Ultra-low energy consumption of preparing unidirectional porous Si₃N₄ ceramics via freeze casting and combustion synthesis

Unidirectional porous (UP) Si₃N₄ ceramics are promisingly applied in high-temperature filtration devices. However, traditional techniques exhibit the drawbacks of high energy consumption and difficult to control the pore structures. Herein, a novel technique of freeze casting combined with combustion synthesis was proposed to prepare the UP Si₃N₄ ceramics using Si powder and Si₃N₄ diluent as raw materials. The effects of Si₃N₄ diluent content and solid loading on the phase composition, microstructure and permeable/mechanical/filtration properties were investigated systematically. The results showed that the porosity and structure wavelength of UP Si₃N₄ ceramics with uniform microstructures can be tailored in a wide range of 50.8–86.0 % and 21.7–45.6 μm, respectively. The products exhibited anisotropic compressive strength, good permeable and filtration properties. This novel route with the advantages of energy-saving and high efficiency offers new insights for fabricating UP ceramics.