ZrSi ₂ –MgO as novel additives for high thermal conductivity of β‐Si ₃ N ₄ ceramics

Abstract

Abstract A novel ZrSi 2 –MgO system was used as sintering additive for fabricating high thermal conductivity silicon nitride ceramics by gas pressure sintering at 1900°C for 12 hours. By keeping the total amount of additives at 7 mol% and adjusting the amount of ZrSi 2 in the range of 0‐7 mol%, the effect of ZrSi 2 addition on sintering behaviors and thermal conductivity of silicon nitride were investigated. It was found that binary additives ZrSi 2 –MgO were effective for the densification of Si 3 N 4 ceramics. XRD observations demonstrated that ZrSi 2 reacted with native silica on the Si 3 N 4 surface to generate ZrO 2 and β‐Si 3 N 4 grains. TEM and in situ dilatometry confirmed that the as formed ZrO 2 collaborated with MgO and Si 3 N 4 to form Si–Zr–Mg–O–N liquid phase promoting the densification of Si 3 N 4 . Abnormal grain growth was promoted by in situ generated β‐Si 3 N 4 grains. Consequently, compared to ZrO 2 ‐doped materials, the addition of ZrSi 2 led to enlarged grains, extremely thin grain boundary film and high contiguity of Si 3 N 4 –Si 3 N 4 grains. Ultimately, the thermal conductivity increased by 34.6% from 84.58 to 113.91 W·(m·K) −1 when ZrO 2 was substituted by ZrSi 2 .