Low thermal conductivity and high porosity ZrC and HfC ceramics prepared by in-situ reduction reaction/partial sintering method for ultrahigh temperature applications

Porous ultra-high temperature ceramics (UHTCs) are potential candidates as high-temperature thermal insulation materials. However, high thermal conductivity is the main obstacle to the application of porous UHTCs. In order to address this problem, herein, a new method combining in-situ reaction and partial sintering has been developed for preparing porous ZrC and HfC with low conductivity. In this process, porous ZrC and HfC are directly obtained from ZrO2/C and HfO2/C green bodies without adding any pore-forming agents. The release of reaction gas can not only increase the porosity but also block the shrinkage. The as prepared porous ZrC and HfC exhibit homogeneous porous microstructure with grain sizes in the range of 300-600 nm and 200-500 nm, high porosity of 68.74% and 77.82%, low room temperature thermal conductivity of 1.12 and 1.01 W.m(-1) K-1, and compressive strength of 8.28 and 5.51 MPa, respectively. These features render porous ZrC and HfC promising as light-weight thermal insulation materials for ultrahigh temperature applications. Furthermore, the feasibility of this method has been demonstrated and porous NbC, TaC as well as TiC have been prepared by this method. (C) 2019 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.