Electrically Conductive and Mechanically Strong Graphene/Mullite Ceramic Composites for High-Performance Electromagnetic Interference Shielding

Abstract

Ceramic composites with good electrical conductivity and high strength that can provide electromagnetic interference (EMI) shielding are highly desirable for the applications in harsh environment. In this study, lightweight, highly conductive, and strong mullite composites incorporated with reduced graphene oxide (rGO) are successfully fabricated by spark plasma sintering at merely 1200 °C using the core−shell structured γ-Al 2 O 3 @SiO 2 powder as a precursor. The transient viscous sintering induced by the γ-Al 2 O 3 @SiO 2 precursor not only prohibits the reaction between mullite and rGO by greatly reducing the sintering temperature, but also induces a highly anisotropic structure in the rGO/mullite composite, leading to an extremely high in-plane electrical conductivity (696 S m −1 for only 0.89 vol % of rGO) and magnitude lower cross-plane electrical conductivity in the composites. As a result, very large loss tangent and EMI shielding effectiveness (>32 dB) can be achieved in the whole K band with extremely low rGO loading (less than 1 vol %), which is beneficial to maintain a good mechanical performance in ceramic matrix composites. Accordingly, the rGO/mullite composites show greatly improved strength and toughness when the rGO content is not high, which enables them to be applied as highly efficient EMI shielding materials while providing excellent mechanical performance.

Controllable fabrication and multifunctional applications of graphene/ceramic composites

“…Moreover, the pressure applied during sintering can further enhance the alignment of 2D graphene sheets and the formation of preferred orientation perpendicular to the pressure axis [65]. Generally, pressure sintering contains the multiaxial-pressed sintering by hot isostatic pressing (HIP) sintering [66] or a multi-anvil apparatus [67], and the uniaxial pressure-assisted sintering including hot-pressed (HP) sintering [68], spark plasma sintering (SPS) [69], and high-frequency induction heated sintering (HFIHS) [70,71], in which the latter is more popular due to easier operation and lower cost.…”

“…5(a) and 5(b) [16,75]. It is difficult to build the special structure of graphene in the ceramic matrix by colloidal processing method, but through building the core-shell structure in the powder nanocomposites and viscous sintering caused by SiO 2 , Ru et al [69] realized the anisotropic structure in rGO/mullite composites. Besides, new technologies with the utilization of ceramic precursors are more promising for the construction of special structures.…”

“…To [15,73,98,99], the single-edge notched beam (SENB) method [52,79], the Chevron notch technique [69,75], the single-edge v-notched beam (SEVNB) method [92,95], and single-edge pre-cracked beam (SEPB) method. Typically, during micro-hardness testing, fracture toughness can be simply determined by measuring the crack lengths produced by Vickers indentation; at the same time, hardness can be obtained.…”

“…Besides, composites with anisotropic structure have a great impact on the electrical conductivity in different directions [106]. For the 0.47 vol% rGO/ mullite composites with a preferred orientation, the cross-plane electrical conductivity was only 0.55 S/m, while the in-plane conductivity increased to 190 S/m [69]. Since studies on the electrical conductivity and percolation threshold of graphene/ceramic composites have been fully investigated [1][2][3]64,107], here we would like to focus on the burgeoning applications in electromagnetic (EM) interference shielding.…”

“…Even though most ceramics are EM transparent, the introduction of conductive fillers such as graphene can easily solve this problem and adjust EM properties of the ceramic matrix; conversely, a low dielectric constant of ceramic can improve impedance matching of highly conductive graphene [60,115]. Recent studies of the graphene/ceramic composites [13,47,[57][58][59][60][61][62]68,69,[116][117][118][119][120][121][122] focus on EM properties in the X-band (8.2-12.4 GHz) for military and communication applications [62], the Ku-band (12.4-18 GHz) for small aperture terminal systems [109], or the K-band (18-26.5 GHz) for intelligent transportation systems and vehicle radar [69]. The excellent EM properties of the composites are achieved, as shown in Fig.…”