3D Printing of Porous Mullite From Sol–Gel Photocurable Powder‐Free Ink

Abstract

Porous mullite (AlVI2(AlIV2+2xSi2−2x)O10−x, where x ranges between 0.17 and 0.57) structures were fabricated by integrating sol–gel chemistry with digital light processing (DLP), enabling complex geometries with coupled micro‐ and macroporosity. The method uses a powder‐free, low‐viscosity photocurable sol–gel ink (0.012 Pa·s) based on molecularly mixed aluminum and silicon precursors, enabling high‐resolution printing and rapid photopolymerization (∼50% C = C conversion within 4 s). Supercritical drying (SCD) was applied after printing to suppress capillary stresses during solvent removal and preserve the printed geometry. After heat treatment at 1000°C, X‐ray diffraction confirmed mullite crystallization, despite this temperature being well below conventional powder‐sintering temperatures. The printed structures exhibit ∼74% total porosity, a dominant mesopore size of ∼12 nm, and a specific surface area of 64 ± 4 m2 g−1. Thermal diffusivity increased only slightly from 0.292 to 0.322 mm2 s−1 between 300°C and 800°C, consistent with heat transport controlled by the porous ceramic framework. This powder‐free sol–gel/DLP route therefore provides a low‐temperature platform for fabricating lightweight, heat‐resistant mullite structures with controlled geometry and hierarchical porosity.