Enhanced thermal conductivity in Si3N4 ceramics prepared by using ZrH2 as an oxygen getter

Abstract

This work reports the two-step sintering method and thermal conductivity of Si3N4 doped with 1.5 wt% MgO and varied contents of ZrH2 in the range of 0-5 wt%. The metal hydride reduction reaction in the first step sintering allows the in situ generations of ZrO2 and the elimination of native SiO2. A smaller amount of liquid phase with reduced oxygen content was produced during the second step sintering as a result of the replacement of ZrO2 by ZrH2. With the aid of ZrH2 as an oxygen getter, the native oxygen in those ZrH2-doped samples was removed via a route of SiO2 →ZrO2 →SiO(g). Consequently, the densified Si3N4 ceramics with larger volume percent of elongated purified β-Si3N4 grains and less glassy phase were obtained. Ultimately, the optimal thermal conductivity of 116.4 W m−1 K−1 was achieved after sintered at 1900 °C for 12 h by using 3 wt% ZrH2 and 1.5 wt% MgO as additives.