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Preparation and characterization of flaky FeSiAl composite magnetic powder core coated with MnZn ferrite
Current Applied Physics 19 (2019) 924–927
Contents lists available at ScienceDirect
Current Applied Physics journal homepage: www.elsevier.com/locate/cap
Preparation and characterization of flaky FeSiAl composite magnetic powder core coated with MnZn ferrite
T
Zhen Wanga,b, Xiansong Liua,b,∗, Xucai Kana,b,∗∗, Ruiwei Zhua,b, Wei Yanga,b, Qiuyue Wua,b, Shengqiang Zhoua,b a b
School of Physics and Materials Science, Anhui University, Hefei, 230601, PR China Engineering Technology Research Center of Magnetic Materials, School of Physics & Materials Science, Anhui University, Hefei, 230601, PR China
A R T I C LE I N FO
A B S T R A C T
Keywords: Ferrite Soft magnetic composite Magnetic powder core Magnetic performance
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.
1. Introduction The magnetic powder core is a product which is uniformly mixed and pressed by using a ferromagnetic substance and an insulating substance. A major feature of the magnetic powder core is that it can be prepared into different shapes and applied to different fields. It is well known that FeSiAl alloys have excellent soft magnetic properties, relatively high magnetic permeability, high saturation magnetization and low cost [1,2]. By covering the surface of the ferrosilicon magnetic powder, it can block the electrical contact between the powder particles, increase the resistivity, reduce the eddy current loss of the magnetic powder core, and improve the high frequency performance of the magnetic powder core [3–5]. However, FeSiAl magnetic powder core has high loss at high frequency and is easy to generate heat, which limits its application in high frequency and wide frequency [6,7]. Ferrite is a ferromagnetic metal oxide. In terms of electrical properties, ferrite has a much higher electrical resistivity than metal and alloy magnetic materials, and also has excellent dielectric properties [8–10]. The magnetic properties of ferrite also show high magnetic permeability at high frequencies. So ferrite has become a non-metallic ∗
magnetic material with a wide range of applications in the field of high frequency and low voltage [11–13]. Using this feature, H. Shokrollahi et al. [14] prepared an iron-based composite magnetic powder core by sol-gel method using Mn–Zn ferrite as a coating agent, effectively insulating contact between iron silicon aluminum particles. The magnetic powder core prepared by the magnetic powder core and the traditional resin coating agent higher magnetic permeability and lower loss. On one hand, magnetic ferrites have higher magnetic permeability and electrical resistivity than conventional non-magnetic coating materials [15]. On the other hand, permeability is an important parameter of the magnetic properties of soft magnetic materials and is closely related to the shape of magnetic particles. The existing research [16,17] shows that the flattened FeSiAl particles can improve the complex permeability and complex permittivity of the material. The orientation of the particles in the cold pressed sheet can improve the effective permeability of the material, which is beneficial to improve its soft magnetic performance. Based on the previous research, MnZn/FeSiAl composite magnetic powder core was prepared by using MnZn ferrite as coating agent, and the effect of MnZn ferrite addition on the soft magnetic properties of FeSiAl was studied.
Corresponding author. School of Physics and Materials Science, Anhui University, 111 Jiulong Road, Hefei, 230601, PR China. Corresponding author. School of Physics and Materials Science, Anhui University, 111 Jiulong Road, Hefei, 230601, PR China. E-mail addresses: [email protected] (X. Liu), [email protected] (X. Kan).
∗∗
https://doi.org/10.1016/j.cap.2019.05.003 Received 26 March 2019; Accepted 7 May 2019 Available online 08 May 2019 1567-1739/ © 2019 Published by Elsevier B.V. on behalf of Korean Physical Society.
Current Applied Physics 19 (2019) 924–927
Z. Wang, et al.
2. Experiment The raw materials required for this experiment, MnZn ferrite (< 5 μm) and FeSiAl soft magnetic powder (< 30 μm), were supplied by Antai Technology. The flattening of FeSiAl soft magnetic powder was achieved by a ball milling process. The ball-to-batch ratio (mass ratio of the grinding ball to the sample) was 10:1, the rotational speed was 300 r/min, and the time was set to 20 h. First, 30 g of each of five sets of composite powders with different contents of MnZn ferrite (the quality scores are 0%, 5%, 10%, 15%, 20%) were weighed in a beaker. They were respectively placed in a ball mill and ball-milled at 100 r/ min for 1 h to make them uniformly mixed. After taking out, uniformly mixed acetone and 1 wt% of a coupling agent (KH-550 solution) were respectively dropped into five sets of samples, stirred uniformly and dried. A solution of uniformly mixed acetone and 3 wt% of a binder (high temperature silicone DC805) was separately dropped into 5 sets of samples, stirred and dried again. Finally, the composite powder was press-formed under a pressure of 1200 MPa and held for 1 min to obtain a toroidal magnetic powder core having an outer diameter of 2.40 cm and an inner diameter of 1.20 cm. After molding, the samples were placed in a tube furnace and annealed at 600 °C for 1 h, and the protective atmosphere was nitrogen. Further, seven composite powders containing 5% MnZn ferrite were prepared and pressed into a ring by the above steps, and then annealed at annealing temperatures of 600 °C, 625 °C, 650 °C, 675 °C, 700 °C, 725 °C and 750 °C, respectively. They are used to study the optimum stress relief annealing temperature of composite magnetic powder cores. In this experiment, the phase structure of the composites was analyzed by X-ray diffraction (XRD, Rigaku D/max-2550V/PC). Scanning electron microscopy (SEM) was used to observe the microscopic morphology of the composite samples and the coating effect of the insulating agent. The saturation magnetization of the composite samples was measured by vibrating sample magnetometer (VSM, Quantum Design PPMS-VSM EC II 9T). The magnetic permeability and power loss of the magnetic powder core were tested using a B–H (B = magnetic flux density, H = magnetic field strength) alternating current (AC) magnetic characteristic analyzer.
Fig. 2. SEM image of flattened FeSiAl after 20 h of ball milling.
faces of FeSiAl, respectively. The Mn0.4Zn0.6Fe2O4 matrix phase appeared in the composite powder coated with MnZn ferrite. With the increase of MnZn ferrite addition content, the peak value gradually increases, and the characteristic peaks correspond to the (2 2 0), (3 1 1), (4 2 2) and (4 4 0) crystal planes, respectively. It is obvious that the addition of ferrite does not change the crystal structure of the FeSiAl alloy. Fig. 2 is a SEM topographical view of flattened FeSiAl after 20 h of ball milling. It can be seen from the figure that the powder particles are relatively regular in size and relatively uniform in thickness, which provides a basis for the good coverage of small particles of MnZn ferrite. The particles have a diameter of about 30 μm, a thickness of about 0.2 μm, a particle aspect ratio (diameter/thickness) of 150, and the flattening effect is good. Porosity directly affects the permeability and loss of composite powder [18]. It can be seen from the data in Table 1 that the composite powder coated with 5% ferrite has the lowest porosity, so it provides a basis for good soft magnetic properties. Fig. 3 shows the magnetization curves of pure FeSiAl and composites coated with MnZn ferrite. It can be clearly seen from the figure that the coercivity and residual magnetization of the five groups of samples are very small, indicating that the samples prepared in this experiment have typical soft magnetic properties. In addition, the uncoated ferrite sample had the highest saturation magnetization of 117.3 emu/g. Since the saturation magnetization of ferrite is significantly lower than FeSiAl, the saturation magnetization of composite samples decreases with the increase of MnZn ferrite coating. The saturation magnetization of the sample with a coating amount of 20% is reduced by 32.2% compared with the pure FeSiAl. Fig. 4 shows the dependence of the initial permeability of the five groups on the frequency at Hm = 200 A/m. As can be seen from the figure, on the one hand, the permeability of the five groups of samples does not change much in the frequency range of 50 kHz–1000 kHz, and exhibits good constant magnetic permeability characteristics. On the other hand, the permeability shows a trend of increasing first and then decreasing with the increase of ferrite content. Among them, the permeability reaches the maximum of 40.84 (Hm = 200 A/m, f = 200 kHz) when the addition content of MnZn ferrite is 5%, which is 28.1% higher than that of the pure FeSiAl magnetic powder core under the same conditions. Since the magnetic ferrite has a high permeability and electrical resistivity, the small MnZn ferrite particles enter into the gaps between the larger FeSiAl particles, reducing the nonmagnetic air
3. Results and analysis Fig. 1 shows the XRD pattern of pure FeSiAl and coated MnZn ferrite composite powder. It can be seen from the figure that the pure FeSiAl powder matrix phase is Al0.3Fe3Si0.7 phase, and there are strong diffraction peaks near 45°, 65.5° and 83°. In contrast to the PDF card, the three strong peaks correspond to the (2 0 0), (4 0 0) and (4 2 2) crystal
Table 1 Magnetic properties of five groups of samples.
Fig. 1. XRD patterns of FeSiAl and coated MnZn ferrite composite powders. 925
The contents of ferrite(%)
Ms (emu/ g)
The permeability at 200 kHz
Pcm (W/kg) at 5 mT,1000 kHz
Porosity(%)
0 5 10 15 20
117.3 112.1 106.7 103.4 79.5
31.99 40.84 39.31 37.53 35.66
12.51 10.85 11.18 11.87 11.96
4.8 3.5 3.8 5.1 6.7
Current Applied Physics 19 (2019) 924–927
Z. Wang, et al.
Fig. 3. VSM spectra of FeSiAl and composite powders coated with MnZn ferrite.
Fig. 5. Trends of loss versus frequency for five groups of samples.
proper addition of ferrite fills the gap. When the coating amount is 5%, a complete coating layer is formed on the surface of the FeSiAl magnetic powder to increase the density, thereby reducing the hysteresis loss. The eddy current loss is given by the following formula [21]:
Pe =
Where Pe is the eddy current loss, C is the constant, B is the magnetic flux density, d is the powder particle size, f is the operating frequency, and ρ is the material resistivity. It can be seen from the publicity that the eddy current loss is proportional to the square of the powder particle size and inversely proportional to the resistivity. When the addition content of ferrite is low, the average particle size and resistivity of the sample do not change much, and the hysteresis loss plays a major role, and the overall loss decreases. As the ferrite continues to increase, the average particle size of the powder becomes irregular, so that the resistivity decreases, and the eddy current loss plays a major role, so the core loss tends to increase slowly. Fig. 6 shows the variation of the magnetic properties of the magnetic powder core at different annealing temperatures. It can be seen from the figure that as the annealing temperature increases, the magnetic permeability of the composite powder core first increases and then decreases, reaching a maximum value near 650 °C. The sample creates internal stresses and dislocations during the press forming process, both of which hinder the movement of the magnetic domain walls in the technical magnetization [22]. As the annealing temperature increases, the internal stress of the sample gradually releases and the density increases, which is beneficial to increase the magnetic permeability. However, when the temperature is higher than 650 °C, the permeability
Fig. 4. Trends of permeability versus frequency for five groups of samples.
gaps and improving the density and permeability of powder cores, the permeability of the composite powder core is greatly increased by the insulating coating of the MnZn ferrite. As the ferrite content continues to increase, the permeability of the composites decreases. This may be due to the excessive content of ferrite, which makes the particle distribution of the powder core as a whole irregular and uneven, and the specific surface area of particles and the interface between the magnetic particles increase, causing the agglomeration of small particle and increase number of the gaps. The magnetic permeability is given by the following formula [19]:
μ=
CB2d 2f 2 ρ
Ls le μo N 2Ae
Where μ is the magnetic permeability, Ls is the inductance of the sample core, le is the average flux density path for ring samples, μo is the permeability of free space, N is the total number of turns of the coil, Ae is the cross-sectional area of the powder core. The permeability strongly depends on the density, number of pores, non-magnetic phase and magnetic anisotropy [20]. Fig. 5 shows the dependence of the five sample loss on frequency at Bm = 5 mT. As can be seen from the figure, on the one hand, the loss of the five groups of samples increases with increasing frequency. On the other hand, as the ferrite content increases, the loss first decreases and then increases. Among them, when the addition content of ferrite is 5%, the core loss of the composite magnetic powder is at least 10.85 W/kg (Bm = 5 mT, f = 1000 kHz), which is 13.3% lower than that of the pure FeSiAl magnetic powder core under the same conditions. As the ferrite content continues to increase, the loss increases. This is because the
Fig. 6. Effect of annealing temperature on magnetic properties of magnetic powder core. 926
Current Applied Physics 19 (2019) 924–927
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References
is gradually lowered due to the destruction of the interface of the MnZn/FeSiAl composite at a high temperature. As the annealing temperature increases, the loss of the composite powder core decreases first and then increases, reaching a minimum near 650 °C. On the one hand, as the annealing temperature increases, the internal stress of the sample gradually releases, and the coercive force decreases, thereby reducing the hysteresis loss. On the other hand, as the temperature increases, the insulating coating of the sample becomes more compact and efficient, and the insulation performance is improved, thereby reducing the eddy current loss [23]. However, when the temperature exceeds 650 °C, the internal stress of the sample is almost completely released, the insulating layer is gradually decomposed at a high temperature, the insulating property is lowered, and the iron loss is increased.
[1] K.H. Liu, L. Zhang, D.R. Li, Novel Fe-based amorphous magnetic powder cores with ultra-low core losses, Sci. China Technol. Sci. 53 (2010) 1290–1293. [2] J. Füzerová, J. Füzer, P. Kollár, Complex permeability and core loss of soft magnetic Fe-based nanocrystalline powder cores, J. Magn. Magn. Mater. 345 (2013) 77–81. [3] S.F. Chen, C.Y. Chen, C.S. Cheng, Passivation layer for the magnetic property enhancement of Fe72.8Si11.2B10.8Cr2.3C2.9 amorphous powder, J. Alloy. Comp. 644 (2015) 17–24. [4] T.D. Zhou, P.H. Zhou, D.F. Liang, Structure and electromagnetic characteristics of flaky FeSiAl powders made by melt-quenching, J. Alloy. Comp. 484 (2009) 545–549. [5] X.X. Zhong, Y. Liu, J. Li, Structure and magnetic properties of FeSiAl-based soft magnetic composite with AlN and Al2O3 insulating layer prepared by selective nitridation and oxidation, J. Magn. Magn. Mater. 324 (2012) 2631–2636. [6] S. Yoshida, M. Sato, E. Sugawara, Permeability and electromagnetic interference characteristics of Fe-Si-Al alloy flakes polymer composite, J. Appl. Phys. 85 (1999) 4636–4638. [7] L. Liu, Z.H. Yang, C.R. Deng, High frequency properties of composite membrane with in-plane aligned Sendust flake prepared by infiltration method, J. Magn. Magn. Mater. 324 (2012) 1786–1790. [8] D. Xie, K. Lin, S. Lin, Effects of processed parameters on the magnetic performance of a powder magnetic core, J. Magn. Magn. Mater. 353 (2014) 34–40. [9] C.R. Vestal, Z. Zhang, Synthesis and magnetic characterization of Mn and Co spinel ferrite-silica nanoparticles with tunable magnetic core, J. Nano Lett. 3 (2012) 1739–1743. [10] S. Sugimoto, S. Kondo, K. Okayama, M-type ferrite composite as a microwave absorber with wide bandwidth in the GHz range, IEEE Trans. Magn. 35 (1999) 3154–3156. [11] C. Caizer, M. Stefanescu, Magnetic characterization of nanocrystalline Ni-Zn ferrite powder prepared by the glyoxylate precursor method, J. Appl. Phys. 35 (2002) 3035–3037. [12] Y. Wang, J. Wang, Q.H. Zhang, Structure and magnetic properties of nickel-zinc ferrite microspheres synthesized by solvothermal method, Mater. Sci. Eng., B 171 (2010) 144–148. [13] M. Wang, Z. Zan, N. Deng, Z. Zhao, Preparation of pure iron/Ni–Zn ferrite high strength soft magnetic composite by spark plasma sintering, J. Magn. Magn. Mater. 361 (2014) 166–169. [14] H. Shokrollahi, K. Janghorban, Effect of warm compactiom on the magnetic and electrical properties of Fe-based soft magnetic composites, J. Magn. Magn. Mater. 313 (2008) 182–186. [15] Z. Yue, J. Zhou, L. Li, Synthesis of nanocrystalline NiCuZn ferrite powders by sol–gel auto-combustion method, J. Magn. Magn. Mater. 208 (2000) 55–60. [16] X. Jin, Q. Wang, W. Khan, FeSiAl/(Ni0.5Zn0.5) Fe2O4 magnetic sheet composite with tunable electromagnetic properties for enhancing magnetic field coupling efficiency, J. Alloy. Comp. 729 (2017) 277–284. [17] H. Watanabe, T. Kimura, T. Yamaguchi, Particle orientation during tape casting in the fabrication of grain‐oriented bismuth titanate, J. Am. Ceram. Soc. 72 (1989) 289–293. [18] D. Liu, C. Wu, M. Yan, Investigation on sol-gel Al2O3 and hybrid phosphate-alumina insulation coatings for FeSiAl soft magnetic composites, J. Mater. Sci. 50 (2015) 6559–6566. [19] G.Q. Lin, Z.W. Li, L. Chen, Y.P. Wu, C.K. Ong, Influence of demagnetizing field on the permeability of soft magnetic composites, J. Magn. Magn. Mater. 305 (2006) 291–295. [20] A.H. Taghvaei, H. Shokrollahi, M. Ghaffari, K. Janghorban, Influence of particle size and compaction pressure on the magnetic properties of iron-phenolic soft magnetic composites, J. Phys. Chem. Solids 71 (2010) 7–11. [21] X. Li, X. Li, X. Wang, Characterization of carbon-encapsulated permalloy nanoparticles prepared through detonation, Mater. Res. Express 4 (2017) 075024. [22] K. Nishimura, Y. Kohara, Y. Kitamoto, M. Abe, Magnetoresistance in magnetite films prepared from aqueous solution at room temperature, J. Appl. Phys. 87 (2000) 7127–7129. [23] J. Li, X.L. Peng, Y.T. Yang, H.L. Ge, Preparation and characterization of MnZn/ FeSiAl soft magnetic composites, J. Magn. Magn. Mater. 426 (2017) 132–136. [24] T. Tsutaoka, Frequency dispersion of complex permeability in Mn-Zn and Ni-Zn spinel ferrites and their composite materials, J. Appl. Phys. 93 (2003) 2789–2796.
4. Conclusion In this paper, the flattening of FeSiAl soft magnetic powder is achieved by ball milling process, and MnZn ferrite is used as a coating agent to obtain MnZn/FeSiAl composite magnetic powder core and improve magnetic properties. Compared with the previous research results, the composite magnetic powder core prepared in this paper has higher magnetic permeability and lower power loss. This is because the flattened FeSiAl powder has strong shape anisotropy [24], which can improve the magnetic permeability of the material, improve the magnetic properties of the material, and reduce the effect of the skin effect, and suppress the eddy current loss at high frequencies. The results show that the addition of MnZn ferrite affects the magnetic properties such as saturation magnetization, permeability and power loss of FeSiAl soft magnetic. With the increase of MnZn ferrite addition content, the saturation magnetization of composites decreases gradually, and the permeability increases first and then decreases, and the loss decreases first and then increases. The FeSiAl sample without coating ferrite has the highest saturation magnetization of 117.3 emu/g. When the addition content of MnZn ferrite is 5%, the permeability reaches the maximum, which is 28.1% higher than that of the pure FeSiAl magnetic powder core under the same conditions. At the same time, the loss is the lowest, which is 13.3% lower than the pure FeSiAl powder core under the same conditions. The optimum stress relief annealing temperature for the composite sample is around 650 °C. Acknowledgments This work was supported by the National Natural Science Foundation of China (Nos. 51872004, 51802002), Education Department of Anhui Province (Nos. KJ2013B293, KJ2018A0039). Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.cap.2019.05.003.
927
Contents lists available at ScienceDirect
Current Applied Physics journal homepage: www.elsevier.com/locate/cap
Preparation and characterization of flaky FeSiAl composite magnetic powder core coated with MnZn ferrite
T
Zhen Wanga,b, Xiansong Liua,b,∗, Xucai Kana,b,∗∗, Ruiwei Zhua,b, Wei Yanga,b, Qiuyue Wua,b, Shengqiang Zhoua,b a b
School of Physics and Materials Science, Anhui University, Hefei, 230601, PR China Engineering Technology Research Center of Magnetic Materials, School of Physics & Materials Science, Anhui University, Hefei, 230601, PR China
A R T I C LE I N FO
A B S T R A C T
Keywords: Ferrite Soft magnetic composite Magnetic powder core Magnetic performance
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.
1. Introduction The magnetic powder core is a product which is uniformly mixed and pressed by using a ferromagnetic substance and an insulating substance. A major feature of the magnetic powder core is that it can be prepared into different shapes and applied to different fields. It is well known that FeSiAl alloys have excellent soft magnetic properties, relatively high magnetic permeability, high saturation magnetization and low cost [1,2]. By covering the surface of the ferrosilicon magnetic powder, it can block the electrical contact between the powder particles, increase the resistivity, reduce the eddy current loss of the magnetic powder core, and improve the high frequency performance of the magnetic powder core [3–5]. However, FeSiAl magnetic powder core has high loss at high frequency and is easy to generate heat, which limits its application in high frequency and wide frequency [6,7]. Ferrite is a ferromagnetic metal oxide. In terms of electrical properties, ferrite has a much higher electrical resistivity than metal and alloy magnetic materials, and also has excellent dielectric properties [8–10]. The magnetic properties of ferrite also show high magnetic permeability at high frequencies. So ferrite has become a non-metallic ∗
magnetic material with a wide range of applications in the field of high frequency and low voltage [11–13]. Using this feature, H. Shokrollahi et al. [14] prepared an iron-based composite magnetic powder core by sol-gel method using Mn–Zn ferrite as a coating agent, effectively insulating contact between iron silicon aluminum particles. The magnetic powder core prepared by the magnetic powder core and the traditional resin coating agent higher magnetic permeability and lower loss. On one hand, magnetic ferrites have higher magnetic permeability and electrical resistivity than conventional non-magnetic coating materials [15]. On the other hand, permeability is an important parameter of the magnetic properties of soft magnetic materials and is closely related to the shape of magnetic particles. The existing research [16,17] shows that the flattened FeSiAl particles can improve the complex permeability and complex permittivity of the material. The orientation of the particles in the cold pressed sheet can improve the effective permeability of the material, which is beneficial to improve its soft magnetic performance. Based on the previous research, MnZn/FeSiAl composite magnetic powder core was prepared by using MnZn ferrite as coating agent, and the effect of MnZn ferrite addition on the soft magnetic properties of FeSiAl was studied.
Corresponding author. School of Physics and Materials Science, Anhui University, 111 Jiulong Road, Hefei, 230601, PR China. Corresponding author. School of Physics and Materials Science, Anhui University, 111 Jiulong Road, Hefei, 230601, PR China. E-mail addresses: [email protected] (X. Liu), [email protected] (X. Kan).
∗∗
https://doi.org/10.1016/j.cap.2019.05.003 Received 26 March 2019; Accepted 7 May 2019 Available online 08 May 2019 1567-1739/ © 2019 Published by Elsevier B.V. on behalf of Korean Physical Society.
Current Applied Physics 19 (2019) 924–927
Z. Wang, et al.
2. Experiment The raw materials required for this experiment, MnZn ferrite (< 5 μm) and FeSiAl soft magnetic powder (< 30 μm), were supplied by Antai Technology. The flattening of FeSiAl soft magnetic powder was achieved by a ball milling process. The ball-to-batch ratio (mass ratio of the grinding ball to the sample) was 10:1, the rotational speed was 300 r/min, and the time was set to 20 h. First, 30 g of each of five sets of composite powders with different contents of MnZn ferrite (the quality scores are 0%, 5%, 10%, 15%, 20%) were weighed in a beaker. They were respectively placed in a ball mill and ball-milled at 100 r/ min for 1 h to make them uniformly mixed. After taking out, uniformly mixed acetone and 1 wt% of a coupling agent (KH-550 solution) were respectively dropped into five sets of samples, stirred uniformly and dried. A solution of uniformly mixed acetone and 3 wt% of a binder (high temperature silicone DC805) was separately dropped into 5 sets of samples, stirred and dried again. Finally, the composite powder was press-formed under a pressure of 1200 MPa and held for 1 min to obtain a toroidal magnetic powder core having an outer diameter of 2.40 cm and an inner diameter of 1.20 cm. After molding, the samples were placed in a tube furnace and annealed at 600 °C for 1 h, and the protective atmosphere was nitrogen. Further, seven composite powders containing 5% MnZn ferrite were prepared and pressed into a ring by the above steps, and then annealed at annealing temperatures of 600 °C, 625 °C, 650 °C, 675 °C, 700 °C, 725 °C and 750 °C, respectively. They are used to study the optimum stress relief annealing temperature of composite magnetic powder cores. In this experiment, the phase structure of the composites was analyzed by X-ray diffraction (XRD, Rigaku D/max-2550V/PC). Scanning electron microscopy (SEM) was used to observe the microscopic morphology of the composite samples and the coating effect of the insulating agent. The saturation magnetization of the composite samples was measured by vibrating sample magnetometer (VSM, Quantum Design PPMS-VSM EC II 9T). The magnetic permeability and power loss of the magnetic powder core were tested using a B–H (B = magnetic flux density, H = magnetic field strength) alternating current (AC) magnetic characteristic analyzer.
Fig. 2. SEM image of flattened FeSiAl after 20 h of ball milling.
faces of FeSiAl, respectively. The Mn0.4Zn0.6Fe2O4 matrix phase appeared in the composite powder coated with MnZn ferrite. With the increase of MnZn ferrite addition content, the peak value gradually increases, and the characteristic peaks correspond to the (2 2 0), (3 1 1), (4 2 2) and (4 4 0) crystal planes, respectively. It is obvious that the addition of ferrite does not change the crystal structure of the FeSiAl alloy. Fig. 2 is a SEM topographical view of flattened FeSiAl after 20 h of ball milling. It can be seen from the figure that the powder particles are relatively regular in size and relatively uniform in thickness, which provides a basis for the good coverage of small particles of MnZn ferrite. The particles have a diameter of about 30 μm, a thickness of about 0.2 μm, a particle aspect ratio (diameter/thickness) of 150, and the flattening effect is good. Porosity directly affects the permeability and loss of composite powder [18]. It can be seen from the data in Table 1 that the composite powder coated with 5% ferrite has the lowest porosity, so it provides a basis for good soft magnetic properties. Fig. 3 shows the magnetization curves of pure FeSiAl and composites coated with MnZn ferrite. It can be clearly seen from the figure that the coercivity and residual magnetization of the five groups of samples are very small, indicating that the samples prepared in this experiment have typical soft magnetic properties. In addition, the uncoated ferrite sample had the highest saturation magnetization of 117.3 emu/g. Since the saturation magnetization of ferrite is significantly lower than FeSiAl, the saturation magnetization of composite samples decreases with the increase of MnZn ferrite coating. The saturation magnetization of the sample with a coating amount of 20% is reduced by 32.2% compared with the pure FeSiAl. Fig. 4 shows the dependence of the initial permeability of the five groups on the frequency at Hm = 200 A/m. As can be seen from the figure, on the one hand, the permeability of the five groups of samples does not change much in the frequency range of 50 kHz–1000 kHz, and exhibits good constant magnetic permeability characteristics. On the other hand, the permeability shows a trend of increasing first and then decreasing with the increase of ferrite content. Among them, the permeability reaches the maximum of 40.84 (Hm = 200 A/m, f = 200 kHz) when the addition content of MnZn ferrite is 5%, which is 28.1% higher than that of the pure FeSiAl magnetic powder core under the same conditions. Since the magnetic ferrite has a high permeability and electrical resistivity, the small MnZn ferrite particles enter into the gaps between the larger FeSiAl particles, reducing the nonmagnetic air
3. Results and analysis Fig. 1 shows the XRD pattern of pure FeSiAl and coated MnZn ferrite composite powder. It can be seen from the figure that the pure FeSiAl powder matrix phase is Al0.3Fe3Si0.7 phase, and there are strong diffraction peaks near 45°, 65.5° and 83°. In contrast to the PDF card, the three strong peaks correspond to the (2 0 0), (4 0 0) and (4 2 2) crystal
Table 1 Magnetic properties of five groups of samples.
Fig. 1. XRD patterns of FeSiAl and coated MnZn ferrite composite powders. 925
The contents of ferrite(%)
Ms (emu/ g)
The permeability at 200 kHz
Pcm (W/kg) at 5 mT,1000 kHz
Porosity(%)
0 5 10 15 20
117.3 112.1 106.7 103.4 79.5
31.99 40.84 39.31 37.53 35.66
12.51 10.85 11.18 11.87 11.96
4.8 3.5 3.8 5.1 6.7
Current Applied Physics 19 (2019) 924–927
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Fig. 3. VSM spectra of FeSiAl and composite powders coated with MnZn ferrite.
Fig. 5. Trends of loss versus frequency for five groups of samples.
proper addition of ferrite fills the gap. When the coating amount is 5%, a complete coating layer is formed on the surface of the FeSiAl magnetic powder to increase the density, thereby reducing the hysteresis loss. The eddy current loss is given by the following formula [21]:
Pe =
Where Pe is the eddy current loss, C is the constant, B is the magnetic flux density, d is the powder particle size, f is the operating frequency, and ρ is the material resistivity. It can be seen from the publicity that the eddy current loss is proportional to the square of the powder particle size and inversely proportional to the resistivity. When the addition content of ferrite is low, the average particle size and resistivity of the sample do not change much, and the hysteresis loss plays a major role, and the overall loss decreases. As the ferrite continues to increase, the average particle size of the powder becomes irregular, so that the resistivity decreases, and the eddy current loss plays a major role, so the core loss tends to increase slowly. Fig. 6 shows the variation of the magnetic properties of the magnetic powder core at different annealing temperatures. It can be seen from the figure that as the annealing temperature increases, the magnetic permeability of the composite powder core first increases and then decreases, reaching a maximum value near 650 °C. The sample creates internal stresses and dislocations during the press forming process, both of which hinder the movement of the magnetic domain walls in the technical magnetization [22]. As the annealing temperature increases, the internal stress of the sample gradually releases and the density increases, which is beneficial to increase the magnetic permeability. However, when the temperature is higher than 650 °C, the permeability
Fig. 4. Trends of permeability versus frequency for five groups of samples.
gaps and improving the density and permeability of powder cores, the permeability of the composite powder core is greatly increased by the insulating coating of the MnZn ferrite. As the ferrite content continues to increase, the permeability of the composites decreases. This may be due to the excessive content of ferrite, which makes the particle distribution of the powder core as a whole irregular and uneven, and the specific surface area of particles and the interface between the magnetic particles increase, causing the agglomeration of small particle and increase number of the gaps. The magnetic permeability is given by the following formula [19]:
μ=
CB2d 2f 2 ρ
Ls le μo N 2Ae
Where μ is the magnetic permeability, Ls is the inductance of the sample core, le is the average flux density path for ring samples, μo is the permeability of free space, N is the total number of turns of the coil, Ae is the cross-sectional area of the powder core. The permeability strongly depends on the density, number of pores, non-magnetic phase and magnetic anisotropy [20]. Fig. 5 shows the dependence of the five sample loss on frequency at Bm = 5 mT. As can be seen from the figure, on the one hand, the loss of the five groups of samples increases with increasing frequency. On the other hand, as the ferrite content increases, the loss first decreases and then increases. Among them, when the addition content of ferrite is 5%, the core loss of the composite magnetic powder is at least 10.85 W/kg (Bm = 5 mT, f = 1000 kHz), which is 13.3% lower than that of the pure FeSiAl magnetic powder core under the same conditions. As the ferrite content continues to increase, the loss increases. This is because the
Fig. 6. Effect of annealing temperature on magnetic properties of magnetic powder core. 926
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References
is gradually lowered due to the destruction of the interface of the MnZn/FeSiAl composite at a high temperature. As the annealing temperature increases, the loss of the composite powder core decreases first and then increases, reaching a minimum near 650 °C. On the one hand, as the annealing temperature increases, the internal stress of the sample gradually releases, and the coercive force decreases, thereby reducing the hysteresis loss. On the other hand, as the temperature increases, the insulating coating of the sample becomes more compact and efficient, and the insulation performance is improved, thereby reducing the eddy current loss [23]. However, when the temperature exceeds 650 °C, the internal stress of the sample is almost completely released, the insulating layer is gradually decomposed at a high temperature, the insulating property is lowered, and the iron loss is increased.
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4. Conclusion In this paper, the flattening of FeSiAl soft magnetic powder is achieved by ball milling process, and MnZn ferrite is used as a coating agent to obtain MnZn/FeSiAl composite magnetic powder core and improve magnetic properties. Compared with the previous research results, the composite magnetic powder core prepared in this paper has higher magnetic permeability and lower power loss. This is because the flattened FeSiAl powder has strong shape anisotropy [24], which can improve the magnetic permeability of the material, improve the magnetic properties of the material, and reduce the effect of the skin effect, and suppress the eddy current loss at high frequencies. The results show that the addition of MnZn ferrite affects the magnetic properties such as saturation magnetization, permeability and power loss of FeSiAl soft magnetic. With the increase of MnZn ferrite addition content, the saturation magnetization of composites decreases gradually, and the permeability increases first and then decreases, and the loss decreases first and then increases. The FeSiAl sample without coating ferrite has the highest saturation magnetization of 117.3 emu/g. When the addition content of MnZn ferrite is 5%, the permeability reaches the maximum, which is 28.1% higher than that of the pure FeSiAl magnetic powder core under the same conditions. At the same time, the loss is the lowest, which is 13.3% lower than the pure FeSiAl powder core under the same conditions. The optimum stress relief annealing temperature for the composite sample is around 650 °C. Acknowledgments This work was supported by the National Natural Science Foundation of China (Nos. 51872004, 51802002), Education Department of Anhui Province (Nos. KJ2013B293, KJ2018A0039). Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.cap.2019.05.003.
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