Hierarchical Structure of Porous Silicon Nitride Ceramics with Aligned Pore Channels Prepared by Ice-Templating and Nitridation of Silicon Powder

A unique hierarchical porous structure of silicon nitride ceramic with 76.5% porosity is fabricated by combining an ice-templating method and nitridation for a silicon powder. The porous silicon nitride ceramics were composed of a lamellar structure with aligned pore channels and ceramic walls filled with fibrous whiskers. This study is focused on the influences of freezing rate on the microstructures and properties of the silicon nitride ceramics. The properties were characterized by compressive strength and gas permeability, which were shown to vary with controlled microstructure. The compressive strength and the permeability reached up to 32.2 MPa and 0.035−12 m2, respectively.