Ultra-low energy consumption of preparing unidirectional porous Si3N4 3 N 4 ceramics via freeze casting and combustion synthesis

Unidirectional porous (UP) Si3N4 3 N 4 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 3 N 4 ceramics using Si powder and Si3N4 3 N 4 diluent as raw materials. The effects of Si3N4 3 N 4 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 3 N 4 ceramics with uniform microstructures can be tailored in a wide range of 50.8-86.0 % and 21.7-45.6 mu m, 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.