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

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-Al₂O₃@SiO₂ powder as a precursor. The transient viscous sintering induced by the γ-Al₂O₃@SiO₂ 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.