Abstract
The effect of the amount of added oxide on the gas-pressure sintering behavior of silicon nitride and high-temperature properties (strength and oxidation resistance) of the sintered materials were investigated. Si3N4 containing 0.5mol% (SN05) to 10% (SN10) of equimolar Y2O3-Nd2O3 was fired at 1900°C for 4h in 10MPa N2 gas. A small amount of the oxide (1mol%; SN1) was effective for densification as well as larger amounts of the oxide (6-10mol%). Composition analysis of the sintered specimens indicated that SN1 densified through a small amount of SiO2-rich liquid phase, whereas SN10 densified by a large amount of additive oxide-rich liquid phase. SN1 had higher strength than SN10 at higher temperatures because of its smaller amounts of glassy phase. SN1 also had an excellent oxidation resistance because the composition lied in the Si3N4-Si2N2O-Y2Si2O7 compatibility triangle, where Si2N2O and Y2Si2O7 were stable with regard to oxidation.
