Dual gradient direct ink writing of functional geopolymer-based carbonyl-iron/graphene composites for adjustable broadband microwave absorption

As a novel type of moulding technology, additive manufacturing (AM) can realise the rapid manufacturing of complex structures. This research applied dual gradient direct ink writing (DGDIW) with in-situ dispersion to fabricate multi-materials in an extensive gradient range. Functionally graded materials (FGM) have emerged as intelligent composites with peculiar advantages in wave absorption applications. An FGM geopolymer containing carbonyl-iron and graphene (CIG) powders with graded structure was successfully fabricated to enhance the wave-absorbing property via DGDIW three-dimensional (3D) printing. Compared with the non-structured homogeneous geopolymer composites, FGM composites performed more consecutive and effective absorbing from 2 to 18 GHz, resulting in a significantly increased electromagnetic (EM) wave absorption property. Combining with the gradient content of CIG fillers, the impedance matching and electromagnetic attenuation of 3D printed gradient lattice structure geopolymer composites has been significantly improved, the minimum reflection loss can reach ?46.47 dB at 17.58 GHz with a broadband absorption of 14.62 GHz (3.38–18.00 GHz). The results provided a promising strategy for fabricating functional graded ceramic composites with great potential as an absorption device in wave absorption applications, especially in protective structures, radiation-proof equipment/architecture, and defence constructions.