Synthesis of Porous Silicon Nitride with Unidirectionally Aligned Channels Using Freeze‐Drying Process

Porous silicon nitride with macroscopically aligned channels was synthesized using a freeze‐drying process. Freezing of a water‐based slurry of silicon nitride was done while unidirectionally controlling the growth direction of the ice. Pores were generated subsequently by sublimation of the columnar ice during freeze‐drying. By sintering this green body, a porous silicon nitride with high porosity (over 50%) was obtained and its porosity was controllable by the slurry concentration. The porous Si 3 N 4 had a unique microstructure, where macroscopically aligned open pores contained fibrous grains protruding from the internal walls of the Si 3 N 4 matrix. It is hypothesized that vapor/solid phase reactions were important to the formation mechanism of the fibrous grains.