A novel method for preparing Si3N4 ceramics with unidirectional oriented pores from silicon aqueous slurries

We describe a low-cost and simple method to prepare porous silicon nitride (Si3N4) ceramics with unidirectional oriented pores. Using Si powders as raw material, porous ceramics were fabricated via solidification of the aqueous slurries followed by the nitridation and post-sintering. The formation mechanism is similar to the ordered porous metals that are fabricated under high temperature and high pressure. Differently, the green bodies with oriented pores were obtained at room temperature and atmospheric pressure. The nucleation and growth of the H2 bubbles generated from hydrolyzed Si powders contributed to the highly oriented pores along the solidification direction of the aqueous slurries. Additionally, the pore microstructure was closely associated with the viscosity of the slurries, which can be well controlled by varying the concentration of organic additive and solid loading.