Multiple thermal resistance induced extremely low thermal conductivity in porous SiC-SiO2 ceramics with hierarchical porosity

摘要

Maximizing interfaces for blocking heat conduction in porous ceramic structures is an efficient approach for achieving maximum thermal resistance. Here, we adopted three strategies simultaneously for maximizing thermal resistance in porous SiC-based ceramics: (1) addition of nano-sized silica into nano-sized SiC powder for generating SiC/SiO2 interfaces, (2) addition of nano-sized carbon into nano-sized SiC powder as the template, and (3) sintering in air, which leads to the partial oxidation of the nano-sized SiC particles and burn-out of nano sized carbon, giving rise to the generation of the SiC-core/SiO2-shell structure and formation of micro-, meso-, and macro-sized pores. The thermal conductivity, compressive strength, porosity, and specific compressive strength of porous SiC-SiO2 ceramics processed at 600 degrees C with the above strategies were 0.066 Wm(-1) K-1, 2.7 MPa, similar to 72 %, and 3.9 MPa.cm(3)/g, respectively.