High-strength, multifunctional and 3D printable mullite-based porous ceramics with a controllable shell-pore structure

The quest for lightweight and functional materials poses stringent requirements on mechanical performance of porous materials. However, the contradiction between high strength and elevated porosity of porous materials severely limits their application scenarios in emerging fields. Herein, high-strength multifunctional mullite-based porous ceramic monoliths were fabricated utilizing waste fly ash hollow microspheres (FAHMs) by the protein gelling technique. Owing to their unique shell-pore structure inspired by shell-protected biomaterials, the monoliths with porosity of 54.69%–70.02% exhibited a high compressive strength (32.3–42.9 MPa) which was 2–5 times that of mullite-based porous ceramics with similar density reported elsewhere. Moreover, their pore structure and properties could be tuned by regulation of the particle size and content of the FAHMs, and the resultant monoliths demonstrated superior integrated performances for multifunctional applications, such as broadband sound insulation, efficient thermal insulation, and high-temperature fire resistance (>1300 °C). On this basis, mullite-based porous ceramic lattices (porosity 68.28%–84.79%) with a hierarchical porous structure were successfully assembled by direct ink writing (DIW), which exhibited significantly higher compressive strength (3.02–10.77 MPa) than most other ceramic lattices with comparable densities. This unique shell-pore structure can be extended to other porous materials, and our strategy paves a new way for cost-effective, scalable and green production of multifunctional materials with well-defined microstructure.