3D-printed impedance gradient Al2O3 ceramic with in-situ growing needle-like SiC nanowires for electromagnetic wave absorption

As a novel type of additive manufacturing, three-dimensional (3D) printing can efficiently realize the manufacturing of ceramic devices with more sophisticated structures. In this study, the method combining digital light processing (DLP) 3D printing technology and modified ceramic precursor polysiloxane (PSO) was not only used to fabricate Al2O3 ceramic devices with a gradient impedance bilayer structure, which consist of a crosstwist/flat structure with a torsion angle of 60 degrees , but also to prepare needle-like SiC nanowire absorbents grown in situ to further endow the ceramic functional characteristics. The microstructure was regulated by different times of impregnation, light-curing, and thermal treatment of ferrocene-modified PSO, and Al2O3/SiCnw/SiOC composites with different electromagnetic absorption properties were prepared. We found that the Al2O3/SiCnw/SiOC composite (sample 1400-2) exhibited the optimal microwave absorption performance when it was immersed and light-cured twice, which was ascribed to its comprehensive satisfaction of the impedance matching and attenuation characteristics. When the thickness of sample 1400-2 was as thin as 2.5 mm, the minimum reflection coefficient (RCmin) reached -44.35 dB, indicating that more than 99.9990% of the electromagnetic waves could be absorbed. As the thickness increased to 2.8 mm, the effective absorption bandwidth (EAB) in the X-band was 3.6 GHz, which indicated that the effective coverage rate was as high as 85.7%. The results indicate that the generation of the stacking fault, dipole and interfacial polarization of the Al2O3/SiCnw/SiOC composites, and increasing conductivity contribute to the promotion of dielectric loss. Thus, the Al2O3/SiCnw/SiOC composite with bilayer gradient impedance structures is a good candidate for stealth radar wave absorption.