Direct-writing assembly of high-strength hierarchical porous mullite-based lattices with a multiscale reinforcing strategy

High-strength mullite-based lattices with a hierarchical porous structure were assembled using waste fly ash hollow microspheres (FAHMs) as the main raw material by a direct ink writing (DIW) technique. The hollow microspheres were uniformly distributed in the strut matrix, creating a pore structure with a size ranging from 54 μm to 97 μm. Wet printed lattices were solidified by a protein gelling technique to further inhibit the shape deformation. Hollow microspheres, together with the dense matrix formed by aluminum silicate powder, formed the three-dimensional skeleton of struts in the mullite-based lattices. The lattice with a porosity of 84.3 % exhibited a high compressive strength of 2.74 MPa, along with a low thermal conductivity of 0.191 W m−1 K−1. Compared to most reported lattices with the same density, such as conventional mullite lattices, the stretching-bending dominated hierarchical porous mullite-based lattice exhibited superior mechanical properties. These lattices with both high porosity and high strength are cost-effective, flexible, scalable, and can facilitate the application of porous ceramics in emerging fields.