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Porous melamine-derived carbon foam
Journal of Alloys and Compounds 791 (2019) 883e891
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Synthesis and microwave absorption properties of novel reticulation SiC/Porous melamine-derived carbon foam Xinli Ye a, b, Zhaofeng Chen a, *, Sufen Ai c, Bin Hou d, Junxiong Zhang a, Xiaohui Liang a, Qianbo Zhou a, Hezhou Liu e, Sheng Cui f a
International Laboratory for Insulation and Energy Efficiency Materials, College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing, 211106, People's Republic of China Suzhou Superlong Aviation Heat Resistance Material Technology Company, Limited, Suzhou, 215400, People's Republic of China c Beijing Spacecrafts, China Academy of Space Technology, Beijing, 100080, People's Republic of China d Department of Reactor Engineering, China Institute of Atomic Energy, Beijing, 102413, People's Republic of China e The State Key Lab of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai, 200240, People's Republic of China f Jiangsu Collaborative Innovation Center for Advanced Inorganic Function Composites, Nanjing Tech University, Nanjing, 211800, People's Republic of China b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 January 2019 Received in revised form 27 March 2019 Accepted 28 March 2019 Available online 30 March 2019
The ultrathin SiC coating/melamine-derived porous carbon foam composite (SiC/PCF) was synthesized for the first time by the stable treatment of the commercial melamine foam (MF), carbonization stage of the steady MF, and chemical vapor deposition of the SiC thin films. The microstructure analysis demonstrated that the SiC/PCF composites with layered structures and altered dielectric response were fabricated eventually. The minimum reflection loss of 25.93 dB was obtained when the thickness was 1.05 mm and the measured frequency was 17.20 GHz. Meanwhile, the reflection loss could drop below 10 dB in the whole thickness with the frequency ranging from 3.00 to 18.00 GHz, which showed a more excellent microwave absorbing performance compared with PCF. Furthermore, the influencing mechanism of both the impedance matching ratio and attenuation constant was discussed to provide actual guidances in designing excellent microwave absorbing materials for functional applications. © 2019 Elsevier B.V. All rights reserved.
Keywords: Composite materials Vapor deposition Thin films Microstructure Dielectric response
1. Introduce Along with the swift development of the modern science and engineering, serious electromagnetic pollution has attracted extensive attention not only in military fields but our daily life [1e7]. At present, many researchers have devoted themselves to the study of the ideal materials having a lower density, higher specific strength, and strong microwave absorbing ability [8e10]. Generally, the conventional materials such as ferrites and metals, are extremely limited by the narrow frequency range and high specific gravity, which needs a further research to address the problem and meet the growing demands effectively [11e13]. Among a large number of the absorbing materials, SiC exhibits a potential application in the next-generation microwave absorber due to the excellent thermal stability, chemical stability, and outstanding mechanical properties. Previous works have proved that the SiC-
* Corresponding author. E-mail address: [email protected] (Z. Chen). https://doi.org/10.1016/j.jallcom.2019.03.384 0925-8388/© 2019 Elsevier B.V. All rights reserved.
based materials could obtain the desired absorbing performance. Cheng at el. prepared the SiC nanowires/graphene aerogel via chemical vapor infiltration technology, and the test results demonstrated that it possessed a wider effective absorbing bandwidth covering the entire X-band, which extended its application in extreme environment [14]. Duan at el. fabricated the SiC nanowires reinforced Si3N4 composites via 3D-printing, polymer precursor infiltration, and pyrolysis process. The formation of the SiC nanowires modified the imaginary and real parts of permittivity, and then the final microwave absorbing capacities [15]. Besides, a novel SiC/SiBCN ceramic composite was synthesized with the SiC nanoparticles, which demonstrated that the SiC composition had more to do with the final performance [16]. However, the pure SiC material could not achieve the superior performance, because the permittivity and absorption performance were still pretty weak compared with the ferromagnetic and carbon absorption materials [17,18]. Hence, to achieve potential applications, the study about the combination of the SiC material and other excellent materials is extremely essential. To our best knowledge, carbon foam (CF) with an open-hole
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network structure has drawn great concern as a suitable microwave absorbing material resulting from its outstanding properties such as ultrahigh surface-to-volume ratio, mechanical stability, excellent electrical transport properties and low density [11,19e21]. Unfortunately, the pure CF could not be applied in many practical uses due to its dielectric loss and high conductivity, but it could be acted as the fundamental material to integrate with other materials [22e24]. Kumar et al. used the multi-wall carbon nanotubes to strengthen the mechanical properties and electromagnetic interference shielding effectiveness of CF, which showed a satisfactory result [25]. Xiao et al. prepared the ultra-lightweight 3D hybrid CF reinforced by the coated SiC nanowires, and the microwave absorbing properties of the as-prepared samples were much better than that of current state-of-the-art counterparts [26]. Farhan et al. also fabricated the CF composite with in-situ formation of the SiC nanowires, and the electromagnetic interference specific shielding effectiveness was twice more than that of the original CF [27]. In this article, a simple and convenient method was introduced to prepare an ultrathin SiC coating on the porous CF which was named as SiC/PCF. The PCF was derived from the commercial melamine foam (MF) having high porosity of ~96%, which was one of the most promising candidates as the 3D interconnected network structure. The ultrathin SiC film was then deposited via chemical vapor deposition (CVD) technology. The cladding structure was considered to be the advanced microwave absorbent, which provided beneficial guidances for the design of the novel absorber. 2. Experimental procedures 2.1. Preparation process The SiC/PCF composite was prepared by the three-step synthetic processes as displayed in Fig. 1. MF with a density of ~7 kg/m3 was used as the starting materials, which was purchased from Henan Zhongyuan Dahua Group Co., Ltd. At the beginning, the unstable MF was placed in a muffle furnace, and the temperature was set to 200 C for the stable treatment (I). The residual molecules were released, which resulted in the stabilization of the skeleton structures. The steady MF was then taken out and shifted to a vacuum anneal furnace during the carbonization stage (II). The sample was annealed to 400 C at a heating rate of 0.5 C/min and then 1100 C with a relatively high rate of 1 C/min in N2 atmosphere. It was annealed for 2 h to achieve the complete carbonation and get the porous carbon foam (PCF). In the third step (III), CVD technique was employed to modify the as-prepared PCF by depositing the
ultrathin SiC coating on the surface of the PCF skeleton. Hydrogen, methyltrichlorosilane, and argon were chosen as the reactant gas, the SiC precursor, and the dilution gas with the molar ratio of 300: 30: 150. After depositing for 8 h, the reticulated SiC film reinforced PCF skeleton was formed, and the resultant SiC/PCF was obtained. 2.2. Characterization The microstructures of the PCF and SiC/PCF composites were gained by the scanning electron microscope (SEM). The phase components and crystallinity were collected by the X-ray diffraction (XRD) patterns. The electromagnetic parameters were tested by a vector network analyzer with a frequency limiting in 2.00e18.00 GHz. Finally, the as-prepared samples were homogeneously mixed with paraffin wax, and then shaped like a round loop with the inner diameter of 3.0 mm, and the outer diameter of 7.0 mm. 3. Results and discussion 3.1. Evolution of SiC/PCF structure The evolution progresses of the SiC/PCF structure were similar to our previous work [28]. A huge volume shrinkage occurred as the size of the starting MF was ~2.0 cm 3.5 cm 6.5 cm, while that of the final PCF was ~1.0 cm 1.7 cm 3.1 cm, which was one-eighth of the original structure. Moreover, the color was transformed from white to black. However, either the shape size or the surface color changed little after the CVD process. As to the microstructures, MF possessed a structure of open cells in a 3D network with a high porosity. The sizes of the inside pores ranged from 20 to 100 mm. After complete carbonization, the thickness of the skeleton decreased along with the decrease in pore size. But in any case, PCF, as well as SiC/PCF inherited the 3D open-celled network structure. The most obvious differences were concentrated on the skeleton thickness and the pore size. Besides, the densities of MF, PCF, and SiC/PCF were ~7.12 kg/m3, ~6.88 kg/m3, and ~15.68 kg/m3. To confirm the existence of the SiC coating, the XRD patterns were detected to get clear on the substance composition. The results listed in Fig. 2 showed that PCF was an amorphous material having two weak peaks, which indicated that PCF consisted of amorphous structures [29]. As for SiC/PCF, three characteristic peaks appeared at (311), (220), and (111), which agreed well with the crystal faces of b-SiC [30]. It indicated the existence of the SiC particles. Fig. 3 showed the micrographs of PCF and SiC/PCF. The 3D open-
Fig. 1. Three-step preparation process of SiC/PCF composite.
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and the SiC structure took the most important component to resist the compression deformation, which aimed at the extreme harsh conditions.
3.2. Electromagnetic property
Fig. 2. XRD patterns of PCF and SiC/PCF.
hole structure could be considered to be composed of junctions and the chain links between the junctions. Note that the surface of the junctions and the chain links of PCF were smooth in Fig. 3a and b, which might not be beneficial to the microwave reflection. After CVD process, the roughened surface was obtained due to the countless SiC particles. By increasing the deposition time, the ultrathin SiC skeleton was formed as shown in Fig. 3c and d. SiC was hard but brittle, which meant many micro interfaces and laminated particles might be induced by the collapse of the SiC coating. It should be stressed that the interfaces and particles played a vital role in the enhancement of the electromagnetic wave absorption ability [31]. Besides, the cladding structure of both the PCF and SiC skeleton could improve the compression strength to some extent,
To study the impact of the SiC coating on the microwave absorption mechanism, the frequency dependence of the permeability and complex permittivity of PCF and SiC/PCF were investigated. The complex permittivity consisted of the storage and loss capacity of electric energy, which were defined as the real part (ε0 ) and the imaginary part (ε00 ) respectively, while the permeability was composed of the real part (m0 ) and the imaginary part (m00 ), which were associated with the magnetic energy [32]. As shown in Fig. 4a and b, both m00 and m0 of the complex permeability almost remained unchanged within the frequency of 2.00e18.00 GHz, which indicated that both PCF and SiC/PCF were non-magnetic or weak magnetic. Hence, the main research was necessarily restricted to the complex permittivity. Fig. 4a exhibited the variation circumstance of ε0 and ε00 of PCF with the measured frequency. It was obvious that the values of ε0 and ε00 dropped immediately as the frequency increased, and then leveled out at high frequencies. However, the changed trend had a great difference compared with that of SiC/PCF in Fig. 4b. Although the ε0 value of SiC/PCF also showed a declining trend, the changes were relatively flat firstly but decreased sharply after a small increase. For ε00 values, it offered upgrade firstly than descending latter tendency, which indicated the complicated variation phenomena, especially at high frequencies. In contrast, a considerable reduction occurred at a specific frequency between 2.00 and 18.00 GHz after CVD process as shown in Fig. 4c and d. The mechanism behind this was that the increase in the angular frequency caused the decline in ε0 , which was regarded as the polarization relaxation, especially at the lower frequency [33]. Besides, the low value of ε00 meant that little attenuation occurred. When the absorbent absorbed the electromagnetic wave, it could not be reflected or transmitted. It indicated
Fig. 3. Chain links of PCF (a) and SiC/PCF (c); Junctions of PCF (b) and SiC/PCF (d).
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Fig. 4. Electromagnetic parameters of PCF (a) and SiC/PCF (b); comparison diagram of real part (c) and imaginary part (d) between PCF and SiC/PCF.
that the SiC coating played a vital role in altering the complex permittivity of SiC/PCF, which might result from the unique dielectric properties of the SiC materials [34]. The complex permittivity of PCF was higher than that of SiC/PCF which resulted in more reflection, and it was harmful to the impedance match. Here, ε00 was also written as [35]: 00
ε ¼ 1=pε0 rf
(1)
Where the ε0 was the dielectric constant in the vacuum, the r was the electrical resistivity, and the f was the measured frequency. When the value of ε00 became higher, r became lower, which would lead to the high electrical conductivity. The high electrical conductivity and skin depth effect were closely interrelated, causing microwave reflection [36]. Therefore, a comparatively low value of the dielectric loss was beneficial to the excellent microwave absorption performance. Moreover, the tangent of the dielectric loss defined as dε usually stated the relationship of ε0 and ε00 as follows [37]:
tan dε ¼ ε
00
. ε0
(2)
Fig. 5 displayed the tandε variation of PCF and SiC/PCF at different frequencies. The red curve was below the gray one
Fig. 5. Dielectric loss tagents of PCF and SiC/PCF.
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Fig. 6. Cole-Cole plots of PCF (a) and SiC/PCF (b).
represented that the dielectric loss of SiC/PCF was much lower than that of PCF. Based on the Debye theory, the link of ε0 and ε00 could also be presented as [38]:
. ε0 ¼ ε∞ þ ðεs ε∞ Þ 1 þ u2 t2 00
ε ¼ ðεs ε∞ Þut
(3)
. 1 þ u2 t2 þ sac =uε0
(4)
Where the sac was the alternative conductivity, the t was the polarization relaxation time, the u was the angular frequency, the εs was the static permittivity, and the ε∞ was the high-frequency limit relative dielectric permittivity. The second part of Eq. (4) provided slight contributions for ε00. Hence, the interrelationship of ε0 and ε00 could be simplified as:
00 2 2 ε þ ðε0 ðεs þ ε∞ Þ=2Þ ¼ ððεs ε∞ Þ=2Þ2
(5)
Eq. (5) was the property of the circle using ((εs þ ε∞)/2, 0) as the center, and the Cole-Cole curves of PCF and SiC/PCF were illustrated in Fig. 6. The Cole-Cole curve of SiC/PCF composing of multiple semi-cylindrical shapes, was much more complicated than that of PCF. It was attributed to the multi-relaxation dielectric properties, which might originate from the incomplete carbon structures in
PCF, the defect polarization of the groups as well as the multiinterface polarizations in SiC/PCF hybrids. For further understanding the microwave absorption mechanism entirely, the impedance matching ratio value (Zr) and the attenuation constant (a) of PCF and SiC/PCF were calculated, which was considered to be two essential factors. Zr represented the effective absorbing microwave, while a meant the integral attenuation ability. In this work, Zr was expressed as follows [39]:
Zr ¼ Z=Z0 ¼ ðmr =εr Þ1=2 00
mr ¼ m0 jm 00
εr ¼ ε0 jε
(6) (7) (8)
Where the εr was the complex permittivity, the mr was the permeability, the Z0 was the impedance of the free space, and the Z was the impedance value of the absorbent. Fig. 7a showed the impedance matching ratio curves of PCF and SiC/PCF. Clearly, the ideal zero-reflection could be obtained only if mr and εr were equal. Although the values of Zr were quite small, a significant enhancement occurred after depositing the ultrathin SiC coating. It was worth noting that Zr was relatively higher at high frequencies around 17.60 GHz, which meant that the optimum absorption property might occur near that range.
Fig. 7. Impedance matching ratio (a) and attenuation constant (b) of PCF and SiC/PCF.
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Meanwhile, to the best of our knowledge, a could be counted as [40]:
a ¼ 20:5 pf
00
00
m ε m0 ε0
2
2 0:5 00 00 þ m0 ε þ m ε0
!0:5 , c
(9)
Where the c was the velocity of light. Obviously, a strong ε00 and m00 might result in a higher a. The attenuation constant value curves of PCF and SiC/PCF were exhibited in Fig. 7b. It could be observed that PCF had a higher attenuation constant than that of SiC/PCF, which showed that a large proportion of the incident microwave was absorbed by the objects in PCF. Based on the above analysis, SiC/PCF possessed a higher impedance matching ratio while the attenuation constant was relatively lower. To probe the microwave absorption properties of PCF and SiC/PCF in more detail, Zin was defined as the input impedance of the absorber in the air, which was given by Ref. [41]:
i h Zin ¼ Z0 Zr tanh jð2pfd=cÞðmr εr Þ1=2
(10)
The reflection loss (RL) was determined by Zin and Z0 according to the metal backplane model, and the expression was as follows [42]:
RL ¼ 20 logjðZin Z0 Þ=ðZin þ Z0 Þj
(11)
Fig. 8 showed the variation of the reflection loss values of the PCF-wax and SiC/PCF-wax composites in the overall frequencies. In general, the values of the reflection loss should be less than 10 dB, that was to say that more than 90% of the microwaves were absorbed by the absorber. The 3D plots of the reflection loss values
of the PCF-wax composite in Fig. 8a displayed that all values were above 10 dB, which was much more significant in Fig. 8b. It could be stated that PCF was not the appropriate microwave absorbing material. However, it was gratifying that SiC/PCF possessed excellent microwave absorbing properties as displayed in Fig. 8c. A minimum reflection loss of 25.93 dB could be gained at 17.20 GHz when the thickness of the absorber was 1.05 mm. And the reflection loss less than 10 dB was located in the whole thickness with the frequency locating in 3.00e18.00 GHz. Compared with PCF, the results indicated the practical application of the resultant SiC/PCF with different thicknesses could be realized at specific frequencies. In addition, we picked the as-prepared samples with the thickness varying from 1.00 to 5.00 mm. Fig. 9a represented the reflection loss value curves of the PCF-wax composite. It further demonstrated that it could not reach 10 dB regardless of the thicknesses and the frequencies. For the SiC/PCF-wax composite, the minimum reflection loss value increased and shifted to lower frequencies with the increasing thickness of the composite as shown in Fig. 9b. The reflection loss value descended to its lowest point at 25.93 dB, while the highest effective absorption bandwidth (fE) was obtained at the thickness of 1.15 mm, which ranged from 14.20 to 17.44 dB (Fig. 9c). Fig. 9d showed the effective absorption bandwidth of the PCF-wax composite with various coating thicknesses. It was obvious that the effective bandwidth frequency could reach the highest point only when the absorber thickness was relatively thin. As the thickness increased, the effective bandwidth frequency decreased, which matched well with Fig. 9b and c. Apparently, the impedance matching ratio of SiC/PCF was higher while the attenuation constant was relatively lower than that of PCF, but it showed enhanced microwave absorbing ability. To evaluate the effect of the impedance matching ratio as well as the
Fig. 8. 3D plots (a, c) and contour plots (b, d) of PCF-wax and SiC/PCF-wax composites in the overall frequency.
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Fig. 9. Reflection loss curves of PCF-wax (a) and SiC/0PCF-wax composites (b); reflection loss curve of SiC/PCF-wax composite at thickness of 1.00 and 1.05 mm (c); effective absorption bandwidth of SiC/PCF-wax composite with different thicknesses (d).
attenuation constant on the reflection loss, we selected SiC/PCF as an example to illustrate the importance of the two factors. Fig. 10 clearly exhibited the frequency dependence of the impedance matching ratio, attenuation constant, and the reflection loss with
the matching thickness of 1.05 mm. When the attenuation constant reached the highest point of 241.86 at 17.60 GHz, the impedance matching ratio was 0.2467 Np/m and the reflection loss was 22.35 GHz. In another case, when the impedance matching
Fig. 10. Reflection loss, attenuation constant, and the impedance matching ratio for SiC/PCF-wax composite with 1.05 mm.
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ratio reached its peak of 0.2474 Np/m at 17.00 GHz, the attenuation constant was 216.53 and the reflection loss was 23.03 dB. In other words, the minimum reflection loss was obtained where the impedance matching ratio was not the highest as well as the attenuation constant. When the minimum reflection loss was gained, the impedance matching ratio and attenuation constant were 0.2471 and 218.26 Np/m, respectively. It demonstrated that the impedance matching ratio was chief factor as the value was close to the highest one. Obviously, the high attenuation effect made no sense with little incident microwaves. Only if most microwaves were absorbed by the absorber, it would show electromagnetic shielding characteristic. Therefore, it provided an actual guidance for designing the excellent microwave absorbing materials by taking into accounts both the impedance matching ratio and the attenuation constant. 4. Conclusion In summary, the exceptional microwave absorbing SiC/PCF composites were fabricated successfully in this paper, and the main results were shown as follows: (1) The preparation process of the SiC/PCF composites consisted of stable treatment, carbonization stage and CVD process. The as-prepared sample possessed a unique cladding structure with the reticulated SiC network wrapping around the PCF skeleton, which was believed to favor the microwave absorption. (2) The SiC coating had a marked impact on the complex permittivity, which further affected the microwave absorbing property. The minimum reflection loss of 25.93 dB was obtained at the measured frequency of 17.20 GHz with the matching thickness of 1.05 mm, and the reflection loss could drop below 10 dB in the whole thickness with the frequency ranging from 3.00 to 18.00 GHz. (3) The absorption mechanism of the SiC/PCF composites was further investigated. The microwave absorbing performance was a function of both the impedance matching ratio and the attenuation constant. It provided some useful guidances for designing the excellent microwave absorbing materials in the future. Acknowledgements This work was supported by the National Natural Science Foundation of China [grant numbers 51772151, 51761145103]; and the Priority Academic Program Development of Jiangsu Higher Education Institutions. References [1] S. Lee, I. Jo, S. Kang, B. Jang, J. Moon, J.B. Park, S. Lee, S. Rho, Y. Kim, B.H. Hong, Smart contact lenses with graphene coating for electromagnetic interference shielding and dehydration protection, ACS Nano 11 (2017) 5318e5324. https://doi.org/10.1021/acsnano.7b00370. [2] Y. Qian, H. Wei, J. Dong, Y. Du, X. Fang, W. Zheng, Y. Sun, Z. Jiang, Fabrication of urchin-like ZnO-MXene nanocomposites for high-performance electromagnetic absorption, Ceram. Int. 43 (2017) 10757e10762. https://doi.org/10. 1016/j.ceramint.2017.05.082. [3] L. Gao, W. Zhou, F. Luo, D. Zhu, J. Wang, Dielectric and microwave absorption properties of KNN/Al2O3 composite ceramics, Ceram. Int. 43 (2017) 12731e12735. https://doi.org/10.1016/j.ceramint.2017.06.158. [4] F. Wu, A. Xie, M. Sun, Y. Wang, M. Wang, Reduced graphene oxide (RGO) modified spongelike polypyrrole (PPy) aerogel for excellent electromagnetic absorption, J. Mater. Chem. A 3 (2015) 14358e14369. https://doi.org/10.1039/ c5ta01577d. [5] Y. Zhang, Y. Huang, H. Chen, Z. Huang, Y. Yang, P. Xiao, Y. Zhou, Y. Chen, Composition and structure control of ultralight graphene foam for highperformance microwave absorption, Carbon 105 (2016) 438e447. https://
doi.org/10.1016/j.carbon.2016.04.070. [6] J. Chen, X. Liang, B. Quan, Z. Yang, Y. Du, G. Ji, 3D flake-like Bi2Te3 with outstanding lightweight electromagnetic wave absorption feature, Part. Part. Syst. Char. 35 (2018), 1700468. https://doi.org/10.1002/ppsc.201700468. [7] H. Zhao, Y. Cheng, X. Liang, Y. Du, G. Ji, Constructing large interconnect conductive networks: an effective approach for excellent electromagnetic wave absorption at gigahertz, Ind. Eng. Chem. Res. 57 (2018). https://doi.org/ 10.1021/acs.iecr.7b05141. [8] Y. Wang, Z. Peng, W. Jiang, Controlled synthesis of Fe3O4@SnO2/RGO nanocomposite for microwave absorption enhancement, Ceram. Int. 42 (2016) 10682e10689. https://doi.org/10.1016/j.ceramint.2016.03.180. [9] Y. Lai, S. Wang, D. Qian, S. Zhong, Y. Wang, S. Han, W. Jiang, Tunable electromagnetic wave absorption properties of nickel microspheres decorated reduced graphene oxide, Ceram. Int. 43 (2017) 12904e12914. https://doi.org/ 10.1016/j.ceramint.2017.06.188. [10] J. Wu, Z. Ye, W. Liu, Z. Liu, J. Chen, The effect of GO loading on electromagnetic wave absorption properties of Fe3O4/reduced graphene oxide hybrids, Ceram. Int. 43 (2017) 13146e13153. https://doi.org/10.1016/j.ceramint.2017.07.007. [11] M. Han, X. Yin, Z. Hou, C. Song, X. Li, L. Zhang, L. Cheng, Flexible and thermostable graphene/SiC nanowire foam composites with tunable electromagnetic wave absorption properties, Acs. Appl. Mater. Interfaces 9 (2017) 11803e11810. https://doi.org/10.1021/acsami.7b00951. [12] D. Ding, Y. Wang, X. Li, R. Qiang, P. Xu, W. Chu, X. Han, Y. Du, Rational design of core-shell Co@C microspheres for high-performance microwave absorption, Carbon 111 (2017) 722e732. https://doi.org/10.1016/j.carbon.2016.10. 059. [13] R. Shu, G. Zhang, X. Wang, X. Gao, M. Wang, Y. Gan, J. Shi, J. He, Fabrication of 3D net-like MWCNTs/ZnFe2O4 hybrid composites as high-performance electromagnetic wave absorbers, Chem. Eng. J. (2017). https://doi.org/10.1016/j. cej.2017.12.106. [14] Y. Cheng, M. Tan, P. Hu, X. Zhang, B. Sun, L. Yan, S. Zhou, W. Han, Strong and thermostable SiC nanowires/graphene aerogel with enhanced hydrophobicity and electromagnetic wave absorption property, Appl. Surf. Sci. 448 (2018) 138e144. https://doi.org/10.1016/j.apsusc.2018.04.132. [15] W. Duan, X. Yin, F. Cao, Y. Jia, Y. Xie, P. Greil, N. Travitzky, Absorption properties of twinned SiC nanowires reinforced Si3N4 composites fabricated by 3dprinting, Mater. Lett. 159 (2015) 257e260. https://doi.org/10.1016/j.matlet. 2015.06.106. [16] F. Ye, L. Zhang, X. Yin, Y. Zhang, L. Kong, Y. Liu, L. Cheng, Dielectric and microwave-absorption properties of SiC nanoparticle/SiBCN composite ceramics, J. Eur. Ceram. Soc. 34 (2014) 205e215. https://doi.org/10.1016/j. jeurceramsoc.2013.08.005. [17] P. Wang, L. Cheng, Y. Zhang, L. Zhang, Flexible SiC/Si3N4 composite nanofibers with in Situ embedded graphite for highly efficient electromagnetic wave absorption, Acs. Appl. Mater. Interfaces 9 (2017) 28844e28858. https://doi. org/10.1021/acsami.7b05382. [18] J. Bi, Y. Gu, Z. Zhang, S. Wang, M. Li, Z. Zhang, Core-shell SiC/SiO2 whisker reinforced polymer composite with high dielectric permittivity and low dielectric loss, Mater. Des. 89 (2016) 933e940. https://doi.org/10.1016/j. matdes.2015.10.050. [19] F. Moglie, D. Micheli, S. Laurenzi, M. Marchetti, V. Mariani Primiani, Electromagnetic shielding performance of carbon foams, Carbon 50 (2012) 1972e1980. https://doi.org/10.1016/j.carbon.2011.12.053. [20] S. Dong, P. Hu, X. Zhang, J. Han, Y. Zhang, X. Luo, Carbon foams modified with in-situ formation of Si3N4 and SiC for enhanced electromagnetic microwave absorption property and thermostability, Ceram. Int. 44 (2018) 7141e7150. https://doi.org/10.1016/j.ceramint.2018.01.156. [21] M. Inagaki, T. Morishita, A. Kuno, T. Kito, M. Hirano, T. Suwa, K. Kusakawa, Carbon foams prepared from polyimide using urethane foam template, Carbon 42 (2004) 497e502. https://doi.org/10.1016/j.carbon.2003.12.080. [22] F. Wu, M. Sun, W. Jiang, K. Zhang, A. Xie, Y. Wang, M. Wang, A self-assembly method for the fabrication of a three-dimensional (3D) polypyrrole (PPy)/ poly(3,4-ethylenedioxythiophene) (PEDOT) hybrid composite with excellent absorption performance against electromagnetic pollution, J. Mater. Chem. C 4 (2016) 82e88. https://doi.org/10.1039/C5TC02887F. [23] S. Farhan, R. Wang, K. Li, Carbon foam decorated with silver particles and in situ grown nanowires for effective electromagnetic interference shielding, J. Mater. Sci. 51 (2016) 7991e8004. https://doi.org/10.1007/s10853-0160068-4. [24] R. Narasimman, S. Vijayan, K.S. Dijith, K.P. Surendran, K. Prabhakaran, Carbon composite foams with improved strength and electromagnetic absorption from sucrose and multi-walled carbon nanotube, Mater. Chem. Phys. 181 (2016) 538e548. https://doi.org/10.1016/j.matchemphys.2016.06.091. [25] R. Kumar, S.R. Dhakate, T. Gupta, P. Saini, B.P. Singh, R.B. Mathur, Effective improvement of the properties of light weight carbon foam by decoration with multi-wall carbon nanotubes, J. Mater. Chem. A 1 (2013) 5727e5735. https://doi.org/10.1039/c3ta10604g. [26] S. Xiao, H. Mei, D. Han, K.G. Dassios, L. Cheng, Ultralight lamellar amorphous carbon foam nanostructured by SiC nanowires for tunable electromagnetic wave absorption, Carbon 122 (2017) 718e725. https://doi.org/10.1016/j. carbon.2017.07.023. [27] S. Farhan, R. Wang, K. Li, Electromagnetic interference shielding effectiveness of carbon foam containing in situ grown silicon carbide nanowires, Ceram. Int. 42 (2016) 11330e11340. https://doi.org/10.1016/j.ceramint.2016.04.054. [28] X. Ye, Z. Chen, S. Ai, B. Hou, J. Zhang, Q. Zhou, H. Liu, S. Cui, Effect of thickness
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[29]
[30]
[31]
[32]
[33]
[34]
[35]
of SiC films on compression and thermal properties of SiC/CF composites, Ceram. Int. (2018). https://doi.org/10.1016/j.ceramint.2018.11.158. Z. Fang, C. Li, J. Sun, H. Zhang, J. Zhang, The electromagnetic characteristics of carbon foams, Carbon 45 (2007) 2873e2879. https://doi.org/10.1016/j.carbon. 2007.10.013. B. Zhong, T. Sai, L. Xia, Y. Yu, G. Wen, High-efficient production of SiC/SiO2 core-shell nanowires for effective microwave absorption, Mater. Des. 121 (2017) 185e193. https://doi.org/10.1016/j.matdes.2017.02.058. X. Liang, B. Quan, Y. Sun, G. Ji, Y. Zhang, J. Ma, D. Li, B. Zhang, Y. Du, Multiple interfaces structure derived from metal-organic frameworks for excellent electromagnetic wave absorption, Part. Part. Syst. Char. 34 (2017), 1700006. https://doi.org/10.1002/ppsc.201700006. Y. Peng, Z. Meng, C. Zhong, J. Lu, W. Yu, Z. Yang, Y. Qian, Hydrothermal synthesis of MoS2 and its pressure-related crystallization, J. Solid State Chem. 159 (2001) 170e173. https://doi.org/10.1006/jssc.2001.9146. X. Liang, B. Quan, G. Ji, W. Liu, H. Zhao, S. Dai, J. Lv, Y. Du, Tunable dielectric performance derived from the metal-organic framework/reduced graphene oxide hybrid with broadband absorption, ACS Sustain. Chem. Eng. 5 (2017) 10570e10579. https://doi.org/10.1021/acssuschemeng.7b02565. P. Wang, L. Cheng, L. Zhang, One-dimensional carbon/SiC nanocomposites with tunable dielectric and broadband electromagnetic wave absorption properties, Carbon 125 (2017) 207e220. https://doi.org/10.1016/j.carbon. 2017.09.052. B. Zhao, G. Shao, B. Fan, W. Zhao, R. Zhang, Enhanced microwave absorption capabilities of Ni microspheres after coating with SnO2 nanoparticles, J. Mater. Sci. Mater. Electron. 26 (2015) 5393e5399. https://doi.org/10.1007/s10854015-3087-z.
891
[36] X. Cui, J. Li, J. Mo, J. Fang, B. Zhou, X. Xiao, Effect of the sheet thickness and current damping exponent on the optimum current frequency in electromagnetic forming, Int. J. Adv. Manuf. Technol. 85 (2016) 843e851. https://doi. org/10.1007/s00170-015-7983-4. [37] X. Liang, X. Zhang, W. Liu, D. Tang, B. Zhang, G. Ji, A simple hydrothermal process to grow MoS2 nanosheets with excellent dielectric loss and microwave absorption performance, J. Mater. Chem. C 4 (2016) 6816e6821. https:// doi.org/10.1039/c6tc02006b. [38] X. Liang, B. Quan, G. Ji, W. Liu, Y. Cheng, B. Zhang, Y. Du, Novel nanoporous carbon derived from metal-organic frameworks with tunable electromagnetic wave absorption capabilities, Inorg. Chem. Front. 3 (2016) 1516e1526. https://doi.org/10.1039/C6QI00359A. [39] H.J. Lv, G. Ji, H. Zhang, Y. Du, Facile synthesis of a CNT@Fe@SiO2 ternary composite with enhanced microwave absorption performance, RSC Adv. 5 (94) (2015) 76836e76843. https://doi.org/10.1039/b000000x. [40] X. Zhang, G. Ji, W. Liu, B. Quan, X. Liang, C. Shang, Y. Cheng, Y. Du, Thermal conversion of an Fe₃O₄@metal-organic framework: a new method for an efficient Fe-Co/nanoporous carbon microwave absorbing material, Nanoscale 7 (2015) 12932e12942. https://doi.org/10.1039/c5nr03176a. [41] B. Zhao, B. Fan, G. Shao, W. Zhao, R. Zhang, Facile synthesis of novel heterostructure based on SnO2 nanorods grown on submicron Ni walnut with tunable electromagnetic wave absorption capabilities, Acs. Appl. Mater. Interfaces 7 (2015) 18815. https://doi.org/10.1021/acsami.5b05482. [42] X. Zhang, G. Ji, W. Liu, X. Zhang, Q. Gao, Y. Li, Y. Du, A novel Co/TiO2 nanocomposite derived from a metal-organic framework: synthesis and efficient microwave absorption, J. Mater. Chem. C 4 (2016) 1860e1870. https://doi.org/ 10.1039/c6tc00248j.
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Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Synthesis and microwave absorption properties of novel reticulation SiC/Porous melamine-derived carbon foam Xinli Ye a, b, Zhaofeng Chen a, *, Sufen Ai c, Bin Hou d, Junxiong Zhang a, Xiaohui Liang a, Qianbo Zhou a, Hezhou Liu e, Sheng Cui f a
International Laboratory for Insulation and Energy Efficiency Materials, College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing, 211106, People's Republic of China Suzhou Superlong Aviation Heat Resistance Material Technology Company, Limited, Suzhou, 215400, People's Republic of China c Beijing Spacecrafts, China Academy of Space Technology, Beijing, 100080, People's Republic of China d Department of Reactor Engineering, China Institute of Atomic Energy, Beijing, 102413, People's Republic of China e The State Key Lab of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai, 200240, People's Republic of China f Jiangsu Collaborative Innovation Center for Advanced Inorganic Function Composites, Nanjing Tech University, Nanjing, 211800, People's Republic of China b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 January 2019 Received in revised form 27 March 2019 Accepted 28 March 2019 Available online 30 March 2019
The ultrathin SiC coating/melamine-derived porous carbon foam composite (SiC/PCF) was synthesized for the first time by the stable treatment of the commercial melamine foam (MF), carbonization stage of the steady MF, and chemical vapor deposition of the SiC thin films. The microstructure analysis demonstrated that the SiC/PCF composites with layered structures and altered dielectric response were fabricated eventually. The minimum reflection loss of 25.93 dB was obtained when the thickness was 1.05 mm and the measured frequency was 17.20 GHz. Meanwhile, the reflection loss could drop below 10 dB in the whole thickness with the frequency ranging from 3.00 to 18.00 GHz, which showed a more excellent microwave absorbing performance compared with PCF. Furthermore, the influencing mechanism of both the impedance matching ratio and attenuation constant was discussed to provide actual guidances in designing excellent microwave absorbing materials for functional applications. © 2019 Elsevier B.V. All rights reserved.
Keywords: Composite materials Vapor deposition Thin films Microstructure Dielectric response
1. Introduce Along with the swift development of the modern science and engineering, serious electromagnetic pollution has attracted extensive attention not only in military fields but our daily life [1e7]. At present, many researchers have devoted themselves to the study of the ideal materials having a lower density, higher specific strength, and strong microwave absorbing ability [8e10]. Generally, the conventional materials such as ferrites and metals, are extremely limited by the narrow frequency range and high specific gravity, which needs a further research to address the problem and meet the growing demands effectively [11e13]. Among a large number of the absorbing materials, SiC exhibits a potential application in the next-generation microwave absorber due to the excellent thermal stability, chemical stability, and outstanding mechanical properties. Previous works have proved that the SiC-
* Corresponding author. E-mail address: [email protected] (Z. Chen). https://doi.org/10.1016/j.jallcom.2019.03.384 0925-8388/© 2019 Elsevier B.V. All rights reserved.
based materials could obtain the desired absorbing performance. Cheng at el. prepared the SiC nanowires/graphene aerogel via chemical vapor infiltration technology, and the test results demonstrated that it possessed a wider effective absorbing bandwidth covering the entire X-band, which extended its application in extreme environment [14]. Duan at el. fabricated the SiC nanowires reinforced Si3N4 composites via 3D-printing, polymer precursor infiltration, and pyrolysis process. The formation of the SiC nanowires modified the imaginary and real parts of permittivity, and then the final microwave absorbing capacities [15]. Besides, a novel SiC/SiBCN ceramic composite was synthesized with the SiC nanoparticles, which demonstrated that the SiC composition had more to do with the final performance [16]. However, the pure SiC material could not achieve the superior performance, because the permittivity and absorption performance were still pretty weak compared with the ferromagnetic and carbon absorption materials [17,18]. Hence, to achieve potential applications, the study about the combination of the SiC material and other excellent materials is extremely essential. To our best knowledge, carbon foam (CF) with an open-hole
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network structure has drawn great concern as a suitable microwave absorbing material resulting from its outstanding properties such as ultrahigh surface-to-volume ratio, mechanical stability, excellent electrical transport properties and low density [11,19e21]. Unfortunately, the pure CF could not be applied in many practical uses due to its dielectric loss and high conductivity, but it could be acted as the fundamental material to integrate with other materials [22e24]. Kumar et al. used the multi-wall carbon nanotubes to strengthen the mechanical properties and electromagnetic interference shielding effectiveness of CF, which showed a satisfactory result [25]. Xiao et al. prepared the ultra-lightweight 3D hybrid CF reinforced by the coated SiC nanowires, and the microwave absorbing properties of the as-prepared samples were much better than that of current state-of-the-art counterparts [26]. Farhan et al. also fabricated the CF composite with in-situ formation of the SiC nanowires, and the electromagnetic interference specific shielding effectiveness was twice more than that of the original CF [27]. In this article, a simple and convenient method was introduced to prepare an ultrathin SiC coating on the porous CF which was named as SiC/PCF. The PCF was derived from the commercial melamine foam (MF) having high porosity of ~96%, which was one of the most promising candidates as the 3D interconnected network structure. The ultrathin SiC film was then deposited via chemical vapor deposition (CVD) technology. The cladding structure was considered to be the advanced microwave absorbent, which provided beneficial guidances for the design of the novel absorber. 2. Experimental procedures 2.1. Preparation process The SiC/PCF composite was prepared by the three-step synthetic processes as displayed in Fig. 1. MF with a density of ~7 kg/m3 was used as the starting materials, which was purchased from Henan Zhongyuan Dahua Group Co., Ltd. At the beginning, the unstable MF was placed in a muffle furnace, and the temperature was set to 200 C for the stable treatment (I). The residual molecules were released, which resulted in the stabilization of the skeleton structures. The steady MF was then taken out and shifted to a vacuum anneal furnace during the carbonization stage (II). The sample was annealed to 400 C at a heating rate of 0.5 C/min and then 1100 C with a relatively high rate of 1 C/min in N2 atmosphere. It was annealed for 2 h to achieve the complete carbonation and get the porous carbon foam (PCF). In the third step (III), CVD technique was employed to modify the as-prepared PCF by depositing the
ultrathin SiC coating on the surface of the PCF skeleton. Hydrogen, methyltrichlorosilane, and argon were chosen as the reactant gas, the SiC precursor, and the dilution gas with the molar ratio of 300: 30: 150. After depositing for 8 h, the reticulated SiC film reinforced PCF skeleton was formed, and the resultant SiC/PCF was obtained. 2.2. Characterization The microstructures of the PCF and SiC/PCF composites were gained by the scanning electron microscope (SEM). The phase components and crystallinity were collected by the X-ray diffraction (XRD) patterns. The electromagnetic parameters were tested by a vector network analyzer with a frequency limiting in 2.00e18.00 GHz. Finally, the as-prepared samples were homogeneously mixed with paraffin wax, and then shaped like a round loop with the inner diameter of 3.0 mm, and the outer diameter of 7.0 mm. 3. Results and discussion 3.1. Evolution of SiC/PCF structure The evolution progresses of the SiC/PCF structure were similar to our previous work [28]. A huge volume shrinkage occurred as the size of the starting MF was ~2.0 cm 3.5 cm 6.5 cm, while that of the final PCF was ~1.0 cm 1.7 cm 3.1 cm, which was one-eighth of the original structure. Moreover, the color was transformed from white to black. However, either the shape size or the surface color changed little after the CVD process. As to the microstructures, MF possessed a structure of open cells in a 3D network with a high porosity. The sizes of the inside pores ranged from 20 to 100 mm. After complete carbonization, the thickness of the skeleton decreased along with the decrease in pore size. But in any case, PCF, as well as SiC/PCF inherited the 3D open-celled network structure. The most obvious differences were concentrated on the skeleton thickness and the pore size. Besides, the densities of MF, PCF, and SiC/PCF were ~7.12 kg/m3, ~6.88 kg/m3, and ~15.68 kg/m3. To confirm the existence of the SiC coating, the XRD patterns were detected to get clear on the substance composition. The results listed in Fig. 2 showed that PCF was an amorphous material having two weak peaks, which indicated that PCF consisted of amorphous structures [29]. As for SiC/PCF, three characteristic peaks appeared at (311), (220), and (111), which agreed well with the crystal faces of b-SiC [30]. It indicated the existence of the SiC particles. Fig. 3 showed the micrographs of PCF and SiC/PCF. The 3D open-
Fig. 1. Three-step preparation process of SiC/PCF composite.
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and the SiC structure took the most important component to resist the compression deformation, which aimed at the extreme harsh conditions.
3.2. Electromagnetic property
Fig. 2. XRD patterns of PCF and SiC/PCF.
hole structure could be considered to be composed of junctions and the chain links between the junctions. Note that the surface of the junctions and the chain links of PCF were smooth in Fig. 3a and b, which might not be beneficial to the microwave reflection. After CVD process, the roughened surface was obtained due to the countless SiC particles. By increasing the deposition time, the ultrathin SiC skeleton was formed as shown in Fig. 3c and d. SiC was hard but brittle, which meant many micro interfaces and laminated particles might be induced by the collapse of the SiC coating. It should be stressed that the interfaces and particles played a vital role in the enhancement of the electromagnetic wave absorption ability [31]. Besides, the cladding structure of both the PCF and SiC skeleton could improve the compression strength to some extent,
To study the impact of the SiC coating on the microwave absorption mechanism, the frequency dependence of the permeability and complex permittivity of PCF and SiC/PCF were investigated. The complex permittivity consisted of the storage and loss capacity of electric energy, which were defined as the real part (ε0 ) and the imaginary part (ε00 ) respectively, while the permeability was composed of the real part (m0 ) and the imaginary part (m00 ), which were associated with the magnetic energy [32]. As shown in Fig. 4a and b, both m00 and m0 of the complex permeability almost remained unchanged within the frequency of 2.00e18.00 GHz, which indicated that both PCF and SiC/PCF were non-magnetic or weak magnetic. Hence, the main research was necessarily restricted to the complex permittivity. Fig. 4a exhibited the variation circumstance of ε0 and ε00 of PCF with the measured frequency. It was obvious that the values of ε0 and ε00 dropped immediately as the frequency increased, and then leveled out at high frequencies. However, the changed trend had a great difference compared with that of SiC/PCF in Fig. 4b. Although the ε0 value of SiC/PCF also showed a declining trend, the changes were relatively flat firstly but decreased sharply after a small increase. For ε00 values, it offered upgrade firstly than descending latter tendency, which indicated the complicated variation phenomena, especially at high frequencies. In contrast, a considerable reduction occurred at a specific frequency between 2.00 and 18.00 GHz after CVD process as shown in Fig. 4c and d. The mechanism behind this was that the increase in the angular frequency caused the decline in ε0 , which was regarded as the polarization relaxation, especially at the lower frequency [33]. Besides, the low value of ε00 meant that little attenuation occurred. When the absorbent absorbed the electromagnetic wave, it could not be reflected or transmitted. It indicated
Fig. 3. Chain links of PCF (a) and SiC/PCF (c); Junctions of PCF (b) and SiC/PCF (d).
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Fig. 4. Electromagnetic parameters of PCF (a) and SiC/PCF (b); comparison diagram of real part (c) and imaginary part (d) between PCF and SiC/PCF.
that the SiC coating played a vital role in altering the complex permittivity of SiC/PCF, which might result from the unique dielectric properties of the SiC materials [34]. The complex permittivity of PCF was higher than that of SiC/PCF which resulted in more reflection, and it was harmful to the impedance match. Here, ε00 was also written as [35]: 00
ε ¼ 1=pε0 rf
(1)
Where the ε0 was the dielectric constant in the vacuum, the r was the electrical resistivity, and the f was the measured frequency. When the value of ε00 became higher, r became lower, which would lead to the high electrical conductivity. The high electrical conductivity and skin depth effect were closely interrelated, causing microwave reflection [36]. Therefore, a comparatively low value of the dielectric loss was beneficial to the excellent microwave absorption performance. Moreover, the tangent of the dielectric loss defined as dε usually stated the relationship of ε0 and ε00 as follows [37]:
tan dε ¼ ε
00
. ε0
(2)
Fig. 5 displayed the tandε variation of PCF and SiC/PCF at different frequencies. The red curve was below the gray one
Fig. 5. Dielectric loss tagents of PCF and SiC/PCF.
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Fig. 6. Cole-Cole plots of PCF (a) and SiC/PCF (b).
represented that the dielectric loss of SiC/PCF was much lower than that of PCF. Based on the Debye theory, the link of ε0 and ε00 could also be presented as [38]:
. ε0 ¼ ε∞ þ ðεs ε∞ Þ 1 þ u2 t2 00
ε ¼ ðεs ε∞ Þut
(3)
. 1 þ u2 t2 þ sac =uε0
(4)
Where the sac was the alternative conductivity, the t was the polarization relaxation time, the u was the angular frequency, the εs was the static permittivity, and the ε∞ was the high-frequency limit relative dielectric permittivity. The second part of Eq. (4) provided slight contributions for ε00. Hence, the interrelationship of ε0 and ε00 could be simplified as:
00 2 2 ε þ ðε0 ðεs þ ε∞ Þ=2Þ ¼ ððεs ε∞ Þ=2Þ2
(5)
Eq. (5) was the property of the circle using ((εs þ ε∞)/2, 0) as the center, and the Cole-Cole curves of PCF and SiC/PCF were illustrated in Fig. 6. The Cole-Cole curve of SiC/PCF composing of multiple semi-cylindrical shapes, was much more complicated than that of PCF. It was attributed to the multi-relaxation dielectric properties, which might originate from the incomplete carbon structures in
PCF, the defect polarization of the groups as well as the multiinterface polarizations in SiC/PCF hybrids. For further understanding the microwave absorption mechanism entirely, the impedance matching ratio value (Zr) and the attenuation constant (a) of PCF and SiC/PCF were calculated, which was considered to be two essential factors. Zr represented the effective absorbing microwave, while a meant the integral attenuation ability. In this work, Zr was expressed as follows [39]:
Zr ¼ Z=Z0 ¼ ðmr =εr Þ1=2 00
mr ¼ m0 jm 00
εr ¼ ε0 jε
(6) (7) (8)
Where the εr was the complex permittivity, the mr was the permeability, the Z0 was the impedance of the free space, and the Z was the impedance value of the absorbent. Fig. 7a showed the impedance matching ratio curves of PCF and SiC/PCF. Clearly, the ideal zero-reflection could be obtained only if mr and εr were equal. Although the values of Zr were quite small, a significant enhancement occurred after depositing the ultrathin SiC coating. It was worth noting that Zr was relatively higher at high frequencies around 17.60 GHz, which meant that the optimum absorption property might occur near that range.
Fig. 7. Impedance matching ratio (a) and attenuation constant (b) of PCF and SiC/PCF.
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Meanwhile, to the best of our knowledge, a could be counted as [40]:
a ¼ 20:5 pf
00
00
m ε m0 ε0
2
2 0:5 00 00 þ m0 ε þ m ε0
!0:5 , c
(9)
Where the c was the velocity of light. Obviously, a strong ε00 and m00 might result in a higher a. The attenuation constant value curves of PCF and SiC/PCF were exhibited in Fig. 7b. It could be observed that PCF had a higher attenuation constant than that of SiC/PCF, which showed that a large proportion of the incident microwave was absorbed by the objects in PCF. Based on the above analysis, SiC/PCF possessed a higher impedance matching ratio while the attenuation constant was relatively lower. To probe the microwave absorption properties of PCF and SiC/PCF in more detail, Zin was defined as the input impedance of the absorber in the air, which was given by Ref. [41]:
i h Zin ¼ Z0 Zr tanh jð2pfd=cÞðmr εr Þ1=2
(10)
The reflection loss (RL) was determined by Zin and Z0 according to the metal backplane model, and the expression was as follows [42]:
RL ¼ 20 logjðZin Z0 Þ=ðZin þ Z0 Þj
(11)
Fig. 8 showed the variation of the reflection loss values of the PCF-wax and SiC/PCF-wax composites in the overall frequencies. In general, the values of the reflection loss should be less than 10 dB, that was to say that more than 90% of the microwaves were absorbed by the absorber. The 3D plots of the reflection loss values
of the PCF-wax composite in Fig. 8a displayed that all values were above 10 dB, which was much more significant in Fig. 8b. It could be stated that PCF was not the appropriate microwave absorbing material. However, it was gratifying that SiC/PCF possessed excellent microwave absorbing properties as displayed in Fig. 8c. A minimum reflection loss of 25.93 dB could be gained at 17.20 GHz when the thickness of the absorber was 1.05 mm. And the reflection loss less than 10 dB was located in the whole thickness with the frequency locating in 3.00e18.00 GHz. Compared with PCF, the results indicated the practical application of the resultant SiC/PCF with different thicknesses could be realized at specific frequencies. In addition, we picked the as-prepared samples with the thickness varying from 1.00 to 5.00 mm. Fig. 9a represented the reflection loss value curves of the PCF-wax composite. It further demonstrated that it could not reach 10 dB regardless of the thicknesses and the frequencies. For the SiC/PCF-wax composite, the minimum reflection loss value increased and shifted to lower frequencies with the increasing thickness of the composite as shown in Fig. 9b. The reflection loss value descended to its lowest point at 25.93 dB, while the highest effective absorption bandwidth (fE) was obtained at the thickness of 1.15 mm, which ranged from 14.20 to 17.44 dB (Fig. 9c). Fig. 9d showed the effective absorption bandwidth of the PCF-wax composite with various coating thicknesses. It was obvious that the effective bandwidth frequency could reach the highest point only when the absorber thickness was relatively thin. As the thickness increased, the effective bandwidth frequency decreased, which matched well with Fig. 9b and c. Apparently, the impedance matching ratio of SiC/PCF was higher while the attenuation constant was relatively lower than that of PCF, but it showed enhanced microwave absorbing ability. To evaluate the effect of the impedance matching ratio as well as the
Fig. 8. 3D plots (a, c) and contour plots (b, d) of PCF-wax and SiC/PCF-wax composites in the overall frequency.
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Fig. 9. Reflection loss curves of PCF-wax (a) and SiC/0PCF-wax composites (b); reflection loss curve of SiC/PCF-wax composite at thickness of 1.00 and 1.05 mm (c); effective absorption bandwidth of SiC/PCF-wax composite with different thicknesses (d).
attenuation constant on the reflection loss, we selected SiC/PCF as an example to illustrate the importance of the two factors. Fig. 10 clearly exhibited the frequency dependence of the impedance matching ratio, attenuation constant, and the reflection loss with
the matching thickness of 1.05 mm. When the attenuation constant reached the highest point of 241.86 at 17.60 GHz, the impedance matching ratio was 0.2467 Np/m and the reflection loss was 22.35 GHz. In another case, when the impedance matching
Fig. 10. Reflection loss, attenuation constant, and the impedance matching ratio for SiC/PCF-wax composite with 1.05 mm.
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ratio reached its peak of 0.2474 Np/m at 17.00 GHz, the attenuation constant was 216.53 and the reflection loss was 23.03 dB. In other words, the minimum reflection loss was obtained where the impedance matching ratio was not the highest as well as the attenuation constant. When the minimum reflection loss was gained, the impedance matching ratio and attenuation constant were 0.2471 and 218.26 Np/m, respectively. It demonstrated that the impedance matching ratio was chief factor as the value was close to the highest one. Obviously, the high attenuation effect made no sense with little incident microwaves. Only if most microwaves were absorbed by the absorber, it would show electromagnetic shielding characteristic. Therefore, it provided an actual guidance for designing the excellent microwave absorbing materials by taking into accounts both the impedance matching ratio and the attenuation constant. 4. Conclusion In summary, the exceptional microwave absorbing SiC/PCF composites were fabricated successfully in this paper, and the main results were shown as follows: (1) The preparation process of the SiC/PCF composites consisted of stable treatment, carbonization stage and CVD process. The as-prepared sample possessed a unique cladding structure with the reticulated SiC network wrapping around the PCF skeleton, which was believed to favor the microwave absorption. (2) The SiC coating had a marked impact on the complex permittivity, which further affected the microwave absorbing property. The minimum reflection loss of 25.93 dB was obtained at the measured frequency of 17.20 GHz with the matching thickness of 1.05 mm, and the reflection loss could drop below 10 dB in the whole thickness with the frequency ranging from 3.00 to 18.00 GHz. (3) The absorption mechanism of the SiC/PCF composites was further investigated. The microwave absorbing performance was a function of both the impedance matching ratio and the attenuation constant. It provided some useful guidances for designing the excellent microwave absorbing materials in the future. Acknowledgements This work was supported by the National Natural Science Foundation of China [grant numbers 51772151, 51761145103]; and the Priority Academic Program Development of Jiangsu Higher Education Institutions. References [1] S. Lee, I. Jo, S. Kang, B. Jang, J. Moon, J.B. Park, S. Lee, S. Rho, Y. Kim, B.H. Hong, Smart contact lenses with graphene coating for electromagnetic interference shielding and dehydration protection, ACS Nano 11 (2017) 5318e5324. https://doi.org/10.1021/acsnano.7b00370. [2] Y. Qian, H. Wei, J. Dong, Y. Du, X. Fang, W. Zheng, Y. Sun, Z. Jiang, Fabrication of urchin-like ZnO-MXene nanocomposites for high-performance electromagnetic absorption, Ceram. Int. 43 (2017) 10757e10762. https://doi.org/10. 1016/j.ceramint.2017.05.082. [3] L. Gao, W. Zhou, F. Luo, D. Zhu, J. Wang, Dielectric and microwave absorption properties of KNN/Al2O3 composite ceramics, Ceram. Int. 43 (2017) 12731e12735. https://doi.org/10.1016/j.ceramint.2017.06.158. [4] F. Wu, A. Xie, M. Sun, Y. Wang, M. Wang, Reduced graphene oxide (RGO) modified spongelike polypyrrole (PPy) aerogel for excellent electromagnetic absorption, J. Mater. Chem. A 3 (2015) 14358e14369. https://doi.org/10.1039/ c5ta01577d. [5] Y. Zhang, Y. Huang, H. Chen, Z. Huang, Y. Yang, P. Xiao, Y. Zhou, Y. Chen, Composition and structure control of ultralight graphene foam for highperformance microwave absorption, Carbon 105 (2016) 438e447. https://
doi.org/10.1016/j.carbon.2016.04.070. [6] J. Chen, X. Liang, B. Quan, Z. Yang, Y. Du, G. Ji, 3D flake-like Bi2Te3 with outstanding lightweight electromagnetic wave absorption feature, Part. Part. Syst. Char. 35 (2018), 1700468. https://doi.org/10.1002/ppsc.201700468. [7] H. Zhao, Y. Cheng, X. Liang, Y. Du, G. Ji, Constructing large interconnect conductive networks: an effective approach for excellent electromagnetic wave absorption at gigahertz, Ind. Eng. Chem. Res. 57 (2018). https://doi.org/ 10.1021/acs.iecr.7b05141. [8] Y. Wang, Z. Peng, W. Jiang, Controlled synthesis of Fe3O4@SnO2/RGO nanocomposite for microwave absorption enhancement, Ceram. Int. 42 (2016) 10682e10689. https://doi.org/10.1016/j.ceramint.2016.03.180. [9] Y. Lai, S. Wang, D. Qian, S. Zhong, Y. Wang, S. Han, W. Jiang, Tunable electromagnetic wave absorption properties of nickel microspheres decorated reduced graphene oxide, Ceram. Int. 43 (2017) 12904e12914. https://doi.org/ 10.1016/j.ceramint.2017.06.188. [10] J. Wu, Z. Ye, W. Liu, Z. Liu, J. Chen, The effect of GO loading on electromagnetic wave absorption properties of Fe3O4/reduced graphene oxide hybrids, Ceram. Int. 43 (2017) 13146e13153. https://doi.org/10.1016/j.ceramint.2017.07.007. [11] M. Han, X. Yin, Z. Hou, C. Song, X. Li, L. Zhang, L. Cheng, Flexible and thermostable graphene/SiC nanowire foam composites with tunable electromagnetic wave absorption properties, Acs. Appl. Mater. Interfaces 9 (2017) 11803e11810. https://doi.org/10.1021/acsami.7b00951. [12] D. Ding, Y. Wang, X. Li, R. Qiang, P. Xu, W. Chu, X. Han, Y. Du, Rational design of core-shell Co@C microspheres for high-performance microwave absorption, Carbon 111 (2017) 722e732. https://doi.org/10.1016/j.carbon.2016.10. 059. [13] R. Shu, G. Zhang, X. Wang, X. Gao, M. Wang, Y. Gan, J. Shi, J. He, Fabrication of 3D net-like MWCNTs/ZnFe2O4 hybrid composites as high-performance electromagnetic wave absorbers, Chem. Eng. J. (2017). https://doi.org/10.1016/j. cej.2017.12.106. [14] Y. Cheng, M. Tan, P. Hu, X. Zhang, B. Sun, L. Yan, S. Zhou, W. Han, Strong and thermostable SiC nanowires/graphene aerogel with enhanced hydrophobicity and electromagnetic wave absorption property, Appl. Surf. Sci. 448 (2018) 138e144. https://doi.org/10.1016/j.apsusc.2018.04.132. [15] W. Duan, X. Yin, F. Cao, Y. Jia, Y. Xie, P. Greil, N. Travitzky, Absorption properties of twinned SiC nanowires reinforced Si3N4 composites fabricated by 3dprinting, Mater. Lett. 159 (2015) 257e260. https://doi.org/10.1016/j.matlet. 2015.06.106. [16] F. Ye, L. Zhang, X. Yin, Y. Zhang, L. Kong, Y. Liu, L. Cheng, Dielectric and microwave-absorption properties of SiC nanoparticle/SiBCN composite ceramics, J. Eur. Ceram. Soc. 34 (2014) 205e215. https://doi.org/10.1016/j. jeurceramsoc.2013.08.005. [17] P. Wang, L. Cheng, Y. Zhang, L. Zhang, Flexible SiC/Si3N4 composite nanofibers with in Situ embedded graphite for highly efficient electromagnetic wave absorption, Acs. Appl. Mater. Interfaces 9 (2017) 28844e28858. https://doi. org/10.1021/acsami.7b05382. [18] J. Bi, Y. Gu, Z. Zhang, S. Wang, M. Li, Z. Zhang, Core-shell SiC/SiO2 whisker reinforced polymer composite with high dielectric permittivity and low dielectric loss, Mater. Des. 89 (2016) 933e940. https://doi.org/10.1016/j. matdes.2015.10.050. [19] F. Moglie, D. Micheli, S. Laurenzi, M. Marchetti, V. Mariani Primiani, Electromagnetic shielding performance of carbon foams, Carbon 50 (2012) 1972e1980. https://doi.org/10.1016/j.carbon.2011.12.053. [20] S. Dong, P. Hu, X. Zhang, J. Han, Y. Zhang, X. Luo, Carbon foams modified with in-situ formation of Si3N4 and SiC for enhanced electromagnetic microwave absorption property and thermostability, Ceram. Int. 44 (2018) 7141e7150. https://doi.org/10.1016/j.ceramint.2018.01.156. [21] M. Inagaki, T. Morishita, A. Kuno, T. Kito, M. Hirano, T. Suwa, K. Kusakawa, Carbon foams prepared from polyimide using urethane foam template, Carbon 42 (2004) 497e502. https://doi.org/10.1016/j.carbon.2003.12.080. [22] F. Wu, M. Sun, W. Jiang, K. Zhang, A. Xie, Y. Wang, M. Wang, A self-assembly method for the fabrication of a three-dimensional (3D) polypyrrole (PPy)/ poly(3,4-ethylenedioxythiophene) (PEDOT) hybrid composite with excellent absorption performance against electromagnetic pollution, J. Mater. Chem. C 4 (2016) 82e88. https://doi.org/10.1039/C5TC02887F. [23] S. Farhan, R. Wang, K. Li, Carbon foam decorated with silver particles and in situ grown nanowires for effective electromagnetic interference shielding, J. Mater. Sci. 51 (2016) 7991e8004. https://doi.org/10.1007/s10853-0160068-4. [24] R. Narasimman, S. Vijayan, K.S. Dijith, K.P. Surendran, K. Prabhakaran, Carbon composite foams with improved strength and electromagnetic absorption from sucrose and multi-walled carbon nanotube, Mater. Chem. Phys. 181 (2016) 538e548. https://doi.org/10.1016/j.matchemphys.2016.06.091. [25] R. Kumar, S.R. Dhakate, T. Gupta, P. Saini, B.P. Singh, R.B. Mathur, Effective improvement of the properties of light weight carbon foam by decoration with multi-wall carbon nanotubes, J. Mater. Chem. A 1 (2013) 5727e5735. https://doi.org/10.1039/c3ta10604g. [26] S. Xiao, H. Mei, D. Han, K.G. Dassios, L. Cheng, Ultralight lamellar amorphous carbon foam nanostructured by SiC nanowires for tunable electromagnetic wave absorption, Carbon 122 (2017) 718e725. https://doi.org/10.1016/j. carbon.2017.07.023. [27] S. Farhan, R. Wang, K. Li, Electromagnetic interference shielding effectiveness of carbon foam containing in situ grown silicon carbide nanowires, Ceram. Int. 42 (2016) 11330e11340. https://doi.org/10.1016/j.ceramint.2016.04.054. [28] X. Ye, Z. Chen, S. Ai, B. Hou, J. Zhang, Q. Zhou, H. Liu, S. Cui, Effect of thickness
X. Ye et al. / Journal of Alloys and Compounds 791 (2019) 883e891
[29]
[30]
[31]
[32]
[33]
[34]
[35]
of SiC films on compression and thermal properties of SiC/CF composites, Ceram. Int. (2018). https://doi.org/10.1016/j.ceramint.2018.11.158. Z. Fang, C. Li, J. Sun, H. Zhang, J. Zhang, The electromagnetic characteristics of carbon foams, Carbon 45 (2007) 2873e2879. https://doi.org/10.1016/j.carbon. 2007.10.013. B. Zhong, T. Sai, L. Xia, Y. Yu, G. Wen, High-efficient production of SiC/SiO2 core-shell nanowires for effective microwave absorption, Mater. Des. 121 (2017) 185e193. https://doi.org/10.1016/j.matdes.2017.02.058. X. Liang, B. Quan, Y. Sun, G. Ji, Y. Zhang, J. Ma, D. Li, B. Zhang, Y. Du, Multiple interfaces structure derived from metal-organic frameworks for excellent electromagnetic wave absorption, Part. Part. Syst. Char. 34 (2017), 1700006. https://doi.org/10.1002/ppsc.201700006. Y. Peng, Z. Meng, C. Zhong, J. Lu, W. Yu, Z. Yang, Y. Qian, Hydrothermal synthesis of MoS2 and its pressure-related crystallization, J. Solid State Chem. 159 (2001) 170e173. https://doi.org/10.1006/jssc.2001.9146. X. Liang, B. Quan, G. Ji, W. Liu, H. Zhao, S. Dai, J. Lv, Y. Du, Tunable dielectric performance derived from the metal-organic framework/reduced graphene oxide hybrid with broadband absorption, ACS Sustain. Chem. Eng. 5 (2017) 10570e10579. https://doi.org/10.1021/acssuschemeng.7b02565. P. Wang, L. Cheng, L. Zhang, One-dimensional carbon/SiC nanocomposites with tunable dielectric and broadband electromagnetic wave absorption properties, Carbon 125 (2017) 207e220. https://doi.org/10.1016/j.carbon. 2017.09.052. B. Zhao, G. Shao, B. Fan, W. Zhao, R. Zhang, Enhanced microwave absorption capabilities of Ni microspheres after coating with SnO2 nanoparticles, J. Mater. Sci. Mater. Electron. 26 (2015) 5393e5399. https://doi.org/10.1007/s10854015-3087-z.
891
[36] X. Cui, J. Li, J. Mo, J. Fang, B. Zhou, X. Xiao, Effect of the sheet thickness and current damping exponent on the optimum current frequency in electromagnetic forming, Int. J. Adv. Manuf. Technol. 85 (2016) 843e851. https://doi. org/10.1007/s00170-015-7983-4. [37] X. Liang, X. Zhang, W. Liu, D. Tang, B. Zhang, G. Ji, A simple hydrothermal process to grow MoS2 nanosheets with excellent dielectric loss and microwave absorption performance, J. Mater. Chem. C 4 (2016) 6816e6821. https:// doi.org/10.1039/c6tc02006b. [38] X. Liang, B. Quan, G. Ji, W. Liu, Y. Cheng, B. Zhang, Y. Du, Novel nanoporous carbon derived from metal-organic frameworks with tunable electromagnetic wave absorption capabilities, Inorg. Chem. Front. 3 (2016) 1516e1526. https://doi.org/10.1039/C6QI00359A. [39] H.J. Lv, G. Ji, H. Zhang, Y. Du, Facile synthesis of a CNT@Fe@SiO2 ternary composite with enhanced microwave absorption performance, RSC Adv. 5 (94) (2015) 76836e76843. https://doi.org/10.1039/b000000x. [40] X. Zhang, G. Ji, W. Liu, B. Quan, X. Liang, C. Shang, Y. Cheng, Y. Du, Thermal conversion of an Fe₃O₄@metal-organic framework: a new method for an efficient Fe-Co/nanoporous carbon microwave absorbing material, Nanoscale 7 (2015) 12932e12942. https://doi.org/10.1039/c5nr03176a. [41] B. Zhao, B. Fan, G. Shao, W. Zhao, R. Zhang, Facile synthesis of novel heterostructure based on SnO2 nanorods grown on submicron Ni walnut with tunable electromagnetic wave absorption capabilities, Acs. Appl. Mater. Interfaces 7 (2015) 18815. https://doi.org/10.1021/acsami.5b05482. [42] X. Zhang, G. Ji, W. Liu, X. Zhang, Q. Gao, Y. Li, Y. Du, A novel Co/TiO2 nanocomposite derived from a metal-organic framework: synthesis and efficient microwave absorption, J. Mater. Chem. C 4 (2016) 1860e1870. https://doi.org/ 10.1039/c6tc00248j.