Preparation of hierarchically porous calcium hexaaluminate ceramics through in-situ gelation-assisted direct ink writing

Abstract

Calcium hexaaluminate (CaO·6Al2O3, CA6) porous ceramics possess excellent properties, including low density and high surface area. However, their inherent brittleness presents challenges in traditional fabrication methods, especially in terms of on-demand molding of macroscopic geometries and modulation of pore structures at the micro and nano scales. In this study, a novel approach was developed for producing CA6 porous ceramics by employing in-situ gelation-assisted direct ink writing with sodium alginate. This method allows for the precise molding of macroscopic geometries and incorporates reaction sintering to prepare hierarchical porous features with macroscopic and microscopic pores. During the slurry printing process, the sodium alginate present in the ceramic slurry undergoes gelation upon contact with the calcium chloride expelled from the atomizer, thus facilitating in-situ curing and shaping. The optimal formation temperature for CA6 is 1550 °C, resulting in grains with a lamellar structure. The ceramics display predominant pore sizes of 346 nm, 5.59 μm, and 8.25 μm, with an apparent porosity of 70.72 %. This printing strategy employs a slurry that offers excellent compatibility and design flexibility, opening up possibilities for tailoring porous structures to precisely meet specific application requirements.