Enhanced microwave absorption properties of epoxy composites reinforced with Fe50Ni50-functionalized graphene

Journal of Alloys and Compounds 653 (2015) 14e21

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Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom

Enhanced microwave absorption properties of epoxy composites reinforced with Fe50Ni50-functionalized graphene Junpeng Wang, Jun Wang*, Renxin Xu, Yu Sun, Bin Zhang, Wei Chen, Tao Wang, Shuang Yang School of Material Science and Engineering, Wuhan University of Technology, Wuhan 430070, China

a r t i c l e i n f o

a b s t r a c t

Article history: Received 7 July 2015 Received in revised form 16 August 2015 Accepted 31 August 2015 Available online 4 September 2015

Surface modified Fe50Ni50 nanoparticles (SMF)-Reduced graphene oxide (RGO) epoxy composites with enhanced microwave absorption properties were successfully prepared using a wet chemical method. The morphology, structure and microwave electromagnetic properties of the as-prepared composites were characterized by XRD, SEM, TEM and VSM. The SMF-RGO epoxy composites exhibit enhanced microwave absorption properties, which are attributed to the better impedance matching and enhanced microwave attenuation. For the SMF-RGO (3) composite, the minimum RL reaches
23.9 dB at 10.8 GHz with layer thickness of 3.0 mm, and the bandwidth of RL less than
10 dB can reach up to 4.3 GHz (from 8.8 to 13.1 GHz). It is believed that such composites are attractive candidates for new types of lightweight high performance microwave absorber. © 2015 Published by Elsevier B.V.

Keywords: Microwave absorption Fe50Ni50- RGO composite Polymer composite

1. Introduction Due to the increased applications of gigahertz mobile phone, LAN, radar systems etc., electromagnetic pollution has become a serious threat to both human health and ecological environment [1e3], the research for high performance microwave absorbing material is becoming an important issue. Polymer composites composed of inorganic fillers and epoxy matrix have strong microwave absorption performance over a broad frequency range that they have attracted great attentions [4,5]. Graphene, a monolayer of sp2-hybridized carbon atoms arranged in a two-dimensional lattice, possesses unique electrical [6], mechanical [7], optical and thermal properties [8,9]. In addition, due to its bi-dimensional shape (large surface area with small thickness), graphene shows promise as an ideal reinforcing agent for polymer composite [10,11]. Recently, research showed that inorganic nanoparticles could be attached on graphene to form hybrid materials. Jin and co-workers assembled Pd nanoparticles on graphene for enhanced electrooxidation of formic acid and demonstrated the great potential of graphene as a support to enhance nanoparticles catalysis and improved stability for chemical oxidation reactions [12]. Gil modified graphene surface with

* Corresponding author. E-mail addresses: [email protected], [email protected] (J. Wang). http://dx.doi.org/10.1016/j.jallcom.2015.08.278 0925-8388/© 2015 Published by Elsevier B.V.

gold nanoparticles and showed potential applications of the nanoparticles in surface enhanced raman scattering [13]. Kim and co-workers reported on a facile strategy for the direct and uniform deposition of a graphene/Co3O4 thin film onto stainless steel substrate through cathodic deposition and the film was employed as an anode material for lithium ion batteries [14]. Guo assembled FePt nanoparticles on graphene by a solution-phase self-assembly method and demonstrates that the graphene was indeed a promising support to improve nanoparticle activity and durability for practical catalytic applications [15]. A good microwave absorber is required to meet the demands of impedance matching and microwave attenuation [16e18]. When the microwave is incident onto the absorber, the reflection of the microwave should be minimal. Besides, the absorber should attenuate electromagnetic energy by converting it into heat or other forms of energy [19,20]. However, for traditional magnetic fillers used in an absorber, the electric permittivity values usually exceed the corresponding magnetic permeability values, which damage the impedance matching. Hence, to reduce the electric permittivity, the magnetic fillers are surface modified by H2O2. Fe-based alloys are kinds of magnetic materials and they have been widely used as microwave absorbers [21e23]. Ferromagnetic alloys possess high saturation magnetization and good electromagnetic wave absorption performance due to their higher Snoek's limit: their permeability could remain high at high frequencies

J. Wang et al. / Journal of Alloys and Compounds 653 (2015) 14e21

2. Experimental section 2.1. Surface modification of Fe50Ni50 nanoparticles Commercially available Fe50Ni50 nanoparticles (99.9% purity, xuzhou Jiechuang New Material Technology Co., Ltd) were used as starting materials. The surface-modified process was performed by sonication of Fe50Ni50 nanoparticles in the mixture of H2O2 and ethanol, allowing forming an oxide layer on the outer surface of the nanoparticles. Typically, 1 g nanoparticles was dispersed in the mixture solution of 20 ml H2O2 and 20 ml ethanol and sonicated for 3.0 h in an ice bath. Then the SMF were separated by a small magnet and dried in an oven. 2.2. Assembly of SMF on graphene Graphene oxide (GO) was prepared by pressurized oxidation method because the as-obtained GO sheets can reserve large lateral dimension [26]. HI-AcOH was selected as the reduction agent system for the high electrical conductivity [27]. The resulting RGO was dispersed in N,N-dimethylformamide (DMF). The SMF were assembled on RGO surface as follows. In a typical procedure, 0.4 g nanoparticle dispersed in 100 mL of hexane was added into 200 mL of DMF solution of RGO (1 mg/mL), and the mixture was sonicated for 1.0 h. Then the hexane was evaporated off by heating the mixture at 40  C in a rotary evaporator. The remaining solvent in the mixture is DMF as the boiling point of hexane is much lower. 2.3. Preparation of epoxy composites reinforced with SMFfunctionalized graphene The DMF in the mixture has two effects. On one hand, it acts as the solvent for assembly of nanoparticles on RGO sheets. On the other hand, as DMF shows the best compatibility with epoxy resin [28], it can be the suitable media to uniform distribute epoxy resin in the mixture via solution processing. According to the mass ratios of SMF: RGO: epoxy of 2:1:100, 5:1:100, 10:1:100 and 1:0:10, the composites were denoted as SMF-RGO (1), SMF-RGO (2), SMF-RGO (3) and SMF, respectively. Typically (SMF-RGO (1)), 14.8 g epoxy resin (EPIKOTE 862, Shell Inc) was added to the above mentioned mixture and magnetically stirred for 2.0 h. Then the solvent was evaporated off by heating the mixture at 80  C. 5.2 g amine curing agent (prepared by our laboratory) was added to the cool down slurry and magnetically stirred for another 30 min. Finally, the mixture was poured into the mold and cured at room temperature for 6.0 h. The composites were cut into samples by a high resolution engraving machine (SE-3230, Woodpecker Inc). For comparison purposes, SMF epoxy composite was prepared by sonicating SMF/ epoxy mixture in DMF solution for 1.0 h and then evaporating the solvent and finally adding amine curing agents. 2.4. Material characterization The morphology and microstructure of samples were characterized using fielding emission scanning electron microscope (FESEM, JEOL-6700F) equipped with an energy dispersion X-ray

spectrometer (EDS, Oxford INCA) and transmission electron microscope (TEM, Hitachi H9500). The structural characterization of Fe50Ni50, SMF and SMF-RGO was conducted by X-ray diffraction (XRD, Bruker D8 Advance diffractometer using a Cu Ka source, l ¼ 0.154056 nm). Magnetic properties of the samples were characterized using a vibrating sample magnetometer (VSM, Riken Denshi, BHV-525) at room temperature. Electromagnetic measurements were performed by a vector network analyzer (Agilent N5247A) via the reflection/transmission method in the frequency range of 0.1e18 GHz. The toroidal-shaped samples were fabricated with inner diameter of 3.04 mm, outer diameter of 7 mm and thickness of about 2 mm. The real and imaginary parts of the complex permittivity and complex permeability were calculated based on Nicolson-Ross-Weir (NRW) method. To reduce errors, all values were obtained by averaging the data measured for five different samples. 3. Results and discussion The XRD patterns of the Fe50Ni50 nanoparticles and SMF-RGO composites with different combination ratios are shown in Fig. 1. The diffraction peaks of Fe50Ni50 (before and after surface oxidation modification) are all perfectly indexed to the face-centered cubic phase of FeNi alloy (JCPDS No.47-1405) and three peaks at 2q ¼ 44.2 , 51.5 , and 75.8 are obtained for the reflection planes (111), (200), and (220), respectively. There are no obvious oxide peaks after surface modification, indicating that there exist only small amounts of oxide [29]. In addition, it is observed that the intensity of diffraction peaks of the composites is weakened compared with the pure SMF nanoparticle sample, which is due to the covering of SMF by RGO sheets. Furthermore, compared with Fig. 1(d and e), Fig. 1(aec) shows a weak and broad peak at around 2q ¼ 20 e30 , which is a typical pattern of amorphous carbon structures. The ordered stacking of part of the RGO was destroyed with increasing SMF contents. Fig. 2 shows the magnetic hysteresis loops (MeH loops) curve of Fe50Ni50 and SMF nanoparticles measured at room temperature. The saturation magnetization Ms and coercivity Hc of the Fe50Ni50 are 148 emu/g and 10.2 Oe. After surface oxidation modification, the Ms and Hc of SMF are 145 emu/g and 10.1 Oe, respectively. The Ms is almost unchanged after surface

SMF-RGO (1) SMF-RGO (2) SMF-RGO (3) Fe50Ni50

(e)

SMF

Intensity (a.u.)

[24,25]. In this paper, we prepared a hybrid surface modified Fe50Ni50 (SMF)-functionalized RGO (Reduced graphene oxide) epoxy composite with SMF nanoparticles assembled on both sides of graphene. The crystalline structure, morphology and microwave electromagnetic properties of the as-prepared composites were investigated. The mechanism of the enhanced microwave absorption performance for the SMF-RGO epoxy composites will also be explained.

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(d) (c) (b) (a) 10

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2 Theta (degree) Fig. 1. XRD patterns of Fe50Ni50, SMF and SMF-RGO composite.

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Fig. 2. Magnetization hysteresis loop of Fe50Ni50 and SMF powders.

modification, which also indicates that there exist only small amounts of oxide [29]. The morphologies of SMF have been studied with TEM (Fig. 3(a)), the mean diameter is around 70 nm. The SMF-RGO dispersed in DMF solution can be rapidly separated by an external magnetic field (Fig. 3(b)), indicating that the SMF particle was successfully assembled on RGO surface. With different SMF combination ratios, the morphologies of SMF-RGO hybrids have been studied with TEM (Fig. 3(c,e and g)) and SEM (Fig. 3(d,f and h)). It is observed that when the mass ratio of SMF to RGO is low, the RGO sheet is not totally filled (Fig. 3(ced)), indicating that Fe50Ni50 on RGO sheets segregated each other and could not form conductive networks. This is also demonstrated in EDS patterns (Supporting Information). Fig. S1 displays that the asreceived hybrid (SMF-RGO (1)) is essentially comprised of Fe, Ni, C and O. The weight ratio of C to Fe, Ni and O is 4.2: 3: 2.8: 1. The oxygen element is detected, which may due to the oxide layer of Fe50Ni50 and the remnant oxide of RGO. More pore space existing in successive RGO sheets could be filled if the combination ratio of SMF to RGO was further increased (Fig. 3(eeh)), which is also verified by the mapping data of Fe and Ni element, as shown in Fig. S2. By increasing the SMF ratios, the conductive networks start to form and strengthen. Besides, the RGO sheets progressively become thinner while the SMF disperse more uniformly, reflecting the supporting role of SMF nanoparticles (Fig. 3(g)). The microwave absorption properties of the composites can be estimated from their dielectric and magnetic properties. The complex permittivity (εr ¼ ε0
jε00 ) and complex permeability (mr ¼ m0
jm00 ) of the SMF-RGO epoxy composites and SMF epoxy composites were measured in the frequency range of 0.1e18 GHz at room temperature, which are shown in Fig. 4(aed). The real parts of the permittivity (ε0 ) and permeability (m0 ) are associated with energy storage while the imaginary parts (ε00 , m00 ) are related to energy dissipation, resulting from conduction loss, resonance and polarization relaxation, etc [30]. As shown in Fig. 4(a), the ε0 values of SMF epoxy composites are almost constant around 4.2 in the whole frequency range with slight fluctuations. For the SMF-RGO (1), SMF-RGO (2) and SMFRGO (3) epoxy composite, the values of ε0 are in the range of 10.3e4.0, 10.8e4.3 and 13.8e4.8, respectively, higher than the pure

SMF composite and pure RGO epoxy composite (RGO: epoxy ¼ 1: 100) in our previous studies [31]. It should be noted that by combining SMF with a small quantity of RGO sheets, the ε0 values exhibit a significant increase. The significant ε0 enhancement may due to interfacial polarization and dipole polarization. According to the MaxwelleWagner interfacial polarization principle, the disparity between the conductivity and permittivity of two adjacent materials results in polarization and charge accumulation at their interfaces [32]. It appears in heterogeneous interface due to the formation of large dipoles [33]. In the SMF-RGO epoxy composites, the existence of interfaces between the SMF and the RGO sheets and between the SMF/RGO sheets and the epoxy matrix give rise to interfacial polarization. The fine dispersion of SMF nanoparticles on RGO sheets can introduce more extra interfaces and as a result the interfacial polarization will be stronger. While in SMF composite, interfacial polarization only occurs between SMF and the epoxy matrix interface. Furthermore, the ε00 values of SMF are almost constant around 0.3 in the frequency range with slight fluctuations. While for SMF-RGO epoxy composites, the ε00 values clearly decrease with increasing frequency in the 0.1e10 GHz range, then tend to stabilize and exhibit slight fluctuations in the 10e18 GHz range. In addition, ε00 values increase with the increasing mass ratio of SMF. According to the free electron theory [34], ε00 ¼ s/uε0, where ε0 is the permittivity of the free space, u is the angular frequency, s is the electrical conductivity. Electrical transport in composites can occur either through direct contact between the conductive fillers or tunneling of electrons between sufficiently close conductive particles [35]. In SMF-RGO composites, conductive networks act as dissipating mobile charge carriers. Due to the bi-dimensional shape (large surface area with small thickness) of RGO, more advanced conducting networks are formed in SMF-RGO composites. As a consequence, the conductivity and the ε00 values of SMF-RGO composite are higher. Fig. 4(c and d) shows the real (m0 ) and imaginary (m00 ) part of the complex permeability of SMF-RGO and SMF epoxy composites. On one hand, the m0 values of SMF-RGO (1) and SMF-RGO (2) clearly decreases in the frequency range of 0.1e18 GHz, dropping from 1.81, 1.82 to 1.11, 1.15. While for SMF-RGO (3) composites, the m0 values first decreases in 0.1e8 GHz and then exhibit strong fluctuation in the 8e14 GHz. Besides, it is observed that within the same SMF content, there is slight increase in m0 values by combining magnetic SMF with RGO. The slight increase is believed to be due to the interactions between the RGO sheets and SMF nanoparticles in the epoxy matrix, which have also been reported in previous study [36]. On the other hand, the values of m00 for the SMF-RGO (1) and SMF-RGO (2) composite are in the range of 0.79e0.01, 0.84e0.05 in the frequency of 0.1e18 GHz. While for SMF-RGO (3) composites, the m00 values first decreases in 0.1e8 GHz and then exhibit strong resonance behavior in the 8e12 GHz, which is different from the m00 spectrum of SMF composite. The enhanced magnetic loss properties are mainly originated from two parts: The first is the coupling between magnetic SMF nanoparticle and RGO sheet, which is similar to the Ni/carbon nanotube structure [37]. The second is the coupling between the neighboring SMF nanoparticles that benefited from the template role of RGO sheet, as magnetic losses between magnetic nanoparticles can be exponentially enhanced when the inter-particle distance is less than 10 nm [38]. In general, the magnetic loss of materials originate mainly from magnetic hysteresis, domain wall resonance, eddy current effect, natural resonance and exchange resonance [39,40]. The magnetic hysteresis loss whose resonance frequency corresponds to the MHz frequency range is not the main magnetic loss mechanism and it is usually negligible in weak applied field. The domain wall resonance occurs only in multi-domain materials and usually at lower frequency range (<1 GHz). The eddy current loss is related to electric

J. Wang et al. / Journal of Alloys and Compounds 653 (2015) 14e21

17

Fig. 3. TEM images of (a) SMF, (c) SMF-RGO (1), (e) SMF-RGO (2), (g) SMF-RGO (3); (b) Photograph of SMF-RGO solution; SEM images of (d) SMF-RGO (1), (f) SMF-RGO (2), (h) SMFRGO (3).

conductivity of the composites, which can be described as C0 ¼ m00 (m0 )
2f
1. If C0 is a constant within the frequency range, then the magnetic loss is determined by the eddy current effect. Fig. 5 shows that in SMF-RGO (1), SMF-RGO (2) and SMF composite, C0 clearly decreases with increasing frequency in the 0.1e3 GHz range and then remains constant in the frequency range of 3e18 GHz, illustrating that the magnetic loss in higher frequency range

(3e18 GHz) is caused by eddy current effect. However in SMF-RGO (3) composite, the C0 exhibits a broad resonance peak at 10e12 GHz, illustrating that the loss mechanism in this frequency region is different. Based on the analyses above, it can be proposed that the magnetic loss in higher frequency region (10e12 GHz) in SMF-RGO (3) epoxy composites results from natural resonance or exchange

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Fig. 4. The real parts (a) and imaginary parts (b) of the permittivity; the real parts (c) and imaginary parts (g) of the permeability of SMF and SMF-RGO composites.

resonance, since the contributions of magnetic hysteresis, domain wall resonance, and eddy current effect could all be excluded. According to the natural resonance equation: 2pfr ¼ gHa , where fr is the resonance frequency, g the gyromagnetic ratio, and Ha the anisotropy energy, the natural resonance usually appears in the frequency range of 0.1e10 GHz [41]. It is well accepted that the particle size in exchange resonance is in the order of 0.1 mm and it occurs at higher resonance frequency than natural resonance. Thus, it is reasonable to conclude that the magnetic loss of the present SMF-RGO (3) composite is mainly from exchange resonance. The resonance due to exchange behaviors is believed to be due to the coupling between the RGO sheets and SMF particles. To further reveal the microwave absorption performance of the composites, the reflection loss (RL) curves were calculated according to the transmit line theory [42]:

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C0

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RL ¼ 20 logjðZin
Z0 Þ=ðZin þ Z0 Þj

(1)

0.00

Zin ¼

pffiffiffiffiffiffiffiffiffiffiffi  pffiffiffiffiffiffiffiffiffi  mr =εr tanh j2pft mr εr c

(2)

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Frequency (GHz) Fig. 5. C0-f curves for SMF and SMF-RGO composites.

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Where Zin is the characteristic input impedance of the absorber, Z0 z377 U is the free space impedance, f is the frequency of microwaves, t is the thickness of the absorber, and c is the velocity of electromagnetic wave in free space.

J. Wang et al. / Journal of Alloys and Compounds 653 (2015) 14e21

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Fig. 6. Reflection loss curves of (a) SMF, (b) SMF-RGO (1), (c) SMF-RGO (2) and (d) SMF-RGO (3) epoxy composites with different thicknesses.

Fig. 6(aed) shows the calculated RL curves of SMF and SMF-RGO epoxy composites with different thicknesses. It can be seen that the thickness of the absorber has a great influence on the microwave absorbing properties. The minimum RL gradually shifts toward lower frequency with the increase of thickness, which matches the quarter-wavelength model [43]. The RL of SMF and SMF-RGO (1) epoxy composites is poor and has no bandwidth under
10 dB in the whole frequency range. As for SMF-RGO (2) epoxy composite, the minimum RL is
12.6 dB for the layer thickness of 3.0 mm while the bandwidth of RL less than
10 dB (indicating 90% attenuation) can reach up to 2.8 GHz (from 10.1 to 12.9 GHz). When the layer thickness changes to 3.5 mm, the bandwidth less than
10 dB can reach up to 2.6 GHz(from 8.7 to 11.3 GHz). In our previous studies, we have found that the RL of RGO epoxy composite (RGO: epoxy ¼ 1: 100) is also poor that there is no absorption bandwidth under
10 dB [31]. However, by decorating RGO with SMF nanoparticles, the SMF-RGO (3) epoxy composite exhibits much enhanced electromagnetic wave absorption property compared with pure SMF and pure RGO epoxy composite. There is a strong broad electromagnetic wave absorbing peak of SMF-RGO (3) composite with layer thickness of 3 mm and the minimum reflection loss reaches about
23.9 dB at 10.8 GHz. The absorption bandwidth less than
10 dB can reach up to 4.3 GHz (from 8.8 to 13.1 GHz). The enhanced microwave absorbing performance of the SMFRGO (3) epoxy composites is mainly attributed to two key factors: better impedance matching and enhanced electromagnetic wave

attenuation. According to Eq. (1), the minimum reflection will take place when imaginary input impedance, Z00 in, approaches zero U while the corresponding real input impedance, Z0 in, approaches 377 U [44]. Fig. 7 shows the complex impedance of SMF and SMFRGO composite samples with the layer thickness of 3.0 mm. It can be seen that at 10.8 GHz, Z00 in for SMF-RGO (3) composite is found to be
22.4 U, the corresponding Z0 in is 423.7 U, which are very close to the required values of zero U and 377 U. As for SMF-RGO (2) composite, Z00 in and Z0 in are found to be 8.3 U and 619.1 U at 10.6 GHz, respectively. The Z00 in is very close to zero U, however, Z0 in is far away from 377 U, leading a worse microwave absorption performance compared to SMF-RGO (3). Whereas for SMF composite, the Z00 in is.3.4 U at 11.6 GHz while the corresponding Z0 in is 1492.6 U, the highest real impedance among the samples. As a consequence, the microwave absorption performance is very poor. In addition, the skin depth (d) is the distance at which the strength of electromagnetic field drops to (1/e) of the incident strength [45]. Mathematically, it can be calculated using Eq. (3) while the conductivity (s) at high frequency can be obtained approximately using s ¼ 2pfε0ε00 :

sffiffiffiffiffiffiffiffiffiffiffi 1 d¼ pf ms

(3)

Where f is the frequency, m is the magnetic permeability (m ¼ m0mr), m0 ¼ 4p  10
7 Hm
1, mr is the relative magnetic permeability.

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Fig. 7. Complex impedance of the composites: (a) imaginary impedance and (b) real impedance.

Using the constitutive parameters measured in Fig. 4, the calculated variation of skin depth is shown in Fig. 8(a). The skin depth of SMF and SMF-RGO composites all decreases as the frequency increases, and the minium skin depth is 2.96 mm, indicating that the microwave could transmit through the 3 mm single layer absorber in the whole frequency. On the other hand, the attenuation constant a determines the microwave attenuation properties of materials and can be expressed by Ref. [46]:

a¼

   00 1=2 1=2  00 00 00 pf 2 m ε
m0 ε0 þ m 2 þ m02 ε 2 þ ε02 c

(4)

Where f is the frequency of microwaves and c is the velocity of electromagnetic wave in free space. In Fig. 8(b), the dependence of attenuation constant on frequency shows that the SMF-RGO (3) composite has the maximum a values among the four composite samples. Therefore, it exhibits better microwave absorption properties. As previous stated, impedance matching and microwave attenuation are two key factors that contribute to the microwave absorption performance. There are still several other factors that can affect impedance matching and microwave attenuation. First, by functionalized graphene with SMF nanoparticles, the composites not only attenuate microwave energy through dielectric loss, but they attenuate it through magnetic loss. Second, the Fe50Ni50

nanoparticles are surface modified to reduce the permittivity values, which is in favor of impedance matching. As in traditional absorber, the electric permittivity values usually exceed corresponding magnetic permeability values. Third, the huge aspect ratio, layered structure, and the existence of residual defects and groups of the SMF-RGO composites could cause multiple reflections, which will further enhance microwave attenuation [47]. Last, the desirable electromagnetic parameter of the absorber is attributed to the compensatory properties of RGO and SMF, by adjusting the (RGO)/(SMF) ratio and layer thickness of the composite. 4. Conclusions In summary, the lightweight SMF-RGO epoxy composite have been successfully prepared using a wet chemical method. The results show that there have been significant changes in the electromagnetic properties of the as-prepared composite when compared with pure SMF and pure RGO epoxy composite. Microwave absorption properties indicate that the minimum RL can achieve
23.9 dB and the absorption bandwidth less than
10 dB can reach up to 4.3 GHz with layer thicknesses of 3.0 mm. The enhanced microwave absorption performance of the composite is due to the better impedance matching and enhanced microwave attenuation.

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Fig. 8. (a): Variation of skin depths and (b) aef curves for the composites.

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Acknowledgments This work was supported by the National Natural Science Foundation of China (Grant No. 51373129). Appendix A. Supplementary data

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[25]

Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.jallcom.2015.08.278.

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