Effects of yttria and magnesia on densification and thermal conductivity of sintered reaction‐bonded silicon nitrides

Abstract A variety of combinations of Y 2 O 3 and MgO were used as additives in preparing Si 3 N 4 ceramics by the sintering of reaction‐bonded silicon nitride (SRBSN) method. By varying the amount of Y 2 O 3 in the range of 0‐5 mol% and that of MgO in the range of 0‐8 mol%, the effects of Y 2 O 3 and MgO additives on nitridation and sintering behaviors as well as thermal conductivity were studied. It was found that appropriate amount and combination of Y 2 O 3 and MgO additives were essential for attaining full densification and achieving high thermal conductivity. The sample doped with 2.5 mol% of Y 2 O 3 and 5 mol% of MgO attained a thermal conductivity of 128 Wm −1 K −1 when sintered at 1900°C for 6 hours, and the sample doped with 2 mol% of Y 2 O 3 and 4 mol% of MgO achieved a thermal conductivity of 156 Wm −1 K −1 when sintered for 24 hours.