Co–extrusion of alumina core–shell structures fabricated by robocasting

Abstract

Porous ceramics have a wide range of applications regarding their exceptional structural and specific mechanical properties, such as adjustable permeability, high surface area, and high specific strength. To enhance the compressive strength of porous alumina further, core-shell structures with a dense core and porous shell were produced by combining co-extrusion and robocasting. Different amounts of spherical cellulose particles were added to the paste and subsequently burned out from the printed green bodies to obtain porous alumina. This leads to a porosity ranging from 18 % to 55 % in the samples, whereas the dense alumina shows a porosity of ∼2 %. Two different core-shell ratios were realized to investigate the influence of the dense core on the properties. The core-shell samples were characterized in terms of their porosity using the rule of mixture. The compressive strength of the fabricated structures was investigated and compared to the theoretical strength of porous samples without a dense core. The theoretical strength of porous reference samples was calculated using an empirical exponential expression. A novel approach to structurally reinforce highly porous ceramics was demonstrated by incorporating the dense core. With a porosity of 20 %, the core-shell structures have an average compressive strength of ∼850 MPa. The macrostructure and microstructure of the core-shell samples were investigated using SEM and µCT imaging. This leads to a lower failure of the structure under mechanical load and thus extends the range of possible applications.