SiBCN composites

Accepted Manuscript Title: Effect of heat treatment temperature on microstructure and electromagnetic shielding properties of graphene/SiBCN composites Authors: Wei Yue, Yongsheng Liu, Mingxi Zhao, Fang Ye, Laifei Cheng PII: DOI: Reference:

S1005-0302(19)30238-5 https://doi.org/10.1016/j.jmst.2019.07.018 JMST 1652

To appear in: Received date: Revised date: Accepted date:

18 July 2018 10 January 2019 15 May 2019

Please cite this article as: Wei Y, Yongsheng L, Mingxi Z, Fang Y, Laifei C, Effect of heat treatment temperature on microstructure and electromagnetic shielding properties of graphene/SiBCN composites, Journal of Materials Science and amp; Technology (2019), https://doi.org/10.1016/j.jmst.2019.07.018 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Effect of heat treatment temperature on microstructure and electromagnetic shielding properties of graphene/SiBCN composites Wei Yue1, Yongsheng Liu1,* [email protected], Mingxi Zhao1, Fang Ye1, Laifei Cheng1 1

Science

and

Technology

on

Thermostructural

Composite

Materials

Laboratory,

Corresponding author.

SC R

*

IP T

Northwestern Polytechnical University, Xi’an 710072, China

[Received 31 July 2018; revised 10 January 2019; accepted 15 May 2019]

Three-dimensional (3D) graphene/SiBCN composites (GF/SiBCN) were prepared by

U

depositing SiBCN ceramics in 3D graphene foam via the chemical vapor infiltration

N

technique. The effect of the heat treatment temperature on the microstructure, phase composition, and electromagnetic properties of the GF/SiBCN composite was

A

investigated. The SiBCN ceramics maintained an amorphous structure in the composite

M

below 1400 oC above which the crystallinity of the free carbon phase gradually increased. While the Si3N4 and B4C phases started to crystallize at 1500 oC and their crystallinity

TE D

increased with temperature, SiC was observed at 1700 ºC. The electromagnetic shielding effectiveness of GF/SiBCN increased with the heat treatment temperature.

EP

Key words: silicon-boron carbonitride ceramics; chemical vapor deposition and

CC

infiltration; heat treatment; electromagnetic shielding effectiveness.

A

1. Introduction

The rapid development of radar detection technologies has resulted in a higher demand of

electromagnetic shielding materials with improved shielding efficiency and temperature resistance for the aerospace industry shielding materials

[3-7]

[1-2]

. As an important candidate for electromagnetic

, graphene presents a number of excellent characteristics such as low

density, high electrical conductivity

[8]

, and large specific surface area

[9]

. However, graphene

has a critical defect that while graphene withstands very high temperatures under an inert

1

atmosphere, this material is susceptible to oxidize under oxygen environments above 200 oC. On the contrary, as a quaternary system based on SiC, Si 3N4, and Si-C-N ceramics, SiBCN has superior thermal stability and oxidation resistance

[10-11]

. In addition, by adjusting the relative

content of each component in the quaternary system, it is possible to tune the relative ratio of the wave-transmission, absorbing, and reflecting phases in the SiBCN ceramics, thereby achieving optimum electromagnetic shielding performance. Therefore, the GF was used as substrate and was surrounded by continuous and compact SiBCN through chemical vapor

IP T

deposition (CVD) process to construct GF/SiBCN composites, which greatly utilized the thermal stability of SiBCN and formed a protective layer of GF to avoid oxidation. Furthermore, the GF/SiBCN integrated the great shielding properties of GF and the

SC R

designability of SiBCN appropriately. Combined the above advantages, the GF/SiBCN composites have great potential to become a new electromagnetic shielding material. Heat treatments have an important influence on the phase composition, microst ructure,

U

and properties of ternary or quaternary Si-based ceramics. Thus, the electromagnetic properties

by the CVD method

[12]

N

of SiBCN ceramics can be adjusted via heat treatment. In the case of SiCN ceramics prepared at high temperatures, nano-SiC and free carbon phases were observed

A

to crystallize at 1400–1600 oC. While these phases gradually improved the electromagnetic

M

absorbing efficiency of the deposited SiCN, the nano-polarization effect disappeared via grain growth at 1700 oC, reducing the electromagnetic absorbing performance. In wave-transparent [13]

(phase composition: Si 3N4 + SiC + C + BN), Si 3N4, BN, and

TE D

type CVD-SiBCN composites

free carbon phases were observed to crystallize at 1500–1600 oC, although the dielectric loss remained nearly unchanged because of the low crystallinity of the free carbon phase. At 1700 C, the dielectric loss of the SiBCN ceramic increased via formation of SiC by the

EP

o

carbothermal reduction reaction.

CC

To reveal the influence of crystallization behavior of SiBCN at high temperatures on the electromagnetic shielding properties, GF/SiBCN composites were heat treated at varying temperatures (i.e., 1400, 1500, 1600, and 1700 oC). The evolution of the microstructure, phase

A

composition, and electromagnetic shielding properties of the GF/SiBCN composites was analyzed. This study aimed to further improve the electromagnetic shielding performance of these materials. 2. Experimental Commercial graphene foam (GF) was used as deposition substrate (Six Carbon Science

2

and Technology Company, Shen Zhen). This material had a bulk density of 0.0033 g/cm3 and an open porosity of 98%. Graphene was grown on the surface of porous nickel, and GF was obtained by subsequently immersing the as-grown graphene in HCl at 80 oC for 24 h to remove Ni. Then, GF was placed in a graphite box with uniform porosity to deposit SiBCN via chemical vapor infiltration at 950 oC. Methyltrichlorosilane (CH 3SiCl3, MTS ≥ 99.99%), boron trichloride (BCl3 ≥ 99.99%), and ammonia (NH 3 ≥ 99.99%) were used as gas precursors. Hydrogen (H2 ≥ 99.99%) was used as the carrier gas of MTS and the dilution gas. Argon (Ar ≥

IP T

99.99%) was used as a protection and dilution gas. The as-obtained GF/SiBCN composites were machined to 24 mm × 12 mm pieces and heat-treated in a hot press furnace under a N 2 atmosphere and at a pressure of 0.3 MPa at varying temperatures (1400, 1500, 1600, and 1700 C).

SC R

o

The weights of the GF/SiBCN composites were measured by electronic balance (Mettler Toledo, AG204) with the precision of 0.0001 g. The shrinkage rate was calculated by the length

U

measured with a Vernier caliper. The microstructure and phase composition were analyzed by

N

scanning electron microscopy (SEM, S-4700, Hitachi, Tokyo, Japan) and X-ray diffraction

A

(XRD, D8-Advance, Bruker, Karlsruhe, Germany), respectively. The Raman spectra of the composites were recorded on a Renishaw Ramoscope device (confocal Raman microscope,

M

inVia, Renishaw, Gloucestershine, UK) to analyze the evolution of the C phase. The chemical bonding was studied by X-ray photoelectron spectroscopy (XPS, K-Alpha; Thermo Scientific,

TE D

Waltham, MA, USA). The shielding effectiveness was calculated by the S parameter, which was measured with a vector network analyzer (VNA, MS4644A; Anritsu, Atsugi, Japan) using the transmission/reflection method

[14-15]

.

EP

3. Results and discussion

CC

3.1 Evolution of microstructure and phase composition of the GF/SiBCN composites 3.1.1 Weight loss and shrinkage rates

A

Table 1 shows the weight loss and shrinkage rates of the GF/SiBCN composites prepared

under an N2 atmosphere for 2 h at varying temperatures (1400–1700 oC). The shrinkage and mass loss rates of the GF/SiBCN composite increased with the heat treatment temperature. The shrinkage of GF/SiBCN composite can be mainly explained in terms of the amorphous state of the deposited SiBCN ceramics. The high-temperature heat treatment increased the energy of the atoms, favored their rearrangement and migration. These phenomena produced a certain volume shrinkage of the SiBCN ceramic in the composite, with graphene also being bent and 3

shrunk simultaneously. The shrinkage of the composite was ultimately manifested as a bending contraction. The GF (impurity-free graphene) exhibited an excellent thermal stability and would not lose weight with temperature under an inert atmosphere. Thus, the weight loss of the GF/SiBCN composite was originated exclusively from the SiBCN ceramics. After the heat treatments at 1400 and 1500 oC, the weight loss rate of the composite was low and it increased significantly after the heat treatment at 1600 oC. Chai

[16]

proposed a

certain solid phase reaction inside the SiBCN associated with the release of gas products ,

IP T

which could interpret the above phenomenon. The shrinkage and mass loss of the composite increased significantly after the heat treatment at 1700 ºC, revealing significant structural changes in the SiBCN ceramic (from amorphous to crystalline).

SC R

3.1.2 Microstructure

The surface morphologies of the GF/SiBCN composites after the heat treatment at different temperatures are shown in Fig. 1. As shown in Fig. 1(a), the surface of the deposited

U

amorphous SiBCN ceramics showed a dense and smooth continuous morphology. As shown in

N

Fig. 1(b), after the heat treatment at 1400 oC, the surface morphology of the GF/SiBCN composite remained nearly unchanged. In contrast, the surface morphologies changed

A

significantly after the heat treatments at 1500–1700 oC. Despite the surface of the composite

M

remained dense and smooth after the heat treatment at 1500 oC, rod-shaped and trapezoidal crystallized products appeared (Fig. 1(c)). The diameter of the rod-shaped particles ranged

TE D

from 0.1 to 0.39 μm and most of them were within 0.1–0.2 μm. The heat treatment at 1600 oC resulted in a uniform and rough surface (Fig. 1(d)), and the crystallized rods and trapezoids was covered. No significant changes in the particle size and the amount of rods. The surface

EP

morphology shifted to a glassy state after the heat treatment at 1700 oC (Fig. 1(e)). At this temperature, the composite showed a rougher and honeycomb-type structure, with higher

CC

amounts of crystallized rod and trapezoid products. We measured the diameter of the crystallized rod and trapezoid products (indicated by arrows). The size of these particles increased significantly (0.4–0.6 μm), suggesting that with new grains crystallized after the heat

A

treatment at 1700 oC, the crystal grains grew simultaneously. At this point, the crystallization process of SiBCN was completed. In summary, the crystallization process of the GF/SiBCN composites was favored with the heat treatment temperature, and the number of types and yield of the crystallized phases also increased with this parameter. The cross-sectional morphologies of the GF/SiBCN composites after the different heat treatments are shown in Fig. 2. The changes of the morphologies of the cross section and the tubular structure on the surface were very different. A smooth and continuous graphene phase 4

was clearly visible after heat treatments at varying temperatures. After the heat treatments at 1400 and 1500 oC, the morphologies of the hollow tubes remained nearly unchanged. When the temperature increased to 1600 oC (Figs. 2(c) and (c-1)), some filaments crystallized in the hollow section of the tube. These filaments possessed curved and straight parts, with diameters ranging from 0.1 to 0.6 μm. The partially enlarged view in the upper right corner of Fig. 2(c-1) revealed that SiBCN nucleated on the inner surface, resulting in line-shaped material. When the temperature was further increased to 1700 oC (Figs. 2(d) and (d-1)), the average diameter of the

IP T

thread increased to 0.5–0.85 μm. As shown in the curve box of Fig. 2(d-1), the SiBCN near graphene (indicated by arrows in Fig. 2(d-1)) crystallized to a higher degree than in other position of the material. Thus, graphene sheets had a significant effect on the crystallization of

SC R

the surrounding SiBCN. Several studies have pointed out that the crystallization of amorphous ceramics is closely related to its phase composition, substrate, and second phase incorporated. The substrate or the second phase incorporated would serve as nucleation centers during the [17-18]

. In this paper, the graphene

U

heat treatment, promoting the crystallization of the ceramic

N

sheets and the amorphous SiBCN matrix possess numerous heterogeneous interfaces. The

A

volume shrinkage of the composite during the heat treatment resulted in an internal stress that gradually concentrated at the heterogeneous interface. The concentrated interfacial stress

M

favored the transition of the SiBCN matrix from amorphous to crystalline state and promoted the crystallization of numerous rod-shaped crystal nuclei. The thermal conductivity of graphene

TE D

is significantly higher than that of SiBCN ceramics. The presence of graphene might provide a driving force for the nucleation and growth of SiBCN on its inner surface, and the tubular center provides enough space for the growth of crystal grains. Therefore, a large number of

EP

curled or linear crystal grains crystallized on the inner surface. These grains showed larger aspect ratios than the surface products. Thus, the closer to graphene is the SiBCN material, the

CC

more complete crystallization will be obtained.

3.1.3 Phase transition

A

The evolution of the crystallization of the C phase is very important in determining the

electromagnetic shielding performance of the composites. Raman spectroscopy is extremely sensitive to the structure of free carbon and therefore is an effective method for tracking the evolution of the C-phase structure. Fig. 3 shows the Raman spectra of the surface of the GF/SiBCN composites. As indicated above, Raman spectra only provides structural transformation on the C phase in SiBCN. All the samples after the heat treatment showed the typical D and G peaks, indicating that the ceramics contained free carbon. After the heat 5

treatment at 1400 oC, the D and G peaks partially overlapped, and the intensities of both peaks were very low, revealing a high level of disorder in the free carbon phase. After the heat treatment at 1500 oC, the D and G peaks separated, revealing higher degrees of crystallization for the free carbon phase. A further increase in the heat treatment temperature resulted in higher D/G peak intensity ratios (ID/IG) and lower FWHM values. The position of the D peak remained unchanged with temperature, while the G peak shifted to higher wave numbers (from 1590 to 1601 cm -1). The 2D peak at 2700 cm -1 appeared after the heat treatment at 1700 oC, and

IP T

the ID/IG reached a maximum. These results indicated that the free carbon phase transformed from amorphous to graphite nanocrystals [19-20].

The crystallization behavior of the GF/SiBCN composites was characterized by XRD. Fig.

SC R

4 shows the XRD patterns of the GF/SiBCN composite after the different heat treatments. After the heat treatment at 1400 ºC, only the (002) diffraction peak of graphene and the amorphous bulge of the SiBCN ceramic were observed, with no new phases crystallized. These results

U

were in line with surface morphology of the composite after the heat treatment at 1400 oC

N

revealed by SEM. The diffraction peaks corresponding to α-Si3N4 and B4C phases appeared at

A

1500 oC. The intensity of these peaks increased with the heat treatment temperature, revealing the crystallinity of these phase increased with the temperature and reached a maximum at 1700 C. The diffraction peaks of SiC only appeared after the heat treatment at 1700 ºC. Since the

M

o

peaks of C phase overlapped with those of α-Si3N4 at 2θ = 26.6°, it was difficult to determine

TE D

the crystallization of the C phase by XRD.

The XPS narrow-spectra showed the existence of B-N species in the original GF/SiBCN composites (Fig. 5) and Nan Chai et al. observed crystallization of BN of a heat-treated [13]

. However, no diffraction peaks of BN were observed in our

EP

wave-transparent SiBCN

samples after heat treatment by XRD. Two possible reasons can explain this phenomenon: (i)

CC

the content of crystallized BN is very low, which prevented XRD from detecting its diffraction peaks and (ii) as proposed by Nan Chai et al., the following carbothermal reduction reaction

A

occurred when the SiBCN prepared by CVD was heat-treated above 1600 °C [21]: 4BN+C→B4C+2N2

(1)

Si3N4+3C→3SiC+2N2

(2)

Since the BN could react with the C-phase and form B4C. Therefore, after the heat treatment at 1700 °C, the intensity of the B4C diffraction peak increased significantly. Fig. 6 shows the XPS bonding analysis of the GF/SiBCN composites after the heat treatments at 1400–1700 oC. Table 2 summarizes the relative contents of the bonds. As shown in Fig. 6, three different B species (B-C, B-N and B-O) were observed, with B-C prevailing at 6

all heat treatment temperatures. These results confirmed the presence of a BN phase. Two different Si species (Si-N and Si-C) were observed. The relative contents of Si-N and Si-C remained constant within the XPS error range after the heat treatments at 1400–1600 oC. However, at 1700 oC, the Si-N content decreased remarkably (from 48.68 to 30.53 at%) while the Si-C content increased (from 51.32 to 69.47 at%). C showed four different species (C -C, C-Si, C-B, and C-O). As mentioned above, the signals of C-B and C-Si overlapped. When the heat treatment temperature increased to 1600 °C, the content of C-Si or C-B species increased

IP T

notably (from 2.77 to 9.44 at%). The change in amounts of Si and C was also indicative of the carbothermal reduction reaction starting at 1600°C, although the extent of the reaction was very low.

SC R

The microstructure of the samples after heat treatments was further studied using transmission electron microscopy (TEM). Fig. 7 shows the TEM images of the GF/SiBCN composites after heat treatment at 1700 oC. As shown in Fig. 7(a), nanoparticles of different

U

sizes (shown by arrows) crystallized after the heat treatment. High-resolution TEM (Fig. 7(a)

N

and (b)) revealed a variety of crystallized phases in the composite. According to the lattice

A

spacing and XRD results, these phases contained nanocrystals of Si 3N4, SiC, B4C and free carbon with chaotic graphite shape. SiC was dispersed with an average grain diameter of 4.4

M

nm, while the Si3N4 grains were larger in diameter. The small-size SiC grains were surrounded by large-size Si3N4, forming numerous nano-interfaces. The content of B 4C was very small, in

TE D

line with the XRD pattern. A layered graphite shaped free carbon phase with numerous defects was also observed. Both the nano-interfaces and defects favor the absorption of electromagnetic wave.

EP

Fig. 8 shows the microstructure evolution of the GF/SiBCN composites during the heat treatment. The prepared composite consisted of an amorphous matrix, graphene, a small

CC

amount of free carbon, and nano SiC grains. Initially, the graphene sheet was straight and flat and, after the heat treatment, it bent because of the shrinkage of the ceramic matrix. After the heat treatment at 1500 oC, both the free carbon content and the crystallinity increased, and

A

Si3N4 and B4C began to crystallize at this point. After the heat treatment at 1600 oC, a curled, thin rod-like Si3N4 phase crystallized in the center of the tube and thickened with the heat treatment temperature. At the same time, SiC gradually crystallized. After the heat treatment at 1700 oC, the crystallization of the free carbon, Si 3N4, B4C, and SiC phases was completed, with some Si3N4 grains gradually growing. In summary, after the heat treatments, GF/SiBCN showed a phase composition comprised of graphene + SiC + α-Si3N4 + B4C + C + BN. 7

3.2 Electromagnetic shielding effectiveness and mechanism The electromagnetic shielding effectiveness of the GF/SiBCN composites after the heat treatments at 1400–1700 oC is shown in Fig. 9. Three kinds of shielding effectiveness gradually increased with the heat treatment temperature. An increase in the reflection shielding effectiveness (SER) reveals an impedance mismatch between the material and the free space increases as the frequency of the electromagnetic wave changes. An increase in absorption

material

[22-23]

IP T

shielding effectiveness (SE A) indicates higher electromagnetic wave attenuation abilities of the . After the heat treatment at 1700 oC, SEA increased by 50% compared to the

untreated sample (16.8 vs 11.2 dB at 10 GHz). SE R improved after the heat treatment at 1400 C and remained nearly unchanged at higher temperatures. SE A improved to a larger extent

SC R

o

compared to SER. After the heat treatment at 1700 oC, the specific shielding effectiveness increased further to 40 dB·cm 3/g. It is generally accepted that a material with a total shielding

most commercial applications

[24]

U

effectiveness of 20 dB (i.e., 99% of the incident electromagnetic wave is shielded) can satisfy . Table 3 summarizes the shielding performance of the

N

C/ceramic composites. After the heat treatments, the GF/SiBCN composites prepared herein

A

showed superior specific shielding effectiveness with minimum thickness. Additionally, the

M

total shielding effectiveness of these materials meet the commercial requirement of 20 dB. Therefore, the GF/SiBCN composites are excellent high-temperature resisting and lightweight

TE D

electromagnetic shielding materials.

The improvement of the electromagnetic shielding effectiveness was carried out in the following two stages: before 1600 oC, the entire GF/SiBCN composite underwent body shrinkage after the heat treatment, and the linear shrinkage rate increased with the temperature

EP

(Table 1). The shrinkage of SiBCN caused the shrinkage of graphene sheets. Since the size of the specimens used in the S-parameter tests was all 22.86 mm × 10.12 mm, the shrinkage of the

CC

composite after the heat treatment resulted in larger volume percentage of graphene in the S-parameter test, thereby increased SEA and SER. At the same time, the Raman spectra showed

A

that the free carbon crystallinity increased with the heat treatment temperature, this resulting in gradual increases of the absorption and shielding effectiveness. In the second stage, at 1700 ºC, the crystallization of SiC and free carbon finalized. At this point, both SiC and free carbon phases were in the form of nanocrystals and formed a conductive network. The carriers could pass through the SiC and free carbon grains by tunneling effect, thereby increasing the leakage current of the ceramic and the conduction losses. Secondly, the number of interfaces, dangling bonds, and defects in the sample increased with the increase in the amount of SiC nanocrystal

8

grains and free carbon phase. Under an alternating electromagnetic field, interfacial and dipole polarizations were generated and relaxation phenomena occurred because the polarizations lagged behind the periodic change of the electromagnetic field, resulting in larger polarizati on losses. Therefore, when the electromagnetic wave penetrated into the interior of the porous composite, part of it was consumed via conduction losses of graphene and another fraction of it was multiply reflected by the skeleton and subsequently dissipated via the conductance and polarization losses of SiBCN.

IP T

When an electromagnetic wave is incident on the surface of a material, reflection precedes absorption. In order to clearly show the contributions of the absorption and reflection shielding effectiveness to the overall shielding effectiveness, Fig. 10 shows the average reflectance,

SC R

transmission and absorption values for the composite as a function of the heat treatment temperature. The total power transmitted was 100% in all cases. The reflected power i ncreased first with the heat treatment temperature and levelled off thereafter at ca. 88% after the heat

U

treatment. The absorbed power followed the opposite trend compared to the reflected power.

N

The absorbed power dropped from 16 to 9% and then increased to 12% with the heat temperature. As indicated above, the free carbon crystallinity was very low, and the absorption

A

of the electromagnetic waves was very weak at 1400 oC. The shrinkage of graphene increased

M

the surface reflection at the expense of decreasing the absorption inside the material. The crystallization of free carbon and SiC increased with the temperature, increasing the absorption

TE D

of electromagnetic waves by the material. Therefore, the absorption coefficient started to increase again. In general, more than 80% of an electromagnetic wave is typically reflected and less than 20% is absorbed before and after heat treatment of materials. The reflection loss was

EP

greater than the absorption loss, in line with the above results. Although the shielding effectiveness (SE) characterizes the ability of a material to shield an electromagnetic wave, it

CC

does not provide the actual shielding of electromagnetic waves. Thus, the absorption shielding effectiveness plays a major role only in the case of there is no surface reflections in the material. The ratio of the electromagnetic wave power reflected on the surface of the material

A

to the power of the original incident electromagnetic wave can therefore characterize the reflective shielding effectiveness of the material. Calculations indicated that this ratio ranged from 0.80 to 0.90 with the heat treatment temperature. The ratio of the electromagnetic wave power absorbed by the material to the electromagnetic wave power incident on the interior of material can be used to characterize the absorbing shielding effectiveness of the material, and the electromagnetic wave power balance diagram revealed this ratio of ca. 0.93–0.98, which meant that as long as the electromagnetic wave penetrated to the interior of the material, most 9

of it could be absorbed. The transmission power decreased from 0.90 to 0.27% with the heat treatment temperature. The transmission power was negligible compared to the reflected electromagnetic wave power and the absorbed electromagnetic wave power. In other words, no electromagnetic wave could substantially penetrate the composite, which reveals the excellent electromagnetic wave shielding properties of the material. 4. Conclusions

IP T

The effects of the heat treatment temperature on the microstructure, phase composition, and electromagnetic shielding properties of GF/SiBCN composites were investigated. The

SC R

following conclusions can be drawn:

(1) The weight loss and shrinkage rates of the composite increased with the heat treatment temperature. After the heat treatment at 1600 oC, the weight loss and the shrinkage of the composite increased significantly as a result of the higher crystallinity of the composite. At this

U

temperature, a weak carbothermal reduction occurred, releasing small amounts of N 2.

N

(2) The amorphous state of the composite was maintained at 1400 oC, and the crystallinity

A

of the free carbon phase gradually increased with the heat treatment temperature. After heat

M

treatment at 1500 oC, Si3N4 and B4C began to crystallize and the crystallinity increased with the heat treatment temperature. SiC did not crystallize until 1700 °C. At this temperature,

TE D

small-sized nano SiC grains were surrounded by large-sized nano-Si3N4 grains, forming many nano-interfaces. These interfaces and defects in the free carbon phases favored the absorption of electromagnetic waves by the material.

(3) The electromagnetic shielding effectiveness of the composites increased with the heat

EP

treatment temperature. After the heat treatment at 1700 oC, the total shielding effectiveness increased from 18.4 to 25.5 dB, while the specific shielding effectiveness increased from 29 to

CC

40 dB·cm3/g. In addition, the absorption shielding efficiency increased to a larger extent than the reflection shielding effectiveness.

A

Acknowledgements This work was supported by the National Natural Science Foundation of China (Nos.

51472201 and 51672217), the National Key Research and Development Program of China (No. 2018YFB1106600) and the Research Fund of the State Key Laboratory of Solidification Processing (Grant No.120-TZ-2015).

10

References [1] M. Chen, X.W. Yin, M. Li, L.Q. Chen, L.F. Cheng, L.T. Zhang, Ceram. Int. 41(2) (2015) 2467-2475. [2] X.M. Liu, Z.J. Yu, L.J. Chen, B.B. Xu, S. Li, X.W. Yin, R. Riedel, J. Am. Ceram. Soc. 100(10) (2017) 4649-4660. [3] A. Bello, O.O. Fashedemi, M. Fabiane, J.N. Lekitima, K.I. Ozoemena, N. Manyala, [4] C. Soldano, A. Mahmood, E. Dujardin, Carbon 48(8) (2010) 2127-2150.

IP T

Electrochim. Acta 114(2) (2013) 48-53. [5] J. Luo, J. Liu, Z. Zeng, C.F. Ng, L. Ma, H. Zhang, J. Lin, Z. Shen, H.J. Fan, Nano Lett. 13(12) (2013) 6136-6143.

SC R

[6] K.S. Kim, Y. Zhao, H. Jang, S.Y. Lee, J.M. Kim, K.S. Kim, J.H. Ahn, P. Kim, J.Y. Choi, B.H. Hong, Nature 457(7230) (2009) 706-710.

[7] S. Bae, H. Kim, Y. Lee, X. Xu, J.S. Park, Y. Zheng, J. Balakrishnan, T. Lei, H.R. Kim, Y.I.

U

Song, Nat. Nanotechnol. 5(8) (2010) 574-578.

N

[8] A.K. Geim, K.S. Novoselov, Nat. Mater. 6(3) (2007) 183-191.

[9] T. Booth, A.K. Geim, D. Jiang, V.V. Khotkevich, S.M. Morozov, K.S. Novoselov, Proc.

A

Natl. Acad. Sci. USA 102(30) (2005) 10451-10453.

M

[10] S.H. Lee, M. Weinmann, F. Aldinger, Acta Mater. 56(7) (2008) 1529-1538. (1996) 796-798.

TE D

[11] R. Riedel, A. Kienzle, W. Dressler, L. Ruwisch, J. Bill, F. Aldinger, Nature 382(6594) [12] J.M. Xue, X.W. Yin, H.X. Pan, X.F. Liu, L.T. Zhang, L.F. Cheng, J. Am. Ceram. Soc. 99(8) (2016) 2672-2679.

EP

[13] J.P. Li, M.X. Zhao, Y.S. Liu, N. Chai, F. Ye, H.L. Qin, L.F. Cheng, L.T. Zhang, Materials 10(6) (2017) 655.

CC

[14] A.M. Nicolson, G.F. Ross, IEEE Trans. on Instrum. Meas. 19(4) (1970) 377-382. [15] W.B. Weir, Proc. IEEE 62(1) (1974) 33-36. [16] N. Chai, The Processing and Electromagnetic Properties of Si-B-C-N Ceramics Fabricated

A

by Chemical Vapor Deposition, Master. Thesis, Northwestern Polytechnical University, 2016. (in Chinese)

[17] Y.J. Zhang, X.W. Yin, F. Ye, L. Kong, J. Eur. Ceram. Soc. 34(5) (2014) 1053-1061. [18] J.M. Xue, X.W. Yin, F. Ye, L.L. Zhang, L.L. Cheng, J. Am. Ceram. Soc. 101(3) (2017) 1201-1210. [19] A.C. Ferrari, J. Robertson, Phys. Rev. B 64(7) (2001) 075-414. [20] A.C. Ferrari, J. Robertson, Phys. Rev. B 61(20) (2000) 14095-14107. 11

[21] H. Zhang, M. Hong, P. Chen, A.J. Xie, Y.H. Shen, J. Alloy. Compd. 665 (2016) 381-387. [22] P.S. Neelakanta, Handbook of Electromagnetic Materials: Monolithic and Composite Versions and their Applications, first ed., Crc Press, Florida, America, 1995. [23] C.R. Paul, Introduction to electromagnetic compatibility, second ed., John Wiley & Sons, 2006, pp. 14-22. [24] Y. Yang, M.C. Gupta, K.L. Dudley, R.W. Lawrence, Nano Lett. 5(11) (2005) 2131-2134. [25] Y.C. Qing, Q.L. Wen, F. Luo, W.C. Zhou, J. Mater. Chem. C 4(22) (2016) 4853-4862.

IP T

[26] Y.C. Qing, Q.L. Wen, F. Luo, W.C. Zhou, D.F. Zhu, J. Mater. Chem. C. 4(2) (2015) 371-375.

[27] Y.Q. Tan, H. Luo, H.B. Zhang, X.S. Zhou, S.M. Peng, AIP Adv. 6(3) (2016) 279-796.

SC R

[28] X.M. Li, L.T. Zhang, X.W. Yin, J. Am. Ceram. Soc. 95(3) (2012) 1038-1041.

A

CC

EP

TE D

M

A

N

U

[29] C.S. Xiang, Y.B. Pan, X.J. Liu, X.W. Sun, Appl. Phys. Lett. 87(12) (2005) 56.

12

Figure and table captions

CC

EP

TE D

M

A

N

U

SC R

IP T

Figure list:

A

Fig. 1. Surface morphologies of the GF/SiBCN composites heat treated at different temperatures: (a) untreated; (b) 1400 oC; (c) 1500 oC; (d) 1600 oC; and (e) 1700 oC.

13

IP T SC R U N A M TE D EP CC

Fig. 2. Cross-section morphologies of the GF/SiBCN composites heat treated at different temperatures:

A

(a) (a-1) 1400 oC; (b) (b-1) 1500 oC; (c) (c-1) 1600 oC; and (d) (d-1) 1700 oC.

14

M

IP T

A

N

U

SC R

Fig. 3. Raman spectra of the GF/SiBCN composites treated at different temperatures.

A

CC

EP

TE D

Fig. 4. X-ray diffraction patterns of the GF/SiBCN composite treated at different temperatures .

15

IP T SC R U N A

M

Fig. 5. High resolution XPS spectra of the surface of the GF/SiBCN composites: (a) C1s; (b) B1s;

A

CC

EP

TE D

and (c) Si2p.

16

IP T SC R U N A M TE D

A

CC

EP

Fig. 6. High resolution XPS spectra of the GF/SiBCN composites annealed at different temperatures.

17

IP T SC R U N A M

A

CC

EP

(c) high magnification.

TE D

Fig. 7. TEM analysis of the GF/SiBCN composite annealed at 1700 oC: (a) low magnification; (b) and

Fig. 8. Schematic diagram showing the evolution of the microstructure for the GF/SiBCN composites

18

A

N

U

SC R

IP T

annealed at different temperatures.

M

Fig. 9. (a) SEA; (b) SER; and (c) SET of the GF/SiBCN composites annealed at 1400–1700 oC and (d)

CC

EP

TE D

SE at 10 GHz.

A

Fig. 10. Reflected, transmitted, and absorbed power of the GF/SiBCN composite as a function of the heat-treatment temperature.

19

Table list: Table 1 Weight loss and shrinkage of the GF/SiBCN composite annealed at different temperatures. Line

Body

temperature

rate

shrinkage rate

shrinkage rate

( C)

(%)

(%)

1400

0.41

0.63

1500

0.84

1.23

1600

1.41

1.67

2.61

1700

2.12

2.10

3.63

o

(%)

1.80 2.07

U

GF/SiBCN

IP T

Weight loss

SC R

Material

Annealing

Table 2 Bonding states and contents analyzed by XPS for the GF/SiBCN composites

N

treated at different temperatures.

HT-1500 oC

HT-1600 oC

HT-1700 oC

Si-N

57.52

52.04

48.68

30.53

Si-C

42.48

47.96

51.32

69.47

C-O

38.85

41.30

24.67

17.31

C-C

59.44

55.92

65.89

75.75

C-Si and C-B

1.71

2.77

9.44

6.94

B-O

6.84

-

-

-

B-N

19.37

12.59

29.76

24.3

B-C

73.79

87.41

70.24

75.67

TE D

M

HT-1400 oC

Si2p

A

CC

EP

C1s

B1s

Bonding content (at%)

A

Bonding type

20

Table 3 Comparison of the EMI SEs and specific EMI SEs for different carbon/ceramic composites.

Matrix

Filler

Filler

Thickness

EMI SE

content

(mm)

(dB)

Specific EMI SE

Ref.

(dB•cm3/g)

GN

2vol%

1.5

22

～6.1

[25]

BaTiO3

GN

4wt%

1.5

41.7

～7.6

[26]

B4 C

GN

5vol%

2

37-39

15

1.4

～36

～17.6

11.7vol% 2.8

43.2 33

MWCNT

10vol%

5

SiBCN

GF

0.5wt%

1.3

25.5

A

CC

EP

TE D

M

A

N

SiO2

21

[27]

SC R

PyC

U

Si3N4

IP T

Al2O3

～21.2 ～15 40

[28]

[29] This

work