Ni@CNTs/Al₂O₃ Ceramic Composites with Interfacial Solder Strengthen the Segregated Network for High Toughness and Excellent Electromagnetic Interference Shielding

Ingenious microstructure design and appropriate multicomponent strategies are still challenging for advanced electromagnetic interference (EMI) shielding materials with excellent shielding effectiveness (SE) and reliable mechanical properties in harsh environments and low filling levels. In this study, nickel@multiwalled carbon nanotubes/alumina (Ni@CNTs/Al2O3) ceramic composites with segregated structures and electric/magnetic-coupling networks anchored by CNTs and magnetic Ni nanofillers were prepared by hot-press sintering. CNTs/Al2O3 ceramic composites exhibit a percolation threshold of only about 0.32013 vol %, which is lower than those of other reported CNTs/Al2O3 composites with segregated or uniformly dispersed structures. The electrical conductivity and EMI SE of 9CNTs/Al2O3 ceramic composites with 9 vol % (4.76 wt %) CNT content were 103.1 S/m and 33.6 dB, respectively. In addition, EMI SE and toughness were both enhanced by the synergistic effect of Ni nanoparticles and CNTs. In the unit of a segregated structure, a three-dimensional (3D) electric/magnetic-coupling network effectively captures and attenuates electromagnetic wave energy by electrical conduction, dielectric loss, and magnetic loss. On the other hand, the pull-out of CNTs and deflection of cracks distributed along the segregated structures synergistically enhance the fracture toughness of Ni@CNTs/Al2O3 ceramic composites. High-performance 3Ni@5CNTs/Al2O3 ceramic composites with 5 vol % (2.64 wt %) and 3 vol % (0.76 wt %) CNT contents have been achieved, whose EMI SE is 41.8 dB, density is 90.99%, flexural strength is 197.83 ± 18.62 MPa, and fracture toughness is 6.03 ± 0.23 MPa·m1/2. This efficient method provides a promising way to fabricate EMI shielding ceramic composites with high mechanical properties.