Preparation of Porous Si2N2O/SiC Ceramics by Microwave Sintering

Two steps strategy were taken to effectively produce porous Si₂N₂O/SiC ceramics: 1) direct foaming combined with sol-gel curing at room temperature to form a green body, and 2) sintering assisted by in-situ production of Si₂N₂O fibers under microwave sintering conditions. Non-toxic silica sol was used to provide silicon source for in-situ synthesis of Si₂N₂O, the silica sol could form a gel that stabilizes the bubbles, creating a porous structure. A thorough investigation was conducted into how different sintering temperatures affected the microstructure, flexural strength, and porosity of the porous Si₂N₂O/SiC composites. The main bonding phase in the porous composites was the Si₂N₂O with fiber morphology. The optimal microwave sintering temperature for fabricating porous Si₂N₂O/SiC ceramics, using a combination of sol-gel and direct foaming techniques, has been determined to be 1200 °C. At this temperature, the porosity can be controlled between 73.32% and 83.16% by proportionally adjusting the ratio of the raw materials. Under the condition of high porosity, the thermal radiation is dominant and the thermal conductivity increases with the increase of temperature. With the decrease of porosity, the heat conduction is dominant, and the thermal conductivity decreases with the increase of temperature.