Formation of hierarchical Si3N4 foams by protein-based gelcasting and chemical vapor infiltration

Silicon nitride foams with a hierarchical porous structure was formed by the combination of protein-based gelcasting, chemical vapor infiltration, and in-situ growth of silicon nitride nanowires. The porosity of the foams can be controlled at 76.3-83.8 vol% with an open porosity of 70.2- 82.8 vol%. The pore size distribution was presented in three levels: < 2 mu m (voids among grains and cross overlapping of silicon nitride nanowires (SNNWs)), 10-50 mu m (cell windows), and >100 mu m (cells). The resulted compressive strength of the porous bodies at room temperature can achieve up to 18.0 +/- 1.0 MPa (porosity = 76.3 vol%) while the corresponding retention rate at 800 celcius was 58.3%. Gas permeability value was measured to be 5.16 (cm(3)center dot cm)/(cm(2)center dot s center dot kPa). The good strength, high permeability together with the pore structure in multiple scales enabled the foam materials for microparticle infiltration applications.

Automated summary

Silicon nitride foams with a hierarchical porous structure were successfully formed by combining protein-based gelcasting, chemical vapor infiltration, and in-situ growth of silicon nitride nanowires. These foams have controllable high porosity, good strength, and permeability at different scales, making them suitable for microparticle infiltration applications.