- Email: [email protected]
Ti3SiC2 hybrid powders in X-band
Journal of Magnetism and Magnetic Materials 365 (2014) 126–131
Contents lists available at ScienceDirect
Journal of Magnetism and Magnetic Materials journal homepage: www.elsevier.com/locate/jmmm
Letter to the Editor
Electromagnetic and microwave absorption properties of the Nickel/Ti3SiC2 hybrid powders in X-band Yi Liu n, Fa Luo, Jinbu Su, Wancheng Zhou, Dongmei Zhu State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an 710072, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 25 September 2013 Received in revised form 17 March 2014 Available online 2 May 2014
The electromagnetic (EM) characteristics and microwave absorption properties of the Nickel/Ti3SiC2 hybrid powders are studied in 8.2–12.4 GHz.With the enhancement of Ti3SiC2 content, the dielectric loss of the hybrid powders increases while the magnetic loss decreases compared with the pure Ni powders. A favorable microwave absorption property can be obtained by changing the Ti3SiC2 content to tailor the EM parameters. The composite with 30 wt% Ni and 30 wt% Ti3SiC2 powders presents the optimum microwave absorption property. For the composite of 2.2 mm thickness, a reflection loss (RL) below 10 dB is obtained in the frequency range of 8.2–12 GHz with a minimum RL of 41.2 dB at the matching frequency 9.7 GHz. This study contributes to exploring the absorber with broad absorption bandwidth, low density and thin thickness. & 2014 Elsevier B.V. All rights reserved.
Keywords: Nickel/Ti3SiC2 hybrid powder EM parameter Microwave absorption property
1. Introduction In recent years, the serious EM wave interference, radiation and pollution problems have attracted considerable attention to exploit the new EM wave absorption materials. Generally, the microwave absorbers are fabricated by adding absorbents with dielectric or magnetic lossy capability to a matrix. Carbon black (CB) [1–3], Carbonyl iron particles (CIPs) and Carbon nanotubes (CNTs) [4–6] are the most widely studied absorbents, which are used in different ways to improve the absorbing property such as optimizing composition, changing shape and hybridizing. The advantage of hybridizing the absorbents with different characteristics is favorable to adjust the EM parameters to meet the matching condition through the synergistic effect of the components [7,8], so that the incident wave can enter and then be attenuated in the materials. Therefore, considerable attention has been paid to blending the dielectric and magnetic lossy absorbents to enhance the EM wave absorption ability. Ti3SiC2 is a novel ternary compound with both metallic and ceramic merits, such as excellent electrical conductivity (4.5 106 Ω 1 m 1), high melting point, low density (4.52 g/cm3) and high temperature oxidation resistance property [9–11]. The dielectric and microwave absorption properties of the Ti3SiC2 powders have been studied in our previous work [12]. The results show that the Ti3SiC2 powders present excellent microwave absorption
properties in X-band. As a promising magnetic absorbent, Ni has attracted considerable interest due to its large saturation magnetization and high Curie temperature than the ferrite material [13,14]. However, the high density (8.9 g/cm3) is contradictory with the current status of exploring absorber with broad absorption bandwidth, low density and thin thickness. The above situations inspire us to investigate the microwave absorption properties of the Ni/Ti3SiC2 hybrid powders. In this study, the samples with different contents of Ni and Ti3SiC2 powders are fabricated by the mixing process using epoxy resin as the matrix. The electromagnetic and microwave absorption properties of the Ni/Ti3SiC2 hybrid powders are investigated.
2. Experimental procedures 2.1. Raw materials The Ni particles (d50 ¼ 0.5 μm) used in this study were purchased from Titd Metal Materials Co. Ltd., Hunan Province, China. The Ti3SiC2 powders were synthesized by a vacuum pressureless sintering method using Ti/Si/TiC as the starting material, which has been reported in our previous work [12]. The average particle size of the Ti3SiC2 powder is about 5 μm. 2.2. Sample preparation
n
Corresponding author. Tel.: þ 86 13289327575. E-mail address: [email protected] (Y. Liu).
http://dx.doi.org/10.1016/j.jmmm.2014.04.056 0304-8853/& 2014 Elsevier B.V. All rights reserved.
Epoxy resin (E-44) was used as a matrix material and polyamide resin (low molecular weight 650) as the curing agent. First
Y. Liu et al. / Journal of Magnetism and Magnetic Materials 365 (2014) 126–131
30
(111)
The XRD patterns of the samples were obtained by a Cu Kα radiation (X-Pert Diffractometer, Philips, The Netherlands). The morphology of the sample was observed by scanning electron microscopy (Model JSM-6360, JEOL, Tokyo, Japan). The complex permittivity and permeability of the sample were measured using the rectangle waveguide method in the frequency range from 8.2 to 12.4 GHz by a vector network analyzer (Agilent Technologies
♦ —TiC
(200)
•
(200)
•
♦
40
(220)
♦
• •♦ •
•
2.3. Characterization
•—Ti3SiC2
• •
the same speed. Then the mixture was heated at 60 1C to remove the solvent.
Intensity(a.u.)
Intensity(a.u.)
•
(104)
of all, the sample with 60 wt% Ti3SiC2 powder was prepared to investigate the dielectric property of Ti3SiC2 in resin matrix. In order to investigate the microwave absorption properties of the hybrid powders, the samples with different contents of Ti3SiC2 and Ni were prepared by the mixing process. The total content of the fillers is fixed at 60 wt%, but the mass ratio of Ni particles to Ti3SiC2 is 1:0, 2:1, 1:1 and 1:2. The two kinds of powders were proportionally weighed and dispersed in acetone medium using an ultrasonic bath for 1 h at room temperature, followed by mechanical stirring with 300 rpm to improve the dispersion quality. Epoxy and polyamide resin were added to the above solution with the weight ratio of 4:1, during which the beater was still revolving at
127
•
•
•
50 2θ (Degree)
60
70
30
40
50 60 2θ (Degree)
70
80
Fig. 1. XRD patterns of the powders: (a) Ti3SiC2 and (b) Ni.
16 14
cps/eV
12
Atomic ratio Ti: 49.52% C: 50.48%
10 8 C
6
Ti
Ti
4 2 0 1
2
3
4
5
keV
Spectrum 2 22 20 18
cps/eV
16
Atomic ratio Ti: 48.73% Si: 16.72% C: 32.12%
14 12 10 8
C Ti
Si
Ti
6 4 2 0 1
2
3
4
5
6
7
8
9
keV
Spectrum 1 Fig. 2. SEM images of (a) Ti3SiC2 with EDS analysis and (b) Ni particles.
6
7
8
9
128
Y. Liu et al. / Journal of Magnetism and Magnetic Materials 365 (2014) 126–131
E8362B: 10 MHz–20 GHz). The reflection loss of the single layer sample was calculated using the measured electromagnetic parameters by the following equations [15,16]: ð1Þ RL ðdBÞ ¼ 20log ðZ in Z 0 Þ=ðZ in þ Z 0 Þ Z0 ¼
pffiffiffiffiffiffiffiffiffiffiffiffi μ0 =ε0
Z in ¼ Z 0
pffiffiffiffiffiffiffiffiffiffiffi 2π pffiffiffiffiffiffiffiffiffi μr εr f d μr =εr tan h j c
ð2Þ ð3Þ
where Zin and Z0 are the input impedance of absorber and free space, respectively. εr and μr are the relative complex permittivity and permeability of the absorber, f is the microwave frequency, d is the thickness, and c is the velocity of light.
3. Results and discussions 3.1. Phase analysis Fig. 1 shows the XRD patterns of the as-prepared Ti3SiC2 and commercial Ni powders. In Fig. 1a, it is evident that the peak of TiC is detected except for the main phase Ti3SiC2. The relative content of Ti3SiC2 in the sample is about 96.3% according to the experimental equation [17]. No other peaks of impurities are detected besides Ni in Fig. 1b; the peaks located at 2θ¼44.481, 51.841, and 76.471 are designated as (111), (200) and (220) planes of the facecentered cubic (fcc) Ni (JCPDS #65-2865), respectively. The sharp diffraction peaks in the patterns indicate that both the Ti3SiC2 and Ni powders are highly crystallized.
paraffin and epoxy resin are low permittivity materials, the density of epoxy resin (1.2 g/cm3) is higher than that of paraffin (0.8 g/cm3). So the volume fraction of Ti3SiC2 is higher in the epoxy resin matrix as the content is given, which results in a larger complex permittivity. It is also observed that the complex permeability stays independent with the frequency. The real and imaginary parts of the permeability are 1 and 0, indicating that Ti3SiC2 is a material with no magnetic loss. In order to distinguish the samples more easily, the composite with 60 wt% Ni is designated as Sample A. Sample B indicates the composite with 40 wt% Ni and 20 wt% Ti3SiC2. Sample C represents the composite with 30 wt% Ni and 30 wt% Ti3SiC2. Sample D denotes the composite with 20 wt% Ni and 40 wt% Ti3SiC2. The EM parameters of the samples as a function of frequency are shown in Fig. 4. The dielectric loss ( tan δ ¼ ε″=ε0 ) and magnetic loss ( tan δ ¼ μ″=μ0 ) reflect the dissipation ability of the absorbers for EM wave. The dielectric properties of the samples are presented in Fig. 4a–c. The dielectric loss of Sample A is around 0.05, suggesting the dielectric lossy mechanism makes little contribution to the dissipation of the EM wave. It is worth noting that both the complex permittivity and dielectric loss increase with the enhancement content of Ti3SiC2. As we know, the real part is mainly ascribed to the polarization effect (orientation and interfacial polarization) of the dipole under the electric filed. The above results suggest that Ti3SiC2 is an obvious dielectric lossy material. So it is reasonable that the increase of real part can be ascribed to the enhancement of polarization ability of the sample with higher Ti3SiC2 content. The imaginary part of the complex permittivity is closely related to the electric conductivity of the sample. Although the dc conductivity of Ni (14.3 106 Ω 1 m 1) 25
The microstructure of Ti3SiC2 with EDS analysis and Ni powders is shown in Fig. 2. It can be seen that Ti3SiC2 presents the obvious layer or column structure with an average particle size of 5 μm. Trace amount of TiC exists among the particles which is consistent with the XRD patterns. The EDS analysis confirms the above results. The particles of Ni appear to be spherical and the sizes are below 1 μm. For the EM wave absorbing materials consists of conductive fillers and insulated matrix, both the content and characteristics of the fillers have great influence on the dielectric and microwave absorption properties [18].
Complex permittivity ( ε', ε")
3.2. Microstructure
15
10
5
3.3. Electromagnetic properties
8
9
10
11
12
Frequency(GHz) 1.5
Complex permeability ( μ', μ'')
The electromagnetic properties of the samples can be expressed by the complex permittivity (ε ¼ε0 jεʺ) and permeability (μ ¼μ0 jμʺ), which reflect the storage capacity and lossy ability, thus play a key role in the microwave absorption properties of the materials. For the absorber with excellent absorption property, the EM parameters need to meet the matching condition, so the microwave can enter and subsequently be attenuated in the materials. For this purpose, the EM parameters of the composites are tailored by mixing Ti3SiC2 powders with the Ni particles. The frequency dependence of the complex permittivity and permeability for pure Ti3SiC2 powders is shown in Fig. 3. The epoxy resin is chosen as the matrix due to its low permittivity and lossy ability for EM wave. It is evident that the complex permittivity decreases with increasing frequency in X-band; the real part changes from 22 to 15 while the imaginary part varies from 10 to 5. The obvious frequency dispersion effect is crucial for broad absorption bandwidth and high absorptivity. It is noticed that the complex permittivity of Ti3SiC2 in the resin matrix is higher than that in the paraffin [12], which is ascribed to the effect between the conductive fillers and insulated matrix. Although both the
ε' ε"
20
μ' μ'' 1.0
0.5
0.0 8
9
10
11
12
Frequency(GHz) Fig. 3. The frequency dependence of the complex permittivity and permeability for pure Ti3SiC2 powders.
Y. Liu et al. / Journal of Magnetism and Magnetic Materials 365 (2014) 126–131
1.2
24
16
1.0
Real part ( μ')
Sample A Sample B Sample C Sample D
20
Real part ( ε')
129
0.8 Sample A Sample B Sample C Sample D
12 0.6 8 8
9
10
11
12
8
9
10
11
12
Frequency(GHz)
Frequency(GHz)
Sample A Sample B Sample C Sample D
4
2
Sample A Sample B Sample C Sample D
0.8
Imaginary part ( μ'')
Imaginary part ( ε")
6
0.6
0.4
0.2
0 0.0 8
9
10
11
12
8
9
Sample A Sample B Sample C Sample D
0.25
11
12
0.20 0.15 0.10
Sample A Sample B Sample C Sample D
0.8
Magnetic loss ( tanσM)
Dielectric loss ( tanσE)
0.30
10
Frequency(GHz)
Frequency(GHz)
0.6
0.4
0.2
0.05 0.00
0.0 8
9
10
11
12
8
9
10
11
12
Frequency(GHz)
Frequency(GHz)
Fig. 4. EM parameters of the samples as a function of frequency: (a) real part of permittivity, (b) imaginary part of permittivity, (c) dielectric loss, (d) real part of permeability, (e) imaginary part of permeability, and (f) magnetic loss.
is higher than that of Ti3SiC2 (4.5 106 Ω 1 m 1), the imaginary part is enhanced with increasing Ti3SiC2 content. Fig. 5 demonstrates the schematic of the conductive fillers dispersed in epoxy resin matrix. For pure Ni, the particles are isolated and the distance between the granular particles is long, which is hard to form the conductive network. As Ti3SiC2 is added, the column Ti3SiC2 acts as a bridge which contributes to improving the conductivity as well as the imaginary part of the sample by connecting with the Ni powders. Fig. 4d–f shows the frequency dependence of the complex permeability and magnetic loss for the samples. It is found that both the complex permeability and magnetic loss for Sample A are higher than that of the others. For the samples containing Ti3SiC2 powders, the complex permeability and magnetic loss decrease
gradually with the increase of Ti3SiC2 content. The magnetic properties of the samples depend on the Ni content due to the fact that Ti3SiC2 powders are almost non-magnetic material according to the above discussion. The theoretical permeability of the composites can be expressed by the following equation [19]: ln μ ¼ ∑λi ln μi where μ is the permeability of the composite, and λi and μi are the volume fraction and permeability of i phase, respectively. It is evident that the enhancement of non-magnetic Ti3SiC2 content and reduction of Ni result in the decrease of complex permeability and magnetic loss. The pronounced oscillation phenomenon is also observed for the samples containing Ni powders. Liu et al. [20] have reported that the reasons for the multi-resonance behavior of
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Y. Liu et al. / Journal of Magnetism and Magnetic Materials 365 (2014) 126–131
the isotropic urchinlike Ni are the nanocrystalline structure, particle size effect, surface effect, and spin wave excitations. However, there are not obvious resonances for the Ni@C nanoparticles [21], which may due to the absence of magnetic particles with spherical shape under surface anisotropy according to the Aharoni's theory mode. Actually, multi-resonance is still a subject of controversy. In this study, the samples containing spherical Ni powders with a particle size up to 1 μm also present the multi-resonance phenomenon with an obvious magnetic resonance at a frequency of 9.7 GHz. It can be ascribed to the Ni/Ti3SiC2/polymer interfacial features, which are expected to have a profound impact on the electrically controlled
Ni
Ti3SiC2 Fig. 5. The schematic of the conductive fillers dispersed in epoxy resin matrix: (L) pure Ni particles (R) Ni and Ti3SiC2 powders.
exchange bias and magnetocrystalline anisotropy property in magnetic particles, and then, contributed to the multi-resonance behavior. 3.4. Microwave absorption properties To further investigate the microwave absorption properties of the composites, the reflection losses (RL) are calculated according to the transmission-line theory and shown in Fig. 6. It is evident that all the RL peaks shift to lower frequency range with increasing sample thickness, which is in accord with the relationship between the matching frequency and thickness expressed by the following equation [22]: pffiffiffiffiffiffiffi 1 f m ¼ c=4dm 1= ε0 μ0 1 þ tan 2 δ=8 where fm and dm are the matching frequency and thickness, and c is the light velocity. It is clear that the matching frequency pffiffiffiffiffiffiffi decreases with increasing thickness at a given ε0 μ0 . For Sample A with 60 wt% Ni, the effective absorption bandwidth is obtained in the frequency range of 9.7–10.8 GHz with the thickness of 1.8– 2.0 mm. The minimum RL value is 22.46 dB at 9.75 GHz corresponding to a 2.0 mm matching thickness. When 20 wt% Ni is replaced by the same content Ti3SiC2 powders, a minimum RL value of 24.7 dB is observed at 9.9 GHz and the absorption bandwidth below 10 dB is from 9.7 GHz to 11.7 GHz. The absorption mechanism of Ni powders is mainly due to the eddy current loss and magnetic resonance loss, while the addition of
0
-5
Reflection loss (dB)
Reflection loss (dB)
0
-10 -15
1.8mm 2.0mm 2.2mm 2.4mm 2.6mm 2.8mm
-20 -25
8
9
Sample A
-10
-20
Sample C
-40
10
11
8
12
9
0
0
-5
-4
-10 -15 1.8mm 2.0mm 2.2mm 2.4mm 2.6mm 2.8mm
-25 -30
9
11
Frequency(GHz)
12
-12 -16
12
1.8mm 2.0mm 2.2mm 2.4mm 2.6mm 2.8mm
-20 Sample D
-24
Sample B
10
11
-8
-28 8
10
Frequency(GHz)
Reflection loss (dB)
Reflection loss (dB)
Frequency(GHz)
-20
1.8mm 2.0mm 2.2mm 2.4mm 2.6mm 2.8mm
-30
8
9
10
11
Frequency(GHz)
Fig. 6. Calculated reflection loss (RL) of the single layer samples in different thicknesses.
12
Y. Liu et al. / Journal of Magnetism and Magnetic Materials 365 (2014) 126–131
131
Table 1 Microwave absorption properties of the samples. Sample
Constituents
Optimum thickness(mm)
Minimum RL value(dB)
Matching frequency(GHz)
Bandwidth RL o 10 dB(GHz)
A B C D
60 wt% 40 wt% 30 wt% 20 wt%
2.0 2.0 2.2 2.0
22.4 24.7 41.2 26.1
9.7 9.9 9.7 9.8
8.7–10.3 8.9–11.7 8.2–12 9.5–10.6
Ni Niþ 20 wt% Ti3SiC2 Niþ 30 wt% Ti3SiC2 Niþ 40 wt% Ti3SiC2
Ti3SiC2 causes polarization and conductance loss for the composite. The broader effective absorption bandwidth of Sample B compared with Sample A is ascribed to the synergistic effect of the dielectric and magnetic losses. Increasing Ti3SiC2 content to 30 wt%, the minimum RL reaches to 41.2 dB at 9.7 GHz for the sample with 2.2 mm thickness, and the absorption bandwidth below 10 dB is almost in the whole frequency range. It is evident that Sample C presents the optimum microwave absorption property with high absorptivity and broad bandwidth. However, further elevating Ti3SiC2 content to 40 wt%, RL increases to 26.1 dB and the effective absorption bandwidth gets narrow. The microwave absorbing materials require the impedance of the absorber matching the free space impedance, so that the incident wave can enter and then be dissipated in the materials. For Sample D, the higher Ti3SiC2 content makes the material deviate from the matching condition, which results in a strong reflection of the EM wave and poor absorptivity. The microwave absorption properties of the hybrid Ni/Ti3SiC2 powders are summarized in Table 1. For all the samples with different Ti3SiC2 and Ni contents the optimum thickness is 2.0 mm and the matching frequency stays around 9.7 GHz. It is evident that Sample C presents the most favorable microwave absorption property, the minimum RL value is 41.2 dB and the effective absorption bandwidth is almost in the whole X-band. The results indicate that the microwave absorption property of the composite is optimized by mixing the Ni/Ti3SiC2 hybrid absorbents. 4. Conclusions In this study, the EM characteristics and microwave absorption property of the Nickel/Ti3SiC2 hybrid powders are investigated. The EM parameters of the hybrid powders can be tailored by changing the content of Ti3SiC2. The composite absorber containing 30 wt% Ni and 30 wt% Ti3SiC2 powders presents the optimum microwave absorption property. The absorber of 2.2 mm thickness has an effective absorption bandwidth in the frequency range of 8.2–12 GHz, and the minimum RL is 41.2 dB at the matching frequency 9.7 GHz. Acknowledgments This work was supported by National Natural Science Foundation of China, No. 51072165. References [1] X.X. Liu, Z.Y. Zhang, Y.P. Wu, Absorption properties of carbon black/silicon carbide microwave absorbers, Composites: Part B 42 (2011) 326–329.
[2] Y.W. Dai, M.Q. Sun, C.G. Liu, Z.Q. Li, Electromagnetic wave absorbing characteristics of carbon black cement-based composites, Cem. Concr. Compos. 32 (2010) 508–513. [3] G.Q. Wang, X.D. Chen, Y.P. Duan, S.H. Liu, Electromagnetic properties of carbon black and barium titanate composite materials, J. Alloys Compd. 454 (2008) 340–346. [4] Y.G. Xu, L.M. Yuan, J. Cai, D.Y. Zhang, Smart absorbing property of composites with MWCNTs and carbonyl iron as the filler, J. Magn. Magn. Mater. 343 (2013) 239–244. [5] G.X. Tong, W.H. Wu, Q. Hua, Y.Q. Miao, J.G. Guan, H.S. Qian, Enhanced electromagnetic characteristics of carbon nanotubes/carbonyl iron powders complex absorbers in 2–18 GHz ranges, J. Alloys Compd. 509 (2011) 451–456. [6] Y.C. Qing, W.C. Zhou, F. Luo, D.M. Zhu, Epoxy-silicone filled with multi-walled carbon nanotubes and carbonyl iron particles as a microwave absorber, Carbon 48 (2010) 4074–4080. [7] B. Belaabed, J.L. Wojkiewicz, S. Lamouri, N.E. Kamchi, T. Lasri, Synthesis and characterization of hybrid conducting composites based on polyaniline/magnetite fillers with improved microwave absorption properties, J. Alloys Compd. 527 (2012) 137–144. [8] C. Zhou, Q.Q. Fang, F.L. Yan, W.N. Wanget al., Enhanced microwave absorption in ZnO/carbonyl iron nano-composites by coating dielectric material, J. Magn. Magn. Mater. 324 (2012) 1720–1725. [9] Y. Zou, Z.M. Sun, S. Tada, H. Hashimoto, Effect of Al addition on lowtemperature synthesis of Ti3SiC2 powder, J. Alloys Compd. 461 (2008) 579–584. [10] H. Li, D. Chen, J. Zhou, J.H. Zhao, L.H. He, Synthesis of Ti3SiC2 by pressureless sintering of the elemental powders in vacuum, Mater. Lett. 58 (2004) 1741–1744. [11] Y. Zou, Z.M. Sun, S.J. Tada, H. Hashimoto, Effect of liquid reaction on the synthesis of Ti3SiC2 powder, Ceram. Int. 34 (2008) 119–123. [12] Y. Liu, F. Luo, W.C. Zhou, D.M. Zhu, Dielectric and microwave absorption properties of Ti3SiC2 powders, J. Alloys Compd. 576 (2013) 43–47. [13] H.T. Zhao, X.J. Han, L.F. Zhang, G.Y. Wang, C. Wang, X.A. Li, P. Xu, Controlled synthesis and morphology-dependent electromagnetic properties of nickel nanostructures by γ-ray irradiation technique, Radiat. Phys. Chem. 80 (2011) 390–393. [14] G.Q. Wang, L.X. Ma, Y.F. Chang, C. Liu, Microstructure and electromagnetic characteristics of BaTiO3/Ni hybrid particles prepared by electroless plating, Appl. Surf. Sci. 258 (2012) 3962–3966. [15] F. Ye, L.T. Zhang, X.W. Yin, Y.S. Liu, L.F. Cheng, The improvement of waveabsorbing ability of silicon carbide fibers by depositing boron nitride coating, Appl. Surf. Sci. 270 (2013) 611–616. [16] K. Cui, Y.L. Cheng, J.M. Dai, J.P. Liu, Synthesis, characterization and microwave absorption properties of La0.6Sr0.4MnO3/polyaniline composite, Mater. Chem. Phys. 138 (2013) 810–816. [17] Z.F. Zhang, Z.M. Sun, H. Hashimoto, T. Abe, Effects of sintering temperature and Si content on the purity of Ti3SiC2 synthesized from Ti/Si/TiC powders, J. Alloys Compd. 352 (2003) 283–289. [18] L. Zhou, W.C. Zhou, M.L. Chen, F. Luo, D.M. Zhu, Dielectric and microwave absorbing properties of low power plasma sprayed Al2O3/Nb composite coatings, Mater. Sci. Eng. B 176 (2011) 1456–1462. [19] Z.Y. Guan, Inorganic Materials Physical Properties, Tsinghua University Publication, China, 2008. [20] T. Liu, P.H. Zhou, J.L. Xie, L.J. Deng, Electromagnetic and absorption properties of urchinlike Ni composites at microwave frequencies, J. Appl. Phys. 093905 (2012) 1–5. [21] H. Wang, H.H. Guo, Y.Y. Dai, D.Y. Geng, Z. Han, D. Li, T. Yang, Optimal electromagnetic-wave absorption by enhanced dipole polarization in Ni/C nanocapsules, Appl. Phys. Lett. 101 (2012) 083116-1–083116-4. [22] J. Sun, H.L. Xu, Y. Shen, H. Bi, W.F. Liang, R.B. Yang, Enhanced microwave absorption properties of the milled flake-shaped FeSiAl/graphite composites, J. Alloys Compd. 548 (2013) 18–22.
Contents lists available at ScienceDirect
Journal of Magnetism and Magnetic Materials journal homepage: www.elsevier.com/locate/jmmm
Letter to the Editor
Electromagnetic and microwave absorption properties of the Nickel/Ti3SiC2 hybrid powders in X-band Yi Liu n, Fa Luo, Jinbu Su, Wancheng Zhou, Dongmei Zhu State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an 710072, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 25 September 2013 Received in revised form 17 March 2014 Available online 2 May 2014
The electromagnetic (EM) characteristics and microwave absorption properties of the Nickel/Ti3SiC2 hybrid powders are studied in 8.2–12.4 GHz.With the enhancement of Ti3SiC2 content, the dielectric loss of the hybrid powders increases while the magnetic loss decreases compared with the pure Ni powders. A favorable microwave absorption property can be obtained by changing the Ti3SiC2 content to tailor the EM parameters. The composite with 30 wt% Ni and 30 wt% Ti3SiC2 powders presents the optimum microwave absorption property. For the composite of 2.2 mm thickness, a reflection loss (RL) below 10 dB is obtained in the frequency range of 8.2–12 GHz with a minimum RL of 41.2 dB at the matching frequency 9.7 GHz. This study contributes to exploring the absorber with broad absorption bandwidth, low density and thin thickness. & 2014 Elsevier B.V. All rights reserved.
Keywords: Nickel/Ti3SiC2 hybrid powder EM parameter Microwave absorption property
1. Introduction In recent years, the serious EM wave interference, radiation and pollution problems have attracted considerable attention to exploit the new EM wave absorption materials. Generally, the microwave absorbers are fabricated by adding absorbents with dielectric or magnetic lossy capability to a matrix. Carbon black (CB) [1–3], Carbonyl iron particles (CIPs) and Carbon nanotubes (CNTs) [4–6] are the most widely studied absorbents, which are used in different ways to improve the absorbing property such as optimizing composition, changing shape and hybridizing. The advantage of hybridizing the absorbents with different characteristics is favorable to adjust the EM parameters to meet the matching condition through the synergistic effect of the components [7,8], so that the incident wave can enter and then be attenuated in the materials. Therefore, considerable attention has been paid to blending the dielectric and magnetic lossy absorbents to enhance the EM wave absorption ability. Ti3SiC2 is a novel ternary compound with both metallic and ceramic merits, such as excellent electrical conductivity (4.5 106 Ω 1 m 1), high melting point, low density (4.52 g/cm3) and high temperature oxidation resistance property [9–11]. The dielectric and microwave absorption properties of the Ti3SiC2 powders have been studied in our previous work [12]. The results show that the Ti3SiC2 powders present excellent microwave absorption
properties in X-band. As a promising magnetic absorbent, Ni has attracted considerable interest due to its large saturation magnetization and high Curie temperature than the ferrite material [13,14]. However, the high density (8.9 g/cm3) is contradictory with the current status of exploring absorber with broad absorption bandwidth, low density and thin thickness. The above situations inspire us to investigate the microwave absorption properties of the Ni/Ti3SiC2 hybrid powders. In this study, the samples with different contents of Ni and Ti3SiC2 powders are fabricated by the mixing process using epoxy resin as the matrix. The electromagnetic and microwave absorption properties of the Ni/Ti3SiC2 hybrid powders are investigated.
2. Experimental procedures 2.1. Raw materials The Ni particles (d50 ¼ 0.5 μm) used in this study were purchased from Titd Metal Materials Co. Ltd., Hunan Province, China. The Ti3SiC2 powders were synthesized by a vacuum pressureless sintering method using Ti/Si/TiC as the starting material, which has been reported in our previous work [12]. The average particle size of the Ti3SiC2 powder is about 5 μm. 2.2. Sample preparation
n
Corresponding author. Tel.: þ 86 13289327575. E-mail address: [email protected] (Y. Liu).
http://dx.doi.org/10.1016/j.jmmm.2014.04.056 0304-8853/& 2014 Elsevier B.V. All rights reserved.
Epoxy resin (E-44) was used as a matrix material and polyamide resin (low molecular weight 650) as the curing agent. First
Y. Liu et al. / Journal of Magnetism and Magnetic Materials 365 (2014) 126–131
30
(111)
The XRD patterns of the samples were obtained by a Cu Kα radiation (X-Pert Diffractometer, Philips, The Netherlands). The morphology of the sample was observed by scanning electron microscopy (Model JSM-6360, JEOL, Tokyo, Japan). The complex permittivity and permeability of the sample were measured using the rectangle waveguide method in the frequency range from 8.2 to 12.4 GHz by a vector network analyzer (Agilent Technologies
♦ —TiC
(200)
•
(200)
•
♦
40
(220)
♦
• •♦ •
•
2.3. Characterization
•—Ti3SiC2
• •
the same speed. Then the mixture was heated at 60 1C to remove the solvent.
Intensity(a.u.)
Intensity(a.u.)
•
(104)
of all, the sample with 60 wt% Ti3SiC2 powder was prepared to investigate the dielectric property of Ti3SiC2 in resin matrix. In order to investigate the microwave absorption properties of the hybrid powders, the samples with different contents of Ti3SiC2 and Ni were prepared by the mixing process. The total content of the fillers is fixed at 60 wt%, but the mass ratio of Ni particles to Ti3SiC2 is 1:0, 2:1, 1:1 and 1:2. The two kinds of powders were proportionally weighed and dispersed in acetone medium using an ultrasonic bath for 1 h at room temperature, followed by mechanical stirring with 300 rpm to improve the dispersion quality. Epoxy and polyamide resin were added to the above solution with the weight ratio of 4:1, during which the beater was still revolving at
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Fig. 1. XRD patterns of the powders: (a) Ti3SiC2 and (b) Ni.
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Spectrum 1 Fig. 2. SEM images of (a) Ti3SiC2 with EDS analysis and (b) Ni particles.
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E8362B: 10 MHz–20 GHz). The reflection loss of the single layer sample was calculated using the measured electromagnetic parameters by the following equations [15,16]: ð1Þ RL ðdBÞ ¼ 20log ðZ in Z 0 Þ=ðZ in þ Z 0 Þ Z0 ¼
pffiffiffiffiffiffiffiffiffiffiffiffi μ0 =ε0
Z in ¼ Z 0
pffiffiffiffiffiffiffiffiffiffiffi 2π pffiffiffiffiffiffiffiffiffi μr εr f d μr =εr tan h j c
ð2Þ ð3Þ
where Zin and Z0 are the input impedance of absorber and free space, respectively. εr and μr are the relative complex permittivity and permeability of the absorber, f is the microwave frequency, d is the thickness, and c is the velocity of light.
3. Results and discussions 3.1. Phase analysis Fig. 1 shows the XRD patterns of the as-prepared Ti3SiC2 and commercial Ni powders. In Fig. 1a, it is evident that the peak of TiC is detected except for the main phase Ti3SiC2. The relative content of Ti3SiC2 in the sample is about 96.3% according to the experimental equation [17]. No other peaks of impurities are detected besides Ni in Fig. 1b; the peaks located at 2θ¼44.481, 51.841, and 76.471 are designated as (111), (200) and (220) planes of the facecentered cubic (fcc) Ni (JCPDS #65-2865), respectively. The sharp diffraction peaks in the patterns indicate that both the Ti3SiC2 and Ni powders are highly crystallized.
paraffin and epoxy resin are low permittivity materials, the density of epoxy resin (1.2 g/cm3) is higher than that of paraffin (0.8 g/cm3). So the volume fraction of Ti3SiC2 is higher in the epoxy resin matrix as the content is given, which results in a larger complex permittivity. It is also observed that the complex permeability stays independent with the frequency. The real and imaginary parts of the permeability are 1 and 0, indicating that Ti3SiC2 is a material with no magnetic loss. In order to distinguish the samples more easily, the composite with 60 wt% Ni is designated as Sample A. Sample B indicates the composite with 40 wt% Ni and 20 wt% Ti3SiC2. Sample C represents the composite with 30 wt% Ni and 30 wt% Ti3SiC2. Sample D denotes the composite with 20 wt% Ni and 40 wt% Ti3SiC2. The EM parameters of the samples as a function of frequency are shown in Fig. 4. The dielectric loss ( tan δ ¼ ε″=ε0 ) and magnetic loss ( tan δ ¼ μ″=μ0 ) reflect the dissipation ability of the absorbers for EM wave. The dielectric properties of the samples are presented in Fig. 4a–c. The dielectric loss of Sample A is around 0.05, suggesting the dielectric lossy mechanism makes little contribution to the dissipation of the EM wave. It is worth noting that both the complex permittivity and dielectric loss increase with the enhancement content of Ti3SiC2. As we know, the real part is mainly ascribed to the polarization effect (orientation and interfacial polarization) of the dipole under the electric filed. The above results suggest that Ti3SiC2 is an obvious dielectric lossy material. So it is reasonable that the increase of real part can be ascribed to the enhancement of polarization ability of the sample with higher Ti3SiC2 content. The imaginary part of the complex permittivity is closely related to the electric conductivity of the sample. Although the dc conductivity of Ni (14.3 106 Ω 1 m 1) 25
The microstructure of Ti3SiC2 with EDS analysis and Ni powders is shown in Fig. 2. It can be seen that Ti3SiC2 presents the obvious layer or column structure with an average particle size of 5 μm. Trace amount of TiC exists among the particles which is consistent with the XRD patterns. The EDS analysis confirms the above results. The particles of Ni appear to be spherical and the sizes are below 1 μm. For the EM wave absorbing materials consists of conductive fillers and insulated matrix, both the content and characteristics of the fillers have great influence on the dielectric and microwave absorption properties [18].
Complex permittivity ( ε', ε")
3.2. Microstructure
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The electromagnetic properties of the samples can be expressed by the complex permittivity (ε ¼ε0 jεʺ) and permeability (μ ¼μ0 jμʺ), which reflect the storage capacity and lossy ability, thus play a key role in the microwave absorption properties of the materials. For the absorber with excellent absorption property, the EM parameters need to meet the matching condition, so the microwave can enter and subsequently be attenuated in the materials. For this purpose, the EM parameters of the composites are tailored by mixing Ti3SiC2 powders with the Ni particles. The frequency dependence of the complex permittivity and permeability for pure Ti3SiC2 powders is shown in Fig. 3. The epoxy resin is chosen as the matrix due to its low permittivity and lossy ability for EM wave. It is evident that the complex permittivity decreases with increasing frequency in X-band; the real part changes from 22 to 15 while the imaginary part varies from 10 to 5. The obvious frequency dispersion effect is crucial for broad absorption bandwidth and high absorptivity. It is noticed that the complex permittivity of Ti3SiC2 in the resin matrix is higher than that in the paraffin [12], which is ascribed to the effect between the conductive fillers and insulated matrix. Although both the
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Frequency(GHz) Fig. 3. The frequency dependence of the complex permittivity and permeability for pure Ti3SiC2 powders.
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Fig. 4. EM parameters of the samples as a function of frequency: (a) real part of permittivity, (b) imaginary part of permittivity, (c) dielectric loss, (d) real part of permeability, (e) imaginary part of permeability, and (f) magnetic loss.
is higher than that of Ti3SiC2 (4.5 106 Ω 1 m 1), the imaginary part is enhanced with increasing Ti3SiC2 content. Fig. 5 demonstrates the schematic of the conductive fillers dispersed in epoxy resin matrix. For pure Ni, the particles are isolated and the distance between the granular particles is long, which is hard to form the conductive network. As Ti3SiC2 is added, the column Ti3SiC2 acts as a bridge which contributes to improving the conductivity as well as the imaginary part of the sample by connecting with the Ni powders. Fig. 4d–f shows the frequency dependence of the complex permeability and magnetic loss for the samples. It is found that both the complex permeability and magnetic loss for Sample A are higher than that of the others. For the samples containing Ti3SiC2 powders, the complex permeability and magnetic loss decrease
gradually with the increase of Ti3SiC2 content. The magnetic properties of the samples depend on the Ni content due to the fact that Ti3SiC2 powders are almost non-magnetic material according to the above discussion. The theoretical permeability of the composites can be expressed by the following equation [19]: ln μ ¼ ∑λi ln μi where μ is the permeability of the composite, and λi and μi are the volume fraction and permeability of i phase, respectively. It is evident that the enhancement of non-magnetic Ti3SiC2 content and reduction of Ni result in the decrease of complex permeability and magnetic loss. The pronounced oscillation phenomenon is also observed for the samples containing Ni powders. Liu et al. [20] have reported that the reasons for the multi-resonance behavior of
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the isotropic urchinlike Ni are the nanocrystalline structure, particle size effect, surface effect, and spin wave excitations. However, there are not obvious resonances for the Ni@C nanoparticles [21], which may due to the absence of magnetic particles with spherical shape under surface anisotropy according to the Aharoni's theory mode. Actually, multi-resonance is still a subject of controversy. In this study, the samples containing spherical Ni powders with a particle size up to 1 μm also present the multi-resonance phenomenon with an obvious magnetic resonance at a frequency of 9.7 GHz. It can be ascribed to the Ni/Ti3SiC2/polymer interfacial features, which are expected to have a profound impact on the electrically controlled
Ni
Ti3SiC2 Fig. 5. The schematic of the conductive fillers dispersed in epoxy resin matrix: (L) pure Ni particles (R) Ni and Ti3SiC2 powders.
exchange bias and magnetocrystalline anisotropy property in magnetic particles, and then, contributed to the multi-resonance behavior. 3.4. Microwave absorption properties To further investigate the microwave absorption properties of the composites, the reflection losses (RL) are calculated according to the transmission-line theory and shown in Fig. 6. It is evident that all the RL peaks shift to lower frequency range with increasing sample thickness, which is in accord with the relationship between the matching frequency and thickness expressed by the following equation [22]: pffiffiffiffiffiffiffi 1 f m ¼ c=4dm 1= ε0 μ0 1 þ tan 2 δ=8 where fm and dm are the matching frequency and thickness, and c is the light velocity. It is clear that the matching frequency pffiffiffiffiffiffiffi decreases with increasing thickness at a given ε0 μ0 . For Sample A with 60 wt% Ni, the effective absorption bandwidth is obtained in the frequency range of 9.7–10.8 GHz with the thickness of 1.8– 2.0 mm. The minimum RL value is 22.46 dB at 9.75 GHz corresponding to a 2.0 mm matching thickness. When 20 wt% Ni is replaced by the same content Ti3SiC2 powders, a minimum RL value of 24.7 dB is observed at 9.9 GHz and the absorption bandwidth below 10 dB is from 9.7 GHz to 11.7 GHz. The absorption mechanism of Ni powders is mainly due to the eddy current loss and magnetic resonance loss, while the addition of
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Fig. 6. Calculated reflection loss (RL) of the single layer samples in different thicknesses.
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Table 1 Microwave absorption properties of the samples. Sample
Constituents
Optimum thickness(mm)
Minimum RL value(dB)
Matching frequency(GHz)
Bandwidth RL o 10 dB(GHz)
A B C D
60 wt% 40 wt% 30 wt% 20 wt%
2.0 2.0 2.2 2.0
22.4 24.7 41.2 26.1
9.7 9.9 9.7 9.8
8.7–10.3 8.9–11.7 8.2–12 9.5–10.6
Ni Niþ 20 wt% Ti3SiC2 Niþ 30 wt% Ti3SiC2 Niþ 40 wt% Ti3SiC2
Ti3SiC2 causes polarization and conductance loss for the composite. The broader effective absorption bandwidth of Sample B compared with Sample A is ascribed to the synergistic effect of the dielectric and magnetic losses. Increasing Ti3SiC2 content to 30 wt%, the minimum RL reaches to 41.2 dB at 9.7 GHz for the sample with 2.2 mm thickness, and the absorption bandwidth below 10 dB is almost in the whole frequency range. It is evident that Sample C presents the optimum microwave absorption property with high absorptivity and broad bandwidth. However, further elevating Ti3SiC2 content to 40 wt%, RL increases to 26.1 dB and the effective absorption bandwidth gets narrow. The microwave absorbing materials require the impedance of the absorber matching the free space impedance, so that the incident wave can enter and then be dissipated in the materials. For Sample D, the higher Ti3SiC2 content makes the material deviate from the matching condition, which results in a strong reflection of the EM wave and poor absorptivity. The microwave absorption properties of the hybrid Ni/Ti3SiC2 powders are summarized in Table 1. For all the samples with different Ti3SiC2 and Ni contents the optimum thickness is 2.0 mm and the matching frequency stays around 9.7 GHz. It is evident that Sample C presents the most favorable microwave absorption property, the minimum RL value is 41.2 dB and the effective absorption bandwidth is almost in the whole X-band. The results indicate that the microwave absorption property of the composite is optimized by mixing the Ni/Ti3SiC2 hybrid absorbents. 4. Conclusions In this study, the EM characteristics and microwave absorption property of the Nickel/Ti3SiC2 hybrid powders are investigated. The EM parameters of the hybrid powders can be tailored by changing the content of Ti3SiC2. The composite absorber containing 30 wt% Ni and 30 wt% Ti3SiC2 powders presents the optimum microwave absorption property. The absorber of 2.2 mm thickness has an effective absorption bandwidth in the frequency range of 8.2–12 GHz, and the minimum RL is 41.2 dB at the matching frequency 9.7 GHz. Acknowledgments This work was supported by National Natural Science Foundation of China, No. 51072165. References [1] X.X. Liu, Z.Y. Zhang, Y.P. Wu, Absorption properties of carbon black/silicon carbide microwave absorbers, Composites: Part B 42 (2011) 326–329.
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