酸化物助剤添加量が窒化ケイ素の焼結および焼結体の高温特性に及ぼす影響

抄録

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.