Ceramic foams possess the advantages of high-melting point, wear resistance, corrosion resistance, and low density in comparison with conventional polymers or metals. [1,2] Many attempts, for example, partial sintering, [3] polymeric sponge method, [4] sacrificial template method, [5] and direct foaming method, [6] have been implemented to develop ceramic foams for the applications of filters, radiant burners, bioreactors, heat exchangers, and catalyst supports. [1] However, there are still some disadvantages, such as the expansion of ice crystals in water-based systems and contraction of organic solvents during freeze forming, cracking of reticulated structure during pyrolysis of the polymeric template, and the toxicity and high cost of organic additives. [2,7] These will affect the stability of foams and practicability of preparation methods. The direct consolidation techniques based on the gelling of organic monomer [5] and several natural raw materials, such as starch, [7] proteins, or ovalbumin, [8] were proposed to improve strength of green body. Furthermore, these natural raw materials are cheap, environmentally friendly and easy to burn out. However, the preparation of the green body requires a heating crosslinking process, [1] and large amounts of pore-forming agents are needed to ensure high porosity. [7] Biological foaming (BF) technique could utilize small amounts of nutrients to release gases to form a lot of bubbles in the ceramic slurry. [7] The content of BF agent and the balance of bubble pressure and resistance of slurry determined the density of pore and pore size. Menchavez and Intong [7] combined direct consolidation technique with BF technique to fabricate red-clay-based ceramic with porosities from 17% to 70%. The starch was adopted as a growth substrate for yeast cell and a binder for ceramic particles. However, relatively complex consolidation process was inevitable due to gelatinization characteristics of starch. This method was designed and implemented on the basis of stable slurry. Thus, it has the potential to be applied to direct ink writing (DIW) technique by designing BF inks with suitable rheological properties. DIW, as a 3D printing technique, directly utilizes pastes or precursors with shear thinning characteristic to build complex geometries. [9,10] Minas et al. [11] and Muth et al. [12] have successfully utilized particle-stabilized foams to 3D print hierarchical porous ceramics, respectively. This strategy eliminates the need to manufacture moulds for custom components and shortens the cycle time from design to production. Si 2 N 2 O ceramic is a promising ceramic for high-temperature applications due to its low density, outstanding strength, superior thermal stability, and oxidation resistance. [13,14] Therefore, it is expected to be applied to high-temperature gas/liquid filters, thermal insulators or engineering components, separation membranes, catalyst carriers, etc. Herein, we report a versatile and simple strategy for the design and preparation of BF ink to fabricate h...
