Precursor design for additive manufacturing of ceramics through hydrogel infusion

Hydrogel-infused additive manufacturing (HIAM) is an emerging technique for the additive manufacturing of ceramics and metals. Distinct from slurry- or powder-based techniques, a hydrogel scaffold is obtained in the desired shape, infused with aqueous metal cations, and subsequently calcined to remove all organic components. This study demonstrates that both organic (hydrogel scaffold formulations) and inorganic (metal salts) precursors shape the quality and morphology of the final ceramic piece. Cu, Ce, Zr, and U oxide-ceramic disks were prepared via HIAM and studied using simultaneous thermal analysis, scanning electron microscopy, X-ray computed tomography, and small-angle X-ray scattering. Hydrogel formulations were found to impact the porosity of the resultant ceramics, with concentrated formulations generally yielding ceramics with a less cracked macrostructure. We hypothesize that this is due to the resulting variation in cation infusion into the matrix. The choice of inorganic salts also influences the morphology and porosity, likely due to the specific cation-polymer interactions and the energetic differences in decomposition pathways upon calcination. In general, chloride salts lead to denser microstructures than nitrate salts with some layer or foam-like macrostructures, while oxo-cations yield denser microstructures and macrostructures when compared to bare (monoatomic) cations. These results demonstrate that the HIAM process can be tailored to deliver a wide range of ceramics successfully, provided precursor feedstocks are adequately optimized.