silicon carbide composites

Materials Letters 256 (2019) 126634

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Powerful and lightweight electromagnetic-shielding carbon nanotube/graphene foam/silicon carbide composites Yanling Yang, Yu Zuo, Lei Feng ⇑, Xiaojiang Hou, Guoquan Suo, Xiaohui Ye, Li Zhang School of Material Science and Engineering, Shaanxi Key Laboratory of Green Preparation and Functionalization for Inorganic Materials, Shaanxi University of Science and Technology, Xi’an 710021, China

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Article history: Received 19 July 2019 Received in revised form 31 August 2019 Accepted 5 September 2019 Available online 5 September 2019 Keywords: Ceramic composites Carbon nanotubes Defects Interfaces Functional

a b s t r a c t Carbon nanotube/graphene foam/silicon carbide (CNT/GF/SiC) composites are prepared by in-situ growth of CNT in GF and followed by infiltration and pyrolysis of CNT-dispersed polycarbosilane. Results show that the CNT/GF/SiC composites exhibit outstanding electromagnetic interface (EMI) shielding effectiveness (SE) of 32.1 dB in X-band, especially the specific SE reaches up to 33.8 dB cm3/g with a low density of 0.95 g/cm3. The interconnected conductive graphene network improves the conductivity and sharply increases electric loss; meanwhile, the rich structural defects and multiscale interfaces including GFCNT interface and CNT-SiC interface offer additional polarization loss, both of which endow composites with outstanding EMI shielding performance. Ó 2019 Elsevier B.V. All rights reserved.

1. Introduction Silicon carbide (SiC) ceramic is one of the most potential hightemperature structural materials by virtue of its extraordinary mechanical and physical properties [1]. However, due to the relatively low electrical conductivity, SiC ceramic is insufficient to meet the requirements of high electromagnetic interference (EMI) shielding efficiency (SE) which is at least 20 dB for commercial applications. To obtain a high SE, conductive carbon materials such as carbon fiber (Cf), pyrocarbon (PyC), graphite and graphene nanoplatelets (GNPs) have been incorporated into SiC ceramics as conductive filler, such as Cf/SiC [1], Cf/SiC-Si [2], Cf/(PyC-SiC)n [3], SiC/PyC-SiC [4], graphite/SiC [5] and GNPs/SiC [6]. However, for lightweight shielding materials, EMI shielding ability is often evaluated by specific SE (SSE, SE divided by density) [7]. Considering this, an attractive strategy of fabricating SiC-based ceramics with high SSE is inspired by use of 3D hybridized carbon nanostructures made by connecting 1D carbon nanotube (CNT) with 2D graphene through CAC bonding, such as CNT/graphene foam (CNT/GF) and graphene/CNT foam. These 3D hybrids have high porosity and electrically conductive network, which are the charming building blocks for lightweight EMI shielding materials. To increase SSE as far as possible, it is necessary to further create more structural defects and complex interfaces in materials, leading to ⇑ Corresponding author. E-mail address: [email protected] (L. Feng). https://doi.org/10.1016/j.matlet.2019.126634 0167-577X/Ó 2019 Elsevier B.V. All rights reserved.

strong polarization and absorption of electromagnetic waves (EMWs) [3,8]. Towards this goal, EMI shielding CNT/GF/SiC composites are prepared by infiltration of CNT/GF with CNTdispersed polycarbosilane (PCS) followed by pyrolysis.

2. Material and methods Graphene was synthesized on nickel foam by chemical vapor deposition (CVD) with a mixture of H2/Ar/CH4 gas flow at 1000 °C for 10 min followed by a rapid cooling to room temperature. Growth of CNT in graphene/nickel foam was conducted by injection CVD (ICVD) according to the procedure described in Ref. [9]. GF (5.7 mg/cm3) and CNT/GF (8.6 mg/cm3) were obtained by etching away nickel templates using hot HCl (2 M) solution. PCS (99.9 wt%) was dissolved into xylene dispersed without and with ICVD-produced CNT to form PCS/xylene and CNT/PCS/ xylene impregnation solution by weight ratios of 2/3 and 3/37/60, respectively. The CNT + GF/SiC + CNT composite (CNT both on GF and in SiC matrix) was fabricated by infiltrating CNT/ PCS/xylene into CNT/GF followed by drying and pyrolysis at 1200 °C in Ar atmosphere. For comparison, porous SiC, GF/SiC, GF/SiC + CNT (CNT in SiC matrix) and CNT + GF/SiC (CNT only on GF) composites were fabricated. Infiltration and pyrolysis processes were repeated until the density of all the samples reached 0.95 g/cm3. The preparation procedure and contents of SiC and CNT in each sample are shown in Fig. 1. Morphology, microstructure and defect level of GF and CNT/GF were investigated by scan-

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Fig. 1. Schematic of preparation procedure of various composites.

ning electron microscopy (SEM, FEI Verios 460), transmission electron microscopy (TEM, FEI Tecnai F20G2), Raman spectroscopy (Renishaw inVia) and X-ray photoelectron spectroscopy (XPS, KAlpha). Weight fraction of composition was calculated by comparing weights of foam and composites. Crystal structure of SiC was detected by X-ray diffraction (XRD, X’ Pert Pro). Electrical conductivities of samples were examined by four-point probe method. Sparameters of samples with dimension of 22.86  10.16  2.5 mm3 were measured on vector network analyzer (VNA, MS4644A) using wave-guide method in X-band (8.2– 12.4 GHz). 3. Results and discussion The GF inherits and copies the interconnected 3D scaffold structure of nickel foam (Fig. 2a), and exhibits a hollow wall structure observed from a broken foam (Fig. 2b). Abundant graphene edges are formed after removing nickel template, offering massive structural defects [8]. Fig. 2c shows the CNT is uniformly grown on pore walls of GF. These nanotubes have multi-walled structure with a diameter of 50 nm (Fig. 2d). High-resolution TEM image at GFCNT junction area exhibits continuous graphitic walls (Fig. 2e),

indicating a seamless CAC bonding [10]. Some five- or sevenmembered ring defects exist in these areas accompanied by sp3 hybridized carbon structures [11], leading to the crystal lattice curvature. Raman spectrum of the GF and CNT/GF are shown in Fig. 2f, where the intensity ratio of disorder-induced D band (1531 cm 1) and tangential G band (1580 cm 1), ID/IG, can reflect their defect level [12]. The ID/IG of GF is 0.16 and increases to 1.19 after CNT growth, indicating a great increase of defects that are due to the formed GF-CNT interfaces containing rich disordered structures. The defect level is quantified by detecting the contents of basal-plane sp2 and defect sp3 carbon atoms using XPS. The C 1s peaks of GF and CNT/GF are displayed in Fig. 2g, which is chiefly deconvoluted into four subpeaks: sp2 CAC (284.4 eV), sp3 CAC (285.5 eV), CAO (286.4 eV) and C@O (287.5 eV) bonds. The ratio of sp3/sp2 increases from 0.08 to 0.17, further confirming the formation of more structural defects after CNT growth. Fig. 3a is a typical SEM image of fractured CNT + GF/SiC + CNT composite, showing clear graphene and abundant CNT pullouts. The composite shows a cellular structure with porosity of 58.3%. The microcellular pores have a homogeneous distribution and are presented into deep holes with diameters of 2–10 lm, resembling GF struts and hollow walls. The XRD spectrum of vari-

Fig. 2. SEM images (a–c), TEM images (d, e), Raman (f) and XPS (g) spectrum of GF (a, b) and CNT/GF (c–e).

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Fig. 3. (a) SEM image of CNT + GF/SiC + CNT composite; (b) XRD spectrum.

Fig. 4. (a) EMI SET and electrical conductivities of various samples, (b) comparison of SER, SEA and SET for various samples; (c) SSE for reported SiC-based composites.

ous samples are shown in Fig. 3b. Main peaks are well matched with the phases of b-SiC (JCPDS card No. 29-1129) and carbon (JCPDS card No. 75-1621) in all composites. The occurrence of carbon peak in neat SiC spectrum suggests the SiC is rich in carbon [3], while the sharp diffraction peaks of carbon found in composites correspond to the crystalline GF and CNT. Comparatively, CNT + GF/SiC + CNT composite with rich structural defects and multiscale interfaces is expected to exhibit a high EMI SE. Fig. 4a and b show average electrical conductivities of various samples and their reflection loss (SER), absorption loss (SEA) and total SE (SET), respectively. The conductivities of porous SiC, GF/ SiC, GF/SiC + CNT, CNT + GF/SiC and CNT + GF/SiC + CNT composites are 6.8  10-4, 1.72, 2.06, 2.19 and 2.24 S/cm, and the corresponding average SET are 17.4, 23.5, 26.1, 29.9 and 32.1 dB, respectively. The interconnected conductive graphene network offers a fast electron transport channel resulting in an improved conductivity and EMI SE. The SER of five samples is 7.6, 8.7, 9.2, 10.1 and 10.8 dB, and the corresponding SEA is 9.8, 14.8, 16.9, 19.8 and 21.3 dB, respectively. Clearly, SEA increases greatly after introducing GF and CNT, while SER results in a slight improvement, i.e., the increase of SET is mainly ascribed to the EMW absorption. By comparing SiC and GF/SiC composites, the SEA is increased by 51%, and further enhanced by 44% after introducing CNT both on GF and in SiC matrix. It has been demonstrated that porous structure not only ensures the penetration of incident EMWs into materials, but also facilitates the dissipation of incident waves by multiple reflection [13,14]. However, the significant increment in SE of porous SiC here is mainly attributed to the GFs which play the key role in the substantially improved EMW absorption. The intricate reticulated conductive structures formed by 3D interconnected GF initiatively and intensely response to the incident EMWs as microwave time-varying electromagnetic-field-induced currents occur. Such long-range induced currents fast decay in the

resistive network and convert into thermal energy, leading to rapid attenuation of incident EMWs [13]. Furthermore, the rich structural defects (edge sites of graphene sheets and deformation of crystal lattice in junction region) [8,14], and multiscale interface (GF-CNT interface and CNT-SiC interface) offer additional polarization loss [3,14], resulting in further increase in SEA. Fig. 4c presents the comparison of SSE between our composites and previously reported SiC-based composites. It is apparent that high EMI SE combined with low density imparts CNT + GF/SiC + CNT composite with great SSE of 33.8 dB cm3/g, indicating an outstanding lightweight EMI shielding material. 4. Conclusions The CNT/GF/SiC composites with great SSE are prepared by infiltration of CNT/GF with CNT-dispersed PCS followed by pyrolysis. The interconnected conductive graphene network, rich structural defects and multiscale interfaces greatly enhance both the electrical loss and polarization loss, which gives composites superior EMI shielding ability. Our work provides a potential way to fabricate lightweight high-performance EMI shielding ceramics. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgments This work has been supported by the National Natural Science Foundation of China (Grant Nos. 51702199, 51704188, 61705125

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and 51802181), the Natural Science Foundation of Shaanxi Province under Grant No. 2018JQ5057. References [1] [2] [3] [4]

L.Q. Chen, X.W. Yin, X.M. Fan, et al., Carbon 95 (2015) 10–19. X.M. Fan, X.W. Yin, L.Q. Chen, et al., J. Am. Ceram. Soc. 99 (2016) 1717–1724. Y. Jia, K.Z. Li, L.Z. Xue, et al., Carbon 111 (2017) 299–308. H.Y. Wang, D.M. Zhu, Y. Mu, et al., Ceram. Int. 41 (2015) 14094–14100.

[5] [6] [7] [8] [9] [10] [11] [12] [13] [14]

M.Y. Sun, Y.H. Bai, M.X. Li, et al., J. Euro. Ceram. Soc. 38 (2018) 5271–5281. C. Chen, Y.Q. Tan, X.C. Han, et al., J. Euro. Ceram. Soc. 38 (2018) 5615–5619. F. Shahzad, M. AIhabeb, C.B. Hatter, et al., Science 353 (2016) 1137–1140. Q. Song, F. Ye, X.W. Yin, et al., Adv. Mater. 29 (2017) 1701583. L. Feng, K.Z. Li, J.J. Sun, et al., Appl. Surf. Sci. 355 (2015) 1020–1027. Y. Zhu, L. Li, C.G. Zhang, et al., Nat. Commun. 3 (2012) 1225. M.S. Dresselhaus, A. Jorio, M. Hofmann, et al., Nano Lett. 10 (2010) 751–758. F. Ye, Q. Song, Z. Zhang, et al., Adv. Funct. Mater. 28 (2018) 1707205. Y. Zhang, Y. Huang, T.F. Zhang, et al., Adv. Mater. 27 (2015) 2049–2053. L. Kong, X.W. Yin, H.L. Xu, et al., Carbon 145 (2019) 61–66.