Gel casting of silicon nitride foams using biopolymers as gelling agents

Si3N4-based foams were prepared by the gel casting route using egg-albumen, agar-agar, or methylcellulose as biopolymer gelling agents. Microstructural, permeability, and mechanical properties of the foams were determined. The use of a variety of environmentally friendly gelling agents produced Si3N4 foams with a wide range of porosity (79–89%), mean cell size (199–852 μm), and mean window size (51–152 μm). The pressureless sintering method was successfully applied and resulted in Si3N4 foams with compressive strengths ranging from 1.6 to 9.4 MPa when treated at 1600 °C and up to 33.5 MPa when sintered at 1700 °C, due to the formation of the β–Si3N4 phase. Darcian (k1) and non-Darcian (k2) permeability coefficients were 4.41 × 10−12 to 1.61 × 10−10 m2 and 5.07 × 10−7 to 1.02 × 10−6 m, respectively, allowing the produced Si3N4 foams to be used in a wide variety of fluid flow and filtering applications.