Abstract
When a silicon nitride (Si3N4) ceramics is fabricated with yttrium oxide (Y2O3) as a sintering aid, the compounds in the Si3N4-SiO2-Y2O3system are formed. The typical compounds of the Si3N4-SiO2-Y2-O3- system are Y2Si3O3N4(melilite), YSiO2N(wollastonite), Y4Si2O2N7(cuspidine) and Y5(SiO4)3N(apatite). In order to improve high temperature strength of silicon nitride ceramics, it is necessary to control the composition of grain boundary phase and important to make clear the properties of the compound in the Si3N4-SiO2-Y2O3 system. In the present study, we fabricated the dense sintered body in the Si3N4-SiO2-Y2O3 system and found that (1) the hot pressing of the high purity compounds made the fabrication of high density ceramics with over 98 % of relative density possible, and (2) the flexural strength of the ceramics was arranged as: YSiO2N>Y2Si3O3N4>Y4Si2O7N2>Y5(SiO4)3N.
