) were obtained by curve fitting and setting the electron binding energy of the C1s peak to 284.8 eV. The two fitted peaks of Zr [31,32] at 181.46 and 183.81 eV correspond to the two split peaks of Zr3d5/2 and Zr3d3/2, respectively. The two fitted peaks of Ti [33,34] at 458.26 and 463.92 eV correspond to the two split peaks of Ti2p3/2 and Ti2p1/2 respectively; the fitted peaks of Mg [35] for the Mg1s orbital with a binding energy of 1304.13 eV correspond to the Mg-O structure, while the two spin split peaks of Ca2p3/2 and Ca2p1/2 at 346.72 and 350.29 eV [36] indicate the presence of Ca-O. The XPS results verified the SEM and EDS results for the Fe-Si-Cr/AOx SMCs. This indicates that the corresponding Zr, Ti, Mg, and Ca elements in the four metal oxides, ZrO2, TiO2, MgO, and CaO, were mainly distributed at the interface and that the core–shell heterostructure of the SMCs did not collapse during the sintering process.

3.2. Effect of Distinct Metal Oxide Insulating Layers on the Magnetic Properties of the SMCs

Figure 5a,b shows the saturation magnetization hysteresis loops and magnified areas of the curves for the Fe-Si-Cr SMCs, respectively. Although the metal oxide insulating layers differ, all the corresponding soft magnetic composite cores exhibit similar characteristics, that is, high saturation magnetization strength (Ms) and low coercivity (Hc) and remanence (Mr). The magnetic susceptibilities of all the Fe-Si-Cr/AOx SMCs became saturated when the applied magnetic field strength reached 15,000 Oe. However, the Ms values of the SMCs were generally lower than those of the Fe-Si-Cr soft magnetic cores (200.1 emu/g). This is because Ms values are derived from the static magnetic properties of the material energy. Furthermore, because the metal oxide insulation layer is a nonmagnetic phase, its introduction leads to a reduction in the number of total magnetic moments per unit volume of the core [37]. Owing to the superior homogeneity and integrity of the metal oxide insulating layer and fewer internal pores in the Fe-Si-Cr/ZrO2 SMCs (184.2 emu/g) and Fe-Si-Cr/TiO2 SMCs (186.9 emu/g) composite cores, the saturation magnetization strengths of these samples were higher than those of the Fe-Si-Cr/MgO SMCs (180.5 emu/g) and Fe-Si-Cr/CaO SMCs (177.6 emu/g). The coercivity of SMCs is an inherent property affected by the number and strength of magnetic dipole moments and the interaction between adjacent magnetic domains. There was no significant difference between the coercivities of the Fe-Si-Cr/AOx SMCs, indicating that the nonmagnetic metal oxide insulating layers and the heterogeneous Fe-Si-Cr/AOx core–shell structures did not significantly affect the magnetic domains.
Quantitative analysis of the uniformity of the insulating layer of SMCs is difficult. However, a more uniform insulating layer can suppress interparticle eddy currents more effectively, improve the electrical insulation between alloy powders, and reduce the magnetic dilution phenomenon caused by the agglomeration of nonmagnetic substances [38]. Therefore, in this study, the effects of four metal oxide insulating layers on the insulating properties of Fe-Si-Cr/AOx SMCs were investigated by introducing resistivity. The results are shown in Figure 6a. The resistivity of the Fe-Si-Cr/AOx SMCs coated with four metal oxide insulating layers was higher than that of the Fe-Si-Cr SMCs. Furthermore, the Fe-Si-Cr/ZrO2 SMCs and Fe-Si-Cr/TiO2 SMCs with uniform and compact insulating layers exhibited higher resistivities. This may be due to the high temperature and pressure during sintering, which promoted the growth of ZrO2 grains [39] and improved the homogeneity of the insulating layer. The high-temperature and high-pressure sintering environment also promotes the crystallization of TiO2, providing additional carrier channels and reducing the carrier concentration; consequently, the insulating characteristics of the corresponding SMCs are significantly improved [40]. Although the inhomogeneity of the insulating layer deteriorates the insulation characteristics of SMCs, the presence of pores therein can suppress this phenomenon. Therefore, the resistivities of the Fe-SMCs-Cr/MgO and Fe-Si-Cr/CaO SMCs did not decrease significantly as compared to those of the Fe-Si-Cr/ZrO2 SMCs and Fe-Si-Cr/TiO2 SMCs. Figure 6b shows the variation in the permeability of Fe-Si-Cr and Fe-Si-Cr/AOx SMCs with frequency. Although the permeabilities of both the Fe-Si-Cr and Fe-Si-Cr/AOx SMCs decreased with increasing test frequency, the permeability of the latter was more stable than that of the former. The Fe-Si-Cr/AOx SMCs exhibited better frequency stability than the Fe-Si-Cr sample. The Fe-Si-Cr/TiO2 SMCs with a more uniform and compact insulation layer displayed higher permeability than Fe-Si-Cr/MgO and Fe-Si-Cr/CaO SMCs, which had less uniform insulating layers. This is because a more continuous and dense insulation layer ensures the integrity of the internal magnetic domain structure of SMCs. Conversely, the accumulation of pores and oxides in Fe-Si-Cr/MgO and Fe-Si-Cr/CaO SMCs enhances the magnetic dilution effect, prevents contact between the alloy powder particles, and increases the magnetic resistance [41]. Although the permeability of the Fe-Si-Cr/ZrO2 core was lower than that of the Fe-Si-Cr/MgO core up to 30 kHz, the decrease in permeability became less pronounced at higher operating frequencies. At >30 kHz, the permeability of Fe-Si-Cr/ZrO2 exceeded that of Fe-Si-Cr/MgO because the intact insulation layer enhanced the depth of the skin effect, which allowed the SMCs to stabilize at lower operating frequencies.
Figure 7a shows the total loss (Pcv) distributions of the Fe-Si-Cr and Fe-Si-Cr/AOx SMCs under an external field of 10 mT. Evidently, the Pcv values of both the Fe-Si-Cr and Fe-Si-Cr/AOx SMCs increased with frequency. For Fe-Si-Cr/ZrO2, having more uniform insulating layers with superior integrity, the Pcv value (580.7 kW/m3, at 10 mT external field, 100 kHz test frequency) decreased by ~62.6% compared to that of Fe-Si-Cr (1552.8 kW/m3). In contrast, Pcv of the Fe-Si-Cr/CaO SMCs (1446.8 kW/m3), which had inferior-quality insulating layers and increased porosity, decreased by 6.8% compared to that of the Fe-Si-Cr SMCs.
According to the classical Bertotti loss separation theory [41], Pcv can be divided into two parts: the hysteresis loss (Physt) and eddy current loss (Pe).
P c v = K h f + K e f m
Kh is the hysteresis loss coefficient, Ke is the eddy current loss coefficient, and f is the frequency. At a fixed magnetic field strength of m = 2, the eddy current loss was proportional to the square of the operating frequency, whereas the hysteresis loss was proportional to the operating frequency. First, the Pcv/f versus f curve was fitted using a linear fitting method. The fitted curve was extrapolated to the zero-frequency point to obtain the intercept of the hysteresis loss under quasi-static conditions, which was multiplied by the frequency to obtain the hysteresis loss at that frequency, as shown in Figure 7b. The eddy-current loss was obtained by subtracting the total loss from the fitted hysteresis loss, as shown in Figure 7c. The Physt values of all Fe-Si-Cr/AOx SMCs increased almost linearly with frequency, while the discontinuous metal oxide insulating layer caused the pores inside the SMCs to restrict domain wall motion. Therefore, the Fe-Si-Cr/MgO and Fe-Si-Cr/CaO SMCs displayed higher hysteresis losses than the Fe-Si-Cr/ZrO2 and Fe-Si-Cr/TiO2 SMCs. Furthermore, the heterogeneous Fe-Si-Cr/AOx core–shell structure affected the loss of the SMCs, mainly by reducing the eddy current loss by enhancing the resistivity and limiting the effective operating diameter of the eddy currents. Hence, TiO2 and ZrO2 insulating layers were more effective than MgO and CaO in reducing the eddy current loss in SMCs.
A comprehensive comparison of the magnetic properties indicated that for equal amounts of each metal oxide, the sintered ZrO2 insulating layer was denser and more homogeneous than the layers derived from common metal oxides such as MgO, CaO, and TiO2. This minimized the magnetic dilution effect and led to the highest resistivity (4.2 mΩ·cm), lowest total loss (P10mt/100kHz of 580.8 kW/m3), and lowest eddy current loss (470.0 kW/m3 for Pec 10mt/100kHz) in the corresponding SMCs, while the permeability stabilized earlier at lower frequencies.

4. Conclusions

By studying the differences between the microscopic morphologies and magnetic properties of Fe-Si-Cr/AOx SMCs prepared using various metal oxides as insulating layers, the following conclusions were drawn:
  • Four metal oxides, ZrO2, TiO2, MgO, and CaO, were successfully coated on the surface of the Fe-Si-Cr alloy powder via ball milling. Thus, a heterogeneous Fe-Si-Cr/AOx core–shell structure was formed, wherein the Fe-Si-Cr alloy powder and the metal oxides comprised the core and shell, respectively. These powdered raw materials were used for the subsequent preparation of Fe-Si-Cr/AOx SMCs.
  • Compared to common metal oxide powders such as MgO, CaO, and TiO2, ZrO2 powder is harder and less prone to breakage and refinement during ball milling. This resulted in a lower degree of agglomeration on the surface of the Fe-Si-Cr alloy powder, forming an insulating layer with superior uniformity and integrity. The insulating layer resists peeling and collapse during subsequent hot pressing and heat treatment processes, ultimately providing a high-quality insulating layer for SMCs.
  • For equal amounts of each metal oxide, the sintered insulating layer comprising ZrO2 possessed the highest density and uniformity, which minimized the magnetic dilution effect, leading to the highest resistivity (4.2 mΩ·cm) and lowest total (580.8 kW/m3 for P10mt/100kHz) and eddy current (470.0 kW/m3 for Pec 10mt/100kHz) losses in the corresponding SMCs. The magnetic permeability also stabilized earlier at lower frequencies (>40 kHz).

Author Contributions

Z.H., Writing—original draft, formal analysis; H.H. (Huaqin Huang), Investigation; H.H. (Hao He), Picture rendering and Review; Z.W., Performance Test; X.W., investigation and Methodology; R.W., Review, and Editing. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Chinese National Science Foundation (52274311), Scientific Research Planning Project of Anhui Province (2022AH040054, 2022AH010024), and the Opening Foundation of the State Key Laboratory of Metal Material for Marine Equipment and Application (SKLMEA-K202202).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Acknowledgments

The authors thank Chao Wang and Lei He from the Shiyanjia Lab (www.shiyanjia.com) for the XRD and XPS analyses.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. XRD spectra of raw Fe-Si-Cr alloy powder and Fe-Si-Cr/AOx composite powders comprising varying metal oxide insulating layers.
Figure 1. XRD spectra of raw Fe-Si-Cr alloy powder and Fe-Si-Cr/AOx composite powders comprising varying metal oxide insulating layers.
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Figure 2. SEM images and EDS results showing the surface morphology and elemental distribution of (a) raw Fe-Si-Cr alloy powder and (b–i) Fe-Si-Cr/AOx composite powders coated with varying metal oxide layers. (b,f) Fe-Si-Cr/ZrO2, (c,g) Fe-Si-Cr/TiO2, (d,h) Fe-Si-Cr/MgO, and (e,i) Fe-Si-Cr/CaO.
Figure 2. SEM images and EDS results showing the surface morphology and elemental distribution of (a) raw Fe-Si-Cr alloy powder and (b–i) Fe-Si-Cr/AOx composite powders coated with varying metal oxide layers. (b,f) Fe-Si-Cr/ZrO2, (c,g) Fe-Si-Cr/TiO2, (d,h) Fe-Si-Cr/MgO, and (e,i) Fe-Si-Cr/CaO.
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Figure 3. BSE images and EDS energy spectra of Fe-Si-Cr/AOx soft magnetic composite cores: (a) Fe-Si-Cr/ZrO2, (b) Fe-Si-Cr/TiO2, (c) Fe-Si-Cr/MgO, and (d) Fe-Si-Cr/CaO.
Figure 3. BSE images and EDS energy spectra of Fe-Si-Cr/AOx soft magnetic composite cores: (a) Fe-Si-Cr/ZrO2, (b) Fe-Si-Cr/TiO2, (c) Fe-Si-Cr/MgO, and (d) Fe-Si-Cr/CaO.
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Figure 4. XPS profiles of oxide metal elements in Fe-Si-Cr/AOx soft magnetic cores: (a) Zr, (b) Ti, (c) Mg, and (d) Ca.
Figure 4. XPS profiles of oxide metal elements in Fe-Si-Cr/AOx soft magnetic cores: (a) Zr, (b) Ti, (c) Mg, and (d) Ca.
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Figure 5. (a) Saturation magnetization hysteresis loops and (b) local magnification of curves for Fe-Si-Cr SMCs and Fe-Si-Cr/AOx soft magnetic composite cores at room temperature.
Figure 5. (a) Saturation magnetization hysteresis loops and (b) local magnification of curves for Fe-Si-Cr SMCs and Fe-Si-Cr/AOx soft magnetic composite cores at room temperature.
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Figure 6. (a) Resistivity and (b) permeability of the Fe-Si-Cr soft magnetic core and Fe-Si-Cr/AOx soft magnetic composite cores.
Figure 6. (a) Resistivity and (b) permeability of the Fe-Si-Cr soft magnetic core and Fe-Si-Cr/AOx soft magnetic composite cores.
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Figure 7. (a) Total loss, (b) hysteresis loss, and (c) eddy current loss of Fe-Si-Cr soft magnetic core and Fe-Si-Cr/AOx soft magnetic composite cores at 10 mT.
Figure 7. (a) Total loss, (b) hysteresis loss, and (c) eddy current loss of Fe-Si-Cr soft magnetic core and Fe-Si-Cr/AOx soft magnetic composite cores at 10 mT.
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MDPI and ACS Style

Huang, Z.; Huang, H.; He, H.; Wu, Z.; Wang, X.; Wang, R. Effect of Various Metal Oxide Insulating Layers on the Magnetic Properties of Fe-Si-Cr Systems. Coatings 2023, 13, 804. https://doi.org/10.3390/coatings13040804

AMA Style

Huang Z, Huang H, He H, Wu Z, Wang X, Wang R. Effect of Various Metal Oxide Insulating Layers on the Magnetic Properties of Fe-Si-Cr Systems. Coatings. 2023; 13(4):804. https://doi.org/10.3390/coatings13040804

Chicago/Turabian Style

Huang, Zhenyi, Huaqin Huang, Hao He, Zhaoyang Wu, Xuesong Wang, and Rui Wang. 2023. "Effect of Various Metal Oxide Insulating Layers on the Magnetic Properties of Fe-Si-Cr Systems" Coatings 13, no. 4: 804. https://doi.org/10.3390/coatings13040804

APA Style

Huang, Z., Huang, H., He, H., Wu, Z., Wang, X., & Wang, R. (2023). Effect of Various Metal Oxide Insulating Layers on the Magnetic Properties of Fe-Si-Cr Systems. Coatings, 13(4), 804. https://doi.org/10.3390/coatings13040804

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