Abstract: Silicon nitride was prepared by pressureless sintering technique using Al 2 O3 together with Y2 O3 as the sintering additives under low temperature .The phase composition and densification of silicon nitride ceramics at low temperature were investigated by using XRD and SEM .The results show that when the additive content is 10%and the sintering temperature is higher than that of 1430 ℃,αto βphases to transition faster .When the sintering temperature reaches 1510 ℃, allαphase shift βphase .

Key words: silicon nitride;pressureless sintering;phase transition;densification