Cup-Stacked Carbon Nanotubes Hybridized Si3n4/Si3n4 Composite Ceramics For High-Effciency Microwave Absorption With Excellent Thermal Stability

Hybridization between carbon nanotubes (CNTs) and Si3N4 is a promising strategy for developing hightemperature microwave absorption (MA) materials for military application. Toward long-life services, it?s important to achieve strong MA at a filler loading as low as possible on account of antioxidant protection against CNTs wastage. Herein, cup-stacked CNTs (CSCNTs) have been prepared in porous Si3N4 ceramics by chemical vapor deposition (CVD) and then CVD Si3N4 has been coated on them, forming CSCNT-Si3N4/Si3N4 composite ceramics. Results show that CSCNTs possess abundant exposed atomic edges on the outer surface and in the inner channel. Such unique defects not only benefit the impedance match but also cause considerable conductive loss, which helps CSCNT-Si3N4/Si3N4 with a filler content of only 0.79 wt% to achieve an effective absorption bandwidth (EAB) of 3.74 GHz in the X band at a thickness of 3.5 mm coupled with a minimum reflection loss of -43.3 dB and an EAB covering the entire Ku band at a thickness of 2.25 mm. The ultralow filler loading generates a high efficiency of CVD Si3N4 in protecting CSCNTs against high-temperature oxidation, leading to a steady MA performance for CSCNT-Si3N4/Si3N4 during 23?1200 ?C thermal shock tests in air.