3D‐printed porous mullite lattice structures by hybrid direct ink writing of silicone suspension‐emulsions

Abstract Silicones added with nano‐sized alumina particles are already known as starting materials for phase pure mullite ceramics, synthesized at quite low temperatures. The present paper deals with a fundamental upgrade, based on a novel suspension‐emulsion concept, for the easy fabrication of highly porous lattice structures. An aqueous suspension of γ‐Al 2 O 3 nanoparticles in water was first distributed as emulsion within an “oily phase,” consisting of a silicone/acrylates blend, with the help of a surfactant. The mixture was later employed to fabricate highly porous structures (∼80% open porosity), by direct ink writing, that is, an extrusion‐based 3D printing technology requiring specific rheological behavior of the feedstock ink. Finally, the structures were rapidly stabilized through a photo‐polymerization step (configuring a form of “hybrid” direct ink writing). The presence of water also allowed the application of a freeze‐curing procedure, for a second series of samples. The abundant water vapor release from the starting mixtures, upon firing (up to 1300°C), led to structures with enhanced pore interconnectivity. The freeze‐curing protocol proved beneficial to the homogeneity of pore distribution and to the achievement of high strength‐to‐density ratios.