Fabrication and flexural strength of porous Si3N4 ceramics with Li2CO3 and Y2O3 as sintering additives

By employing sintering additives of Li 2 CO 3 and Y 2 O 3 , porous Si 3 N ceramics are prepared after experiencing the processes of sintering and post-vacuum heat treatment at 1680 and 1550 °C, respectively. The experimental results demonstrate the completed phase transformation from α to β -Si 3 N 4 in Si 3 N 4 ceramic samples with a amount of 1.60 wt% Li 2 CO 3 (0.65 wt% Li 2 O) and 0.33 wt% Y 2 O 3 additives. The as-synthesized porous Si3N4 ceramics exhibit high flexural strength ((126.7±2.7) MPa) and high open porosity of 50.4% at elevated temperature (1200 °C). These results are attributed to the significant role of added Li 2 CO 3 as sintering additive, where the volatilization of intergranular glassy phase occurs during sintering process. Therefore, porous Si 3 N 4 ceramics with desired mechanical property prepared by altering the addition of sintering additives demonstrate their great potential as a promising candidate for high temperature applications.